Assignment #6 (64 points total)
IE 337
Joining Processes
Materials & Manufacturing Processes
Multiple Choice (2 points each):
30.6 For metallurgical reasons, it is desirable to melt the weld metal with minimum
energy input. Which one of the following heat sources is most consistent with this
objective: (a) high power, (b) high power density, (c) low power, or (d) low power
density?
Answer. (b).
30.7 The amount of heat required to melt a given volume of metal depends strongly on
which of the following properties (three best answers): (a) coefficient of thermal
expansion, (b) heat of fusion, (c) melting temperature, (d) modulus of elasticity, (e)
specific heat, (f) thermal conductivity, and (g) thermal diffusivity?
Answer. (b), (c), and (e).
30.8 The heat transfer factor in welding is correctly defined by which one of the following
descriptions: (a) the proportion of the heat received at the work surface that is used for melting,
(b) the proportion of the total heat generated at the source that is received at the work surface, (c)
the proportion of the total heat generated at the source that is used for melting, or (d) the
proportion of the total heat generated at the source that is used for welding?
Answer. (b).
30.9 The melting factor in welding is correctly defined by which one of the following
descriptions: (a) the proportion of the heat received at the work surface that is used for melting,
(b) the proportion of the total heat generated at the source that is received at the work surface, (c)
the proportion of the total heat generated at the source that is used for melting, or (d) the
proportion of the total heat generated at the source that is used for welding?
Answer. (a).
30.10 Weld failures always occur in the fusion zone of the weld joint, since this is the part of the
joint that has been melted: (a) true, (b) false?
Answer. (b). Failures also occur in the heat-affected zone because metallurgical damage often
occurs in this region.
31.6 Which one of the following arc welding processes uses a nonconsumable electrode:
(a) FCAW, (b) GMAW, (c) GTAW, or (d) SMAW?
Answer. (c).
31.7 MIG welding is a term sometimes applied when referring to which one of the
following processes: (a) FCAW, (b) GMAW, (c) GTAW, or (d) SMAW?
Answer. (b).
31.8 "Stick" welding is a term sometimes applied when referring to which one of the
following processes: (a) FCAW, (b) GMAW, (c) GTAW, or (d) SMAW?
Answer. (d).
31.11 Resistance welding processes make use of the heat generated by electrical
resistance to achieve fusion of the two parts to be joined; no pressure is used in these
processes, and no filler metal is added: (a) true, (b) false?
Answer. (b). Pressure is applied in RW processes and is key to the success of these
processes.
31.12 Metals that are easiest to weld in resistance welding are ones that have low
resistivities since low resistivity assists in the flow of electrical current: (a) true, or (b)
false?
Answer. (b). Metals with low resistivities, such as aluminum and copper, are difficult to
weld in RW. Higher resistance is required in the conversion of electrical power to heat
energy; hence, metals with high resistivity are generally preferable.
31.13 Oxyacetylene welding is the most widely used oxyfuel welding process because
acetylene mixed with an equal volume of air burns hotter than any other commercially
available fuel: (a) true, (b) false?
Answer. (a).
31.16 The term weldability takes into account not only the ease with which a welding
operation can be performed, but also the quality of the resulting weld: (a) true, (b) false?
Answer. (a).
31.17 Copper is a relatively easy metal to weld because its thermal conductivity is high:
(a) true, (b) false?
Answer. (b). True that copper has a high thermal conductivity, one of the highest of any
metal, but this is one of the main reasons why copper is generally difficult to weld. The
heat readily flows into the body of the parts that are to be welded, rather than remaining
at the localized region where the joint is to be made.
32.5 Which of the following is an advantage of brazing (three best answers): (a)
annealing of the base parts is a by-product of the process, (b) dissimilar metals can be
joined, (c) less heat and energy required than fusion welding, (d) metallurgical
improvements in the base metals, (e) multiple joints can be brazed simultaneously, (f)
parts can be readily disassembled, and (g) stronger joint than welding?
Answer. (b), (c), and (e).
Review Questions (3 points each):
30.3 What is meant by the term faying surface?
Answer. The faying surfaces are the contacting surfaces in a welded joint.
30.5 What is the fundamental difference between a fusion weld and a solid state weld?
Answer. In a fusion weld, the metal is melted. In a solid state weld, the metal is not
melted.
30.6 What is an autogenous weld?
Answer. An autogenous weld is a fusion weld made without the addition of filler metal.
31.1 Name the three principal groups of processes included in fusion welding.
Answer. The principal groups of processes included in fusion welding are (1) arc
welding, (2) resistance welding and (3) oxyfuel welding.
31.6 What are the two basic methods of arc shielding?
Answer. (1) Shielding gas, such as argon and helium; and (2) flux, which covers the
welding operation and protects the molten pool from the atmosphere.
32.1 How do brazing and soldering differ from the fusion welding processes?
Answer. In brazing and soldering, no melting of the base metal(s) occurs.
32.3 What is the technical difference between brazing and soldering?
Answer. In brazing the filler metal melts at a temperature above 450°C (840°F). In
soldering the filler metal melts at a temperature of 450°C or below.
32.4 Under what circumstances would brazing or soldering be preferred over welding
(five possible answers)?
Answer. Brazing or soldering might be preferred over welding if (1) the base metals have
poor weldability, (2) the components cannot tolerate the higher heat and temperatures of
welding, (3) production rates need to be faster and less expensive than welding, (4) joint
areas are inaccessible for welding but brazing or soldering is possible, and (5) the high
strength of a welded joint is not a requirement.
Problems:
(4 points) 30.6 Compute the unit energy for melting for the following metals using SI
units: (a) aluminum and (b) plain low carbon steel.
Solution: (a) From Table 30.2, Tm for aluminum = 930 K (1680 R)
Eq. (30.2) for SI units: Um = 3.33(10-6)Tm2 Um = 3.33 x 10-6 (930)2 = 2.88 J/mm3
(b) From Table 30.2, Tm for plain low carbon steel = 1760 K (3160 R)
Eq. (30.2) for SI units: Um = 3.33(10-6)Tm2 Um = 3.33 x 10-6 (1760)2 = 10.32 J/mm3
(8 points) 30.16 The welding power generated in a particular arc welding operation =
3000 W. This is transferred to the work surface with a heat transfer factor = 0.9. The
metal to be welded is copper whose melting point is given in Table 30.2. Assume that the
melting factor = 0.25. A continuous fillet weld is to be made with a cross-sectional area =
15.0 mm2. Determine the travel speed at which the welding operation can be
accomplished.
Use formula 30.6 in your book.
Solution: From Table 30.2, Tm = 1350°K for copper.
Um = 3.33 x 10-6(1350)2 = 6.07 J/mm3
v = f1 f2 RH/UmAw = 0.9(0.25)(3000)/(6.07 x 15) = 7.4 mm/s.