Process Modeling of Piercing Micro-hole with High Pressure Water Beam

During the fabrication of very small or fine hole, usually referred to as micro-hole, technical difficulties often arise due to limitation on the precision capability of tooling systems including those associated with alignment. The present project attempts to develop a new process for piercing micro-hole, using high pressure water beam. In this paper, a numerical model for the micro-hole manufacturing is developed which provides helpful insight into the mechanics of the micro-hole forming process and the tooling design. The ALE (Arbitrary Lagrangian-Eulerian) method of dynamic FEM model is used to simulate water hammer and the water beam penetration into the workpiece material. An experiment for hydro-piercing process is also developed to validate the numerical model. The effects of micro-hole parameters, diameter and workpiece thickness, and water pressure on the micro-hole formation are investigated. It is found that the fracture occur near the die corner in workpiece material and that the pressure increases dramatically when the ratio of hole diameter to thickness is less than 1.