Towards an efficient life cycle assessment of production processes for mechanical fastening elements

Abstract Purpose In the automotive industry, the ecological evaluation of products and communication of CO 2 emissions are increasingly important. Joining elements used within the products represent an important aspect of production. The aim of the paper was, therefore, to identify essential process indicators in the manufacturing and joining process of mechanical elements using the example of Helicoil® and self-tapping AMTEC® thread inserts to enable both the efficient measurement of process data and the optimization of the production processes. Methods Within the study, the production processes of a supplier of mechanical joining elements were analyzed. Furthermore, a scenario for joining the investigated elements in a manual and a semi-automated process was investigated. The primary data was obtained within a production plant in Germany. For this purpose, direct measurement data were generated during production, and indirect consumption and production data were accessed. Three LCIA methods, ReCiPe 2016, CML-IA baseline, and EF 3.0, were applied at the midpoint level. The product system boundaries were cradle-to-gate, as only a sub-product and the associated joining process were investigated. An uncertainty analysis was carried out to identify influences of data accuracy and applied methods, and a sensitivity analysis was performed to verify the impact of varying assumptions on the study. Results and discussion Within the investigations, all three methods applied show comparable results and can be employed equally for the analysis of the investigated processes. The global warming potential (GWP) of the Helicoil® element is significantly influenced by the use of material and the coating process. The rolling and winding processes have a lower impact. The GWP of the Quicksert® element, on the other hand, is significantly influenced by the material and, to a slight extent, by the processing. Within the joining processes, manual processes such as positioning and operating the tool result in an increased GWP. Automated feeding of the joining elements, positioning of the tools, and process control, on the other hand, clearly lead to a reduction in GWP. Conclusions This study highlights essential influences on the GWP in the manufacturing process of mechanical joining elements and the subsequent joining processes. These enable manufacturers to efficiently define their data acquisition and assessment processes for necessary product emission key figures. The results further imply a potential reduction in both cycle times within the process and GWP due to the use of secondary materials and renewable energy sources, an adapted coating strategy, and partial automation.