Optimering av dragkroksdesign i sandgjutet aluminium – en studie i småskalig tillverkning

A towbar is a load-bearing component used for towing or transporting heavy objects and is therefore subjected to significant mechanical stress. Its design requires a combination of high strength, good manufacturability, and low weight. In a previous project, a lightweight towbar in aluminum was developed using sand casting as the manufacturing method. While the original design met the specified requirements, it also exhibited stress concentrations, manufacturing challenges and excessive material usage. This bachelor thesis constitutes an exploratory study aimed at improving the previous design by analyzing and addressing the identified shortcomings. The optimization process was carried out in two stages. First, the component’s geometry was improved, followed by an investigation into the potential for increasing material strength through heat treatment. The geometric optimization began with refining the previous design to smooth out critical transitions, improve stress distribution and adapt the geometry for sand casting. Subsequently, topology optimization was applied using CAD software to identify and reduce excess material, resulting in a new design that maintained mechanical performance despite a lower volume. Once the new geometry had been developed, a total of ten towbars were cast using an aluminum alloy suited for casting. Of these, five underwent a simplified T6 heat treatment, consisting of solution treatment, quenching and artificial aging. The aim was to investigate how this treatment affects the strength of sand-cast aluminum in small-scale production. The process was carried out using available workshop equipment, simulating conditions found in hobby-level or prototype-oriented manufacturing. To evaluate the material’s strength, tensile tests were performed on cast specimens, while compression tests on all towbars provided insight into their actual performance under load. Results from the compression tests showed that both the optimized geometry and the heat treatment contributed to increased load capacity. The heat-treated towbars generally demonstrated higher fracture loads than the untreated ones, indicating that even simple heat treatments can yield noticeable improvements in material strength. The topologically optimized design also achieved a significantly improved weight-to-strength ratio compared to the original towbar. This work demonstrates that both performance and efficiency in a mechanical component can be improved through a combination of simulation tools, manufacturing expertise, and material understanding - even in environments with limited resources. The results are particularly relevant for small-scale product development where low weight and high strength must be achieved without access to advanced equipment.