Pipe blank necking is a shaping process that reduces the diameter of the pipe blank end. Under the action of axial force, the pipe blank enters the deformation zone, where it undergoes tangential shrinkage plastic deformation, then moves into the stable zone, ultimately forming a reduced end diameter.

Pipe expanding is a forming process that increases the diameter of the pipe blank end. The expanded shape can be conical or cylindrical. Under the action of axial force, the pipe blank enters the deformation zone, where it undergoes tangential stretching plastic deformation. It then moves into a stable deformation zone for further shaping.