Electrodes for resistance welding made of tungsten and molybdenum

Welding electrodes are exposed to very demanding conditions. During the resistance welding process, the parts to be joined are pressed together while being heated by an electric current until the material starts to melt at individual points at the interface.

This requires high currents and large pressing forces, reaching up to 450 MPa between the electrode and the workpiece during the welding of thick sheets.

Naturally, this represents a considerable challenge for the welding electrodes to withstand these loads.

Combining excellent stability at high temperatures with high electrical conductivity, welding electrodes made from Plansee refractory metals and their alloys exhibit a considerably longer service life than conventional materials such as copper and copper alloys.

Plansee welding electrodes made of tungsten, molybdenum and their alloys are particularly suitable for welding highly conductive materials such as copper. 

They are used in the following processes: spot welding, roller welding, projection welding and upset welding.

Back casting versus soldering

Good and reproducible welding results can only be assured with optimal joints between the tungsten and the copper electrode since defective joins reduce thermal conductivity and cause the electrical resistance of the electrode to fluctuate. 

Back-cast electrodes offer the following advantages:

•    Reliable contact between the electrode and the shaft material

•    Constant level of resistance

•    Low variations in thermal conductivity

•    High reproducibility of the electrode quality

•    Process stability in practical application

This leads to the benefits of longer service life and uniform welding parameters. 

Plansee produces rods made of molybdenum, tungsten and alloys in different dimensions.

Spot welding is a process where two electrically conductive metal parts are joined via the heat generated as a result of electrical resistance when an electrical current is passed through. The metal sheets are pressed together by two electrodes and the welding current is converted to heat at the contact surfaces.

Since the current that is forced through the welding point is very high, the metal melts at this point and the welded joint is created. 

The precision of spot welding is one main advantage, as a large amount of energy can be concentrated on the spot in a very short time. Therefore, the rest of the sheet is not subjected to excessive heating. Precision spot welding is normally applied for sheet thicknesses between 0.5 and 3 mm.