Towards automated design of fastening systems for accelerated product development

Copyright © 2014 by ASME. Although considered a well-established machine element, screw fastening systems are required to fulfill ever increasing demands for performance, reliability, economy, and sustainability. Yet there are limitations to the capabilities of existing design procedures which often neglect a comprehensive analysis of both soft and hard design parameters over the entire system life cycle. This paper presents a holistic approach towards automated design of screw joints, going beyond established methods by incorporating soft (intangible) design parameters additionally. Based on the vectorial design method developed by Friedrich, a multi-objective optimization process is used to tradeoff various, often conflicting design parameters from the vectorial design approach (such as screw diameter, assembly method, preload loss, material strength, etc.) to derive an optimum solution with a high level of confidence. For this, a complex network of strategy parameters and safety factors is used (optimization parameters). It is referred to geometry, material, contact, assembly and production for boundary conditions. A definite solution for the model of the fastening system must incorporate analytical functions, numerical relationships and correlation with technical and nontechnical aspects (including cost and environmental impact). This multi-objective approach entails inherent flexibility enabling designers to set application specific design priorities as a key part prior to defining an optimized solution. Overall, this gives the capability for an automated design process, which can be performed with computational engineering. A major benefit from this is saving product development time and therefore cost as well as evaluating influence-intensity of design parameters (rating of influencing values). An example of a wheel bolt connection is provided to demonstrate this approach referring to a well-known application. From this it is outlined that conflicting safety factors lead to an optimum which is determined by the level of reliability or performance. The presented process offers considerable benefits in reduced development time particularly for complex, customized fastening systems, reducing unnecessary design iterations and empirical testing. The following process is intended to give a modern structure for fastener selection procedures linked with computational engineering capabilities and design experience