Core Temperature Measurement in Subtractive Manufacturing Processes

Temperature variation is one of the most important factors that affect the dimensional accuracy and surface integrity of workpieces during machining processes. Several attempts have been made towards estimating machine tool and workpiece temperature. The techniques used generally depend on the type of material and the level of accuracy required. However, none of the existing techniques gives a true representation of the core temperature of the workpiece. The speed of sound in any material depends on the temperature of the material. This dependence can be used to obtain the temperature of the material, provided that the speed of sound can be obtained. The speed of sound can be obtained using the length of the material and the ultrasonic time of travel through the material. The challenge however arises in developing a cost effective acquisition device that can resolve up to 0.5 °C variation with ± 1 °C accuracy. In order to achieve this goal, simulations were done in MATLAB using the k-wave toolbox to determine the required parameters needed for achieving the stated resolution and accuracy. Sensitivity analysis was conducted and the results show the output of simulation of two viable ultrasonic thermometry methods-the pulse-echo method and the continuous wave method. The results of this study will serve as the input for designing and developing an in-process temperature measurement system for subtractive manufacturing processes.