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Manufacturing Engineering Technology in SI Units, 6th Edition

Chapter 23: Machining Processes: Turning and Hole MakingCopyright 2010 Pearson Education South Asia Pte Ltd

Chapter Outline1. 2. 3. 4. 5. 6. 7.

Introduction The Turning Process Lathes and Lathe Operations Boring and Boring Machines Drilling, Drills, and Drilling Machines Reaming and Reamers Tapping and Taps

Copyright 2010 Pearson Education South Asia Pte Ltd

IntroductionMachining processes has the capability of producing parts that are round in shape Such as miniature screws for the hinges of eyeglass frames and turbine shafts for hydroelectric power plants Most basic machining processes is turning where part is rotated while it is being machined Turning processes are carried out on a lathe or by similar machine tools Highly versatile and produce a wide variety of shapes

Copyright 2010 Pearson Education South Asia Pte Ltd

Introduction

Copyright 2010 Pearson Education South Asia Pte Ltd

Introduction

Copyright 2010 Pearson Education South Asia Pte Ltd

Introduction1.

2. 3.

Turning is performed at various: Rotational speeds, N, of the workpiece clamped in a spindle Depths of cut, d Feeds, f, depending on the workpiece materials, cutting-tool materials, surface finish, dimensional accuracy and characteristics of the machine tool

Copyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessMajority of turning operations use simple single-point cutting tools, which is a right-hand cutting tool Important process parameters have a direct influence on machining processes and optimized productivity Tool Geometry Rake angle control both the direction of chip flow and the strength of the tool tip Side rake angle controls the direction of chip flow Cutting-edge angle affects chip formation, tool strength and cutting forcesCopyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessTool Geometry Relief angle controls interference and rubbing at the toolworkpiece interface Nose radius affects surface finish and tool-tip strength

Copyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessTool Geometry

Material-removal Rate The material-removal rate (MRR) is the volume of material removed per unit time (mm3/min)

Copyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessMaterial-removal Rate D0 D f The average diameter of the ring is Davg !2

Since there are N revolutions per minute, the removal rate isMMR ! TDavg dfN or reduce to MMR ! dfV

Since the distance traveled is l mm, the cutting time isl t! f

The cutting time does not include the time required for tool approach and retractionCopyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessMaterial-removal Rate

Copyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessForces in Turning The 3 principal forces acting on a cutting tool are important in the design of machine tools, deflection of tools and workpieces for precision-machining operations Cutting force acts downward on the tool tip and deflect the tool downward and the workpiece upward Thrust force (or feed force) acts in the longitudinal direction

Copyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessRoughing and Finishing Cuts First practice is to have one or more roughing cuts at high feed rates and large depths of cut Little consideration for dimensional tolerance and surface roughness Followed by a finishing cut, at a lower feed and depth of cut for good surface finish

Copyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessTool Materials, Feeds, and Cutting Speeds The range of applicable cutting speeds and feeds for a variety of tool materials is shown

Copyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessTool Materials, Feeds, and Cutting Speeds

Copyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessTool Materials, Feeds, and Cutting Speeds

Copyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessCutting Fluids Recommendations for cutting fluids appropriate to various workpiece materials

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The Turning ProcessEXAMPLE 23.1 Material-removal Rate and Cutting Force in Turning A 150-mm-long, 12.5-mm-diameter 304 stainless steel rod is being reduced in diameter to 12.0 mm by turning on a lathe. The spindle rotates at N 400 rpm, and the tool is travelling at an axial speed of 200 mm/min. Calculate the cutting speed, material-removal rate, cutting time, power dissipated, and cutting force.

Copyright 2010 Pearson Education South Asia Pte Ltd

The Turning ProcessSolution Material-removal Rate and Cutting Force in Turning The maximum cutting speed isT .5400 12 V ! TD0 N ! ! 15.7 m/min 1000

The cutting speed at the machined diameter isV ! D0 N !

12.0400 ! 15.1 m/min1000 12.5 12.0 ! 0.25 mm 2Copyright 2010 Pearson Education South Asia Pte Ltd

The depth of cut is d !

The Turning ProcessSolution Material-removal Rate and Cutting Force in Turning200 ! 0.5 mm/rev The feed is f ! 400

The material-removal rate isMMR !

12.250.250.5400 ! 1924 mm3 /min ! 2 v10 6 m3 /min150 t! ! 0.75 mm 0.5400 Copyright 2010 Pearson Education South Asia Pte Ltd

The actual time to cut is

The Turning ProcessSolution Material-removal Rate and Cutting Force in Turning The power dissipated is

41924 ! 128 W Power !60

Since W=60 Nm/min, power dissipated is 7680 N m/min. Also, power is the product of torque:T! 7680 ! 3.1 Nm 2 400

3.11000 ! 506 N T ! Fc Davg 2 , we have Fc ! Since 12.25 / 2 2010 Pearson Education South Asia Pte Ltd Copyright

Lathes and Lathe OperationsLathes are considered to be the oldest machine tools Speeds may range from moderate to high speed machining Simple and versatile But requires a skilled machinist Lathes are inefficient for repetitive operations and for large production runs

Copyright 2010 Pearson Education South Asia Pte Ltd

Lathes and Lathe Operations: Lathe ComponentsBed Supports all major components of the lathe Carriage Slides along the ways and consists of an assembly of the cross-slide, tool post, and apron Headstock Equipped with motors, pulleys, and V-belts that supply power to a spindle at various rotational speedsCopyright 2010 Pearson Education South Asia Pte Ltd

Lathes and Lathe Operations: Lathe ComponentsTailstock Slide along the ways and be clamped at any position, supports the other end of the workpiece Feed Rod and Lead Screw Powered by a set of gears through the headstock Lathe Specifications 1. Max diameter of the workpiece that can be machined 2. Max distance between the headstock and tailstock centers 3. Length of the bedCopyright 2010 Pearson Education South Asia Pte Ltd

Lathes and Lathe Operations: Lathe ComponentsLathe Specifications

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Lathes and Lathe Operations: Workholding Devices and AccessoriesWorkholding devices must hold the workpiece securely Chuck is equipped with three or four jaws Three-jaw chucks used for round workpieces Four-jaw (independent) chucks used for square, rectangular, or odd-shaped workpieces Power chucks are used in automated equipment for high production rates Chuck selection depends on the type and speed of operation, workpiece size, production and dimensional accuracy requirements and the jaw forces required

Copyright 2010 Pearson Education South Asia Pte Ltd

Lathes and Lathe Operations: Workholding Devices and Accessories

Copyright 2010 Pearson Education South Asia Pte Ltd

Lathes and Lathe Operations: Workholding Devices and AccessoriesA collet is a longitudinally-split, tapered bushing Used for round workpieces and shapes like square or hexagonal It can grips the entire circumference of the part, suitable for parts with small cross sections Face plates are used for clamping irregularly shaped workpieces Mandrels used to hold workpieces that require machining on both ends or on their cylindrical surfaces

Copyright 2010 Pearson Education South Asia Pte Ltd

Lathes and Lathe Operations: Lathe OperationsCutting tool removes material by travelling along the bed Facing operations are done by moving the tool radially with the cross-slide and clamping the carriage for better dimensional accuracy Form tools are used to produce various shapes on solid, round workpieces by moving the tool radially inward while the part is rotating Boring on a lathe is similar to turning Drilling can be performed on a lathe by mounting the drill bit in a chuck in the tailstock quillCopyright 2010 Pearson Education South Asia Pte Ltd

Lathes and Lathe Operations:

Types of LathesBench Lathes Have low power, operated by hand feed, and are used to machine small workpieces Special-purpose Lathes Used for applications such as railroad wheels, gun barrels, and rolling-mill rolls Tracer Lathes Cutting tool follows a path that duplicates the contour of a templateCopyright 2010 Pearson Education South Asia Pte Ltd

Lathes and Lathe Operations:

Types of LathesAutomatic Lathes For fully automatic lathe, parts are fed and removed automatically For semiautomatic machines, functions are performed by the operator Automatic Bar Machines Designed for high-production-rate machining of screws and similar threaded parts

Copyright 2010 Pearson Education South Asia Pte Ltd

Lathes and Lathe Operations:

Types of LathesTurret Lathes Perform multiple cutting operations, such as turning, boring, drilling, thread cutting, a