Matching Design Method For Damping Of Precision Horizontal Machining Centres

As the main carrier of high precision processing technology,precision horizontal machining centres need to have good static,dynamic and thermal properties.As one of the main factors influencing the dynamic characteristics of the machining centre,the researches of damping mechanism and design method are the difficulty and the emphasis in the relevant field.The reasonable design of damping is also the goal of the designer,thus the research of damping has very important significance.The various types of damping exist in the precision horizontal machining centre,which contain the joint interface damping,the material damping of the basic parts and the applied damping treatment.However,single type of damping or local structure damping is only concerned without systematic research in the design process of machine centres.This is the bottleneck to improve dynamic characteristics and dynamic machining accuracy.According to the requirement of design and actual processing of machine tool,three types of damping are studied systematically in this work,and a damping matching design method is proposed based on the response at the end of the machine tool.The main contents of this dissertation are listed as following:An energy dissipation model between fixed joint interfaces with elastic-plastic contact is established based on contact theory and micro-slip theory.According to equivalent virtual material model of joint interface,the equivalent loss factor of virtual material is presented.Through the numerical simulation,the influences of the joint parameters(such as tangential force,normal force,and friction factor)on damping loss factor are investigated.It provided a theoretical reference frame for the reasonable selection of the value of the damping of the joint interface.The damping experiments of the joint interface are carried out and the influence of tangential load on the damping is studied.Material damping influences the dynamic characteristics and dynamic machining accuracy,thus,how to choose the material of base structure is very important.Under this guidance,milling forces simulation of common spiral milling cutter is taken,and the curve between cutting force and tool rotation speed is obtained.The mechanical models of the bed,column,slide carriage,slide table and headstock are established under the cutting force.The responses of these basic parts under variable loads in a certain frequency range with three different materials are analyzed.The dynamic performance influenced by the material damping is evaluated through the displacement amplitude.The results can provide some references for material selection of the machine tool structure.Location and shape optimization method of the applied constraint damping structure on the basic parts of precision horizontal machining center is proposed based on the evolutionary structural optimization method.The applicability of the modal strain energy method in the constraint damping structure is studied according to theory,simulation and experiment analyses.Damping loss factor sensitivity of composite damping structure is deduced based on the modal strain energy method.In order to obtain the optimal damping performance,topology optimization design is carried out to find the best position and shape of the damping material,with the goal function of maximizing the first order modal loss factor,damping materials consumption and low order natural frequency as constraint.Based on the end of the response of the precision horizontal machining center,the whole machine damping matching design method is presented by combining response surface model and multi-objective genetic algorithm.The dynamic characteristic optimization design of the whole structure based on joint interface damping is proceeded by setting the bolt pre-tightening force as the design parameter,and the best pre-tightening force value is obtained.The optimization design of the whole structure based on material damping is carried out by setting the materials of five basic parts as the design variable,and the best combination of material for each basic part is obtained.The optimization design of the whole structure based on applied damping treatment is proceeded by setting the thicknesses of damping layer and constraining layer as the design parameters,and the optimal thickness for each layer is obtained.The research results in this dissertation enrich and develop the damping design theory of precision horizontal machining centre,and have important engineering value and social value.