Resistance Weldable Material
It is not possible to state with finality what materials may or may not be satisfactorily resistance welded by one or more of the several processes. The principal reason is that there is no accepted definition or understanding of what constitutes a satisfactory weld. A weld that may be satisfactory for one application may not be for another.
Most of the common metals may be readily spot welded. Principal exceptions are silver, copper, lead and zinc. Even these may be welded under certain conditions. For example, the main difficulty with copper and silver is that due to their high electrical and thermal conductivity, the material readily welds to the electrodes themselves. If electrode material such as tungsten or molybdenum is used, the resistance of the joint between the electrode and work is greater than between the two pieces being welded. The result is often such severe surface marking and indentation as to render the finished work unacceptable.
The various types of steel possess the unique quality of a wide plastic range. That is, the temperature ranges from the point at which it starts to soften to the point at which it becomes liquid. This entire range runs approximately 1000° F, over which a considerable portion of the weld may be consummated.
By comparison, the plastic range for the aluminum alloys is only 50° F to 100° F. This is the principal reason for the necessity of precision controls for aluminum and various other metals with a narrow plastic range.
Other metals, such as tin and lead fall into this category. In the case of aluminum and magnesium, a tremendous amount of research has been done to bring spot welding of these alloys up to their present standards of perfection. There is very little application for spot or other types of resistance welding on lead, zinc or tin; consequently, no satisfactory processes have been developed.
Usually, those metals that cannot be satisfactorily spot welded may be either soft soldered or brazed.
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