The Effects of Emissivity and Camera Point Spread Function on the Temperature Measurement of Segmented Chip Formation Using Infrared Thermography

This paper uses simulation to investigate measurement errors resulting from the camera point spread function (PSF) when measuring the temperature of segmented chip formation using infrared (IR) thermography. The PSF of the IR camera effectively filters the results which can cause significant errors due to the large temperature gradients and abrupt transitions between features and their corresponding emissivity values. The different emissivity values of the tool, workpiece, chip body, and shear band affect the apparent difference in the emitted energy of these different features. This decreases the measured temperature in the regions of most interest: along the tool-chip interface and the periodic shear zone. The method in this study creates an appropriate emissivity map from post-process measurements and applies it to results from the temperature distribution of the cutting zone predicted by commercial finite element analysis (FEA) software. Comparisons between the simulation results and experiment results show that the emissivity values obtained form the post process chip analysis lead to good agreement. The resulting radiant intensity distribution becomes the input for an IR camera simulation module developed by the authors and presented in earlier work [1]. The earlier work used the true temperature distribution predicted by the FEA as the simulation module input, and did not incorporate the IR camera’s PSF. Implementation of the actual IR camera’s PSF allows the simulation module to more accurately represent the measurements of the IR camera and ultimately allow the comparison of the simulation results to the measurement results. Simulation results show that the PSF accounts for 45% of the 42 °C radiance temperature error at the tool-chip contact along the rake face. The PSF accounts for approximately 15% of the 46 °C radiance temperature measurement error at a point in the center of the catastrophic shear band. These errors consider the effects of motion blur (integration time) and magnification (size-of-source), as described in the earlier work [1].