Journal of the Faculty of Engineering and Architecture of Gazi University 34:2 (2019) 581-596 The influence of depth of cut on cryogenic machining performance of hardened steel Armin Gharibi , Yusuf Kaynak* , Marmara University, Faculty of Technology, Department of Mechanical Engineering, 34722, Istanbul, Turkey Highlights: Graphical/Tabular Abstract  The effects of cryogenic coolants on machining performance is investigated  Depth of cut plays critical role to determine the effectiveness of cryogenic coolants  Utilizing carbon dioxide significantly helps to improve chip breakability Figure A. Measured resulting forces as a function of cutting length for various machining conditions, ap=0,8 mm Purpose: The purpose of this study is to investigate the effect of depth of cut on cutting performance including tool wear, cutting forces, frictional conditions, chip morphology and surface topography of the workpiece in cryogenic machining (carbon dioxide and liquid nitrogen-assisted coolant) process of hardened steel. Theory and Methods: Liquid nitrogen and carbon dioxide are used in the machining performance experiments of hardened steel as cryogenic coolants. Turning process is carried out to test the role of cryogenic coolants for improving the machining performance of selected work material. During machining tests, the feed rate, f, was kept constant at 0.15 mm/rev. Cutting speed, V, was also kept constant as 90 m/min. Two different depth of cut, ap, 0.8 and 1.6 mm were used. Results: Experimental study shows that depth of cut does not alter the wear mechanism. While cryogenic cooling leads to abrasive wear, adhesion is dominating wear mechanism in dry machining. Surface quality of dry machined samples is negatively induced from the debris stick on the surface of the machined surface. Built-up-edge is only observed in liquid nitrogen-assisted cryogenic machining among all conditions and depth of cut does not play any role in forming built-up-edge phenomena. Conclusion: Liquid nitrogen-assisted cryogenic cooling shows much better performance in comparison of carbon dioxide-assisted cryogenic machining considering reduction of progressive tool wear, force components, and friction coefficient. At lower depth of cut, carbon dioxide-assisted machining is much effective to improve machining performance as compared to larger depth of cut. Cryogenic machining processes reduce cutting temperature substantially as compared to dry machining. Besides, cryogenic machining process leads to generating much better surface quality in comparison with dry cutting in machining process of this particular material. Keywords:  Cryogenic machining  Machining Performance  Hardened steel  Depth of cut Article Info: Research Article Received: 24.02.2017 Accepted: 13.06.2017 DOI: 10.17341/gazimmfd.416423 Acknowledgement: Financial support from Marmara University Scientific Research Projects Committee under project number FEN-E- 080415-0113 is greatly acknowledged. Correspondence: Author: Yusuf Kaynak e-mail: yusuf.kaynak@marmara.edu.tr phone: +90 216 336 5770 400 500 600 700 800 900 1000 1100 1200 0 100 200 300 400 500 600 Resultant Force, F r , (N) Cutting Distance (mm) Dry CO2 LN2