Manufacturing Processes Cutting (Machining)

Cutting 

Manufacturing Processes 

© 2011 Su-Jin Kim GNU 


Cutting (Machining)


1. Cutting mechanics 

2. Tool wear 

3. Tool material 

4. Turning, Turning center 

5. Milling, Machining center 



© 2011 Su-Jin Kim GNU

Cutting mechanics 

• Chip formation Shear break off 

• Cutting force = Specific energy x Area 

• Chatter (vibration) 

• Cutting temperature 

• Tool wear 

• Tool life equation 




Mechanics of Chip Formation 

• Chips are produced by the shearing taking place along a 

shear plane. 




Cutting Force (Theory) 

• According to maximum‐shear‐stress criterion, yielding 

occurs when the max shear stress within an element is 

equal to or exceeds a critical value (shear yield stress). 

Stock 




Tool 

σ 1 

(Assume no friction) 

Fc 

σ 1 

τ 

Mohr’s circle 

σ 

τ 

Ф 

Shear angle 

Shear plane





w 

t 0 

• Shear Area = Width x Depth / sin (Shear Angle) 

t0 

As w 

sin 

t 0 /sin(φ) 

φ 

F s 

• Shear Force = Shear Stress * Shear Area 

wt0 

Fs A 

s 

sin 

Tool


• Resultant force 

= Shear force / cos (shear angle + friction angle –rake angle) 




R 

 

cos 

F 

s 

 

wt 

sin 

cos 

0


• Cutting force 

= Resultant force x cos (friction angle –rake angle) 

• Shear angle 

= pi/4 + rake angle/2 –friction angle/2 




F c 

R cos 

 

 

 

 

 

4 2 2

Cutting Force 

• Rake angle ↑ shear angle ↑, cutting force ↓ chip thickness ↓, cooler chip 

↓ 

• Rake angle ↑ tool section ↓ strength at cutting edge ↓, heat conductivity 

↓ 

• Relief angle ↑ friction ↓ tool life ↑, surface quality ↑ 

• Relief angle ↑ strength at cutting edge ↓ 

• Nose radius ↓ heat ↓, surface quality ↑ 

• Force ↑< yield stress of stock ↑, cut depth ↑, cut width ↑ 




Shear angle, φ 

Rake angle,α 

+ 

Nose radius 

Relief angle, 

r

Cutting Force (Specific cutting energy) 

• Cutting force = Specific cutting energy x Cutting area 

Power c 




Fc ut 

Ac 

ut 

Tool 

Stock A c F c 

F V 

wt0 

Specific cutting energy (

Chip morphology 

• Type of chips produced 

influences surface finish 

and machining operation. 

1. Continuous chips 

Steel: http://www.youtube.com/watch?v=4bOzJiYAZD4 

Stainless: http://www.youtube.com/watch?v=DzAjpHFy4fw 

2. Built‐up‐edge chips 

3. Serrated chips 

4. Discontinuous chips 

Cast Iron: http://www.youtube.com/watch?v=RoooeTEEMxY&feature=related 




Chip morphology 

Chip curl 

• Chip breaker shorter chip 




Groove Chip breaker

Chatter (Self‐excited vibration) 

• Chatter vibrating with high frequency noise is caused by 

interaction of chip‐removal process with flexibility of the 

tool. 

• It could be avoided by increasing dynamic stiffness and 

damping, by decreasing depth of cut and proper 

selection of spindle speed . 




Safe 

Chatter 

http://www.youtube.com/watch?v=uv3yUCl27wM

Temperature 

• Cutting power P=FV Heat Increase the 

temperature of chip, work piece, and tool 




Tool wear 

• Mechanical wear 

1. Abrasive wear ‐ hardness 

2. Adhesive wear ‐ junction 

3. Fatigue wear ‐ crack 

• Thermo Chemical wear 

1. Diffusion wear (확산) 

2. Solution wear (용해) 




Tool wear 

• The wear behaviour of cutting tools are flank 

wear(measure width of wear land), crater wear(at high 

speed, diffusion wear is the major reason, measure 

depth), nose wear, and chipping of the cutting edge. 




Tool wear 




Tool life (F.W. Taylor) 

• Tool‐wear relationship for cutting various steels is 




VT n 

C 

V = cutting speed 

T = time (min) 

C = constant. 

n = exponent depends on cutting conditions 

HSS 0.14-0.16, Uncoated carbides 0.21-0.25, TiC insert 0.30, 

Polydiamond 0.33, TiN insert 0.35, Ceramic coated insert 0.40

Tool life curve 

• Tool‐life is effected by depth and feed rate. 

VT 

• Tool wear is also depend on 

tool and workpiece material 




n 

d 

x 

f 

y 

 

C 

d = depth of cut 

f = feed rate (in mm/rev) in turning

Ex 

Increasing tool life by reducing the cutting speed 

Given that n=0.5 and VT n =C, if the V reduced 50%, calculate the 

increase of tool life. 

Solution 

VT 0.5 =C (1) 

0.5VT 2 0.5 =C (2) 

(2)/(1) 

0.5(T 2/ T) 0.5 =1 

T 2 =4T 

Increase tool life 4 times. 




Surface Finish and Surface Integrity 

Feed marks 

• In turning, peak‐to‐valley roughness is 




Stock 

R 

t 

 

2 

fr 

8R 

R 

Tool 

f r = feed per revolution 

R = nose radius 

f 

R t

Cutting Tool Materials 

• HSS 

• Carbide 

• Ceramic 

• Diamond 

• CBN 




Cutting‐Tool Materials 

• A cutting tool has the following characteristics: 

1. Hardness 

2. Toughness 

3. Wear resistance 

4. Chemical stability 




HSS 

HSS (High‐speed steels) 

• HSS cuts faster than carbon tool steel, hence the name 

high speed steel, but slower than carbide tools. 

• It is often used in power saw blades and drill bits. 

TiN‐Coated HSS 

• PVD (physical vapor deposition), TiN coating reduces 

tool wear. 

HSS Drill: http://www.youtube.com/watch?v=98DvSQNHLMU 




Carbides 

Carbides (초경) 

• Better wear resistance, stiffness, hot hardness 

• Tungsten carbide: WC + Co(for toughness) powder 

metallurgy (sintered), suitable for non‐ferrous, grey cast 

iron 

• Titanium carbide: TiC + Co : TiC is suitable for steel and 

cast iron 

Coated Carbide 

• Carbide + TiC, TiN, Al 2O 3 coated 

by CVD (chemical vapor deposition) 

• Chemically stable greatly reduce crater wear 




Cermets 

Ceramics 

Aluminum oxide(Al 2O 3), Silicon‐nitride(SiN), cold pressed and 

hot sintered 

Hot hardness ↑, toughness ↓ (chipping), thermal shock 

Cermets 

Ceramic(Al 2O 3) + metal binder(TiC) 

Hot hardness ↑, toughness ↓, thermal expansion ↑ 

http://www.youtube.com/watch?v=Om9gzgNPf80 

Insert: less thermal stress, eliminate grinding by user, less 

setting time 




Diamond, CBN 

Diamond (Poly crystal diamond) 

• Hardest material, Not good for steel 

http://www.youtube.com/watch?v=vAvfrrlMZg4 

CBN (polycrystalline cubic boron nitride) 

• 2nd hardest material, brittle, expensive 

http://www.youtube.com/watch?v=mKxX50OMBd4&p=9B6D9EAE75875D9D 




Tool materials 

Tool materials, feeds, and cutting speeds 

• Characteristics of cutting‐tool materials gives a range of 

cutting speeds and feeds for different applications. 




Workpiece materials 

Workpiece materials and cutting speeds 




Cutting Tool Makers 

• www.taegutec.co.kr 

• www.yg1.co.kr 




Cutting Fluids 

• Also called lubricants and coolants, cutting fluids. 

• Used extensively in machining operations to: 

1. Cool the cutting zone 

2. Reduce friction and wear 

3. Reduce forces and energy consumption 

4. Wash away chips 

5. Protect surfaces from any environmental attack 




Turning 

• A piece of material is rotated and a single point cutting 

tool is traversed along 2 axes of motion to produce the 

cylinder, tubular components and various rotational 

geometries. 




Lathe 

• Turning can be done manually, in a traditional form of 

lathe, which frequently requires continuous supervision 

by the operator. 




Turning center (CNC Lathe) 

• Turning can be done by using a computer numerical 

control, known as CNC. 




Turning process 

• Straight turning 

• Taper turning 

• Profiling (Couture turning) 

• External grooving 

http://www.youtube.com/watch?v=tDc0l9Gm8D4 




http://www.youtube.com/watch?v=5AB_etoHesI&p=9B6D9EAE75875D9D

Math for Turning 

• Cutting speed(mm/min) = 3.14 x Diameter x Spindle 




V = π D S 

• MRR (Material Removal Rate) = Volume / Time = 3.14 x 

Diameter x Depth x Feed per revolution x Spindle 

D 

df S 

MMR avg r 

• Cutting time = Distance / (Feed per revolution x Spindle) 

V 

S 

t 

 

l 

f S 

r 

S

TurnMill 

• Turning center has additional 

milling axis is called TurmMill 

(복합기) 




http://ma.gnu.ac.kr/vod/machining/TurnMill.AVI

Milling 

• Cutting tool is rotated and traversed along 3 axes of 

motion to produce from simple rectangular plane, slot, 

hole and complex contour. 




Milling 




Machining center (CNC Milling) 

C Type 




Horizontal M/C 

Bridge Type 

Vertical M/C 

http://www.youtube.com/user/GlacernMachineTools 

5AX M/C

Automatic Tool Changer (ATC) 




Changer Arm 

Tool 

Spindle

Automatic Pallet Changer (APC) 

Pallet #1 




Pallet #2

Work holding Vise, Clamp 

• Work is fixed by vise or clamp on the table with T‐slot 




http://www.youtube.com/user/GlacernMachineTools#p/u/5/J1VtofzVG24 

Flex clamp: http://ma.gnu.ac.kr/vod/Machining/Clamp.MP4

Tool holder, Tools 

Holder + Collet + Solid Endmill Insert Endmill 

http://www.youtube.com/watch?v=IPWGV_EGAHw&feature=related 




Tool holder, Tools 




Milling operations 

• Face cutter 

• Endmill : Flat, Ball, Rounded 

Face Cutter 

Basic: http://www.youtube.com/watch?v=j0vRYe9uvnI 

Face: http://www.youtube.com/watch?v=9OsNUi_o6C4 




Flat endmill (Slotting) 

Endmill: http://www.youtube.com/user/GlacernMachineTools#p/u/1/HfIaISnqHOk

Math for milling 

• Cutting speed(mm/min) = 3.14 x Diameter x Spindle 




V = π D S 

• Feed per tooth = Feed / (Spindle x Number of teeth) 

F / Sn 

 

• MMR = Depth x Width x Feed 

MRR = d w F 

f t 

f t 

F (mm/min) 

w 

d

Huge 3+2 axis Milling 

• Has additional rotation BC axis on 

head. 

• Used for automobile door panel and 

bumper mold. 

http://ma.gnu.ac.kr/vod/machining/Huge_machine_tools.AVI 




http://ma.gnu.ac.kr/vod/machining/Huge_5axis.AVI

5‐axis machining 

• Has 2 tinting A C or B C axis on table or head. 

Rotary table: http://ma.gnu.ac.kr/vod/Machining/Rotaty_table.MP4 




Impeller : http://ma.gnu.ac.kr/vod/Machining/5axis_machining_impeller.MP4

Drilling 

• Drills produces deep holes. 




Drill 

Drilling machine 

Insert drill 

Max drill 

Drill: http://www.youtube.com/watch?v=ul20R32HJ3E 

Drill: http://ma.gnu.ac.kr/vod/Machining/Drill.MP4

Tapping 

• Tap produces thread inside the hold. 

• Tap Feed Rate = RPM x Pitch 

Ex) M6 x 1 at 2000 RPM = 2000 mm/min 




Tapping Tapping holder and tool 

http://www.youtube.com/watch?v=vCHQLFZHHJc

Reaming, Boring 

• Reamer enlarges an hole to the diameter of the tool. 

• Boring produce precise circular internal profiles. 




Reaming 

Boring 

Drilling, Tapping, Boring: http://vimeo.com/8642433 

http://www.youtube.com/user/GlacernMachineTools#p/u/0/om6GQKfoS1g

Planer and Shaper 




Broaching 

• Linear broaching: the broach is run linearly against a 

surface of the workpiece to effect the cut. 

• Rotary broaching: the broach is rotated and pressed into 

the workpiece to cut an axis symmetric shape. 

Broaching gear 

http://www.youtube.com/watch?v=2K45B6tDqsg&p=9B6D9EAE75875D9D 




Rotary broaching: 

http://www.youtube.com/watch?v=gUEcagEmmZo&p=9B6D9EAE75875D9D

Sawing and saws 

• A cutting operation where the tool consists of a series 

of small teeth that removes material. 




Disk saw 

Belt saw

Gear Hobbing 

• A hob (cutter) is rotated one revolution to transfer each 

tooth profile onto a rotating gear blank. 

• Used very often for medium to high sizes of production 

runs. 




http://www.youtube.com/watch?v=DwFssm9trSc

Design for Machining 

• Geometric compatibility 

• Dimensional compatibility 

1. Availability of tools 

2. Drill dimensions, aspect ratio 

• Constraints 

1. Process physics 

2. Deep pocket 

3. Machining on inclined faces 

• Set up and fixturing 

1. Tolerancing is $$$ 

2. Minimize setups 




Economics of Machining 

Total cost per piece consists of four items: 

C 

m 

C 

C 




s 

l 

t 

p 

where 

C 

C 

C 

C 

C 

p 

m 

C 

cost per piece 

s 

l 

C 

t 

machining cost 

cost of setting up for machining 

cost of loading, unloading and machine handling 

tooling cost

Example 8.4 

Material‐removal rate and cutting force in turning 

A 15.24-cm-long, 1.27-cm-diameter 304 stainless-steel rod is being reduced in 

diameter to 1.2192 cm by turning on a lathe. The spindle rotates at N=4000 rpm 

and the tool is travelling at an axial speed of 20.32 cm/min. Calculate the cutting 

speed, material-removal rate, cutting time, power dissipated, and cutting force. 

Solution 

Maximum cutting speed is 

Cutting speed at machined diameter is 

Depth of cut and feed is 




V 

D N 

1. 

27 1. 

219 

20. 

32 

d 

0. 

0255 cm and f 

2 

400 

0 

1. 27400 

15. 

959 m/min 

V 

1. 2192400 

15. 

321m/min 

 

0. 

0508 

cm/rev

Example 8.4 

Material‐removal rate and cutting force in turning 

Solution 

Material-removal rate is 

MMR 

The torque and cutting force is 




3 

1. 24450. 

02550. 

0508400 

2. 

02586 cm / min 

15. 

24 

Actual time taken to cut is t 

0. 

75 min 

0. 0508400 

Amount of power dissipated is 

3 410 Power 2. 02586 

135 

W 

82597 

T 32. 

8643 kg - cm and Fc 

 

4002 60 

32. 86432 

1. 2445 

 

52. 

8153 

kg

References: Machine Tool Makers 

• www.doosaninfracore.co.kr 

• www.wia.co.kr 

• www.hwacheon.co.kr 

• www.mazak.jp (Japan) 

• www.haascnc.com (USA) 

• www.deckelmaho.com (EU)

Manufacturing Processes Cutting (Machining)

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