The advent of high intensity low momentum surface heating devices is having a natural impact on the field of materials processing, particularly fusion welding. The laser and electron beam offer potential capability for precise control of energy and location which cannot be approached by older sources such as arcs and flames, and the fact that under certain operating conditions they transmit little or no thrust to the material being worked is an important advantage. However, the extreme intensity of these sources, expressed in dimensions of power per unit area, presents problems as well as advantages when addressed to the objective of local melting as in fusion welding.
With more conventional welding heat sources, there was seldom, if ever, any question of too high an intensity. Indeed, the problem has generally been quite the reverse, in that there is a tendency for metals having relatively high thermal conductivity to conduct the heat away from the weld region almost as fast as it is supplied. In this sense, the term "melting efficiency" has been used to express the fraction of the total heat which is actually used for melting, and with a typical open arc, this melting efficiency will generally fall below 50%. Melting efficiency is directly related to the intensity of the heat source, and as the intensity increases, the melting efficiency also increases.
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| Number of Pages : | 40 |
| Published : | 1971 |
