| The CNC machine tools are one of typical products controlled by the digital information technology and integrated of mechanics,electricity,and hydraulic.They can be performed with high flexibility and efficiency,and have a wide range of applications on processing the complex precision parts,mass production,and multivariate machining.China has the world's largest market for machine tools.The annual output and export volume of the metal cutting CNC machine tools are still growing.Machine tools are widely used in manufacturing,and since they consume large amounts of electricity,are responsible for large amounts of carbon dioxide emissions.Modeling,evaluating and optimizing the energy consumption of the NC machining process can save energy,reduce environmental impact in machining process,and provide economic benefits.More importantly it has strategic significance for green and healthy development in the manufacturing.Comprehensive considering the situation both at home and abroad in energy shortages and environmental consequences attributable to the generation and usage of the energy,current situation of industry production technology and energy saving potential of machine tools,the laws and regulations on environment and the green manufacturing strategy of our country,research on machine tools energy consumption modeling and energy efficiency improving has gained urgent demand.In this paper,based on the national high technology research and development program(863 program)"Green Process Technology Assessment and Related Basic Database Development for Machine Tools and Engineering Machinery Products",the energy consumption modeling of metal cutting machine tool and the optimization of energy-oriented NC machining parameters are studied.The main work is as follows:(1)Firstly,complex energy consumption characteristics of CNC machine tools are summarized from the perspectives of energy components and systems,energy transformation and loss,changes in running status,and variable and fixed energy consumption properties.Secondly,the energy consumption modeling method of CNC machine tools is described in terms of energy consumption breakdown,hypotheses and neglect processing,mathematical modeling method,experimental design method,and data processing.Finally,this paper proposed an energy consumption modeling method based on changes in running status,combine empirical and mechanism model to describe the relationships between system parameters and energy.A milling machine,a lathe machine,and a vertical milling machining center were tested by a power meter to verify our method.(2)A standby state power model under weak current and strong current loops of the machine tools was established.The strong current loop standby power model included preheat phase,phase of lubrication and cooling device supplying oil and pausing work.Hydraulic,volumetric,and mechanical energy losses in the lubrication cooling system were analyzed.Equations of the power transmission and loss balance,the minimum theoretical supply cycle,and the interval time of pause in the lubrication cooling system were derived,which revealed that intermittent operating characteristics of the lubrication cooling device had influence on the changes in standby power.(3)An auxiliary state power model of the machine tools was established.Through analysis of the working principles and energy consumption forms of the lighting device,cutting fluid spraying device,manual tool change device,automatic tool change device,chip removal device,and air blowing device,their power consumption empirical equation were deduced.(4)An air-cutting state spindle power model of the machine tools was established.Firstly,theoretical equations of the main shaft system power loss were derived including power loss of frequency converter,motor,and mechanical rotation load.Secondly,the spindle power was treated as a linear function of rotation speed empirically.Finally,it was found that the spindle power increased with the increase of spindle speed,and was basically subject to linear relationship in the tests.It was also found that the configuration of spindle unit had great influence on spindle power.The spindle driven by the motor directly had a lower power than the one driven by the gearbox,because the friction torque loss was small due to its compact structure.The spindle power of the lathe was larger than milling machine,because the lathe needed extra power to overcome its large inertia of clamp.(5)An air-cutting state feed axis power model of the machine tools was established.Firstly,the friction torque equations of guide rail,bearing,and cutting load,the gravity torque of working table in the horizontal and vertical feed movement were derived.Then considering the viscous friction torque,the theoretical feed axises power models in the horizontal and vertical directions under air-cutting state were gained.Secondly,the feed power was treated as a quadratic polynomial of feed rate by simplifying the theoretical model.Finally,it was found that the feed power increased with the feed rate increasing.At the slow feed rete,the growth slope of feed power curves was small,and at large feed rate the feed power had larger increment.Some feed motor showed constant power characteristics above a special feed rate.The feed power in upward movement was biger than other directions because it needed to overcome the force of gravity.(6)An cutting state power model of the machine tools considering material hardness was established.Firstly,the energy consumption mechanism in metal cutting was analyzed,and then the theoretical specific cutting energy calculation formula including metal shear deformation energy and the friction energy between cutter and chip was derived.Aiming at the problems of the existing empirical models of cutting state power,this paper put forward an improved cutting state power model considering different material hardness.By analyzing the theoretical model,experiment results in vertical milling and cylindrical turning tests,the influences of the material hardness,spindle rotation speed,material removal rate,and cutting parameters had on the specific cutting energy were explained,especially for influences on elastic-plastic item,velocity item,and thermal softening item in the equivalent shear stress calculation.The proposed model in this paper showed the improvement in accuracy,rapidity and adaptability to predict cutting state power of the machine tools.It was found that the metal cutting power in milling was increasing with the increase of material removal rate.The spindle rotation speed affected the velocity item,and thermal softening item in material equivalent shear stress,and also affectted the undeformed average chip thickness,thus showing the complex influence rules on the metal cutting power.The material hardness affected the elastoplastic term of equivalent shear stress.Under the same cutting conditions,metal cutting power increased with the increase of material hardness.It was also found that metal cutting power in turning increased with the increase of removal rate of material.When the material was too soft,the friction between the chip and the cutter increased,which increased the cutting power.When the material hardness was very high,the cutter suffered more cutting resistance to increase the cutting power.(7)Research on energy-oriented optimization of NC machining parameters.Firstly,the energy consumption per unit of removed material and processing time functions in the whole NC machining process were established,and minimizing these functions is the optimal target.The optimization variables in NC milling process were determined as spindle rotation speed,axial cutting depth,radial cutting depth,and feed rate.The optimization variable in NC turning process were were determined as the spindle rotation speed,the diameter of the workpiece,cutting depth,and feed rate.Constraint conditions,such as the processing capacity of the machine tool,the tool life,the surface roughness of the part,and wasted ploughing energy are considered.A genetic algorithm was used to solve the optimization model.To verify the proposed method,an end milling operation was presented as case study,and the effects of parameters on objective function and constraint equations were discussed.The optimization results showed that the spindle energy consumption,cutting energy consumption,and tool durability were affected by spindle rotation speed.The high feed rate reduced the idle time of machine tool,but also increased the surface roughness and tool wear.When the axial cutting depth and the radial cutting depth increased,the material removal rate increased,thus reduced the processing time,and made the metal cutting energy consumption increasd.Due to decrement of time was greater than increment of energy consumption,eventually the energy consumption per unit of removed material process decreased.The changes in the radial cutting depth,feed rate,and spindle rotaion speed would affect the energy efficient in shear cutting zone and the waste of ploughing energy. |
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