Investigation On Tool Wear Properties Of Milling Inconel Overlays And Its Application

Nuclear steam turbines are working in saturated hot and wet steam environment for a long period time.The the rotor supported intake port and exhaust port on equatorial plane of the cylinder are prone to corrosion and cracking,resulting in device failure.The use of anti-corrosion and anti-wear Inconel overlays depositing and covering on them can be an effective way to prevent this failure.A smooth flat surface of deposited Inconel overlays are obtained by milling process to ensure the upper and lower half of the cylinder fit tightly.However,the poor thermal conductivity and strong adhesive properties of Inconel as well as the low surface quality and poor consistency of the overlays make the tool wear or breakage severely,which is an urgent manufacuring problem to overcome.In this paper,the irregular,non-uniform Inconel overalys covering on rotor supported intake port and exhaust port on equatorial plane of the nuclear steam turbine cylinder are studied as an object,wear properties of cemented carbide milling tool are studied as a breakthough.Finally,the tool wear prediction model of milling Inconel overlays is established by real-time monitoring the milling characteristic parameters with or without the green manufacturing technology Minimal Quantity Lubrication.The main work are shown as following:（1）The effect of overlay thickness on the material and machining properties are studied.By investigating the micro-hardness and metallographic structure of Inconel overlays at different overlay thickness.It is concluded that each welding process will lead to carbides precipitation of Inconel overlays,which is the main reason of its machinability variation.After analyzing the effects of overlay thickness on milling variables including milling force,milling temperature,surface roughness and surface morphology,the optimal overlay thickness is determined by multi-objective optimization.It shows that the machinability of Inconel overlays is acceptable when overlay thickness is less than welding wire diameter,it is poor when overlay thickness is larger than welding wire diameter but no more than twice welding wire diameter,and it is stable when overlay thickness is larger than twice welding wire diameter.（2）The friction and wear properties of Inconel overlays are investigated.Tool material cemented carbides and workpiece material Inconel overlays are adopted as friction pairs to conduct friction and wear test.The effects of temperature on friction coefficient and wear rate are investigated.Focus is concentrated on worn surface morphology,phase composition and wear mechanism of uncoated and coated cemented carbides.The results show that when the temperature rises,the friction coefficient decreases and the wear rate increases.When the temperature is less than 600°C,the main wear mechanism is adhesive wear and abrasive wear.When the temperature is higher than 600°C oxidation wear began to appear.TiAlN coating has strong oxidation resistance at high temperature,but its wear resistance and anti-adhesion properties are relative poor at low temperature.On the contrary,TiN coating has strong wear resistance at low temperature,but its strong oxidation resistance at high temperature are relative poor.（3）Tool wear of milling Inconel overlays are studied.Cutting parameters optimization tests are conducted by S/N ratio of surface roughness when face milling Inconel overlays.Wear performance and mechanism of uncoated tool blades,TiAlN/TiN coated blades and TiN/Al₂O₃ coated blades are evaluated by comparison during up and down face milling Inconel overlays using the obtained optimal cutting parameters with or without MQL.Focus are concentrated on the influence of MQL nozzle positions on tool wear.The result shows that the uncoated tool blades are not suitable for face milling Inconel overlays due to the severe wear and catastrophic tool breakage even with the help of MQL.The wear resistant of TiAlN/TiN coated blades are determined by milling mode and lubrication method.MQL nozzle positioned at both tool cut into workpiece and tool cut out of workpiece in down milling as well as MQL nozzle positioned at tool cut out of workpiece in up milling can be selected as the optimal lubrication methods for cutting Inconel overlays with TiAlN/TiN coated blades.TiN/Al₂O₃ coated blades show the best wear resistance.With the help of MQL,its maximum removal volume reaches to 76.8cm³,much higher than uncoated carbide blade of 3.5cm³ and TiAl/TiN coated carbide blade of 18.1cm³.The best way of cutting Inconel overlays with this kind of blades is up milling with MQL nozzle positioned at tool cut out of workpiece.（4）Characteristic signals of milling force,milling temperature,AE and milling power are monitored by comparison with or without MQL to investigate the influence of MQL on these characteristic signals and on the corresponding tool wear.The result shows that milling force signals perpendicular to the feed direction can be used accurately to estimate the lubrication effects of MQL.Compared to milling force signal,there is a time delay when using milling temperature signal.The AE signal data are relative larger and require secondary treating,thus,it cannot be used to real-time monitoring tool wear.Besides,it should be noted that self-excited vibration may be introduced when the tool pass frequency is the multiple of MQL jet frequency especially in down milling process,leading to milling unstable.Thus,the up milling process is more appropriate.During the material remove process of nuclear steam turbine manufacturing using TiN/Al₂O₃ coated blades,up milling with MQL can reduce energy consumption about-3%and can save 114 tool inserts（$1025.4）.Finally,based on the previous study,Taylor tool wear empirical formula is used to match the machinability of tool material and workpiece material.Then milling tool wear prediction model of machining Inconel overlays is established by real-time monitoring the milling characteristic parameters and variables conversion.The experimental data proved that the model can accurately predict the milling tool wear effectively.