| Clean cutting technology,as an important approach to achieve the Peak Carbon Emissions and Carbon Neutrality,is widely used in the machining of various difficult-to-cut materials.How to coordinate the development of machining environment,production resources and cutting efficiency by means of minimum quantity lubrication（MQL）has become the focus of current research.316L stainless steel is considered as a typical difficult-to-cut material due to its high cutting heat generation,fast tool wear and severe surface hardening.It is of great significance to improve the milling processability of 316L stainless steel by MQL.Aiming to improve the tool cutting performance of MQL milling 316L stainless steel and solve the difficulty of cutting fluid penetrating into the tool-chip contact area,new design methods are proposed including micro-groove structure of milling cutter rake face based on simulation data driven and micro-channel structure considering the influence of cutting fluid flow characteristics on cutting temperature in this thesis.The cutting experiments of the microgroove-microchannel tool are carried out to explore the cooling lubrication mechanism for MQL milling.Furthermore,the cutting power model based on infinitesimal cutting force is established.The cutting parameters are optimized with the goal of specific cutting energy and surface quality,which provides reference for the selection of process parameters for new tools.The main contents are demonstrated as follow.The penetration process of MQL cutting fluid is analyzed and the formation conditions of lubricating film are explored.The lubrication model of tool-chip contact area is constructed to reveal the formation mechanism of boundary lubrication film.The experiments of 316L stainless steel under dry cutting and MQL cutting are carried out to investigate the influence of cutting parameters,cooling and lubrication environment on cutting force,cutting temperature and tool wear.The fluid distribution characteristic in milling is studied,and the influence of chip curling state on the penetration for cutting fluid into the tool-chip contact area is analyzed.It is found that larger cutting parameters are not conducive to the improvement of cooling and lubrication effect,furthermore,the design method of microgroove-microchannel structure on the rake face of milling cutter is proposed.Combined with the structural characteristics of bull-nose end mill,the design concept of inserting optimized two-dimensional micro-groove structure into the three-dimensional tool model to obtain the rake face modeling of micro-groove tool is proposed.The MQL milling simulation model is established,and the effects of four micro-groove cross-section shapes and their structural parameters on cutting force,cutting temperature and chip curling are analyzed.The results show that the arc-straight groove（ASG）structure has the best comprehensive cutting performance.Based on the support vector regression（SVR）optimized by the Bayesian method,the cutting performance prediction models of micro-groove tool are established,and the optimal micro-groove size parameters are obtained by multi-objective optimization with intelligent algorithm.The optimal two-dimensional micro-groove is placed into the milling cutter model to obtain a micro-groove tool.The simulation results verify the superiority of the cutting performance for the micro-groove tool compared to the original tool.Furthermore,the tool strength adjacent cutting edge area is checked,and the new tool entity is prepared.By analyzing the variation of spray flow field velocity,droplet diameter and spray cone angle during MQL injection,the optimal compressed air pressure and cutting fluid flow rate are determined.On the premise of the optimal spray coverage state,the optimal distance and angle of nozzle arrangement at different positions are calculated,and the droplet distribution characteristics and permeability of tool surface in dynamic milling are analyzed.The heat flux distribution model of the tool-chip contact area in different milling stages is established,and the droplet distribution and the maximum cutting temperature of the tool during single tooth milling are analyzed,then the optimal elevation angle of the nozzle arrangement is determined.Under the optimal injection condition and nozzle position,the micro-channel is designed to improve the permeability of oil mist fluid to the micro-groove region.Two indexes including single micro-channel area(Scs)and micro-channel proportion factor（λc）are introduced to evaluate the influence of micro-channel structure parameters on the maximum cutting temperature,and the optimal micro-channel structure is obtained and the microgroove-microchannel tool is prepared.The cutting performances of the new tools in MQL milling are studied experimentally,and the cutting force,maximum cutting temperature and surface roughness of the original tool,micro-groove tool and microgroove-microchannel tool are compared and analyzed.The internal mechanism of the improvement for cooling and lubrication effect after the placement of microgroove and microchannel is further revealed.The results demonstrate that structural changes of the microgroove tool and the microgroove-microchannel tool increase effectively the time of the wear curve for each stage,and reduce the corresponding wear amount,especially in the normal wear stage,indicating a significant increase in their service life.The wear mechanism of the new tools is revealed by combining the wear morphology and element distribution,and the results indicate that the main wear mechanisms of the three tools are abrasive wear,adhesive wear and oxidation wear.The adhesive wear and oxidation wear of the original tool are serious,while the micro-groove tool and the microgroove-microchannel tool improve the mechanical load and thermal load adjacent cutting edge area,and relieve the rake wear and flank wear.The transient cutting thickness is calculated according to the cutting characteristics of the bull-nose end mill.Combined with the judgment conditions of the tool-workpiece contact state in MQL milling,the cutting force model is established based on the infinitesimal cutting edge.The cutting force coefficient is calibrated by the variable feed cutting test,and the cutting force prediction model is obtained.Based on the infinitesimal cutting force,the material removal power consumption model is constructed to predict the specific cutting energy,and the influences of cutting parameters on the material removal power consumption and specific cutting energy for the new tools are explored.The prediction model of surface roughness is established by response surface method,and the relationship between specific cutting energy and surface roughness is analyzed.Aim to reduce specific cutting energy and surface roughness,the multi-objective optimization models are established and the optimal cutting parameters are obtained.According to different milling process requirements,the sub-mode TOPSIS method and the entropy weight TOPSIS method are proposed to obtain the optimum cutting parameters,which provide an optimized process scheme for new tools. |
