Welding Cycle: The welding cycle for spot welding machine, projection welding machine, and seam welding machine consist basically of 4 elements as, squeeze time, weld time, hold time, and off time. These timings are preset by supplier depending upon the type of metal, the thickness of that metal and requirements of welding status and cannot be changed by the operator. Each of these four times phases has its own role to play in achieving the sound weld of required size. Welding Variable: The fundamental variable in resistance welding like spot welding includes time of current flow, electrode pressure. To achieve the quality welds in most metals, these variables are required to be kept within very close limit.
The spot welding machine is one of the commonest forms of resistance welding machine. We at Cruxweld manufactures best of quality in the spot welding machine. We here detailed the spot welding process.
Welding Process in Spot: The spot welding process is automatic as all the resistance welding by its nature. Here all the variables are preset and maintained those parameters consistently. Once a welding operation is initiated there is no way where you can control the welding in any manner which is in progress after initiation, thus weld cycle is completed as per the preset variables of time and current.
Weld Time: This is the time interval which the welding current actually flow to melt the metal at the interface.
Hold Time: It is the time or which the electrodes are held in that position after the current is switched off, to assure the application of pressure so as to consolidate the molten metal into a bead which is then cooled by dissipation of the heat to the surrounding work material. If the force and hold time is more it may result in the expulsion of molten metal from in between the sheets.
Off Time: The electrode are kept off the work during this time and cycle is repeated to the next location during this off time.
Welding Current: The size o the weld nugget does not depend upon the heat being generated faster than it is dissipated by conduction. The welding current is thus the most critical variables in resistance welding. Both AC and DC current used or the spot, seam, and projection welding machines. The most application use single-phase AC of the main frequency of 50 Hertz. However, DC is used for applications that need heavy current and load for which can be balanced on 3 phase power line With DC current the machines, the rate of current fall and rise can be programmed as per the requirements. The current rise period or upslope and current decay or downslope can be programmed with an electronic control system. The control of upslope helps to avoid overheating and expulsion of molten metal at the beginning of the weld time as the resistance at the interface is highest at that time. The Downslope is helpful in controlling the nugget solidification to avoid cracks in weldments particularly in metals that are prone to quench hardening and hot tearing
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