HIGH STIFFNESS CLOSED-FORM KINEMATIC STRUCTURAL DESIGN OF A LOW-COST 4/5-AXIS MICRO/MESO-SCALE INVERTED HIGH-SPEED MACHININGCENTER

摘要

The demand for miniaturized components is increasing in various industries, such as the biomedical, consumer electronics, optics and defense-related industries. The production of the micro/meso-scale components and parts in these industries is typically undertaken using MEMS-type photolithographic production techniques that have limitations in the materials and geometries that can be produced. However, numerous research efforts during the course of the last five to ten years have developed micro-scale EDM processes, micro-laser processes and micro-machining operations. In particular, the micro-machining processes have been demonstrated to provide a credible solution to the production of micro/meso-scale parts with complexes geometries in a broad range of materials. The development of mMTs is growing with the rapidly increasing demand for tighter tolerances. Traditionally, mMTs have been developed based on horizontal or vertical Cartesian co-ordinate machine tool structures. However, as the need for increased process flexibility and productivity is continuously being driven higher, there is a need to develop higher degree of freedom machining systems, including 4-axis and 5-axis machining centers. In this paper, the design of a low-cost, high-precision, high-speed 4/5-axis micro/meso machining center is presented as a cost-competitive alternative to existing open-form kinematics precision machining centers. A key departure from traditional machine tool design approach that has been adopted in this design is the utilization of closed-form kinematic structural design to create a high-stiffness, low-cost machine tool base. In addition, the lower thermal mass of the mMT base enhances rapid thermal washout in the structure and significantly reduces the thermal gradients in the structure. Consequently the thermal errors present in the structure are limited and simply and adequately handled using existing error compensation strategies. Initial results from an analytical and numerical investigation of the thermo-mechanical response of an innovative, kinematically closed-form inverted micro-machining center are presented. A coarse resolution parametric study was undertaken to evaluate the preferred preferred design space for maximum stiffness and minimum thermal distortion in low-cost, high precision, high-speed micro-machining centers. In addition, in order to facilitate part loading and unloading operations will be considered as a key design characteristic. A key result of this study has been the identification of a preferred design space for kinematic form selection, material selection and structural design options for increased rigidity, reduced thermal error and reduced production costs for flexible 4/5-axis micro/meso-scale machining centers. The proposed mMT design achieves a 3X increase in rigidity over a comparable tradition kinematically open horizontal mMT system