Study On Machining Performance And Parameter Optimization Of Low Temperature Micro Lubrication Turning 304 Stainless Steel

Minimum Quantity Lubrication(MQL)has been proposed to solve environmental and health problems caused by flood cutting.It's also a new and efficient solution for difficult-to-process materials like 304 steel which is widely used in the modern manufacturing industry because of its corrosion resistance and mechanical characteristics.MQL has been proved to be superior to flood cutting,but there is still a lack of feasibility study on it.Due to this lack,the practical application relies much on operational experience.In most studies,the MQL parameters and cutting parameters were studied and optimized separately,and the results can only be applied to specific processing.The friction heat between the flank and the workpiece was frequently neglected in the analysis of tool surface temperature distribution.In this study,cutting experiments of 304 steel under the condition of Minimum Quantity Cooling Lubrication(MQCL)were carried out,as well as related research.Firstly,the shearing and friction between tool and workpiece in turning process were analyzed.Based on shear friction theory,the tool wear mechanism and the influencing factors of workpiece surface quality were analyzed.Based on Zorev's power law of stress distribution,the relationship between the stress distribution and the division of tool wear area was obtained.Based on Fourier heat transfer equation,the heat source intensity model in cutting was established.And the moving line heat source model was used to approximate the ones in the shear zone,tool-chip friction zone,and tool-work friction zone.Besides,a temperature distribution model of the cutting tool was established to analyze the factors that caused the cutting heat.Additionally,the cooling and lubrication effects of the droplet on cutting were analyzed based on Willimas and Tabor's "capillary" theory and boundary lubrication film.An orthogonal experimental scheme considering both lubrication and cutting parameters was designed.And an experimental system with seven adjustable parameters,including cutter feed,cutting speed,air temperature,fluid flow,wind speed,and injection direction,was built for the study.Surface roughness,surface contour curve,surface hardness,and tool vibration data were collected during the experiment.The effects of tool feed rate,cutting speed on surface roughness,surface hardness,and tool vibration was analyzed by single factor experiments.The results show that the surface roughness is related to the feed rate,but the tool vibration can also reflect the change of the surface roughness.Higher cutting speed can reduce tool vibration,but in this case,cutting tool impact will occur when cutting into the workpiece.The results show that the relationship between surface roughness and cutting parameters is similar to that of flood cutting type,which proves that MQCL has sufficient cooling and lubricating capacity for cutting zone.The tool wear's morphology and wear surface composition were analyzed by SEM and EDS.The results show that adhesion wear is the main form of tool wear at MQCL.The increase of cutting speed will aggravate tool wear,while feed speed and cutting depth mainly affect the distribution of wear area.Also,the injection angle of MQCL has an important influence on chip discharge.The injection from the rake face can blow the chip off the tool surface and make the cutting fluid penetrate the tool-chip contact area effectively,which has good lubrication and cooling effect.On the contrary,spraying from the main flank may blow chips into the direction of tool feed,which increases the risk of twining tools and workpieces.While spraying from the secondary flank was beneficial to chip cleaning,but the cooling and lubrication of the cutting area were reduced due to the occlusion of the tool and the surface which is to be machined.Finally,the range analysis of the orthogonal experimental results was carried out to obtain the relationship between the surface roughness and tool wear under the condition of MQCL,and the optimal combination of parameters was selected.An empirical model considering cutting and lubrication parameters was established,and a multivariate linear regression equation was established by the least square method.Meanwhile,the data outliers were removed by the residual diagram.Multivariate linear regression analysis of experimental data was taken out using MATLAB.The accuracy of the model was verified by residual analysis,comparison between predicted and actual values.With the objective of minimizing surface roughness and tool wear,the parameters were optimized by using FOA algorithm,and then the optimal parameters combination has been obtained.