Research On The Representation Method Of The Assembly Position Of The Parts Based On The Nominal Geometric Model

Assembling is an essential procedure in manufacturing process.With the development of production pattern of one-piece product,small mass and increasingly high degree of product complication,the proportion of assembling procedure in total production and manufacturing cost and hours is larger and larger.As a result,improving the assembling technical level has become the key of overall manufacturing process development.In order to break through the pattern of design-production-verification-improvement-production-reverification which is from traditional manufacturing industry and promote the development of mechanical manufacturing industry,virtual assembly technology arises at the historic moment.The virtual assembly technology can predict manufacturing error of parts and assembly quality by simulating assembly results of machine in computer.Due to the existence of manufacturing error,the error of geometry of parts deviating from ideal status changes complicatedly.It is difficult to simulate real part based on real modeling technology.Then how to simulate assembly results rapidly and visualize assembly results is a very useful technology.For this purpose,simulation method of product assembly results based on ideal three-dimensional geometric model are proposed in this thesis,whose main idea is to place ideal three-dimensional geometric model in practical assembly place according to practical assembly place calculated by variation geometry through simulating geometric change resulted from manufacturing error,thus displaying assembly results of parts,allowing designers to observe visibly possibly arising assembly situation when making practical assembly in product design stage,thus guiding designers to make precise design and improvement over parts,in order to achieve lower product development costs?shorten product development cycle.The research of the thesis mainly includes the following contents:1)Take advantage of ideal assembly model to gain place of each assembly part and mutual assembly relationship;select tolerance math model and Monte Carlo simulation method based on control point to analyze degree of deviation of practical assembly parts from ideal place under all kinds of possible practical assembly circumstances,thus gaining variation parameter of each practical assembly part in CAD coordinate.2)Study practical part assembly method based on ideal model;make adjustment over ideal model's place in assembly according to geometric variation parameter of part assembly standard,thus realizing the purpose to simulate real machine assembly by taking advantage of ideal nominal model;3)Study judgment method over assembly quality and confirmation method about the most unfavorable assembly base geometric parameter;propose assembly variation repetitive rate of assembly KC concept,and the method to take advantage of assembly variation repetitive rate KC to judge assembly quality;propose coordinate aligning to calculate KC value;Propose calculation method of axis-aligned bounding box and oriented bounding box of coordinate with KC value.4)Take VC++6.0 as instrument to make secondary development as to SolidWorks2010,realize simulation of real machine assembly in all kinds of possible practical assembly situation by taking use of ideal three-dimensional nominal model in SolidWorks2010 and find the most unfavorable assembly situation.Through analysis on typical practical cases,the thesis verifies feasibility of nominal model to simulate assembly of real machine,and verifies reasonability of assembly quality judgment method proposed by the thesis.