Increased precision in variation simulation by considering effects from temperature and heat

Doktorsavhandling, 2014

Every manufactured product deviates from the intended product. In a production series a number of noise sources will influence the product resulting in geometric variation. This variation leads to functional and aesthetical variation of the product. In geometry assurance, focus is on knowledge, methods, and tools to assure that the aesthetical and functional properties of a product are maintained for the non-nominal product. In this thesis, the effect of temperature and heat are considered in combination with variation. The relative ease of the manufacturing techniques and their flexible physical properties has made plastics an attractive alternative to metals in many industries. However, the thermal expansion of plastics is often much larger than metal, and is often of the size of other effects considered in geometry assurance. During assembly welding is a common joining technique. During welding a large amount of heat is induced into the welded assembly. It has previously been shown that welding deformations depend on positioning errors prior to welding. Therefore, in order to evaluate the robustness of an assembly that is welded; variation- and welding simulation need to be considered in combination. For this, methods and tools need to be developed. In this thesis an interview study is performed that reports current issues and problems when simulating for robustness in plastic design. This led to a framework for descriptive studies for robust plastic design where part-, assembly and functional assembly are considered as different levels of robustness. This study influenced the focus of this thesis toward temperature and heat. A study on the combination of thermal expansion and variation showed that geometric variation is dependent on temperature. In order to evaluate the effect of variation in combination with thermal expansion a method and tool to simulate the distribution of stresses was developed. Including contact modeling in variation simulation considering thermal expansion was shown to lead to long simulation times in some instances. Therefore, a new contact modeling approach for variation simulation has been developed and shown to reduce simulation time significantly. A study focusing on rattle and squeak simulation showed that this is a further area where thermal expansion for the non-nominal geometry needs to be considered. In order to enable variation simulation of welded assemblies, a method called the Steady state, Convex hull, Volumetric shrinkage-method (SCV-method) has been developed in a number of studies, giving reasonable results. Also, the influence of using clamps to reduce the effect of variation on weld induced deformation has been studied.