may hinder the economical benefit of hard turning. Previous hard turning of stainless steel 43–45 HRC has been successfully performed using coated carbide tool Noordin
et al., 2007. It is likely that coated carbide tool has the potential to turn steels of even higher hardness within the moderate range of hard turning. This is because of the
continuous development of carbide tool taking place in the form of fine grained substrate, better binder that optimizes strength and toughness and improved coating
using Physical Vapor Deposition PVD technique. Therefore, the potential of using inexpensive coated carbide cutting tools needs to be investigated.
In order to encourage machine shops to fully adopt hard turning, assessments should be made to clarify the aspects of the tool life and machined surface’s quality. The
machining cost per part is a function of tool life and, thus, machine shops demand long tool life. Additionally, finish machining should produce fine surface finish as requested
by the users of the machined parts to meet the specific requirements of certain application Gillibrand et al., 1996. Therefore, in order to generate information on the
performance of coated carbide tool and the resulting machined surface, hard turning was conducted using various cutting parameters within finish machining parameters.
2.4 Hard Turning of Stainless Steel Using Wiper Coated Carbide Tool
Hard turning has been explored as an alternative to grinding for finish machining of machine parts made of hardened steels. The introduction of tools with high hot hardness
Polycrystalline Cubic Boron Nitride PCBN and ceramic has contributed in enabling a hardened steel blank to be finish machined by single point turning process. Hard turning
simplifies the current technique to manufacture hardened parts which involve three sequential steps, for example, rough machining of unhardened steel, heat treating to the
required hardness and finish machining to the required dimensional accuracy. Potential advantages in economical and ecological aspects have made hard turning a profitable
alternative to the incumbent grinding as the finishing operation. High material removal rate and relatively low tool cost are some of the economical benefits. Nevertheless, the
drive to minimize the use of coolant whenever feasible has advantaged hard turning
8
which has been successfully performed in dry condition Mamalis et al., 2002 and Noordin et al., 2007.
Along with developing researches and studies, types of materials being cut by hard turning method are growing in numbers and applications. Stainless steel is among the
materials being investigated to employ hard turning method due to its wide application in automotive, tool and die industries. High wear resistance and compressive strength
are some properties required for some high performance parts. Martensitic stainless steel seems the appropriate type of stainless steel since it is hardenable by quenching and
tempering and therefore can achieve high strength and hardness levels Sourmail and Bhadeshia, 2005.
However, the advanced tools commonly used in hard turning, PCBN and ceramic, are relatively high in price. The need for lower cost tool materials to perform hard turning is
still on demand. Coated carbide tool is the proposed alternative for some applications within moderate range of hard turning. Recent development has provided commercially
available coated carbide tools very fine substrate grain size, modified binder that optimizes strength and toughness, and improved coating using Physical Vapor
Deposition PVD technique which may ensure reasonable tool life at minimal cost per cutting edge Jindal et al., 1999.
Finish machining is intended to achieve high level of surface finish and is characterized with low feed and depth of cut Shaw, 2005. In order to improve the productivity, tools
with wiper geometry have been provided by tool manufacturers. This tool geometry has wiper radii adjacent to the nose radius and has little or no clearance angle to improve
finish by burnishing action by the flank face of the insert Shaw, 2005. This modification can double the current feed and still achieve surface finishes comparable to
conventional inserts. Alternatively, if surface finish is the most important consideration, then the same feed can be maintained to achieve better surface roughness values
Castner, 2000.
2.5 Performance of Coated Carbide Tools in Hard Turning
