Copper Welding Caps

It has been discovered that deep cryogenic treatment of copper resistance welding electrodes will dramatically increase their useful life. Conservatively, they now experience an increase in service life of at least 3 to 5 times over untreated electrodes. These particular electrodes are Mallory Class 3 and are used for welding caps on TO-3 headers (power transistors).

The typical mode of failure for welding electrodes is thermal cyclic fatigue. The part is heated and cooled many times which causes cracks to form. The cracks then propagate and the surface starts to collapse. This changes the surface area which throws off the welding parameters and the part starts to fail rapidly. Cryogenic processing delays the initial cracking and reduces the resistivity of the part. The increased life reduces welding costs and increases profits. It also improves the quality of the weld.

Service life of deep cryogenically treated electrodes is extended in three ways:

• Average life of the untreated electrodes is 5 days: after treatment they last 22 days.
• The untreated electrode is redressed by removing 0.008 to 0.010 inches of material; the treated electrode required only 0.003 to 0.005 inches of stock removed during each redress.
• Untreated electrodes can be dressed only 5 times before they must be scrapped; deep cryogenically treated electrodes can be redressed 10 times before they must be scrapped.