Machining (기계가공) g ( )

Chapter 8. Material-Removal Processes: Cutting

Processes: Cutting

Sung-Hoon Ahn

Machining (기계가공) g ( )

ƒ Machining is the broad term used to describe removal of material from a workpiece

from a workpiece.

ƒ

Cutting (절삭가공)

ƒ

Abrasive processes (입자가공)

ƒ

Advanced machining processes (특수기계가공)

High speed machining

Chip formation (칩형성) ( )

ƒ Orthogonal cutting (직교절삭)

ƒ Oblique cutting (경사절삭)Oblique cutting (경사절삭)

ƒ Positive Rake angle (경사각)

Chi f th k i

(경사각)

ƒ Chip away from the workpiece

ƒ Negative Rake angle

ƒ Sturdy

(여유각)

(전단면) (전단각)

Orthogonal cutting model

Shear-angle relationships – Merchant model

φ

φ

( )

i

t

OD

=

t

= ^C where = <1

t

r t

α φ α

α φ φ

sin 1

tan cos

) cos(

sin

r r

= −

−

t

_C

α α

α α

sin cos

cos sin

T C

N

T C

R

F F

F

F F

F

−

=

+

=

α α

sin

cos _T

C

N

F F

F

Strain hardening

ƒ Machined material (chip) has higher hardness than uncut material due to high strain hardening (shear uncut material due to high strain hardening (shear strain, ~20)

Vi k i d i

γ

ƒ Vickers indentation test :

Chip morphology (칩형상) (1) gy ( ) ( )

Chip morphology (칩형상) (2)

ƒ Continuous chips (연속형 칩)

ƒ High cutting speeds / high rake angles

gy ( ) ( )

ƒ Serrated chips (톱니형 칩)

ƒ Nonhomogeneous / segmented chips High cutting speeds / high rake angles

(secondary shear zone)

ƒ Good for tool life & surface finish (may need chip breaker)

Nonhomogeneous / segmented chips

ƒ Zones of low and high shear strain

ƒ Ti : sharp decrease of strength and thermal conductivity with increased need chip breaker)

ƒ Ductile materials with low coefficient of friction

thermal conductivity with increased temperature

ƒ Built-up Edge chips (BUE, 구성인선)

ƒ High friction coefficient – workpiece weld on the tool edge

ƒ Discontinuous chips (불연속 칩)

ƒ Brittle materials (ductile materials with hi h f i ti ffi i t) C t i weld on the tool edge

ƒ Periodical separation of material bad surface

It b d d b i i th

high friction coefficient) : Cast iron, bronze

ƒ Chatter, vibration

ƒ It can be reduced by increasing the

cutting speed and the rake angle,

Chip morphology (칩형상) (3) gy ( ) ( )

ƒ Depending on :

cutting speed temperature cutting speed, temperature, tool angle, friction, vibration

Oblique cutting (경사절삭) g ( )

ƒ Inclination angle (기움각), i

Turning tool

Vfw removal

of Rate

Where

Vfw removal

of

Rate =

(mm) cut

of depth :

(mm/rev) feed

:

(m/min) speed

cutting :

w f V

(mm) cut

of depth :

w

Temperature

Tool wear (공구마멸) ( )

ƒ Flank wear

ƒ Crater wear

ƒ Crater wear

ƒ Chipping

Flank wear

ƒ F. W. Taylor’s tool life equation

T n

C V

C VT ⁿ

log log

log = −

=

70m/min

0.25, Carbide)

(Tungsten

50m/min

0.15, (HSS)

=

=

=

=

V n

V n

log C

Tool condition monitoring

Surface finish

Machinability (절삭성) y ( )

ƒ Surface finish & integrity

ƒ Tool life

ƒ Tool life

ƒ

Machinability rating: cutting speed per 60min, e.g. 100 100ft/min (0.5m/s)

ƒ Force and power requirements

ƒ Chip control

ƒ Free-machining steel (쾌삭강)

St l ith l d bi th lf l i

ƒ

Steel with : lead, bismuth, sulfur, calcium

ƒ Easy to machine : aluminum, brass, magnesium

ƒ Difficult to machine : wrought-copper, titanium, tungsten Difficult to machine : wrought copper, titanium, tungsten

Cutting-tool materials

ƒ Carbon steels

ƒ High Speed Steels (HSS 고속도강)High Speed Steels (HSS, 고속도강)

ƒ (M and T series)

ƒ Cast cobalt alloys C bid (초경합금)

ƒ Carbides (초경합금)

ƒ WC (tungsten carbide)

ƒ TiC (titanium carbide)

ƒ Inserts

ƒ Easy to replace tools

Coated tool (피복공구) ( )

ƒ TiN, TiC, TiCN

ƒ AlAl

_{2 2}

OO

_{3 3}

(알루미나)(알루미나)

ƒ Diamond

ƒ Ion implantation M l i h

ƒ Multiphase

Cutting Processes

Lathe-round shape

Lathe components

Drill

Drilling operations

Milling

ƒ Depth of Cut (DOC)

ƒ Width of Cut (WOC)

DOC

DOC

Width of Cut (WOC)

ƒ Slab milling (평밀링)

C i l Milli ( ^DOC

WOC

ƒ Conventional Milling (up WOC

milling, 상향절삭)

ƒ Recommended, clean surface before machine

ƒ Climb Milling (down milling, 하 향절삭)

향절삭)

ƒ Efficient cut (larger chip)

ƒ Less chatter

ƒ Production work

ƒ Production work

Material removal by milling

ƒ Cutting speed (m/min)

ƒ

V = πDN

ƒ

V = πDN

(D : diameter of cutter(m), N : rotational speed of the cutter(rpm))

ƒ Material Removal Rate (MRR)

ƒ

MRR = WOC * DOC * f

ƒ

f = feed rate (mm/min) = n * N * t

Cutting Tool - cross section f feed rate (mm/min) n N t

ƒ Example

ƒ

V = 50 m/min, t = 0.1 mm/tooth, number of tooth (n)= 2,

ƒ

D = 4 mm, DOC = 0.2, WOC = 3, Cutter RPM (N) = 50000/(πx4) = 3979

ƒ

f = 2 *3979 * 0.1 = 796 mm/min, MRR = 3* 0.2 * 796 = 4776 mmf 2 3979 0.1 796 mm/min, MRR 3 0.2 796 4776 mm /min

³

/min

Burr Formation

FEM Simulation

ƒ Demo: EMSIM

ƒ http://mtamri me uiuc edu/testbeds/emsim/html/index2 shtml

ƒ http://mtamri.me.uiuc.edu/testbeds/emsim/html/index2.shtml

Cost Estimation

Turning conditions

Drilling conditions

Milling conditions

Broaching(브로칭) & Sawing(톱작업) g( ) g( )

Micro Machining System

Micro endmills

Spindle

Ti f 127 d ill

Main computer

Tip of 127μm endmill

ƒ Positional resolution :

1 ㎛

Controller

Microscope X-Y stage

Vice

Positional resolution :

1 ㎛

ƒ Tool diameter :

50 ㎛~1000 ㎛

ƒ High speed :g p

46,000 RPM ,

ƒ Tool material : HSS &

TiN coating

Prototyping Size & Time

Typical Typical Feature Size

Rapid

Prototyping

Injection Molding 1m

10

100mm

1mm 100 10mm

1

μ

m

MEMS Micro Machining

10

μ

m 100

μ

m

1

Typical

0 10 100 1000 (Days)

1

μ

m

yp

Prototyping

DFM - Micro Milling g

ƒ 10mm endmill

ƒ 10mm endmill

ƒ 10μm stage error

ƒ 0.1% for slot cutting

A tip is not exact edge in micro scale

average TiAlN coating

ƒ 100μm endmill

ƒ 10μm stage error

100,000 Tool Cost (₩)

ƒ 10% for slot cutting

10,000

ƒ Cost structure of micro machining is different from machining is different from that of macro machining.

Spindle run-out

Run-out effect on the final geometry is critical in micro machining Total run out = TIR (Total Indicator Reading) + Error Terms

Total run-out = TIR (Total Indicator Reading) + Error Terms (vibration, thermal deformation, etc)

10

5 6 7 8 9

t (㎛)

100㎛

200㎛

1 2 3 4 5

Run-ou

< Concept of run-out >

< Result of Total Indicator Reading (TIR) >

0

0 5 10 15 20 25

Tool length (mm)

Micro walls

Barrier ribs

Rib width: 60㎛

^×300

Height: 500 ㎛ Tool: φ200 ㎛ Spindle: 24 000rpm Spindle: 24,000rpm DOC: 25㎛

Feed rate: 100㎛/s Time: 3hr 28min

×100×10000

G i 5 (i l di f i )

×300

Geometric error: ~ 5 ㎛ (including error of microscope)

×1200×600 ×600×600

Micro machined mold

0.993mm 1.221mm

0.753mm 0.993mm

1.005mm

1.221mm

From Concept to Part

„

Part for UAV/MAV

„

Part for UAV/MAV

„

ABS plastic

„

l = 2.9mm,

„

t= 300mm

CAD design Micro machining

„

t= 300mm,

„

Pivot D=250 mm

Specification CAD design Micro machining

Specification

More Meso/Micro Parts

Micro rotor c o oto

Micro molding (ABS)

300mm

Micro pyramid Freeform surface

3 Micro pyramid

3mm

Micro Tools

ƒ Drill

PCBs for semiconductor

Shape of Micro drill

PCB f ll h

ƒ End mill

PCBs for cell phone

CNC Lathe

ƒ CNC lathe can achieve multi-functional machining using attached milling turret, sub-spindle, etc.

Cutting tool Turret

Spindle Spindle

Workpiece

Chuck Workpiece

Milling tool

Turret Cutting

Cutting + Milling Cutting + Milling

Dynamometer (공구동력계) y ( )

Measured Signal

Amplifier

The whole system configuration

Amplifier

Cable