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Chapter 12

Joining and Fastening Processes

Questions

12.1 Explain the reasons that so many different

mechanical, physical, and metallurgical prop-

erties and characteristics. Also, there are

tive processes. Furthermore, the workpiece may

not be suitable for in-plant welding, and the

welding process may have to be brought to the

12.2 List the advantages and disadvantages of me-

chanical fastening as compared with adhesive

(a) often costlier;

12.3 What are the similarities and differences be-

tween consumable and nonconsumable elec-

trodes?

12.4 What determines whether a certain welding

process can be used for workpieces in horizon-

tal, vertical, or upside-down positions, or for all

types of positions? Explain, giving appropriate

welding operations (see Table 12.2 on p. 734)

cannot take place under any conditions ex-

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12.6 Discuss the need for and role of fixtures in hold-

ing workpieces in the welding operations de-

12.7 Describe the factors that influence the size of

the two weld beads in Fig. 12.13.

12.8 Why is the quality of welds produced by sub-

merged arc welding very good?

there are no sparks, spatter, or fumes as in

12.9 Explain the factors involved in electrode selec-

12.11 What are the similarities and differences be-

tween consumable and nonconsumable elec-

trode arc welding processes?

12.12 In Table 12.2, there is a column on the distor-

tion of welded components, ranging from lowest

to highest. Explain why the degree of distortion

where the weld zones are large and distortion

Fig. 12.16 because of the same reasons grains

meaning a temperature gradient exists in that

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lar group of materials. Consequently, it can be

12.15 Explain what is meant by solid state welding.

Figs. 12.19 through 12.21.

they can consider the crack locations, develop

an ability to identify them through inspection,

12.17 What advantages does friction welding have

over the other joining methods described in this

chapter?

with proper process control, the weld zone can

be very small and thin, so that thermal distor-

12.18 Why is diffusion bonding, when combined with

superplastic forming of sheet metals, an attrac-

tive fabrication process? Does it have any lim-

itations?

figurations? Explain.

pressure (normal stress) between the sheets to

be joined be sufficiently high and the interfaces

come not uniform and unreliable. The student

is encouraged to search the literature and at-

Fig. 12.40.

observed are actually due to stress waves in

the interface, and help improve joint strength

12.21 If electrical components are to be attached to

both sides of a circuit board, what soldering

process(es) would you use? Explain.

circuit board (see Section 13.13) has both

surface-mount and in-line circuits on the same

board and it is desired to solder all the joints

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12.22 Discuss the factors that influence the strength

of (a) a diffusion bonded component and (b) a

cold welded component.

12.23 Describe the difficulties you might encounter in

By the student. Explosives are very dangerous;

after all, they are generally used for destructive

purposes. There are safety concerns such as

•The outer layers, which are made of the

more expensive alloy, are thin for cost re-

duction.

12.25 What advantages do resistance welding pro-

cesses have over others described in this chap-

ter?

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12.26 What does the strength of a weld nugget in re-

sistance spot welding depend on?

Fig. 12.33b). This question can be answered

from different viewpoints. Thus, for exam-

ple, one may consider this question as a stress-

analysis problem, whereby the joint strength

12.27 Explain the significance of the magnitude of the

pressure applied through the electrodes during

resistance welding operations.

12.28 Which materials can be friction stir welded, and

which cannot? Explain your answer.

12.29 List the joining methods that would be suitable

for a joint that will encounter high stresses and

p. 733. Disassembly can be a difficult feature

to assess when selecting joining methods. If the

part has to be disassembled often, bolted con-

nections are likely to be the best solution, or

12.30 Inspect Fig. 12.31, and explain why the par-

ticular fusion-zone shapes are developed as a

function of pressure and speed. Comment on

roll spot welding process shown in Fig. 12.35c?

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12.33 Could the projection welded parts shown in

Fig. 12.36 be made by any of the processes de-

scribed in other parts of this text? Explain.

By the student. The projection-welded parts

shown could possibly be made through resis-

tance spot welding (although it would require

ical fastening and adhesive bonding also could

12.34 Describe the factors that influence flattening of

the interface after resistance projection welding

takes place.

(c) Important factors are the nature of the

12.35 What factors influence the shape of the upset

joint in flash welding, as shown in Fig. 12.37b?

The important factors are the amount of heat

generated (if too little heat, the material will

the rate, the greater the force required for up-

setting, due to strain-rate sensitivity of the ma-

terial at elevated temperatures).

12.36 Explain how you would fabricate the structures

shown in Fig. 12.41b with methods other than

diffusion bonding and superplastic forming.

12.37 Make a survey of metal containers used for

observations.

By the student. This is an interesting project

12.38 Which process uses a solder paste? What are

the advantages to this process?

12.39 Explain why some joints may have to be pre-

heated prior to welding.

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12.40 What are the similarities and differences be-

tween casting of metals (Chapter 5) and fusion

welding?

in that solidification begins with the formation

12.41 Explain the role of the excessive restraint (stiff-

ness) of various components to be welded on

weld defects.

Refer to Section 12.6.1. The effect of stiffness

on weld defects is primarily through the stresses

developed during heating and cooling of the

weld joint. Note, for example, that not allowing

for contraction (such as due to a very stiff sys-

12.42 Discuss the weldability of several metals, and

explain why some metals are easier to weld than

others.

12.43 Must the filler metal be of the same composi-

tion as that of the base metal to be welded?

Explain.

It is not necessary for the filler metal, rod, or

wire to be the same as the base metal to be

welded. Filler metals are generally chosen for

the favorable alloying properties that they im-

ably close temperatures. To visualize why this

is the case, consider a copper filler used with a

material with a much higher melting tempera-

ture, such as steel. When the copper melts, the

12.44 Describe the factors that contribute to the dif-

ference in properties across a welded joint.

steel’s carbon content increases? Why?

By the student. Review Section 12.6.2. As the

carbon content increases, weldability decreases

because of martensite formation, which is hard

and brittle (see p. 238).

12.46 Are there common factors among the weldabil-

ity, solderability, castability, formability, and

machinability of metals? Explain, with appro-

challenging, assignment and appropriate for a

student paper. As to be expected, the rela-

tionships are complex, as can also be seen by

12.47 Assume that you are asked to inspect a weld

for a critical application. Describe the proce-

dure you would follow. If you find a flaw during

your inspection, how would you go about deter-

mining whether or not this flaw is important for

the particular application?

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brazing and soldering arbitrarily by tempera-

ture of application? Comment.

12.49 LoctiteR

from vibrating loose; it basically glues the bolt

to the nut once the bolt is inserted in the nut.

12.6 on p. 782), meaning that it cures in the

absence of oxygen, hence it does not solidify in

12.50 List the joining methods that would be suitable

brazed.

(e) Adhesive bonding can also be suitable, as

12.51 Why is surface preparation important in adhe-

sive bonding?

strength depends greatly on its ability to prop-

erly bond to a surface (see also Section 4.5). If,

methods been developed? Give several specific

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12.53 Explain why hole preparation may be impor-

tant in mechanical joining.

By the student. See Section 12.15.1. Note,

for example, that if a hole has large burrs

12.54 What precautions should be taken in mechani-

cal joining of dissimilar metals?

one must be careful about their possible chemi-

12.55 What difficulties are involved in joining plas-

tics? What about in joining ceramics? Why?

notch sensitivity of these materials are impor-

of the joints, the type of materials used, their

geometric features, and the locations and direc-

tions of the forces applied.

12.57 How different is adhesive bonding from other

joining methods? What limitations does it

have?

the necessity for clean surfaces, tight clearances,

12.58 Soldering is generally applied to thinner com-

ponents. Why?

joining thin components is that it takes place at

Fig. 3.30.) Note, however, that tougher adhe-

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12.60 Inspect various household products, and de-

scribe how they are joined and assembled. Ex-

plain why those particular processes were used.

formed to desired shapes. The reason pots have

a number of layers different materials is to com-

12.61 Name several products that have been assem-

bled by (a) seaming, (b) stitching, and (c) sol-

cardboard and wood boxes, insulation

12.62 Suggest methods of attaching a round bar made

of thermosetting plastic perpendicularly to a

flat metal plate.

12.63 Describe the tooling and equipment that are

operation shown in Fig. 12.53, starting with flat

sheet. (See also Fig. 7.23.)

12.64 What joining methods would be suitable to

assemble a thermoplastic cover over a metal

frame? Assume that the cover has to be re-

is due to the elastic recovery of the lid after it is

stretched over the edge of the container. Note,

12.65 Repeat Question 12.64, but for a cover made of

(a) a thermosetting plastic, (b) metal, and (c)

i. A method similar to Answer 12.64

above, since thermosetting plastics

ics would be a significant concern as

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12.66 Do you think the strength of an adhesively

bonded structure is as high as that obtained

by diffusion bonding? Explain.

By the student. Because they rely on bond

strength, the joint strength in adhesively

fused into each other, making the joint very

12.67 Comment on workpiece size limitations, if any,

for each of the processes described in this chap-

ter.

12.68 Describe part shapes that cannot be joined by

the processes described in this chapter. Gives

specific examples.

cesses and possibilities available. The student

By the student. See also Section 12.14.4 where

several examples are given.

12.70 Give several applications for fasteners in vari-

ous household products, and explain why other

joining methods have not been used instead.

and 14.10. Note that fasteners are commonly

12.71 Comment on workpiece shape limitations, if

any, for each of the processes described in this

chapter.

welding requires parts be mounted into chucks

or similar fixtures in order to be able to rotate

one of the comments to be joined. Spot weld-

lowed to avoid cracks in welded joints, such as

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