25.1 What are the advantages and disadvantages of welding compared to other types of assembly operations?
Answer. Advantages: (1) it provides a permanent joint, (2) joint strength is typically as high as the strength of base metals, (3) it is most economical in terms of material usage, and (4) it is versatile in terms of where it can be accomplished. Disadvantages: (1) it is usually performed manually, so labor cost is high and the skilled labor to perform it is sometimes scarce, (2) welding is inherently dangerous, (3) a welded joint is difficult to disassemble, and (4) quality defects are sometimes difficult to detect.
25.2 What were the two discoveries of Sir Humphrey Davy that led to the development of modern welding technology?
Answer. The two discoveries of Sir Humphrey Davy were (1) the electric arc and (2) acetylene gas.
25.3 What is meant by the term faying surface?
Answer. The faying surfaces are the contacting surfaces in a welded joint.
25.4 Define the term fusion weld.
Answer. A fusion weld is a weld in which the metal surfaces have been melted in order to cause coalescence.
25.5 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.
25.6 What is an autogenous weld?
Answer. An autogenous weld is a fusion weld made without the addition of filler metal.
25.7 Discuss the reasons why most welding operations are inherently dangerous.
Answer. Most welding operations are carried out at high temperatures that can cause serious burns on skin and flesh. In gas welding, the fuels are a fire hazard. In arc welding and resistance welding, the high electrical energy can cause shocks that are fatal to the worker. In arc welding, the electric arc emits intense ultraviolet radiation that can cause blinding. Other hazards include sparks, smoke, fumes, and weld spatter.
25.8 What is the difference between machine welding and automatic welding?
Answer. An automatic welding operation uses a weld cycle controller that regulates the arc movement and workpiece positioning; whereas in machine welding, a human worker must continuously control the arc and the relative movement of the welding head and the work part.
25.9 Name and sketch the five joint types.
Answer. Five joint types are (1) butt, (2) corner, (3) lap, (4) tee, (5) edge. For sketches see Figure 25.3 in the text.
25.10 Define and sketch a fillet weld.
Answer. A fillet weld is a weld joint of approximately triangular cross section used to fill in the edges of corner, lap, and tee joints. See Figure 25.4 in text for sketch.
25.11 Define and sketch a groove weld.
Answer. A groove weld is a weld joint used to fill in the space between the adjoining edges of butt and other weld types except lap. See Figure 25.5 in text for sketch.
25.12 Why is a surfacing weld different from the other weld types?
Answer. Because it does not join two distinct parts, but instead adds only filler metal to a surface.
25.13 Why is it desirable to use energy sources for welding that have high heat densities?
Answer. Because the heat is concentrated in a small region for greatest efficiency and minimum metallurgical damage.
25.14 What is the unit melting energy in welding, and what are the factors on which it depends?
Answer. The unit melting energy is the amount of heat energy required to melt one cubic millimeter or one cubic inch of metal. The factors on which it depends are (1) specific heat, (2) melting point, and (3) heat of fusion of the metal.
25.15 Define and distinguish the two terms heat transfer factor and melting factor in welding.
Answer. Heat transfer factor is the ratio of the actual heat received at the work surface divided by the total heat generated by the source. Melting factor is the ratio of heat required for melting divided by the heat received at the work surface.
25.16 What is the heat-affected zone (HAZ) in a fusion weld?
Answer. The HAZ is a region of base metal surrounding the fusion zone in which melting has not occurred, but temperatures from welding were high enough to cause solid state microstructural changes.