| In the modern age of Industry 4.0 and the servitization of manufacturing,energy saving and environmental awareness are regarded as important themes for reducing carbon tax and achieving sustainable development in the manufacturing process.Green manufacturing has gradually become an advanced concept recognized by the world’s manufacturing powerhouses.Milling,as a basic material removal method,is commonly used for the machining of complex parts with the characteristics of adapting various cutting tools to various machining topographies.Due to the intense friction between the milling cutter and the workpiece and chips,insufficient lubrication can lead to defects such as thermal damage to the workpiece and reduced tool serviceability.For this reason,the pouring type with outstanding cooling and lubricating ability is often widely used in the milling field,but the flow of cutting fluid used by the pouring type is large,which will cause unnecessary waste.And the components of the cutting fluid contain substances that are harmful to living things.This is contrary to the concept of clean,low carbon.Compared with the pouring type,the minimal quantity lubrication(MQL)technology using vegetable oil-based cutting fluid is more in line with the concept of green and sustainable development.However,the nozzle of the external cooling equipment has a poor correlation with the milling area,and cannot be adaptively adjusted according to the tool path,and there is a problem that the cutting fluid cannot fully cover the milling area.In addition,in the process of cutting fluid transportation,the scattering of droplets,the airflow field generated by the milling cutter,and the jet parameters all affect the efficiency of the cutting fluid entering the machining area.Although the electrostatic atomization MQL technology alleviates the problem of droplet drift,it lacks the reference for the regulation of heat flow and jet parameters in the processing area,and the workpiece surface is prone to processing defects such as thermal damage.Combining the above problems,with the support of the national natural science foundation,the model spectrum construction of the machining data and the MQL tracking mechanism was carried out,combined with the simulation results of the airflow field to find the best jet position and attitude point,a precise transport system for MQL was developed,and a convective heat transfer model based on electrostatic atomization was established.Milling experiments were carried out to verify the precision transport system of MQL.The specific research contents are as follows:(1)The mapping relationship between the machining data of the three-axis milling machine and the tracking mechanism of MQL is studied.Combined with the idea of product type spectrum,a series of spectrum of tracking mechanism is constructed,and the coding rules of spectrum are compiled and formulated.Based on the spectrum,the kinematic analysis of the function realization of the MQL tracking mechanism is carried out,and the realization of the tracking mechanism for machining regular surfaces and irregular surfaces is theoretically guided from the point of view of Adams simulation analysis and machine tool data acquisition.(2)The Fluent simulation analysis of the vortex flow field at the end milling cutter workpiece constraint interface is studied,and the distribution characteristics of the vortex flow field is preliminarily explored.According to the theory of gas dynamics,starting from the structure of the milling cutter,the causes of the vortex flow field are analyzed,and the Rankine vortex is selected to express the speed and position of the vortex flow field.And Matlab is used to numerically simulate the vortex flow field to find the velocity distribution law of the vortex flow field,and the numerical relationship between the optimal jet pose point and the milling cutter parameters(rotational speed,diameter,helix angle).(3)The structural design of the precise transport system for MQL is carried out.According to the machining process,plan the movement process of the precise transportation system of MQL,and select the control hardware to compile the embedded program,so as to realize the intelligent control of the optimal jet position and posture point of the cutting fluid supply mechanism.(4)The temperature rise analysis of the workpiece by the milling heat source was carried out.Through the discretization in space and time,the mirror image method is used to construct the representation of the milling rectangular heat source based on the shearing and ploughing effects,and further accumulate them to form the milling heat source model.The air natural convection heat transfer coefficient and the charged cutting fluid convection heat transfer coefficient were theoretically analyzed respectively,and the convection heat transfer model under the condition of electrostatic atomization was obtained,and the influence of the jet parameters on the heat flow was analyzed.(5)The milling lubrication performance of aviation aluminum alloy 7075 was studied under different working conditions(dry type,pouring type,20 k V/0.2MPa MQL precision transport system,30 k V/0.2MPa MQL precision transport system).First,the experimental data of milling force and workpiece surface roughness under different working conditions were obtained.On the basis of considering low carbon and environmental protection,further milling performance analysis(specific energy,surface profile autocorrelation function curve,cross-correlation function curve)was carried out on the working conditions of the two MQL precision transport systems.It is concluded that the 30 k V/0.2MPa precise transport system with minimal quantity lubrication can obtain better workpiece surface quality. |
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