Changes

Since welded contact assemblies are usually produced in rather high quantitiesthe quality of the weld joints is monitored closely. This is especially true becauseof the high mechanical and thermal stresses quite often exerted on the jointareas during switching operations. The quality of the joints is dependent on theprocess control during welding and on the materials used to manufacture thewelded assemblies.

Despite the ability to closely monitor the relevant welding parameters such asweld current, voltage and energy, simultaneous testing during and aftermanufacturing are necessary.

A simple and easy to perform quality test is based on the shear force.Evaluations of welding assemblies in electrical performance tests have shownhowever that the shear force is only a valid measure if combined with the size of2 the welded area. As rule of thumb the shear force should be > 100 N/mm withthe welded area > 60% of the original wire or profile cross-sectional area. Forcritical applications in power engineering, for example for high currents and/orhigh switching frequency, a higher percentage of the joint area is necessary.

During series production every weld is usually probed in a testing stationintegrated in the manufacturing line with a defined shear force – mostly 20% ofthe maximum achievable force. In this way defective welds and missingcontacts can be found and sorted out. The monitoring of the actual shear forceand size is performed during production runs based on a sampling plan.

Besides destructive testing for shear force and weld area the non-destructiveultrasound testing of the joint quality is also utilized for welded contactassemblies ''(Fig. 3.16)''.