Robust Form Division - Manging the Effect of Manufacturing Variation

Doctoral thesis, 2007

Product development is a necessity for manufacturing companies to keep market shares as well as gaining new ones. Decisions made in the beginning of the process will affect the final product to a large extent. It is thereby of great importance to be able to detect possible obstacles in the early phases of the product development process. Manufacturing variation is always present during production and needs to be treated. By designing robust, the manufacturing variation will influence less. A robust solution suppresses manufacturing variation whereas a sensitive one amplifies it. The appearance of the spatial relation between visible parts (i.e. split-lines) in an assembled product is important for the overall quality appearance of the product. Variation in the split-lines affects the visual quality appearance of the product. Split-lines are the result of a form division activity carried out in the early stages of the product development process, most likely by industrial design. Two main relations, gap and flush of a split-line, have been in focus in this thesis; the relations shall be tight and parallel. The position of the split-line can in certain cases determine the robustness of the assembled product, which has been used as a prerequisite in this thesis. Such can be the case if the locating schemes are pre-specified due to use of product platforms or reuse of assembly lines. The main objective of this research project is to support the form division activity in the concept development phase. The focus in the work is on reducing the effect of manufacturing variation by creating robust form division concepts. The adopted approach has been to link computer-aided tolerance analysis with computer-aided industrial design to support the form division activity in order to achieve a robust solution in accordance with aesthetical aspects. This result in solutions that meets both aspects as much as possible can be found. The analysis results are presented in a way suitable for shape generation and not as numerical parameter values, which are commonly used today. Throughout this research project, empirical studies have been woven together with synthesis activities to make a proposal of how to support form division. Empirical studies, in the form of interviews, have provided an understanding of the industrial form division activity as well as the customer perspective on split-line appearance. The main conclusion from this thesis is that today industrial designers are creating the form division concepts with minor considerations to robustness. The form division concept is then iterated with engineering design to find a robust solution, fulfilling aesthetical, functional and manufacturing requirements. These iterations are often time consuming. The proposed toolbox allows for aesthetical aspects as well as robustness to be considered simultaneously. Thereby, timely and costly, design loops can be reduced.