Automated seam variation and stability analysis for automotive body design

Book chapter, 2003

The spatial relations between parts in assembled products are often critical. In the automotive industry, the relations between the doors, hoods and panels are important quality characteristics. Functionally it must be possible to open the door without interference with other parts, but the esthetical aspect is also important. Today, the quality appearance of a vehicle is judged by the quality of the gaps between the body panels, i.e. doors, hoods, fenders and panels. This paper presents three basic types of analysis that can be used to evaluate design concepts and predict the final variation: stability analysis, seam variation analysis and quality appearance evaluation. The stability analysis focuses on the locating schemes in the assembly and aims at making the concept as insensitive to variation as possible. Seam variation analysis focuses on the relation between parts in an assembly. A seam, as introduced here, is a relation between two parts over a distance. Typically, seam variation is measured and evaluated in two directions, the gap and flush directions. The paper introduces two goodness values for automotive body variation evaluation. The instability index reflects the total locating scheme stability for the whole assembly while the quality appearance index rates the total variation in all seams of the body. The latter is calculated as the mean variation in all defined seams of a body and allows for evaluating the final appearance of the body, with one measure, already in the early concept phase. The analyses are implemented and performed in the CAT software, RD&T, presented numerically and visualized by color coding. An auto body example is used to illustrate the analyses. The analyses are however general and valid for most assembled products.