Question & Answer

Compute the unit energy for melting for the following metals: (a) copper and (b) titanium.

Compute the unit energy for melting for the following metals: (a) aluminum and (b) plain low

carbon steel.

A welding heat source is capable of transferring 150 Btu/min to the surface of a metal part. The

heated area is approximately circular, and the heat intensity decreases with increasing radius as

follows: 50% of the power is transferred within a circle of diameter = 0.1 inch and 75% is

transferred within a concentric circle of diameter = 0.25 in. What are the power densities in (a) the

0.1-inch diameter inner circle and (b) the 0.25-inch diameter ring that lies around the inner circle?

(c) Are these power densities sufficient for melting metal?

In a laser beam welding process, what is the quantity of heat per unit time (J/sec) that is transferred

to the material if the heat is concentrated in circle with a diameter of 0.2 mm? Assume the power

density provided in Table 29.1.

A heat source can transfer 3500 J/sec to a metal part surface. The heated area is circular, and the

heat intensity decreases as the radius increases, as follows: 70% of the heat is concentrated in a

circular area that is 3.75 mm in diameter. Is the resulting power density enough to melt metal?

There are 14 correct answers in the following multiple choice questions (some questions have multiple

answers that are correct). To attain a perfect score on the quiz, all correct answers must be given. Each

correct answer is worth 1 point. Each omitted answer or wrong answer reduces the score by 1 point, and

each additional answer beyond the correct number of answers reduces the score by 1 point. Percentage

on the quiz is based on the total number of correct answers

29.1 Welding can only be performed on metals that have the same melting point; otherwise, the metal

with the lower melting temperature always melts while the other metal remains solid: (a) true, (b)

false?

29.2 A fillet weld can be used to join which of the following joint types (three correct answers): (a) butt,

(b) corner, (c) edge, (d) lap, and (e) tee?

29.3 A fillet weld has a cross-sectional shape that is approximately which one of the following: (a)

rectangular, (b) round, (c) square, or (d) triangular?

29.4 Groove welds are most closely associated with which one of the following joint types: (a) butt, (b)

corner, (c) edge, (d) lap, or (e) tee?

29.5 A flange weld is most closely associated with which one of the following joint types: (a) butt, (b)

corner, (c) edge, (d) lap, or (e) tee?

29.6 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?

29.7 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?

29.8 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?

29.9 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?

29.10 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?

What is the heat-affected zone (HAZ) in a fusion weld?

Define and distinguish the two terms heat transfer factor and melting factor in welding.

What is the unit melting energy in welding, and what are the factors on which it depends?

Why is it desirable to use energy sources for welding that have high heat densities?

Why is a surfacing weld different from the other weld types?

Define and sketch a groove weld.

Define and sketch a fillet weld.

Name and sketch the five joint types.

What is the difference between machine welding and automatic welding?

Discuss the reasons why most welding operations are inherently dangerous.

What is an autogenous weld?

What is the fundamental difference between a fusion weld and a solid state weld?

Define the term fusion weld.

What is meant by the term faying surface?

What were the two discoveries of Sir Humphrey Davy that led to the development of modern

welding technology?

What are the advantages and disadvantages of welding compared to other types of assembly

operations?

A batch of 40 identical parts is to be chrome plated using racks. Each part has a surface are = 22.7

cm2. If it is desired to plate an average thickness = 0.010 mm on the surface of each part, how long

should the plating operation be allowed to run at a current = 80 amps?

From Table 29.1, C = 0.92 x 10^-4 in³/A-min, cathode efficiency E = 15%.

Plated volume V = EC∫Idt = EC∫(12 + 0.2t)dt = EC(12t + 0.1t2) over the range 0 to 20 min.

V = 0.15(0.92 x 10^-4)(12 x 20 + 0.1(20)²) = 0.00386 in3

Increasing current is applied to a workpart surface in an electroplating process according to the

relation I = 12.0 + 0.2t, where I = current, amps; and t = time, min. The plating metal is chromium,

and the part is submersed in the plating solution for a duration of 20 min. What volume of coating

will be applied in the process?