The Research On Reliability For Framing Fixture Switching System Of Automotive Flexible Welding Line

With the continuous development of automobile industry in our country and under the state requirements for the transformation and upgrading of the manufacturing sector,Body in white flexible welding production line has become the development direction of automotive welding.The higher flexibility degree of the welding line,the more complex structure of the system.The BIW framing fixture switching system is one of the most important and complex part of flexible welding production line,so it's reliability is paid urgent attention by auto companies.With the complexity of system continuous improving,the reliability research become more and more difficult,many of the existing reliability assessment methods can't meet the engineering requirements gradually in some cases.In engineering reality,it exists the problems that system structure is very complex,experimental analysis is very difficult and subjectivity of reliability assurance and improvement program is too strong in the reliability research of framing fixture switching system.Aiming at the above problems,the research work of this thesis that the reliability of the framing fixture switching system are as follows:(1)Elaborating the concept,characteristics and key technologies of automobile flexible welding production line.Taking the latest type of framing fixture switching system of a car company in Chongqing as an example,the work flow,structure and function of each part were introduced.(2)Based on the modularization of functional decomposition,framing fixture switching system is decomposed modularly and the functional decomposition model is established,and the failure modes of the modules in the functional decomposition model are analyzed respectively.According to the results of the failure mode analysis and combing the logical relationship between the various failure modes,the dynamic fault tree model of the framing fixture switching system is established.(3)A method of converting hot spare gate to and gate is proposed,and the dynamic fault tree of the framing fixture switching system is converted to static fault tree.The minimum cut sets and the structural importance of the bottom event of the system fault tree are solved through the BDD(Binary Decision Diagram)method.Considering the engineering reality situation of the enterprise,a method for determining the failure probability of bottom event based on fuzzy expert evaluation is proposed to solving the problems that the uncertainty and trial missing of the bottom event of fault tree.The analytical solution of the occurrence probability of top event and the importance of bottom event of system fault tree are calculated,and recommendations for reliability improvements are put forward according to the solution.(4)For the problem that the system reliability degrades significantly after working for a period of time,a reliability improvement program of positioning subsystem based on precision on-line detection is proposed and designed.The condition of the system is determined by monitoring the positioning accuracy using sensor technology,so the decisions of dynamic maintenance are made according to the condition,achieving the purpose of improving system reliability.