Machine tool design optimization considering thermo-mechanical behaviour in the structure and at the interfaces

The structural performance of a machine tool is affected strongly by structural connection elements such as bearings, ball-screws, and guides which are generally accepted as the most flexible components in complex assemblies. These structural connection elements in contact regions deliver loads between structural components, which can result in deformation. These contact regions are important thermally because the evaluation of the thermal field is related to deformation and dissipative mechanisms such as friction. Thus, deformation and temperature interact with each other in these contact regions, and these problems are classified as thermo-mechanical contact problems. A topology optimization with contact constraints significantly impacts the structural behavior of the entire assembly. The static and dynamic compliance can be reduced, and these improvements can be extended to the thermal behavior of the machine tool by considering thermo-mechanical contacts on these structural connection elements. In particular, spindle bearings are one of the major heat sources that affect the total thermal deformation in a machine tool structure. In this study, thermo-mechanical contacts are considered to optimize a machine tool for the best structural performance. A novel thermo-mechanical contact model is proposed for machine tools. The proposed model is coupled with topology optimization methodology, and the optimization problem with thermo-mechanical contact constraints is solved for two objectives by using gradient search algorithms. A milling machine was loaded thermally and statically by considering the thermal effects of spindle bearings and heavy cutting conditions. First, the structural performance of the machine tool assembly was investigated for the minimum thermal compliance by employing the proposed contact model according to the loading scenario. Then, the same procedure was applied for the minimum static compliance. As a result, an approximately 27% mass reduction was achieved while maintaining thermal and static structural stiffness values for all axes.