Rethinking Hairpin Winding Design and Manufacturing: Aluminum as a Drop-in Replacement for Copper: A Discussion to Lower Environmental Impact and Higher Recyclability

The awareness of sustainability in the design of electric machines is growing rapidly, driven by the goal of reducing carbon emissions throughout the entire product life cycle, from raw material sourcing and manufacturing to operation, recycling and reuse. Recent research trends reflect this shift, leading to design strategies that reduce environmental impact [1], [2] and improve recyclability [3], [4], through ease of disassembly [5], [6] and the use of fully recyclable materials. Meanwhile, the implementation of sustainable strategies in the development of electric machines can pose challenges in boosting other key performance indicators (KPIs), such as power density and efficiency, and, in some cases, requires modifications to traditional and widespread manufacturing equipment. Accordingly, designers need to face trade-offs across multiple aspects of the design, carefully balancing electromagnetic performance, thermal behavior, and manufacturability. In this context, addressing the sustainability challenge requires a paradigm shift in the definition of the design priorities: from performance driven to application driven, where the focus is no longer solely on the product itself but on the user needs. Focusing on a concrete case, this article addresses the challenge of replacing copper hairpin windings with aluminum, which are more sustainable because of their lower environmental impact and higher recyclability but feature higher electric resistivity and ensuing DC Joule losses, possibly leading to higher thermal load and a decrease in efficiency. Similarly, different material workability requires re-adaptation of the manufacturing processes. The aim of this article is to support the transition toward more sustainable electric machines for the traction of both passenger and utility vehicles. These applications are characterized by transient peak-load operation during acceleration, continuous power operation in demanding conditions such as road gradients, and low-load operation across urban, extra-urban, and highway driving. Accordingly, these real operating conditions, including the representative Worldwide Harmonized Light Vehicles Test Procedure (WLTP) driving cycle, form the basis of the analysis. On this foundation, the paper provides guidelines and best practices for the design and development of aluminum hairpin stators, covering electromagnetic, thermal, and manufacturing aspects.