Research On The Key Technologies Of Unit-based Assembly Design Oriented On CNC Machine Tools

In order to occupy a favorable position in market competition under the background of global economic integration, the manufacturers of CNC machine tools must not only improve their product innovation ability, product quality and performance, but also try hard to shorten the product design and manufacturing cycle, reduce the costs and extend the product life cycle. Assembly, which has the heaviest workload and is the most time-consuming process in the product design and manufacturing, directly affects the quality and reliability of the final product. However, the technical progress of the assembly process is far behind that of the design and manufacturing process. Whether the product has good assembly performance has very important significance for improving the assembly efficiency, reducing the assembly costs, ensuring the assembly quality and enhancing the market competitiveness. CNC machine tools are the key foundational manufacturing equipment and the carrier of advanced manufacturing technology. Carrying out the research on the assembly design of CNC machine tools has very important theoretical meaning and practical value. The main contents of this thesis are outlined as follows:(1) Based on the analysis and summary of existing assembly modeling methods, the assembly semantic relationships graph model is established through distinguishing the connectors and the functional parts. For describing the complexity of assembly process, the connector, the transmission semantic information and the geometric constraint information between the parts are quantified, which is named the assembly connection strength.(2) Through applying the trust transitivity between people to the assembly connection strength between the parts, the transitivity of assembly connection strength is put forward. In order to reduce the assembly time and avoid the "combinatorial explosion" problem in the assembly sequence planning, the product is divided into several assembly units based on the assembly connection strength. After getting the division results, the assembly units in which there is the interference are identified by checking the assembly interference and corrected to produce the units without interference.(3) Genetic algorithm is introduced to carry out the assembly design. Combined with the needs of the assembly sequence planning, the coding scheme, the control parameters, the fitness function, the genetic operators and the method for generating the initial population are determined. The final results of assembly sequence optimization for the parts in the assembly unit and for the assembly units are obtained by using genetic algorithm.(4) Based on the theory of the assembly unit division, the interference checking and the assembly sequence planning, the assembly design system oriented on CNC machine tools is developed by MATLAB, and the running example of the system is given.This thesis carried out a positive exploration on the assembly unit division, the interference checking and the assembly sequence planning, realized the assembly sequence optimization of CNC machine tools, and provided the theoretical basis and technical support for improving the quality and efficiency of assembly design.