More about Resistance Welders

Click here to find Resistance Welders Manufacturers | Discuss Resistance Welders & Other Topics

There are three basic types of resistance welding processes: resistance spot welding, resistance seam welding, and projection welding. Resistance welders produce coalescence by inducing electric current through the work piece and applying pressure. As the current is induced, the electrical resistance of the work piece causes the part to generate heat; eventually this heat, coupled with applied pressure, causes coalescence to occur—often without melting. Typically resistance welding processes take a very short time, and are therefore effective for long production runs.

Resistance spot welding uses a pair of opposing electrodes to produce small welds. The metal to be welded is placed between the two electrodes, whereupon pressure and current are applied, quickly creating the weld. The weld shape is determined by the design of the electrodes used in the operation. Welding machines employed in the process generally fit under two categories: press type and horn, or rocker-arm, machines. Rocker arm units use a stationary electrode and an electrode mounted on a pivot arm, which is lowered onto the work piece through pneumatic or manual operation. Press type machines have higher kVa capacities, and use one or more slide-positioned electrodes to achieve multiple welds in a short period of time.

Resistance seam welding is similar to the resistance spot welding process, except that seam welding involves a progression of overlapping spot welds. Eventually, enough welds form an airtight, high-quality seam. Provided the proper pressure is applied, the process can be used to create butt welds between two pieces of metal or spot welds on layered metal sheets. The equipment used for the operation uses wheel-shaped electrodes that rotate as the work piece is passed through them.

Projection welding differs from seam and spot welding in that it uses much larger electrodes and requires preformed projections to be machined on the work piece. In projection welding, a work piece containing numerous projections, or dimples, is placed between large electrodes. As pressure is applied, the sheet makes contact with the electrodes through the projections, and welds form wherever the dimples are located. Unlike spot welds, which are determined by the shape of the electrode, projection welds are largely defined by the shape of the original projection, and can therefore be made in a wide assortment of forms.