Uncertainty of temperature measurements by infrared thermography for metal cutting applications

Abstract

This paper presents a comprehensive analysis of the uncertainty in the measurement of the peak temperature on the side face of a cutting tool, during the metal cutting process, by infrared thermography. The analysis considers the use of a commercial off-the-shelf camera and optics, typical of what is used in metal cutting research. A physics-based temperature measurement equation is considered and an analytical method is used to propagate the uncertainties associated with measurement variables to determine the overall temperature measurement uncertainty. A Monte Carlo simulation is used to expand on the analytical method by incorporating additional sources of uncertainty such as a point spread function (PSF) of the optics, difference in emissivity of the chip and tool, and motion blur. Further discussion is provided regarding the effect of sub-scenel averaging and magnification on the measured temperature values. It is shown that a typical maximum cutting tool temperature measurement results in an expanded uncertainty of U = 50.1 • C (k = 2). The most significant contributors to this uncertainty are found to be uncertainties in cutting tool emissivity and PSF of the imaging system.

Handy method to estimate uncertainty of temperature measurement by infrared thermography

“…Furthermore, the comparisons made to the work presented in Ref. 11 show very similar results for contributions from emissivity uncertainty. A discrepancy can be seen between the results for the uncertainty of emissivity of the inspected object when compared to the work presented in Ref.…”

“…11 The nondependence of temperature considers that no significant superficial changes, which could affect its emissivity, occur to the inspected object. 11 …”

“…11 suggests a laboratorial procedure to determine the function that relates the internal camera signal to the temperature of the inspected object. Unfortunately, this procedure is not practical for the regular thermographer because the resources needed are not common in service shops and because thermal imagers may use different internal calibration models.…”

“…Unfortunately, this procedure is not practical for the regular thermographer because the resources needed are not common in service shops and because thermal imagers may use different internal calibration models. 11 In addition to the recommendation that all measurements should be accompanied by their associated uncertainty, 3 the estimation of measurement temperature uncertainty helps the thermographer to make more accurate diagnoses. For instance, in electrical maintenance, the criteria of temperature difference indicative of faults is ∼5°C, 12-15 a value for which the measurement uncertainty should be a maximum of 1 to 2°C (approximately one third of the tolerance of the measurement process).…”

Insights Into Machining of a β Titanium Biomedical Alloy from Chip Microstructures

“…Therefore, the actual temperature at the interface between the cutting face of the tool and the chip may be substantially higher than those reported. Additionally, infrared thermography temperature measurements are acknowledged to be subject to substantial error [32,33] and temperatures in the cutting zone are far from uniform, being typically characterised by regions of high temperature gradient [34,35]. The microstructural characterisation of the chips gives some insight into the degree of these temperature gradients for machining of the solution treated and aged Ti-25Nb-3Mo-3Zr-2Sn alloy.…”