Improving machinability of alloy steel

Abstract

In this study the improvement of machinability of an annealed AISI 4340 ALLOY STEEL workpiece material was investigated by using coated carbide tool insert with CVD multilayer coating consisting of (Ti/TiCN//ZrCN) cylindrical straight turning under dry environment. By annealing this material a coarse pearlitic microstructure developed and this effect of mechanical properties on the machinability of workpiece. This led to an increase in ductility and therefore the decrease in hardness and increases the tool life for better the machinability. Here also discussed optimized the machining parameters for minimum cost and maximum production rate in terms of depth of cut. In this work a series of experiment were conducted in order to determine the machinability index n, p, q and C based on (VB = 0.3 mm) flank wear of tool insert, the effects of tool material and type of coating on the insert (for coated tools). The experimental data were further analyzed to predict the optimal range of cutting velocity, feed rate and depth of cut. The machining of furnace cool (coarse pearlite structure) workpiece material was carried out in a high speed lathe to assess the machinability. The influence of machining parameters such as cutting velocity, feed rate and depth of cut on machining force, surface roughness, maximum flank wear, chips thickness and chips morphology was studied. Optical and scanning electron microscope were used to find the tool insert wear and chip morphology. The machining forcedata used in the analyses and this forces measured by a three-dimensional force dynamometer (piezoelectric type). By adopting techniques such as two way general linear model analysis of variance ANOVA, the consequences of cutting parameters (cutting velocity, feed and depth of cut) on surface roughness (Ra, Rmax and Rz), machining forces (Ff, Fc, and Fr) and maximum flank wear (VBmax) are explored with 95% confidence level. Also the statistical significance has been checked (depending on P value, F value and percentage of contribution). The results show that feed rate is the principal machining parameter influencing surface roughness, followed by cutting velocity. The machining forces parameter leads to increase significantly with majorly an increase in cutting velocity and depth of cut. However, flank wear is affected by the cutting speed and depth of cut. Chip morphology indicates the formation saw-tooth/serrated chips at higher feed rate.