A Top-down Design Method For Static And Dynamic Stiffness Of Precision Horizontal Machining Centres

The precision horizontal machining center is the foundation of the equipment manufacturing industry,and its level of manufacturing has a direct impact on the overall level of China's equipment manufacturing industry.Static and dynamic stiffness of the entire machine is the key factor in its machining accuracy.At present,the static and dynamic stiffness is designed by analogy based on the experience of designers,lacks of systematic,quantitative design.Therefore,with user requirements' static and dynamic stiffness as the goal,a top-down design method for the static and dynamic stiffness of precision horizontal machining centers is proposed in this work.The following contributions are included:1.A new stiffness characterization for characterizing the stiffness of the components is proposed.The stiffness values at some specific positions are considered as stiffness coefficients to characterize components stiffness.These positions are directly related to the entire stiffness,and also can represent the stiffness of components themselves.This approach helps to abstract the physical model of stiffness into a mathematical model in the case of the initial design stage.And these stiffness coefficients can also become future goals of the detailed structural design.2.Based on the stiffness coefficient,the whole stiffness model of the machine tool is built by using the multi-body system theory.In the modeling process,taking into account the flexible of the structure,the influence factor is added to describe the effect of the force acting upon one point on the deformation of another point.Comparisons with stiffness experiments indicate the validity of the model.The proposed stiffness model reflects the stiffness characteristics of the horizontal machining centre with box-in-box construction both qualitatively and quantitatively in the skeleton design stage.It also shows the effect of the basic dimensions of the machine tool on the entire machine stiffness.3.The stiffness matching design for the stiffness of the entire machine is proposed.Aiming at stiffness of user requirements,reasonable stiffness of components can be obtained via the stiffness matching design based on the stiffness model during the skeleton model stage.In the matching process,analysis of the contributions of the stiffness values of the components to the entire machine stiffness is accomplished by using the Do E method,by which the weak link is found.Simulation studies verify the proposed matching design.4.Based on the CAD/CAE co-simulation analysis platform,NSGA-II optimization design method is used to calculate the structure parts' outer shape of the structural design and layout of the internal ribs,which are corresponding to the stiffness of the structure parts.Then,all the structure schemes for the structural parts corresponding to the commonly used stiffness values are calculated,to form the database of structure schemes.In this way,aiming at stiffness of the entire machine,reasonable stiffness values of components are obtained by the stiffness matching design.And aiming at these components' stiffness,the structure schemes are selected for each structure parts.Finally,the top-down design for the entire stiffness of the machine tool is completed.5.By establishing the parametric model of the entire machine,the CAD / CAE co-simulation analysis platform is used to study the influence of mass of the structure parts on the natural frequency of the entire machine.The Do E method is used to analyze the contributions of the mass of the structure parts to the natural frequency of the entire machine.It is found that the mass of the bed,especially the bed-behind,is the key to affect the natural frequency of the entire machine.Then,the dynamic stiffness matching design method of the entire machine is proposed.Aiming at the given first natural frequency of the entire machine,the function of bed mass and the first natural frequency of the entire machine is used to determine the mass and structure of the bed to meet the requirements,in the case of the stiffness matching design is completed.The above achievements provide theoretical support for the top-down design of precision horizontal machining centers.A corresponding top-down design software is developed and used in the design of precision horizontal machining centers.