70 “We produce 100% comparable prototypes of hairpin or wave-wound stators in just four weeks, and support well-known tier ones and OEMs in their prototyping processes.” The company creates motors with many different topologies, including synchronous, asynchronous and axial flux machines. “In addition, our 3D printing processes enable new winding-head designs and conductor structures, for which we also rely specifically on 3D simulation,” he explains. “We have used additive manufacturing techniques to assess our designs at very early stages to check the feasibility of some of the more challenging aspects of manufacture,” another notes. “We have also found that lead times for prototypes have greatly reduced as there is more competition in the low-volume manufacturing space.” The key technologies for any stator are around wire forming, wire insertion and welding, notes our major automotive systems developer. For hairpin technology, the twisting operation comes on top, he adds. The company makes extensive use of commercially available, CNC wireforming technology, of which recent advances have significantly improved flexibility for prototyping, in addition to some specialised equipment of its own. Testing and validation New motor designs must go through the challenging processes of testing, validation and, if necessary, further optimisation and iteration. “We try to break down a lot of testing to the individual components and, for example, to test conductors or conductor pairs for qualification,” our first motor developer’s expert says. “Based on these test results, we draw conclusions about the behaviour of the assemblies before they are finally put together. “We do end-of-line tests on every stator, sometimes with very high voltages, to ensure our parts are of the best quality and reach the customer safely. Of course, we also validate our simulation results on the test bench, but we have a very good tool chain that provides us with the desired results during the design phase, so that we can keep the number of iterations to a minimum. “Finally, we carry out accelerated life-cycle tests on the overall motors and mirror these back to the results of the individual components to check whether they meet expectations.” Mathematical models are used to predict service life and failure probabilities, with parameterisation being a major challenge, the expert says. “The basis for this is formed by various test scenarios, which we customise in order to achieve the best results.” Parameterisation is the process of determining and setting the values of the variables (parameters) that characterise the model and influence its behaviour. It is a challenge because motors are used in diverse environments, and they are subjected to varying loads, temperatures and usage patterns. The process requires a lot of data on motor performance and failure incidents under many conditions (which may be incomplete) and often involves the use of complex statistical methods and algorithms. It also demands detailed knowledge of physical degradation mechanisms and environmental factors. Price pressure is significant, our major automotive systems developer stresses, explaining that optimising the bill of materials (BOM) to meet both technical and financial requirements is the most important aspect for any product’s development. “This demands a high degree of cost awareness in the technical project team, and the flexibility to introduce innovative technologies and materials from any potential new supply chain offering quickly,” the expert says. “The key challenge is time in all aspects of project execution, from design and supply chain evaluation up to testing and validation.” He adds that the testing process presents a complex problem that engineers break down into smaller steps that can be executed quickly; for example, in the validation of insulation systems. “We developed our own testing methods, helping us to significantly speed up the time required for base validation. Nevertheless, the final product must undergo complete durability testing, but only for final confirmation of its conformance with requirements.” Lead time can be a major issue in prototype testing, often driven by specialist materials, our core stack manufacturer points out. Its expert says: “In general, the material/alloy lead time related to iron cobalt alloys has been significant (say, 20 to 26 weeks) followed by stack manufacturing (another 18 to 24 weeks), so it can take a very long time to assemble prototype motors and perform the first tests, which generally takes another three to six months. “Design verification/validation and freezing takes several iterations, making motor development a multi-year cycle. For fast-moving applications, such as urban air mobility (UAM), the development cycle needs to be much shorter,” its expert says. The company has reduced its lead time on iron cobalt alloy stacks to 10-16 weeks. Furthermore, it uses testing techniques that enable motor designers to see the July/August 2024 | E-Mobility Engineering A stator made using innovative, S-wind wire-forming technology, which enables high-volume production of high-voltage EV motors. S-wind stators feature continuous copper-wire segments formed into a zig-zag S-shape (Image courtesy of BorgWarner)
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