Research On Thermal Quenching Damage Mechanism Of Tool In High Speed Inner-cooling Wet Machining

Cutting heat is one of the most important factors that affect the tool life.The tool suffers a periodical alternating thermal load and mechanical load in high speed milling process.The alternating load can lead to the tool breakage failure.Therefore,the change rule of tool temperature can reveal the mechanism of tool thermal quenching damage in high speed inner-cooling wet machining.At present,the following problems are mainly found in the research on cutting tool breakage.Geometric modeling is mostly based on the simplified two-dimensional model.The theoretical results of the temperature field are mostly the average temperature of the tool surface,while the temperature gradient is critical to reveal the failure of the tool formed in the cutting zone.The continuous temperature during the milling process is obtained by cyclic loading the heat flow,and there is an error with the actual generation of cutting heat.In this paper,the method of integrating simulation with experiment is used to study the tool thermal quenching damage during high speed wet milling process,and the mechanism of tool thermal quenching damage is revealed.Firstly,the three-dimensional dry and wet milling models were established based on the workpiece material constitutive model,tool-chip contact friction model and the convective heat transfer characteristic of fluid medium.Through extracting the timetemperature curves of the temperature measuring point at the flank face of tool,it is found that the peak temperature of cutting in and the minimum temperature of cutting out are both rapidly increasing in dry milling,and then the two temperatures reach steady state.However,the peak temperature increases slowly,and the tool temperature of cutting out quickly reduces to room temperature in wet milling.It is indicate that the temperature fluctuation amplitude is the largest at the tip of the blade,and the temperature fluctuation decreases gradually in the direction of the bottom cutting edge and the side edge.It forms a greater temperature gradient at the bottom edge and the side edge of tool in the direction away from the tool nose in wet milling than that in dry milling.So the tool suffers a greater cold and heat inhomogeneity in wet milling than that in dry milling.The temperature fluctuation of the tip is greater in wet milling than that in dry milling.Therefore the tool tip suffers more severe hot and cold alternating shock.Secondly,the continuous cutting real-time temperature of a point is obtained at the flank by using the embedded temperature measuring shank.It is found that the monitored point temperature increases rapidly in dry milling and is higher than that in wet milling.The temperature fluctuation in wet milling is larger than that in dry milling,and it also verifies the simulation model is accurate and reliable.In addition,it is also found that the amplification of tool peak temperature is constant although the cutting speed increases in dry milling.While it decreases gradually in wet milling.The larger diameter of the tool,the lower temperature of tool,and the better surface quality of the milling holes in milling the same diameter holes with different diameter tools.Finally,through analysis the damaged surface morphology after the high speed inner-cooling milling process,it is found that relative fragile interlaced crack takes place at the position close to the edge of end mill with the increase of the cutting speed.The tool thermal stress is obtained by applying the simulated tool temperature field as a body load to the tool surface.By comparing the heat flow in dry milling and wet milling,it is found that the heat flow mainly transmitted to the inside of the tool in dry milling but the heat flow in wet milling is mainly transmitted to the surrounding medium.By analyzing the thermal Mises stress and the maximum tensile stress of the tool,it is observed that the maximum tensile stress has reached the tensile strength range of the cemented carbide material and the cyclic alternating thermal shock can encourage the initiation and propagation of the tool thermal quenching crack.