Understanding resistance welding processes
Resistance welding, a form of plastic welding, represents a group of welding processes, which are used to create a joint on the metal pieces, usually called a job in the workshops. The process is aided with electric current and the pressure-surfaces are joined by the heat produced due to resistance of the metal pieces to the electric current passing, and application of the mechanical pressure, thereafter.
From another view, it is understood as a process for welding two job pieces with the help of electric current and the mechanical pressure. Welding electrodes conduct electric current to the metal, and with the help of resistance of the metal against mechanical pressure applied, these metal pieces get welded together. However, small pools of molten metal appear around the weld, which is mainly due to the high amount of current that is passed through the pieces of metal.
Due to the simplicity and the versatility of this type of welding, resistance welding is used for welding all engineering metals except a few in automobile industries, aircraft industries, piping, and tubing production.
Process of Resistance Welding
Two copper electrodes are used in this process and the metal piece is placed between these electrodes. The process of resistance welding involves both melting and cooling of metal, i.e., the first step is to take the metal to molten state with the help of electric current through a limited area, and then making it to cool by applying pressure until it attains the strength to hold the metal pieces together.
The time for which the electric current is passed is very important for successful operation of resistance welding. However, the amount of electric current and the pressure to be applied must be within the limits sufficient to create a weld and should not exceed the limits, as it will directly lead to the outflow of molten metal from the weld zone. The pressure could be applied manually, by air pressure, or through any other means.
Types of Resistance Welding Processes
Though resistance welding is efficient and lesser polluting, it still has a limited use. This is mainly due to the cost of equipments that are used in this type of welding, which is sufficiently higher. Below are some of the commonly used types of resistance welding processes:
" Resistance Spot Welding
" Resistance Seam Welding
" Butt welding (upset and flash)
" Projection Welding
" Percussion welding
Benefits of Resistance Welding
Though the resistance welding has limited use in industrial use, it still has got some advantages:
" It is a high speed welding process
" Automation of the process is easy
" Very good results for high rate production
Limitations of Resistance Welding
The main disadvantages and drawbacks of this process are:
" It involves higher initial equipment costs, which makes it rather costly for smaller jobs.
" The welded joint produced by resistance welding possesses lower tensile and fatigue strengths, which is clearly a major drawback on the application front of the welded pieces.
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