Machining process can be defined as machining hardened materials into finished components. The extreme advantage of using finish hard turning is the reduced machining time and difficulty involved to manufacture metal parts. In hard machining, surface quality is one of the most important performance measures. The Surface roughness is mainly a result of process parameters such as tool geometry and cutting conditions. In any metal cutting operation, more heat is generated due to plastic deformation of the work material, friction at the tool-chip interface and friction between tool and the work piece. 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 important to ensure good surface quality in machining. 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.
1.1.2 Utilization of cutting liquids
The application of cutting fluids is one of the alternatives to obtain higher material removal rates. Cutting fluids have been used widespread in all machining processes. However, because of their damaging influences on the environment, their applications have been limited 1-4. New approaches for elimination of application of cutting fluids in machining processes have been examined and “dry machining” was presented as an important solution (5-6). The development of new cutting tool materials also helped dry machining method to be a positive solution for cutting fluids applications. However, the usage of cutting fluids has been increased due to high production levels in the world.
The first study about cutting fluids had been presented by W.H. Northcott in 1868 with a book entitled “A treaties on lathes and turning”. In the middle of 1890’s, F.W. Taylor emphasized that using cutting fluids would allow for higher cutting speeds resulting in longer tool lives and higher material removal rates. The primary function of cutting fluid is temperature control through cooling and lubrication. Application of cutting fluid also improves the quality of the work piece by continually removing chips from the tool and from the cutting zone. In fact, cutting fluids have been in use extensively in metal cutting operations for the last100 years. In the beginning most of the cutting fluids consisted of single oils that were applied with brushes for lubricating and cooling effects. Sometimes animal fat or whale’s blubber were added to improve the oil’s lubricating capacity. In due course of time, as cutting operations became more difficult, formulation of cutting fluids became more complex. As such, the latest cutting fluids have become special blends of chemical additives, lubricants and water that have been formulated to meet the performance demands of the metal working industry.
There are various types of cutting fluids at present, the most common of which are broadly categorized as cutting oils and water-miscible fluids. In fact, water-miscible fluids which include soluble oils, synthetics and semi-synthetics are now commonly used in about 90% of all applications. The selection of cutting fluids in machining process depends varies factors as discussed(5) .The most important factor in the selection of cutting fluids is the underlying characteristics of machining process. The different varieties of machining processes would indicate the relation between the work piece and the material-cutting, tool-chip combinations. In other words, the more the difficulty in machining processes, the more the use of the cutting fluid. The second factor is the type of work piece material, because the application of cutting fluids should provide easy machining operation of all materials.
The third factor is the selection of a cutting tool material as various cutting tool materials are available for all kinds of machining processes. As such, high speed steel cutting tools can be used with all types of cutting fluids. However, waterless cutting fluids are preferred when difficult-to-cut materials are machined. In fact, in case of Tungsten Carbide WC cutting tools application, the presence of more cooling characteristics from cutting fluids is required. This is due to high heat generation at the interface of the cutting tool and the work piece material. The heat thus generated while machining with the use of Tungsten Carbide cutting tools because rapid tool wear, as a result the tool life reduces and the surface finish quality falls.
It is noteworthy that cutting fluids play a significant role in machining operations, but adversely affect shop productivity, tool life and the health of the worker. With the frequency in use and passing of time, the quality of the fluids is degraded which are to be eventually disposed. It becomes more complex and me expensive in the proper management of waste and its disposal. Poor waste disposal practices have become problematic for many companies as it affects environment and the obvious legal threat from the regulatory authorities.