PRODUCT INNOVATION NEEDS IMPROVED DESIGN PROCESS OF SCREW JOINTS

An essential task in today's engineering is to realize a multifunctional design which needs an optimization process to achieve highest performance (load profile), minimized energy consumption (fuel, gas, electricity in production and life time of product) and maximized sustainability (during entire life cycle from idea to end of life) at an affordable prize in combination. Another point is that the performance of products is increased steadily up to now, which shifts the load profile towards higher peak loads. Consequently, a related design methodology is necessary which takes into account modern techniques of CAD (Computer Aided Design) and FEA (Finite Element Analysis) besides analytical engineering calculation and testing. Also the inclusion of nontechnical aspects must be possible (e.g. experience, rating of economy). Besides this the local stressing, time dependency and non-linear behavior must be considered in more detail; examples are proposed below. This methodology can be illustrated very well for the example of screw joints in products with high mechanical loading between components. Established technical literature mainly refers to pure technical aspects of bolted joints, e.g. [1, 2, 3]. Another important aspect for modern products is the increased use of mechatronic functions (mechanical system added by sensors, actuators and controller as well as controlling software). These functions raise the variety of failure modes significantly, which requires improved reliability. The paper describes, how screw joints are affected, because the number of screw joints increases and that engineers have to use reliable design methods to develop robust products. Looking to the packaging of mechatronic products, smaller screws joints are used because of space restrictions coming from the high number of components. In the end this means higher stressing of smaller screws. Countersunk heads offer benefits regarding space requirements, but need to consider positioning tolerances. For optimization process always non-linear relations are challenging; they need special description of the mechanisms and increase the demand for quality of the optimization method (e.g. convergence of numerical methods). Conclusions from this result in fastening perspectives for the design of innovative products for the future (automation of engineering design for fast product development considering complex interactions).