Research On The Stiffness Characteristics And Testing Method Of Machine Tool Under Spindle Rotation Status

The stiffness characteristics of CNC machine tool directly affects the machining accuracy and surface quality.The spindle rotation will affect the stiffness characteristics of machine tool by changing the bearing stiffness and the joint surface stiffness of tool handle.At present,the evaluation of machine tool stiffness characteristics at home and abroad is carried out under the static status of the spindle.It cannot truly reflect the stiffness characteristics of machine tool under the working status.The research on the stiffness of spindle under rotating status is mainly based on theoretical analysis.Purposed theoretical models have not been fully verified caused by the lack of measuring tools.Therefore,it is of great significance to research and develop the stiffness testing system under the spindle rotating status of the machine tool.It is also most meaningful to obtain the impact of the spindle speed of on the stiffness of the machine tool,especially for the optimal design of high-grade CNC machine tool design.Firstly,a non-contact stiffness measurement system based on electromagnetic loading under spindle rotation is researched and developed.The electromagnetic model of non-contact force loading device is established.Thermodynamic analysis was carried out.After that,the serious heating problem of the electromagnetic load measuring device has been successfully solved by optimizing electromagnetic parameters and structural parameters.The experimental results show that the measurement system can work properly for a long time under the high rotation speed of the spindle,it can work continuously for more than 90 minutes.The results also realize the stiffness test under the rotating status of the spindle of the machine tool.The relationship between loading force and current at various rotational speeds also has been determined.Secondly,based on qualitative analysis of the influence of spindle speed on machine tool stiffness,the stiffness characteristics of machine tool under spindle rotating status are quantitatively tested by the developed measurement system.The results show that the spindle speed has an impact on the machine tool stiffness through bearing preload,bearing roller centrifugal force,bearing temperature,bearing oil film stiffness and so on.Specifically,a basic rule has been founded that the spindle stiffness first decreases and then increases with the increasing of the speed.Finally,this thesis has put forward some suggestions for machining process and machine tool optimal design,that is,machining process should avoid the working speed with poor stiffness as far as possible,and machine tool designer should appropriately enhance the x-direction stiffness.In this thesis,a reliable technical method for the measurement of stiffness characteristics and optimal design of machine tool under spindle rotation,is provided.