Review Paper on Machaniability of Inconel

A  review paper on Machinability of Inconel 718  Alloy

Ayush Agrawal ( 15BME0326 ) , Salil Madhav ( 15BME0271 ) , Mayank Agarwal (15BME0330 )

ABSTRACT

The increasing attention to the environmental and health impacts of industry activities by governmental regulation and by the growing awareness in society is forcing manufacturers to reduce the use of lubricants. Inconel 718, a high strength, thermal resistant Nickel-based alloy, is mainly used in the aircraft industries. Due to the extreme toughness and work hardening characteristic of the alloy, the problem of machining Incone1 718 is one of ever-increasing magnitude. Stringent control on the quality of machined surface and sub-surface during high-speed machining of Inconel 718 is necessary so as to achieve components with greater reliability and longevity. The residual stress analysis, micro hardness measurements and degree of work hardening in the machined sub-surfaces were used as criteria to obtain the optimum machining conditions that give machined surfaces with high integrity. It is observed that the highest cutting speed, the lowest feedrate, and the moderate depth of cut coupled with the use of honed cutting edge can ensure induction of compressive residual stresses in the machined surfaces, which in turn were found to be free of smeared areas and adhered chip particles. Machining of Inconel 718 is still very problematic. During the machining the cutting edge is stressed by high temperature and pressure in a small area. So it is important to use fluids with high pressure and a very accurate and high quality cutting wedge. When cutting inserts are used we can do this by special internal cooling systems and special inserts. When a monolithic cutter is used the options for it are not broad when standard machines are used. Main aim for the increasing of the cutting tool life is in the cutting edge micro geometry which is designed by special processes after grinding or after deposition of the thin layer. When the special edge modification is used the cutting edge has high quality, an identifiable edge radius and better roughness on the back and rake area and identifiable K factor. For the good deposition of the thin layer and longer tool life of a monolithic cutting tool it is important to have an optimal value of the radius. When all parameters have optimal values, this can prolong cutting tool life. In this paper, attention is focussed on Inconel 718 and recent work and advances concerning machining of this material are presented. In addition, some solutions to reduce the use of coolants are explored, and different coating techniques to enable a move towards dry machining are examined.

keywords : Inconel 718, Machining, Feed rate, Cutting forces, Cutting tools, Tool wear, Surface roughness, Surface Integrity, Cutting lubrication.

1. INTRODUCTION

Inconel 718 is a high-strength, thermal-resistant (HSTR) Nickel-based alloy that plays an increasingly important part in the development and manufacture of jet aeroengines. It is also noted for its excellent corrosion resistance. Due to its extremely tough nature, the difficulty of machining Inconel 718 resolves itself into two basic problems: i) The inability of the tool material to give long tool lives due to the work hardening and attrition properties of the alloy and  ii) The metallurgical damage to the workpiece due to the very high cutting forces which also gives rise to work hardening, surface tearing and distortion in finally machined components due to induced stresses.[1]

Machinability studies [2-6] of this material have been carried out by different researchers. In a study using C2 carbide grade tools, it was found that [2] the dominant causes of tool failure were localized groove wear on the side flank and chipping on the side cutting edge. It was further observed that the effect of depth of cut on tool wear was not so significant in comparison to the effects of speed and feed. However, it was found [3] that surface finish deteriorated with increasing speed for Incone1 718. The effect of tool nose radius and feed was not significant on surface roughness. A study [4] on the performance of machinability oflncone1 718 showed that the tool life of the silicon nitride based material was mainly dependent on flank wear, whereas for the silicon carbide whisker-reinforced alumina, the tool life criterion was depth of cut notch wear. It has been found [5] that at lower speeds, ceramic tools were prone to depth of cut (DOC) notch wear with minimal damage to the tool nose and at higher speeds, there was a reduction in depth of cut notching and an increase in nose and flank wear. A recent study [6] was carried out using coated cemented carbide inserts of four different grades and a ceramic insert of grade NS13OC. It was found that the coated cemented carbide inserts performed best at the lowest speed and feedrate. The ceramic insert was unsuitable for machining Incone1 718 as the tool life was less than one and a half minutes for all the cutting conditions tested. The major failure mode of the inserts were DOC notch wear. Both the carbide and the ceramic inserts exhibited excellent resistance to crater wear.