machine tools and digital manufacturing -...

(For B.E. Mechanical Engineering Students)

As per New Revised Syllabus ofAPJ Abdul Kalam Technological University

Dr. S. Ramachandran, M.E., Ph.D.,

Prof. YVS. Karthik

AIR WALK PUBLICATIONS

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Machine Toolsand

Digital Manufacturing

ISBN:978-93-84893-72-9

and

thFirst Edition: 8 , July 2017

ISBN : 978-93-84893-72-9

Price :

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Syllabus : Machine Tools and Digital Manufacturing

Chapter 1: Theory of Metal Cutting

Introduction to metal cutting: Tool nomenclature – Attributes of each

tool nomenclature – Attributes of feed and tool nomenclature on surface

roughness obtainable, Orthogonal and oblique cutting - Mechanism of metal

removal - Primary and secondary deformation shear zones, Mechanism of

chip formation – Types of chips, need and types of chip breakers – Merchant’s

theory, Analysis of cutting forces in orthogonal cutting – Work done, power

required (simple problems), Friction forces in metal cutting – development of

cutting tool materials, Thermal aspects of machining - Tool wear and wear

mechanisms, Factors affecting tool life - Economics of machining (simple

problems), Cutting fluids.

Chapter 2: General Purpose Machine Tools

General purpose machine tools: Principle and operation of lathe -

Types of lathes and size specification, Work holding parts of lathes and their

functions - Main operations, Taper turning and thread cutting - Attachments,

Feeding mechanisms, Apron mechanisms, Drilling Machines - Types - Work

holding devices, Tool holding devices - Drill machine operations, Drilling

machine tools - Twist drill nomenclature - cutting forces in drilling,

Chapter 3: Reciprocating Machines (or) Other Machine Tools

Reciprocating machines: Shaping machines - Types - Size - Principal

parts - Mechanism, Work holding devices - Operations performed - Tools,

Cutting speed, feed and depth of cut - Machining time. Slotting machines -

Types - Size - Principal parts - Mechanism - Work holding devices,

Operations performed - Tools - Cutting speed, feed and depth of cut, Planing

machines - Types - Size - Principal parts - Mechanism - Work holding

devices, Operations performed - Tools - Cutting speed, feed and depth of cut

- Machining time - Surface roughness obtainable.

Syllabus S.1

Chapter 4: Milling Machine

Milling machines - Types - Principal parts - Milling mechanism, Work

holding devices - Milling machine attachments, Types of miling cutters -

Elements of plan milling cutters, Nomenclature - Cutting forces in milling -

Milling cutter materials, Up milling, down milling and face milling operations,

Calculation of machining time, Indexing - Simple indexing - Differential

indexing

Chapter 5: Grinding Machines

Grinding machines - Classification - Operations - Surface, cylindrical

and centreless grinding, Grinding mechanisms - Grinding wheels: Specification

- types of abrasives, grain size, Types of bond, grade, structure - Marking

system of grinding wheels - Selection of grinding wheels, Glazing and loading

of wheels - Dressing and Truing of grinding wheels, surface roughness

obtainable, Superfinishing operations: Lapping operation - Types of hand

lapping - Lapping machines - Types of honing - Methods of honing, Types

of honing stones - Honing conditions - Cutting fluids - Types of broaches -

Force required for broaching - Surface roughness obtainable in lapping, honing

and broaching operations. Semi-automatic machine tools - Turret and capstan

lathes. Automatic machine tools - Single and multi spindle machines.

Chapter 6: Introduction to Digital Manufacturing

Introduction to Digital Manufacturing - Concepts and research and

development status of digital manufacturing. Definition of digitalmanufacturing - Features and development of digital manufacturing. Theorysystem of digital manufacturing science - Operation Mode and Architecture

of Digital Manufacturing System.Operation reference mode of digital

manufacturing system - Architecture of digital manufacturing system.

Modeling theory and method of digital manufacturing science. Critical

modeling theories and technologies of digital manufacturing science. Theory

system of digital manufacturing science - Basic architecture model of digital

manufacturing system.

S.2 Machine Tools and Digital Manufacturing

Contents

Chapter 1Theory of Metal Cutting

1.1 Introduction to Metal Cutting . . . . . . . . . . . . . . . . . . . . . . . . 1.1

1.2 Cutting Tool Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3

1.3 Parts and Nomenclature of Single Point Cutting Tool . . . 1.3

1.4 Tool Signature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7

1.4.1 Influence of Tool angles in machining . . . . . . . . 1.81.5 Methods of Metal Cutting Processes . . . . . . . . . . . . . . . . . 1.10

1.5.1 Differences between orthogonal and oblique cutting. 1.111.6 Mechanism of Metal Removal Processes . . . . . . . . . . . . . . 1.12

1.6.1 Classification of Metal Removal Processes . . . . . . 1.121.6.2 Chip forming Processes . . . . . . . . . . . . . . . . 1.121.6.3 Turning, Boring and other Lathe Operations . . . . 1.13

1.6.3.1 Machining parameters and related terms in turning operation . . . . . . . . . . . . . . . . . . 1.15

1.6.4 Shaping, Planing and Slotting . . . . . . . . . . . . 1.181.6.4.1 Machining Parameters in Shaping, Planing . . . 1.20

1.6.5 Drilling and Reaming . . . . . . . . . . . . . . . . . 1.211.6.5.1 Machining Parameters for Drilling . . . . . . . . . 1.22

1.6.6 Milling . . . . . . . . . . . . . . . . . . . . . . . . . 1.221.6.6.1 Machining Parameters in Milling . . . . . . . . . 1.25

1.6.7 Broaching . . . . . . . . . . . . . . . . . . . . . . . . 1.261.6.8 Thread Cutting . . . . . . . . . . . . . . . . . . . . . 1.26

1.6.8.1 Machining Parameters in thread cutting . . . . . 1.27

1.6.9 Grinding . . . . . . . . . . . . . . . . . . . . . . . . 1.281.6.10 Honing and Lapping . . . . . . . . . . . . . . . . . 1.291.6.11 Gear Cutting . . . . . . . . . . . . . . . . . . . . . 1.29

1.7 Primary and Secondary Deformation Shear Zones . . . . . 1.30

1.8 Mechanism of Chip Formation . . . . . . . . . . . . . . . . . . . . . . 1.32

1.8.1 Types of Chips . . . . . . . . . . . . . . . . . . . . . 1.321.8.1.1 Variables affecting type of chip . . . . . . . . . . 1.33

Contents C.3

1.8.1.2 Continuous Chips . . . . . . . . . . . . . . . . . . . 1.331.8.1.3 Continuous Chips with Built up Edges. . . . . . . 1.341.8.1.4 Discontinuous Chips . . . . . . . . . . . . . . . . . 1.351.8.1.5 Chip Breakers . . . . . . . . . . . . . . . . . . . . 1.38

1.8.2 Geometry of Chip Formation . . . . . . . . . . . . . 1.391.8.2.1 Velocity Relationships . . . . . . . . . . . . . . . 1.40

1.8.2.2 Shear Plane angle and chip Thickness ratio . 1.41

1.8.2.3 Force Analysis in Metal Cutting . . . . . . . . . 1.431.8.2.4 Force analysis in orthogonal cutting (Merchant Circle diagram and Theory) . . . . . . . . . . . . 1.451.8.2.5 Power and workdone required in cutting process 1.501.8.2.6 Stress and Strain in Chip . . . . . . . . . . . . . 1.511.8.2.7 Shear Strain in Cutting . . . . . . . . . . . . . . . 1.521.8.2.8 Energy in cutting . . . . . . . . . . . . . . . . . . 1.54

1.9 Development of Cutting Tool Materials. . . . . . . . . . . . . . . 1.54

1.9.1 Desirable Properties of Cutting Tools . . . . . . . . 1.551.9.2 Types of Cutting Tool Materials . . . . . . . . . . . 1.57

1.10 Thermal Aspects of Machining Tool Wear and Wear Mechanism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.63

1.10.1 Tool Wear Mechanisms . . . . . . . . . . . . . . . . 1.651.10.1.1 Shearing at High Temperature . . . . . . . . . . 1.651.10.1.2 Diffusion Wear . . . . . . . . . . . . . . . . . . . 1.661.10.1.3 Adhesive Wear (Attrition Wear) . . . . . . . . . 1.661.10.1.4 Abrasive Wear . . . . . . . . . . . . . . . . . . . . 1.671.10.1.5 Fatigue Wear . . . . . . . . . . . . . . . . . . . . 1.681.10.1.6 Electrochemical Effect . . . . . . . . . . . . . . . 1.691.10.1.7 Oxidation Effect . . . . . . . . . . . . . . . . . . . 1.691.10.1.8 Chemical decomposition . . . . . . . . . . . . . . 1.69

1.10.2 Types of Tool Damage in Cutting . . . . . . . . . . 1.691.10.3 Tool Failure . . . . . . . . . . . . . . . . . . . . . . 1.721.10.4 Measurement of Wear . . . . . . . . . . . . . . . . 1.72

1.11 Tool Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.72

1.11.1 Tool failure Criterion . . . . . . . . . . . . . . . . . 1.73

C.4 Machine Tools and Digital Manufacturing

1.11.2 Factors affecting Tool Life . . . . . . . . . . . . . . 1.741.11.3 Economics of Machining - Machining Cost . . . . 1.781.11.4 Machinability . . . . . . . . . . . . . . . . . . . . . 1.79

1.11.4.1 Factors affecting machinability . . . . . . . . . . 1.79

1.11.5 Surface finish . . . . . . . . . . . . . . . . . . . . . 1.801.11.5.1 Factors affecting surface finish . . . . . . . . . . 1.811.11.5.2 Measurement of Roughness . . . . . . . . . . . . 1.821.11.5.3 Specification of Surface Roughness . . . . . . . . 1.84

1.12 Cutting Fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.85

1.12.1 Functions of cutting fluids . . . . . . . . . . . . . . 1.851.12.2 Properties of Good Cutting fluid . . . . . . . . . . 1.851.12.3 Types of Cutting Fluids . . . . . . . . . . . . . . . 1.861.12.4 Composition of Cutting Fluids . . . . . . . . . . . 1.871.12.5 Method of applying cutting fluid . . . . . . . . . . 1.89

1.13 Solved Problems On Cutting Forces, Work Done and Power Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.89

Chapter 2General Purpose Machine Tools

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1

2.1.1 Principle and operation of Lathe . . . . . . . . . . . 2.12.2 Types of Lathes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2

2.2.1 Speed lathe . . . . . . . . . . . . . . . . . . . . . . . 2.22.2.2 Engine lathe or Centre lathe . . . . . . . . . . . . . 2.32.2.3 Bench Lathe . . . . . . . . . . . . . . . . . . . . . . 2.32.2.4 Tool room lathe . . . . . . . . . . . . . . . . . . . . 2.42.2.5 Special purpose lathe . . . . . . . . . . . . . . . . . 2.42.2.6 Capstan and Turret lathes . . . . . . . . . . . . . . 2.52.2.7 Automatic lathes . . . . . . . . . . . . . . . . . . . . 2.52.2.8 Numerically controlled lathes . . . . . . . . . . . . . 2.5

2.3 Size and Specification of A Centre Lathe . . . . . . . . . . . . . . 2.6

2.4 Centre Lathe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7

2.4.1 Constructional features of centre lathe . . . . . . . . 2.7

Contents C.5

2.4.1.1 Bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.72.4.1.2 Head stock . . . . . . . . . . . . . . . . . . . . . . 2.102.4.1.3 Tail stock . . . . . . . . . . . . . . . . . . . . . . . 2.112.4.1.4 Carriage . . . . . . . . . . . . . . . . . . . . . . . . 2.11

2.5 Lathe Accessories and Attachments . . . . . . . . . . . . . . . . . . 2.17

2.5.1 Lathe Accessories . . . . . . . . . . . . . . . . . . . . 2.172.6 Lathe Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.28

2.6.1 Centering . . . . . . . . . . . . . . . . . . . . . . . . 2.282.6.2 Plain or Straight Turning . . . . . . . . . . . . . . . 2.292.6.3 Shoulder Turning (or) Step turning . . . . . . . . . 2.312.6.4 Taper Turning . . . . . . . . . . . . . . . . . . . . . 2.312.6.5 Eccentric Turning . . . . . . . . . . . . . . . . . . . 2.322.6.6 Cam Turning . . . . . . . . . . . . . . . . . . . . . . 2.332.6.7 Chamfering . . . . . . . . . . . . . . . . . . . . . . . 2.332.6.8 Facing . . . . . . . . . . . . . . . . . . . . . . . . . . 2.342.6.9 Knurling . . . . . . . . . . . . . . . . . . . . . . . . . 2.342.6.10 Filing . . . . . . . . . . . . . . . . . . . . . . . . . . 2.352.6.11 Polishing . . . . . . . . . . . . . . . . . . . . . . . . 2.362.6.12 Grooving or Necking . . . . . . . . . . . . . . . . . 2.362.6.13 Parting-Off . . . . . . . . . . . . . . . . . . . . . . . 2.372.6.14 Spinning . . . . . . . . . . . . . . . . . . . . . . . . 2.382.6.15 Spring Winding . . . . . . . . . . . . . . . . . . . . 2.382.6.16 Forming . . . . . . . . . . . . . . . . . . . . . . . . 2.382.6.17 Drilling . . . . . . . . . . . . . . . . . . . . . . . . 2.392.6.18 Reaming . . . . . . . . . . . . . . . . . . . . . . . . 2.392.6.19 Boring . . . . . . . . . . . . . . . . . . . . . . . . . 2.402.6.20 Counter boring, counter sinking and spot- facing . 2.412.6.21 Tapping . . . . . . . . . . . . . . . . . . . . . . . . 2.412.6.22 Under cutting . . . . . . . . . . . . . . . . . . . . . 2.422.6.23 Taper boring . . . . . . . . . . . . . . . . . . . . . . 2.422.6.24 Milling . . . . . . . . . . . . . . . . . . . . . . . . . 2.422.6.25 Grinding . . . . . . . . . . . . . . . . . . . . . . . . 2.42


2.7 Taper Turning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.43

2.7.1 Taper turning by using a form tool . . . . . . . . . 2.432.7.2 Compound rest swiveling method . . . . . . . . . . . 2.442.7.3 Set over or tailstock offset Method: . . . . . . . . . 2.452.7.4 Taper turning attachment method . . . . . . . . . . 2.462.7.5 Template and tracer attachment . . . . . . . . . . . 2.482.7.6 Combination of longitudinal and cross feed . . . . . 2.48

2.8 Thread Cutting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.49

2.8.1 Change Gear Calculations . . . . . . . . . . . . . . . 2.502.8.2 Types of Gear connections . . . . . . . . . . . . . . . 2.512.8.3 Metric Thread on English Lead Screw . . . . . . . 2.542.8.4 Procedure for cutting external thread . . . . . . . . 2.562.8.5 Cutting Internal thread procedure . . . . . . . . . . 2.602.8.6 Cutting Left hand threads . . . . . . . . . . . . . . 2.612.8.7 Cutting Tapererd threads . . . . . . . . . . . . . . . 2.612.8.8 Square thread cutting . . . . . . . . . . . . . . . . . 2.612.8.9 Cutting Multiple Start threads . . . . . . . . . . . . 2.62

2.9 Feed Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.62

2.9.1 End Gear Train . . . . . . . . . . . . . . . . . . . . 2.632.9.2 Feed gear box . . . . . . . . . . . . . . . . . . . . . . 2.652.9.3 Feed rod and Lead screw Drive Mechanism . . . . 2.662.9.4 Apron mechanism . . . . . . . . . . . . . . . . . . . 2.67

2.9.4.1 Half nut mechanism (Thread cutting mechanism) 2.68

2.9.5 Head stock mechanisms . . . . . . . . . . . . . . . . 2.692.9.5.1 Belt drive - cone pulleys . . . . . . . . . . . . . . 2.692.9.5.2 Back gear arrangement . . . . . . . . . . . . . . . 2.70

2.10 Drilling Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.73

2.10.1 Types - Classification of drilling machine . . . . . 2.732.10.2 Specification of drilling machine . . . . . . . . . . 2.812.10.3 Feed mechanism . . . . . . . . . . . . . . . . . . . 2.822.10.4 Drill machine operations . . . . . . . . . . . . . . . 2.832.10.5 Drilling Machine Tools - Twist drill nomenclature 2.87

Contents C.7

2.10.6 Drill (Tool) holding devices . . . . . . . . . . . . . 2.902.10.7 Work holding devices . . . . . . . . . . . . . . . . . 2.922.10.8 Drilling machine tools - Reaming tools . . . . . . . 2.932.10.9 Tapping tool . . . . . . . . . . . . . . . . . . . . . . 2.952.10.10 Drilling parameters - Calculations . . . . . . . . . 2.982.10.11 Machining time and Power calculation . . . . . 2.100

2.11 Solved Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.104

Chapter - 3Reciprocating Machines (or) Other Machine Tools

3.1 Reciprocating Machine Tools . . . . . . . . . . . . . . . . . . . . . . . . . 3.1

3.2 Shaping Machine (or) Shaper . . . . . . . . . . . . . . . . . . . . . . . . 3.1

3.2.1 Working Principle . . . . . . . . . . . . . . . . . . . 3.23.2.2 Types of shapers . . . . . . . . . . . . . . . . . . . . 3.23.2.3 Crank shaper . . . . . . . . . . . . . . . . . . . . . . 3.33.2.4 Geared type . . . . . . . . . . . . . . . . . . . . . . . 3.33.2.5 Hydraulic shaper . . . . . . . . . . . . . . . . . . . . 3.33.2.6 Horizontal shaper . . . . . . . . . . . . . . . . . . . 3.43.2.7 Vertical shaper . . . . . . . . . . . . . . . . . . . . . 3.43.2.8 Travelling head shaper . . . . . . . . . . . . . . . . 3.43.2.9 Standard shaper . . . . . . . . . . . . . . . . . . . . 3.43.2.10 Universal shaper . . . . . . . . . . . . . . . . . . . 3.43.2.11 Push cut type shaper . . . . . . . . . . . . . . . . . 3.53.2.12 Draw cut type shaper . . . . . . . . . . . . . . . . . 3.5

3.3 Principal Parts of A Shaper . . . . . . . . . . . . . . . . . . . . . . . . . 3.5

3.4 Shaper Drive Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7

3.5 Feed Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.13

3.6 Work Holding Devices in Shaper . . . . . . . . . . . . . . . . . . . . 3.14

3.7 Shaper Operations Performed . . . . . . . . . . . . . . . . . . . . . . . 3.17

3.8 Shaper Tools (Shaper Cutting Tools) . . . . . . . . . . . . . . . . . 3.19

3.9 Shaper Cutting Speed, Feed and Depth of Cut . . . . . . . . 3.22

3.10 Planing Machine (or) Planer . . . . . . . . . . . . . . . . . . . . . . . 3.24


3.10.1 Types of Planer . . . . . . . . . . . . . . . . . . . . 3.243.11 Planer Size and Specifications . . . . . . . . . . . . . . . . . . . . . 3.28

3.12 Principal Parts of A Planer. . . . . . . . . . . . . . . . . . . . . . . . 3.28

3.13 Driving Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.31

3.14 Electrical Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.33

3.14.1 Advantages of Electrical Drive . . . . . . . . . . . 3.343.15 Types of Planing Tool. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.34

3.16 Planer Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.36

3.16.1 Workholding devices in planer . . . . . . . . . . . . 3.373.16.2 Planing - Cutting speed, Feed and Depth of cut . 3.37

3.17 Slotter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.38

3.17.1 Principle parts of the slotter . . . . . . . . . . . . . 3.383.17.2 Slotter operation method . . . . . . . . . . . . . . . 3.39

3.18 Types of Slotter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.40

3.18.1 Specification of slotter . . . . . . . . . . . . . . . . 3.413.19 Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.41

3.20 Feed Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.43

3.21 Work Holding Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.44

3.22 Slotter Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.46

3.23 Slotter Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.46

3.24 Surface Roughness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.48

3.24.1 Measurement of Ra . . . . . . . . . . . . . . . . . . 3.49

3.24.2 Factors Affecting the surface finish . . . . . . . . . 3.50

Chapter 4Milling Machine

4.1 Milling Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1

4.2 Milling Machines and Types . . . . . . . . . . . . . . . . . . . . . . . . . 4.1

4.3 Principal Parts of Milling Machine . . . . . . . . . . . . . . . . . . . 4.9

4.4 Size and Specification of Milling Machine . . . . . . . . . . . . 4.10

Contents C.9

4.5 Work Holding Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11

4.6 Cutter Holding Device (or) Tool Holding Device . . . . . . . 4.16

4.7 Milling Machine Attachments . . . . . . . . . . . . . . . . . . . . . . . 4.17

4.8 Milling Cutters - Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.18

4.9 Nomenclature Elements of Plain Milling Cutter . . . . . . . 4.23

4.9.1 Cutter Angle . . . . . . . . . . . . . . . . . . . . . . 4.254.9.2 Milling cutter materials . . . . . . . . . . . . . . . . 4.26

4.10 Fundamentals of The Milling Operations . . . . . . . . . . . . 4.27

4.11 Milling Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.29

4.12 Milling-cutting Speed, Feed and Depth of Cut . . . . . . . 4.33

4.13 Indexing Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.34

Chapter - 5Grinding Machines

5.1 Grinding Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1

5.2 Principle Operations of Grinding . . . . . . . . . . . . . . . . . . . . . 5.2

5.3 Classification of Grinding Machines and Processes . . . . . . 5.2

5.3.1 Rough grinders . . . . . . . . . . . . . . . . . . . . . 5.45.3.2 Precision grinding machines . . . . . . . . . . . . . 5.75.3.3 Cylindrical grinding (centre type) machines . . . . . 5.7

5.3.3.1 Plain centre type grinder . . . . . . . . . . . . . . . 5.95.3.3.2 Universal centre type grinder . . . . . . . . . . . 5.115.3.3.3 Plunge-centre type grinding machine . . . . . . . 5.13

5.3.4 Centre-less type grinding machines . . . . . . . . . . 5.135.3.4.1 Principle of working . . . . . . . . . . . . . . . . . 5.145.3.4.2 Methods of centreless grinding . . . . . . . . . . . 5.155.3.4.3 Advantages of centreless grinding over cylindrical grinding . . . . . . . . . . . . . . . . . . 5.17

5.3.5 Internal Grinders . . . . . . . . . . . . . . . . . . . . 5.175.3.6 Surface grinding machines . . . . . . . . . . . . . . 5.215.3.7 Tool and cutter grinder . . . . . . . . . . . . . . . . 5.24


5.3.8 Special grinding machines . . . . . . . . . . . . . . 5.275.4 Abrasive Machining. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.28

5.5 Abrasives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.29

5.5.1 Natural Abrasives . . . . . . . . . . . . . . . . . . . 5.315.5.2 Artificial Abrasives . . . . . . . . . . . . . . . . . . . 5.325.5.3 Abrasive grain size or Grit Number and Geometry . 5.34

5.6 Grinding Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.36

5.7 Grinding Wheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.38

5.7.1 Characteristics of Grinding wheel . . . . . . . . . . 5.385.7.1.1 Type of abrasive used . . . . . . . . . . . . . . . . 5.385.7.1.2 Grain size or Grit size . . . . . . . . . . . . . . . 5.385.7.1.3 Wheel Grade and Hardness . . . . . . . . . . . . . 5.385.7.1.4 Grain spacing or structure . . . . . . . . . . . . . 5.395.7.1.5 Type of Bond . . . . . . . . . . . . . . . . . . . . . 5.40

5.8 Specification and Selection of Grinding Wheel . . . . . . . . . 5.45

5.8.1 Standard marking system of Grinding wheel . . . . 5.455.8.2 Selection of Grinding wheels . . . . . . . . . . . . . 5.46

5.8.2.1 Constant factors . . . . . . . . . . . . . . . . . . . 5.465.8.2.2 Variable factors . . . . . . . . . . . . . . . . . . . . 5.485.8.2.3 Other Factors . . . . . . . . . . . . . . . . . . . . . 5.48

5.9 Glazing, Loading and Gumming of Grinding Wheels . . . 5.49

5.10 Dressing and Truing of Grinding Wheel . . . . . . . . . . . . . 5.50

5.11 Microfinishing Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.53

5.11.1 Honing . . . . . . . . . . . . . . . . . . . . . . . . . 5.545.11.1.1 Honing tool . . . . . . . . . . . . . . . . . . . . . 5.545.11.1.2 Honing machines . . . . . . . . . . . . . . . . . . 5.555.11.1.3 Advantages of Honing . . . . . . . . . . . . . . . 5.555.11.1.4 Applications . . . . . . . . . . . . . . . . . . . . . 5.565.11.1.5 Methods of honing . . . . . . . . . . . . . . . . . 5.565.11.1.6 Honing conditions . . . . . . . . . . . . . . . . . . 5.56

5.11.2 Lapping . . . . . . . . . . . . . . . . . . . . . . . . 5.575.11.2.1 Methods of lapping . . . . . . . . . . . . . . . . . 5.585.11.2.2 Types of lapping operations . . . . . . . . . . . . 5.61

Contents C.11

5.11.2.3 Advantages of lapping . . . . . . . . . . . . . . . 5.615.11.2.4 Application of lapping . . . . . . . . . . . . . . . 5.61

5.11.3 Super finishing . . . . . . . . . . . . . . . . . . . . 5.615.11.3.1 Principle of operation . . . . . . . . . . . . . . . . 5.625.11.3.2 Factors controlling surface finish . . . . . . . . . 5.625.11.3.3 Applications . . . . . . . . . . . . . . . . . . . . . 5.63

5.12 Buffing and Polishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.63

5.12.1 Polishing . . . . . . . . . . . . . . . . . . . . . . . . 5.635.13 Types of Honing Stones . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.64

5.14 Cutting Fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.65

5.15 Parameters in Grinding . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.67

5.16 Broaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.68

5.16.1 Types of broaching operations . . . . . . . . . . . . 5.685.16.2 Force required for broaching . . . . . . . . . . . . . 5.695.16.3 Calculating the cutting forces . . . . . . . . . . . . 5.705.16.4 Surface roughness obtainable in lapping, honing and broaching operations . . . . . . . . . . . . . . 5.70

5.17 Capstan and Turret Lathe. . . . . . . . . . . . . . . . . . . . . . . . . 5.70

5.17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . 5.705.17.2 Capstan and Turret lathe . . . . . . . . . . . . . . 5.71

5.17.2.1 Principle parts of Capstan and Turret lathe . . 5.72

5.17.3 Types of Turret Lathes . . . . . . . . . . . . . . . . 5.765.17.4 Difference between Capstan - Turret lathe and Engine Lathe. . . . . . . . . . . . . . . . . . . . . . 5.775.17.5 Difference between Capstan and Turret lathe . . . 5.785.17.6 Size and specification of Turret Lathe . . . . . . . 5.795.17.7 Work holding devices . . . . . . . . . . . . . . . . . 5.805.17.8 Tool holding devices . . . . . . . . . . . . . . . . . 5.825.17.9 Turret Tools . . . . . . . . . . . . . . . . . . . . . . 5.895.17.10 Tooling layout for Capstan and Turret Lathes . . 5.89

5.18 AUTOMATS Automatic Machine Tools . . . . . . . . . . . . . . 5.90

5.18.1 Introduction . . . . . . . . . . . . . . . . . . . . . . 5.90


5.18.2 Classification of Automatic lathes . . . . . . . . . . 5.915.18.3 Single spindle chucking automatics . . . . . . . . . 5.925.18.4 Cutting off Machines . . . . . . . . . . . . . . . . . 5.945.18.5 Swiss type Automatics or Sliding Headstock Automatics . . . . . . . . . . . . . . . . . . . . . . . 5.955.18.6 Automatic Screw Machines . . . . . . . . . . . . . 5.985.18.7 Multiple Spindle Automatics . . . . . . . . . . . . 5.100

5.18.7.1 Multi-spindle bar automatics . . . . . . . . . . . 5.101

5.18.8 Advantages of Automatic Lathes . . . . . . . . . 5.1025.18.9 Applications . . . . . . . . . . . . . . . . . . . . . 5.102

Chapter - 6Introduction to Digital Manufacturing

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1

6.2 Concepts and Research and Development Status of Digital Manufacturing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1

6.2.1 Definition of Digital Manufacturing . . . . . . . . . 6.26.2.2 Features and Development of Digital Manufacturing 6.4

6.3 Basic Concept of Digital Manufacturing Science . . . . . . . . 6.6

6.4 Theory System of Digital Manufacturing Science . . . . . . . 6.7

6.4.1 Operation Mode and Architecture of Digital Manufacturing system . . . . . . . . . . . . . . . . . 6.76.4.2 Operation reference mode of digital manufacturing system . . . . . . . . . . . . . . . . . . . . . . . . . . 6.76.4.3 Architecture of Digital Manufacturing System . . . 6.10

6.5 Modeling Theory and Method of Digital Manufacturing Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.13

6.5.1 Modeling Theory . . . . . . . . . . . . . . . . . . . . 6.136.5.2 Critical modeling theories and technologies in digital manufacturing . . . . . . . . . . . . . . . . . 6.15

6.5.2.1 Generalised Modeling Theory and Method . . . . 6.15

6.5.3 Modeling Technique . . . . . . . . . . . . . . . . . . 6.186.5.3.1 IDEF . . . . . . . . . . . . . . . . . . . . . . . . . . 6.18

Contents C.13

6.5.3.2 IDEF0 (Function Modeling) . . . . . . . . . . . . . 6.196.5.3.3 IDEF1X (Information Modeling) . . . . . . . . . . 6.206.5.3.4 GRAI Modeling Method . . . . . . . . . . . . . . . 6.216.5.3.5 GRAI Grid . . . . . . . . . . . . . . . . . . . . . . . 6.226.5.3.6 GRAI Net . . . . . . . . . . . . . . . . . . . . . . . 6.226.5.3.7 Petri Net Modeling method . . . . . . . . . . . . . 6.246.5.3.8 Object-Oriented Modeling Method . . . . . . . . . 6.25

6.6 Theory System of Digital Manufacturing Science . . . . . . 6.27

6.6.1 Basic Architecture Model of Digital Manufacturing System . . . . . . . . . . . . . . . . . . . . . . . . . . 6.276.6.2 Definition of Digital Manufacturing System . . . . . 6.276.6.3 Organization Model of DM System . . . . . . . . . . 6.32

6.6.3.1 Alternative Competence Team (ACT) . . . . . . . 6.336.6.3.2 Virtual Working Team (VWT) . . . . . . . . . . . 6.336.6.3.3 Virtual Affairs Cooperative Center (VACC) . . . . 6.33

6.6.4 Function Model of Digital Manufacturing System . 6.336.6.5 Information Model of Digital manufacturing system 6.356.6.6 Operation and Control Model of DM system . . . . 6.376.6.7 Theory system of Digital Manufacturing Science . . 6.38


Chapter 1

Theory of Metal Cutting

Introduction to metal cutting: Tool nomenclature – Attributes of each

tool nomenclature – Attributes of feed and tool nomenclature on surface

roughness obtainable, Orthogonal and oblique cutting - Mechanism of metal

removal - Primary and secondary deformation shear zones, Mechanism of

chip formation – Types of chips, need and types of chip breakers – Merchant’s

theory, Analysis of cutting forces in orthogonal cutting – Work done, power

required (simple problems), Friction forces in metal cutting – development of

cutting tool materials, Thermal aspects of machining - Tool wear and wear

mechanisms, Factors affecting tool life - Economics of machining (simple

problems), Cutting fluids.

1.1 INTRODUCTION TO METAL CUTTING

A metal cutting process involves workpiece, tool (including holding

devices), chips and cutting fluid. For removing the metal, a wedge shaped

tool is considered stationary and the work piece moves to the right. The area

of metal in front of tool gets compressed causing high temperature shear. The

stress in workpiece just ahead of the cutting tool reaches ultimate strength

and particles shears to form chip elements. Fig 1.1 (a) shows position of tool

in relation to work in order to cut metal. There are three basic angles of

importance-rake angle, clearance angle and setting angle.

III

III

Shear P laneChip Too l

Rake Angle( )

Clearance A ng le( )Shear

A ng le( )

Setting Angle

Depth o f Cut

W ork

A

B

Fig. 1.1 (a) Position of tool in relation to work.

The outward or shearing movement of each successive is arrested by

work hardening and the movement is transferred to the next element. The

process is continuous and repetitive to give continuous chip which is

compressed, burnished and slightly serrated top side caused by shearing action.

The place of element shearing is called shear plane. Thus chip is

formed by plastic deformation of grain structure of metal along the shear

plane. The deformation occurs along a narrow band across the shear plane.

The structure begins elongating along AB below shear plane and

continue elongating till it completely deforms along the line CD above shear

plane as shown in Fig 1.1 (b) and chip is born.

The region between AB and CD is called shear

zone or primary deformation zone.

Actually lines AB and CD are not

parallel and may produce wedge-shape which is

thicker near the tool face at the right than at

the left.

Because of this, Curling of the chipoccurs in metal cutting. Also the non uniform

distribution of the forces at the chip-tool interface and on the shear plane,

the shear plane is curved slightly downward causing curling of the chip from

the cutting face of tool.

Observations in any cutting operation

Metal is cut by removal of chips either continuous ribbon or

discontinuous chips. Chip is thicker than the actual depth of cut

and correspondingly shortened.

Hardness of chip is greater than the hardness of parent material

There is no flow of metal at right angles to direction of flow.

Flow lines on side and back of chip indicates shearing mechanism.

Front surface is smooth due to burnishing action.

Lot of heat is generated in the process of cutting due to friction

between the chip and tool. Friction can be reduced by using sharp

BA

DC

C h ip

Too l

Fig.1.1 (b) Shear zone during metal cutting

1.2 Machine Tools and Digital Manufacturing

cutting edge, good tool finish, good tool geometry, using cutting

fluid etc.

In front of cutting tool point, generally no crack is observed. Due

to strain hardening, the hardness of metal in chip, the built up

edge and near the finished surface is usually greater than that for

the metal.

Sometimes a built up edge is formed at the tip of the tool and it

significantly alters the cutting process. It deteriorates the surface

finish and rate of tool wear is increased.

1.2 CUTTING TOOL NOMENCLATURE To perform cutting operations satisfactorily the tool bit or tool is

provided with various angles known as basic tool angles and

compose what is often termed as tool geometry.

Tool signature for a single point cutting tool is a sequence of

numbers listing the various angles in degrees and the nose radius.

1.3 PARTS AND NOMENCLATURE OF SINGLE POINT CUTTING TOOL

The various parts of a single point cutting tool are shank, neck, face,

base, heel, cutting edge or lip flank, point, height and width. A single point

tool is shown in Fig 1.2.

Attributes of Tool Nomenclature (Parts of Single Point Cutting Tool)

Shank : Shank is the main body of the tool at one end of which thecutting portion is formed.

Neck : The portion which is reduced in section to form necessarycutting edges and angles is called the neck.

Face : Face of the tool is the surface across which the chips travelas they are formed and is visible to the operator when lookingdown at the top from above.

Base : Base is the surface on which the tool rests.

Theory of Metal Cutting 1.3

Heel : Heel also known as lower face is the horizontal surface atthe end of the base in the neck portion which do notparticipate in cutting process.

Cuttingedge

: Cutting edge or lip is the portion of the face edge along whichthe chip is separated from the workpiece.

Standard Angles of Single Point Cutting Tool

These are angles which depend upon the shape of tool. These are

described below.

(i) Side rake angle: Side rake angle is the angle by which the face of the

tool is inclined side-ways whereas the back rack angle is the angle by which

the face of the tool is inclined towards back.

End C utting Edge Ang le

N ose Angle

S ide cuttingEdge Ang leFaceC utting

Edge

N eck

Face

Shank

Back R ake Ang le

FlankL ip Angle

BaseH eel

C learance A ng le

End R elie f A ng le

Po in t

H e ight

S ide R e lie f A ng le

S ide R ake Angle

w id th

Fig 1.2 Single point cutting tool

(a)

(b)

(c)


The side rake angle is the angle between the

tool face and a line parallel to its base and

measured in a plane right angles to the base and

at right angles to the centre line of the point of

the tool (side cutting edge). It varies between 0to 22.

The side rack angle of a tool determines the

tool thickness behind the cutting edge.

(ii) Back rake angle: Back rake angle is the

angle between the face of the tool and a line

parallel to the base of the shank in a plane parallel to the centre line of the

point (or parallel to the side cutting edge) and at right angles to the base.

If the inclination of face

backwards is downwards, the back

rake angle is positive, and if the

slope is upwards, then the angle is

negative.

This angle helps in turning

the chip away from the work piece.

Back rake angle affects the

direction of chip flow. Tool life

increases and cutting force is reduced by increasing back rake angle.

Increasing the rake angle facilitates easy flow of chip which increases

tool life, improves surface finish and reduces cutting force. Increasing rake

angle also minimizes size and effect of built up edges, cutting temperature,

cutting force and power consumption. As a result better surface is obtained.

Higher rake angle makes the point weak which may induce tool chatter. It

varies between 0 to 35 for various applications.

(iii) End relief angle: End relief angle is provided on tool to provide

clearance between the workpiece and the tool so as to prevent the rubbing

of workpiece with end flake of tool. It is the angle between the surface of

H e ight

S ide R e lie f Ang le

S ide R ake Angle

w id th

(b)Fig. 1.2

Face Back R ake Ang le

FlankL ip Angle

BaseH eel

C learance A ng le

End R elie f A ng le

Po in t

(c)Fig. 1.2


the flank immediately below the point and a line drawn from the point

perpendicular to the base.

Excessive relief angle reduces the strength of tool, therefore, it should

not be too large. Generally its value varies from 6 to 10

(iv) Side relief angle: Side relief angle is provided on the tool to provide

clearance between its flank and the workpiece surface. It is the angle between

the surface of the flank immediately below the point and a plane at right

angles to the centre line of the point of the tool. This angle must be large

enough for turning operations to allow for feed helix angle on the shoulder

of workpiece.

(v) End cutting edge angle: It

provides clearance between the tool

cutting edge and workpiece, and the

side cutting edge angle is

responsible for turning the chip

away from the finished surface. Sidecutting edge angle is the angle

between the straight cutting edge on

the side of the tool and side of the

tool shank. It provides the major

cutting action and should, therefore, be kept as sharp as possible. Too much

of this angle causes chatter. It’s value varies from 0 to 30.

(vi) Nose Angle: It is the angle between the side cutting edge and the end

cutting edge.

(vii) Nose radius: It is provided to remove the fragile corner of the tool.

It increases the tool life and improves surface finish.

(viii) Clearance angle: It is the angle between the portion of the flank

adjacent to the base and the plane perpendicular to the base. This angle

provides free-cutting action, minimises tool forces and decreases cutting

temperature. Excessive clearance angle may cause chatter and excessive tool

wear.

Fig. 1.2 (a)

End Cutting Edge Angle

Nose Angle

S ide cuttingEdge AngleFaceCutting

Edge

Neck Shank


(ix) Lip Angle: It is the angle between the tool face and the ground end

surface of flank. It is usually between 60 and 80

1.4 TOOL SIGNATURE

Tool signature is numerical method of identification of tool

standardized by American Standards Association (ASA) according to which

the seven elements comprising signature of a single point tool are always

stated in the following order:

(i) Back rake angle

(ii) Side rake angle

(iii) End relief angle

(iv) Side relief angle

(v) End cutting edge angle

(vi) Side cutting edge angle, and

(vii) Nose radius.

Symbols of degrees of angles and units for nose radius are omitted

and only numerical values of those components are indicated.

Example: A tool specified with the following as per ASA

8-16-7-7-8-16-6 has the following angles.

8 Back rake angle, 16 side rake, 7 end relief, 7 side relief, 8 end

cutting edge, 16 side cutting edge angles and 6 mm nose radius.

Tool Signature 8 16 7 7 8 16 6 mm

Back rake Angle

Side rake Angle

End relief Angle

Side relief Angle

End Cutting edge Angle

Side cutting edge Angle

Nose radius

Fig. 1.2 (a)

End Cutting Edge Angle

Nose Angle

S ide cuttingEdge AngleFaceCutting

Edge

Neck Shank


1.4.1 Influence of Tool angles in machining

1. Rake Angle

Rake angle has the following functions.

Helps in flow of chip in convenient direction.

Reduces cutting force and helps to increase tool life and reduce

power consumption.

Improves surface finish.

Amount of Rake angle to be given depends upon the following parameters.

Type of material being cut: Small rake angle is given for harder

material and large rake angle is given for soft material.

Type of Tool Material used: High speed tools (eg. cemented

carbide) are given minimum or negative rake angle to increase tool

strength.

Depth of Cut: Higher the depth of cut lower should be rake angle.

Smaller depth of cut have high rake angle tools.

Rigidity of the tool holder and condition of machine: An

improperly supported tool and old machine should have tool with

large rake angle to reduce cutting pressure.

Rake angle may be positive, zero or negative as shown in Fig 1.3.

A tool has positive rake when the face of tool slopes away from the

cutting edges and slants towards the back or side of the tool.

R

T

R

TT

Fig. 1.3. Positive, zero and negative rake R-Rake, T -Thrust


A tool has zero rake when the face of tool has no slope and in the

same plane or parallel to upper surface of shank. Turning brass usually have

zero rake tools. Zero rake increases strength of tool and prevents cutting edge

from digging into the work.

A tool has negative rake when the face of the tool slopes away from

the cutting edge and slants upwards towards the back or side of tool. It is

used in turning metal with cemented carbide tipped tool in mass production.

Advantages of negative rake angle

Point of application of cutting force is changed from weak to

stronger section.

Can work at very high speed.

Increases tool life and reduces tool wear.

Increases lip angle and hence permits higher depth of cut.

2. Clearance angle

Clearance angle prevents the flank from rubbing against the surface of

work allowing only cutting edge to come in contact with the workpiece.

Front clearance angle prevents front flank of tool from rubbing work

piece. It is large for large work diameter.

Side clearance angle prevents the side of the tool from rubbing work

when longitudinal feed is given. Larger feed requires large side clearance

angle.

3. Nose radius

Nose radius clears feed marks caused by previous shearing action.

It increases strength of cutting edge and hence increase tool life.

High heat dissipation.

4. Side cutting edge angle

Increases tool life and force distribution on wider surface.

Helps in greater cutting speed.

Improves surface finish and quickly dissipates heat

Usually its value is 15


5. End Cutting edge Angle

It is given to prevent the trailing front cutting edge of tool from

rubbing against work piece. Its value varies between 8 to 15. High value

of this, weakens tools.

6. Lip Angle

Lip angle influences the strength of cutting edge. Lip angle directly

depends upon rake clearance angle. Large lip angle helps in machining harder

metals, giving high depth of cut, increases tool life and improves dissipation

of heat.

1.5 METHODS OF METAL CUTTING PROCESSESMetal Cutting processes are generally classified into two types.

(i) Orthogonal cutting process (Two dimensional)

(ii) Oblique cutting process (Three dimensional)

Orthogonal cuttingprocess is one in which

the cutting face of the

tool is 90 to the line of

action or path of the tool.

In other words, the edge

of tool is perpendicular

to the cutting velocity

vector as shown in Fig.1.4 (a)

Oblique cutting processis one in which the

cutting face is inclined at

an angle less than 90 to the path of the tool, the cutting action is known

as oblique as shown in Fig 1.4 (b)

Fig 1.5 shows the chip flow in orthogonal and oblique cutting. In

orthogonal cutting the chip coils in a tight, flat spiral where as in oblique

cutting the chip flows sideways in a long curl. Angle’s i and nc are of

Feed

90 o

Rake

Knife edge

Feed

60oRake

Roughing

Depth o f cut

(a) Orthogonal (b) Oblique

Fig. 1.4. Orthogonal and Oblique cutting


importance in oblique cutting. In orthogonal cutting i 0 & nc 0. Orthogonal

cutting is used for knife turning, broaching and slotting where as bulk

machining is done by oblique cutting.

1.5.1 Differences between orthogonal and oblique cutting.

S.No.

Orthogonal Cutting Oblique Cutting

1. The cutting edge of the toolremains at 90 to the direction offeed (of the tool or the work)

The cutting edge of the toolremains inclined at an acute angleto direction of feed.

2. The chip flows in a directionnormal to the cutting edge of thetool.

The chip flow is not normal butat an angle to the normal tothe cutting edge.

3. The cutting edge clears the widthof the work piece on either ends.

The cutting edge may or may notclear the width of the workpiece.

4. Only two components of cuttingforce which are perpendicular toeach other are acting on tool.

Three components of cutting forceperpendicular to each other acts onthe tool.

5. Maximum chip thickness occurs atthe middle.

Maximum chip thickness may notoccur at middle.,

v

c

o

vw

ork

Ch i

p

o

ab

c

di

nc

(c) Oblique

Fig. 1.5. D irection of chip flow in orthogonal and oblique cutting.

(a) Orthogonal (b) Oblique


S.No.

Orthogonal Cutting Oblique Cutting

6. The shear force acts on a smallerarea, so shear force per unit areais more.

The shear force acts on a largearea, hence shear force per unitarea is smaller.

7. Tool life is smaller than that inoblique cutting.

Tool life is higher than orthogonalcutting.

8. The cutting edge is bigger than thewidth of cut.

The cutting edge is smaller thanthe width of cut.

1.6 MECHANISM OF METAL REMOVAL PROCESSESMetal removal process is a manufacturing process by which a work

piece is given (i) a desired shape (ii) a desired size and (iii) a desired

surface finish.

To achieve one or all of these, the excess material from the work piece

is removed in the form of chips with the help of some properly shaped and

sized tools. The metal removal processes are chip forming processes.

1.6.1 Classification of Metal Removal Processes

Metal removal processes are broadly classified into two categories.

(i) Chip forming (Metal Cutting / Removal) Processes: Examples

are Turning, Boring, Shaping, Planing, Slotting, Drilling, Reaming,

Milling, Broaching, Thread Cutting, Grinding, Honing, Gear

cutting etc.,

(ii) Chipless Forming Processes: Examples are Rolling, Spinning,

Forging, Extrusion, Stamping etc.,

1.6.2 Chip forming Processes

Chip forming processes are manufacturing processes in which the

desired shape, size and surface finish of work piece is obtained by separating

layer from parent workpiece in the form of chips, whereas in chipless forming

processes no chips are formed.


1.6.3 Turning, Boring and other Lathe Operations

Traditional machining operations like turning, boring, facing, grooving,

thread cutting, drilling, chamfering etc are carried out on a machine tool called

Lathe. Lathe is one of the most important machine in any workshop. Its

main objective is to remove material from outside by rotating the work against

a cutting tool. The various Lathe Operations are discussed as below.

Turning: Turning is a machining operation for generating external surfaces

of revolution (cone-shaped or cylindrical shaped) on the workpiece. In turning,

work is rotated where as tool has a linear motion, parallel to the axis of the

work. In this operation, the work is held either in the chuck or between

centers and the longitudinal feed is given to the tool either by hand or power.

Turning operation is shown in Fig. 1.6. The turning operation in which there

are steps on the work is called step turning as shown in Fig 1.7

Facing: When the feed motion of the tool is axial i.e parallel to the work

piece axis, a cylindrical surface is generated. If on the other hand, feed motion

is radial (normal to the axis of rotation), an end face or shoulder is produced.

This operation is called facing as shown in Fig. 1.8.

Boring: Boring is a machining operation for generating internal surface of

revolution i.e., it is an operation of enlarging of a hole already made in

workpiece with the help of a single point tool called boring tool. Boring tool

is held in the tool post and fed into the work by hand or power by movement

of carriage. Boring is shown in Fig. 1.9

W ork

ChuckChuck

W ork

Fig 1.8 FacingFig 1.6 Plain turn ing

Chuck

W ork

Fig 1.7 Step turning


Drilling: Drilling is an operation of making a hole in a workpiece with the

help of a drill. In this operation, the work piece is held in the chuck and

drill is held in the tail stock. The drill is fed manually into the rotating

workpiece by rotating the tailstock hand wheel. Drilling is shown in Fig.1.10.

Reaming: Reaming is an operation of finishing the previously drilled hole.

In this operation as shown in Fig. 1.11, a reamer tool is held in tail stock

and it is fed into the hole in the similar way as for drilling.

Undercutting or Grooving: It is an operation of making a groove on the

body of work, by feeding the tool perpendicular to the axis of the workpiece.

In this operation as shown in Fig 1.12, a tool of appropriate shape is fed

C huck

W ork

Boring tool

Fig 1.9 Boring Fig 1.10 Drilling

C huck

W ork

D rill

C huck

W ork

Too l

Fig 1.12 U nder cutting

C huck

W orkR eam er

Fig 1.11 Reaming


into the rotating work piece upto the desired depth at right angles to the

centre line of the work piece.

Threading: It is an operation of cutting helical grooves (threads) on the

external cylindrical surface of workpiece as shown in Fig. 1.13. The work is

held in a chuck or between centers and the threading tool (V-tool) is fed

longitudinally to the rotating workpiece. The longitudinal feed is equal to the

pitch of the thread to be cut.

Knurling: Knurling is a process of impressing diamond shaped or straight

line pattern on to the surface of a work piece. The diamond shaped pattern

or impressions are called knurls. In this operation, a knurled tool is moved

longitudinally to a rotating workpiece. The projection on the knurled tool

reproduces depressions on the work surface as shown in Fig. 1.14.

1.6.3.1 Machining parameters and related terms in turning operation

The different machining parameters or variables in turning are

discussed below (Refer Fig. 1.15)

Cutting speed (V): Cutting speed is the relative velocity between work piece

and cutting edge of tool responsible for cutting action. It is given by

relationship

W ork

Fig 1.13 Threading

Thread ing V -Too l

W ork

KnurlingTool

Fig 1.14 K nurling


V DN1000

in m/min

where D Diameter of work at engagement

N Rotational speed of work in RPM

Uncut chip thickness: It is the thickness of the layer of material being

removed by the cutting tool in the direction of the feed motion. The feed in

turning is normally expressed in mm per revolution.

Uncut chip thickness t f cos s

where f Feed per revolution.

s Side cutting edge angle of turning tool.

Depth of cut: It is the normal distance between the machined and

unmachined surfaces measured along a normal to the machined surface. In

turning, it is the radial distance between machined and unmachined surface.

From the Fig. 1.15, the cutting edge engagement is ‘b’ while the depth of

cut is ‘d’, hence,

W ork p iece

Direction of ro tation

b

d

fToo l

Position of Too l a t sta rt

Position of Too l a fter

one revo lu tion

s

Fig 1.15 Geom etry of Cut in Turning


Depth of Cut d b cos s

Area of Uncut Chip: It is the cross sectional area Ac of the layer of the

work being machined.

Area of Uncut chip Ac f d.

Metal removal rate (Rw: It is the volume of material being removed per

unit time from the work piece.

Rw 1000 f d V in mm3/min

Here, f, d are in mm, V is in m/min

Machining time: If L is the length of workpiece to be turned, then the time

of cutting Tc per pass is given by

Time Tc L/f N

In machining, however tool is not positioned in direct contact with the

work piece at the start of cut. It is kept at a small distance away from the

job. This is called approach allowance or approach length la. Then,

The Machining Time Tm L laf N

Problem 1.1 Evaluate the machining time for turning of a 100 mm diameterrod to 92 mm diameter over a length of 60 mm at a spindle speed of 500RPM. The maximum depth of cut is limited to 3 mm and the feed f is 0.5mm per rev. The side cutting edge angle of the tool is 30. Approach

allowance 5 mm. Also calculate cutting speed for each pass.

Given: Initial diameter Di 100 mm, Final diameter Df 92 mm, Length

L 60 mm, Speed N 500 RPM, d 3 mm,

f 0.5 mm/rev, s 30, la 5 mm

Solution

Total diameter to be reduced Di Df 100 92 8 mm

Diameter reduced in one pass d 2 3 2 6 mm


No. of pass required to reduce 8 mm 2 pass.

One Rough pass of 3 mm depth of cut and one finish pass of 1 mm

depth of cut.

3 2 1 2 8 mm

Cutting Speed for 1st rough pass

V1 DiN

1000 100 500

1000 157.1 m/min

Cutting Speed for 2nd finish pass

V2 Di 6 N

1000 94 500

1000 147.6 m/min

Since for both the passes, the spindle speed and feed are common

Machining time Tm No. of passes L la

f N

Tm 2 60 50.5 500

2.4 mins

1.6.4 Shaping, Planing and Slotting

Shaping is a machining operation for generating flat surface by means

of single point cutting tool reciprocating over a stationary work piece. The

feed motion is intermittent i.e. imparted to the work piece at the end of each

stroke. The reciprocating motion of the tool is obtained either by the crank

and slotted lever quick return motion mechanism or whitworth quick return

motion mechanism. The shaping action is shown in the Fig. 1.16. The surfaces

produced in shaping may be horizontal, vertical or inclined. Shaping is

performed on the machine tool called shaper. In general, shaper can produce

any surface composed of straight line elements.

Some of examples of the parts produced by shaping operation are

shown in Fig. 1.17.

Planing is a machining operation similar to shaping operation primarily

intended to produce plane and flat surfaces by a single point cutting tool.

The fundamental difference between a shaping and planing is that in planing


W ork P iece

f

d

Tool

Tool m otion

Fig 1.16 Shaping Action

(a) Grooved b lock (b) Dovetail slide

(c) Guide grib(d) V-b lock

Fig. 1.17 Parts produced on a shaper


the work which is supported on the table reciprocates past the stationary

cutting tool and the feed is supplied by the lateral movement of the tool,

whereas in shaping the tool which is mounted upon the ram reciprocates and

the feed is given by the crosswise movement of the table. Planing operations

are carried on machine tool called “planer”.

Slotting operation falls into the category of shaping and planing. The major

difference between a slotting and shaping is that in a slotting, the ram holding

the tool reciprocates in a vertical axis, whereas in shaping the ram holding

the tool reciprocates in a horizontal axis. A vertical shaper and slotter are

almost similar to each other as regards their construction, operation and use.

Slotting operation is used for cutting grooves, keyways, slots of various

shapes, for cutting internal and external gears etc.

1.6.4.1 Machining Parameters in Shaping, Planing

In shaping or planing, the cutting speed V varies even in a single

stroke. Cutting speed V is calculated as follows.

Cutting Speed V N L 1

1000 in m/min

where N : No. of Complete Strokes per minute (one working stroke return stroke)

L : Length of stroke in mm;: Ratio of time taken in return stroke to time taken in cutting

stroke.

Depth of Cut d: Depth of cut is equal to the normal distance between

the unmachined and machined surface measured along a normal to the

machined surface.

Nominal feed rate f is equal to the movement given to the workpiece in

a shaper (or to the tool in planer) in a direction normal to other cutting

velocity direction.

Area of uncut chip Ac f d

Metal removal rate Rw f d Lw N


Machining time Tm Bw

f N For Shaping

where Lw : Length of workpiece along stroke

Bw : Width of the workpiece

Machining Time for Planer

Tm Bw

fs

lsVc

1

Bw

fs tr.

where ls Length of stroke

fs Feed per stroke

Vc Average cutting speed in m/min

Average cutting speed to average return speed ratio

tr Time for reversal of work table.

1.6.5 Drilling and Reaming

Fig 1.18 D rilling Action

D rill

W ork p iece

ft

b

b


Drilling is a machining operation in which a hole is produced or

enlarged by use of a cutting tool called drill, usually having more than one

cutting edge. The primary cutting motion is a rotary motion given to either

work piece or to drill and the feed motion is a translation motion given to

drill as shown in Fig. 1.18. The cutting action is done by the cutting edges

on the end face.

Reaming is a hole finishing process. The motion of tool is similar as in

case of drilling. Cutting edges of a reamer are on its periphery. These cutting

edges are either straight or helical.

1.6.5.1 Machining Parameters for Drilling

Cutting Speed V D N

1000 in m/min

where D Drill diameter in mmN Speed of dr ill in RPMd Depth of Cut d D/2

Feed f Feed per revolution of drill (or) movement of drill alongits axis in one revolution.

Uncut chip thickness tc f cos

90 where 2 is point angle of drill.

Area of Uncut chip Ac f D/n 2

where n No. of cutting edges.

Metal removal rate Rw D2 f N

4 in mm3/min

Machining time Tm L

f N

where L Length of hole.

1.6.6 Milling

Milling is a machining process in which flat as well as curved surfaces

are produced by rotating multi-edges cutting tools called milling cutters and

the work is fed past it. The work piece is rigidly mounted on the machine


table and the cutter is on the spindle or arbor. The work is fed slowly past

the cutter while the cutter revolves at fairly high speed. The main milling

operations are

Slab milling, Form milling,

Face milling, Angular milling etc.

Slot milling,

These may be classified into two types i.e peripheral milling and face

milling. The operations are shown in Fig. 1.19.

W ork p iece

C utte r

(a )S lab m illing (b )Pro file m illing

(c) G ang m illing (d ) M illing w ith angle cu tte r

(a ) S lot m illing w ith end m ill (b ) Face m illing

Fig 1.19 (b) End milling Operations on a Vertical M illing Machine

Fig 1.19(a) Peripheral milling Operations on a Horizontall M illing Machine


Following are the two methods commonly used in milling operations.

(a) Conventional or up milling: In this method, the work is fed in a

direction opposite to the rotation of the milling cutter Fig. No. 1.20 (a)

(b) Climb or down milling: In this method, the work is fed in the

direction of rotation of cutter. Fig 1.20 (b)

Fig 1.20 (c) shows that the chips produced are not uniform in cross

section. In up milling, each tooth starts with a minimum thickness and ends

with maximum thickness (of the chip). In down milling, the reverse happens

i.e. each tooth starts with the maximum thickness and ends up with minimum.

Total volume of the chip for a cut by a tooth is same in both the cases.

TableStop

Cutte r

C lim b m illing

W ork

(b ) Down m illingFig. 1.20. M illing Operation

TableStop

Cutter

Conventional m illing

W ork

(a ) Up m illingFig. 1.20. M illing Operation


1.6.6.1 Machining Parameters in Milling

Cutting Speed V : It is the circumferential speed of cutter.

Cutting Speed V D N

1000 in m/min

where D Cutter diameter in mm,

N Speed of cutter in RPM.

In slab milling, the work piece is fixed on the machine table and feed

motion is given by table which is expressed in mm/min. If F is table feed

in mm/min and f is feed per tooth of cutter, then.

f F

nc N mm/rev/tooth

where nc No.of cutting edges or teeth on cutter.

w Width of work piece

d Depth of cut

Plane Area of cut Ac w d

Metal removal rate Rw w d F in mm3/min

t- depth o f cu t

(c) To ta l cross - sectional area of the uncu t ch ipFig. 1.20. M illing Operation


Machining Time Tm lw A a1 a2

F

l2, Length of workpiece in the feed direction.

a1 and a2, over travels at beginning and end of cut.

A [D d] d

1.6.7 Broaching

Broaching is a machining operation in which a multitooth cutter called

a broach is pushed or pulled over the surface to be machined while keeping

a desired interference between broach teeth and the surface. Generally it is a

single stroke operation. Broaching is generally limited to the removal of 6

mm of stock or less. A continuous Broaching Operation is shown in Fig.1.22.

1.6.8 Thread Cutting

Tapping and die cutting are machining operations in which internal

and external screw threads are produced by the helical (cutting) motion of

multi-point tools called taps and dies respectively. Taps and dies can be

visualized as helical broaches. Nowadays thread rolling is very popular in

manufacture of components like screw and bolts.

W ork p iece

a2 a1

Fig 1.21 A pproach Length and over Travel in slab milling

Cutte r Cu tte r

A


A schematic of cutting threads on a Lathe Machine is shown in

Fig.1.23 by using a ‘V’ tool.

Let Nl Speed of lead screw in RPM,

Ns Speed of lathe spindle in RPM,

P, Pitch of thread to be cut and

l, Pitch of the lead screw.

Then, Ns P Nl l

Gear ratio Ns

Nl

lP

Pitch of lead screw

Pitch of thread to be cut

1.6.8.1 Machining Parameters in thread cutting

Cutting speed V D N

1000 in m/min.

D : Diameter of tool (tap of die) and

N : Speed of tool in RPM.

Unload ing

Broach Support

Com ponentLoading

Support

Fixtures

Fig 1.22 A Continuous Broaching Machine


Feed Per min (f P N

Machining Time (Tm lw lt

f

Where P Pitch of thread

lw Length of surface of work

lt Length of tool

1.6.9 Grinding

Grinding is a machining operation in which a multi-edged rotating

abrasive tool called grinding wheel removes excess material from the work

piece. Grinding is finishing operation removing material usually 0.25 to 0.5

mm in most operations and accuracy in dimensions is in order of 0.000025

mm. Typical grinding operations are shown in Fig. 1.24.

Grinding operations are broadly classified as rough or non precision

grinding and precision grinding.

Head stock Chuck W ork piecep

Tool

Lead screwCarriageL

Changegears

Fig 1.18 A Schematic View of Thread Cutting on Lathe1.23


1.6.10 Honing and Lapping

Honing and Lapping are fine finishing operations. Very little stock is

removed during these operations. They are used to correct dimensional and

geometrical inaccuracies and to obtain high surface finish.

Honing is fine finishing operation in which abrasive sticks are used as

tool which rotate and simultaneously reciprocate on the surface of the

workpiece and slowly abrade the work piece surface to the desired finish and

accuracy. Though honing can be performed on lathes and drilling machines,

special honing machines, both horizontal and vertical are often used.

Lapping is a fine finishing operation in which a lap made of material

softer than the work piece lightly rubs abrasive particles against work piece.

Flat or curved surface can be lapped.

1.6.11 Gear Cutting

Gears are important elements in mechanical transmission of power.

Gears may be manufactured by casting, stamping, machining or by powder

metallurgical processes. The most common and accurate method of production

of gears is by machining. The various methods of machining gears are:

(a) Formed Cutter method

(i) By a formed disc cutter or formed end mill in milling machine.

(ii) By a formed single point tool in shaping or planing machine.

(iii) Formed cutter in a broaching machine.

.

... ..... ...

..... .

.

....

.

....

.

......

.... ...

.. ..

...... .

....

.............

Fig 1.24 B asic kinds of precision grinding


(b) Generating Method

(i) By a rack tooth cutter in gear cutting machine.

(ii) By a pinion cutter in a gear cutting machine.

(iii) By a hob cutter in a gear cutting machine.

(iv) By a bevel gear generator.

1.7 PRIMARY AND SECONDARY DEFORMATION SHEAR ZONESAll the mechanical work done during metal cutting is converted into

equivalent amount of heat. The heat generated has three distinct sources as

follows:

Zone 1 - The shear zone or primary deformation zone: This is

where the primary plastic or shear deformation takes place.

Zone 2 - The secondary deformation zone: This occurs at the chip

- tool interface. Here the secondary plastic deformation due to

friction between the heated chip and tool takes place.

Zone 3 - This takes place at the work tool interface ie at the flanks

where frictional rubbing occurs.

The heat generated at the work tool interface occurs when the cutting

tool is not sharp. Usually the heat generated at this source is small and hence

could be neglected.

Fig:1.25 Deform ation zones in metal cutting

W ork

VC

V f

Too l

W orkToo lin terface

Prim ary deform ation zone or shear zone

Secondary deform ation zone

Chip


Therefore, equivalent rate of heat generation during machining,

Pm Ps Pf ...(i)

where, Ps Rate of heat generation in the primary deformation zone

(shear-zone heat rate)

Pf Rate of heat generation in the secondary deformation zone

(fractional heat rate)

Now; Pm Fc Vc ii Pf Fs Vf iii

where; where;

Fc Cutting component of resultant

tool force

Fs Frictional force on the tool face

Vc Cutting speed Vf Velocity of chip flow

0

10 20 30 40 50 60 70 80 90

25

50

75

100

% o

f to

tal h

ead

gene

rate

d

Cu tting feed m /m in

t

w

C

Fig: 1.26 Distribution of head during metal cutting


From, equation (i), we get the shear zone heat rate as

Ps Pm Pf

Heat is removed from the three zones by the workpiece, chip and thetool. The relative amount of heat transformed to chip, workpiece and tool atdifferent cutting speeds is shown in Fig. 1.26. This diagram is for machiningof steel with a single point tool having cemented carbide tip. As the cuttingspeed increases, more heat is carried away by the chip and less heat istransferred to the workpiece and the tool. High speed machining is, thereforeadvantageous to the tool life.

The tool rate of heat generation,

Pw c w t

where, c - rate of heat transportation by the chip

w - rate of heat conduction into the workpiece

t - rate of heat conduction into the tool

t forms a very small proportion of Pw and may be neglected.

1.8 MECHANISM OF CHIP FORMATION

Chip formation has already been explained in mechanism of metalcutting. All machining processes involve formation of chips by deforming thework material on the surface of the job with the help of a cutting tool. Theextent of deformation that the material suffers not only determines the typeof the chip but also determines the quality of the machined surface, cuttingforces, temperature developed and dimensional accuracy of the job. Dependingupon the tool geometry, cutting conditions and work material, a large varietyof chip shapes and sizes are produced during different machining operations.

1.8.1 Types of Chips

The chips are broadly classified into three categories:

(i) Continuous Chip

(ii) Continuous chip with built up edges.

(iii) Discontinuous Chip


1.8.1.1 Variables affecting type of chip

The type of chip produced in a particular operation depends upon the

following variables.

Properties of material being cut (i.e ductile or brittle)

Cutting speed

Depth of cut

Feed rate

Rake angle

Type and way of application of cutting fluid

Surface roughness of the tool face.

Coefficient of friction between the chip and tool interface

Temperature of the chip on the tool face.

Nature of cutting i.e. continuous or intermittent

1.8.1.2 Continuous Chips

During the cutting of ductile materials like low carbon steel, copper,

brass, aluminium alloys etc., a continuous ribbon type chip is produced. The

pressure of tool makes the material ahead of the cutting edge deform

plastically. It undergoes compression and shear. The material then slides over

the tool rake face for some distance and then leaves the tool. Friction between

the chip and tool may produce secondary deformation on chip. The plastic

zone ahead of the tool edge is called the Primary Zone of deformation and

the deformation Zone on the rake face is usually called Secondary Zone of

Prim ary zone of deform ation

Secondary zone o f deform ation

W ork p iece

Tool

Ch ip

Fig.1.27 (a) Continuous chip


deformation as shown in Fig. 1.27 (a). Both these zones and the sliding of

chip on rake face produce heat.

The extent of primary zone deformation depend upon.

(i) Cutting speed (ii) Rake angle of tool (iii) Friction on rake face

(iv) Work material characteristics.

With large rake angle tools, the chip formation is gradual and material

suffers less overall deformation. Cutting forces are also low. With small or

negative rake angle tools, the material suffers more severe deformation with

large cutting forces.

At high cutting speed, the thickness of the primary zone of deformation

shrinks i.e it becomes narrower.

Conditions favorable for continuous chip are

(i) Ductile Material

(ii) Large rake angle

(iii) High cutting speed

(iv) Small depth of cut

(v) Small feed rate

(vi) Efficient way of applying cutting fluid to prevent built up edge

(vii) Low coefficient of friction at chip tool interface

(viii) Polished face of the cutting tool

(ix) Use of material having low coefficient friction as cutting tool,

(Ex) cemented carbide.

Continuous chips pose difficulty while machining, it gets wrapped over

the machined portion of work if not quickly disposed. So during machining

a device known as “Chip Breaker” is attached over the tool post (near the

tool nose) which breaks the chip into smaller fragments.

1.8.1.3 Continuous Chips with Built up Edges.

The temperature is high at the interface between the chip and the tool

during cutting. As the chip moves over the tool face due to the high normal

load on the tool face, high temperature and high coefficient of friction between


chip and tool interface, a portion of chip gets welded on the tool face forming

the embryo of built up edge (BUE). The strain hardened chip is so hard that

now it becomes part of the cutting edge and starts cutting the material. Since

this built up edge is irregular in shape, the surface produced becomes rough.

As the machining continues, more and more chip material gets welded on

the embryo built up edge, this increases its size and ultimately, it becomes

unstable and gets sheared off. This cycle is repeated. During the unstable

stage, some fragments of the built up edge are carried along the under surface

of chip while some escape along the flank thus worsening the surface finish

of the machined surface. [Fig. 1.27(b)]

However there is a remedy. Increasing in cutting speed, increases the

interface temperature which softens the built up edge. As a result, the critical

size of the built up edge completely disappears. Fig 1.28 shows the formative

cycle of built up edge. After the embryo of built up edge reaches the final

stage,. it is sheared off. Again the embryo is formed and the whole cycle is

repeated.

1.8.1.4 Discontinuous Chips

Discontinuous chips are produced during the cutting of brittle material

like cast iron, brasses etc containing higher % of Zinc. The chip formation

mechanism is different from that of ductile material. A slight plastic

deformation produced by a small advance of the cutting tool edge into the

job leads to a crack formation in the deformation Zone. With further advance

W ork p iece

Bu ilt up edge

BU E = Built U p Edge

Fragem ents o f B U E

Fig.1.27 (b) Continuous chip with B U E


C hip

Too l

W ork p iece

In itiation o f B U E

(a) n itiation o f B U E I

C hip

Too l

W ork p iece

G row th of B U E

(b) Growth of B U E

C hip Too l

W ork p iece

Fragm ents of B U E

(c) Breaking of B U E

Fig. 1.28. Formation of Built up Edge and Fragmentation


of the cutting tool, the crack travels and a small lump of material starts

moving up the rake face as shown in Fig. 1.29.

The force and constraints of motion acting on the lump make the crack

propagate towards the surface, and thus a small fragment of chip gets

detached. As the tool moves further, this sequence is repeated.

Following are conditions at which discontinuous chips are formed

Use of brittle material

Smaller negative rake angle

Large chip thickness i.e. large depth of cut and high feed rate.

Low cutting speeds

Dry cutting i.e. cutting without use of cutting fluid.

Fig. 1.29. Formation of Discontinuous Chip.

Too l Too l Too l

W ork p iece W ork p iece W ork p iece

(a) (b) (c)

In itia ldefo rm ation C rack

Form ation

C h ipsegm ent

W ork p iece

Too l

C h ips

Fig.1 .27 (c) D iscontinuous chip


1.8.1.5 Chip Breakers

Chip breakers are important components of tool design particularly

when tool has to cut ductile materials like low carbon steels, copper,

aluminium, low zinc brasses etc. These materials produce long continuous

chips which are difficult to handle and occupy large volumes. Such chips

fouls the tool, clutter up the machine and work place and are difficult to

remove. These chips are to be broken into small pieces for ease of handling

and to prevent it from becoming hazardous. Hence chip breakers are used to

break this continuous chips into small pieces. The general types of chip

breakers are

(i) Step type

(ii) Groove type

(iii) Clamp type.

These types are shown in Fig. 1.30

In general shop practice, the chips are broken by the following

methods.

(i) By a stepped type breaker in which a step is ground on the face

of the tool along the cutting edge.

(ii) By clamping a piece of sheet metal in the path of the coil.

(iii) By a clamp type breaker in which a thin carbide plate is brazed

or screwed on the face of tool.

(iv) By a groove type breaker in which a small groove is ground

behind the cutting edge.

Step type Groove type Clam p typeFig. 1.30 Chip Breakers


1.8.2 Geometry of Chip Formation

When a wedge shaped tool is pressed against the workpiece, chip is

produced by deformation of material ahead of cutting edge because of

shearing action taking place in a zone known as shear plane. This shear plane

separates the deformed and undeformed material.

The Geometry of chip formation is shown in the Fig. 1.31(a)

Considering the Geometry of chip formation we have the following.

Vc : Velocity of tool against workpiece (Cutting Velocity).

AB : Shear plane.

t : Depth of Cut (Feed in turning operation)

tc : Chip thickness

Vt : Velocity of chip relative to tool acting along tool face.

Vs : Velocity of chip relative to workpiece along shear plane

t

B Too l

V C

tCV S

-G A

E

V t

Fig.1.31 (a) Geom etry of C hip form ation

C hip


Considering the principles of kinematics, the three velocity vectors

(Vt, Vc, Vs) form a closed velocity triangle ABD as shown in Fig. 1.31(b).

Also from the kinematics, the vector sum of cutting velocity Vc and chip

velocity Vt is equal to the shear velocity vector Vs

1.8.2.1 Velocity Relationships

[Fig. 1.31 (b)]

From Right Angle triangle ACD, BDC we have

DC Vc sin ; DC Vt cos

From above relation, we have

Vc sin Vt cos

So, Vt Vc sin

cos ...(1.1)

Similarly, from right angle triangle AED, AEB we have

AE Vc cos ; AE Vs cos

Vc cos Vs cos

So, Vs Vc cos

cos ...(1.2)

V C

V t

B

C

V S

A

E

D

Fig.1.31 (b) Cutting velocities triangle


1.8.2.2 Shear Plane angle and chip Thickness ratio

The chip thickness ratio is defined as the ratio of depth of cut t to

the chip thickness tc

Chip thickness ratio r ttc

From the Geometry of Fig. 1.31(a) we see that AE perpendicular to

tool chip interface represents tc i.e. Chip Thickness.

From right angle triangles ABG & ABE we have

AB t

sin , AB

tccos

dividing the above two equations we have

ABAB

t/sin

tc/cos

i.e. ttc

sin

cos r

. . . r

ttc

r ttc

sin

cos cos sin sin

. . . cos cos cos sin sin

r cos cos sin sin sin

r cos cos sin sin

sin 1

r cos tan

r sin 1

r cos tan

1 r sin

. . . tan r cos

1 r sin


(or) Shear Angle tan 1

r cos 1 r sin

...(1.3)

(Here the term 1r

is termed as chip reduction coefficient or chip

compression factor and is denoted by K)

The cutting ratio or chip thickness ratio is always less than unity and

can be evaluated by measuring chip thickness and depth of cut. But it is

difficult to measure chip thickness precisely due to roughness on back surface

of chip.

The chip reduction coefficient can also be estimated in a different

manner by measuring the length of the chip (lc

Volume of metal removed Volume of Chip.

So, t b l tc bc lc c ...(1.4)

(Here t, b, l, being thickness or depth, width, length and density of

metal cut and ‘c’ standing suffix for chip).

If width of chip is same as workpiece i.e b bc, and density is same

for both ie c we have

t l tc lc

ttc

lcl

We know ttc

r so, r ttc

lcl

[chip thickness ratio or cutting ratio]

Also density of metal can be used to find the chip reduction coefficient

r t b

m ...(1.5)

where m is Weight per unit length of metal.


1.8.2.3 Force Analysis in Metal Cutting

Fig 1.32 shows a turning operation with oblique cutting. In this thecutting edge ab makes an angle with the direction of feed. The metal beingcut undergoes cutting forces. These forces are resolved in three mutuallyperpendicular direction as shown in Fig. 1.32.

The three forces are

(i) Feed Force Fd: It is horizontal component of the cutting force, acting

in the direction of feed of the tool. It is acting tangent to the generated

surface.

(ii) Thrust force Fr: It is reaction force between the tool and the work

piece acting in radial direction perpendicular to feed direction.

(iii) Main cutting force Fc: It is the vertical component of the cutting

force acting in vertical direction.

The resultant force R Fd2 Fr

2 Fc2

Analysis of cutting forces in Orthogonal Cutting

Fig 1.33 shows an orthogonal cutting process. In this process, the

cutting force has two components only, one in the feed direction Fd and

other in vertical direction - cutting force Fc

Fd

F r

Fc

F y

F z

Fx

c

a

b

Feed

R

Fig.1.32. Forces in oblique Turning


The two components of forces Fd, Fc and forces acting on chip are

shown in Fig. 1.33(a).

As the cutting tool moves along the feed direction, the metal gets

plastically deformed along the shear plane and the chip moves along the rake

surface of tool and due to roughness of chip, frictional Force F is acting

on the tool.

Following are the forces developed.

Force F : It is the Frictional resistance of chip acting on tool.

Force N : It is reaction provided by the tool.

Force Fs : It is shear force on metal.

Force Fn : It is normal to shear plane and it is backing up forcecausing compressive stress on the shear plane.

Fig 1.34 shows the free body diagram of forces acting on chip.

Here the Resultant

R Fn2 Fs

2 ; R F2 N2

Both R and R are equal in magnitude and opposite in direction and

are collinear since chip is in equilibrium.

Fc

Fa

F dFs

F nF cF d

Feed

Tool

Feed

W orkp iece

N

F

Chip

Fig. 1.33. Orthogonal Turning.(a )


1.8.2.4 Force analysis in orthogonal cutting (Merchant Circle diagramand Theory)

From a fixed geometry of the cutting tool, there exists a definite

relationship among the above mentioned forces (section 1.8.2.3)

The components of forces could be measured by a dynamometer and

all the forces could be calculated.

Merchant represented these forces in a circle, known as Merchants

circle diagram shown in Fig 1.35.

Following are the assumptions made in merchants to workout force

relations.

(i) Tool is perfectly sharp and there is no contact along the clearance

face.

(ii) The shear surface is a plane extending upward from the cutting

edge.

(iii) The cutting edge is a straight line.

Fs

F n

R

F

R �

N

Chip

Fig. 1.34. Free body diagram


(iv) The chip does not flow to either side.

(v) The depth of cut is constant.

(vi) Width of the tool is greater than that of workpiece.

(vii) The work moves relative to tool with uniform velocity.

(viii) A continuous chip is produced with no built up edge.

(ix) Plain strain condition exists i.e width of chip remains equal to

width of the workpiece.

In the Fig 1.35 we have

back rake angle

shear angle

angle of friction ;

Forces Fd and Fc can be measured by dynamometer

Shear angle can be measured by photomicrograph or by measuring

thickness of chip and depth of cut. (discussed earlier).

Fig. 1.35 Merchant Circle diagram .


Once the Fd, Fc, and are known, all the other components of forces

acting on the chip can be determined by the geometry shown in Fig 1.35.

We can draw the following figures from Fig 1.35 and find relations.

From the Fig 1.36(a) we have from the geometry

Fs AB AC BC ; Fc AD ; Fn BE

Fs AB Fc cos Fd sin

Fn BE Fc sin Fd cos ...(1.6)

Again from Fig 1.36(a) we have

Fc R cos [From le ADE]

Fs R cos [From le ABE]

So R Fs

cos ...(1.7)

Substituting R in Fc we get

Fc Fs

cos cos

...(1.8)

Fd

F c

a

F d

Fs

Fc

F n

A

c

e

d

f

F

N

b

R

o

(b)

-

D

C

B

R

(a)E

Fig. 1.36. Geom etry of Forces


or Fs Fc cos

cos ...(1.9)

From Fig 1.36(b) we have.

N ab oe od de

N Fc cos Fd sin

Since F ao be

ef fb cd fb

F Fc sin Fd cos ...(1.10)

Let coefficient of friction, then we have

F N

Coefficient of friction

FN

Fc sin Fd cos Fc cos Fd sin ...(1.11)

dividing the numerator and denominator by cos we get

Coefficient of friction Fc tan Fd

Fc Fd tan ...(1.12)

Condition For maximum cutting force

From the equation (1.8) we have

Fc Fs

cos cos

where Fs shear force

Fs shear stress Area of shear plane

Fs s b tsin ...(1.13)

Substituting 1.13 in 1.8 we get


Fc s b tsin

cos

cos ...(1.14)

For maximum Fc, we have

d Fc

d 0

d Fc

d

dd

s b t

sin

cos cos

0

s b t cos dd

1sin cos

0

d Fc

d s b t cos

cos cos sin sin

sin cos 2

0

(or) cos cos sin sin 0

cos [ ] 0

[. . . cos A B sin A sin B cos A cos B]

cos 2 0 cos /2[. . . cos /2 0]

2 /2

or Shear Angle 4

2

2 ...(1.15)

The above relationship is based on Earnest Merchant Theory and also

called as “Modified Merchant Theory”, which makes the following

conclusions.

1. The stress is maximum at the shear plane and it remains constant.

2. The shear takes place in a direction in which the energy required

for shearing is minimum.


Merchant modified the relationship desired by Earnest - Merchant, by

assuming that the shear stress along the shear plane varies linearly with

normal stress. It is given as

s 0 K n ...(1.16)

Where s Shear stress

0 Static stress

n Normal stress

K constant

Equation 1.14 becomes,

Fc 0 K n b tsin

cos

cos

For maximum Fc, we have

d Fc

d 0, we get cos 2 K

or 2 cos 1 K

Shear Angle cos 1 K

2 2

2 ...(1.17)

1.8.2.5 Power and workdone required in cutting process

Let Pc Horse Power (HP) in kW required for cutting.

Pm Gross Horse Power HP in kW of the motor.

PI Idle Horse power ie Horse Power consumed while running idlein kW

Vc Cutting Velocity

Work done in cutting W Fc Vc in Nm/s or Watt ...(1.18)

Where Fc Cutting Force in N


Work done in shear Ws Fs Vs ...(1.19)

Where Fs Shear force and

Vs Velocity of chip relative to work in m/s.

Work done in friction Wf Ff V

Ff Frictional force,

V Velocity of chip relative to cutting tool in m/s.

Now Total work done in cutting W Ws Wf

Fc Vc Fs Vs Ff V ...(1.20)

Also cutting Power in Pc Fc Vc

60 75 1.36 kW

...(1.21)

Here Fc Vc is workdone in kgm/min.

Or Force of Cutting Fc Pc 6120

Vc ...(1.22)

Here Fc is in kg, Vc in m/min, Pc in kW

Also we have Pc Pm PI ...(1.23)

Mechanical Tool efficiency (tool Pc

Pm ...(1.24)

1.8.2.6 Stress and Strain in Chip

Let avg Average Shear Stress on Shear plane

As Area of Shear Plane

w Width of the chip

t Thickness of chip

We have Shear Stress s Fs

As where Fs Shear force


We know that As w.t

sin

s Fs sin

w t ...(1.25)

From the equation 1.6 we have

Fs Fc cos Fd sin

s [Fc cos Fd sin ] sin

w.t

Shear Stress s Fc cos sin Fd sin2

w.t ...(1.26)

1.8.2.7 Shear Strain in Cutting

Let us consider the chip consists of a large number of element as

shown in Fig. 1.37

Let x Thickness of each element

s Displacement of each element through shear plane

e Strain

Tool

xs

x

s

-

A B C D

90-

O

x

s

Fig.1.37. Shear Strain.


We know that Strain e s

x

ACx

AB BC

x

e ABx

BCx

x tan 90

x x tan

x

e tan tan 90 ...(1.27)

e tan cot

sin cos

cos sin

e sin sin cos cos

sin cos

e sin [sin cos cos sin ] cos [cos cos sin sin ]

sin cos

. . . sin A B sin A cos B cos A sin B

cos A B cos A cos B sin A sin B

e sin2 cos sin cos sin cos2 cos cos sin sin

sin cos

e cos [sin2 cos2 ]

sin cs

strain e cos

sin cos

... (1.28)

From the equation 1.2 we have

VS VC cos

cos

Substituting (1.2) in 1.28

Strain e Vs

Vc sin

Vs e Vc sin ... (1.29)


1.8.2.8 Energy in cuttingTotal energy consumed per unit time in cutting

Energy E Fc Vc ... (1.30)

Total energy consumed per unit volume of metal removed

Em E

Vc w t

Fc Vc

Vc w t

Fc

w t ... (1.31)

The total energy required per unit volume of metal removed is

ETot Es Ef Ea Em

where Es Shear energy per unit volume

Ef Specific friction energy

Ea Surface energy per unit volume (negligible)

Em Momentum energy per unit volume (negligible)

Es s Vs

Vc sin and Ef

Fw tc ... (1.32)

Practically all the energy required in metal cutting is consumed in the

plastic deformation on the shear plane and the friction between chip and tool.

1.9 DEVELOPMENT OF CUTTING TOOL MATERIALS

The materials having certain specific properties and characteristics are

used as tool materials. Tool material is harder than the material to be cut.

Type of cutting tool material to be used depends upon.

(i) Physical and chemical properties of metal to be cut

(ii) Type of manufacturing process ie either Turning, Milling,

Grinding etc.

(iii) Rate of production & volume of production.

(iv) Condition of the machine tool.

(v) Complexity of tool and material to be cut.


1.9.1 Desirable Properties of Cutting Tools

The various and important properties of cutting tools are

(i) Hot Hardness

(ii) Wear resistance

(iii) Mechanical and Thermal shock resistance

(iv) Toughness

(v) Friction properties between tools & workpiece

(vi) Chemical reactivity between tool and workpiece

(vii) Ease of availability and manufacture

(viii) High thermal conductituty

(ix) Low coefficient of thermal expansion

(x) Cost of tool.

The most important proporties of tool material are hot hardness, wear

resistance and toughness

(i) Hot Hardness

Hot Hardness is a measure of the ability of a tool material to retain

its hardness even at elevated temperature without loosing its cutting edge. In

metal cutting, heat is generated during the process due to which the hardness

of the cutting material reduces and consequently the cutting ability of the tool

(or the cutting edge of the tool) will reduce. Therefore, it is a very important

factor for any materials to be used as a cutting material. In practice, the

harness is increased by adding element like chromium, molybdenum,

vanadium, tungsten.

(ii) Wear Resistance

Wear means loss of material. Wear of tools is caused by abrasion,

adhesion and diffusion. Abrasive action is because of flow of chip over the

rake face under high pressure and rubbing action of the machined surface

with tool flank. Adhesion is gradual loss of tool material when its particles

adhere to the chip or machined surface and get torn away. Diffusion wear is


due to transfer of atoms of hard alloy constituents of tool material into work

or chip materials resulting in heating of tool.

A wornout tool will have following effects

(i) Poor surface finish dimensional tolerence on work piece.

(ii) Increase in cutting force and thus increase in power consumption.

(iii) Increase in temperature and vibration.

Therefore tools must have high wear resistance.

(iii) Toughness

Toughness is the ability of a material to absorb deformation energy

before fracture. Tougher the material, higher the ability of material to absorb

impact loads and intermittent cuts. It is however observed from experience

that materials which are wear resistant and have high hot hardness are also

more brittle and therefore less tough.

(iv) Mechanical and Thermal Shock Resistance

If a material has high hardness, its resistance to wear is more. But

increase in hardness, renders it to shock, because it loses toughness and

fracture under impact load easily. There is shock load to the tool when it

just engages with the work and at regular interval if the cutting is intermittent.

Therefore, the tool material should have high mechanical and thermal shock

resistance.

(v) Friction

There should be low friction between the tool and workpiece since the

friction generates heat. The coefficient of friction between the tool and work

piece should be as low as possible.

(vi) Chemical reaction/affinity between the Tool and Workpiece

If there is a high affinity of work material with tool material, the tool

will wear out easily and hence the tool material should have less affinity or

no affinity with work material.


(vii) Availability and Manufacture

A tool material with the above mentioned properties must be easily

available or can be easily manufactured. If its manufacture is very hard, it

may not be of much use to the machining.

(viii) High Thermal Conductivity

Tool material should have high thermal conductivity so that the heat

generated during cutting is easily removed from the chip-tool interface.

(ix) Coefficient of Thermal expansion

Tool material should have low coefficient of thermal expansion to

avoid distortion during heat treatment.

(x) Tool Cost

The cost of material is also an important factor for its selection as tool

material. Tool material should be of low cost.

1.9.2 Types of Cutting Tool Materials

The various types of cutting tool materials are:

(i) Carbon tool steels or carbon steels.

(ii) Medium alloy steels or Alloy tool steels

(iii) High Speed Steels (HSS)

(iv) Cast alloys (or) Stellites

(v) Cemented Carbide tool Materials

(vi) Oxide or Ceramic tool Materials

(vii) Diamond

(i) Carbon Tool Steels or Carbon Steels

The composition of general carbon steels are Carbon 0.8 to 1.3%,

Manganese - 0.1 to 0.4% and Silicon - 0.1 to 0.4%. Few alloying elements

are added to improve properties of Carbon Steels. These are Vanadium and

Chromium. The composition of Carbon-Vanadium Steels and Carbon

Chromium Steels are:


(i) Carbon Steels : 0.8 to 1.3% C, 0.1 to 0.4% Mn, 0.1to 0.4%Si

(ii) Carbon-VanadiumSteels

: 0.8 to 1.3% C, 0.1 to 0.4% Mn, 0.1 to 0.4%Si, 0.15-0.25% V

(iii) Carbon-ChromiumSteels

: 0.8 to 1.3% C, 0.1 to 0.4% Mn, 0.1 to 0.4%Si, 0.40-0.60% Cr

Characteristics of Carbon Steels

Carbon Steels have low hot hardness and poor hardenability. They

can be worked upto 200 to 250C. At higher temperature, they

loose hardness rapidly.

Carbon Steels are used for Cutting soft materials like Wood,

Plastic, Aluminium, Copper etc.,

Carbon steels are used for making Taps and Core drills for

machining soft materials and for making wood working tools.

Effect of alloying element:

Tungsten increases the wear resistance

Chromium and Manganese improves hardenability.

Vanadium increases toughness by giving heat treatment.

(ii) Medium Alloy Steels

In medium alloy steels, alloying elements like Tungsten, Chromium,

Molybdenum are added to improve hardenability. The carbon content in these

alloy steel is around 1.2 to 1.3%. Higher Carbon content increases hardness

and wear resistance. Tools of these material can work between 250C to

300C and speed is 20 to 40% more than carbon steels. These steels materials

are used in making drills, taps and reamers.

(iii) High Speed Steels (HSS)

The composition of High Speed Steel is 18% Tungsten, 5.5%

Chromium 0.7%, Carbon and small amount of Manganese, Vanadium and

Silicon. This HSS steel was developed by Fredenck W.Taylor and M.White.

It can work upto 600C at 40 m/min.

HSS is of three types:


(i) High Tungsten HSS

(ii) High Molybdenum HSS

(iii) Tungsten-Molybdenum HSS.

The composition of the above HSS is given below:

(i) High Tungsten HSS : 18% W, 4% Cr, 1% V, 0.6% C &Balance Fe

(ii) High Molybdenum HSS : 1% W, 4.5% Cr, 1.5% V, 8.5% Mo,0.8% C and Balance Fe.

(iii) Tungsten-Molybdenum HSS

: 6% W, 4% Cr, 2% V, 6% Mo andBalance Fe

Characteristics of HSS

High Tungsten HSS is the best of the above three for all purpose

tool steels.

Tungsten and Molybdenum increase the hot hardness.

Vanadium iron Carbide tools are very hard constituents of HSS

and imparts high wear resistance to tool at all temperatures.

To increase the cutting efficiency, 2 to 5% of Cobalt is added.

One of the composition 2% W, 4% Cr, 2% V, 12% Cobalt are

called Super high Speed Steels. Because of heavy cost, it is used

for heavy cut operations only.

HSS hot hardness is quite high so it retains the cutting ability upto

600C at 40 m/min.

HSS has high wear resistance and good hardenability.

Uses: HSS is used in Drill, Broaches, Reamers, Milling Cutters,

Taps, Lathe Cutting Tools, Gear hobs etc.

(iv) Cast Alloys (or) Stellites

Stellites or cast alloys are non-ferrous alloy containing Tungsten,

Chromium, Cobalt and Carbon used for cutting tools. These alloys contain

no iron and hence cannot be shaped because they cannot be heat treated.

They are casted into final shape. They are casted from a temperature about


1300C. The Chemical Composition of these cast alloys are 12 to 17% W,

30 to 35% Cr, 45 to 55% Co, 2 to 4% C.

Characteristics of Stellites

Cast alloys are not hard at room temperature but becomes very

hard above 1000F (hardness more than HSS)

Cast alloys are very brittle hence not widely used.

Cast alloys have less toughness but more wear resistance than HSS

and allow cutting speed thrice than that of HSS.

Uses: Used in manufacture of Valve seats, Push rod sheets and

Erosion shield of steam turbine etc.

(v) Cemented Carbide Tools

The main constituents of cemented carbide tools is tungsten carbide

(WC). This material was discovered by Moissan. Tungsten carbide materials

are produced by powder metallurgy by pressing and bonding. Cemented

carbide tools are of three types.

(i) Straight Cemented Carbides: Containing tungsten carbide held in

matrix of Cobalt. These are more ductile and less brittle.

(ii) Titanium-tungsten Cemented Carbides: Consisting of solid grains,

solid solution of tungsten carbide in carbide of titanium and surplus grains

of tungsten carbide all bonded by cobalt in cobalt matrix.

Symbolically given by WC Co WC TiC. These are very brittle.

(iii) Titanium-Tantalum-Tungsten Cemented Carbide: Consists of grains

of solid solution of carbide of titanium, tantalum and tungsten and surplus

grains of tungsten carbide cemented together by Cobalt Symbolically:

WC Co WC TiCTaC

Characteristics of Cemented Carbide Tools

These tools have / are

High hardness, heat resistance, wear resistance, high hot hardness.

These tools can be used upto 1000C


High thermal conductivity and low thermal expansion compared

to steel.

No plastic flow to stress upto 3500 N/mm2

Low impact resistance.

Very expensive.

Operate at cutting speed upto 45 to 360 m/min.

These are very brittle and hence rigidly supported and have low

shock resistance.

Uses: Used to machine cast iron, non-ferrous and light metal and

alloys, non-metallic materials like rubber, glass, plastics, plastics

carbon electrodes, in machining unhardened carbon and alloy

steels, heat resistance steels and super alloys workpieces.

Generally cutting tools are six inches in length and have square

cross sections, but carbide tools consists of shank made in steel

and at one end it has cemented carbide piece called bits and are

divided into 2 groups namely brazed tip carbide tools and throw

away inserts.

(vi) Ceramic Tools

Ceramic tools are also called cemented oxides. The main constituent

of ceramic tools are aluminium, tauxite (a dehydrated alumina) converted into

crystalline form called alpha aluminium. Fine grains are obtained from the

precipitation of alumina (in powder form) and tool tips are produced by hot

or cold pressing of the powder. (sintering process at 1600 1700C). Certain

amount of magnesium oxide or titanium oxide are used along with some

binder.

Characteristics of ceramic tools

They have very high compressive strength. It is quite brittle.

Low heat conductivity, so no coolant is required during machining.

Have high strength and hot hardness upto 1200C.

Have low coefficient of friction and hence low heat generated.

Have 2 to 5 times more cutting speed than other tools.


Advantages

Very high cutting speed so low machining time.

High tool life with large depth of cuts.

Low wear rate and hence high dimensional accuracy with high

surface finish.

Low cost of production.

Disadvantages

High initial cost-40 to 200% more than carbide tools.

High rigidity of machine tools is required.

More power required since high speed and feed rate.

Tools are brittle so proper tool geometry, holding devices are to

be used.

Application

Turning, boring and facing at high speeds, used for finishing

operation on non-ferrous and ferrous metals, machining of casting

and hard steels.

Cermets are ceramic metal combinations of Iron, Chromium,

Titanium and other metals, added to aluminium oxide and boron

carbide. The brittleness of the ceramic tools is considerably

reduced.

(vii) Diamond Cutting Tools

Diamond is the hardest known material today. They are used in cutting

tools. Diamond is of four classes-carbons, ballar, boarts and ornamental stones.

Cutting tools are made from boarts which are single crystal, less clear and

fault free.

Characteristics of diamond

They are very hard, hence very brittle.

They are abrasion resistant with low coefficient of friction and low

thermal coefficient of expansion.

They burn to Co2 at 800C


They cannot take shock loads.

High heat conductivity and poor electrical conductor.

Advantages

Very high production rate with close tolerance, high surface finish.

Small depth of cut can be given (0.215 micron).

Cost of grinding is reduced.

Chances of built up edge formation is nil.

Disadvantages

Very high cost.

Interrupted cut machining is not possible.

Machine tool should have high rigidity.

Cannot be used for machining beyond 800C.

Exclusively used for shallow cuts.

Applications

Used for machining non metals like rubber, ceramic, graphite and

plastic.

Used for machining precious metals like Platinum, Gold and Silver,

Soft metals like Copper, Brass, Zinc alloys.

1.10 THERMAL ASPECTS OF MACHINING TOOL WEAR AND WEAR MECHANISM

A new or newly ground tool has sharp cutting edges and smooth flanks.

During machining operation it is subjected to cutting forces, temperatures,

sliding action, mechanical and thermal shocks. Under these severe conditions,

the tools gradually wear out and even fractures, necessitating a tool change.

This tool wear causes the following effects

The cutting forces increases.

The dimensional accuracy of the work decreases.

The surface roughness of work increases.

Increase in the temperature between tool and workpiece.

The tool-work-machine starts vibrating.


The work piece/tool may get damaged.

Loss of production and increase in cost.

Hence the study of tool wear is very important. The tool wear occurs

at two places on a cutting tool.

(i) At the cutting edge and the principal flank of the tool.

(ii) At the rake face of the tool. Refer Fig 1.38.

The wear at the flank is called flank wear and the wear at the rake

face is called crater wear.

C ra te r w ear C ra te r w id th

Flank w earFlank w earheigh t

(a)

Fig. 1.38. Tool W ear

A

B B ��B ��B �

C ra te r w ear

Flank w ear

ABC -O rig inalcross-section

AB B B C -C ross-sectiono f w orn ou t too l

� ��

(b)

C


1.10.1 Tool Wear Mechanisms

Some of the important tool wear mechanisms of a hard tool are:

(i) Shearing at High Temperature

(ii) Diffusion Wear.

(iii) Adhesive Wear (Attrition Wear)

(iv) Abrasive Wear

(v) Fatigue Wear

(vi) Electrochemical effect

(vii) Oxidation effect

(viii) Chemical decomposition

1.10.1.1 Shearing at High Temperature

The strength of hard metal decreases at high temperatures. The shear

yield stress becomes smaller at high temperature than at room temperature.

Though the metal sliding over it has lower yield stress, nevertheless, the chip

may got so much work hardened as to be able to exert frictional stress

sufficient to cause yielding by shear of the hard tool metal. The higher the

temperature at the interface, the greater is the effect as shown in Fig. 1.39.

C h ip m otion

Shear s tress dueto chip

C h ip

Too l

Shearing ofa ridge

M ach inedsurface

Fig. 1.39. Wear by P lastic Yield ing and Shear.


1.10.1.2 Diffusion Wear

When a sliding metal is in contact with another metal, the temperature

is very high and the alloying atom from harder metal starts diffusing into the

softer matrix, thereby increasing the hardness and abrasiveness of the soft

material. Also atoms from softer material diffuse into the harder medium thus

weakening the surface layer of the tool. Diffusion process is highly dependent

upon the temperature. Diffusion process doubles for an increase of temperature

of order of 20C in machining using HSS tools. Fig 1.40 shows diffusion

process.

1.10.1.3 Adhesive Wear (Attrition Wear)

When a soft metal slide over a hard metal such that it always presents

a newly formed surface to the same portion of the hard metal. Due to friction,

high temperature and pressure, particles of soft material adhere to a few high

spots of the hard metal as shown in Fig 1.41. As a result, flow of the softer

metal over the surface of the hard metal becomes irregular or less laminar

and contact between the two becomes less continuous. More particles join up

to form “Built up edge”. These Built up edges when grow up are torn out

from the surface. This process continues and appears as if the surface of hard

metal is nibbled and looks uneven.

Stee l ch ip

C h ip

Too l

Fig. 1.40. Diffusion Wear Process

C

H SS

H SS Too l

.


1.10.1.4 Abrasive Wear

C hip

C h ip

Too l

Fig. 1.41. Adhesive W ear Mechanism.

W eld

W eld

Too l

Too l partic lew e lded to chip

Chip

Chip

Too l

Fig. 1.42. Abrasive Wear M echanism .

Tool

Hard partic lein chip& m achined surface

M achined surface


The softer metal sliding over the surface of the harder metal may

contain appreciable concentrations of hard particles (Eg). Casting may have

sand particles. Under such condition, hard particles act as small cutting edges

like those of a grinding wheel on the surface of a hard metal which in due

course, is wornout through abrasion (Fig. 1.42). Also the particles of the hard

tool metal, which intermittently get torn out from its surface are dragged

along the tool surface or rolled over. These particles plough grooves into the

surface of the hard tool metal.

1.10.1.5 Fatigue Wear

Asperities are formed when two surface slides in contact with each

other under pressure. These asperities interlocks with each other. Due to

friction, compressive stress is developed on one side of asperity and tensile

stress on the other side (Fig 1.43). After the asperities of a given pair has

moved over or through each other, the above stresses are relieved. New pair

of asperities are soon formed and the stress cycle is repeated. Thus the

Chip

Ch ip Flow

Tool

Fig. 1.43. Fatigue Wear Mechanism .

Tool

Tension

Compression

Force by chip


material of the hard metal near the surface undergoes cyclic stresses. This

phenomenon causes surface cracks and ultimately crumbling of hard metal.

The variable thermal stresses due to high temperature also contribute to fatigue

wear.

1.10.1.6 Electrochemical Effect

Due to the high temperatures existing on tool chip interface, a

thermoelectric EMF is set up in closed circuit due to formation of junction

at the chip tool interface assisting the tool wear.

1.10.1.7 Oxidation Effect

Grooves and notches are formed at rake face and flank due to the

reaction of sliding portion of chip and machined surface with atmospheric

oxygen to form abrasive oxides causing wear.

1.10.1.8 Chemical decomposition

Local chemical reaction may occur that weaken the tool material

through formation of weak compounds or dissolution of the bond between

the binder and the hard constituents of carbide tool. These weakened particles

are easily torn away by the aspirities of the chip or on machined surface.

1.10.2 Types of Tool Damage in Cutting

The main types of Tool Wear / Damage are

(i) Flank Wear

(ii) Crater Wear

(iii) Groove formation

Flank Wear

(Refer Fig 1.38)

The wear at the side and end of flank of tool is called Flank wear.

Flank wear is caused by the rubbing action of the machined surface. The

worn out region is called wear land. Wear land is not of uniform width. It

is widest at a point farthest from the nose. When diffusion becomes

predominant wear mode on the flank, a critical wear land is formed and

accelerating wear rate takes place and then Rapid wear. It is advisable to


C ra te r w ear C ra te r w id th

Flank w earFlank w earheigh t

(a)

Fig. 1.38. Tool W ear

A

B B ��B ��B �

C ra te r w ear

Flank w ear

ABC -O rig inalcross-section

AB B B C -C ross-sectiono f w orn ou t too l

� ��

(b)

C

Tim e

Wid

th o

f fla

nk w

ear

In itial rapid w ear

C onstant rate w ear region

R apid w earC

O C T

B

Fig. 1.44. A Typical Wear Curve for a Cutting Tool.


change the tool well before the on-set of the rapid wear in order to avoid

catastrophic tool failure. A typical wear curve for cutting is shown in Fig.1.44.

Crater Wear

Crater Wear occurs on the rake face of tool in the form of a pit called

crater. It is formed at a distance from the cutting edge. It is a temperature

dependent phenomenon caused by diffusion, adhesion etc. Fig 1.45 shows the

radius of curvature Rc, depth of crater KT, width of crater KB KM and the

distance of the start of the crater from the tool tip KM change with time. The

A

KB

K M

K B

K T

R C

K T

R C

(a)

Time

Val

ue o

f Cha

ract

ristic

A

(b)

Fig.1.45. Progress of Crater Wear


crater significantly reduces the strength of the tool and may lead to total

failure.

1.10.3 Tool Failure

Tool failure is said to have occurred when a tool is unable to produce

desired shape, size and finish on the work piece. A tool failure can occur

due to any one of the following.

(i) Loss of form stability due to high temperature and stresses.

(ii) Mechanical breakage of tool.

(iii) By the process of gradual wear on flank.

1.10.4 Measurement of Wear

Tool wear can be measured by any one of the following methods with

different degree of accuracy and convenience.

(i) Measurement of height of Wear land.

(ii) Measurement of Volume (or depth).

(iii) Measurement of loss of weight of the tool.

(iv) Diamond Indentor technique.

(v) Radioactive technique.

1.11 TOOL LIFETool life is defined as the time elapsed between two successive

grinding of tool (or) the time for which a cutting edge or a cutting tool can

be usefully employed without grinding (in case of HSS tools) or replacement

(in the case of throwaway carbide or oxide inserts) is called as tool life.

The other ways of expressing tool life are

(i) Machine time: Tool life is the total time of operation of this

machine tool.

(ii) Actual cutting time: The tool life is the time elapsed during

which the tool is actually cutting, between two successive

grindings.

(iii) Volume of metal: Once a certain volume of metal is removed,

the life of the tool is assumed to be over.


1.11.1 Tool failure Criterion

The various criterion for judging tool failure are:

(i) Complete Failure

A tool is continued to be used until it can cut the workpiece. So when

a tool fails to cut, then the tool has to be ground.

(ii) Flank Failure

The wear on the flank causes the reduction in depth of cut. The work

piece becomes taper if the cutting is continued. Therefore, if the wear on

flank reaches certain height, the tool is removed and reground. This is most

general criterion of tool failure.

Flank wear is measured in Maker’s microscope.

(iii) Finish Failure

When the surface roughness of the workpiece reaches a certain high

value, then the cutting of the tool is discontinued and regrinding is done.

This criterion becomes specially important when close fitting is required

between the mating surfaces. Due to rough and uneven surfaces, the fitting

may not be very close.

(iv) Size Failure

A tool is said to be failed when there is a change in the dimension

of the finished work piece by a certain specified value.

(v) Cutting Force Failure

If the cutting forces are increased by certain amount, the tool is said

to be failed and regrounded.


1.11.2 Factors affecting Tool Life

The various factors which affect the tool life are

(i) Cutting Speed

(ii) Depth of Cut

(iii) Feed rate

(iv) Tool material properties

(v) Tool geometry

(vi) Work material properties

(vii) Type of cutting fluid and method of application

(viii) Rigidity of machine-tool-workpiece system

(ix) Nature of cutting.

(i) Cutting Speed

Cutting speed is one of the important factor which affects the tool life.The temperature increases with the increase in the cutting speed which reducesthe hardness of tool and increases the flank and crater wears thereby reducingthe tool life.

Frederick W.Taylor conducted number of experiments and derived anempirical relationship between tool life and the cutting speed given by

VTn C ...(1.33)

Where V Cutting speed in m/min

T Tool life in min

n Tool life index [depending upon tool andwork material and cutting environments]

C Constant

In equation if T 1 then V C

Here the constant C can be physically interpreted as the cutting speed

for which the tool life is one minute.

In Taylor’s equation the tool life equation becomes straight line on

log-log scale as shown in Fig. 1.46 i.e log V n log T log C ...(1.34)


The values of n for different tool materials are:

n 0.2 to 0.25 for HSS

0.25 to 0.45 for Carbide Tools

0.4 to 0.55 for Ceramic Tools

Equation 1.33 may be generalized to include the effects of feed f and

depth of cut d.

VTn f n1 dn2 C1

Where n, n1, n2, C1 are constants depending upon tool and work material, tool

geometry and type of coolant used etc.

(ii) Effect of Feed rate and depth of cut

With the increase in the feed rate and depth of cut the tool life

decreases. The life of the cutting tool is influenced by the amount of metal

removed by the tool per minute which in turn depends upon the feed rate

and depth of cut.

The effect of feed and depth of cut on tool life for cemented carbide

tool and low carbon steel combination is given by:

V T0.2 260

f0.35 t0.08

Too l life T (m in )

Cut

ting

spee

d V

(m/m

in)

Log

V

L og V+n Log T = Log C

Log T

Fig.1.46. Tool life Vs Cutting speed


Where V Cutting Speed in m/min

T Tool life in min

f Feed in mm/min

t Depth of cut in mm

(iii) Effect of Tool Material

Fig 1.47 shows the tool

life variation against cutting

speed for different tool

materials. The tool life is

greatest for ceramic tools and

lowest for HSS.

(iv) Effect of work materialhardness and microstructure

A general emphirical

relationship between the

hardness and cutting speed for

a given tool is given as

VH1.7 Constant

Where V Permissible cutting speedH Brinell hardness number % reduction in size

If hardness is more, corresponding velocity should be less as given by

the expression.

Micro structure of work material affects the tool life. As percentage

of pearlite increase, the tool life decreases at any and every cutting speed.

(v) Effect of Cutting Fluid

As the tool cuts the work piece, a lot of heat is generated due to

friction and rubbing. Heat produced during metal cutting is carried away from

the tool and workpiece by means of cutting fluid. It also reduces the friction

between the chip tool interface and increases the tool life.

30

60

150

300

90

1 2 3 5 10 20 30 50 100

Too l life,T, m in

Fig. 1.47 Effect Tool materialCutting Speed on Tool life

Ideal

Ceram ic too lCarb ide too l

H igh speed s tee l too l


An empirical relationship between tool life and temperatures of chip

tool interface has been established and is given as

T n K

Where T Tool life in min Interface Temperature in Cn An exponent indexK Constant

(vi) Tool Geometry

Tool geometry having various angles influences the life of the tool.

Back rake angle affects the shear angle, shear strain and cutting

force.

High back rake reduces cutting force but makes the wedge thinner

and rise in temperature consequently more wear rate and lower

tool life.

Negative back rake increases cutting force but the wedge becomes

more stronger.

Therefore optimum back rake angle should be used and its range

is 5 to 10.

Principle cutting edge angle also affects the tool life.

For the tool with 90 cutting edge angle (orthogonal cutting), the

cutting edge is impact loaded over a small area and hence the

cutting force is very high there by reduces the life of tool.

For the tool with less cutting edge angle (oblique cutting) the tool

experiences cutting force gradually and over a larger area and

hence tool is safer and has more life.

(vii) Rigidity of Workpiece-Machine tool System

If the rigidity of workpiece-machine tool system is low, higher the

vibration of the system and higher the chances of tool failure. The vibration

induces chipping of tool (specifically brittle tools), because of impact loading

on the tool due to intermittent cutting. Its rigidity is very high then the


damping is more and vibration is less and less chatter and more life. Chatter

causes fatigue or catastrophic failure of tool.

(viii) Nature of Cutting

Sometimes the job is such that cutting edge has to frequently enter

and exit from the cut as for example in turning a work piece having

longitudinal slots (Intermittent Cutting). Each entrance and exit gives an

impact on the cutting edge that can shorten the tool life, especially if the

tool material is hard or brittle.

(ix) Effect of nose radius of tool

Nose radius of the tool improves tool life and surface finish of the

workpiece. A relationship between cutting speed, tool life and nose radius is

given below.

VT0.09 300 R0.25

Where R Nose radius in mm

T Tool life in min

V Cutting speed in m/min

Nose radius has an optimum value at which tool life is maximum

beyond which the tool life reduces. Larger nose radius means more contact

area which inturn increases friction there by reducing life of tool.

1.11.3 Economics of Machining - Machining Cost

Cost of machining involves the following cost

(i) Machining cost (cutting cost or machine/operating cost)

(ii) Tool cost (Tool cost and Grinding Cost)

(iii) Idle cost (or) non productive cost.

Total cost per piece CTot Cm CI CT CG

Where CM Machining cost C1 D L

1000 VS

Where C1 Direct labor cost Over head cost in Rs/min


D Diameter of work piece machined in mm

L Length of machining in mm

V Cutting speed in m/min

S Feed in mm/rev

CI Idle cost C1 Idle time per piece

CT Tool changing cost

C1 Tool failure per workpiece T1.

Where T1 Tool changing time.

CG Tool grinding cost per piece

Tool cost per grind No. of failures per piece.

Optimum Tool life for minimum cost is

Topt 1n

1 C1 T1 C2

C1

Where C2 Tool cost per grind

also VTn Constant (Taylor equation)

1.11.4 Machinability

The term machinability is used to refer to the ease with which a given

workpiece material can be machined under a given set of cutting conditions.

It is of considerable economic importance for a production engineer to know

in advance the machinability of a work material, so that its processing can

be efficiently planned.

1.11.4.1 Factors affecting machinability

The various factors affecting machinability are

(i) Chemical and physical properties of work material.

(ii) Microstructure of work material.

(iii) Mechanical properties of work material.

(iv) Geometry of Tool (Various angles and nose radius)


(v) Rigidity of tool and machine.

(vi) Type of tool material.

(vii) Nature of operation and cutting condition.

1.11.5 Surface finish

A surface can be characterised by its topography and microstructure.

The topography describes its micro geometrical properties or texture in terms

A

(a)

Lay

Inclus ion

B low ho le

B

C ut o ff leng th

Valleys M ean line

B M agn ified Peaks

R oughness spacing

Waviness spacing

(b)

(c)

A M agn ified

Fig. 1.48. Elem ents of Surface Texture

Waviness he ight


of roughness, waviness and lay. Microstructure describes the depth and nature

of the altered material zone just below the surface.

Surface finish (or surface texture) refers to the following properties of

a machined surface as shown in Fig. 1.48.

Roughness: Roughness consists of relatively close-spaced or fine surface

irregularities, mainly in the form of feed marks left by cutting tool on the

machined surface. The mean height or depth is measured over a 1 mm cut

off length or roughness sampling length.

Waviness: It consists of all surface irregularities whose spacing is greater

than the roughness sampling length. Vibration, chatter and tool or workpiece

deflections due to cutting loads and cutting temperature may cause waviness.

Lay: Lay denotes the predominate direction of the surface irregularities. The

lay is usually specified with respect to an edge called the reference edge of

workpiece.

Surface flaws: These are random spaced irregularities i.e those which occur

at some particular location on the surface or at widely varying intervals. Flaws

could be due to inherent defects such as inclusions, cracks, blow-holes etc.

1.11.5.1 Factors affecting surface finish

The factors which affects the surface finish are:

(i) Cutting tool geometry

(ii) Workpiece geometry

(iii) Machine tool rigidity

(iv) Workpiece material

(v) Cutting condition (speed, feed and depth of cut)

(vi) Tool material.

(i) Cutting Tool Geometry

The various angles rake, relief, cutting edge and nose radius directly

affects the surface finish on the workpiece.


(ii) Workpiece Geometry

Long slender workpiece have low stiffness against both static and

dynamic forces. As a result waviness effects are more in long work than

small workpieces

(iii) Machine Tool Rigidity

A sufficient high rigid machine produce less vibration which inturn

reduces the waviness in workpiece and produce high surface finish.

(iv) Workpiece Material

Chemical composition, hardness, microstructure and metallurgical

properties of the workpiece material largely affects the surface finish of

workpiece. (eg) steel having 0.1% or less carbon produce build up edge and

thereby spoil surface finish.

(v) Cutting Condition

High speed cutting produces better surface finish than at low cutting

speed. Feed also affects the surface finish. A coarse feed produces rough

surface and fine feed produces good surface finish. Also depth of cut directly

affects the surface finish. Light depth of cut produces fine surface finish,

while heavy depth of a cut produces rough surface.

(vi) Tool Material

Different tool material have different hot hardness, toughness and

frictional behavior which affects the surface finish

1.11.5.2 Measurement of Roughness

Following are the parameters measured in surface roughness (Fig. 1.49)

(i) Overall height hmax

Overall height is height of separation between upper and lower surface

line occurring within sampling length (L)

hmax Lp Lv

(ii) Leveling depth hp

It is the mean height of profile above the mean line Lm. Mathematically


hp 1L

0

L

ydx

(iii) Centre Line Average hCLA

It is defined as the arithmetic average of the deviation of the profile

above and below the mean line Lm

hCLA 1L

0

L

|Y| dx

(iv) Root mean Square Value hRms

It is defined as geometrical average value of the deviation of the profile

above and below mean line.

hRms

1L

0

L

y2 dx

1/2

L p

L m

L v

y h p

h m ax

L

X

Fig. 1.49. Measures of Surface Roughness.

Y


1.11.5.3 Specification of Surface Roughness

ISO recommendation on surface roughness in machining specification

is given in the Fig 1.50

Symbols are described as below:

a hCLA or centre line average value;

b Production method heat treatment and continuing

C Sampling length

d Direction of lay

e Machining allowance

The symbol d can take following symbols.

– When lay is parallel to plane of view

– The lay is perpendicular to plane of view

X – The lay is in 2 directions

M – The lay is multi-directional

C – The lay is circular

R – The lay is radial

60 o 60o

e d

a

b

c

Fig. 1.50. Drawing Symbols for Surface Roughness in Machining


1.12 CUTTING FLUIDS

In metal cutting process, heat is generated due to plastic deformation

of metal, friction between chip and rake face of tool and rubbing between

the flank and work. This increases the temperature of both tool and workpiece.

The temperature affects the tool life causing tool failure and surface finish

of the workpiece is deteriorated. Hence cutting fluids are used to remove the

heat produced.

1.12.1 Functions of cutting fluids

The main functions of cutting fluids are:

(i) To cool the cutting tool and increase the tool life.

(ii) To cool the workpiece and helps in lubrication of machine.

(iii) To reduce the friction between the chip and the tool.

(iv) To flush away the chip to keep the cutting region free.

(v) To produce the machined surface free from corrosion.

(vi) Reduce the cutting forces and energy consumption.

1.12.2 Properties of Good Cutting fluid

A good cutting fluid should have the following characteristic properties.

(i) Good Lubricating Qualities

A cutting fluid should have good lubricating property to remove the

chip from touching and adhering to the tool face and preventing formation

of built up edge.

(ii) High heat absorbing capacity or cooling capacity

A good cutting fluid will remove more heat and remove the heat

quickly thus reducing the temperature between tool and workpiece.

(iii) Rust resistance

Cutting fluid should prevent rusting of work, tool or machine.


(iv) Cutting fluid should have low viscosity so that chip and dirt easily

settles.

(v) Cutting fluid should not be toxic in nature.

(vi) Cutting fluid should have high chemical stability such that it can

be used for longer time.

(vii) Cutting fluid should have high flash point

(viii) It should not be harmful to worker or operator

(ix) It should be non flammable

(x) It should not produce smoke or foam easily

(xi) It should not produce bad smell

(xii) It should be of low cost.

1.12.3 Types of Cutting Fluids

Cutting fluids are of the following types:

(i) Solid based cutting fluids: It may be included in the work material itself

or applied on the chip tool interface with some liquid mainly to facilitate

machining by reducing friction. Ex. graphite, molybdenum disulphide etc.

(ii) Straight cutting fluid: These are of three types

(i) Mineral oils (ii) Fatty oils (iii) Combination of mineral and fatty

oils.

These oil have good lubricating properties but poor heat absorption

quality and are used for low cutting speeds.

(iii) Oil with additives: The beneficial effects of mineral oils can be

improved with the help of additives which are generally compounds of sulphur

or chlorine. Addition of sulphur compounds reduces chances of chip welding

on tool rake face.


The additives and function are given below:

Additive Function(i) Mineral oils and other hydrocarbon Base oil(ii) Polyglycoether (water soluble) Emulsifier(iii) Aliphatic amines (water soluble) Neutralizing agent(iv) Aliphatic amines in neutralized form Corrosion protection(v) Sulfonates Corrosion protection, pressure

additive(vi) Fatly acid amides Lubricity Improvement(vii) Sulphur / Phosphorous additives Pressure additives(viii) Aldehyde Derivatives Biocides

(iv) Water Soluble Cutting Fluids

These are also called water based cutting fluids. These comprise of

mineral oils, fat mixtures and emulsifiers added to water. The oil is held in

the form of microscopic droplets (colloidal) in water, which assumes a white

milky appearance. Because of water, these have very good cooling effects.

Mixture is prepared in different ratios of cutting oil and water to get the

desired heat transfer and lubricating characteristics.

1.12.4 Composition of Cutting Fluids

A cutting fluid may contain the following.

Base oil

Emulsifier

Corrosion Inhibitor

Lubricating-antiwear-extreme pressure additives

Neutralising agents

Biocides and Fungicides

Foam inhibitors

Stabilizing agent.

Table 1.1 shows the different types of coolants and lubricants used

for different type of operations.


Table 1.1 Coolants and Lubricants for Different Operations

Coolants and lubricants

MaterialTurning

& boringThreading

Drilling ReamingShaping,Planing,Slotting

Milling

Cast iron Dry Dry Dry Dry,Tallow,Lard oil

Dry Dry

Soft steel Cuttingcompound,Cuttingoil,Soap-water

Cuttingcompound,Cuttingoil,Soap-water

Anycoolant

Cuttingcompound

Soap-water, Sodawater

Solublesulphurized, ormineraloil

Hard steel Minerallard oil

Minerallard oil

Kerosene, Strongsodawater

Minerallard oil

Minerallard oil

Solublesulphurized, ormineraloil,minerallard oil

Brass Dry Dry,Kerosene, Turpentine

Dry Dry,Kerosene, turpentine

Dry Dry

Bronze Minerallard oil

Minerallard oil

Dry oranycoolant

Dry,Minerallard oil

Dry Solublesulphurized, minerallard oil

Aluminium Kerosene Kerosene Dry,Kerosene

Kerosenewith25%solublecutting oil

Kerosene Solublesulphurized, ormineraloil andkerosene


Coolants and lubricants

MaterialTurning

& boringThreading

Drilling ReamingShaping,Planing,Slotting

Milling

Copper Mixtureof lardoil andturpentine

Dry or amixtureof lardoil andturpentine

Dry,coolingcompound,lard oilandturpentine

Dry or acoolant

Dry Solublesulphurizedorminerallard oil

1.12.5 Method of applying cutting fluid

The method of applying a cutting fluid is very important if one wants

to use full benefit and to conserve it or reduce its wastage. The various

methods are

(i) Nozzle-pump tank method: A pump is mounted on the tank containing

fluid and outlet of pump is connected to nozzle through flexible hose. The

nozzle directs the stream of fluid at desired point.

(ii) Mist application: In this method fluid is passed through a specially

designed nozzle so that it forms very fine droplets of cutting fluid or produce

a mist of size 5 to 25 m directed at cutting zone.

(iii) High jet method: A narrow jet at high velocity is directed at the flank

surface of the tool. It is the most recent method.

1.13 SOLVED PROBLEMS ON CUTTING FORCES, WORK DONEAND POWER REQUIRED

Problem 1.2 A dynamometer measures the following feed force 100 kgs,cutting force 375 kgs, rake angle 12, Chip thickness ratio 0.3, Findthe following (i) Shear Angle (ii) Shear force (iii) Coefficient of friction (iv) Compressive force at shear plane.

Given:

Feed force (Fd 100 kgs, cutting force Fc 375 kgs, rake Angle

12 Chip thickness ratio r 0.3


Solution:

(i) Shear Angle

We know that tan r cos

1 r sin (from Eqn. 1.3)

Shear Angle tan 1

0.3 cos 121 0.3 sin 12

tan 1 [0.3129]

Shear Angle 17.38

(ii) Shear force Fs

Shear force Fs FC cos Fd sin

(From Eqn. 1.6)

375.cos 17.38 100 sin 17.38

Fs 328 kgs

(iii) Normal or Compressive force Fn

Compressive force Fn FC sin Fd cos (From Eqn. 1.6)

375 sin 17.38 100 cos 17.38

Fn 207.45 kgs

(iv) Coefficient of friction

We know that coefficient of friction

FC tan Fd

FC Fd tan (From Eqn. 1.12)

375 tan 12 100375 100 tan 12

0.508

0.508

Friction Angle tan 1 tan 10.508 26.93


Problem 1.3 In orthogonal cutting process which has depth of cut 0.3 mm, Chip thickness ratio 0.5, Width of cut 6 mm, Cutting Velocity

60 m/min, cutting force parallel to cutting velocity 1200 N, Cutting force

normal to cutting velocity 160 N, Rake angle 12. Determine the shearAngle, Resultant cutting force, Power required for cutting, coefficient offriction, force component parallel to shear plane?

Given:

Depth of cut t1 0.3 mm, Chip thickness ratio r 0.5, Width of cut

b 6 mm, Cutting Velocity Vc 60 m/min, Cutting force Parallel to cutting

velocity Fc 1200 N, Cutting force normal to cutting Velocity

Fd 160 N, Rake angle 12

Solution

(i) Shear Angle


1 r sin

0.5 cos 121 0.5 sin 12

Shear Angle tan 1

0.5 cos 121 0.5 sin 12

tan 10.5458

28.62

(ii) Resultant Cutting Force F

We know that F Fc2 Fd

2 12002 1602

F 1210 N

(iii) Power required for cutting P

Power P Fc Vc

P 1200 60 72,000 Nm/min

P 72000

60 1200 Nm/sec 1200 watts

Power P 1.2 kW


(iv) Coefficient of Friction

We know that

Fc tan Fd

Fc Fd tan

1200 tan 12 1601200 160 tan 12

0.356.

Friction Angle tan 1 tan 1 0.356 19.59

(v) Force Component Parallel to shear plane Fs

We know that Fs Fc cos Fd sin

1200 cos 28.62 160 sin 28.62

Fs 976.74 N

Problem 1.4 The machining of a steel with a tool having signature0-12-6-8-8-90-1 mm ORS shaped tool has the following observations. Feed 0.7 mm/rev,

depth of cut 3 mm, cutting speed 60 m/min, Shear Angle 15. Power

consumed while in machining 6 kW and idle power 1 kW. Calculate (i)The cutting force, (ii) Chip thickness ratio, (iii) Normal pressure on thechip (iv) Chip thickness.

Given:

From tool signature we have rake angle 12 Feed

f 0.7 mm/rev, depth of cut d 3 mm, cutting speed Vc 60 m/min,

Shear Angle 15.

Power for machining P 6 kW, Idle Power PI 1 kW.

Solution

(i) Cutting Force Fc

Net Cutting Power Pc P PI 6 kW 1 kW

Pc 5 kW

We know Power Pc Fc Vc


50 103 Fc 60

60

Vc 60 m/min

6060

m/sec

Cutting force Fc 50 103

60 60 50 kN

(ii) Chip thickness ratio r

We know tan r cos

1 r sin

tan 15 r cos 12

1 r sin 12

0.268 r 0.978

1 0.208 r

0.268 r 0.978 0.208 0.268

r 0.2593

(iii) Normal Pressure on the chip

Pressure P Force FcChip Area

Fc

w t

here w Depth of cut 3 mm

t Feed 0.7 mm

Pressure P 50 103

3 0.7 23.81 kN/mm2

(iv) Chip Thickness tc

tc Feed

Chip thickness ratio

0.70.2593

2.7 mm


Problem 1.5 A seamless tube 40 mm outside diameter is turnedorthoganally. The following data are obtained. Rake angle 40, Cutting

Speed 25 m/min, feed 0.15 mm/rev. Length of Chip ( 1 rev) 60 mm.

Cutting force 300 kg, feed force 100 Kg. Calculate (i) Coefficient offriction (ii) Shear Angle (iii) Velocity of Chip along tool face (iv) Chipthickness.

Given:Diameter of tube D 40 mm, Rake angle 40, Feed f 0.15 mm/rev, Cutting Speed Vc 25 m/min, Length of Chip (rev)

60 mm, Fd 100 kg, Fc 300 kg

Solution

(i) Coefficient of friction

Fc tan Fd

Fc Fd tan

300 tan 40 100300 100 tan 40

1.628

(ii) Shear Angle


1 r sin

Chip thickness ratio

r t1t2

l1l2

60

D

60 D

60

40 0.4775

tan 0.4775 cos 40

1 0.4775 sin 40

0.36580.6931

0.5265

Shear Angle tan 1 0.5265 27.77

(iii) Chip Velocity Vf

Vf Vc r 25 0.4775 11.94 m/min

(iv) Chip Thickness t2

r t1t2

; t2 t1r

0.15

0.4775 0.314 mm


Problem 1.6 In orthogonal cutting of Mild steel rod of diameter 200 mmand depth of cut 1.5 mm with a cutting speed of 50 m/min and feed of 0.3mm/rev, the following were obtained, cutting force 200 kg, Feed force

50 kg, Chip thickness 0.35 mm, Contact length 1 mm, Net Power

2.5 kW and Back rake angle 15. Calculate the shear strain and strainenergy per unit volume, normal pressure.

Given:Diameter of rod D 200 mm; Depth of cut d 1.5 mm, Cutting

Speed Vc 50 m/min, Feed f 0.3 mm/rev, Cutting force Fc 200 kg, Feed

force Fd 50 kg, Chip thickness t2 0.35 mm, Contact length

L 1 mm, Net Power 2.5 kW, Back rake Angle 15

Solution:

(i) To Calculate Shear Angle


1 r sin

Chip thickness ratio r t1t2

0.30.35

0.857

Shear Angle tan 1

0.857 cos 151 0.857 sin 15

0.6775

tan 1 [0.6775] 34.12

(ii) Shear Strain eWe know that Shear Strain

e cos

sin cos

(from Eqn. 1.28)

e cos 15

sin 34.12 cos 34.12 15

0.966

0.561 0.6545 2.631

Shear Strain e 2.631


(iii) Shear Stress s

Shear Force Fs Fc cos Fd sin (Eqn.1.6)

200 cos 34.12 50 sin 34.12

137.53 kg

Shear Stress s Shear ForceShear Area

Fs sin

w.t

(From Eqn. 1.27)

137.53 sin 34.12

1.5 0.3 171.43 kg/mm2

s 171.43 9.81 1681.7 N/mm2

Shear Velocity Vs Vc cos

cos (From Eqn. 1.25)

50 cos 15

cos 34.12 15 73.8 m/min

(iv) Shear Energy Es

Shear Energy Es s Vs

Vc sin (From Eqn. 1.32)

Shear Energy 1681.7 73.850 sin 34.12

4425 N/mm2

(v) Normal Pressure

Fc

Area of chip

200Feed Depth

200

0.3 1.5 444.44 kg/mm2

Normal Pressure 4.44 kN/mm2


Problem 1.7 In an orthogonal cutting operation on a workpiece of width2.5 mm, the uncut chip thickness was 0.25 mm and the tool rake angle waszero degree. It was observed that the chip thickness was 1.25 mm. The cuttingforce was measured to be 900 N and the thrust force was found to be810 N.(i) Find Shear Angle(ii) If the Coefficient of friction between the chip and tool was 0.5, what isthe machining constant Cm?

Given:

Width w 2.5, Uncut chip thickness t1 0.25 mm, Rake Angle

0, Chip thickness t2 1.25 mm, Cutting force Fc 900 N, Thrust

Force Fd 810 N, Coefficient of friction 0.5

Solution

(i) To find Shear Angle

Chip Thickness ratio r t1t2

0.251.25

0.2

Shear Angle

tan r cos

1 r sin

tan 1

r cos 1 r sin

tan 1

0.2 cos 01 0.2 sin 0

tan 1 [0.2] 11.31

Shear Angle 11.31

(ii) To find Machining Constant Cm

Machining Constant Cm 2

Shear Force Fs Fc cos Fd sin

900 cos 11.31 810 sin 11.31

Fs 723.67 N


Shear Stress s Shear force

Area

Fs sin w.t1

s 723.67 sin 11.31

2.5 0.25 227.1 N

Coefficient of friction tan

tan 1 tan 10.5 26.565

Machining Constant Cm 2

2 11.31 26.565 0

Cm 49.185

Problem 1.8 In an orthogonal machining with a tool rake angle of 10, thechip thickness was found to be 3 mm when the uncut chip thickness is setto 0.5 mm. Find the Shear Angle and friction angle [Assume Merchantformula is holding good for the machining].

Given:

Rake Angle 10, Chip thickness t2 3 mm, Uncut chip thickness

t1 0.5 mm

(i) Shear Angle

Chip Thickness ratio r t1t2

0.53

0.167

Shear Angle : tan r cos

1 sin

tan 1

r cos 1 r sin

tan 1

0.167 cos 101 0.167 sin 10

tan 1 0.16450.971

9.613


(ii) According to Merchant Theory [ Friction angle ]

2 /2

2 9.613 10 90

Friction Angle 80.77

Problem 1.9 In orthogonal machining of a tube in lathe whose outerdiameter is 80 mm and wall thickness of 4 mm to reduce its length. Thespeed of workpiece is 150 rpm and longitudinal feed is 0.4 mm/rev, cuttingratio is 0.25 with tangential force of 1000 N and axial force of 500 N. Findchip velocity and power consumed?

Given:

Outer diameter Do 80 mm,

Wall thickness tw 4 mm, N 150 rpm, f 0.4 mm/rev,

Cutting ratio 0.25, Fc 1000 N, Fd 500 N

Solution

1. Chip Velocity

Cutting ratio Velocity of Chip

Velocity of workpiece

Velocity of workpiece V D N in m/min

Where D Mean diameter

D Do di

2

di Do 2tw 80 2 4 72 mm

D 80 72

2 76 mm

Velocity of workpiece V 76 150 35814 mm/min

V 35.814 m/min

Velocity of Chip Vc 0.25 35.814 8.954 m/min

Power Consumed P Fc V


P 1000 35.814

60 570 watts

Problem 1.10 In an orthogonal cutting of a mild steel, following wereobserved cutting force 1200 N, Feed force 500 N, Cutting velocity

100 m/min Rake Angle 12 and shear plane angle is 20. Determine thefollowing (i) Shear velocity (ii) Chip flow Velocity (iii) Work done perminute in shearing and against friction (iv) show that work input is sum ofwork done in shearing and friction.

Given:

Cutting force Fc 1200 N, Feed force Fd 500 N, Cutting Velocity

Vc 100 mm/min. rake angle 12 Shear Angle 20

Solution

(i) Shear Velocity Vs

Vs Vc cos

cos (From eqn. 1.2)

Vs 100 cos 12

cos 20 12 98.78 m/min

(ii) Chip flow velocity Vt

Vt Vc sin

cos (From Eqn. 1.1)

Vt 100 sin 20

cos 20 12 34.54 m/min

(iii) Work done in Shearing and Friction

Work done in shear Ws Fs Vs.

Fs Fc cos Fd sin 1200 cos 20 500 sin 20

Fs 956.62 N

Ws 956.62 98.78

60 1575 W


Friction Force Ff Fd cos Fc sin

500 cos 12 1200 sin 12

Ff 738.57 N

Work done in friction WF Ff Vt 738.57 34.54

60

425.17 W

(iv) Total workdone W

Ws WF 1575 425.17 2000 W

Work input WI Fc V 1200 100

60 2000 W

Hence WI W

Problems on Economics of Machining Tool life and wear.

Problem 1.11 The Taylor tool-life equation for machining C-40 steel witha HSS cutting tool at a feed of 0.2 mm/rev and a depth of cut of 2 mm is

given by VTn C Where n and c are constants. The following V and Tobservations have been noted.

V, m/min – 25 35

T, min – 90 20

Calculate (i) n and C (ii) Hence recommend the cutting speed for a desiredtool life of 60 min

Given:

Feed f 0.2 mm/rev, d 2 mm ; Taylors Eqn.

VTn C, V1 25 m/min, V2 35 m/min, T1 90 min, T2 20 min

Solution

(i) To find n & C

According to Taylors Eqn. VTn C


V1T1n C V2 T2

n

25 90n 35 20n

9020

n

3525

4.5n 1.4

n log 4.5 log 1.4

n log 1.4log 4.5

0.223

Now

V1T1n C

C 25 900.223 68.192

(ii) To find Cutting Speed at 60 min

Given: T3 60 min

Again V3 T3n C

V3 68.192

600.223 27.37 m/min

Cutting Speed V3 27.37 m/min

Problem 1.12 A HSS tool gave a tool life of 120 min at 15 m/min and 25min at 70 m/mm. Calculate (i) C and n for Taylor’s equation. (ii) CuttingSpeed for minimum life say 1 min?

Given:

T1 120 min, V1 15 m/min, T2 25 min, V2 70 m/min

Solution

(i) To find C and n for Taylor’s Equation.

We know that VTn C

V1 T1n V2 T2

n


15 120n 70 25n

12025

n

7015

n log 4.8 log 4.67

n log 4.67log 4.8

0.9825

Now, V1 T1n C

C 15 1200.9825 1655.33

The Taylor Equation is VT0.9825 1655.33

(ii) Cutting Speed for Minimum Tool life say 1 min

VT0.9825 1655.33 (T 1 min)

V 10.9825 1655.33

V 1655.33 m/min

Problem 1.13 The tool life equation for HSS and carbide tool are given as

follows. Carbide: VT0.3 C1 and HSS Tool: VT0.2 C2. If the tool life is 100

min at 50 m/min, Compare the tool life of both tools at 150 m/min.

Given:

For HSS tool VT0.2 C2 and

For Carbide Tool VT0.3 C1

T 100 min at V 150 m/min

Solution:

(i) To Find C1 & C2

VT0.2 C2

50 1000.2 C2

VT0.3 C1


50 1000.3 C1

C2 125.6 ; C1 199.1

To Find T1 & T2 at 150 m/min

For Carbide Tool: VT0.3 C1

150 T10.3 199.1

T1 199.1150

1/0.3

2.57 min

HSS Tool VT0.2 C2

150 T20.2 125.6

T2 125.6150

1/0.2

0.412 min

T1

T2

2.570.412

6.24

Life of Carbide Tool is 6.24 Times life of HSS tool.

Problem 1.14 The modified Taylor equation for a Carbide tool is given as

VT0.3 f0.4 d0.2 C. It was obtained a tool life of 100 min under the following

condition. V 50 m/min, f 0.5 mm d 1 mm. Calculate the effect of tool oflife if feed is increased by 20%, Speed by 15% and depth of cut by 50%together.

Given:

VT0.3 f0.4 d0.2 C, T 100 min, V 50 m/min,

f 0.5 mm, d 1 mm

Solution

(i) To Find the Constant C

C VT0.3 f0.4 d0.2


C 50 1000.3 0.50.4 10.2 150.854

(ii) Effect on Tool life

Increase in Feed

20% f1 f 20100

f 1.2 f 1.2 0.5

f1 0.6

Increase in Speed 15% V1 1.15V 1.15 50 57.5

Increase in depth of cut 50% d1 1.5 d 1.5 1 1.5

V1 T10.3 f1

0.4 d10.2 C

57.5 T1

0.3 0.60.4 1.50.2 150.854.

life T1

150.854

57.5 0.60.4 1.50.2

1/0.3

150.85450.833

1/0.3

2.9671/0.3

life T1 37.56 mins

The effect on tool life is

T T1 100 37.56 62.44 min

Tool life is reduced by 62.44 mins.


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