Cutting Force Modeling When Milling Nickel-Base Superalloys

Superalloys are a relatively new class of materials that exhibit high mechanical strength, ductility, creep resistance at high operating temperatures, high fatigue strength, and typically superior resistance to corrosion and oxidation even at elevated temperatures. These properties make superalloys ideal for applications in aircraft, cryogenic tanks, submarines, nuclear reactors, and petrochemical equipment. In the aerospace industry, the most commonly used superalloy is the nickel-base alloy and it accounts for 30–50% of the total material required in the manufacturing of the aircraft engine. It is used for rotating parts of gas turbines such as blades and disks, engine mounts, turbine casings and components for rocket motors and pumps. To make full use of nickel-base superalloys, a machining process must be developed that is capable of controlling and identifying tool wear, and identifying the onset of subsurface damage and controlling its formation during processing. To accomplish this, a model relating process characteristics and cutting parameters need to be developed. Due to high tool wear, the cutting forces increase drastically during machining, thus making impossible to estimate the forces with existing models. This research proposes an update to the specific cutting forces model taking into consideration rapid tool wear. As milling is the most common machining processes used to cut superalloys (e.g., turbine blades), it is specifically targeted by this research. Experiments were conducted under different cutting conditions to observe the cutting characteristics of nickel-base superalloys. Empirical observations were used to formulate updated coefficients. Later this model will be applied for real-time control of the process results, such as geometry, tool wear and subsurface damage, and also for estimation and control of other quantities such as force, deflection, surface quality and energy consumed. This will provide new insights into machining these advanced alloys.