Tribology

Manufacturing Processes for Engineering Materials, 5th ed. Kalpakjian • Schmid© 2008, Pearson EducationISBN No. 0-13-227271-7

Surfaces


FIGURE 4.1 Schematic illustration of the cross-section of the surface structure of metals. The thickness of the individual layers depends on processing conditions and the environment. Source: After E. Rabinowicz and B. Bhushan.

Contaminant

Adsorbed gas

Oxide layer

Work-hardened layer

Metal substrate

Beilby (amorphous) layer

1–100 nm1 nm

1–100 nm10–100 nm

1–100 mm


Terminology for Surface Finish

FIGURE 4.2 (a) Standard terminology and symbols used to describe surface finish. The quantities are given in µin. (b) Common surface-lay symbols.

Maximum waviness height

Maximum Ra

Minimum Ra

Lay

12563

0.005

0.010

0.002-2 Maximum waviness width

Roughness-width cutoff

Maximum roughness width

X

Laysymbol Interpretation Examples

P

Lay parallel to the line representing the surfaceto which the symbol is applied

Lay perpendicular to the line representing thesurface to which the symbol is applied

Lay angular in both directions to line representingthe surface to which symbol is applied

Pitted, protuberant, porous, or particulatenondirectional lay

X

P

(a)

(b)

Surface profile Error of form Waviness Roughness

+ +=

Flaw

Roughnessheight, Rt

Wavinessheight

Waviness width

Roughness spacing

Roughness-width cutoff

Lay direction


Surface Roughness

FIGURE 4.3 Coordinates used for measurement of surface roughness, used in Eqs. (4.1) and (4.2).

y

a b c d e f g h i j k l

Digitized data

Surface profile

A

Center (datum) line

x

B Ra Roughness

Rq Roughness

Ra =ya+ yb+ yc+ · · ·+ yn

n=1n

n

∑i=1yi =

1l

Z l

0|y| dx

Rq =

!y2a+ y2b+ y2c + · · ·+ y2n

n=

"1n

n

∑i=1y2i =

#Z l

0y2dx

$1/2


Stylus Profilometry

FIGURE 4.4 (a) Measuring surface roughness with a stylus. The rider supports the stylus and guards against damage. (b) Path of the stylus in measurements of surface roughness (broken line) compared with the actual roughness profile. Note that the profile of the stylus' path is smoother than the actual surface profile. Typical surface profiles produced by (c) lapping, (d) finish grinding, (e) rough grinding, and (f) turning processes. Note the difference between the vertical and horizontal scales.

(a)

Rider

Stylus

Head

Workpiece

(b)

Stylus

Stylus path

Actual surface

5 µm (200 µin.)

(f) Turning

3.8 µm (150 µin.)

(e) Rough grinding

0.5 µm (20 µin.)

0.4 mm (0.016 in.)

(c) Lapping

0.6 µm (25 µin.)

(d) Finish grinding


Micro-Scale Adhesion

FIGURE 4.5 (a) Schematic illustration of the interface of two contacting surfaces, showing the real areas of contact. (b) Sketch illustrating the proportion of the apparent area to the real area of contact. The ratio of the areas can be as high as four to five orders of magnitude.

N

Microweld

Plastic

Elastic

F

Projectedcontactpatches


Friction in Manufacturing

FIGURE 4.6 Schematic illustration of the relation between friction force F and normal force N. Note that as the real area of contact approaches the apparent area, the friction force reaches a maximum and stabilizes. At low normal forces, the friction force is proportional to normal force; most machine components operate in this region. The friction force is not linearly related to normal force in metalworking operations, because of the high contact pressures involved.

Ar<<A A

r<A A

r~A

F

N

Frictio

n f

orc

e, F

Normal force, N

Forging, extrusion

Drawing, rolling

Metal cuttingDeep drawing

Stretch forming

Bending

Coulomb Friction

Tresca Friction

µ=FN

=τArσAr

=τσ

m=τik


Coefficient of Friction in Metalworking

Coe!cient of Friction (µ)Process Cold HotRolling 0.05-0.1 0.2-0.7Forging 0.05-0.1 0.1-0.2Drawing 0.03-0.1 —Sheet-metal forming 0.05-0.1 0.1-0.2Machining 0.5-2 —

TABLE 4.1 Coefficient of friction in metalworking processes.


Effect of Lubrication

FIGURE 4.7 (a) The effects of lubrication on barreling in the ring compression test. (a) With good lubrication, both the inner and outer diameters increase as the specimen is compressed; and with poor or no lubrication, friction is high, and the inner diameter decreases. The direction of barreling depends on the relative motion of the cylindrical surfaces with respect to the flat dies. (b) Test results: (1) original specimen, and (2-4) the specimen under increasing friction. Source: A.T. Male and M.G. Cockcroft.

(b)

1 2 3 4

Good lubrication Poor lubrication

(a)


Ring Compression Test

FIGURE 4.8 Charts to determine friction in ring compression tests: (a) coefficient of friction, µ; (b) friction factor, m. Friction is determined from these charts from the percent reduction in height and by measuring the percent change in the internal diameter of the specimen after compression.

Reduction in height (%)

70

60

50

40

30

20

10

0

210

220

Re

du

ctio

n in

in

tern

al d

iam

ete

r (%

)

0 10 20 30 40 50 60 70

0.7

0.5

0.3

0.2

0.15

0.10

0.05

m = 1.0

Reduction in height (%)

Original dimensionsof specimen:OD = 3/4 in.= 19 mmID = 3/8 in.= 9.5 mm

Height = 1/4 in.= 0.64 mm

0.40

0.30

0.20

0.15

0.12

0.10

0.08

0.09

0.07

0.06

0.05

0.04

0.03

0~0.02

0.055

240

250

230

220

210

0

10

Re

du

ctio

n in

in

tern

al d

iam

ete

r (%

)

20

30

40

50

60

70

80

100 20 30 40 50 60 70

µ =

0.5

77

(a) (b)


Profile Evolution Due to Wear

FIGURE 4.9 Changes in originally (a) wire-brushed and (b) ground-surface profiles after wear. Source: E. Wild and K.J. Mack.

Scale:

25 µm

250 µm

(a)

Unworn

Worn

(b)

Unworn

Worn


Adhesive Wear Model

FIGURE 4.10 Schematic illustration of (a) asperities contacting, (b) adhesion between two asperities, and (c) the formation of a wear particle.

(a) (b) (c)

Plastic zone(microweld)

Hard

Soft Metal transfer(possible wearfragment)

Archard Wear Law:

V = kLW3p

Unlubricated k Lubricated kMild steel on mild steel 10!2 to 10!3 52100 steel on 52100 steel 10!7 to 10!10

6040 brass on hardened tool steel 10!3 Aluminum bronze 10!8

Hardened tool steel on 10!4 on hardened steel 10!9

hardened tool steel Hardened steel 10!9

Polytetrafluoroethylene (PTFE) 10!5 on hardened steel 10!9

on tool steelTungsten carbide on mild steel 10!6

TABLE 4.2 Approximate order of magnitude for the wear coefficient, k, in air.


Abrasive and Other Wear

FIGURE 4.11 Schematic illustration of abrasive wear in sliding. Longitudinal scratches on a surface usually indicate abrasive wear.

Chip

Hard particle

FIGURE 4.12 Types of wear observed in a single die used for hot forging. Source: After T.A. Dean.

CL

2 5 1 5 3 4 2 1

5 1 5 3 4 1

Top die

EjectorBottom die

Erosion

Pitting (lubricated dies only)

Thermal fatigue

Mechanical fatigue

Plastic deformation

1

2

3

4

5


Regimes of Lubrication

FIGURE 4.13 Regimes of lubrication generally occurring in metalworking operations. Source: After W.R.D. Wilson.

Boundary film

(a) Thick film (b) Thin film

(d) Boundary(c) Mixed

Tooling

Lubricant

Workpiece


Roller Burnishing

FIGURE 4.14 Examples of roller burnishing of (a) the fillet of a stepped shaft, (b) an internal conical surface, and (c) a flat surface.

Roller

Workpiece

(a)

Roller

Burnishedsurface

(b)

Roller

(c)


Thermal Wire Spraying

FIGURE 4.15 Schematic illustration of thermal wire spraying.

Wire or rod

Oxygen

Gas nozzle Air cap

Combustion chamber

Workpiece

Moltenmetal spray

Deposited coating

High-velocity gas

Fuel gas


Chemical Vapor Deposition

FIGURE 4.16 Schematic illustration of the chemical vapor deposition process.

Carrier gases

TiCl4

Stainless steel retort

Tools to be coated

Graphite shelves

Exhaust scrubber

Exhaust

Electric furnace


Electroplating

FIGURE 4.17 (a) Schematic illustration of the electroplating process. (b) Examples of electroplated parts. Source: Courtesy of BFG Electroplating.

(a) (b)

+ -

Sacrificial(copper) anode

Cu++

Cu++

Cu++

Cu++Cu++

SO4--

SO4--

SO4--

H+

H+H+

H+

H+

SO4--

SO4--

SO4--

Part to be plated(cathode)

Agitator

Heating coils


Coordinate Measuring Machine

FIGURE 4.18 (a) A coordinate measuring machine with part being measured; (b) a touch signal probe measuring the geometry of a gear; (c) examples of laser probes. Source: Courtesy Mitutoyo America Corp.

Machine stand

z-axis spindle

Probe adapter

Measuring table

(b)

(c)

Probe

Computercontroller


Dimensional Tolerancing

FIGURE 4.19 (a) Basic size, deviation, and tolerance on a shaft, according to the ISO system. (b)-(d) Various methods of assigning tolerances on a shaft. Source: L.E. Doyle.

(a)

(b) (c) (d)

Ba

sic

siz

e

Min

imu

md

iam

ete

r

Min

imu

md

iam

ete

r

Ma

xim

um

dia

me

ter

Ma

xim

um

dia

me

ter

Ba

sic

siz

e

Zero line or lineof zero deviation

To

lera

nce

To

lera

nce

Lo

we

r d

evia

tio

n

Lo

we

r d

evia

tio

n

Up

pe

r d

evia

tio

n

Up

pe

r d

evia

tio

n

Shaft

Hole

Bilateraltolerance

mm

in.

40.00 + 0.05- 0.05

1.575 + 0.002- 0.002

Unilateraltolerance

mm

in.

40.05 + 0.00- 0.10

1.577 + 0.000- 0.004

Limitdimensions

mm

in.

40.0539.95

1.5771.573


Tolerances by Process

FIGURE 4.20 Tolerances and surface roughness obtained in various manufacturing processes. These tolerances apply to a 25-mm (1-in.) workpiece dimension. Source: After J.A. Schey.

0.5 1 2 4 8 16 32

Surface roughness, Ra (µin.)

63 125 250 500 1000

0.005

0.01

0.05

0.1

0.5

1.0

2.0

0.025 0.05 0.1 0.2 0.4 0.8 1.6 3.2 6.3 12.5 25 50 µm

2000

N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 ISO No.

0.100

0.010

0.001

0.0001

Tole

rance r

ange (

in.)

mm

Broach

, reamFinish m

ill

ECM-EDM

Finish grind, fi

nish turn, b

ore

Rough, grin

d, turn

Shape, pla

ne, rough m

ill

Drill, p

unch

Plaster

ShellSan

d ca

st

Polish, lap, hone

Precision blankCold draw

Cold extrude, r

oll

Inve

stment c

astHot roll,

extru

de, forg

e

Zn dieAl-d

ie cast

Powder met

Permanent m

old


Frequency Distribution

FIGURE 4.21 (a) A plot of the number of shafts measured and their respective diameters. This type of curve is called a frequency distribution. (b) A normal distribution curve indicating areas within each range of standard deviation. Note: The greater the range, the higher the percentage of parts that fall within it. (c) Frequency distribution curve, showing lower and upper specification limits.

(b)(a)

(c)

99.73%

95.46

68.26

-4! +4!-3 -2 -1 +1 +2 +30F

req

ue

ncy o

f o

ccu

rre

nce

13.00 13.05

2

0

10

8

6

4

Diameter of shafts (mm)

12.95

Fre

qu

en

cy o

f o

ccu

rre

nce

(nu

mb

er

of

sh

aft

s)

13.00 13.05

2

0

10

8

6

4

Diameter of shafts (mm)

12.95

Fre

qu

en

cy o

f o

ccu

rre

nce

Lo

we

rsp

ecific

atio

n

Up

pe

rsp

ecific

atio

n


Control Charts

0.12

0.08

0.06

0.04

0.02

0 LCLR

UCLR 0.10

Range, R

(m

m)

R (average range)

Time

(a)

13.04

13.02

13.01

13.03

12.99

12.98

12.97

12.96

0

13.00

Avera

ge d

iam

ete

r, x

(m

m)

Average of 5 samples

Average of next 5 samples

Average of next 5 samples

Time

LCLx

x (average of averages)

(b)

UCLx

_ _

FIGURE 4.22 Control charts used in statistical quality control. The process shown is in good statistical control, because all points fall within the lower and upper control limits. In this illustration, the sample size is five, and the number of samples is 15.


Constants for Control Charts

Sample Size A2 D4 D3 d2

2 1.880 3.267 0 1.1283 1.023 2.575 0 1.6934 0.729 2.282 0 2.0595 0.577 2.115 0 2.3266 0.483 2.004 0 2.5347 0.419 1.924 0.078 2.7048 0.373 1.864 0.136 2.8479 0.337 1.816 0.184 2.97010 0.308 1.777 0.223 3.07812 0.266 1.716 0.284 3.25815 0.223 1.652 0.348 3.47220 0.180 1.586 0.414 3.735

TABLE 4.3 Constants for Control Charts.


Control Chart Trends

Time

(c)

Time

(b)

Time

Tool changed

(a)

x__

UCLx

_

LCLx

_

UCLx

_

LCLx

_

UCLx

_

LCLx

_

Ave

rag

e d

iam

ete

r, x

(m

m)

_A

ve

rag

e d

iam

ete

r, x

(m

m)

Ave

rag

e d

iam

ete

r, x

(m

m)

__

FIGURE 4.23 Control charts. (a) Process begins to become out of control, because of factors such as tool wear. The tool is changed, and the process is then in good statistical control. (b) Process parameters are not set properly; thus, all parts are around the upper control limit. (c) Process becomes out of control, because of factors such as a sudden change in the properties of the incoming material.


Micrometers

Display examplesDigital gages

Floppydisk drive

Bar-code reader

CRT

Printer

(c)

(a) (b)

FIGURE 4.24 Schematic illustration showing integration of digital gages with a miniprocessor for real-time data acquisition and SPC/SQC capabilities. Note the examples on the CRT displays, such as frequency distribution and control charts. Source: Mitutoyo Corp.

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