Research On The Calculation Method Of Clearance Distributions Of Pin-hole Assembly Based On Real Parts Assembly

In the process of practical mechanical production, the final performance of productalways affected by the quality of assembly considerably. Pin-hole assembly is commonassembly form of the mechanical products and higher pin-hole assembly quality is requiredwhen the product has specific performance. At present, the cases that quality of the pin-holeassembly affected by a number of assembly datum has never be considered. In this paper, inorder to research the affect to the pin-hole assembly clearance of datum tolerance, a pin-holeassembly as an example to perform tolerance analysis which has three orthogonal plane topositioning by simulating geometric elements changes and real assembly condition based onthe theory that control points of geometric elements.With the development of computer technology, the technology of computer aidedtolerance design (Computer Aided Tolerancing, referred to as CAT) are used widely in thetolerance analysis of the mechanical product.In this paper, using UG NX7.53D softwareplatform for secondary development by VC++. Firstly, the assembly tolerance informationmodel graph was established based on the theory of tolerance model representing by controlpoints of geometric elements. Then determined the closed loop, constructed the3D assemblyfeature surface chain groups associate to the dimension by searching the assembly toleranceinformation model graph according to the rule of shortest path of establishing assemblydimension chain. Finally, analysis the clearance distribution of pin-hole assembly.In theprocess of analyzing the clearance distribution of pin-hole assembly the following mainlyworks is done:(1) The extraction of three-dimensional tolerance annotations information using PMImodules of UG three-dimensional solid model. UG NX7.5system provides UG/Open APIsecondary development module, by calling functions of UG/Open API secondarydevelopment modules, something can be achieved on extraction of the three-dimensionaltolerance information and its associated features information.(2)The establishing of model figure based on the Computer tolerance assemblytolerances based on the geometric elements of the control point representation theory(referred to as assembly tolerance information model graph). Knowledge based on acombination of geometric elements, said control point data structure model based on graphtheory, the establishment of assembly tolerance information model diagram. The toleranceinformation model in Figure innovative feature faces as nodes to the size of undirected edgesand fitted to the side and there are a variety of geometric tolerances side edges of mixedgraphs.(3) Self-generated assembly tolerances side chain group methods written in assemblytolerance information model created on the basis of Fig. The assembly tolerance surface tobreak the traditional concept linked group assembly dimension chain, is a traditional assembly dimension chain features associated with the reference plane parts assemblysequence separated by characteristic features of surface side chain group includes thetolerance range of changes, a new method for tolerance analysis, automatically generatethree-dimensional assembly tolerances surface linked group in the true sense.(4) The pin-hole assembly with three orthogonal planar assembly data is taken asresearch objective and with its pin-hole assembly gap astarget element, and on the basis of its3D assembly feature surface chain groups associate to the dimension, the variationalsimulation of the planar feature and cylindrical feature are represented by the control pointsvariational model of geometric element and the variational sample are generated with TheMonte Carlo simulation, the probability distribution of the clearance between the pin and thehole are obtained.