workpiece so slowly that, before any melting occurs, a large amount of heat is already conducted away into the bulk workpiece. Excessive heating can damage the workpiece, weakening and distorting it. Contrarily, the same material heated by a sharply focused electron or laser beam can melt or even vaporize to form a deep keyhole instantaneously. This allows welding to be completed before much heat is conducted away into the bulk workpiece to cause any damage [1].
Figure 1.1 The size of the heat source and its effect on welding.
Figure 1.2 Heating of and hence damage to workpiece vs. power density of heat source.
Therefore, the advantages of increasing the power density of the heat source include deeper weld penetration, higher welding speed, and better weld quality with less damage to the workpiece, as indicated in Figure 1.2. Figure 1.3 shows that the weld strength (of aluminum alloys) increases as the heat input per unit length of the weld per unit thickness of the workpiece decreases [2]. Figure 1.4a shows that the angular distortion of the workpiece is much smaller in EBW than in GTAW [2]. Unfortunately, as shown in Figure 1.4b, the costs of laser and EBW machines are very high [2]. This higher equipment cost is also shown in Figure 1.2.
Figure 1.3 Variation of weld strength with heat input per unit length of weld per unit thickness of workpiece.
Source: Mendez and Eagar [2]. © ASM.
Figure 1.4 Comparisons between welding processes: (a) angular distortion; (b) capital equipment cost.
Source: Mendez and Eagar [2]. © ASM.
1.1.1.2 Welding Processes and Materials
Table 1.1 summarizes the fusion welding processes recommended for carbon steels, low‐alloy steels, stainless steels, cast irons, nickel‐base alloys, and aluminum alloys [3]. For one example, GMAW can be used for all the materials of almost all thickness ranges while GTAW is mostly for thinner workpieces. For another example, arc welding processes that require the use of a flux, such as SMAW, SAW, FCAW, and ESW, is not used for aluminum alloys.
Table 1.1 Overview of welding processes. Source: Welding Handbook [3], vol 1, 7th edition, © American Welding Society.
| Joining processa | |||||||||||
| Material | Thicknessb | SMAW | SAW | GMAW | FCAW | GTAW | PAW | ESW | OFW | EBW | LBW |
| Carbon steels | S | x | x | x | x | x | x | x | |||
| I | x | x | x | x | x | x | x | x | |||
| M | x | x | x | x | x | x | x | ||||
| T | x | x | x | x | x | x | x | ||||
| Low‐alloy steels | S | x | x | x | x | x | x | x | |||
| I | x | x | x | x | x | x | x | ||||
| M | x | x | x | x | x | x | |||||
| T | x | x | x | x | x |
x
| |||||
