Abstract— Hard turning is characterized by development of high temperatures at the cutting zone, which impairs the surface quality of the final product. Thus, an effective control of heat generated at the cutting zone is essential to ensure workpiece surface quality. Cutting fluids are generally used to avoid this. However, cutting fluids are being restricted due to their direct influence to human health and environment. New alternative approaches are in process to alleviate the problems associated with dry and wet hard turning. This study deals with an investigation of molybdenum disulphide as a solid lubricant as an alternative to the cutting fluids to reduce friction and thereby improve the surface finish of bearing steels. Experiments have been conducted using central composite rotatable design, to study the effect of molybdenum disulphide lubricant on surface roughness while hard turning bearing steel. Results indicate that there is a considerable improvement in the performance of hard turning of bearing steels using molybdenum disulphide as a solid lubricant when compared with dry hard turning in terms of surface roughness Index Terms- Hard turning, surface roughness, solid lubricant, tool geometry, I. INTRODUCTION Hard turning process can be defined as turning hardened materials into finished components. The greatest advantage of using finish hard turning is the reduced machining time and complexity required to manufacture metal parts. In hard turning, surface quality is one of the most important performance measures. Surface roughness is mainly a result of process parameters such as tool geometry and cutting conditions. In any metal cutting operation, lot of heat is generated due to plastic deformation of the work material, friction at the tool-chip interface and friction between tool and the workpiece. The heat produced in hard turning adversely affects the quality of the products produced. Thus, the effective control of heat generated at the cutting zone is essential to ensure good workpiece surface quality in machining [1, 2]. Cutting fluids have been the conventional choice to deal with this problem. Cutting fluids are introduced onto the machining zone to improve the tribological characteristics of the machining processes and also to dissipate the heat generated. Manuscript received February 13, 2008. Dilbag Singh is with the Mechanical Engineering Department, Beant College of Engineering & Technology, Gurdaspur-143521, Punjab, India (phone: +91-1874-221463; fax: +91-1874-221463; e-mail: singh_dilbag@yahoo.com ). P. Venkateswara Rao is with the Mechanical Engineering Department, Indian Institute of Technology Delhi, New Delhi, India (e-mail: pvrao@mech.iitd.ernet.in ). But, the application of conventional cutting fluids creates some techno-environmental problems like environmental pollution, biological problems to operators, water pollution, etc [3]. Further, the cutting fluids also incur a major portion of the total manufacturing cost [4]. All these factors prompt investigations on the use of biodegradable cutting fluids or the elimination of the use of cutting fluids. But any attempt to minimize or to avoid the coolant can be dealt with only by the substitution of the functions normally met by the coolants with some other means. Machining with solid lubricants [5, 6, 7, 8] and cryogenic cooling by liquid nitrogen [9, 10] and minimum quantity lubrication [11, 12] are some of the alternative approaches in this direction. Application of solid lubricant in machining has proved to be feasible alternative to cutting fluids, if it can be applied properly. If the friction at the tool and workpiece interaction can be minimized by providing effective lubrication, the heat generated can be reduced to some extent. Advancement in modern tribology has identified many solid lubricants, which can sustain and provide lubricity over a wide range of temperatures [13, 14]. If a suitable lubricant can be successfully applied in the machining zone, it leads to process improvement. The feasibility of application of graphite as a solid lubricant in surface grinding was investigated by applying it in a suitable paste form to the working surface of the wheel, with a special attachment [5]. The effective role of graphite as solid lubricant was evident from the process results related to frictional factors. If the lubricant can be applied in a more refined and defined way, just sufficient for effective lubrication, improved process results may be expected. The present study focuses on the application of molybdenum disulphide (MoS 2 ) solid lubricant, which is a high temperature lubricant, as a means to reduce the heat generated at the cutting zone and to study the process performance in hard turning. An experimental set-up was developed for supplying solid lubricant powder during hard turning. Comparative performance analyses of solid lubricant assisted hard turning with dry hard turning were made. II. EXPERIMENTAL SET-UP The experimental study was conducted using a NH-22 HMT lathe machine. A new experimental set-up was designed and developed for the supply of fine graphite at the desired flow rate as shown in Fig.1. The solid lubricant powder apparatus was attached to the tool post. The fine solid lubricant powder of 2 µm average particle size was placed in the container. On the top of the container, a DC motor having variable speed was attached for the rotation of the rotary feeder. A spiral shaft was attached to the motor shaft. A desired quantity of the solid lubricant can be supplied onto the cutting zone with the rotation of the Improvement in Surface Quality with Solid Lubrication in Hard Turning Dilbag Singh, P. Venkateswara Rao Proceedings of the World Congress on Engineering 2008 Vol III WCE 2008, July 2 - 4, 2008, London, U.K. ISBN:978-988-17012-4-4 WCE 2008