Controls & Transformers
Questions and Answers
During welding operations some high alloy materials become brittle in the area near the nugget due to the cooling rate. The parts in fact are quenched in this area and are brittle. Tempering will alleviate this quenched condition. This means bring the material back up to a modest tempering temperature and hold briefly and then cool slowly.
In some materials there is a tendency for voids to form in the weld nugget. Aluminum often has this problem. Forging the nugget in the plastic state is a desirable means of improving the nugget’s strength and acceptance.
In some instances it is advantageous to immediately repeat the same weld sequence on a spot weld. This is usually done in an attempt to grow the nugget larger or to permit a brief cooling of the part. Immediately at the end of the weld sequence one or two cycles of cool or current off are introduced with full force maintained then the original weld sequence is repeated.
Steppers are a means of changing the weld schedule to match the increase in the face size of the electrode as it mushrooms/wears during use. All spot-welding electrodes mushroom as they are used. As this face increases in size the original weld schedule is no longer sufficient to maintain a constant weld nugget size. The current density has decreased due to the increased electrode face area. To counteract this one can either dress the face back to original size or increase the weld schedule to match the face growth.
Weld controls like most other components on a resistance welder conduct large currents. This current can generate heat. This heat must be dissipated for the equipment to operate efficiently. Yes, weld controls must be cooled. Lower amperage units can be air cooled. Higher rated units are water cooled.
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