Early Fault Elimination Technology Research In Vertical Processing Center

As one of the pillar industries in China,the quality and production efficiency of key components is directly related to the dynamic,economical and environmental protection of automobile.As one of the main machine tools for automotive powertrain components,the high precision,high efficiency and high reliability of vertical processing centers are our goals and the basis for upgrading the automotive industry.The reliability of foreign processing centers has reached a high level,however,the domestic processing center in the early stage of use of frequent failures,has been restricting the machine tool industry and the automotive industry from the mid-end to high-end development,so the elimination of vertical processing center early failure,improve its reliability has been urgent.Based on the Chongqing Science and Technology Commission’s “Key Components of Automotive Power System Processing CNC Machine Tool Efficiency Technology Development and Application” project(project number: cstc2017zdcy-zdzxX0005),a machine tool enterprise in Chongqing produced vertical processing center(VTC-32S)as the research object,The reliability model matching the fault data is established by the statistical test law,the early fault period of the machine tool is determined,the failure mode effect and analysis(FMEA)and the fault tree analysis(FTA)technology are combined to determine the serious fault mode of the early fault period and the important bottom event that causes the corresponding early failure.For the subsystem with frequent failures,the early fault test scheme is designed and the corresponding test is carried out,and the assembly accuracy of the assembly process is analyzed.The main research topics include the following aspects:(1)Vertical machining center failure rate curve modeling.The independent homogenization test of machine tool fault data is used by statistical test method,and the fault data conforms to the non-homogeneous Poisson process(NHPP)of the random point process,the trend test is carried out by graph inspection method,the fault data is further determined to conform to the bathtub curve model in NHPP.Several types of tub curve model parameters that may conform to fault data were solved by the expectation maximization algorithm,and the bathtub bounded intensity process(B-BIP)model was determined by the Akaike information criterion(AIC)and the fit goodness R is the optimal model,thus determining the early failure period of about 1588 h.(2)The structural division of vertical processing center and the analysis of early fault.According to the early fault period,the fault data in the early fault period is calculated,and the automatic tool changing(ATC)system is a subsystem with frequent failures,and based on the group analytics hierarchy process(GAHP)and the technique for order preference by preference to ideal solution(TOPSIS),an early FMEA analysis model is established to obtain “geometric precision exceeding the standard” is the most serious failure mode.According to the fault statistics,the “Z-axis verticality” as the top event,the qualitative and quantitative analysis is carried out by the downstream and fuzzy evaluation methods,and the low assembly accuracy of components is an important bottom event leading to the top event.(3)Early troubleshooting tests for automatic tool changers based on load spectrum.For the automatic tool change(ATC)system with frequent failures,the actual operating condition information is collected,and the relative weight spectrum of a single-tool that obeys the normal distribution of two-pair positive stakes,the relative weight spectrum of the tool library that obeys the Weibull distribution,and the two-dimensional load spectrum that obeys the Joint Function of Clayton Copula;The design of early fault test scheme according to the two-dimensional load spectrum,including graded load table,task profile and so on.Finally,through the analysis of the test results,the corresponding corrective measures are taken.(4)An analysis of assembly accuracy based on the state space model.The assembly link is the final link of the whole machine quality formation,its assembly accuracy directly affects the performance of the whole machine,so the first part assembly deviation transmission analysis is carried out on the basis of the theory of small displacement torsors(SDT),and then the state space model of the machine assembly process is established by taking into account the effects of part processing error and its own gravity caused by deformation.Finally,the assembly precision analysis and calculation is carried out for the Z-axis verticality of the machine tool.