Design, manufacture and performance evaluation of a machine tool ram based on a steel/foam sanwich structure

Because of their interesting damping properties, aluminum foams are widely considered a promising material for applications in which the dynamic behavior of a mechanical structure needs to be improved [1]. The present work focuses on the application of an innovative kind of composite foam, the Hybrid APM foam, used to improve the overall dynamic performance of machine tools structures and in particular of milling centers steel structures. Hybrid APM foams were chosen as a filling material because they have been proven [2] to be able to enhance the performance of smaller but comparable steel structures and because the foaming phase can be easily integrated in the well-established manufacturing process of welded steel components [3]. The machine tool analyzed in the present study is LinX Compact 20 produced by Jobs, one of the most important Italian machine tool manufacturers. LinX is a high speed 5-axis milling centre (Fig. 1) with mobile crossbeam characterized by linear motors on linear axes. The transversal axis stroke (Y) is 2000 mm, the vertical stroke (Z) is 1250 mm while the longitudinal stroke (X) is modular up to 8200 mm. The machine can be equipped with a wide range of milling heads, specifically designed for car design & prototyping, high power machining for aerospace industry and mould and die machining. Even if the use of a damping material is a core part of this work, its main goal is the development of an overall redesign strategy of the machine tool structure, focusing on the maximization of performance indexes directly related to customer needs identified for the specific machining centre, i.e. increasing the material removal rate for steel roughing and tracking accuracy for finishing operations. This strategy goes through few phases: experimental measurement of the current performance of the milling centre, identification of the critical issues and components limiting the indexes, FEM assisted re-design, prototyping, performance reassessment and economic evaluation of the improved performance indexes. The performance assessment on the LinX, both original and foam filled, was carried out using milling tests, to determine the maximum achievable depth of cut for a selected operation, and a tracking test, to measure the maximum deviation from the nominal trajectory. An experimental modal analysis was then performed on the original machine in order to identify the critical components. These components were redesigned using FE models and structural optimization. The resulting preliminary redesign was then extensively discussed and revised in close collaboration between JOBS spa, and MUSP laboratory in order to ensure the feasibility of the components and their integration with the existing structure. The new components were then prototyped by JOBS and foamed at MUSP Laboratory. Finally, a new complete series of tests was performed on the assembled milling centre, allowing a comparison with the original machine. Economic aspects involved in the manufacturing of the new components were also critically evaluated.