n order to address methodological challenges during life cycle sustainability assessment (LCSA), this article combines the results of a life cycle assessment (LCA), a life cycle costing, and a social LCA using the example of a complex product: a rare earth permanent magnet for use in wind turbines. The article presents different approaches for combining the results of separate assessments with its attendant methodological challenges. Different normalization, aggregation methods, and weighing factors are applied and their impacts on the results are compared. The underlying case study makes an evaluation of these different methodologies more concrete. Results show that the normalization method applied has a greater influence on the overall results than the aggregation method or weighting factors. Additionally, this study shows that indifference thresholds should be applied to avoid overestimation of small impacts. Indifference thresholds ensure that impact categories with nearly the same results for all analyzed options are treated as identical results. The study also indicates the importance of the question of how much compensation between impacts is desirable. Despite the impact of these factors, the chosen case study of an LCSA for permanent magnets with different supply routes for rare earths shows that the ranking of Chinese production is the most problematic irrespective of the approaches applied.
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