| The CNC lathe plays a very important role in the processing of all kinds of parts. With the rapid development of production technology, the accuracy requirements of the product have been improving, which continuously improve the requirement of the comprehensive performance of the CNC machine tool. The traditional design method has some limitations in its application range, which restricts the development of machine tools with high speed, high precision and complicated. Therefore, it is particularly necessary to introduce the modern design method into all aspects of machine design.In the design stage of the machine tool, to obtain the static and dynamic characteristics, the effective mathematical model of parts or machine must been established. Comparing the performance parameters to the requirements of the machine, the weaknesses of the machine can be found, which can provide basis and guidance for the modification and the optimization of the structure. This can not only improve the comprehensive performance of the machine, but also can shorten the development cycle of the products and reduce their cost.The paper takes the head frame of the La6150 CNC lathe as the research object. For the initial design issues of machining accuracy of machine tools, finite element method is used to analyze head frame’s mechanical properties and to optimize its dimension parameters.According to the typical working conditions of the type of CNC lathe, external forces of head frame, the spindle and the transmission system are calculated. The amount of heat per unit time of the bearings is also calculated. Comparing the results of the calculation, the dangerous working condition of machining can be found, which provides an accurate boundary conditions for subsequent analysis.In the dangerous working condition, the steady state thermal structural coupling analysis is carried on to the head frame. The counters of stress, strain and total deformation are obtained, which provides a numerical basis for the subsequent optimization design, namely determination of the object functions and constraint conditions. Then several measures to improve the thermal characteristics of the head frame are put forward.To get the front six order natural frequencies and vibration modes of free vibration without damping, constrained modal analysis is done to the head frame. According to the results, the dynamic stiffness of the head frame is analyzed, which provides numerical basis for subsequent optimization, namely determination of part of constraint conditions.Through the sensitivity analysis, the response curves of the maximum deformation and the first order natural frequency to the main design parameters are got, the impact of each design parameter to the objective function and state variables can be clearly observed, which provides the basis and guidance for the optimization design of the structure. It has important reference value and practical significance.Finite element analysis and experimental design are used to establish the head frame’s multi-objective optimization mathematical model, in which the thicknesses of the head frame’walls and the internal ribs are regarded as the variables of optimization design, the largest stress and the first order natural frequency of the structure are state variables, the maximum deformation and mass of the head frame are regarded as the objective function. The genetic algorithm is used to solve the problem, and the optimal design variables values are finally obtained, which meet part’s performance indexes.Finally, for the weak links found by thermo mechanical coupling analysis and the optimal parameters, designing a better performance of box structure by modifying the structure,which provides a reference for the retrofit design of enterprise. |
PDF Full Text Request