machining manufacturing processes © 2012 su-jin kim gnu manufacturing processes cutting (machining)...

MachiningMachiningManufacturing ProcessesManufacturing Processes

Manufacturing Processes Manufacturing Processes

CuttingCutting (Machining) (Machining)절삭가공절삭가공

Su-Jin Kim

School of Mechanical EngineeringGyeongsang National University

Cutting

1. Cutting mechanics2. Tool wear3. Tool material

4. Turning, Turning center5. Milling, Machining center

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).

(Assume no friction)Fcσ1

Mohr’s circle

Shear angle

Shear plane

Cutting Force (Shear force theory)

sin0wt

• Shear Force = Shear Stress * Shear Area

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

t0 /sin(φ)

sin0twAs

Cutting Force (Theory)• Resultant force

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

cossincos0wtF

Workpiece

Cutting Force (Theory)• Cutting force

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

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

cosRFc

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

Rake angle,α

Relief angle, r

Shear angle, φNose radius

Cutting Force Approximation ( 절삭력 )• Cutting force ≈ Specific cutting energy( 비절삭에너지 ) x

Cutting areaFc ≈ ut Ac

• Cutting power = force x velocityP = Fc V

Stock Ac

Material Specific cutting energy (GPa)

Tensile strength (MPa)

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

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 chips3. Serrated chips4. Discontinuous chips

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

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

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

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 .

Chatter

http://www.youtube.com/watch?v=uv3yUCl27wMSpindle (rmp)

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 wear1. Abrasive wear - hardness2. Adhesive wear - junction3. Fatigue wear - crack (toughness)

• Thermo Chemical wear1. 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

flank wear nose wear

broken edge

Material (ISO P K M)

• Steel cutting All and upper face wear and deformation

• Stainless cutting Built-up-edge & notch wear

• Cast iron cutting All face wear and deformation

Tool life (F.W. Taylor, 공구수명 )

• Tool-wear relationship for cutting various steels is

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

CVT n V : cutting speed / T : time (min) / C : constant.n : exponent depends on cutting conditionsHSS 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

Tool life T

CfdVT yxn d : depth of cut, f : feed rate

Carbide

Ceramic

Given that n=0.5 and VTn=C, if the V reduced 50%, calculate the increase of tool life.

SolutionVT0.5=C (1)0.5VT2

0.5=C (2)(2)/(1)0.5(T2/T)0.5=1T2=4TIncrease tool life 4 times.

ExIncreasing tool life by reducing the cutting speed

Surface Finish ( 표면조도 )

Feed marks• In turning, peak-to-valley roughness is

fr rt 8

rr <Rfr : feed rate (mm/rev)R : tool nose radius (mm)

StockR

Cutting Tool Materials ( 공구 재질 )• HSS ( 하이스 )• Carbide ( 초경 )• Cermet• CBN• Diamond

Cutting-Tool Materials

• A cutting tool has the following characteristics:1. Hardness ( 경도 ) at high temperature ~ Speed2. Toughness ( 인성 ) ~ Feed & depth3. Wear resistance ( 내마모성 )4. Chemical stability ( 화학적 안정성 )

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.

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, Al2O3 coated by CVD (chemical vapor deposition)• Chemically stable greatly reduce crater wear

CermetsCeramicsAluminum oxide(Al2O3), Silicon-nitride(SiN), cold pressed and hot

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

CermetsCeramic(Al2O3) + metal binder(TiC)Hot hardness ↑, toughness ↓, thermal expansion ↑

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

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

Diamond, CBN

Diamond (Poly crystal diamond)• Hardest material, Not good for steel

CBN (polycrystalline cubic boron nitride)• 2nd hardest material, brittle, expensive

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

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.

Coated HSS / HSS

Feed (Toughness)

Coated carbideCarbide

CermetCeramic

PCDCBN

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 zone2. Reduce friction and wear3. Reduce forces and energy consumption4. Wash away chips5. 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.

Belt sawDisk 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.

1st 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

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

Turning process ( 선삭공정 )

• Straight turning• Taper turning• Profiling (Couture turning)• External grooving

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

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

SdfDMMR ravg

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 rpmand the tool is travelling at an axial speed of 20.32 cm/min. Calculate the cuttingspeed, material-removal rate, cutting time, power dissipated, and cutting force.

SolutionMaximum cutting speed is

Cutting speed at machined diameter is

Depth of cut and feed is

Ex) Turning

m/min 959.1540027.10 NDV

m/min 321.154002192.1 V

cm/rev 0508.0400

32.20 and cm 0255.0

219.127.1

SolutionMaterial-removal rate is

Actual time taken to cut is

Amount of power dissipated is

The torque and cutting force is

Ex) Turning

min/cm 02586.24000508.00255.02445.1 3 MMR

min 75.04000508.0

24.15t

W13502586.260

kg 8153.522445.1

28643.32 and cm-kg 8643.32

82597 cFT

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)

Horizontal M/C

Bridge TypeC Type

Vertical M/C

5AX M/C

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

• 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

3+2 axis machining (5 면가공기 )

5-axis machining (5 축가공기 )

• 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

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

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

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

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 CutterBasic: 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)

• Face cutter

• Endmill : Flat, Ball, Rounded

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)

• MMR = Depth x Width x Feed MRR = d w F

SnFft /ft

F (mm/min)

Drilling

• Drills produces deep holes.

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

Max drill

Drilling machine

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

Tapping Tapping holder and tool

Tapping

• Tap produces thread inside the hold.• Tap Feed Rate = RPM x PitchEx) M6 x 1 at 2000 RPM = 2000 mm/min

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.

BoringReaming

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

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

• 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

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.

unloading & loading up, setting

machining

cost total

Economics of Machining

Total cost per piece consists of four items:

Cutting speed

Setting up

Machining Total

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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