Translated Abstract
Lacking of high speed precise CNC machine tools has become a restricting "bottleneck" in the upgrade of China's manufacturing business, it has significant meaning to improve the machining accuracy of CNC machine tools, and to narrow the gap with foreign-made machines for improving the market share and revitalizing China's equipment manufacturing industry. With advances in designing, manufacturing and assembling technology of parts, the static geometric precision of China-made high-end machine tools has come close to the international standard, hence in the meantime, thermal error induced dynamically in machining process has become a major source of high-speed precise CNC machine contour error, and significantly reduces the machining accuracy. Therefore, the research on the generating mechanism of CNC machine tool thermal error, the error suppression strategies and the compensation techniques, has important theoretical and engineering application value to improve the precision of CNC machine tools.
According to the problem of thermal error of formation mechanism for the assembling of dual–drive servo feed system, transient simulation analysis of thermal behavior of the machine tool is proposed. Heat dissipating and transferring laws in the feed system and the motorized spindle are studied, heat conducting partial differential equations of transient temperature field of a machine tool is established, and a numerical approach for transient temperature field based on Galerkin weighted finite element method is given. Secondly, the thermal-elastic equations of the machine tool is duduced, and the transient thermal–structural coupling finite element analysis model of the machine tool is also built. Gives a precise prediction model driven by the working condition parameter of the heat generated by the inner heat source , and introduced a contact resistance fractal model based on fractal theory and Monte Carlo method, have calculated the boundary conditions of thermal contact resistance and convective heat transfer coefficient.The method heat production power of rolling bearing based on contact angle iterative method was proposed,improved the traditional Newton-Raphson algorithm bearing pseudo-static school low precision and slow convergence flaws, effectively improve the convergence speed and simulation precision. Thermal performance test show that the established model can accurately describe the dynamic heat transfer characteristics of the CNC machine tool, realize the feed system with motorized spindle temperature field/thermal deformation field of quantitative analysis.
An measurement method for testing thermal characteristics of the whole machine is proposed to investigate the thermal errors and the temperature field of machine tools under different working conditions. Based on the accomplishment of the soft/hardware design of the measurement system, some important parameters (such as the spatial location of thermal error, the temperature of the whole machine and the heat sensitive point of its key parts, the grating scale signal and heat transfer coefficient) are under the online synchronous measurement, which solves the problem that the spindle radial hot dip angle is beyond the measurement with the three-point method and consequently provides a base for the traceback and modeling of the thermal error. Additionally, a large number of heat balance tests were performed to study the time-domain characteristic and its evolution of thermal error and the temperature field of machine tools under different working conditions for the precision coordinate boring and milling machining center and the big car milling compound machining center. It was mainly focused on the influence of the dual drive structure, the master-slave motor synchronization, the feed speed/spindle speed, the multi-axis linkage, the beam position and the pre-tightening force and the control mode on the thermal characteristics of machine tools, and at the same time, the improvement project of machine tools was proposed to improve machining accuracy. The work above provides an important test support for the validation of the machine tool thermal error theory model, the optimization of the thermal symmetric topology, the intelligent control of the cooling system and the modeling/compensation for the thermal error.
Aiming at the defects of ignorance of the radial thermal inclination error and the problems in temperature measuring points optimization for thermal error in the spindle system, variable temperature grouping and optimization strategies are proposed, four thermal error modeling methodology are put forward, and an evaluation criteria for thermal error prediction model is established. Inherent mechanism of spindle thermal characteristics and prediction models are revealed, physical relevance of the timing model and spindle thermal errors are explained. The results indicate that the packet optimization strategy can effectively reduce the dimension of arguments, lower the temperatures multicollinearity between temperature variables, improve stability of the thermal error prediction model, the model can also accurately predict the axial thermal elongation, radial thermal wobbling angle error and thermal pitch angle error.
According to the the imprecision of thermal error compensation functions and the difficult issues of compensation thchnology in idustrial aplications , a systemactic set of thermal error compensation stategies are proposed.Mechanism of the effcts of thermal error of motorized spindle on maching accuracy is revealed, the thermal error compensation comprehensive equation is deduced, the model contains the axial thermal elongation, the radial thermal wobbling angle error, the thermal pitch angle error and the variables of length of the cutting tool, hence the imperfection of impresion and lack of versatality of the compensation equation based on three-points method is resolved,the precise prediction of the motorized spindle system is achived.Secondly, thermal error compensation equation of the feed system is also built, relationships between the feed function mapping error and the screw axis thermal characteristic temperature , and between the thermal equilibrium time and the coordinate positions are effectively characterized. At last, a thermal error compensation system of CNC machine tools is developed, a thermal error compensation module is designed based on the Siemens 840D system, and the feedback interruption integral method is applied to achieve the real-time compensation for thermal errorof the precise coordination boring and milling machining center, hence effectively improve it’s machining accuracy.
In summary, this paper presents a systematic set of methods to study the thermal characteristics of the CNC machine tools,including the mechanism analysis,the testing technology, the modelling methods and the compensation technology.The maching accuracy CNC machine tools is at last improved together in 2 levels of theoretical analysis and engineering application, an useful reference for thermal equillibrium designing and thermal error compensation is provided.
Corresponding authors email