Precision Reliability Modeling And Assessment Of Heavy-Duty Computer Numerical Control Machine Tools

With the rapid development of modern industry, the heavy-duty CNC machine tools play important role in advanced manufacturing processes. On the other hand, the performance of machine tools is also becoming increasingly demanding. Among many measures, reliability is an important performance of machine tools. The reliability issues of the heavy-duty CNC machine tools have been extensively studied and greatly improved in the past few years. The precision reliability as one of components of machine tool reliability has also been greatly enhanced. Since the last century, the heavy-duty CNC machine tools in China have achieved great progresses and the developing technologies become matured. However, the technological level is still far behind the most advanced products in the world. The manufacturing process and the reliability are the two key factors that restrict the development of the heavy-duty CNC machine tools in China. This thesis devotes to analyze the precision reliability of the heavy-duty CNC machine tools from the perspective of the manufacturing process and reliability assessment, which would be significant to the improvement of the performance and competitiveness of the heavy-duty CNC machine tools.To date, a variety of modeling approaches to the geometric kinematic errors of the heavy-duty CNC machine tools have been proposed. Among all of these existing approaches, the machine tool geometric/kinematic error models based on the multi-body system(MBS) theory have been extensively used. On the basis of the MBS theory, the thesis mainly focuses on three aspects, including the geometric errors modeling, the sensitivity analysis of the precision of processing and the precision reliability of the heavy-duty CNC machine tools. The major contributions of this thesis can be summarized as follows:(1) Establishing of a machining accuracy error model through the application of the kinematics of the MBS theory. In this work, the precision error models of the TK69 series heavy-duty CNC machine tools produced by the Qigihar Second Machine Tool Factory is developed by the MBS theory. The factors that influence the machining precision are very complicated, from many possible sources. The MBS theory allows for taking account of various factors and errors of the heavy-duty CNC machine tools in geometric modeling so as to facilitate the precision reliability assessment of the heavy-duty CNC machine tools.(2) Developing the sensitivity analysis method for the heavy-duty CNC machine tools. To identify the important factors or sources which yield significant contributions to the precision of the heavy-duty CNC machine tools, a sensitivity analysis method is developed in this work with which both the wear and tolerances of components can be considered and compared. The results of the sensitivity analysis can provide useful insight to the tolerance allocation in design stage.(3) Developing a Bayesian approach to precision reliability analysis of the heavy-duty CNC machine tools. To overcome the challenges, such as the limited data, in precision reliability assessment of the heavy-duty CNC machine tools, a Bayesian precision reliability assessment method is proposed in this work. Together with the degradation models of components, the precision reliability of the heavy-duty CNC machine tools over time can be evaluated and dynamically updated with collected condition monitoring data.