Research On Atmospheric Pressure Cold Plasma Jet Assisted Machining Of Pure Iron Material

Pure iron materials are widely used in the fields of aerospace instrumentation,electrical communication and detonation physics due to their excellent plasticity properties,impact toughness and low cost.However,due to the high plasticity and toughness,work hardening tends to be serious,and built-up-edge easily forms,which affects the surface integrity of the machined pure iron surface and tool life.The introduction of atmospheric pressure cold plasma jet with rich active particles in the cutting area can effectively control the complex thermal conditions of the tool-workpiece contact area,improve the surface wettability and reduce its tensile strength,further improving the machinability of pure iron materials.In this paper,we proposed a new machining method using atmospheric pressure cold plasma jet to adjust material properties of pure iron during micro-milling and precision turning process,and then compared the machining performance under different atmospheres.The main research work of this paper was summarized as follows:The influence mechanism of atmospheric pressure cold plasma jet on pure iron surface wettability and mechanical properties was investigated by cold plasma modification test,tensile test and nano-indentation test,respectively.The experimental results show that the cold plasma can effectively improve pure iron surface wettability by changing surface composition while not influencing surface microstructures,which indicated that the cold plasma helped lubrication medium to fully enter the tool-workpiece contact area.In addition,the tensile strength and micro-hardness of the workpiece after cold plasma treatment were also decreased,resulting in the surface material of the workpiece removed easily,suppressing the plastic lateral flow and improving the quality of the machined surface.On the basis of the surface modification mechanism investigation,micro-milling experiments with PCD tool were performed under different atmospheres.Then,the influences of different cooling/lubrication conditions on surface roughness,surface microtopography,micro-milling force and residual stress were also discussed in details.The experimental results show that the plastic lateral flow of the machined surface was suppressed to obtain the surface roughness of Ra= 0.027 ?m with cold plasma+fog assisted micro-milling.And compared with dry micro-milling,the surface roughness,cutting force and residual stress of cold plasma+fog assisted micro-milling were reduced by about 42%,72% and 50%,respectively.In order to further expand the application of atmospheric pressure cold plasma jet in the large-scale machining of pure iron,precision turning experiments were performed under different atmospheres.The effects of cold plasma jet on the surface integrity,cutting force and tool wear in the process of turning pure iron were also analyzed.The experimental results show that the surface integrity of workpiece was significantly improved with cold plasma assisted turning,and its surface roughness was reduced by about 59.6% compared with dry turning.In addition,the tool marks,chips and plastic flow on the machined surface with cold plasma assisted turning were also relived.The cutting force and friction coefficient of tool-chip with cold plasma+MQL assisted turning were significantly decreased.The cold plasma was also found to reduce the flank face wear and notch wear of carbide tool during turning process.Even after 60 min of high-speed turning,compared with dry turning,the flank face wear,major notch wear and minor notch wear with cold plasma assisted turning were reduced by 12%,15% and 14.5%,respectively.