| With the development of science and technology, China’s CNC bending machinescontinue to make progress in terms of high-speed, high-precision, high automation, butis less developed in terms of reliability. Low reliability will not only affect the normalwork of the machine and the market share of the company, but also affect thedevelopment of China’s industrial technology. As a hydraulically-powered machine, thereliability of hydraulic system is the bottleneck of the CNC bending machine’sreliability, and the key of the bottleneck is the reliability of the cylinder-pistoncomponent which is an important part of the hydraulic system. Reduce the failure rateof the cylinder-piston component will greatly improve the reliability of CNC bendingmachine.With the support of National Major Scientific and Technological Special Project,the paper select the cylinder-piston component of some series of domestic CNC bendingmachine as the research object, and some research about reliability analysis and controlwere made on the object. The main contents of the paper are as follows:①To make reliability analysis on cylinder-piston component, its structure andfunction were analyzed firstly, then followed by FMECA, which results were the failurecourses and effects of some common failure modes and the most critical failure mode ofthe cylinder-piston component was the damage of the piston seal. Further analysis andcontrol research must be made on the failure mode of damage of piston seal.②For further reliability analysis and control research on the piston seal, a Markovchain model of a single contamination particle of the hydraulic system was established.Based on the model, the expression of MTTF of the piston seal was deduced andthrough the analysis on the expression, the two major factors that affect the MTTF ofthe piston seal were derived which were the fit clearance of the cylinder-pistoncomponent and the particle contamination of the hydraulic system.③In order to control the consistency of the fit clearance of the cylinder-pistoncomponent, technique of process capability analysis was used firstly to ensure the sizeof the component had a good consistency. And then an optimized match model thatbased on quality loss function was established to make sure the fit clearanceconcentrated around the ideal value. Thirdly, reliability-driven assembly technique forthe cylinder-piston component was made to ensure the component has a high reliability from the assembly level. At last, analysis and evaluation on the PSFs (PerformanceShaping Factor) of the assembly task of the cylinder-piston component was made basedon the AHP (Analytic Hierarchy Process) and expert judgment evaluation techniques,and the result of the analysis and evaluation helped identify the PSFs and their specialelements which mainly impact the assembly workers’ assembling error probability,meanwhile, some corresponding measurements where proposed to improve those PSFsin order to reduce the assembling error probability and thus improve the consistency ofthe fit clearance and reliability of the cylinder-piston component.④In order to control the oil contamination of the hydraulic system of the CNCbending machine, a mathematical model of the particle concentration was establishedfirst which revealed the relationship between the particle concentration and invasiveratio of the particle. Then use FTA (Fault Tree Analysis) techniques to find the rootcauses of the hydraulic oil pollution. Finally, some control strategies for hydraulic oilpollution were proposed from the perspectives of users and manufacturer: users shouldtake proactive maintenance as their main hydraulic oil pollution control measurement,but combined with preventive maintenance and predictive maintenance; Manufactureshould take the TCC (Total Cleanliness Control) strategy which is similar to TQM(Total Quality Management) to control the hydraulic oil pollution. |
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