Joint Design Of VSI T_r Control Chart And Equipment Maintenance In High Quality Process

With the increasing attention to product quality in the market,consumers are demanding products with both low price and high quality instead of blind pursuit in low price,which brings challenges of quality and cost control to manufacturing enterprises.As the most commonly tool in statistical process control,control chart can monitor the fluctuations of quality to judge whether the production is in controlled.With the development of technology and the improvement of production standards,modern production is often a high quality process with low defect rate where traditional counting control charts are no longer applicable.Abnormal fluctuations are often caused by external factors,among which decline in equipment performance caused by continuous production is one of the important reasons for process out of control.Therefore,a good status of equipment can improve the stability of product quality.However,control chart only carries out production management for quality,ignoring the influence of equipment.Although equipment managers can maintain its status through planning maintenance,they cannot observe all decline in equipment directly in actual production.As a result,they are required to make maintenance decisions based on experience,which can be improved in modern production management.Based on high quality process,this paper designs a joint model of variable sampling intervals T_rchart and equipment maintenance,which transforms the unobservant internal state of equipment into observable product quality fluctuations,monitors through control charts,infers equipment status and takes maintenance measures to achieve product quality,realizing a comprehensive management of quality and equipment maintenance and reducing production costs.The main research contents are as follows:Firstly,it uses VSI T_rchart(a control chart of time between events)in the joint model in high quality process.It applies variable sampling intervals(VSI)strategy to T_rchart,deducing the design of VSI T_rchart under Gamma distribution and the average time to signal(ATS)as the evaluation index,and analyzing the statistical performance of VSI T_rchart.Through the analysis of process shift,sampling intervals and shape parameter,it finds that ATS of VSI T_rchart is always smaller than that of T_rchart with fixed sampling interval(FSI)strategy,that is,VSI T_rchart can detect process shift faster than FSI T_rchart.Secondly,it constructs a joint model of VSI T_rchart and equipment maintenance for production system that conforms to the mixed failure mechanism.It considers the transformation relationships among“in controlled”,“potential failure”and“shutdown failure”of equipment.Based on delay monitoring,it derives the calculation of expected cost of unit time(ECT)under nine scenes.After that,it employs Monte Carlo simulation to verify the accuracy of scenes probabilities of the model.Through orthogonal experiment,it carries out a sensitivity analysis of 14 parameters and concludes the effect of parameters on ECT.Finally,it solves the joint model of VSI T_rchart and equipment maintenance through a case,comparing it with the independent model and a joint model without delay monitoring to analyze its performance and verify its effectiveness in reducing the ECT of high quality process.