| Heavy-duty CNC machine tools are complex systems with some coupled components and subsystems, which leads to great difficulties in their design optimizations. This problem may be solved by applying multidisciplinary design optimization (MDO) methods that can consider the interactions between coupled disciplines. Using MDO approaches in Heavy-duty CNC machine tool design has real significance in promoting the designers' capabilities in design and creation.Supported by the National "863" High-Tech Development Project of China under the grant No. 2007AA04Z136 and National Natural Science Fund under the grant No. 60573178 and 60736019, some key problems are studied in the MDO applications to heavy-duty CNC machine tool designs. The researches involve establishment of MDO model of the overall design, disciplinary mathematical modeling and MDO problem solving.The MDO methods and technologies are reviewed. The development situation of heavy-duty CNC machine tools is also discussed. Taking heavy duty CNC vertical turning mill as the research object, MDO modeling problem of the overall design is introduced and studied, and its MDF, IDF, CO and BLISS models are given subsequently.Aiming at the difficulty of statically indeterminate problem, i.e., the hydrostatic pressure calculation of multipad hydrostatic guideways sustained complex spatial forces, under an assumption that stiffnesses of guideways and their jointing structure are sufficiently large, a new approximation method is presented by taking co-planarity/co-linearity equations that constrains pocket centers as compatibility conditions. Then, the disciplinary analytical model is constructed by the approximation method for hydrostatic pressure calculation of beam & slide-rest guideways in a heavy duty CNC vertical turning mill. Based on this, hydrostatic system of the beam & slide-rest guideways is optimized by metamodeling technology.The new approximation method of hydrostatic pressure calculation is also used for tool head system design of the machine tool, and an accuracy calculation model of finish machining is constructed for the tool head. On the basis of this, MDO model of the tool head system is set up. The MDO problem is high-order, multimodal and nonlinear whose global optimum is only located in such a narrow and irregular area that it is difficult to find the solution using metamodeling technology and heuristic methods. To solve this problem, a metamodel-based design space alternation (DSA) strategy is proposed. In this strategy, metamodels are created in the narrow area of interest; then, heuristic exploration in the narrow area and local search in global design space with metamodels, system analysis and metamodel updating are sequentially executed in every iteration cycle until the convergence criterion is met. The DSA strategy is applied successfully to the tool head MDO problem and its global solution is obtained.Mathematical modeling of hydrostatic pressure calculation for worktable guideway considering fluid-structure coupling and MDO of worktable in a heavy duty CNC vertical turning mill are studied. In the case that the worktable spindle is in a state of floating in z direction, it is difficult to set the constraint of the spindle part in z direction when finite element methods are used to analyze its deformations. To address this issue, a new method is proposed to predict the rigid displacement of the worktable and a novel correction-improvement method is presented to iteratively calculate hydrostatic pressures. Thus, the oil film thickness and hydrostatic pressure in each pocket are obtained. The new correction-improvement method is also suitable for the case that central unloading device or floating restriction device is active. Then, an optimization model is built including structural analysis and hydrostatic pressure calculation disciplines which are coupled bi-directionally. The optimization problem is solved using the concurrent subspace design (CSD) method and its global optimum is attained. |
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