Research On Key Indexes And Technical Specifications Of Dynamic Quality Inspection Of Mechanical Assembly By Inverse Substructuring Method

Mechanical assembly quality influences directly the quality of a whole electro-mechanical product.Its inspection is an important part of quality assurance(QA)of complex electromechanical products.Nowadays,modern mechanical manufacturing is being developed towards light-weight,high speed,efficiency and precision,and intelligentialization.It requires higher on the quality inspection of mechanical assembly.How to set up a simple normative technical method with complete functions,testing criterion and indexes is a critical problem to be solved in the field of mechanical assembly quality inspection.At present,conventional inspections on mechanical assembly concentrate mostly on such “static quality” testing indexes as tolerances and or sizecoordination,etc.,but lack of “dynamic quality” inspection due to less attention of researches.This is a shortcoming and disadvantageous to control and assurance of the whole dynamic quality(vibration,noise and dynamic stability,etc.)of the products.On the basis of mechanical structural dynamics,this thesis applies the method of inverse substructuring dynamic analysis(simply called ‘inverse substructuring scheme')to the dynamic quality inspection of mechanical assembly,in order to improve existing fundamental theory and technical method of the quality inspection by use of the properties and advantages of the inverse scheme.The main works and investigations have been carried out in this thesis as follow: 1.Introduction on the fundamental theory and technical principles of inverse substructuring SchemesAfter systematically introducing the fundamental theory of substructuring dynamic analysis,the theories of inverse substructuring dynamic analysis are explained in complete,including two sorts of technical principles for identifying the coupling dynamic stiffness of mechanical assembly— Direct and five indirect inverse substructuring schemes(simply called ‘direct scheme' and ‘indirect schemes' respectively).Finally,the two key indexes,which are called ‘coupling dynamic stiffness' and ‘dynamic quality matrix' of the assembly,have been clarified to effectively evaluate the influence of the dynamic characteristics of assembling connection interface on the dynamic quality of a mechanical assembly.This part of work lays a foundation for the follow-up theoretical and experimental studies.2.Experimental study on application of the inverse substructuring schemes in cases of nonideal assembling connection interfacesBased on the theories and principles introduced in Chapter 2,the experimental models of twolevel substructures of non-ideal mechanical assemblies with ‘line-' and ‘planar-' connection interfaces are designed(four types totally).The frequency response functions(FRFs)before and after assembly for the four models are tested by vibro-excitation,and the coupling dynamic stiffness are then identified by the first and second indirect schemes,respectively.The feasibilities of their application in identifying the stiffness have been verified,which provides experimental basis for their engineering applications.Finally,error analysis is carried out to determine the optimal equivalent discretized points on the ‘line-' and ‘planar-' connection interfaces of mechanical assembly models.The results can be used to guide the test-points' selection for dynamic quality inspection of mechanical assembly.3.Exploration on the cause of destructive modal couplingsThe finite element analysis(FEA)is used to do modal analysis on the two-level substructures of the experimental models with ‘line-' and ‘planar-' connection interfaces.Two types of critical modal parameters have been extracted — natural frequencies and modal shapes,which are then analyzed to explore the cause of destructive modal couplings occurred in the process of mechanical assembly,especially the frequency-ranges in which the modal couplings are easily occurred.This work provides a base for analyzing the low-accuracy problem in identifying the stiffness by the inverse substructuring schemes.4.Establishment on a complete set of normative technical approach for dynamic quality inspection of mechanical assembly and its self-contained softwareOn the basis of all results of the theoretical and experimental researches,a complete set of normative technical approach and its self-contained software have been developed for the dynamic quality inspection of electro-mechanical products.This part of works provides the solid supports for practical engineering application of inverse substructuring schemes in the dynamic quality inspection,and thus lays the theoretical base for improving the existing technical approach of quality inspection of a mechanical assembly.