Rotary piercing

Rotary piercing is a hot working metalworking process for forming thick-walled seamless tubing.

The stress exceeds the yield strength of the billet and causes circumferential fissures to propagate at various radii near the outer surface, and a central longitudinal void to form at the axis.

A tapered mandrel is set inside and a short distance from the start of the central void.

This compressive loading fuses the circumferential fissures and sets the initial internal and external diameter values.

The formed tube is then cooled and can be cold worked to refine the diameters and to achieve the desired yield strengths.

A schematic of rotary piercing. Key:
  1. Roller configuration
  2. The process starts with the blank fed in from the left.
  3. The stresses induced by the rolls causes the center of the blank to fracture.
  4. Finally, the rolls push the blank over the mandrel to form a uniform inner diameter.