Machining of sub-cooled low carbon tool steel by wire-EDM

ABSTRACT

AISI P20 tool steel is a low-carbon steel which is widely used in plastic-molds, die holders, bolsters, backers, shaft and rail making industries. It undergoes metallurgical and microstructural changes when conventionally heat treated with sub-cooling. As Wire-Electro Discharge Machine (WEDM) has become an integral part of finishing most products, this paper gives the influence of sub-cooling of workpiece on its machinability. It also presents the effects of discharge current (I), Pulse on time (Ton), flushing pressure (Fp), wire speed (Ws) and wire tension (Wt) on individual machining response. Sub-cooled metal (SCM) is having more cutting speed (CS) and material removal rate (MRR), and less kerf width (KW), surface roughness (SR) and micro-hardness as compared to parent metal (PM), as both the electrical and thermal conductivities increases with full annealing followed by sub-cooling of metal which affects the thermal diffusivity of metal. It is observed that the machined surface of the SCM is having more spherical globules and smaller melted deposits as compared to that of PM. This is due to the difference in thermal and electrical conductivities, and driving energy with respect to the presence of different phases at the surface.

KEYWORDS:

• WEDM
• machinability
• sub
• cooling
• surface
• morphology

Acknowledgments

The authors would like to thank Central Tool Room and Training Center (CTTC), Govt. Of India, Bhubaneswar, for their support in conducting the experiment at ease.