*4.3. Contacting Technologies*

Due to the high number of insulated single wires of a high-frequency litz wire, the process step of contacting is a challenging process. In order to enable an electrical and mechanical connection of the high-frequency litz wire with contact elements such as cable lugs or terminals, the primary insulation of the single wires must be removed. The high number of single wires precludes mechanical stripping prior to the actual contacting process. Chemical stripping processes are also extremely challenging and do not allow a sufficient stripping. However, in order to enable the contacting of primary-insulated litz wires, combined contacting processes can be used. These realize the necessary stripping process directly during the actual contacting. The hot and ultrasonic crimping processes are particularly suitable for this purpose. In both processes, the contacting is realized by a crimping process with tubular cable lugs. On the other hand, the primary insulation is removed thermally. While the hot crimping process utilizes the resistance heating of electrodes and tubular cable lugs for this process, ultrasonic crimping uses only the damping of ultrasonic oscillations. The resulting conversion of oscillation energy into thermal energy also enables a thermal stripping. Furthermore, high-frequency litz wires can be stripped by means of an ultrasonic compacting process. Again, the damping of mechanical oscillations leads to thermal stripping. At the same time, the tooling system used produces a defined node cross section with welded single wires. The compacted high-frequency litz wire can subsequently be welded onto contact terminals using the ultrasonic welding process. A direct welding of high-frequency litz wires with terminals is rather difficult to implement since the primary insulation hinders the welding process [23].
