| With the rapid development of science and technology, and the industrial upgrading of domestic manufacturing, the demand of CNC machine tools in China turned to high-end products. The proportion of medium and high grade CNC machine tools has risen every year. However, due to the big chasm in reliability between domestic and foreign products, a large number of imported medium and high CNC machine tools are needed, which hinder the development of domestic manufacturing seriously. The main cause that results in domestic CNC machine at a low reliability is that the key functional components are not reliable. As one of the critical functional components, CNC turret tool’ reliability directly affects the reliability level of machine tool. CNC turret tool breaking down will inevitably lead to machine tool breaking down and even stopping. So it is necessary to do the in-depth research on the reliability of CNC turret tool.Supported by the National Major Scientific and Technological Special Project, with a certain series CNC turret tool as the study project, this paper studies the reliability key technology in depth and systematically. The research findings have very important significance to improve the reliability of CNC turret tool. The main research contents of this paper are as follows:① According to product structure and working principle, the CNC turret tool was divided into subsystems, and the reliability model was obtained. Through analysing the factors that affect CNC turret tool reliability allocation, considering the knowledge of experts in many fields, and working on CNC turret tool reliability allocation by fuzzy comprehensive evaluation method, the reliability allocation quotas was gotten. Then the result was compared to the failure position frequency of similar products to verify the rationality of allocation quotas.② Structure Analysis and Design Techniques(SADT) was used to make functional analysis of CNC turret tool, and then product function motion was decomposed into element action. Assembly control points and detailed control measures for each element action were made and CNC turret tool reliability driven assembly process scheme was formulated. Then the SADT model of function analysis was transformed into corresponding Generalized Stochastic Petri Nets(GSPN) model with the capabilities of dynamic analysis and quantitative research. To make the quantitative research of the model, the isomorphic Markov chain was used. In order to obtain credible and accurate analysis model, the gray theory was used to express the rate of change in GSPN. As for the reliability characteristics of assembly product, the product was evaluated by using the assembly reliability index. Finally, a certain series of CNC turret tool was analysed with this model, and control measures were proposed to improve the assembly reliability of CNC turret tool.③ The adjustability technology was studied of CNC turret tool with the mainframe machine, including the reliability of screws connection when a turret was installed on the mainframe machine and the control matching between turret and CNC system. For the reliability of screws connection, the CNC lathe working conditions were analysed first to make sure the size and direction of cutting force, and then combined with the screws connection scheme that turret was installed on the mainframe, the screws group stress state was analysed and its pretightening force range was calculated. At last, a screws group tightened test was made based on the pretightening force range. As for the matching problem between CNC turret tool and CNC system, first the logical way to achieve two-way tool changing was determined, the tool changing operation flowchart was given, and the interface circuit diagram was designed between CNC turret tool control circuit and the CNC system. Then the high effective PLC programs were compiled. At last, the common control system failures of CNC turret tool were analysed, and the corresponding PLC alarm and handler programs were designed. |
PDF Full Text Request