Metal Forming - Plastic Deformation

	Cross-sectional view of the rollers' footprint on the workpiece and the corresponding grain structures for each area. Shown on the left (thick section) is the preform starting wall. On the far right is the flowformed wall.

plastic deformation: The permanent change in shape or size of a body without fracture, produced by a sustained stress beyond the elastic limit of the material.

The Process: A cylindrical workpiece, referred to as “preform”, is fitted over a mandrel. After both are made to rotate, compression forces are applied to the outside diameter of the preform by three equally-spaced, hydraulically-driven, CNC-controlled rollers. By a precalculated amount of wall reduction, in one or more passes, the material is compressed above its yield strength, plastically deformed and made to flow. The desired geometry of the workpiece is achieved when the outer diameter and the wall of the preform are decreased and the available material volume is forced to flow longitudinally over the mandrel.

In flowforming, cross-sectional wall reductions for most materials are in excess of 75% of the starting wall thickness. Typically, the preform can be flowformed four to six times its starting length before a need for reannealing of the metal is required.