MM SCIENCE JOURNAL I 2019 I JUNE 2927 MINIMIZING TEMPERATURE AND TOOL WEAR ON ROCK CUTTING WITH NEGATIVE RAKE ANGLE YUNI HERMAWAN 1,2 , RUDY SOENOKO 2 , YUDY SURYA IRAWAN 2 , SOFYAN ARIEF SETYABUDI 2 1 University of Jember, Faculty of Engineering, Mechanical Engineering Department Jember, Indonesia 2 Brawijaya University, Faculty of Engineering, Mechanical Engineering Department Malang, Indonesia DOI: 10.17973/MMSJ.2019_06_2019004 e-mail: yunikaka@unej.ac.id This research discusses the effect of negative rake angle, to the temperature and tool wear on rock cutting. The cutting process was conducted on marble rock material, without coolants and utilized tungsten carbide inserts with 0 o , -5 o , -10 o , -15 o , -25 o , - 30 o and -40 o rake angles; meanwhile, the feed rate, spindle speed and depth of cut were applied constantly. Temperature measurement used K-type thermocouples, and the scanning electron microscope observed the tool wear. The data collection was monitored in real time from initial conditions until cutting 150 mm in length. The tool wear data was observed after the turning process of 150 mm in length. The results show that at negative rake angle -25 o produce the smallest temperature and tool wear compared to other negative rake angles. This phenomenon occurs because the cutting mode changes from brittle cutting mode to ductile cutting mode. The pile of chip powder in front of the cutting tool was implemented to protect the cutting tool from direct friction with the workpiece and enhance thrust force on the surface of the marble rock. It would greatly affect the cutting temperature and tool wear. KEYWORDS Rake angle, rock cutting, temperature, and tool wear 1 INTRODUCTION Most of the rock materials are classified as brittle materials [Kaitkay 2004]. Rock cutting technology has been applied in many industries such as in gas drilling, mining, oil drilling, raw building materials, and handicrafts. The manufacturing can be done by the process of drilling, milling, sawing and turning [Che 2015]. Negative rake angles are used in machining because of their ability to form a large amount of pressure in front of the tool bit and change the cutting mode from a brittle to ductile cutting mode [Kaitkay 2004, Wilson 2003]. The application of negative rake angles to machining has several advantages, i.e., increasing tool strength, having slower tool wear [Hamade 2010], being capable of cutting very tough materials and creating a pressure effect in front of the cutting tool, thus producing a smooth surface for the workpiece. Requiring a large amount of force, generating high friction and high cutting temperatures are some of its drawbacks [Wilson 2003]. There have been only a small number of studies researching the effects of negative rake angles on temperature and tool wear on rock material longitudinal turning. Research on temperature and tool wear on rock turning has been done by Che, et al. [2015] on the face turning of Indiana Rock with Polycrystalline Diamond Compact (PDC). The temperature was measured using a K-type thermocouple with a rake angle of -25 o . It showed the highest temperature of face turning at 50 o C for a length of 2.54 mm from the PDC tool edge. The other research conducted by Wilson, et al. [2003] includes longitudinal turning of granite with a diameter of 14.55 mm, a workpiece length of 254 mm and rake angle of -10 o . The temperature measurement was conducted with K-type thermocouples from a distance of 2.54 mm, cutting depth of 1.4 mm and a feed rate of 0.185 mm/rev. From this research: the initial tool cuts the rock material, the temperature increases from 200 o C until the tool would burn at temperatures above 500 o C and the tool would start to break until it reaches 700 o C. The tool wear is proportional to the chip volume. The largest tool wear after the granite cutting was measured as big as 1.4 mm. Cools [1993] has investigated the effect of the positive rake angle of 36 o on temperature and tool wear on rock cutting. The temperature measurement used a K-type thermocouple from a distance of 1 mm from the cutting tool. The result showed a maximum temperature of 800 o C with the tool wear of 0.5 mm. These researchers discussed that the magnitude of the temperature occurred during cutting, and it should be noted that only one research study used a negative rake angle; therefore, it would require more research to determine the most optimal temperature for rock cutting. Research on the analytical model on tool wear for rock cutting has been done by Chekina, et al. [1995]. In this research using a rake angle of 15 o , cutting depth of 1 mm and cutting speed of 15 m/s, it was found that the tool wear increased in accordance with the cutting force. The tool wear gradually increased until the end of the cutting process. Ortega [1984] has done modeling of temperature on Tennessee Marble Rock that resulted in safe cutting with temperatures below 750 o C. For cuts above 750 o C, micro-chipping occurs, where grains would exfoliate from parent material of the tool. Researchers [Chekina 1995, Ortega 1984] conducted the modeling to determine the safe temperature at which to attend rock cutting. Further discussion on the research of negative rake angles to determine temperature and tool wear would be beneficial. Moreover, Hamade, et al. [2010] has researched the effects of the negative rake angle on the force and tool wear in the drilling process. The machining was using Basalt Rock as the working material, a PDC tool, and a negative rake angle. It showed that the wear decreased while increasing a negative rake. The research, however, mostly focused on the drilling process and did not discuss longitudinal turning and cutting temperature, and did not provide answers about negative rake angle circumstances in turning processes. Nishimatsu [1971] was conducted research regarding orthogonal rock cutting with the rake angle ranging from 10 o - 40 o and a cutting speed of 5.2 m/min. The mechanism of chip formation is analogous to chip formation by metal cutting. Three zones of rock cutting are primary crushed zone, secondary crushed zone, and overcutting zone. Hough [1986] conducted an experiment of the effect of rake angles by 7 o , 15 o , 20 o and 25 o with a diamond tool bit with black marble as the working material and a spindle speed of 500 and 750 rpm. This research showed that the rake angle of 20 o produced the maximum pressure. The optimum pressure and torsion acceleration were obtained from rake angles 7 o and 20 o . Verhoef, et al. [1996] have experimented with a tri-axial rock testing machine for changing mode from the brittle to ductile cutting mode by conditioning the pressure and surface of the workpiece. The research emphasized that the brittle-ductile