Measurement of grinding temperatures using a foil/workpiece thermocouple

Abstract

The high temperature generated in abrasive processes is the main factor responsible for thermal damage to a ground surface. It can be predicted through the thermal balance of the heat fluxes in the process. Such predictions can be experimentally verified using a foil/workpiece thermocouple. To estimate the thermal behaviour of such a sensor, it was dynamically calibrated with a laser beam to measure its frequency response. It was found that the response of the sensor has a time constant dependant on the thermal load and cannot be modelled by a simple first order function. In the calibration conditions used, the sensor is fast enough to measure the surface temperature with a time constant less than 100 microseconds.A high frequency acquisition system allows the signal to be measured at the local grit scale so that the activity of grits and the contact stability between the foil and the workpiece during grinding can be studied. By using the peak temperature and the local cooling after a peak, suitably processed, a local background temperature can be defined. It is shown that this background temperature can be evaluated more accurately by matching the global cooling curve to a finite element solution. The temperatures obtained from the local minima of the local diffusive cooling curve agree better with measured results than a temperature obtained by low pass filtering, which can overestimate the background temperature and so the partition ratio.Keywords: grinding; temperature; thermocouple; dynamic calibration; heat transfer; signal processing Measurement of grinding temperatures using a foil/workpiece thermocouple AbstractThe high temperature generated in abrasive processes is the main factor responsible for thermal damage to a ground surface. It can be predicted through the thermal balance of the heat fluxes in the process. Such predictions can be experimentally verified using a foil/workpiece thermocouple. To estimate the thermal behaviour of such a sensor, it was dynamically calibrated with a laser beam to measure its frequency response. It was found that the response of the sensor has a time constant dependant on the thermal load and cannot be modelled by a simple first order function. In the calibration conditions used, the sensor is fast enough to measure the surface temperature with a time constant less than 100 microseconds.A high frequency acquisition system allows the signal to be measured at the local grit scale so that the activity of grits and the contact stability between the foil and the workpiece during grinding can be studied. By using the peak temperature and the local cooling after a peak, suitably processed, a local background temperature can be defined. It is shown that this background temperature can be evaluated more accurately by matching the global cooling curve to a finite element solution. The temperatures obtained from the local minima of the local diffusive cooling curve agree better with measured results than a temperature obtained by low pass filtering, which can overestimate...

Effect of grinding on the sub-surface and surface of electrodeposited chromium and steel substrate

“…The experimental background temperature was determined by the lower envelope (see Fig. 8) of the signal delivered by the thermocouple [13]. The signals are shown in Fig.…”

“…For the modelling under dry grinding condition (sample Td), the thermal load is a triangular heat distribution with a length l e = 4 mm moving at the 2 m·min − 1 workpiece velocity. The mean heat flux q w,m = 29 W·mm −2 was obtained by fitting the FE temperature rise on the experimental temperature curve in the cooling zone behind the arc of contact [13]. Under wet grinding conditions (sample Tw), the fluid cooling is taken into account by using a heat transfer coefficient h. During the wet grinding test (sample Tw), the background temperature largely exceeds the boiling temperature of the cooling fluid (about 100-150°C for water based emulsion), so that burnout occurs and convection in the fluid is greatly reduced.…”

“…These previous works have essentially focused on the chip formation [10], the modelling of the stresses and temperature fields [11], the evaluation of the temperature at the tool/material interface and within the material [12,13] and on the microgeometry and topography of the machined surface in conjunction with the variation of some grinding wheel characteristics [14]. These investigations were essential to better understand the grinding process and to improve its effectiveness.…”

Determination of the Partition Coefficient for the Grinding of a HardWC-Co-CrCoating with a Diamond Wheel

“…In the second method, the junction consists of numerous microcontacts, which are formed directly at the surface by the plastic deformation induced by the grinding grits. Earlier work on the single pole grindable thermocouple (Lefebvre et al, 2006(Lefebvre et al, , 2012 has identified the sources of uncertainty in the temperature measured at the interface: • The thermal inertia: as the response time of the thermocouple (between a few microseconds and a few milliseconds) is considerably less than the contact time of the wheel with the junction (several tens of milliseconds), this error can be ignored for surface grinding. • The intrusive effect of the thermocouple itself: the maximum temperature measured and the absorbed flux depend on the thermophysical properties of the materials used in the thermocouple assembly, the thickness of the junction and the grinding conditions.…”

On a stochastically grain-discretised model for 2D/3D temperature mapping prediction in grinding

“…Besides, thin film thermocouples or foil thermocouples were also utilised in Refs. [2,[37][38][39][40][41], which have the advantages including the extremely small size of the measure junction to capture temperature signals within a very small area [42].…”