12-09-2012, 04:19 PM
OPTIMIZATION OF MACHINING PARAMETERS IN CNC TURNING OF MARTENSITIC STAINLESS STEEL USING RSM AND GA
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ABSTRACT
Metal cutting process is one of the complex process which has numerous factors contributing towards the quality of the finished product. CNC turning is one among the metal cutting process in which quality of the finished product depends mainly upon the machining parameters such as feed, speed, depth of cut, type of coolant used, types of inserts used etc. Similarly the work piece material plays an important role in metal cutting process. Hard materials such as stainless steel grades, Nickel alloys , Titanium alloys are very difficult to machine due to their high hardness. While machining these hard materials, optimized machining parameters results in good surface finish, low tool wear, etc. This study involves in identifying the optimized parameters in CNC turning of martensitic stainless steel. The optimization technique used in this study are Response surface methodology, and Genetic algorithm. These optimization techniques are very helpful in identifying the optimized control factors with high level of accuracy.
INTRODUCTION
Hard turning is a process, in which materials in the hardened state (50–70 HRC) are machined with the single point cutting tools. This has become possible with the availability of the new cutting tool materials. Since a large number of operations are required to produce the finished product, if some of the operations can be combined, or eliminated, or can be substituted by the new process, product cycle time can be reduced and productivity can be improved. The traditional method of machining the hardened materials includes rough turning, heat treatment, and then grinding process. Hard turning eliminates the series of operations required to produce the component and thereby reducing the cycle time and hence resulting in productivity improvement. The various advantages of hard tuning are the higher productivity, reduced set up times, surface finish closer to grinding and ability to machine the complex parts. Various work materials which can be machined by the hard turning process include high speed steels, die steels, bearing steels, alloy steels, case hardened steels, white cast iron and alloy cast iron. Rigid machine tools with adequate power, very hard and tough tool materials with appropriate tool geometry, tool holders with high stiffness and appropriate cutting conditions are some of the prerequisites for hard turning.
LITERATURE REVIEW
The performance of hard turning is measured in terms of surface finish, cutting forces, power consumed and tool wear. Surface finish influences functional properties of machined components. Surface finish, in hard turning, has been found to be influenced by a number of factors such as feed rate, cutting speed, work material characteristics, work hardness, cutting time, tool nose radius and tool geometry, stability of the machine tool and the work piece set-up, the use of cutting fluids, etc. König et al. [1] have reported that CBN and ceramic cutting tools are widely used in industries for the machining of the various hard materials. In many applications, the cutting of ferrous materials in their hardened condition can replace grinding to give significant savings in cost and increase in productivity. Cutting tool geometry plays a very important role in hard turning process. The rake angle and the nose radius of the turning inserts directly affect the cutting forces, power and surface finish. The edge strength of the cutting inserts depends upon edge preparation, i.e. by the honing radius, chamfer angles. Some investigations related to the effect of tool geometry have been reported by the researchers. Thiele and Melkote [2] have investigated the cutting edge geometry and the workpieces hardness on surface generation in the finish hard turning of AISI 52100 steel. CBN inserts, with various representative cutting edge preparations, were used as the cutting tool materials.
METHODOLOGY
Design of experiments Design of experiments is a standard tool to conduct the experiment in an optimum way to investigate the effects of process parameters on the response or output parameter. The various steps involved in the design of experiments are identifying the important process parameter, finding the upper and lower limit of selected process parameter and developing the box benhen design matix. The design matrix for three factors involves three blocks in which each of two factors are varied through the four possible combinations of higher and lower limits. In each block a certain number of factors are put through all combinations for the three factorial design, while the other factors are kept at central values.
CONCLUSION
This paper provides a detailed study on the surface roughness of the martensitic stainless steel (SS40). The detailed study and the optimization procedure has been made to study the effect of speed, feed and depth of cut while machining which would help in real practice. The machining parameter ranges were analyzed and then the experimentation was carried out according to the optimization approaches. The results obtained from RSM are R-Sq obtained was 99.9% which indicates that selected parameters (speed, feed, depth of cut )significantly affect the response (surface roughness). The Best ranges obtained by using the genetic algorithm approach are Cutting velocity (speed) -119.93 m/min, Feed-0.15 m/min and Depth of cut -0.5mm. Hence the Optimal surface roughness from GA is 0.74 microns.