Feasibility of alternative manufacturing processes for winding and stator components of electric machines

One of the features of the 21st Century is the development of new electric vehicles. This has been accelerated at this time through a combination of political will and consumer adoption. The technologies that can be used in the manufacture of electric vehicles range from the tried and tested to the state of the art. One of the major aspects of an electric vehicle is, naturally, the electric motor (electric machine) which provides the drive to the vehicle. The science and understanding of how to design electric machines is fairly well known. However, it is in the application and mass manufacturability of electric machines of the required capability and at the required scale that there is much less knowledge. The research conducted in this thesis aims to bridge the gap between manufacturing technology and business operations impact, providing a holistic view on the performance of processes and identifying areas for opportunity and concern. The research conducted in this thesis has been centred on the components of the stator and windings.

The manufacturing implications of a shift from windings to hairpins has been considered, with an analysis of the manufacturing route employed in wire winding and hairpin winding produced and examined. A comprehensive study of potential alternative materials for windings and hairpins for conducted, revealing that aluminium has the potential to be a cheaper and lighter winding material to copper. Following these results, a review of the manufacturing efficacy of alternative joining methodologies for Al-Cu hairpin assembly was performed, with the highest potential being seen in friction stir, laser beam and cold press joining. This research was backed up with a structural analysis of the potential benefits of incorporating a hollow section in a hairpin design to reduce the thermal expansion of the hairpin component.

A review of stamping as a method of stator laminate production was considered alongside the creation of a stamping model for stator production and an evaluation of innovative stator manufacturing processes. Following an analysis of the stamping manufacturing route employed in stator production, areas for operational improvements were identified. This knowledge was incorporated into the development of a stamping process manufacturing model. A further study was produced to develop a tool wear dynamic system within the stamping model, with the resulting sub-model used within the system. The stamping model was used to generate a greater understanding of the of the effect of various stamping parameters on the overall performance of a stamping operation. An analysis of alternative stator materials was produced, identifying METLGAS and cobalt iron as potential alternatives to electrical steel, where electrical steel remains the best material from an overall cost and mass perspective. A feasibility study of slinky style stator as an alternative manufacturing process was conducted, with the results demonstrating the need to create bespoke stator designs to reduce the stresses as a result of bending.

Laser cutting was identified as a potential alternative to stamping in the mass manufacture of stators. A laser cutting model was developed and an evaluation of laser cutting as an alternative approach was performed. The development of a laser cutting manufacturing model required incorporating a laser optimisation procedure. The optimisation procedure was able to achieve either cost or time efficient results based on any given set of manufacturing parameters. The optimisation model showed that different manufacturing setups are required based on the type of optimisation being considered. A full analysis of laser cutting process parameters was performed, with considerations to cost and time factors, allowing identification of areas of opportunity such as improving the changeover function with an automated transit system.

Experiments were performed using a laser cutting machine. Samples were manufactured and a series of tests were performed to ascertain the feasibility of performing cuts as stacks. The act of cutting multiple laminates in a single operation is henceforth referred to as polystromata. The polystromata cut samples were also tested for their electro-magnetic performance qualities post cutting. A materials study of laser cut samples using microscopy was conducted to understand the effect of polystromata cutting.

An economic and operational comparison of stamping and laser cutting was performed, using the knowledge gained throughout the studies conducted within this research. The comparison study was able to identify performance trade-offs of stamping and laser cutting for various stator design parameters. Laser cutting was found to be more suitable than stamping for smaller sized machines. A follow-up study of the economic order quantity of raw materials for stator production was performed.