Study On Micro-texture Self-lubricating And Pulsating Heat Pipe Self-cooling Dry Cutting Tools

The concept of self-lubricating and self-cooling dry cutting tool based on surface texturing and pulsating heat pipe is proposed in this paper. A new micro-texture self-lubricating and pulsating heat pipe self-cooling dry cutting tool has been developed successfully, as well as its tribological behaviors, heat dissipation performance, cutting performance, more over, the self-lubricating and self-cooling mechanisms are studied and analyzed in detail.Based on the analysis of the mechanism of friction and lubrication in cutting process, the concept and design ideas of micro-texture self-lubricating tool is proposed. Micro-textures are made on the rake face of tool inserts, and solid lubricants are filled into the textured grooves to form micro-texture self-lubricating tools. During cutting process, due to the friction and extrusion of the chip which slides against the tool rake face at high speed, the solid lubricants may be released from the textured grooves and smeared on the tool-chip interface. Then a thin lubricating film, which can be acted to reduce the friction coefficient and adhesion, may be formed between the tool-chip interface. The structure of the micro-textures is studied and optimized. The effect of micro-textures on stress distribution of the cutting tools is analyzed and the appropriate structural parameters of micro-textures are put forward:the micro-textures are with double-elliptic structure, the long diameter and short diameter of the external elliptic are0.8mm and0.6mm respectively, the distance between micro-textures and cutting edge is150μm, the distance between textured grooves is150μm, the width and depth of the textured grooves are50μm and100μm respectively. Molybdenum disulfide solid lubricants(MoS2) are selected as the used lubricating material. The micro-texture self-lubricating tools are fabricated by laser machining.The concept and design ideas of pulsating heat pipe self-cooling tool is proposed, namely that by the excellent heat transfer performance of the pulsating heat pipe, enhance the dissipation of cutting heat to achieve the self-cooling tools. Based on the temperature environment of cutting process and the structure size of tool inserts, the pulsating heat pipe is designed and the appropriate parameters are put forward:the working fluid is water, the pipe wall material is copper, the outer diameter and inner diameter of the pipe are2mm and1.2mm respectively, the filling rate of working fluid is60%. Four-bend, six-bend and eight-bend pulsating heat pipe self-cooling tools are fabricated by electrical discharge machining.The effect of surface textures on friction properties of cemented carbide tool material is studied. Dry sliding friction and wear tests against titanium alloy balls were carried out with the smooth surface without solid lubricants (SS), the smooth surface burnished with molybdenum disulfide solid lubricants (SSL), the textured surface without (TS) and with solid lubricants (TSL) for comparison. The results show:the SSL sample can not effectively improve the frictional performance of the cemented carbide, the TS sample has a worse tribological behavior compared with the SS sample, however, only the TSL sample shows the benefit in improving the tribological properties. The average friction coefficient and average friction temperature of the TSL sample are reduced by20～25%and8～15%compared with that of the SS sample respectively. Adhesion of titanium alloy materials on the worn cemented carbide surface is the main wear form, the TSL sample can reduce the width of wear scars on the cemented disks and wear loss of titanium alloy balls. The anti-friction mechanism of the TSL sample is put forward:in friction process, the solid lubricants filled in the textured grooves are released and smeared on the worn surface by frictional extrusion, as a result, forms a dynamic thin lubricating film at the ball-disk interface. Meanwhile, the textured grooves can trap wear debris, which is also benefical to the reduction in friction and wear.The effect of pulsating heat pipe on cutting heat dissipation is studied by numerical simulation. The heat flux loaded on the tool-chip interface is solved by a method of inverse evaluation, and then the temperature field of cutting tools is analyzed. The results show:the maximum cutting temperatures of the pulsating heat pipe self-lubricating tools are lower than those of the conventional tool, the pulsating heat pipe self-cooling tools can also reduce the time from the beginning of cutting to the steady state of cutting temperature.Cutting tests on Ti6A14V alloy are carried out with the micro-texture self-lubricating tool(SLT), the pulsating heat pipe self-cooling tool(SCL), the micro-texture self-lubricating and pulsating heat pipe self-cooling tool(SLCT) as well as the conventional cutting tool(CT). The results show:compared with the CT tool, the SLT and SLCT tools can reduce three direction cutting force, friction coefficient at the tool-chip interface and chip thickness ratio, and increase curly degree of the chip. The SLT, SCT and SLCT tools can reduce cutting temperature and tool wear compared with the CT tool, operation with the SLCT tool could obtain the lowest cutting temperature and tool wear.The mechanism of that the micro-texture self-lubricating and pulsating heat pipe self-cooling dry cutting tool improves the cutting performance is analyzed. On the one hand, during cutting process, the solid lubricants filled in the textured grooves are released and smeared on the tool-chip interface and form a lubricating film, which can reduce the frictional shear strength and tool-chip contact length, as a result, the cutting force, cutting temperature and chip thickness ratio are reduced and the curly degree of the chip is improved. On the other hand, the pulsating heat pipe can enhance the dissipation of cutting heat, as a result, reduce the cutting temperature.