Influence of hole making processes on the hole expansion ratio of high strength steel grade SP153-590
Pakorn Chumrum ^1* Nobuhiro Koga ² and Varunee Premanond ^1
1 Department of Tool and Materials Engineering, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand.
² Department of Mechanical Engineering, Nippon Institute of Technology, Saitama, Japan.

Abstract

Hole flanging is one of a process that tearing is easily occurred on the hole edge. The purpose of this research work is to study the influences of hole making processes including; laser, wire-EDM, water-jet and piercing by punch and die on the limiting hole expansion ratio. The mention processes produced the hole with different characteristics i.e. surface roughness, hardness and microstructure. The hole flangeability was evaluated by limiting hole expansion ratio from hole expansion test. This sheet material used for the experiments was high strength steel grade SP153-590 of 1.2 mm thickness. This results showed that the hole cut by laser and pierced by piercing punch which cause changing in microstructure thus increasing hardness introduced low ability of hole flanging. In this case, the process of hole making by wire-EDM and water-jet which cause no effect to raw material, lower the surface roughness (Ra) as the higher is the limiting for hole expansion ratio.