Study On The Machinability In High Efficiency Machining Of Powder Metallurgy Superalloy

High efficiency and high speed are the development directions of modern manufacturing technologies. In the last two decades years, High efficiency/speed machining is successfully applied in cutting steel and alumina alloy, due to its unique advantages. However, it is not yet prevalent in powder metallurgy (PM) superalloy machining. This dissertation focuses on the machinability and influencing rules in high efficiency/speed machining PM nickel based superalloy, systematically analyzes the selection of the tool material, deformation mechanism, cutting forces, cutting temperature, tool failure mechanism, surface characteristic and corrosion resistance, in order to provide reliable theoretical and practical methods in high efficiency/speed machining this kind of material in production practice.Tool material selection trials were carried out by face milling, and the experimental results show that the TiAlN-TiN coated carbide is the proper cutting tool material for machining PM nickel based superalloy. Shear angles at different cutting parameters were obtained by slot milling trials, the constitutive model for PM nickel based superalloy was established, which can reflect the relationship of shear flow stress, shear strain and strain rate in high speed machining. Considering the effect of work material and cutting speed range, the new shear angle model of PM nickel based superalloy was established by correcting the Merchant shear angle model. Chip deformation rules in machining PM nickel based superalloy were researched, and the model of the mechanism of lamellar type chip was established.Cutting force models of face milling cutting tool were established, and the parameters were fixed by cutting trials so as to correct the model. The empirical formula of cutting force when face milling PM nickel based superalloy using coated carbide tools has been founded by orthogonal experiments. The theoretical models of drilling force of the main cutting edge and chisel edge were established. The empirical formulae of cutting force and torque when drilling PM nickel based superalloy using coated carbide tools at coolant condition have been founded by orthogonal experiments. Because of the porous structure and hard spots in microstructure of the work material, the wavelike phenomena of cutting forces when machining was obviously, which deteriorates the cutting condition. Cutting temperature when milling PM nickel based superalloy has been researched by theoretical analysis and experimental approaches, and also the empirical formula has been founded. Drilling average temperature models of shear plane and chip-tool interface were developed according to the drilling equivalent model, which can obtain the drilling average temperature-of any point in the main cutting edge. The temperatures near drilling area when using coated carbide tools at coolant condition were obtained by orthogonal experiments, and also the empirical formula was founded. The drilling temperatures were obtained by reverse estimate, the empirical formula of drilling temperature was founded.The effects of cutting speed on surface roughness and work hardening when milling PM nickel based superalloy were researched by single factor trials. The results indicate that, the better surface roughness can be obtained while in higher cutting speed; the hardening phenomenon is serious and the hardening degree reaches to 125%-140%; when cutting speed increase to 70-90m/min, the thickness of damaged layer reaches to 20-30?m. The empirical formula of surface roughness when face milling PM nickel based superalloy using coated carbide tools has been founded by orthogonal experiments. Salt mist corrosion testings and analysis were carried out on machined surface. The results indicate that, the corrosion resistance of machined surface is consisted with the surface roughness. The relationship model between corrosion resistance and cutting parameters was founded.Systematic researches have been conducted on tool failure patterns and failure mechanisms in face milling and drilling PM nickel based superalloy. Adhesive wear, diffusion wear, abrasive wear and peeling off are predominating failure mechanisms of milling cutting tools. Adhesive wear and oxidation wear are the main failure mechanisms of drilling cutting tools at coolant condition. Fatigue failure under the coupled thermo-mechanical load is the main failure mechanism of drilling cutting tools without coolant supply. The empirical formula of tool life when face milling PM nickel based superalloy using coated carbide tools has been founded, the results show that cutting speed and feed ratio have a great influence on the tool life of milling.Comparison of the machinabilities of PM nickel based superalloy and Inconel 718 was carried out by tool life, tool wear, cutting forces, chip formation and surface roughness. The machinability rate of Inconel 718 is higher than that of PM nickel based superalloy. Comparing the machinability at the maximum cutting speed of the two alloys, it can be deduced that the machinability of the PM nickel based superalloy could be approximately 30% of the Inconel 718.This work is sponsored by the National Basic Research Program of China (973) (Grant number 2009CB724401) and the Key Projects in the National Science & Technology Pillar Program (Grant number 2008BAF32B01).