Controls & Transformers

Questions and Answers

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.

In many manufacturing facilities the power in the plant is not sufficient to maintain constant power throughout the workday. A resistance weld schedule can be developed and during the course of the day the operators notice that by mid-morning their welds are getting smaller. They need more power. Then when second shift comes in they have too much power and have to turn it back again. In some cases this can be traced back to a lack of power in the plant and a voltage drop due to the large usage during the main productive hours of the plant.

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