| Ti-6Al-4V has been widely used in aerospace,automotive industry.Efficient and clean machining technology for machining Ti-6Al-4V has been a hot research area in recent years.Ti-6Al-4V is seen as a typical difficult-to-machine material due to its low thermal conductivity,small elastic modulus and active chemical properties at high temperatures.A large amount of cutting heat is generated during the Ti-6Al-4V machining process and accumulates in the cutting area,which impairs the machined surface quality and seriously deteriorates the dimensional accuracy and service life of the machined components.In order to improve the machinability and improve the surface integrity of Ti-6Al-4V,high-pressure coolant(HPC)has been proposed to improve the heat exchange in the machining process.The effects of HPC on the surface integrity of Ti-6Al-4V were analyzed.The purpose of improving the machinability and service life was achieved.Cutting fluid can effectively exchange heat,increase the energy dissipation efficiency with the cutting area during machining Ti-6Al-4V process and improve the Ti-6Al-4V machinability effectively.First,the supply strategies of cutting fluid were analyzed.Based on the principle of capillary penetration,a penetration model of the cutting fluid was established.The penetration velocity and the penetration pressure calculation formula of the cutting fluid were deduced.Then the permeation mechanism of the cutting fluid between the tool-chip and the tool-workpiece contact surfaces was analyzed.The lubrication mechanism and cooling mechanism of cutting fluid on machining process were stated.The lubrication model and cooling model of the cutting fluid in the cutting process were established based on heat transmission science and fluid mechanics.The calculation formula for the forced convection heat transfer coefficient of the cutting fluid under HPC was deduced.When the coolant is injected from two nozzles and the cutting fluid pressure is 200 bar,the heat transfer coefficient of the cutting fluid is 3.7 times than that of the conventional cooling.Secondly,the cutting force and cutting temperature were measured by the orthogonal turning experiments of Ti-6Al-4V.Different cutting environment has been analyzed,including dry cutting,conventional fluid,and high-pressure coolant.The influence mechanism of injection position on cutting force and cutting temperature was investigated.The cutting force decreases with the increase of coolant pressure when the coolant is injected from the rake face or the both faces.However,the cutting force increases with the increase of coolant pressure when the coolant is injected from the flank face injection.The average friction coefficient of the cutting area was derived and calculated.Then the friction coefficient histogram under different cuttingenvironments and nozzle positions was plotted.And the influence of cutting environment and nozzle positions on the lubricating performance of cutting fluid was analyzed.The lubricating effect of the cutting fluid is greatest when the liquid is injected from rake face.Finally,the machined surface integrity of Ti-6Al-4V was observed and analyzed,including surface morphology,plastic deformation,micro hardness and residual stress.Under wet cutting environment,the surface integrity of Ti-6A1-4V has been improved and the surface roughness is reduced.In addition,the influence depth of the plastic deformation layer is reduced,the degree of surface layer hardening is reduced and the residual compressive stress is increased.With the increase of cutting coolant pressure,the surface integrity of Ti-6Al-4V has been further improved.When the coolant is injected from the rake face nozzle,is improved with minimal level.The effect of flank face injection is secondary.Greatest improvement of the Ti-6Al-4V surface integrity can be achieved when the coolant is injected from the double nozzles. |
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