Forward Extrusion

Forward extrusion is a cold forming operation in which a wire blank or preform is forced through a die orifice whose diameter is smaller than the incoming material. The metal flows in the same direction as the punch or ram travel — forward, into the die — and exits with a reduced diameter and increased length.

How It Works

A blank is positioned in front of the die opening. The punch (or the machine ram acting through the tooling) applies compressive force to the rear face of the blank. As pressure builds, the metal yields and flows through the restricted die orifice. The extrusion land — the minimum diameter section of the die — determines the final diameter of the extruded section.

The degree of reduction is expressed as a percentage of area reduction:

% Area Reduction = (A₁ − A₂) / A₁ × 100

where A₁ = original cross-section area, A₂ = extruded cross-section area

Higher area reductions require greater forming force and place more stress on tooling. Typical area reductions per pass in cold forming range from 15% to 35%, depending on the material.

Open vs Trapped Extrusion

• Open extrusion: the blank is only partially contained by the die during the extrusion stroke. Used for moderate reductions.
• Trapped extrusion: the blank is fully enclosed in the die cavity before and during extrusion. Used when the blank must be supported to prevent buckling, or when tighter tolerances are required.

Typical Applications

Forward extrusion is used to:

• Reduce shank diameter to form the body of a bolt or screw
• Create stepped shafts with multiple diameters in a single part
• Produce pointed ends (pointing operation)
• Reduce diameter as a preform step before subsequent upset operations

Effect on Material Properties

Like all cold forming operations, forward extrusion induces work hardening — the metal becomes progressively stronger and harder with each pass. The unbroken grain flow along the extruded shank gives the final part superior fatigue resistance compared to a machined equivalent of identical geometry.

Relationship to Manzoni Technology

On Manzoni machines, the Manzoni Absolute Zero Clearance® system — which eliminates all play in the ram and transfer by mounting them on special bearings instead of bronze liners — ensures that the punch remains perfectly aligned with the die axis throughout the forming stroke. This alignment is critical in extrusion: even minor lateral deflection of the punch produces off-center extrusions, concentricity defects, or premature tool failure.