Effects Of TiAlN Tool Coating On Tool-Chip Heat Partition And Cutting Temperature

The cutting tools are admired as the "tooth" of manufacturing industry.The coated tools could be taken as the "tooth with the protective dental crowns".The tool coatings avoid the direct contact between workpiece material and tool substrate in metal cutting process,which can protect tool substrate.The tool coatings affect the cutting heat generation and tool-chip heat partition,prevent the heat diffusion into tool body,thus decrease the tool substrate temperature and exhibit the thermal barrier effect.Consequently,the tool coatings affect the heat transfer and cutting temperature.The tool coating thickness,structure,and component content have influences on coating thermal properties,thus affect the tool-chip heat partition and cutting temperature.The guide line of this paper is to determine the effects of tool coatings on tool-chip heat partition and cutting temperature.The research aims to illustrate the influences of tool coating thickness,component content and thermal physical properties on heat transfer process within coated tools.The machining of GH4169 with TiAlN coated carbide tool is researched.The researches on cutting temperature of coated tool are conducted with the methodologies including the characterization of material physical properties,the theoretical analyzation of heat transfer and cutting principle,the observation of cutting experiment and simulated heat transfer experiments.The exploration for the effects of tool coatings on tool-chip heat partition and cutting temperature,and the guidance for proper design and selection of coated tools to decrease cutting temperature are expected.Firstly,the effects of tool coating thickness and component content on coating thermal conductivity are investigated.The temperature-dependent thermal conductivities of TiAlN coatings deposited by PVD-DC are method are measured.Based on the measurement results and the extended irreversible thermodynamic theory,the temperature-dependent effect and scale effect of tool coating thermal conductivity are illustrated.The effects of Al component content in TiAlN tool coating on coating thermal conductivity are revealed.The research results illustrate that the thermal conductivity of PVD Ti0.55Al0.45N coating increases in the form of a quadratic function with the increase of temperature within temperature ranges 25?500?.The scale effect is existed between the TiAlN coating with the thickness of several nanometers and its thermal conductivity.The scale effect of coating thermal conductivity could be neglected when the TiAlN coating thickness reaches tens of nanometers?micrometers.The different crystal structure of Ti1-xAlxN coating with varied Al component content influences the coating thermal conductivity.The thermal conductivity of Ti1-xAlxN coating firstly decrease with the increase of Al component content,then which increases with Al component content.The coating thermal conductivity is at least 4.6 W/(m·K)when the Al/Ti atomic ratio is 0.72.Secondly,the coated tool-chip heat partition mechanism is analyzed.The time-varying coated tool-chip heat partition prediction model is established with the base on the concept of tool-chip contact micro-element body.The time-varying effect of tool-chip heat partition coefficient is clarified.The continuous turning and interrupted milling nickel-based superalloy GH4169 with coated carbide tools are taken as the examples.The coupling effects of tool coating thickness,thermal physical properties of tool coating,tool substrate and workpiece,and the interrupted milling speed on tool-chip heat partition mechanism are revealed.The two-color temperature measurement device is established and cutting temperature is measured for verification of the time-varying coated tool-chip heat partition prediction model.The research shows that the tool-chip heat partition coefficient is small due to the short duration time of the initial tool-chip contact stage.The tool-chip heat partition coefficient increases and gradually stabilizes with the increase of tool-chip contact time.Thick tool coatings can significantly reduce the tool-chip heat partition coefficient in the initial tool-chip contact stage.With the increase of tool-chip contact time,the influence of coating thickness on the tool-chip heat partition coefficient gradually weakens.The tool coatings and substrates with lower thermal conductivity and higher thermal conductivity could increase the tool-chip heat partition coefficient in machining GH4169.Thirdly,the thermal barrier effect of tool coating is revealed.The tool coating thermal barrier analytical model with the single-sided constant temperature is established.The existence conditions and duration time of coating thermal barrier effect in metal cutting process are revealed.The influencing mechanism of the temperature-dependent thermal properties of tool coating and substrate on coating thermal barrier effect are revealed.The simulated heating device with constant temperature is established.The duration time required from transient heat transfer stage to steady heat transfer stage is measured.The accuracy of the proposed tool coating thermal barrier analytical model is verified.The research shows that the duration time of significant coating thermal barrier effect is within a few to tens of milliseconds.The temperature drop gradient induced by the TiAlN tool coating increases linearly with the increase of tool rake face temperature.The coating thermal barrier effect is more significant under high temperature.The thermal physical properties of the tool substrate also affect the coating thermal barrier effect.The lower coating thermal conductivity,higher substrate thermal conductivity and lower substrate thermal conductivity could enhance the coating thermal barrier effect.Finally,the cutting temperature distribution within coated tool and its influencing factors are studied.The transient and steady cutting heat transfer analytical model under the time-varied heat source applied on tool rake face are proposed and solved.The effects of time-varied heat source,tool coating and substrate thermal properties,the boundary conditions on cutting temperature distribution within coated tool are illustrated.The proposed analytical models could guide for the design of coated tool geometry and selection of material thermal properties,which are verified with the simulated cutting heat transfer experiment.The research shows that the different types of time-varied heat sources affect the heat amount applied per unit area of tool rake face,which induce the difference of the internal temperature rise within coated tool body.In transient heat transfer stage,the thicker TiAlN tool coating,higher coating thermal conductivity,lower coating thermal conductivity,lower tool substrate thermal conductivity,and higher substrate thermal diffusivity could reduce the internal temperature rise within coated tool.In steady heat transfer stage,the thinner TiAlN tool coating and higher coating thermal conductivity could reduce the internal temperature within tool coating.The higher substrate thermal conductivity and higher heat exchange coefficient at the cutting tool-tool holder contact interface could reduce the internal temperature within coated tool body.The results show that for continious turning of GH4169,the thinner TiAlN tool coating should be used.In addition,compared to PVD Ti0.55Al0.45N tool coating,the Ti0.41Al0.59N coating with higher Al component content and higher thermal conductivity can also reduce the cutting temperature in machining GH4169.