Predictive modeling for the cryogenic cooling condition of the hard turning process
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This paper presents a numerical model for the hard turning process under the cryogenic cooling condition. This numerical model was developed on the basis of the modified Oxley’s cutting theory with implementing the cryogenic cooling condition. The cooling effect of cryogenic coolant on the tool flank face was modeled as a forced convective heat transfer coefficient as a function of the Nusselt number. The heat generated in the primary and secondary deformation zones was also modeled using moving heat source technique. This model was validated with experimental works under cryogenic and dry conditions for oblique cutting. The minimum and maximum errors in predictions were 1.8 and 15.2% for cutting force (P1), 1.6 and 33.7% for thrust force (P2), and 2.3 and 7.9% for feed force (P3), respectively, under the cryogenic cooling condition. In the case of predicting the temperature at the thermocouple location, the minimum and the maximum errors of these comparisons were 2.0 and 30.5%. It was observed that the cryogenic coolant during the hard turning process reduces the thermal softening effect and in turn increases the cutting forces. In addition, the use of cryogenic coolant can increase the segmented angle (ϕseg) and segmented frequency. Flank wears were observed in both cryogenic cooling and dry conditions. LN2 decreases the length of the flank wear by 12.4~27.5%. In this study, there is the performance improvement of hard turning process by adopting cryogenic cooling method.
KeywordsHard turning Cryogenic coolant Numerical model Chip morphology
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This research was supported by the development of liquid nitrogen based cryogenic machining technology and system for titanium and CGI machining funded by the Ministry of Trade, Industry and Energy (MOTIE) of Korea (No. 10048871) and by Mechatronics optimization of high speed and high accuracy machinery equipment funded by the Korea Institute of Machinery and Materials.
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