| CNC machine tools are integrated high-tech modern manufacturing equipment,at the same time,they are able to reflect a country's overall strength.However,the majority of domestic high-end CNC machine tools are also dependent on imported products,which has been a bottleneck restricting the reliability of domestic CNC machine tools to high-end,although the Mean Time Between Failure(MTBF)indicator of most mainframe products in China has increased from 500 hours to more than 900 hours,however,compared with the same type of machine tool abroad,its reliability level at least doubled.The low level of reliability not only causes unnecessary downtime during normal use.thus reducing production efficiency,but also brings great maintenance costs to the machine tool manufacturing enterprises,what is more,the domestic machine tools show no solution situation in the competitive market.Therefore,it is urgent to improve the reliability of domestic CNC machine tools.This article relies on the national "high-end CNC machine tools and basic manufacturing equipment,“science and technology major project”machine tool manufacturing process reliability assurance technology research and application"(project number: 2016ZX04004-005),with a CNC grinding machine(YK7332A)of a domestic machine tool enterprise as the research object,the principle of minimum statistics is adopted to select the optimal reliability evaluation model.The reliability analysis method is used to determine the key components that affect the weakness of the machine tool,The reliability optimization and analysis were carried out by using ANSYS,which improves the reliability of the key components,ultimately,it has a certain contribution to the improvement of the reliability of the whole machine.The main contents of the dissertation include the following:(1)Interquartile range(IQR)method is used to identify the outliers of fault data,and the distribution type that the effective fault data may obey is preliminarily judged.Secondly,using MINITAB to draw the probability map of the hypothetical distribution model to realize the optimization of the fault distribution model,the maximum likelihood estimation method is used to determine the exponential distribution of machine tool obeying the failure rate is ?(28)0.00213,the rule of the reliability characteristic quantity of machine tool has been mastered,which provides the reference basis for the designers to improve the reliability.(2)Failure Mode and Effect Analysis(FMECA)is carried out to analyze he fault location of the machine,failure mode,analysis of the cause of the malfunction,and the frequent fault parts of the machine are found.Using the mathematical model of importance to determine the spindle system as the most core subsystem in the whole machine,and then combine the Fault Tree Analysis(FTA)and Analytic Hierarchy Process(AHP)to determine the key failure factors affecting the electric spindle system and the key functional components(spindle),and proposed reliability improvement measures to improve the reliability of machine tools.(3)By ANSYS Workbench analysis to determine the actual spindle failure mechanism is the lack of static stiffness,therefore,a spring unit(Combin14)with tension and compression is established instead of bearing support.The static and dynamic characteristics of main shaft under actual working conditions are analyzed.In order to improve the dynamic and static performance of the electric spindle,genetic algorithm response types of response surface optimization is adopted,and the first natural frequency is increased by 9.65%,which has better dynamic and static performance.(4)In consideration of the influence of the random variables(structural geometry,external load,material performance and bearing stiffness)on the static stiffness of the motorized spindle,Sensitivity and correlation analysis of random variables by using the 3sigma principle in ANSYS Workbench,finally,the Latin hypercube sampling method was used to sample random samples,the results show that the reliability of the optimized electrical spindle structure is improved from 87.731% to 99.99%,which ensures the optimized electrical spindle has higher reliability. |
PDF Full Text Request