Optimizing the design of electric traction motors: analyzing the benefits of a circular economy

In the prevailing model of the linear economy (LE), products follow a direct path from creation to disposal. Companies design designs, procure raw materials, perform production processes to convert these materials into finished goods, conduct quality inspections, products are distributed to consumers, consumers use the goods, and finally the used product is disposed of (Vimala, 2024; Pacheco et al., 2024 ). However, this linear consumption pattern causes significant waste and environmental damage, leading to resource depletion and negative environmental impacts. To combat this, designers must prioritize solutions that enable continuous reuse of resources, especially in the initial design phase. This proactive approach focuses on extended product life, easy disassembly for recycling, and the use of recycled or renewable materials (van Dam et al., 2020).

The emergence of the circular economy (CE) challenges the traditional linear approach, both in terms of production and consumption patterns (Lewandowski, 2016; Lüdeke-Freund et al., 2019). At its core, CE aims to transform our current linear system into one that operates with minimal waste. In this desired zero-waste life cycle paradigm, the term waste as we traditionally understand it becomes obsolete. The CE is based on two basic principles. First, it redefines the way materials circulate within the economy, with an emphasis on a closed-loop system in which resources are continually repurposed, reused, or recycled (Negrei & Istudor, 2018). This minimizes waste and reduces the need for new raw materials. Second, the CE calls for a reassessment of the necessary conditions to support such resource-efficient material flows, including incentives for recycling, sustainable design and manufacturing, and responsible consumption.

The transition from a linear to a circular economy is undoubtedly challenging and multifaceted in many ways (Afteni et al., 2021; Kayikci et al., 2021). It requires a fundamental shift in mindset across all industries and society as a whole. This change requires changes in production methods, business models and consumer behavior. Companies need to adopt circular strategies such as leasing products, designing products to last, and creating systems for recycling and sanitation (Lewandowski, 2016). Policymakers also play a critical role in facilitating this transition by implementing regulations and incentives that promote sustainable practices (Kirchherr et al., 2018; Milios, 2018; Schröder et al., 2020).

The CE was also partly criticized. As reported by Millar et al. (2019), due to the second law of thermodynamics, there will always be waste and byproducts due to increasing entropy. Closed material cycles are therefore theoretically not possible. Additionally, Allwood (2014) noted that it is currently impossible to mine certain types of waste or purify certain liquids. Recycling this waste would require far more energy than producing virgin material and would not be worthwhile. Allwood (2014) also argued that there is currently no evidence that primary production can be completely displaced by secondary production. Korhonen et al. (2018) further argued that if the global economy continues to grow at an unsustainable pace, resource depletion will occur due to increased demand for material resources, regardless of whether an LE or CE is adopted.

Despite the criticism of CE and the complexity of this transition, CE promises to significantly reduce waste, conserve our finite natural resources and mitigate the environmental impact of our economic activities. Beyond these environmental benefits, it also offers economic opportunities, such as job creation and innovative business models (Sulich and Sołoducho-Pelc, 2022). As a result, the concept of CE has gained increasing attention and interest among a wide range of stakeholders, including academics, practitioners and policy makers (Geissdoerfer et al., 2017). Researchers are actively studying the principles and implications, companies are exploring innovative circular practices, and governments are considering policy measures to accelerate the transition to a sustainable circular economy model (Berry et al., 2022; Centobelli et al., 2021; Haas et al., 2020; Morseletto , 2023).

The work of Pearce & Turner (1989) has been widely recognized by numerous researchers (Andersen, 2007; Ghisellini et al., 2016; Greyson, 2007) as the seminal achievement that first introduced the concepts of “circularity” and economic interdependence and economy introduced systems and the consequences for the environment. Although Olson and Sutherland (1993) did not explicitly mention the word “circularity,” they emphasized the need to close material cycles and emphasized the economic benefits through the concept of “demanufacturing.” De Pascale et al. (2021) provided a systematic review of 61 indicators used to measure CE strategies at the micro (company/product), meso (eco-industrial parks) and macro (city/region/rural) levels.

CE indicators are evaluated based on various criteria, including their methodology (quantitative or qualitative), their alignment with the core CE principles (often referred to as the 6Rs: reduce, reuse, recycle, recover, remanufacture, redesign) and the consideration of various sustainability dimensions (typically ecological and economic, with less social aspects being included) (Geissdoerfer et al., 2017; Velenturf et al., 2021). It is worth noting that there is often a significant focus on recycling metrics, particularly in the environmental and economic sectors. However, the current situation shows a lack of standardized methods for measuring CE performance (Muradin and Foltynowicz, 2019). This lack of consistency makes it difficult to evaluate change across different initiatives (Flynn and Hacking, 2019). Indicators can range from single, specific metrics to more comprehensive composite indicators that span multiple dimensions of CE performance. At the micro level, common indicators focus on aspects such as recyclability, material circularity and the ease of dismantling of the product (Kristensen et al., 2020). At the macroscale, circularity is typically assessed at the overall system level, where material flow analysis is commonly used (Barreiro-Gen, et al., 2020). Lightweight products by replacing materials can reduce their environmental footprint, but require the creation of new recycling systems. Process improvements, such as redesigning machine tools and implementing intelligent manufacturing techniques, can significantly improve energy and resource efficiency (Sutherland et al., 2020).

To increase the effectiveness of CE initiatives and provide clearer guidance for policy and business decisions to adopt circular models, there is an urgent need to standardize CE measurement methods. An emerging field, green manufacturing planning, integrates environmental goals with traditional process planning and scheduling metrics. However, there are persistent obstacles to a CE that focuses on increased recycling and reuse. These challenges include increasing product complexity and the mismatch between waste streams and market demand for recycled materials. The path to industrial sustainability is to focus on sustainable product and process design, develop environmentally friendly planning tools and effectively close material cycles. Creating a common framework for measuring CE performance will facilitate more accurate assessments, comparisons and ultimately the further development of CE practices (De Pascale et al., 2021; Sutherland et al., 2020; Triebe et al., 2023).

To overcome some of the current challenges in implementing a CE, the engineering design methodology should be transformed towards a more comprehensive life cycle thinking to measure CE performance holistically. Taking this as the main motivation, the first aim of this paper is to propose a CE design approach that can be part of a parametric design model that integrates life cycle assessment (LCA) and techno-economic assessment (TEA); The design model can then be optimized. The approach of this design method builds on previous studies (Pérez-Cardona et al., 2023, 2024a-b). The proposed model applies a new disassembly planning algorithm that quantifies the outcomes (reuse, remanufacturing, recycling, disposal) for each subassembly/part of a single product collected at the end of life (EoL). Specifically, this model is used as part of the life cycle inventory (LCI) to include post-consumer processing steps and discount the reused materials and components. Figure 1 shows the life cycle stages of a general product for linear and circular economies. A case study was selected for illustration: a permanent magnet synchronous motor (PMSM) (for scenarios with Sm-Co and sintered Nd-Fe-B magnets) applied to an electric vehicle (EV). This case study could be suitable because the design of a PMSM is complex and there are critical materials present in the permanent magnets that have a high supply risk and high environmental impact. The parametric design model used for this engine is based on a previous study (Pérez-Cardona et al., 2023).

Achieving the first goal can help standardize CE measurement methods by including comprehensive performance metrics and comparing them to LE performance. Therefore, the second aim of this work is to compare the benefits of considering CE versus LE in the context of an analysis of the product design phase. The performance metrics used for this comparison are engine mass, energy consumption per unit distance traveled, supply risk equivalent (SR-eq.), environmental impact single score (I), levelized cost of engine production (LCOP), and levelized cost of EV Driving (LCOD). The benefits of CE, if any, compared to LE are quantified by comparing the differences in optimized performance metrics.

The rest of the paper is organized as follows. First, the method for modeling the CE is proposed as part of the design phase. The CE is then integrated as part of the parametric design model for optimization. Then the results of non-dominated optimal solutions and CE benefits are analyzed. Finally, a summary and conclusions for this study are provided.