Högskolan i Skövde

This thesis is a framework for evaluating fixture performance in a virtual environment addressing the need for precise prediction of final from errors. By doing so, the aim is to provide a solution where shortcomings in fixture designs can be identified and rectified upfront, ultimately saving valuable resources that would otherwise be spent on physical fixture production. A major challenge in machining is chatter vibration, influenced by the vibrational characteristics of a system and outside stimuli. Bolted joints are difficult to simulate due to micro slip and nonlinearities but at the same time they contribute with the 90 % of the damping of the whole system. For validating the FEM models, an experimental set up has been build up with a hammer as exciter and an accelerometer including two main configurations, mounted on table and on foam, with metal and plastic tips, and 100 g and 150 g hammer masses. Furthermore, some other tests have been made to determine precisely the material characteristics of every part (for instance, the density of the sheet is 7.75 g/m³ and its Young’s Modulus 213 GPa). The similar behaviour of hammer masses and material types was found to allow rationalisation of future tests. Three level dynamic models have been developed, increasing in complexity from simple boundary conditions, to a non-linear hole model with sliding interactions and a bolt connection. Although the more complex the model the more accurate results are obtained for stiffness, natural frequencies and damped period within an error of 20 %, the damping behaviour of the sheet is not captured accurately enough. Because of that, this is not a sufficient model, although it is enough to settle the bases for a more accurate model with the goal of eventually obtaining a perfectly matching one that can be compared with reality.