*5.3. Insulating*

A dielectric potting material should be selected as secondary insulation to keep eddy current losses low and to prevent electrical breakdown. Epoxy resin is characterized by excellent product and process properties and is therefore widely used in encapsulation processes [24].

Several sub-process steps are necessary to prepare a self-leveling, thermosetting, dielectric molding mass. Figure 4 gives a detailed view of the insulation process and its integration into the IPT process chain. Each sub-process step is characterized by different process parameters. subject to only minor fluctuations. By slightly adjusting the process parameters, it is also possible to join taped and PAI primarily insulated high-frequency litz wires to tubular

*Energies* **2022**, *15*, x 9 of 13

The process for encapsulating the electrical components consists of the resin preparation, the dosage and the mixing of the resin and hardener, the potting, and finally the curing of the molding mass. During the preparation phase, the resin and the hardener get tempered and dried to reduce moisture and set the process relevant viscosity for the mixing and potting. The mixing step is needed to homogenize the resin and hardener to a reactive molding mass. Within this step, the polymerization begins and the potlife must be monitored carefully. The potting phase is the actual insulation process of the IPT, where the molding mass is dosed via the casting nozzle into the coil and carrier. By processing in a vacuum chamber (see Figure 6a), a higher degree of litz wire impregnation can be achieved [26]. After the potting, the coil is transferred to the curing stage, where the crosslinking and therefore the viscosity of the resin material increases. By processing in a convection oven, the material specification such as the glass transition temperature and the degree of crosslinking can be set to defined values. By varying these, the challenges in the processing of resin-based insulation materials for wireless power transfer applications can be evaluated in more detail. cable lugs. Therefore, the hot crimping process is used as a reference contacting process in this research project. However, the extremely promising torsional ultrasonic crimping and welding process will be further optimized for future applications. Figure 5 (right) shows, in addition to exemplary test samples, the ultrasonic welding system used and various contacts produced. *5.3. Insulating* A dielectric potting material should be selected as secondary insulation to keep eddy current losses low and to prevent electrical breakdown. Epoxy resin is characterized by excellent product and process properties and is therefore widely used in encapsulation processes [24]. Several sub-process steps are necessary to prepare a self-leveling, thermosetting, dielectric molding mass. Figure 4 gives a detailed view of the insulation process and its integration into the IPT process chain. Each sub-process step is characterized by different

The studies of M. Kneidl et al. [26], summarized the most important process parameters of the complete encapsulation process, which result in a good product quality of the insulation system. By analyzing the process chain, the overall process time is mostly determined by the curing step of the insulation resin. Therefore, the curing time can be reduced by 75% with increased temperatures of up to 80 ◦C. Another positive effect due to higher material and curing temperatures is a better impregnation of the high-frequency litz wires, due to the lower viscosity of the resin. This results in optimized dielectric properties. Further on, optimizing the insulation quality by using a vacuum process is dependent on the type of primary insulation, which is used for the litz wires [26]. process parameters. The process for encapsulating the electrical components consists of the resin preparation, the dosage and the mixing of the resin and hardener, the potting, and finally the curing of the molding mass. During the preparation phase, the resin and the hardener get tempered and dried to reduce moisture and set the process relevant viscosity for the mixing and potting. The mixing step is needed to homogenize the resin and hardener to a reactive molding mass. Within this step, the polymerization begins and the potlife must be monitored carefully. The potting phase is the actual insulation process of the IPT, where the molding mass is dosed via the casting nozzle into the coil and carrier. By pro-

#### *5.4. Assembly of the Ferrites* can be achieved [26]. After the potting, the coil is transferred to the curing stage, where

For the assembly of the ferrites, the following process steps result in the system setup, shown in Figure 6b). The system components are mounted on the workstation base with numerous mounting options. The components include the cycle chains as provisioning tools for material replenishment, a cobot as the central handling device with the vacuum gripping system, and the measuring station with an optical 2D industrial camera. the crosslinking and therefore the viscosity of the resin material increases. By processing in a convection oven, the material specification such as the glass transition temperature and the degree of crosslinking can be set to defined values. By varying these, the challenges in the processing of resin-based insulation materials for wireless power transfer applications can be evaluated in more detail.

cessing in a vacuum chamber (see Figure 6a), a higher degree of litz wire impregnation

**Figure 6.** Vacuum potting machine (**a**), robot-based ferrite structure assembly (**b**). **Figure 6.** Vacuum potting machine (**a**), robot-based ferrite structure assembly (**b**).

The studies of M. Kneidl et al. [26], summarized the most important process parameters of the complete encapsulation process, which result in a good product quality of the

In the first process step, the fixture of ferrites in the charge pad housing is prepared. The fixation can be realized by adhesives, tapes or varnishes.

The next process step is the individual conveying of a ferrite through the system. In interaction with the vacuum end effector, the robot arm takes a ferrite tile from the workpiece carrier and conveys it to the measuring table. For the robot to pick up the ferrite, the control program must know the information about the arrangement and current stock of materials in the workpiece carrier. A constant supply of compressed air for the vacuum gripper is necessary so that a secure fixation can be maintained permanently. The most important tasks are the safe holding of the workpiece and the fast and collisionfree movement through the process plant. All stations must logically be accessible in the COBOT's workspace.

For high process speeds, the travel distances must be kept as short as possible and nonlinear. This means that speed-optimized conveying additionally contributes to economical production. However, adapted and linear movements should be used for the "pick-up", "measure" and "assemble" process stations. This increases the process reliability and precision of the work steps and ensures collision-free pickup and assembly processes.

The optical 2D industrial camera records the geometric dimensions, any damage present, and the orientation of the current ferrite on the backlit measuring table. The COBOT moves to a defined position in the detection range of the camera. There it remains in a waiting position until the inspection is completed. The dimensions in length and width of the ferrite, as well as its position on the vacuum gripper, are recorded with a certain accuracy. These data can be evaluated and interpreted with suitable software. The *actual* values are compared with the *target* values and manufacturing tolerances from the data sheets. In addition to the deviations of the ferrite dimensions, the deviations from the ideal position of the tile on the gripper is also checked.

When picking up from the blister, twisting or displacement of the breakpoint could occur due to incorrect orientation of the ferrite. All captured and determined data is fed back into the process and included for the assembly process. After being conveyed from the measuring station, the ferrite reaches the mounting station. The COBOT moves to the planned position for the current tile above the housing. The correct position is defined to the robot controller using the coordinate system for the layout according to the loading pad design. Using the information from the survey station, it is known whether the current ferrite has deviations in its manufacturing dimensions and in its position on the gripping system. If this is the case, the robot controller can make the necessary corrections. This means that the ferrite is brought into a suitable position by the movements of the COBOT. The correct positioning of the ferrite tile is thus achieved. However, the accuracy of this result depends on the quality of the measurement data and the robot accuracy. The ferrite is over its assigned place and is ready for the curing of the chosen fixation.
