Study On Key Techniques Of CAPP Based On Tolerance

Based on the project of "Theories and Methods of integrated Tolerance Design Oriented onGeometric Production Specification" (Nationai Nature Science Fund Project, No. 50275136) and the"Study on Process Tolerance Oriented on Computer Aided Process Planning"(Nature Science FundProject of Zhejiang, No. 502016), the key techniques of CAPP such as location datum, process, andprocess tolerance are studied in this dissertation. The prototype system for key techniques of CAPPbased on tolerance is developed and verified by examples.In the first chapter, State-of-the-art of setup planning, Computer aided process planning (CAPP)and Computer aided Tolerancing (CAT) at home and abroad are summarized. Based on those, the keytechniques in CAPP are proposed. The background, main contents, general structure scheme andoriginalities of this dissertation are presented.In the second chapter, the basic theories and methods in setup planning, process planning andtolerance designing are analyzed. The architecture, basic theories and functions of GeometricProduction Specification are elaborated. Based on group theory, the new feature types are defined byISO/TC 213. The main objective of this chapter is to establish a solid basis for setup planning, which isto be examined in the following chapter.In the third chapter, based on theories of variational geometric constraints, the rules of geometriclocation datum designing are discussed. All tolerance types are classified into local and relativetolerance, and the models of relative tolerance factor are constructed. Based on graph theories, thecomputer aided design (CAD) model of workpiece is expressed as a directed graph of features andrelative tolerance factor. According to this directed graph, the optimal design rules of location datumbased on tolerance constraints are proposed.In the fourth chapter, the main factors of process method are analyzed. Based on the theory offuzzy, the fuzzy member models of dimension tolerance and process method, surface roughness andprocess method, geometric tolerance and process method, material of workpiece and process method areall constructed, and the method of fuzzy reasoning and decision making for process method designingare studied. In addition, a library of process method link oriented on feature is established in terms ofprocess literature, and all process method links of features in manufacturing are developed by thislibrary. What's more, the principles of machine selecting are analyzed, the fuzzy member models ofprocess capability and machine type, dimension of workpiece and machine type are established, and themethod of fuzzy reasoning and decision making when selecting machine types is studied. Furthermore,the relationship of cost and tolerance of different process methods is studied based on sampling the dataof cost and tolerance. Finally, the cost-tolerance models of different process methods are constructed.In the fifth chapter, the process route design is classified into two levels, firstly, the design of setupsequences in machining is studied, and the basic rules of setup sequences are presented; secondly, themachining sequence of features in the same process and same location datum is studied, and a algorithmof machining sequence design is developed; Then, according to the process method links for everyfeature developed in fourth chapter, all process routes in workpiece machining are designed. The typesof integrated CAPP are reviewed, and the architecture of a new integrated CAPP oriented onmanufacturing is presented. In addition, the new integrated CAPP design is optimized, the optimalmodel is developed, and the constraints are analyzed. Furthermore, based on graph theory, the process route can be expressed as a parameter tree, and according to this tree, the process tolerance is studied.Then, the model of process tolerance design is established, and the constraints in process tolerancedesign is analyzed. At last. the process tolerance is optimized based on different cost-tolerance models,the optimal model is established and the constraints are analyzed and the genetic algorithm (GA) is usedto optimally design the process tolerance.In the sixth chapter, the prototype system for key technologies in CAPP based on tolerance isdeveloped, and the examples are used to demonstrate that the system can effectively design locationdatum, process and process tolerance.In the seventh chapter, all of the work in this dissertation is summed up, and the future research onkey techniques in CAPP is proposed.