Research On Key Techniques For Concurrent Design Of Product Conceptual Structure And Geometric Tolerance

From a design point of view, conceptual design has the most important influence on the innovation in the whole design process of product. From manufacture perspective, tolerance has a big influence on the ability of being manufactured and assembled of a product. If the conceptual design and tolerancing can be considered in a concurrent way, an innovative design scheme with strong feasibility will be obtained directly after one design step. This can reduce the probability of re-design and shorten the period from an idea to a real product. Therefore, under the support of National Nature Science Fund Project (No:50475129), named Study on evolving theory and technology of synchronous synthetic tolerancing in product conceptual design, This thesis researches on the concurrent design process of product conceptual structure and geometric tolerance.The contents and contribution of this thesis are as follows:Firstly, the current research methods and contents in the field of computer aided conceptual design (CACD), tolerancing and their integration were summarized systematically. In order to solve the problems existed in the filed of conceptual design integrated with tolerancing, the method of growth design was borrowed for using its thinking about the product conceptual structure design and its representation. The research contents were presented with studying on the theories, technologies and software development.On theoretical studies, based on the investigation of functional surface, conceptual product and decomposition&reconsititution principle, the theoretical contents of concurrent growth design of product conceptual structure and tolerance were proposed, involving function decomposition oriented whole design phase, the growth design of conceptual structure and mechanism of concurrent design process of conceptual structure and geometric tolerance. The function decomposition oriented to whole design process is executed simultaneously with conceptual structure design process. The function that can be realized by existing structure will be mapped to its relative structure on time along with the function decomposition process. The growth design of conceptual structure takes functional surfaces as the object of operation in design process. The decomposition and reconstitution of functional part makes the conceptual design process operable and overcome the problem that the conceptual design process is hard to be controlled. The geometric attributes of functional surfaces allow tolerance information to associate with the product structure directly. The mechanism of concurrent design of conceptual design and tolerance was presented. Tolerancing of new parts was performed simultaneously with every step of conceptual structure design. According the relations of product function, structure and tolerance in conceptual design process, the design process model of structure and tolerance concurrent design was proposed.On technological research involving in this paper, the information model of product was built to support structure and tolerance design. It includes three models: function model, structure model and tolerance model. Function model was built by the support of database technology. It includes information on function, behavior, and status. It can describe the relations between function items and record which functional surface or part can implement the function stored in this model. Base on generalized location principle, the functional pattern was defined for the reasoning from function to structure. The classes of functional surface, part and product were defined using the object-oriented method, and then the structure model was built. Tolerance model was built based on structure model to realize the integration of product structure and tolerance.For implementing the conceptual structure design, the function decomposition oriented to whole design process was integrated with the growth design. QFD (Quality Function Deployment) was used to realize the function decomposition. Functional pattern needed in design process can be obtained by functional reasoning. The library of reasoning principles was built. The functional pattern associated function decomposition with the design of functional part. It makes function can drive structure design concurrently along with function decomposition. Conceptual structure design process is the basis of tolerancing.Tolerancing integrated with conceptual structure design was studied. Instead of only considering dimensional tolerance, the geometric tolerance was considered in this paper. The concept of DOF (Degree of freedom) was redefined to suitable for functional surface. Geomantic tolerance can be considered as constrains to the geometric variation between two functional surfaces. Three-dimensional tolerance chain was form between the new and old parts by following 4 steps: the standardization of DRF (Datum referred frame) of functional patterns, the generation of constrain variation chain between toleranced and referred surface on the new and old parts, the generation of tolerance types and three-dimensional tolerance chain. The genetic arithmetic was used to optimize the tolerance distribution results. For evaluating structures by tolerance, 4 criteria were presented and used in the method of fuzzy assessment.Based on above theories and technologies, a new system supporting the concurrent design of conceptual structure and tolerance, Darfad-Tolerancing, was developed on the basis of MDT Its system function, structure and development environment were introduced. The validity of proposed theories and technologies was proved by the design example of piston clamp. The concurrent design process of structure and tolerance of the piston clamp was described. Through analyzing the design result, it was found that one-step tolerance chain can lead to a tolerance allocation problem, and then some solution methods were discussed.