4.2.3. Winding of HF-Litz Wires

There are three basic concepts to perform relative movements between the laying tool and the base plate, which are also realizable with robots [22]. While manually produced demonstrators usually have certain imperfections and higher manufacturing tolerances, automated test setups are usually expensive and inflexible. The use of a universal and flexible robot kinematics in combination with the realization of a cad-cam chain makes it possible to use a robot for demonstrator assembly as well as for serial production.

For validation, a layout was created which includes different radii as well as parallel windings and winding intersections. In addition, various installation tests were carried out in which the strands (material, diameter, structure), the shunt radii and the setting radii can be varied. These tests make it possible to draw conclusions about the reproducibility of a pad during the electromagnetic design phase.

For example, an R14 radius can no longer be produced with a 768 × 0.1 mm HF strand, or a radius of 1 mm with an angle of attack of 90 degrees, but only with insulated strands (e.g., a 300 × 0.2 mm baked varnish strand).

Within the framework of research, basic production concepts have been realized. In order to achieve high-quality IPT systems, not only the basic production concepts but also the material behavior must be considered in detail. To reflect critical material behaviors, selected production concepts were therefore implemented and scrutinized. Overall, it became evident that self-bonding wires can be processed more easily without external insulation. However, HF litz wires without external insulation have the disadvantage of a lower cohesion of the individual strands and less protection against mechanical damage. As shown, problems can occur in the winding process with tighter curves if the wires are twisted and deformed in the winding direction.

Complex coil constructions require external insulation to keep the wires in shape and ensure sufficient electrical insulation, even in difficult environments. However, inelastic adhesive tapes make stranded wires very stiff and therefore difficult to wind, especially in tighter curves, and the tape needs to be removed before contact to avoid residues and vapors. Outer insulation with silk offers the best compromise, namely high HF stranded wire stability and good protection against mechanical damage, while at the same time offering flexibility. A disadvantage is the need to wipe the silk before the contacting process to avoid residues and vapors.

In summary, the tests described above can be used to determine production-relevant parameters in order to assess the suitability of HF stranded wires for winding as well as the necessary winding and wire laying tools and to produce prototypes.
