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Hairpin Gauging And Inspection Of The Stripped Area

Several researches showed that there are significant advantages in using flat wire hairpin windings in some types of motors. The advantage is a much higher copper slot fill factor reducing heat and improving torque and power density, which ultimately can reduce the motor size for EV application.

However, in order to obtain this performance improvement, it is necessary to guarantee an adequate quality level of the component and that its production process is perfectly under control.

One of the most critical aspects of the hairpin production concerns the stripping process and the control of the perfect removal of the insulating enamel from the terminals, before welding. The combustion of enamel residues or other contaminants during the welding phase can in fact generate gas inclusions and cavities within the welding meniscus, resulting in a reduction in the mechanical strength of the joint and an increase in its electrical resistance.

Hairpin Gauging And Inspection Of The Stripped Area

Depending on the stripping method adopted, different types of defects can occur and it is therefore necessary to propose different process control strategies.

Chromatic confocal technology is able to measure the thickness of the enamel coating on magnet wires, when the coating is transparent to the white light (as it normally is).

When the enamel removal operation is carried out mechanically by means of a milling tool, it may be necessary to measure in-line the amount of material removed, in order to verify that the tool has reached the copper core and no residual enamel is present. The use of in-line confocal sensors can, in this case, allow to measure the enamel thickness in the unworked wire section and the height of the step in the stripped area. The insertion of multiple confocal sensors in a fork configuration then allows for a complete measurement of the dimensions and symmetry of the stripped zone.

In laser ablation operations, it can instead occur that a thin layer of enamel is left in some specific areas, depending on the number and orientation of the laser heads. In this case the use of interferometric technology allows to measure the amount of residual enamel, starting from thicknesses of a few microns.

White light interferometer can be used in an off-line measuring stations, to carry out a sample check of the laser removal process of the enamel. When the location where the residual enamel concentrates is known, the same technology can be integrated in-line for 100% process control.



In other cases, it may eventually be necessary to inspect the entire cleaned surface, looking for defects and contaminants such as laser-charred enamel residues. The use of STIL confocal technology, applied in linear optical sensors with the MPLS family, guarantees a high field of focus and therefore allows to perform an in-line analysis of the entire stripped area, and to identify different types of defects.

  • Complete dimensional gauging and inspection of the stripped area
  • Possible use for control of the stripping process
  • Prevention of defects in the hairpin welding operation
  • Available solutions for off-line or in-line check
  • Measurement of enamel thickness with confocal sensors
  • Complete gauging of the stripped area with multiple confocal sensors
  • Measurement of the residual enamel thickness with white light interferometer
  • Confocal optical line sensors MPLS for inspection of defects in the stripped area
  • Possible integration of multiple technologies in the same gauging station

Defined according to customer’s requirements.

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