Study On The Theories And Methods Of Functional Tolerancing Based On New GPS

Based on the research of National Nature Science Fund Project "Research on Theories and Methods of Computer Aided Functional Tolerancing based on new generation GPS (No. 50775204)" and "Research on 3D Tolerance Modeling based on GPS (No. 50505046)", tolerance modeling and representation, functional tolerance specification, functional tolerance analysis and synthesis, manufacturing oriented tolerance analysis, etc. are studied.In chapter 1, the enactment and tracking study of new generation GPS are expounded, the State-of-the-arts of computer aided tolerancing (CAT) are summarized and the research background and significance of this project are discussed. Finally, the main contents, the overall frame and innovation points of this dissertation are given.In chapter 2, some basic definitions consistent with new generation GPS standard of geometric product are presented. The information composing of geometric dimensioning and tolerancing (GD&T), tolerance type, tolerance principle, etc are analyzed. The theory of 3D tolerance parameterized modeling is studied based on the concept of TTRS, MGRE and SDT, etc. And, case study of tolerance modeling of several familiar features belong to some invariance class are done.In chapter 3, the classification of positioning joints of part assembling based on the definition of invariance class and the principle of ascertaining its preponderance order are studied. The assembly oriented graph (AOG) which is already in existence has been improved and the expression of assembly poisoning constraint is added in AOG. The methods of representing and decomposing of functional geometrical requirement are studied. Then, the tolerance specification technology of interface between part-part based on the improved AOG is studied. The definition of invariant DOF and mark of tolerance zone are given. General rules for validating datum reference frame are studied. The functional tolerancing process and method of geometrical functional requirement-geometrical specification are given. Lastly, a simple assembly example and functional tolerance specification result are presented.In chapter 4, based on the tolerance modeling of feature, the propagation and accumulation of geometrical variation in assembly are described using HTM (homogeneous transformation matrix), and the tolerance accumulation model including tolerance information of part and gap information of part-part are established. Then, tolerance loop and matrix equation is established. Several examples are used to explain the tolerance analysis process oriented to assembly feasibility and functionality.In chapter 5, a tolerance synthesis scheme is put forward. On the base of mapping of tolerance zone to deviation space, the mapping of cost-tolerace model to cost-deviation model is studied. The small displacement torsor representation of geometric requirement constaints, assembly connection constaints are studied, and a simple example is used to demonstrate the tolerance synthesis process.In chapter 6, CAD model of part and its feature are represented by a group of points. The space relations of each component in process system are described by homogeneous transformation, and then stack-up model of geometric error of process system is established. Machining process can be regarded as the points-group of tool path updating the points-group of part. The manufacturing geometric variation of feature/surface of part is analyzed by Monte-Carlo simulation. Thereby, manufacturing geometric variation can be considered in tolerance design stage and concurrent tolerance design is actualized.In chapter 7, the prototype system for Computer Aided Functional Tolerancing(CAFT) is preliminary developed. The function of each module and workflow of CAFT system are analyzedIn chapter 8, the main content of the dissertation research is summarized, and the prospect of Computer Aided Tolerancing research is presented.