Bin Shen Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109 Guoxian Xiao Manufacturing Systems Research Laboratory, General Motors R&D, Warren, MI 48092 Changsheng Guo United Technologies Research Center, East Hartford, CT 06108 Stephen Malkin Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA 01003 Albert J. Shih Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109 Thermocouple Fixation Method for Grinding Temperature Measurement A new thermocouple fixation method for grinding temperature measurement is presented. Unlike the conventional method using a welded thermocouple, this new method uses epoxy for affixing the embedded thermocouple within a blind hole in the workpiece subsurface. During grinding, the thermocouple junction is exposed and bonded to pro- vide direct contact with the ground surface by the smearing of the workpiece material. Experiments were conducted to evaluate this simplified thermocouple fixation method including the effect of thermocouple junction size. Heat transfer models were applied to calculate the energy partition for grinding under dry, wet, and minimum quantity lubri- cation (MQL) conditions. For shallow-cut grinding of cast iron using a vitreous bond aluminum oxide wheel, the energy partition using a small wheel depth of cut of 10 m was estimated as 84% for dry grinding, 84% for MQL grinding, but only 24% for wet grinding. Such a small energy partition with wet grinding can be attributed to cooling by the fluid at the grinding zone. Increasing the wheel depth of cut to 25 m for wet grinding resulted in a much bigger energy partition of 92%, which can be attributed to fluid film boiling and loss of cooling at the grinding zone. DOI: 10.1115/1.2976142 1 Introduction The grinding process generates an extremely high input of en- ergy per unit volume of the material removed 1. Virtually all this energy is converted to heat, which can cause high temperatures and thermal damage to the workpiece such as workpiece burn, phase transformations, undesirable residual tensile stresses, cracks, reduced fatigue strength, and thermal distortion and inac- curacies 1. Numerous studies have reported on both the theoret- ical and experimental aspects of heat transfer in grinding. Early research concentrated on predicting workpiece surface tempera- tures in dry grinding in the absence of significant convective heat transfer 2–5. Subsequent investigations have provided a detailed understanding of heat transfer to the workpiece, abrasive grains, grinding fluid, and the chips 6–12. Thermal models have been developed to estimate the workpiece surface temperature, heat flux distribution in the grinding zone, fraction of energy entering the workpiece, and convective heat transfer coefficient for cooling on the workpiece surface. Experimental investigations of heat transfer in grinding require accurate temperature measurements. Methods for temperature measurement in grinding include thermal imaging 13,14, optical fiber 15–17, foil/workpiece single pole thermocouple 18–22, and embedded double pole thermocouple 23–28. The embed- ded thermocouple method is the most widely used of these tech- niques because of its relative simplicity, low cost, accuracy, and reliability. With this method, a double pole thermocouple is welded to the bottom of a blind hole drilled close to the ground surface from the underside of the workpiece 25,26. Welding the small tip of a double pole thermocouple at the bottom of the small hole requires special discharge welding equipment and skills. Dur- ing grinding, the thermocouple measures the temperature below the workpiece surface during successive passes until the welded junction is broken by the grinding action. Accurately determining the position of the temperature measurement below the surface being ground is complicated by its size and also the blind hole. Furthermore the embedded thermocouple and the hole can disturb the local temperature field. Therefore it is desirable to make the thermocouple and hole very small. The present investigation was undertaken to evaluate a simpler embedded thermocouple method for grinding temperature mea- surement, which uses epoxy instead of welding to affix the ther- mocouple at the bottom of the blind hole. During grinding the thermocouple junction is exposed and bonded to the workpiece by smearing of the workpiece material, thereby providing direct con- tact with the workpiece surface and a direct temperature measure- ment at the workpiece surface. Experiments are conducted that compare the performance of epoxy fixated thermocouples with that of welded thermocouples in terms of temperature measure- ment and energy partition for dry grinding, wet flood grinding, and minimum quantity lubrication MQL using minuscule amounts of grinding fluid. 2 Experimental Setup 2.1 Grinding Test Setup. Straight surface plunge grinding experiments no crossfeed were conducted on an instrumented Chevalier Model Smart-B818 surface grinding machine using the setup shown in Fig. 1. The grinding wheel was vitreous bonded aluminum oxide Saint-Gobain/Norton, Worcester, MA, 32A46- HVBEP of initial diameter d s = 177.8 mm and width b s = 12.7 mm. The workpiece material was Dura-Bar 100-70-02 ductile iron with a carbon content of 3.5–3.9%, Rockwell hard- ness HRC 50, thermal conductivity of 63 W / m K, and thermal diffusivity of 1.63  10 -7 m 2 / s. The workpieces were of length 57.5 mm in the grinding direction and width b w = 6.5 mm corre- sponding to the grinding width. Experiments were conducted without fluid dry, under wet flood application conditions, and with MQL. The same fluid 5 vol % Cimtech 500 synthetic grind- ing fluid in water was used both for MQL and flood application. MQL grinding utilized a special fluid application device shown in Fig. 1b provided by AMCOL Hazel Park, MI. The flow rate was 5400 ml/min for flood wet grinding, but only 15 ml/min for MQL. All experiments were conducted in the down mode with the wheel and workpiece velocities in the same direction at the grind- Manuscript received September 22, 2007; final manuscript received June 10, 2008; published online September 11, 2008. Review conducted by Professor Shreyes N. Melkote. Journal of Manufacturing Science and Engineering OCTOBER 2008, Vol. 130 / 051014-1 Copyright © 2008 by ASME Downloaded 11 Oct 2008 to 141.213.232.87. 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