Managing Geometrical Variation in Complex Assemblies through Visualization and Tolerance Allocation

Licentiatavhandling, 2007

To stay competitive in the market today, manufacturing companies have to shorten their time to market. This implies that time also has to be saved during the product development phase. This thesis will mainly focus on how to be more efficient in the detail design phase through different design activities. These activities are related to methods and tools regarding how to manage geometrical variation when digital CAD models are available. Controlling the variation in a digitalized environment can save time and resources by decreasing the need for test series and avoiding quality problems during production start/ramp-up. The research in the thesis discusses and suggests methods regarding how to manage variation in the detail design phase. The research project presented in this thesis is divided into two parts: 1) decomposition of requirements and 2) visualization of variation. The first part investigates how geometry requirements or functional requirements can be decomposed into design parameters. One example of a requirement could be the allowed variation between a door and a fender of a car. This allowed variation shall be decomposed into design parameters. In this case those parameters are tolerances on dimensions of parts and locators in the assembly that affect the variation in critical dimensions. This can be done automatically, which implies an optimization problem with the constraints on an allowed variation in the critical dimension. The decomposition can be done in a number of different ways and is discussed in this thesis. The second part of this research focus on visualization of variation. The research behind this thesis has concentrated on methods for visualization of the total volume a part or assembly creates when affected by variation or motion. This total volume is called motion envelope. A part of the result has been implemented in an industrial product development process. The results were used to calculate and visualize the total volume an engine creates when being affected by motion. The main advantage was time savings when the motion envelope is used as design support. This was due to fewer loops of controlling the packaging. Now it is possible to look for conflicts within the whole engine compartment. Earlier this was made between different parts or even between individual points. The envelope also decreases the risk of finding conflicts too late in the product development process, which might imply in late and costly tool changes.