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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?
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
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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?
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
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reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
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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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
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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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