Evaluation of dimensional deviation in nickel-base, Inconel 718, alloy after grinding under different cooling-lubrication techniques

Inconel 718 is a nickel based alloy that has high resistance to fatigue and creep, ductility, stiffness, chemical inertia and the ability to operate at high temperatures. These properties make the Inconel 718 attractive to be employed in high performance parts. These parts require narrow dimensional and geometric tolerances that can usually be achieved by the grinding process. However, this material presents low machinability, especially because its susceptibility to thermal damages during grinding. In this sense, both lubrication and cooling properties of the cutting fluid must predominate during grinding of this alloy, so any attempt to improve the cutting fluids properties will represent a great contribution. Also, specific literature is still scarce in scientific studies about evaluation of dimensional deviation of ground workpieces and how they are affected by the cutting parameters. In this sense, this work aims to contribute with knowledge in the grinding field by evaluating the influence of different cooling-lubrication techniques on the dimensional deviation of the Inconel 718 workpieces. The machining atmospheres tested were: dry and with cutting fluid. For the latter, cutting fluid was applied via conventional coolant technique (flood) and via the Minimum Quantity Lubrication (MQL) technique. Two values of depth of cut 20 mu m and 40 mu m were testes as input parameters. The results showed that the lowest values of depth of cut (20 mu m) generated smaller dimensional deviations, as would be expected. In addition, grinding with the MQL technique proved to be advantageous in generating the lowest dimensional deviation values. After measurements of the dimensional deviations, IT tolerance grades were calculated and they were within the IT6 - IT5 range, which is in agreement with the one usually mentioned in the specific literature for parts manufactured in nickel-base, Inconel 718, alloy.