Hot Forging

Above the metal's recrystallization temperature (e.g., >1000°C for steel).

Metal is very ductile, allowing for significant shape change. No strain hardening. Most common method.

Engine crankshafts, connecting rods, gear blanks.

Cold Forging

Room temperature.

Excellent dimensional accuracy and surface finish. Increases strength via strain hardening. Higher forces required.

Fasteners (bolts, screws), gears, shafts.

Warm Forging

Below recrystallization but above room temperature (e.g., 500-900°C for steel).

Balances the lower force of hot forging with the precision of cold forging. Reduces strain hardening.

Complex automotive components.

Open-Die Forging

The workpiece is compressed between two flat or simple-shaped dies while being manipulated by the operator. Also called smith forging.

Produces large, simple shapes (blanks). Excellent mechanical properties. Requires significant skill.

Impression-Die Forging (Closed-Die Forging)

The workpiece is compressed between two dies containing a precut impression of the desired part shape. Excess metal forms flash, which is trimmed off.

The most common method for complex, net-shape parts. High production rates. Excellent material utilization.

Roll Forging

Round or flat bars are passed through opposing rolls with shaped grooves that reduce the cross-section and increase the length.

Used to produce parts with tapered sections, like leaf springs and levers.

Upset Forging

The diameter of a bar or wire is increased by compressing its length. This is done in a special upsetter or a horizontal forging machine.

Ideal for creating heads on fasteners like bolts and nails.

Billet / Bloom / Slab

A semi-finished, rectangular or square form that is the starting stock for many forging processes.

Ingot

A large, cast metal block that is the initial product of a steel mill, often broken down into billets.

Die

A hardened tool steel block containing the impression of the part to be forged.

Flash

The thin layer of metal that squeezes out into the gap between the dies during impression-die forging. It is later trimmed off.

Grain Flow (Fiber Flow)

The directional pattern of the metal's grain structure after forging, which follows the part's contour and is key to its strength.

Draft Angle

A taper applied to the vertical walls of a forging to facilitate its ejection from the die.

Parting Line

The plane where the two die halves meet.

Trimming

The secondary operation where the flash is removed from the forged part.

Heat Treatment

A critical post-forging process (e.g., annealing, normalizing, quenching & tempering) used to achieve the final mechanical properties.

Superior Mechanical Properties: Unmatched strength and toughness.

High Tooling Cost: Dies, especially for impression-die forging, are expensive.

Reliability: The refined grain structure provides consistent performance.

Limited Complexity: Part geometry is constrained; deep holes and undercuts are not possible.

Material Efficiency: Near-net-shape process reduces scrap.

Size Limitations: Very large forgings require immense, costly equipment.

High Production Rate: Impression-die forging is suitable for mass production.

Secondary Operations: Often require machining, drilling, and heat treatment.