Tolerance analysis of compliant, feature-based sheet metal structures for fixtureless assembly

Products made of compliant sheet metals are widely used in automotive, aerospace, appliance and electronics industries. One of the most important challenges for the assembly process with compliant parts is dimensional quality, which affects product functionality and cost. Joining fixtures serve to position and secure the parts in the assembly process and thus significantly contribute to product quality. However, these fixtures are costly and inflexible. Feature-based fixturing is an approach to reduce fixtures in the assembly process. The approach relies on part-inherent fastening features that ensure the fixture functions. This paper presents an approach to calculate assembly variations for feature-based fixturing in the automotive body shop. The mathematical fundamentals are described and the approach was implemented using a numerical model. The model was validated and applied to car body structures. The validation shows a high quality of the model and the suitability to predict assembly variations. Finally, an assembly that is built with conventional fixtures is compared to an assembly that is set up with feature-based fixturing. This comparison shows that the approach of feature-based fixturing has a high potential to meet the requirements and thus being applied in the future.