manufacturing processes - staff.fit.ac.cystaff.fit.ac.cy/eng.os/amem201_lecture3.pdf · 1...

17
1 MANUFACTURING PROCESSES - AMEM 201 – Lecture 3: Machining Processes DR. SOTIRIS L. OMIROU Introduction Machine Tools Tool Materials Cutting Fluids 2 The machining is the most broad technological process used in manufacturing. Generaly, in the field of manufacturing, the term of Machining means removal of material from a raw material, by cutting small chips, in order to obtain the desired shape and dimensions for final part. The machining is strictly necessary when finished part has to have very tight tolerances of dimensions or when the roughness of surfaces need to be very smooth. Introduction to Machining

Upload: phungthu

Post on 10-Mar-2018

273 views

Category:

Documents


2 download

TRANSCRIPT

Page 1: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

1

MANUFACTURINGPROCESSES

- AMEM 201 –

Lecture 3: Machining Processes

DR. SOTIRIS L. OMIROU

Introduction

Machine Tools

Tool Materials

Cutting Fluids

2

The machining is the most broad technological process used in manufacturing.

Generaly, in the field of manufacturing, the term ofMachining means removal of material from a raw material, by cutting small chips, in order to obtain the desired shape and dimensions for final part.

The machining is strictly necessary when finished part has to have very tight tolerances of dimensions or when the roughness of surfaces need to be very smooth.

Introduction to Machining

Page 2: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

2

3

Removal of chips, from a raw material, is performed by a cutting tool that need a motion relative to raw material. This motion, named cutting motion, could be practically a rotation one or a translation one.

The next two examples will illustrate in a synopsis way the cutting process, the chip removal from a raw material.

First example is related to the case when the cutting motion is a rotation one, like in turning machining.The second example is related to the case when the cutting motion is a translation one, like in shaping machining.

Introduction to Machining

4

The raw material performs a rotation motion (cutting motion) and to assure the process continuity the tool performs a translation motion (feeding motion)

Introduction to Machining

Page 3: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

3

5

Introduction to Machining

The figure presents a shaping machine. In this case the cutting motion is executed by the cutter while the workpiece (raw material) remain stationary.

6

Examples of tool-machines

Page 4: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

4

7

Examples of machined parts

MILLING

DRILLING

TURNING

GRINDING

8

The chip removal

• Chip removal is a technological process by that a raw material is transformed into a final part.

•The condition for the existing of chip removal is a relative motion between the raw material and tool. This motion is named effective chip removal motion and it has the speed “V”.

Page 5: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

5

9

The ECONOMIC Chip removal

• There is only one speed V for each pair of raw material and tool material, when the chip removal is done in an economical way.

• If the motion is a rotation one, then

V = (π . D . n)/1000 [m/min]

where- D [mm] is part or tool diametern [1/min] is the rotation freqeunce

• There is only one speed V for each pair of raw material and tool material, when the chip removal is done in an economical way.

• If the motion is a rotation one, then

V = (π . D . n)/1000 [m/min]

where- D [mm] is part or tool diametern [1/min] is the rotation freqeunce

10

Elements of an Effective Tool

High hardness at elevated temperatures Wear resistance Strength to resist bulk deformation Adequate thermal properties Consistent tool life Correct geometry Chemical stability

Tool Materials

Page 6: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

6

11

Wide variety of materials and compositions are available to choose from when selecting a cutting tool

Tool Materials

12

Tool steels - low end of scale. They have been used since the 1880s for cutting tools. However tool steels start to soften at a temperature of about 180oC. Used to make some drills, taps, reamers, etc. Low cost equals low tool life.

Tool Materials

Page 7: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

7

13

Tool Materials

High speed steel(HSS)Prior to World War II the most common type of lathe bit was made from high speed tool steel. High speed tooling is a steel alloy with a predetermined percentage of tungsten mixed in. There is also a hardening process that makes high speed tooling very hard and wear resistant. These tools are able to withstand high work temperatures. Tools typically made from high speed are end mills, drills, reamers, and lathe tool bits.

14

Tool Materials

Fig. 1: End mill

Fig. 3: Reamer

Fig. 2: Drill

Fig. 4: Lathe tool bit

High speed steel(HSS)

Page 8: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

8

15

Tool Materials

Cobalt alloys - one step above HSS. Introduced in early 1900s these alloys have compositions of about

40 - 55% cobalt,

30% chromium

10 - 20% tungsten

They are not heat treatable. They have good wear resistance but are not as tough as HSS but can be used at 25% higher speeds than HSS.

16

Carbides - Most widely used cutting tool today. Cutting speeds are three to five times faster than HSS. Carbides are made by blending micron-sized tungsten carbide and cobalt powders, then pressing the mixture in a mold and at a temperature high enough to cause the cobalt to flow. This process is called "sintering" and the resulting tool is called "cemented" carbide. In addition to tool composition, coatings are added to tool materials to increase resistance to wear.

Tool Materials

Page 9: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

9

17

Carbides

Tool Materials

18

– Ceramics - Contain pure aluminum oxide and can cut at two to three times faster than carbides. Ceramic tools have poor thermal and shock resistance and are not recommended for interrupted cuts. Caution should be taken when selecting these tools for cutting aluminum, titanium, or other materials that may react with aluminum oxide.

Tool Materials

Page 10: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

10

19

– Diamond - The hardest known substance is diamond. Single crystal diamond has been used as a tool but they are brittle. For this reason they have been mainly replaced by polycrystalline diamond (PCD). Because of its reactivity, PCD is not suitable for machining plain carbon steels or nickel, titanium and cobalt based alloys. PCD is most suited to light uninterrupted finishing cuts at almost any speed and is mainly used for very high speed machining of aluminium - silicon alloys, composites and other non - metallic materials.

Tool Materials

20

– Cubic Boron Nitride (cBN) - Introduced in the early 1960s, this is the second hardest material available after diamond. Cubic boron nitride is the standard choice for machining alloy and tool steels with a hardness of 50 Rc or higher.

Tool Materials

Page 11: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

11

21

Inserts

Tool Materials

22

Inserts are individual cutting tool with severed cutting points. They are clamped on tool shanks with locking mechanisms or can be brazed to the tools. Clamping is preferred method for securing an insert

Carbide Inserts are available in various shapes-Square, Triangle, Diamond and Round

Strength depends on the shape

Tool Materials

Page 12: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

12

23

Insert AttachmentMethods of attaching inserts to toolholders :

(a) Clamping

(b) Wing lockpins.

(c) Examples of inserts attached to toolholders side screws.

(d) brazed

Tool Materials

24

Cutting Fluids

Page 13: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

13

25

Cutting Fluids

26

Cutting Fluids

Taylor Tool Life Equation

Relationship is credited to F. W. Taylor

CvT n where,

v = cutting speed;

T = tool life;

and n and C are parameters that depend on feed,depth of cut, work material, tooling material, etc

Page 14: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

14

27

Cutting Fluids

TWO MAIN CATEGORIES

(a) Water based for cooling

(b) Oil based for lubricating. (low cutting speed)

28

Cutting Fluids

Page 15: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

15

29

Cutting Fluids

30

Cutting Fluids

Page 16: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

16

31

Cutting Fluids

32

Cutting Fluids

Page 17: MANUFACTURING PROCESSES - staff.fit.ac.cystaff.fit.ac.cy/eng.os/AMEM201_LECTURE3.pdf · 1 MANUFACTURING PROCESSES-AMEM 201 – Lecture 3 : Machining Processes DR. SOTIRIS L. OMIROU

17

33

Cutting Fluids

34

Cutting Fluids