Seam welding is very similar to spot welding. There is still an electrode but it is two opposing wheels rather than two pointed electrodes. Force and current is applied through the wheel just as in spot welding. The control timing and wheel speed determine the spacing of the spots. They can be made to overlap and be fluid tight or separated. If separated this is called a roll spot weld. Fluid tight applications could be dishwashers, washing machines, tin cans and metal drums.
Repeat or pulsing refers to repeating the weld and hold portion of a weld schedule. Normally there is a very short off period of one or two cycles with continued application of force between the two weld sequences. This gives you the ability to dissipate the heat energy a little further into the part away from the center of the weld nugget.
Aluminum has a tendency to form voids or cracks in the weld nugget as it solidifies. These voids are generally not desirable. In many cases this condition can be improved with good force follow up or application of a secondary forging force near the end of the weld cycle.
Squeeze is the first segment of the weld schedule. It’s function is to apply force on the work pieces to bring them together. This pressure under the face of the electrode in turn makes good electrical contact and controls and contains the resultant weld nugget during the weld and hold portion of the weld cycle. If current is applied prematurely before the proper force has been reached these functions will be compromised and expulsion and poor nuggets should be expected.
Part fit up is very important in determining the quality of resistance welds. All weld schedules call out a force value with the purpose of holding the part together, containing the weld nugget and performing a little forging as the weld cools. If the part does not fit up properly then part of this force is used to force or form the part into place and is not available to contain and forge the weld nugget.
ALIGNMENT, FIT UP & WORN CYLINDERS CAN CASUE PROBLEMS
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