Combined Effects of Stress and Temperature During Ductile Mode Microlaser Assisted Machining Process

Abstract

This work emphasizes the stress and temperature effects during the microlaser assisted machining (μ-LAM) process using three approaches: normalized cutting force approach, yield strength as a function of temperature approach and yield strength as a function of pressure and temperature approach. μ-LAM is a ductile mode material removal process developed for precision machining of nominally brittle materials augmented with thermal softening (provided by laser heating). In the μ-LAM process, a laser is used for heating the workpiece where the laser passes through the optically transparent diamond tool and emerges at the tool-workpiece interface, in the chip formation zone. This work is mainly focused on ductile mode machining of Silicon Carbide. 2D Numerical simulations were conducted using the software AdvantEdge (developed by Third Wave Systems) to predict the cutting forces and pressures that occur during the μ-LAM process. A thermal softening curve was developed based on various references to incorporate this behavior in the simulations. A thermal boundary condition was defined on the workpiece top surface to mimic the laser heating effect. The thermal boundary temperatures were varied from room temperature (20 °C) to 2700 °C, close to the melting point (2830 °C) of silicon carbide (SiC). The decrease in yield strength is also predicted from the thermal softening curve. The first approach (normalized cutting force) is based on the cutting forces obtained from the simulation output. It is an approximate way to represent the relative dominance of stress and temperature. The second approach determines the temperature (percentage) contribution using the yield strength at room temperature and at higher temperatures. The third approach (yield strength) is based on calculated yield using the Drucker–Prager pressure sensitive yield criterion. The stress values for the calculation of yield are obtained from the simulation output. The results from all of the approaches show a similar effect of stress and temperature on the workpiece at the simulated temperature points. The cutting pressures also decrease rapidly above the thermal cutoff point.