Machinability assessment and enhancement of aerospace alloys through workpiece preheating in end milling

Abstract

Aerospace alloys such as nickel based superalloy Inconel 718 as well as titanium based T1-6A1-4V are generally regarded as difficult to cut materials. Numerous research works have been conducted on their machinability in the past few decades with the main objective of reducing cost of machining. Though classified as "difficult-to-cut" materials, they are attractive materials due to their high strength, which is maintained up to elevated temperatures and their exceptional corrosion resistance. Induction preheating is one of the new variable parameters to improve the machinability of Inconel 718 and Ti-6A1-4V. In the current work the influence of heating parameter i.e. preheating temperature; cutting variable, such as cutting speed, feed and axial depth of cut were investigated during end milling operation on a CNC Vertical Machining Center (VMC). The inserts used were TiAIN coated carbide filled onto a 20 mm diameter end mill tool. The machining experiments were conducted under room temperature and preheated conditions. Response Surface Methodology (RSM) was used to develop empirical models of tool life, cutting force and surface roughness both for room temperature and preheated machining conditions using the data generated from the machining experiments. The developed RSM models for tool life were further coupled with Genetic Algorithm (GA) to maximise metal removal per tool life by optimising the cutting conditions and preheating temperature. The comparison between room temperature and preheated machining were made in terms of tool life, cutting force, surface roughness and machine tool vibration. It was found that preheating had reduced the tool wear, surface roughness, vibration/chatter amplitudes and chip formation stability to a desired level.