Reliability growth rate calculation method for hydrostatic spindle of heavy-duty machine tool using analytic network process

Aiming at the problem that the difference of the equipment between before and after implementation of reliability growth technology is not considered in calculating reliability growth rate of computer numerical control machine tools, this article takes the hydrostatic spindle of the heavy-duty machine tool as an example and introduces the concept of "net growth rate" to propose a new method to calculate reliability growth rate. First, based on the value of mean time between failures of the whole machine before implementation of reliability growth technology, a model of the "net growth rate" of the whole machine is established. Second, the reliability relationship between the whole machine and the subsystems is established through the reliability block diagram, so the problem is transformed into solving the value of mean time between failures of the subsystems. Then, a superposition model of "net growth rate" of subsystems is established by making full use of experimental data and product information. When dealing with product information, multiple factors including composition structure, design requirement, manufacture and assembly, and use environment which influence equipment reliability are considered comprehensively and analytic network process is employed to obtain the weights of the influencing factors. Based on the weights, the reliability comprehensive scores which can reflect the reliability level in the corresponding design, manufacturing, and use environment are calculated and the reliability growth rate caused by the differences of the equipment is solved. In order to add ambiguity of human judgment, interval numbers are applied to network analysis process models. Finally, this article verifies the feasibility of the proposed method with an example.