Manufacturing Processes for Engineering Materials (5th Edition in SI ...

Machining 

Manufacturing Processes 

© 2012 Su-Jin Kim GNU 


Cutting (Machining) 

절삭가공 

Su-Jin Kim 

School of Mechanical Engineering 

Gyeongsang National University

Cutting 

1. Cutting mechanics 

2. Tool wear 

3. Tool material 

4. Turning, Turning center 

5. Milling, Machining center 



© 2012 Su-Jin Kim GNU

Cutting mechanics (절삭역학) 

• Chip formation Shear break off 

• Cutting force = Specific energy x Area 

• Chatter (vibration) 

• Cutting temperature 

• Tool wear 

• Tool life equation 




Chip Formation (칩생성) 

• Chips are produced by the shearing taking place along a 

shear plane. 




Cutting Force (전단이론) 

• 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

Cutting Force (Shear force theory) 




w 

t 0 

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

t0 

As w 

sin 

Tool 

t0 /sin(φ) 

φ 

F s 

• Shear Force = Shear Stress * Shear Area 

wt0 

Fs A 

s 

sin

Cutting Force (Theory) 

• Resultant force 




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

R 

 

cos 

F 

s 

 

wt 

 

sin cos 

 

 

0 

β 

Chip 

ф 

β-α 

Fs 

R 

α 

Tool 

Workpiece

Cutting Force (Theory) 

• Cutting force 




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

F c 

• Shear angle 

Rcos 

 

 

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

 

 

4 2 2 

Chip 

ф 

α 

R 

Tool 

Fc 

β-α 

Workpiece

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 ↑ 

Rake angle,α 

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

+ 




Shear angle, φ 

Nose radius 

Relief angle, 

r

Cutting Force Approximation (절삭력) 

• Cutting force ≈ Specific cutting energy(비절삭에너지) x 

Cutting area 

F c ≈ u t A c 

• Cutting power = force x velocity 




P = F c V 

Stock A c 

Tool 

F c 

Material Specific cutting 

energy (GPa) 

Aluminum alloys 0.4-1.1 480 

Copper alloys 1.4-3.3 500 

Cast irons 1.6-5.5 200 

Steels 2.7-9.3 840 

Tensile 

strength (MPa)

Ex ) Cutting Force 

Turning steel, depth of cut d = 0.1 mm, feedrate f = 0.01 

mm/rev, Specific cutting energy of steel u = 2.7~9.3 GPa. 

Cutting force? Cutting speed v = 10 m/s. Cutting power? 

F = u A = u d f 

= 2.7~9.3 (10^9 N/m^2) x 0.001 x 10^-6 m^2 = 2.7~9.3 N 

P = F v = 2.7 ~ 9.3 N x 10 m/s = 27 ~ 93 W 




Chip morphology (칩생성) 

• Type of chips produced 

influences surface finish 

and machining operation. 

1. Continuous chips 

2. Built-up-edge chips 

3. Serrated chips 

4. Discontinuous chips 




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

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

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

Chip breaker 

• 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 . 




Depth of cut (mm) 

Chatter 

Safe 

Spindle (rmp) 

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

Temperature (절삭열) 

• Cutting power P=FV Heat Increase the 

temperature of chip, work piece, and tool 

- Temperature increase = specific heat x mass : dT = c m 

- Specific heat (kJ/kgK): iron 0.45, aluminium 0.91, copper 

0.39 

• As temperature increases, it will affect the properties of 

the cutting tool, dimensional accuracy. 

- Thermal extension: dL = a dT L 

- Thermal extension coefficient of iron 10 x 10^-6 




Ex) Temperature of chip 

Material removal rate? m/t = ρ A v = (kg/s) 

If we assume 100% of cutting power used to heat chip, 

Temperature of chip? P = Q/t = c dT m/t 

If workpiece temperature increased 10 ℃, thermal 

expansion of workpiece? 




Tool wear (공구마모) 

• Mechanical wear 

1. Abrasive wear - hardness 

2. Adhesive wear - junction 

3. Fatigue wear - crack (toughness) 

• 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. 




crater wear 

broken edge 

flank wear nose wear

Tool life (F.W. Taylor, 공구수명) 

• Tool-wear relationship for cutting various steels is 

• Tool-life is also effected by depth and feed rate. 




VT C 

n 

VT 

n 

d 

x 

f 

Cutting speed V 

C 

y 

Log 

C 

V : cutting speed / T : time (min) / C : constant. 

n : exponent depends on cutting conditions 

HSS 0.14-0.16, Carbides 0.21-0.25, TiC insert 0.30, 

PCD 0.33, TiN insert 0.35, Ceramic coated insert 0.40 

d : depth of cut, f : feed rate 

-n 

Tool life T 

Log

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 (표면조도) 

Feed marks 

• In turning, peak-to-valley roughness is 




Stock 

r 

t 

 

2 

fr 

8r 

r 

Tool 

f r : feed rate (mm/rev) 

r : tool nose radius (mm) 

f r 

r t

Cutting Tool Materials (공구 재질) 

• 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 (하이스) 

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 (초경) 

Carbides 

• 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. 




Speed (Hardness) 

PCD 

CBN 

Cera 

mic 

Cermet 

Coated carbide 

Carbide 

Coated HSS / HSS 

Feed (Toughness)

Workpiece materials (소재 재질) 

• Workpiece materials and cutting speeds when Carbide 

tool or coated carbide tools is used for turning 




Material Cutting speed (m/min) 

Aluminum alloys 200-1000 

Copper alloys 50-700 

Cast iron, gray 60-900 

Steels 50-500 

Titanium alloys 10-100

Cutting Tool Makers (공구 제작사) 

• www.taegutec.co.kr 

• www.yg1.co.kr 




Cutting Fluids (절삭유) 

• 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 




Sawing and saws (톱) 

• A cutting operation where the tool consists of a series 

of small teeth that removes material. 




Disk saw 

Belt saw

Turning (선삭) 

• 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 (선반) 

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

lathe, which frequently requires continuous supervision 

by the operator. 




1 st Korean Lathe 




CNC Lathe, Turning center 

• Turning can be done by using a computer numerical 

control, known as CNC. 




Turning center 

• Turning center has additional 

milling axis is called TurmMill 

(복합기) 




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

Turning process (선삭공정) 

• 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

Ex) 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 

0 

1. 27400 

15. 

959 m/min 

V 

1. 2192400 

15. 

321m/min 

 

1. 

27 1. 

219 

20. 

32 

d 

0. 

0255 cm and f 

2 

400 

0. 

0508 cm/rev

Ex) Turning 

Solution 

Material-removal rate is 

The torque and cutting force is 




MMR 

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

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

3+2 axis machining (5면가공기) 

• 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 (5축가공기) 

• 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 


Automatic Tool Changer (ATC) 




Changer Arm 

Tool 

Spindle

Automatic Pallet Changer (APC) 




Pallet #1 

Pallet #2

Work holding Vise, Clamp (치구) 

• 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 



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


Flat endmill (Slotting)

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 

f t 

MRR = d w F 

 

f t 

F (mm/min) 

w 

d

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 




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

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 


Design for milling 

• Minimize machining, use casting and forging. 

• Minimize the length to diameter ratio of the tools. 

• Design features to be machined from one side. 




Design for milling 

• The inside edges must have the radius of the end mill. 

• For outside corners, chamfers are preferable over fillet. 

• For flatness, bosses should be used. 




Ⓒ http://www.efunda.com/processes/machining/mill_design.cfm

Economics of Machining 

Total cost per piece consists of four items: 

C 

 




t 

p 

p 

m 

s 

C 

where 

C 

C 

C 

C 

total cost 

machining 

setting up, loading & unloading 

 

m 

tool 

C 

s 

C 

t 

Cost 

Setting up 

Total 

Cutting speed

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)

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