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Turning operation is widely used in workshop practice for applications carried out in conventional machine tools, as well as in NC and CNC machine tools, machining centers and related manufacturing systems. Turning involves the use of a lathe and is used primarily to produce conical and cylindrical parts. With common attachments, flat faces, curved surfaces, grinding and boring can be done with a lathe. Therefore, it is valuable to increase tool life, to improve surface accuracy, to reduce main cutting force, feed force and to reduce machining zone temperatures (chip-tool interface temperature) in turning operations through an optimization study. Cutting fluids are generally used in machining process to reduce friction and wear, thus improving the tool life and surface finish. These are also used to reduce the cutting forces and energy consumption, to cool/lubricate the machining zone, wash away the chips, and to protect the machined surfaces from environmental corrosion.
Machinability is defined as ease of machining of a material, characterized by low cutting forces, high material removal rate, good surface finish, accurate and consistent work piece geometrical characteristics, low tool wear rate and good curl or
chip breakdown of chips etc.
In machinability studies investigations, statistical design of experiments is used quite extensively. Statistical design of experiment refers to the proper planning of the experiment so that a reliable data may be obtained under all possible combinations of parameters and can be analyzed using statistical methods, resulting in valid and objective conclusions (Montgomery, 2005), With statistical design of experiments large data is selected in small number of experimental value.
In order to establish an adequate functional relationship between the tool life and cutting parameters a large number of tests are needed in one-factor-at-a-time approach. So, the experimentation cost also increases (Chaudhury, 1998). Most researchers have investigated the effects of various cutting parameters on responses
(output) by the one variable at a time approach. The present study takes into account
the simultaneous variation of cutting speed, feed, depth of cut, tool nose radius and
percentage concentration of solid-liquid lubricants according to factorial design of
experiment, and predicts, the responses. This approach is known as response surface methodology (RSM). Response surface methodology (RSM) is a statistical method
for heuristic optimization, which is basically a combination of design of experiments,
regression analysis and statistical inferences. It is very useful technique for modeling
and analysis of problem in which a response of interest is influenced by several
variables and the objective of this approach is to optimize the response (Montgomery,
2005). By using this approach mathematical models have been developed based on
experimental results. The purpose of developing mathematical models relating to the
machining response and their factor is to facilitate the optimization of the machining
process. Modeling and optimization are necessary for the control of the steel turning
process to achieve improved product equality, high productivity and low cost.
In this work experimental investigations have been conducted to study the machinability of En31 steel while turning with tungsten carbide tools. En-31 is
selected for machinability studies, because it is widely used in automotive industry for the production of axle, roller bearings, ball bearings, shear blades, spindle mandrels, forming and molding dies, rollers, blanking and forming tools, knurling tools and spline shafts, etc. (Kalapakjian, 1997)). Turning is the main machining process for the production of these parts (HMT, 1996).
Main interest of present research is to a solid-liquid lubricant for chip-tool interface while turning, so that the machinability of En-31 steel is improved and an attempt a new technique of applying the lubricant so that real minimum quantity lubricant can be achieved.

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