Analysis And Optimization Of Machining Process Based On Power Model Of CNC Machine Tools

Nowadays,the environment and energy are the two serious issues which all of the world are concentrated on.Energy saving and environmental protection are the main connotations of the new industrial revolution.Industrial activities have a significant impact on the environment and energy.The electrical energy consumption of industry occupies of more than 60%of the total global energy consumption.As the main body of manufacturing,CNC machine tools have the characteristics of high power and energy consumption.The processing technology has a significant impact on energy consumption.The diversity of machining processes makes CNC machine tools have more energy-saving space.Therefore,studying the power characteristics of CNC machine tools and establishing accurate prediction models can provide theoretical support for multi-objective trade-off analysis and optimization of machining processes and analysis of energy-saving strategies in machining processes.However,the existing CNC machine tool power model,whether established at the machine level or at the system level,cannot be combined with the machining processes and accurately predict the power consumption based on input conditions such as cutting parameters.Therefore,from the perspective of cutting principle,the relationship between cutting parameters,tool path,tool wear,and cutting power is revealed.The modeling and application research of CNC machine tool power prediction model is carried out to analyze the influence of different cutting parameters on energy consumption.The impact grades can provide theoretical support for multi-objective trade-off analysis of processing parameters for green manufacturing.Considering the requirements of lower energy consumption and higher efficiency of green manufacturing,this research analyzed the power characteristics of CNC machine tools.According to the time sequence of the machining process of CNC machine tools and the factors affecting the power,the power model is established from the non-cutting state and the cutting state.The proposed model was applied to analyze the influence of tool path and tool wear on energy consumption,machining efficiency and surface quality.On this basis,multi-objective trade-off analysis and comprehensive optimization of machining process were carried out.The main research work is as follows:First,the power characteristics and influencing factors of CNC machine tools were analyzed.Combined with the power consumption characteristics of different structures or components,the corresponding power models were established from the non-cutting state and the cutting state.For any machining process,the working state of the CNC machine tool includes two status:cutting and non-cutting states.In this study,the typical milling process was taken as an example to analyze the power characteristics of the machining process.The non-cutting status include the CNC machine’s standby,spindle acceleration,spindle idling,feed motion(before the tool contacts the workpiece),and rapid feed motion.The non-cutting status power model was establish including the machine tool’s own parameters and partial cutting parameters;then from the perspective of the working principle of the motor,the power flow characteristics in the numerical control system were explained and the validity of the theoretical model was preliminarily verified.The power model of the cutting status was related to many machining factors,according to the basic principle of P=F· v,the cutting power model was established based on the infinitesimal cutting force theory.Finally,the prediction accuracy of the non-cutting status and the cutting status power model was verified by the verification experiments with randomly cutting parameters combination.The established model has higher prediction accuracy in the speed range.The average prediction error of the mean values and the power peak were 0.076%and 0.208%.respectively.Secondly,the energy consumption model was established according the proposed power model.Different energy consumption characteristics of the same machining process were analyzed considering different tool paths,and the mechanism and law of the influence of the tool path on energy consumption were explored.The tool path was comprehensively optimized combining the two goals of machining efficiency and surface quality.Six common plane milling tool paths were selected,and the energy consumption model was used to predict the energy consumption of different tool paths.The experimental results were used to verify the prediction accuracy.Effects of the six paths on energy consumption,processing efficiency and surface quality were analyzed.A comprehensive analysis model of "energy consumption-machining efficiency-surface quality" based on tool path was established.Finally,the tool path comprehensive optimization based on multi-objective trade-off analysis was realized to achieve the processing goal of low energy consumption,high efficiency and high surface quality.Finally,cutting force increased with the tool wear becoming serious,which will affect the cutting power indirectly.During the multi-objective optimization resolution process,in order to make it closer to the actual machining condition,the comprehensive influence analysis and optimization of cutting parameters on energy consumption,tool wear and surface quality were carried out.In this research,cutting tools with two kinds of coating materials and the same geometry were selected to analyze the wear characteristics under the same cutting parameters.Based on the theory of grey relational analysis,the importance of cutting parameters on power,tool wear and surface quality was analyzed.The variation of cutting power with tool wear was studied.The relationship between tool wear and cutting power was studied.Considering the influence of tool wear on surface quality,a three-dimensional trade-of’f analysis relationship model of "cutting power-surface quality-tool wear" was established to solve the optimal cutting parameters to minimize tool wear and cutting power,while maximizing the surface quality.In this research,the power of CNC machine tools was divided into two parts:non-cutting power and cutting status power.Considering the different influencing factors of different status power of CNC machine tools,the power was analyzed and established,respectively.A piecewise function modeling method was proposed to build up the non-cutting status power;while the cutting status power was established based on the infinitesimal cutting force theory.This modeling method was applicable to different types of machine tools and cutting tools.The model contains the coefficients related to the CNC machine tool,cutting tool types.etc.,which can be re-calibrated when applying it to power prediction.The power model established in this study can be used in multi-objective optimization research of cutting parameters,tool path optimization and online monitoring of tool wear status,which provides a theoretical basis for multi-objective trade-off analysis and comprehensive optimization of machining process.