Research On Reliability Improvement Technology Of Crankshaft Grinding Automation Flexible System

China's economic structure is facing a critical period of strategic transformation.Automobile manufacturing industry has developed into a pioneer of leading the transformation and upgrading of traditional manufacturing industry,and has gradually become an important support of China's national industry.China's automobile production is increasing year by year,however almost all the domestic high-grade engine production lines utilize imported equipment,and most of the mainstream engine production lines have entered the renewal period,a large number of equipment needs to be updated.Therefore,how to make full use of domestic high-grade CNC equipment,renovate the existing production line and even set up a new production line with independent intellectual property rights is very urgent.In order to research and develop the automatic engine processing system independently,we must overcome the technical problems such as reliability assurance technology under the condition of efficient processing and continuous operation,so as to break the monopoly position of developed countries in the high-end automatic production line industry,reduce the production cost of domestic high-end automobiles,improve the ability of Chinese manufacturing enterprises to provide outfits of equipment for users,and improve the international competitiveness of China's automobile manufacturing industry.Based on the 2016 National Science and Technology Major Project of China "Demonstration project of high efficiency flexible unit for automotive engine crankshaft grinding automation",this paper focuses on the research of reliability improvement technology of crankshaft flexible production line,and the main research work is as follows:(1)The processing equipment,technological process and system layout of crankshaft flexible manufacturing system were analyzed.Based on 234 equipment failure and maintenance data collected on site,the reliability indexes such as productivity,failure rate and maintenance rate of each processing equipment in Flexible Manufacture System(FMS)were analyzed.Based on the characteristics of crankshaft grinding system,the Markov state transition diagram and state transition matrix of FMS were analyzed by using Markov process theory,and the steady availability of FMS with buffer zone was discussed.Then,based on the theory of Petri net,the Generalized Stochastic Petri Net(GSPN)model of FMS was established and its working principle was described.The Markov chain with 16 dominant states was constructed.The steady state probability of various working states was studied by solving the excitation rate matrix of degenerate embedded Markov chain,furthermore,the inherent availability of crankshaft FMS was discussed.(2)To comprehensively analyze the operation characteristics of mechanical and electrical system maintenance such as the maintenance as old of the crankshaft flexible production line,the reliability of production system was defined,six commonly used operation methods of serial system reliability index(MTBF)were summarized,and then all of the six algorithms according to the operation data of the system were calculated.The results were compared and analyzed accordingly.(3)Two kinds of reliability-growth-prediction models based on delayed correction strategy were studied: AMSAA prediction model and AMPM Stein-prediction model.According to the different subsystems,the fault data were reorganized,the Steincontraction factors of each group were solved,the Stein estimates of the failure-strength function of each subsystem were calculated,the failure strength-prediction values of the whole system were derived,and an AMPM based on similar failure mechanism and maintenance strategy was proposed.The robustness of the new model was verified based on Relia Soft's reliability data.Based on the different failure mechanism and maintenance characteristics,the CNC grinding machine participating in reliability growth test was divided into five subsystems,and the application of the new prediction model was demonstrated through three stages of reliability growth test.(4)Two kinds of continuous system reliability-growth-planning models,PM2 model and CE model,based on the delay correction strategy were studied.The sensitivity of the parameters of the two models was analyzed.The results showed that the overall test time of CE model is inconvenient to control,and PM2 model cannot correctly reflect the influence of the changes of the model's parameters on the growthplanning curve.The lower limits of the parameters in PM2 model,such as management strategy,fix effectiveness factor and initial MTBF of system were analyzed,and the lower limits of the product of management strategy and fix effectiveness factor was discussed.Based on the negative correlation between parameters,300 sets of simulation data pairs were generated by MATLAB,data fitting and model solving were carried out by using curve-fitting module,a non-linear mathematical equation describing the test duration by management strategy and fix effectiveness factor was constructed,and the constant coefficient recommended value of 95% confidence interval was given.Based on this mathematical equation,an extended PM2 programming model without test duration was proposed.The validity of the new planning model was verified by the 4 200 hour reliability growth test of a company's crankshaft-handling system.(5)The function relationship among equipment reliability,equipment-repair rate,equipment productivity and cost were established.The objective function was the lowest improvement cost of the crankshaft FMS,the established function expressions and buffer capacity unit cost were the constraint conditions.The functional relationship among test duration,fix effectiveness factor,management strategy and cost were established.The distribution model of equipment reliability growth based on reliabilitygrowth-planning technology was established with the minimum cost of equipment reliability improvement as the objective function.By using the genetic algorithm with global-optimization function,the target MTBF of the flexible manufacturing system is not less than a special value and the cost of system reliability improvement is not more than a special value.The reliability optimization assignment of the crankshaft flexible manufacturing system was studied,and the direction of reliability improvement of the crankshaft-flexible-manufacturing line is pointed out.Taking the target MTBF of the equipment not less than one special value and the cost of equipment reliability improvement not more than one special value as the optimization target,the optimization work of reliability growth test for the equipment OP110 was studied,which provides the basis for the reliability-growth test for designing the processing equipment.