Chapter 4. Surfaces, Tribology, Dimensions, Inspection

M2794.001800 M A T E R I A L A N D M A N U F A C T U R I N G P R O C E S S E S

Chapter 4. Surfaces, Tribology,

Dimensions, Inspection & Quality

Sung-Hoon Ahn

School of Mechanical and Aerospace Engineering

Seoul National University

© Prof. Ahn, Sung-Hoon

Introduction

Surface properties affect

Friction and wear

Lubrication

Painting, coating, welding, soldering, adhesive bonding, corrosion

resistance

Crack initiation

Thermal and electrical conductivity

Tribology

Friction

Wear

Lubrication

2


Surface structure

Oxide layer (hard, brittle, abrasive)

Iron: FeO, Fe3O4, Fe2O3

Aluminum: Al2O3

Copper: Cu2O, CuO

Stainless steel: CrO

Beilby layer: melting & surface flow → rapid quenching

Work-hardened layer: residual stress

3


Surface texture

Flaw ( )/ defect ( ), lay ( ), roughness ( ), waviness ( )

4


Surface roughness

Surface profilometers ( )

5


Ra and Rq

Arithmetic mean value arithmetic ave. (AA)

center-line ave. (CLA)

Root-mean-square ave. (RMS)

Rough surface: Lower precision, short fatigue life, higher electrical & thermal contact

resistance, lower corrosion resistance, better painting & coating, lower cost

dxyl

ynn

yyyyR

ln

i

idcba

a

01

11

21

0

2

1

22222

11

dxyl

ynn

yyyyR

ln

i

idcba

q

6


Atomic Force Microscope (AFM)

Force

Distance( d )

d

Tip

Sample

Force

Feedback Loop

Laser

Photodiode

Y

X

Z

Cantilever

Display

X-Y Scan Control

7


AFM Tip

piezoresistor

region PZT regionTip

High doping region

Before PZT process After PZT process

8


Adhesion theory of friction ( ) Intimate contact of asperities creates an adhesive bond

Friction coefficient ( )

Friction

hardness

A

A

N

F

r

r

577.03

2.03

3

2/) (

, )(

Y

Y

Y

Y

hardness

Ystressyieldsheark

kmfactorshearfriction i

9


Measuring Friction

Ring compression test

4.0 09.0

)%(1310015

1315

5)39(4

10)1530(4

2222

mand

decreaseIDinchange

IDvolume

10


Friction in Manufacturing11


Wear (1)

Progressive loss of material from

a surface

Adhesive wear ( )

p

LWkV

3

ftinkW

VpL

inlbmmkgp

lbW

k

inV

2132560)200)(10(

)700,170)(001.0)(3(3

/700,170/120

200

)2.4 tablefrom(10

001.0

3

22

3

3

Archard wear law

12


Wear (2)

Abrasive wear

Corrosive wear

Fatigue wear

13


Lubrication

4 regimes of lubrication Geometric defects

14


Surface Treatment

Shot peening, water-jet peening, laser peening

Case hardening(carburizing, carbonitriding, etc.)

Roller burnishing (surface rolling)

15

Shot peening Carburizing Roller burnishing


Surface Treatment 16

Cladding (clad bonding)

Mechanical plating

Thermal spraying

Thermal spraying

Cladding

Mechanical plating


Surface Treatment

Vapor deposition (CVD/PVD/ Ion implantation)

Electroplating/ electroless plating

Anodizing

17

Ion implantation Electroplating Anodizing


Cold spray (1)

Schematic diagram

• High deposition rate at low temperature

• Accelerated powder particles are sprayed onto substrate.

• Fabrication type : constructive process

• Typical substrate materials : metal

18


Cold spray (2)

Repair of damaged mold

1. Mold fabrication 3. Deposition of particles

2. Damaged mold 4. Machining mold surface

5. Repaired mold

19


Nano particle deposition system (NPDS)

TiO2 coating on Stainless steel

Mn-Zn ferrite coating on Al 6061 with niddles

0.17mm

0.1mm0.46mm1.03mm

2.5 μm 250 nm

Schematic diagram

• High deposition rate at room temperature

• Aerosol with particles is accelerated by a gas

flow and sprayed onto substrate.

• Fabrication type : constructive process

• Typical substrate materials : metal, ceramic

20


Measurement

Length: dial indicator, LVDT

Straightness : autocollimators

Flatness: interferometry

Roundness: total indicator reading (TIR), full indicator movement

Profile

Coordinate measuring machines (CMM) and layout machines

Gages

Microscopes

21


Precision & Accuracy

Accuracy( )

degree of conformity of a

measure to a standard or a true

value(closeness to the true value,

δm)

Precision( )

the degree of refinement with

which an operation is performed

or a measurement stated(size of

standard deviation, σ)

Probability

density

ValueTrue value

δm

σ

22


Precision & Accuracy – example

Accurate

Not precise

Accurate

Precise Precise

Not accurate

23


Dimensional Tolerance24


Quality Assurance

1

)()()()(

,

22

3

2

2

2

1

minmax

321

n

xxxxxxxx

xxRRange

n

xxxxx

n

n

RAxxLCL

RAxxUCL

x

x

2

2

3)(lmit controlLower

3)(lmit controlUpper

Normal (Gaussian) Distribution

Control Chart

Six sigma (3~4 ppm)

ISO 9000 (quality management &

quality assurance)

ISO 14000 (environmental

management)

25


Control Chart

2

3R

4

d

R

RDLCL

RDUCLR

26


Statistical Process Control (SPC)27


Process Capability Indices

Minimum acceptable value for Cp is 1

Desirable value : 1 ~ 2

x

p

LSLUSLC

6

3USL-LSL ①

USL-LSL ②

USL-LSL ①

USL-LSL ②

Process Capability Index, Cp

Process Capability Index, Cpk

0.13

)( , min

mean process :

min

min

ZC

ZorZZ

LSLZ

USLZ

pk

LSLUSL

x

x

xLSL

x

xUSL

28


Process Capability Indices - example

3

10

130100

6

10

130190

LSL

USL

Z

Z

LSL

130100

USL

190

σx=10

1.03

3

3

)3( , 6minmin

pkC

Z

29

Documents

Chapter 4. Surfaces, Tribology, Dimensions, Inspection