Industrial Engineering Chapter 4 The Hardness The Pencil Material Can Mea Impurities And Voids Sured Through

Chapter 4

Surfaces, Tribology, Dimensional

Characteristics, Inspection, and

Product Quality Assurance

Questions

4.1 Explain what is meant by surface integrity.

Why should we be interested in it?

tion 4.2 starting on p. 132, surface integrity has

4.2 Why are surface-roughness design requirements

in engineering so broad? Give appropriate ex-

(a) Precision required on mating surfaces,

(b) Tribological considerations, that is, the ef-

fect of surface roughness on friction, wear,

the resistance will be.

(f) Subsequent processing, such as painting

4.3 We have seen that a surface has various layers.

Describe the factors that influence the thickness

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4.4 What is the consequence of oxides of metals be-

ing generally much harder than the base metal?

result, is wear resistant [see Eq. (4.6) on p. 145],

and it can also protect the substrate from fur-

4.5 What factors would you consider in specifying

the lay of a surface?

4.6 Describe the effects of various surface defects

(see Section 4.3 starting on p. 134) on the per-

spect to the direction of tensile stresses or direc-

4.7 Explain why the same surface roughness values

do not necessarily represent the same type of

surface.

(a)

(e)

(f)

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role in cutoff selection. The cutoff should be

related to the spacing of asperities, which has

been found to be about an order of magnitude

0.05 0.25

0.2 0.25

0.8 0.8

3.2 2.5

12.5 2.5

lus path and the actual surface profile generally

are not the same?

sured smoother than they really are. This can

have significant effects on the estimating the fa-

4.11 Explain why surface temperature increases

when two bodies are rubbed against each other.

What is the significance of temperature rise due

to friction?

cance of this temperature rise is that surfaces

velop higher thermal stresses and possibly re-

essarily detrimental because chemical reactiv-

pressure lubricants to bond to a surface.

4.12 To what factors would you attribute the fact

ble 4.1?

4.13 In Section 4.4.1, we note that the values of the

coefficient of friction can be much higher than

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tensive microwelds during sliding, then the load

4.14 Describe the tribological differences between

ordinary machine elements (such as meshing

pieces in contact with tools and dies).

loads and stresses, relative speeds between slid-

ing members, workpiece temperatures, temper-

4.15 Give the reasons that an originally round spec–

imen in a ring-compression test may become

oval after deformation.

4.16 Can the temperature rise at a sliding interface

exceed the melting point of the metals? Ex-

sary for changing from a solid to a liquid phase.

4.17 List and briefly describe the types of wear en-

•Adhesive wear, where material transfer oc-

curs because one material has bonded to

cause material loss through spalling.

•Erosion, caused by the abrasive action of

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microwelds, hence the higher the adhesive

4.19 How can adhesive wear be reduced? How can

fatigue wear be reduced?

effects outlined in the answer to Problem 4.18

Problem 4.18 above;

(b) improving the quality of the contacting

materials, such as eliminating inclusions,

creases, abrasive wear is reduced. Explain why

this is so.

For abrasive wear to occur, the harder or

rougher surface must penetrate the softer sur-

4.21 Does the presence of a lubricant affect abrasive

be suitable for literature search on the part of

students.

of the wear coefficient for a pencil writing on

distance can be determined, we can then cal-

culate the dimensionless wear coefficient, k/H.

The hardness of the pencil material can be mea-

wear coefficient kin Eq. (4.6). What would

be the difficulties in applying the results from

this test to a manufacturing application, such

as predicting the life of tools and dies?

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rial a function of its hardness?

Higher hardness indicates greater resistance to

4.25 We have seen that wear can have detrimen-

tal effects on engineering components, tools,

dies, etc. Can you visualize situations in which

wear could be beneficial? Give some examples.

(Hint: Note that writing with a pencil is a wear

60/40 leaded brass 0.24 24,000

PTFE 0.18 2000

Stellite 0.60 310

4.27 You have undoubtedly replaced parts in various

appliances and automobiles because they were

worn. Describe the methodology you would fol-

low in determining the type(s) of wear these

components have undergone.

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4.28 Why is the study of lubrication regimes impor-

tant?

regime, ranging from full-fluid film to sliding of

dry surfaces, has its own set of variables that

The student may discuss this topic, based on

4.30 Differentiate between (1) coolants and lubri-

cants, (2) liquid and solid lubricants, (3) direct

and indirect emulsions, and (4) plain and com-

bricants is that they have different phases.

However, although solid lubricants are

ditives in the base oil to fulfill special crite-

ria such as lubricity and workpiece surface

4.31 Explain the role of conversion coatings. Based

on Fig. 4.13, what lubrication regime is most

suitable for application of conversion coatings?

4.32 Explain why surface treatment of manufactured

products may be necessary. Give several exam-

ceramic-coated cutting or forming tools.

•Jewelry and tableware are electroplated

4.33 Which surface treatments are functional, and

which are decorative? Give several examples.

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4.34 Give examples of several typical applications of

mechanical surface treatment.

•Crankshafts, rotors, cams, and other simi-

lar parts are shot peened in order to in-

4.35 Explain the difference between case hardening

and hard facing.

4.36 List several applications for coated sheet metal,

including galvanized steel.

4.37 Explain how roller-burnishing processes induce

residual stresses on the surface of workpieces.

4.38 List several products or components that could

not be made properly, or function effectively in

service, without implementation of the knowl-

4.2 through 4.5 include:

•Brake drums, rotors, and shoes could not

on bolts and nuts, and hard chrome coat-

indirect-reading linear measurements.

In direct reading, the measurements are ob-

4.40 Why have coordinate-measuring machines be-

come important instruments in modern manu-

facturing? Give some examples of applications.

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4.41 Give reasons why the control of dimensional tol-

form best when they are at their design spec-

4.42 Give examples where it may be preferable to

specify unilateral tolerances as opposed to bi-

lateral tolerances in design.

4.43 Explain why a measuring instrument may not

to measure a 0.0005 in. press-fit clearance be-

4.44 Comment on the differences, if any, between (1)

roundness and circularity, (2) roundness and ec-

of roundness being commonly used. Circu-

larity is defined as the condition of a sur-

face of revolution where all points of the

surface intersected by any plane perpen-

dicular to an axis or passing through a cen-

ter are equidistant from the center. Also,

we usually refer to a round shaft as being

round, whereas there are components and

parts in which only a portion of a surface

is circular. (See, for example, circular in-

terpolation in numerical control, described

in Fig. 14.11c on p. 882).

(c) Cylindricity is defined similarly to circu-

straight shaft with the same roundness

4.45 It has been stated that dimensional tolerances

for nonmetallic stock, such as plastics, are usu-

strength, are soft, have high thermal expansion,

4.46 Describe the basic features of nondestructive

trical energy are magnetic particle, ultrasonic,

4.47 Identify the nondestructive techniques that are

capable of detecting internal flaws and those

that only detect external flaws.

Internal flaws: ultrasonic, acoustic emission, ra-

diography, and thermal. External flaws: liq-

uid penetrants, magnetic particle, eddy current,

and holography. Some of these techniques can

be utilized for both types of defects.

4.48 Which of the nondestructive inspection tech-

niques are suitable for nonmetallic materials?

Why?

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portant aspect of manufacturing engineering?

4.50 Describe situations in which the use of destruc-

tive testing techniques is unavoidable.

duction of the product. This approach is partic-

ularly important for parts that are critical, such

as jet-engine turbine components and medical

4.51 Should products be designed and built for a cer-

tain expected life? Explain.

4.52 What are the consequences of setting lower and

curve in Fig. 4.23?

such factors.

in a heat-treating operation,

(d) a change in the properties of the incoming

4.54 In reading this chapter, you will have noted that

the specific term dimensional tolerance is often

used, rather than just the word tolerance. Do

you think this distinction is important? Ex-

As a general term, tolerances relate not only

4.55 Give an example of an assignable variation and

a chance variation.

4.9.1 starting on p. 176, with an example on

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4.56 Referring to the surface profile in Fig. 4.3, give

values. Then give another set of values for the

ure and enlarged it, one with a copy machine,

the other by scanning it into a computer and

e 2.0 2.5 1.90

g -5.0 -6.5 -4.93

i -4.0 -5.0 -3.79

l -1.0 -1.0 -0.76

Note that the scales are slightly off, due to the

fact that the grids used were different. To have

Source RaRq

Student 1 3.69 5.45

well; a second-order mapping of data points

4.57 Calculate the ratio of Ra/Rqfor (a) a sine wave,

p. 134.

(a) The equation of a sine wave with amplitude

π(cos π−cos 0) = −a

π(−1−1)

π

Zsin2u du =u

which can be obtained from any calculus book

or table of integrals. Therefore, from Eq. (4.2),

l

2π2πx

2l−1

4sin 4πx

ll

0

=a2

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0

From Eq. (4.2),

Ra

(c) For a square wave with amplitude a,

Ra=1

a dx =a

0=a

Rq

=a

a= 1.0

4.58 Refer to Fig. 4.7b and make measurements of

the external and internal diameters(in the hor-

izontal direction in the photograph) of the four

d2

o−d2

i

1 0.375 0.75 0.25

4 0.1757 1.04 0.100

The reduction in height is calculated from

1 0 0 —

3 58.4 24.8 0.10

4 60 53.1 0.20

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4.59 Using Fig. 4.8a, make a plot of the coefficient of

friction versus the change in internal diameter

and (3) 60%.

Typical data obtained from Fig. 4.8a on p. 142

are summarized in the table below. Note that

0.04 -3 -5 -12

0.055 0 0 0

0.577 15 38 —

4.61 How would you go about estimating forces re-

quired for roller burnishing? (Hint: Consider

The procedure would consist of first determin-

ing the contact area between the roller and the

surface being burnished. The force is then the

a 50-mm solid metal ball using a current of 1

4πr2, so that the volume of the plating is V=

4πr2h, where his the plating thickness. From

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lZl

0

4.65 Calculate the control limits for averages and

ranges for the following: number of samples =

D3= 0.078. Equations (4.11) and (4.12) give

LCRR=D3¯

R= (0.078)(7) = 0.546

¯

R=UCLR

D4

=4.85

1.924 = 2.521

Therefore, Eqs. (4.11) and (4.12) give the upper

LCL¯x=¯

¯x−A2¯

R= (40.5)−(0.419)(2.521) = 39.444

p. 180 give the upper and lower control limits

for the averages as

UCL¯x=¯

¯x+A2¯

R= (75)+(0.308)(10) = 78.080

0.69 0.73 0.70 0.68

0.65 0.68 0.65 0.61

0.69 0.73 0.70 0.68 0.7000 0.05

0.64 0.65 0.60 0.60 0.6225 0.05

0.68 0.72 0.70 0.66 0.6900 0.06

0.6733, and the average range is ¯

R= 0.07.

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4.69 Calculate the mean, median and standard de-

viation for all of the data in Problem 4.68.

The mean is given by Eq. (4.8) on p. 178 as

σ=r(0.65 −0.6733)2+. . . + (0.71 −0.6733)2

4.70 The average of averages of a number of sam-

ples of size 7 was determined to be 125. The

average range was 17.82, and the standard de-

viation was 5.85. The following measurements

were taken in a sample: 120, 132, 124, 130, 118,

132, 121, and 127. Is the process in control?

For the ranges, Eqs. (4.13) and (4.14) yield

UCLR=D4¯

R= (1.924)(17.82) = 34.28

4.71 Assume that you are asked to give a quiz to stu-

By the student. This is a challenging, open-

ended question that requires considerable focus

and understanding on the part of the students,

and has been found to be a very valuable home-

work problem.

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