ME 306 Slides

ME 306

Manufacturing Technology II

S. N. JoshiOffice: D 203

E-mail: [email protected]: [email protected]

Phone: 2678

Course syllabus

• Metal Cutting: mechanics, tools (material, temperature, wear, and life

considerations), geometry and chip formation, surface finish and

machinability, optimization

• Machine tool: generation and machining principles, Setting and Operations

on machines: lathe, milling (including indexing), shaping, slotting, planing,

drilling, boring, broaching, grinding (cylindrical, surface, centre-less), threaddrilling, boring, broaching, grinding (cylindrical, surface, centre-less), thread

rolling and gear cutting machines

• Tooling: jigs and fixtures, principles of location and clamping

• Batch production: capstan and turret lathes; CNC machines

• Finishing: micro-finishing (honing, lapping, super-finishing)

• Unconventional methods: electro-chemical, electro-discharge, ultrasonic,

LASER, electron beam, water jet machining,

• Rapid prototyping and rapid tooling

2Indian Institute of Technology Guwahati

Course syllabus

Texts:

1. G Boothroyd, Fundamentals of Metal Cutting Machine Tools, Tata McGraw

Hill, 1975

2. Production Technology, H M T Publication Tata McGraw Hill, 1980.

3. P C Pandey and C K Singh, Production Engineering Sciences, Standard

Publishers Ltd. 1980.Publishers Ltd. 1980.

4. A Ghosh and A K Mallik, Manufacturing Science, Wiley Eastern, 1986.


Course structure

• Quiz(s) and tutorials: 15%

• Course project: 15%

• Mid-semester exam: 25%

• End-semester exam: 45%• End-semester exam: 45%


Machining

• Machining of materials

– Higher surface finish

– Close tolerances

– Complex geometric shapes


– Complex geometric shapes

• Metal cutting: expensive one

– Substantial amount of work removal from

workpiece

– Lot of energy will be expended

INDISPENSABLE

• Machine tool (Mother of machines): It is a

machine with a tool(s) and tool holding device

produces the job of required dimensions

(size), shape, and surface finish.

Machine tools


(size), shape, and surface finish.

• Machine: Converting the source of power

from one form to the other.

• Manufacturing in 21st Century: Micro-

electronics technology- CNC technology

Brief history of machine tools

• 1775 - John Wilkinson- Horizontal Boring Machine

• 1794 - Henry Maudsley - Engine Lathe

• 1817 – Roberts Planer

• 1818 - Eli Whitney - Milling Machine

• 1840 - John Nasmyth - Drill Press• 1840 - John Nasmyth - Drill Press

• 1845 - Stephen Fitch - Turret Lathe

• 1869 - Christopher Spencer - Automatic Turret Lathe

• 1880 - Surface Grinder

• 1952 – Numerical Control


Manufacturing processes

• Casting , Metal working and Metal removal

(machining) processes

• Casting and metal working processes converts “first

shape” into “intermediate” shape

• Metal removal processes converts “Intermediate”

into “final” shape

• Assembly- mating surfaces: required forms and

surface finish


Material removal processes


(20th Century)

Machine tools

• Turning machines (Lathes)

• Drilling machines

• Boring machines

• Milling machines

• Grinding machines• Grinding machines

• Shaping and Planing machines

• Gear cutting machines

• Sawing machines

• Unconventional machining machines


Some facts

• Metal cutting operations share about 80% of

total material removal

• About 15% of material removed is converted

into chipsinto chips

• Research in “Metal cutting”

– Before 19th century Tresca, Thime maalock etc.

– After 19th century F. W. Taylor (ASME, 1907)

Indian Institute of Technology Guwahati 11

Rake and clearance angles


Rake angles


Chip formation

• The metal in front of the tool rake

face gets immediately

compressed first elastically and

then plastically.

• The actual separation of the

metal starts as a yielding or metal starts as a yielding or

fracture, depending upon the

cutting conditions, starting from

the cutting tool tip.

• The chip after sliding over the

tool rake face would be lifted

away from the tool, and the

resultant curvature of the chip is

termed as “chip curl”.


http://electron.mit.edu/~gsteele/mirrors/www.nmis.org/EducationTr

aining/machineshop/physics/intro.html

Possible deformations


Piispanen's Model

• He considers the un-

deformed metal as a

stack of cards which

would slide over one

another as the wedge another as the wedge

shaped tools moves

under these cards.

• A practical example is

when paraffin is cut,

block wise slip is clearly

evident.Indian Institute of Technology Guwahati 16

Types of chips

• Discontinuous chip

• Continuous chip

• Continuous chip with built-up-edge (BUE)


Discontinuous chips

• When brittle materials like • Cutting force becomes cast iron are cut, the

deformed material gets

fractured very easily and

thus the chip produced is in

the form of discontinuous

segments.

• Cutting force becomes

unstable with the variation

coinciding with the

fracturing cycle.

• Higher depths of cut (large

chip thickness), low cutting

speeds and small rake

angles are likely to produce

discontinuous chips.Indian Institute of Technology Guwahati 18

Cutting forces in discontinuous

chip formation


Continuous chip

• Continuous chips are normally

produced when machining steel

or ductile metals at high cutting

speeds.

• Continuous chip is possible

because of the ductility of metal because of the ductility of metal

flows along the shear plane

instead of rupture.

• Sharp cutting edge, small chip

thickness (fine feed), large rake

angle, high cutting speed, ductile

work materials and less friction

between chip tool interface

through efficient lubrication.


Continuous chip with built-up edge

(BUE)• When the friction between tool

and chip is high while machining

ductile materials, some particles

of chip adhere to the tool rake

face near the tool tip.

• When such sizeable material piles • When such sizeable material piles

up on the rake face, it is termed

as built up edge (BUE).

• As the size of BUE grows larger, it

becomes unstable and parts of it

gets removed while cutting. The

removed portions of BUE partly

adheres to the chip underside

and partly to the machined

surface

• Low speed, high feed rate,

low rake angle

• HardenabilityIndian Institute of Technology Guwahati 21

BUE cycle


Shear zone

• Thin shear plane model

– Easier for analysis

• Thick shear plane model

– More realistic– More realistic


Orthogonal cutting

• Oblique cutting is more practical while orthogonal

cutting is convenient for analysis.


Example of orthogonal cutting


Mechanics of orthogonal cutting

• The current analysis is based on Merchant's thin

shear plane model considering the minimum energy

principle.

• This model would be applicable at very high cutting

speeds, which are generally practised in production.


Assumptions

• The tool is perfectly sharp and no contact along the clearance

face.

• The surface where shear is occurring is a plane.

• The cutting edge is a straight line extending perpendicular to the

direction of motion and generates a plane surface as the work

moves past it.moves past it.

• The chip does not flow to either side or no side spread.

• Uncut chip thickness is constant.

• Width of the tool is greater than the width of the work.

• A continuous chip is produced without any BUE.

• Work moves with a uniform velocity.

• The stresses on the shear plane are uniformly distributed.


Merchant’s analysis

• Fv-Force perpendicular to

the primary tool motion

(thrust force)

• Fs-Force along the shear

plane

• Ns-Force normal to the

shear plane

• F -Frictional force along

the rake face

• N -Normal force

perpendicular to the rake

face

• R = R'


Free body diagram of chip


Tool materials

• Need

– to meet the growing demands for high

productivity, quality and economy of machining

– to enable effective and efficient machining of the – to enable effective and efficient machining of the

exotic materials that are coming up with the rapid

and vast progress of science and technology

– for precision and ultra-precision machining

– for micro and even nano machining demanded by

the day and future.


Capability and overall performance

of cutting tools

• Cutting tool materials

• Cutting tool geometry

• Proper selection of materials and geometry

• Machining conditions and environment• Machining conditions and environment


Productivity of various cutting tool materials


(Courtesy NPTEL, IIT Kharagpur,

http://nptel.iitm.ac.in/courses/Webcourse-

contents/IIT%20Kharagpur/Manuf%20Proc%20II/New_index1.html)

Chronological

developments of

cutting tool

materials


materials

(Courtesy NPTEL,

IIT Kharagpur

http://nptel.iitm.ac.i

n/courses/Webcour

se-

contents/IIT%20Kh

aragpur/Manuf%20

Proc%20II/New_ind

ex1.html)

Cutting tool materials: required

properties

• Higher hardness

• Hot hardness

• Wear resistance

• Toughness• Toughness

• Low friction

• Better thermal characteristics


Carbon tool steels

• C (0.6 to 1.5%) + Mn + Si + W + Mo + Cr + V

• Earliest tool steel

• After 200o C, not working

• Low speed cutting, 0.15 m/s• Low speed cutting, 0.15 m/s

• Machining of wood, brass, aluminium

• Easy to manufacture angles by grinding


HSS (High speed steel)

• Taylor and white in early of the 20th Century

• Machining speed 0.5 m/s, 3 to 5 times more

than Carbon tool steel

• W+Mo+V+Cr• W+Mo+V+Cr

• High hardness and good abrasion resistance

• High hot hardness

• After 650o, hardness drops

• Can be made by using Powder Metallurgy

techniqueIndian Institute of Technology Guwahati 37

Typical compositions of HSS


Variation of hardness of various

cutting tool materials


Cast cobalt alloys (Stellites)

• Cutting of non-ferrous metals

• Cr + Mo + W + C + Mn + Si + Ni + Cobalt

• Can be manufactured by powder metallurgy

techniquetechnique

• Form tools

• At elevated temperatures provides good

hardness and toughness

• Provides cutting speed of about 25% more

than HSSIndian Institute of Technology Guwahati 40

Typical compositions of Stellites


Cemented carbides• 1926, Germany: important invention in cutting tool

industry, Contributes largest % share nowadays

• Cemented carbides are produced by the cold

compaction of the tungsten carbide (WC) powder in

a binder such as cobalt (Co), followed by liquid-phase

sintering.sintering.

• High hot hardness.

• Higher Young's modulus.

• Carbides are more brittle and expensive

• The usual composition of the straight grade carbides

is 6wt% Co and 94wt% WC with the cobalt

composition ranging from 5 to 12wt%. Indian Institute of Technology Guwahati 42

Cemented carbides• Addition of titanium carbide (TiC) increases

the hot hardness, wear resistance, and

resistance to thermal deformation, but

decreases the strength. The usual composition

is about 5–25wt%.

• Choose a grade with the lowest cobalt content

and the finest grain size consistent with

adequate strength to eliminate chipping.

• Use straight WC grades if cratering, seizure or

galling are not experienced in case of work

materials other than steels.Indian Institute of Technology Guwahati 43

Cemented carbides

• To reduce cratering and abrasive wear when

machining steel, use grades containing TiC.

• For heavy cuts in steel where high

temperature and high pressure use a multi-

carbide grade containing W-Ti-Ta and/or lower carbide grade containing W-Ti-Ta and/or lower

binder content

• Cemented carbides being expensive are

available in insert form in different shapes

such as triangle, square, diamond, and round.


Tool-insert assembly


Coated carbides (WW II)

• Hard and refractory coatings on conventional

tool materials

• Since late 60's thin (about 5 m) coating of TiN

has been used on cemented carbide tools.

• Ceramic coatings used are hard materials and

therefore provide a good abrasion resistance.

• They also have excellent high temperature

properties such as high resistance to diffusion

wear, superior oxidation wear resistance, and

high hot hardness. Indian Institute of Technology Guwahati 46

Schematic of multi-coated

cemented carbide Hardness and

refractoriness

Chemical vapor

deposition (CVD)

technique

Ion-by-ion deposition


Strength and toughness

Coated carbides


Role of coating even after rupture



contents/IIT%20Kharagpur/Manuf%20Proc%20II/New_index1.html

Coated carbides

• Share : 40% of all cutting tools used in

industry

• Multiple coatings

– Higher tool life– Higher tool life

– Broader range of materials


Ceramics• Ceramics are essentially alumina (Al2O3) based high

refractory materials introduced specifically for high

speed machining of difficult to machine materials

and cast iron.

• These can withstand very high temperatures, • These can withstand very high temperatures,

chemically more stable and have higher wear

resistance than the other cutting tool materials.

• The main problems of ceramic tools are their low

strength, poor thermal characteristics and the

tendency to chipping.


Diamond• Diamond is the hardest known (Knoop hardness ~

8000 kg/mm2) material that can be used as a cutting

tool material.

• It has most of the desirable properties of a cutting

tool material such as high hardness, good thermal

conductivity, low friction, non-adherence to most conductivity, low friction, non-adherence to most

materials, and good wear resistance.

• Artificial diamonds which are basically polycrystalline

(PCD) in nature. These are extensively used in

industrial application because they can be formed for

any given shape with a substrate of cemented

carbide.Indian Institute of Technology Guwahati 53

Diamond tool


Cubic Boron Nitride (CBN)

• Cubic Boron Nitride (CBN) next in hardness only to

diamond (Knoop hardness ~ 4700 kg/mm2).

• It is not a natural material but produced in the

laboratory using a high temperature/ high pressure

process similar to the making of artificial diamond.

• These are more expensive than cemented carbides

but in view of the higher accuracy and productivity

possible for difficult to machine materials, they are

used in special applications.


Cutting tool materials


Cutting temperatures

• Sources of generation

http://nptel.iitm.ac.in/courses/

Webcourse-

contents/IIT%20Kharagpur/Ma

nuf%20Proc%20II/New_index1


nuf%20Proc%20II/New_index1

.html

Distribution of heat generated



contents/IIT%20Kharagpur/Manuf%20Proc%20II/New_index1.html

Effects of high cutting

temperatures• Rapid tool wear, reduces tool life

• Plastic deformation of the cutting edge

• Thermal flaking and fracturing of cutting edges

• Formation of BUE• Formation of BUE

• Dimensional inaccuracies of job due to thermal

distortion

• Surface damage by oxidation, rapid corrosion and

burning

• Induction of thermal residual stresses and micro-

cracks on machined surface.Indian Institute of Technology Guwahati 59

Cutting temperature distribution


Effect of cutting speed on

Temperature


Effect of feed rate on cutting temperature


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