CHAPTER 1 INTRODUCTION 1.1 RESEARCH MOTIVATION Hard turning is a turning process in which steels having hardness between 50 and 70 HRC are turned to

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1 CHAPTER 1 INTRODUCTION 1.1 RESEARCH MOTIVATION Hard turning is a turning process in which steels having hardness between 50 and 70 HRC are turned to the near net shape eliminating the conventional process cycle consisting of turning in the soft state and subsequently hardening and finish grinding to the final dimension. Hard turning yields numerous benefits including low process cost, low process time, better surface quality and reduced rework. Since work pieces are turned in the hardened state, hard turning results in high heat generation and excessive tool wear. Because of these reasons, hard turning cannot be implemented easily on the shop floor as it calls for ultra-hard cutting tools and extremely rigid machine tools. The most common strategy is to adopt conventional wet turning which requires thousands of liters of in order to exploit cooling and lubrication actions of. Use of in large quantity increases the cost of procurement and storage. The cost of ranges from 7% to 17% of the total machining cost whereas the tool cost is only 2% to 4% (Klocke and Eisenblatter, 1997). In addition, introduction of often produces airborne mist, smoke and other particulates in the shop floor air. These products bring forth environmental, health and safety concerns (Shokrani et al., 2012). Disposal of has to comply with environmental legislation such as OSHA regulations (Sutherland et al., 2000) which has become more stringent due to the recent awareness on the environmental and occupational aspects on the shop floor. There are going to be more stringent environmental legislation limiting the Permissible Exposure Level (PEL) on the shop floor. Due to the technological innovations such as new tool materials, new tool coatings material, and optimized tool geometry, machining without called dry cutting, was developed. However in dry cutting operations, the friction and adhesion between chip and tool tend to be higher, which causes higher temperatures, higher wear rates and, consequently, shorter tool lives. Further, dry 1

2 turning needs extremely rigid machine tool and difficult to implement on the shop floor with the existing machine tools. All these problems related to turning with conventional flood cooling and pure dry turning lead to research on machining with minimal fluid application. Hard Turning with Minimal Fluid application (HTMF) is a technique to minimise the use of on the shop floor. In this technique, extremely small (2 to 5 ml) quantities of proprietary s are applied at the critical zones as a pulsing slug. It is reported that (Philip et al., 2001), this new technique not only reduced the usage of drastically but offered better cutting performance as well when compared to wet turning. Employing HTMF with fluid application at the tool work interface gave better cutting performance (Varadarajan et al., 2002). This technique can be easily adopted on the shop floor without the need for any major modifications on the existing setup. Cooling and lubrication in conventional flood cooling is achieved with very large quantity of where as it is achieved with the application of a few ml. of during minimal fluid application. Since the quantity of cutting fluid is very small, some performance enhancers should be thought off to achieve maximum lubrication and cooling even with small quantity of. In the literature practically there are no reports connected with improving cutting performance during minimal fluid application. The present work aims at bridging this gap by introducing some performance enhancing schemes that can further improve the cutting performance by improving lubrication, cooling and environment friendliness of this new technique. Such Performance enhancement schemes are sought to be achieved by promoting chip curl, improving rake face lubrication, and cooling the cutting tool. 1.2 SCOPE OF THE PRESENT WORK The first phase of the present work was the design and development of a viable minimal fluid delivery system which can effectively lubricate and cool the critical zones. The minimal fluid delivery system could deliver in the form of a high velocity pulsing slug with facilities to vary the fluid velocity, 2

3 frequency of pulsing and rate of delivery. The cutting force can be reduced by reducing the tool-chip contact length. Tool-chip contact length can be reduced by increasing chip curl and in the present investigation an auxiliary high velocity minimal pulsing slug of was applied on the top side of the chip to achieve this. An attempt was made to replace the auxiliary high velocity pulsing slug of on the top side of the chip with a high velocity pulsing slug of pure water with an intention of exploiting the high cooling ability of water in the evaporative mode. The cooling of the top side of the chip promotes bending of the chip away from the tool and causes reduction in tool-chip contact length. This will result in further reduction in the amount of used. An attempt was made to enhance the cutting performance by the application of semi solid lubricants during hard turning with minimal fluid application. A pneumatic semisolid lubricant applicator was developed for this purpose. An investigation was made to study the effect of a semi solid lubricant such as silicon grease (in its pure form and as a mixture with 10% graphite by weight) on the cutting performance during hard turning with minimal fluid application. An alternate cooling technique consisting of installing a heat pipe in contact with cutting inserts was explored to cool and thereby improve the life of the cutting tool. Air cooled as well as water cooled heat pipes were used for cooling the tool. Considering the environment friendliness, thermal and oxidation characteristics, it was decided to formulate a with coconut oil as the base. Figure 1.1 presents the research plan for the present work that aims at improving the cutting performance during hard turning with minimal fluid application which is sought to be achieved by (1) Promoting chip curl by introducing an auxiliary pulsing slug of cutting fluid and a pulsing slug of pure water on the top side of the chip. (2) Improving rake face lubrication by introducing a semi solid lubricant such as silicon grease impregnated with graphite and in its pure form at critical zones. 3

4 (3) Cooling of cutting tool by introducing an air and water cooled heat pipe on the tool holder near the cutting tool and, (4) Enhancing its environment friendliness by replacing the mineral oil based with a vegetable oil based. Performance Enhancers for Hard Turning with Minimal Fluid Application Literature Review Fabrication of minimal fluid delivery system Promotion of Chip Curl Improvement of Rake Face Lubrication Cooling of Cutting Tool Enhancement of Environmental the pulsing slug semi solid lubrication heat pipe assisted cooling coconut oil based Studies on the high velocity pulsing slug of Studies on the high velocity pulsing slug of water Application of air cooled heat pipe Application of water cooled heat pipe Use of silicon grease Use of silicon grease impregnated with graphite Use of raw coconut oil as Use of emulsified coconut oil as Comparison of the effectiveness of performance enhancers and conclusion Figure 1.1 Block diagram of the research plan 4

5 1.3 ORGANIZATION OF THE WORK The research work is presented in detail through the following seven chapters. Chapter 1 presents the introduction of the research work that includes its relevance and scope. It also provides information on the general organization of the thesis. Chapter 2 gives information on issues related to procurement, storage and disposal of and a comprehensive study on the related literature. Chapter 3 outlines schemes for promoting chip curl by applying a pulsing slug of and a pulsing slug of pure water on the top side of the chip during turning of hardened AISI 4340 steel with minimal fluid application. Chapter 4 contains information on scheme to improve rake face lubrication by introducing silicon grease at critical zones during turning of hardened AISI 4340 steel with minimal pulsed jet application of. A report on the effect of cooling of the cutting tool using heat pipes on cutting performance during turning of hardened AISI 4340 steel with minimal fluid application is presented in Chapter 5. Chapter 6 presents details on formulation of coconut oil based and its performance as a during turning of hardened AISI 4340 steel with minimal fluid application. The conclusion and scope for future work are summarized in Chapter 7. 5