Machining new

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Indian Institute of Technology Delhi

Definition of Machining :

Machining is an essential process of finishing bywhich jobs of desired dimensions and surface

finish are produced by gradually removing theexcess material from the preformed blank in theform of chips with the help of cutting tool(s)moved past the work surface(s).

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Machining

Process

Power

Blank

MachineProduct

Analysis

Fixture

Tools Environment

Correction

Machining requirements

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Machine Tool - definition

A machine tool is a non-portable, poweroperated and reasonably valued device or system

of devices in which energy is expended to producejobs of desired size , shape and surface finishby removing excess material from the preformeblanks in the form of chips with the help ofcutting tool(s) moved past the work surface(s).

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(i) Working principle of Machine Tools

Machine Tools produce geometrical surfaces : flat surfaces cylindrical surfaces contour surfaces

Major functional components of machine tool devices for holding job and tool drive(s) for providing power and motions kinematic system(s) to transmit motion and

power to the tool and job automation and control system structure / body strong and rigid


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(iii) Machine Tool Drives.refers to source and transmission of motion and power.

Source(s) of power and motion electrical motors

hydraulic power driveMachine Tools need wide ranges of speed & feed for:

machining different jobs (material & size) using different tools (matl., geometry & size) various types of operations varying degree of surface finish.

(contd.)


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Configuration & use of basic machine tools(i) Centre Lathe -

configuration

Headstock

Tool postTool Job(rod)

Leadscrew

SaddleBed

feedscrew


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Common machining operations done in

centre lathesturning facing grooving forming threading

External

Internal


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Methods of mounting job & cutting tools ingeneral purpose machine tools

(a) Job and tool mounting in Lathes In centre lathes :

Mounting of job / blank

The general methods :

without additional support from tailstocko chucks : 3 jaw self centering chuck

: 4 independent jaw chucko Face plate : without or using fixture


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Mounting of jobs in centre lathes - continuation


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Job-mounting with tailstock support in centre lathes

Methods : in between centres in between chuck and centre in between headstock & tailstock with

additional support from rest

driving plate

lathe dog

Dead centres

Revolving centre


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Job mounting in centre lathe with additionalSupport - continuation

In between chuck and tailstock centre

4- jaw

3- jaw

Using rest


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General purposes of using drilling machines

To originate through or blind straight cylindricalholes in solid bodies and / or enlarge existingor premachined holes :

of different diameter of varying length

in different work materials excepting veryhard and very soft materials like rubber,polythenes etc.

Main purpose

Other purposes : boring, reaming, tapping etc.


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(ii) Classification of drilling machines - contd . Pillar drilling machine

= 3 ~ 20 mm

Power 0.55 ~ 1.1 kW

Long tubular column andmoveable table


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Classification of drilling machines - contd. Column drilling machine

strong, powerful, rigid most common have SGB & FGB

quick change ofN and s o

automatic feed wide ranges of

N and s o blanks simple, odd

or heavy


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Classification of drilling machines - contd. Radial drilling machine

very large work vol. can work on odd

shape and size jobs spindle may be

vertical swivelling swivelling &

tilting


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(iv) Application ( operations ) of drilling machine

Drilling through or blind holes most common straight, taper, stepped & deep

Centering Slotting Boring

Counterboring and countersinking Reaming Tapping


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Classification of drills and drilling operations According to material

HSS

cemented carbides diamond According to size (diameter)

micro 25 ~ 500 m moderate 3 to 25 mm most widely used large 25 to 40 mm

According to number of flutes two fluted most common single flute e.g. gun drill three or four flutes slot drills


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Use of drilling machines other thangeneral drilling

slot drilling and slotting

boring after drilling Counterboring, countersinking etc.

(a) (b)

spot facing


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Basic functions of milling machines

Production of

flat surfaces in any orientation helical surfaces surfaces of revolution (external)

contour surfaces of various configurations


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Up-milling & Down milling concept & effects

Cutting motion


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Major uses of milling machines making flat surfaces in H, V & any inclined plane

making slots and steps slitting or parting making helical grooves or surfaces long thread milling & short thread milling 2-D contouring (e.g. cam profiles) and 3-D

contouring (e.g. die cavities) cutting teeth of gears,worm wheels, sprockets etc making flutes, gushing etc in drills, taps, reamers,

hobs etc.


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According to spindle orientation

Horizontal arbour type

o hollow plain or disc typecutters mounted onthe horizontal arbour

o bed is usually knee typeo used for non-automatic

prod. in piece or batcho the work table may or

may not be swivelled inaddition to feeds alongX-Y-Z directions


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According to spindle orientation contd. Vertical spindle type

o end mill or face millingcutter(s) is mounted onthe vertical spindle

o it may be knee or bedtype

o the table may,additionally,be swivelled


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According to spindle orientation contd. Universal head type


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semi-automatic Tracer controlled copy milling

o low to moderate rate prod.o piece or batch productiono used for making cams,

dies etc using masterpiece

o machines are small butautomatic & productiveo example short thread

milling (lot production)

automatic fast productioncutter

tracer


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o flexible automationo change-over needs

less effort, time & costo complex shape- possible

o lesser maintenancerequirement

o lesser or no jigs /fixtures are needed

CNC milling machines


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(d) According to automation and prod. contd.

Machining Centre

omuch more versatile& productive

o Tool magazine

(bank)o ATC


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Various applications of different milling cutters inMilling machinesUses of profile sharpened cutters

plain or slab milling cutters

o no. of teeth 4 ~ 16o diameter 40 ~ 80 mm

feedjob job

CM


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Use of profile sharpened cutters - continuation Side & slot milling cutters and slitting saw

Parting by slitting saw

Parallel facing bytwo sided single cutter

Slotting by sidemilling cutter


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Use of profile sharpened cutters - continuationEnd mill and shell millMaterials : Solid HSS or steel body with carbide

Inserts (uncoated or coated)Configurations and applications

Face milling

angular milling

slotting Shell milling


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Form relieved cutters - continuationGear ( teeth ) milling cutters

Material essentially HSS Types - disc type end mill type configurations and applications


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Thread milling cutters : - short thread milling long thread milling

Short thread milling long thread milling


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Config. & basic functions of shaping machine

tool work motions basic functions

cutting tool in action


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Configuration and functions of Planing machines

tool work motions basic functions special applications

cutting tool in action


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(i) BASIC PRINCIPLE OF BROACHINGCutting motion

a 1 a 1workpiece(b) broaching

(a) shaping

In-feed


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Basic principle of broaching - continuationBroaching holes

(b) vertical push type

(a) horizontal pull typeCM

CM

Chip breaker (groove)


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Learning Geometry of SPTT

Material and geom. of tools equally important Those play important roles on

Effectiveness, effici. and econ. of machining Tool geometry substantially affects :

mechanism & mechanics of chip formation cutting temperature and wear tool life and products accuracy and finish

Cutting tools may be single point e.g., turning, shaping, boring, etc. double point e.g., drills. multipoint e.g., milling cutters, hobs, etc.


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(a) Geometry of SPTT - continued(i) Concept of rake and clearance angles

Tool geometry refers to some specific anglesor slopes of its salient faces and edges

Rake angle and clearance angle most imp.

Illustration of rake and clearance of SPTT.


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(i) Concept of rake and clearance angles contd. Definition of

Rake angle :

clearance angle :

Sign of rake and clearance angles

+

+ + +

- =0

VC

VCVC

VC

VC

R R R


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Reference systems of description of tool geom. Tool in Hand system

Tool in Hand system :

rake surface

Auxiliary cuttingedge

Tool nose

Auxiliary flank

(clearance) surface

principal cuttingedge

principal flank (clearance) surface


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Chip formation in machining brittle materials


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(i) Sources of heat and causes of development ofcutting temperature

VC

Vf

123

Primary shear zone:

Secondary deformationzone:

Work tool(flanks)

interfaces:


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Apportionment of heat in chip, tool and job

Cutting velocity, V C

share of h

eat %

0

100blank

tool

chip

job chip

tool

Vc

cutting velocity, V C


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Measurement of temperature distribution atthe tool tip by Infra ray detection.

7

65

4

8 lowest temp.Rake surface

Auxiliary flank

8

1 highest temp.1


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(i) Role of development of cutting tool materials

MRR (for turning MS)

1910 1930 1965 1980 2000Year

HSS

25 m/min

Carbide (brazed) 60 m/min

Carbid

e (tips) 80 m/min

High perf. Ceramics 750 m/min

Coated carbide 250 m/m

in

0

1020

30

40

50

6070

80


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Jet engines,Space programmes

1900

1910

1920

1930

1940

1950

1960

1970

1980

1986

1990

NEED DEVELOPMENT

HSS (W: 18%; Cr: 4%; V: 1%; C: 0.7%)

Stellite

Sintered Carbide for C.I

Carbide for steels

HSS with high V, Mo, Co & CPlain ceramics, Syn. Diamond

Ceramics and Cermets

Coated carbides, PM HSS,PCD

CBN, coated HSS, SIALON

High performance ceramics

Diamond, coated carbides

Automobile

World War - I

Aircraft

World War - II

Reduction of cost ofmanufacturing

DefenceSuperalloys

Just-in-time

HSS (V: 2~4%, Co: 5 12% in W & Cr)

Chem. Petro-chem., NU &polymer industries


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(i) (a) High Speed Steel ( HSS)Basic composition

W 18%, Cr 4%, 0.70% C, V 1%, rest FeVC for machining low carbon steels - 20 to 30 m/min

HSS are still used where; tool is slender e.g. drills, reamers, end mills tool geometry is complex drill, gear cutters,

broach etc the tool needs high TRS and toughness the M-F-T-W system does not permit high V

C


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Sintered Carbide (tools)o Manufacturing : - Powder metallurgical process

Mixing powders, briquetting and sinteringo Basic two categories single and composite

carbides

Single carbides WC grains; 90 to 95 wt% and Co (binder); 5 to 10% Performance tool life 2 to 3 times of that of HSS Application machining cast iron, brass, bronze

etc at VC = 40 ~ 80 m/min


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Types and applications of alumina tools

Characteristics Type1 2 3 (mixed ceramic)

Composition

Al2O3 +

trace ofadditives

Al2O3 with or

withoutadditive

Al2O3 + TiC(20~30%)

Sintering Coldpressed Hot pressed Hot pressed

Colour White orpink Black black

Hardness Medium Higher less

Toughness Less Medium higher

Applications Grey castiron Steels & C.I.Stronger steeland hard C.I.

VC, m / m in 200 ~ 250 200 ~ 300 150 ~ 250

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Machining new