Acknowledgements The author would like to thank Jasmina Simon at BASF; Fabrice Giaume and Yun (Katie) Ling at the Automotive Electrification Center of Excellence laboratory at Celanese; experts at Eaton; Pierric Gueguen at Mersen; Martin Bauer, Stefan Munz and Torsten Luik at Wafios; and Mark Lakis at Wiegel for their help with researching this article. 72 September/October 2023 | E-Mobility Engineering experts stresses the importance of getting from the first CAD file to a ready-to-use busbar quickly, so the company has developed software to support that goal. “Ten or 15 years ago, the operator had to program the geometry manually, but now it is almost completely automated,” he says. “You just push a few buttons and the system checks, simulates and finally produces a part that is very quickly corrected.” The chemicals company provides customers with close support with what its expert describes as a very accurate simulation of the thermal stresses between busbars and plastic insulation during temperature cycles. The stresses lead to cracks during thermal shock testing. “With our simulation model we are able to predict the location of cracks and can propose countermeasures for customer-specific geometries,” he says. Improvements and future directions The technology in and around busbars and interconnects is still evolving, with numerous improvements to products and processes emerging. For example, busbar insulation inside the battery pack has to be coloured a specific orange for safety reasons. However, when subjected to heat ageing, some material classes turn dark brownish, the expert adds, so the company has introduced new materials designed to ensure that the highvoltage conductors retain their colour throughout the product’s life cycle. Meanwhile, a range of improved crack-resistant materials for overmoulded busbars – especially for those in e-motors and power electronics – has been introduced by the chemistry and specialty materials supplier. They are based on toughened polyphenylene sulphide, and are said to exhibit “superb” high-temperature dielectric properties and perform far better than reference grades in thermal shock testing. Other solutions based on different grades of PPS are in development, as are solutions based on high-temperature nylon PPA. The company has also developed tools for its own use to validate material performance; one of them is a scouting tool to help find candidate materials, the other is a representative busbar for thermal shock testing. The best candidate materials have proven to be free of cracks even after more than 1500 cycles from -40 to +150 oC, its expert says. “However, prediction is as important as scouting and testing, since the better you can simulate and predict outcomes, the more time you can save,” he says. “With that in mind, our colleagues have developed new methodologies for predicting busbar failure, and to evaluate how the processing, design and materials all work together.” The electrical, industrial and power management company sees value in multiple busbar manufacturing processes, and continues to develop and refine its ability to extrude insulation onto flexible busbars, which eliminate waste and are easy to customise. The power transfer, management and materials supplier has launched a new design of laminated busbar with integrated monitoring that is designed to ease assembly and improve battery module safety. One type uses insulation that resists high temperatures for new applications. The precision metal stamping and ultrasonic welding specialist has patented a new means of producing busbars of variable and compound thickness that enables cell-to-busbar connections to be produced quickly and at low cost. The company’s expert says providing a current collector complete with cell connection tabs enables customers to eliminate a step at the pack assembly stage. In future, thermal management will remain a critical issue, says the chemicals provider, and busbars might come to adopt technologies such as liquid cooling, advanced thermally conductive materials or other new concepts. As voltages get higher, aluminium could come to replace copper, according to the chemistry and specialty materials expert, as the self-heating effect will not be as significant as it is at lower voltages, although higher voltages bring their own challenges. “Perhaps aluminium will harden over the many temperatures cycles, but if heat can be extracted efficiently from it through heat sinks and thermally conductive insulators, it might become a relevant conductor and an alternative to copper in the coming years,” he says. “If that’s the case, we’ll be ready.” Focus | Busbars and interconnects This CNC machine can perform twisting and insulation stripping processes in addition to conventional straightening, bending and cutting operations (Courtesy of Wafios)
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