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→Selection of Attachment Methods
*Ultrasonic testing <br />This method is based on the disruption of the propagation of sound waves in different media. High resolution modern test systems with graphic print-out capabilities and analytical software are capable to detect even small (<0.5 mm diameter) voids in the braze joint. The portion of the wetted areas is calculated as a percentage of the whole joint area. <xr id="fig:Ultrasound print-out of braze joints"/><!--(Fig. 3.15)--> shows an example of different braze qualities for a Ag/SnO<sub>2</sub> contact tip brazed to a copper carrier and illustrates the position and size of void areas as well as the final joint quality.<br />
<figure id="fig:Ultrasound print-out of braze joints">
[[File:Ultrasound print-out of braze joints.jpg|right|thumb|Figure 2: Ultrasound print-out of braze joints between Ag/SnO 88/12 tips and Cu carrier with 2
different degree of wetting (dark areas = voids)]]
</figure>
A simple and easy to perform quality test is based on the shear force. Evaluations of welding assemblies in electrical performance tests have shown
however, that the shear force is only a valid measure if combined with the size of the welded area. As rule of thumb, the shear force should be > 100 N/mm with the welded area > 60% of the original wire or profile cross-sectional area. For critical applications in power engineering, for example for high currents and/or high switching frequency, a higher percentage of the joint area is necessary.
During series production every weld is usually probed in a testing station integrated in the manufacturing line with a defined shear force – mostly 20% of the maximum achievable force. In this way defective welds and missing contacts can be found and sorted out. The monitoring of the actual shear force and size is performed during production runs, based on a sampling plan.
<figure id="fig:Ultrasonic picture of a weld">
[[File:Ultrasonic picture of a weld.jpg|right|thumb|Figure 3: Ultrasonic picture of a weld joint, Ag/C tip on Cu carrier (ABB-STOTZ-KONTAKT)]]
</figure>
Besides destructive testing for shear force and weld area, the non-destructive ultrasound testing of the joint quality is also utilized for welded contact assemblies (<xr id="fig:Ultrasonic picture of a weld"/><!--(Fig. 3.16)-->).
=== Selection of Attachment Methods===
In the lower and medium load range, contact rivets and welded contacts are used. For high switching loads brazing, especially resistance and induction methods, are utilized. For extremely high loads, for example in high voltage switchgear, percussion welding, electron beam welding and copper cast-on processes are preferred.
<figure id="fig:Correlation between Contact Joining Methods and Switching Currents">
[[File:Correlation between Contact Joining Methods and Switching Currents.jpg|right|thumb|Figure 4: Correlation between Contact Joining Methods and Switching Currents]]
</figure>