Key terms in Forging

Forging

The manufacturing process of shaping metal using localized compressive forces, typically delivered by a hammer, die, or press.

Hot Forging

Forging performed above the metal's recrystallization temperature. This increases ductility and reduces required force, allowing for complex shapes.

Cold Forging

Forging performed at or near room temperature. This increases strength via strain hardening and provides excellent dimensional accuracy.

Warm Forging

Forging performed below the recrystallization temperature but significantly above room temperature. A balance between hot and cold forging.

Open-Die Forging

Forging between simple, flat or contoured dies where the workpiece is not fully constrained. The operator manipulates the workpiece to achieve the desired shape. Ideal for large, simple parts.

Closed-Die Forging

Forging between two dies containing a precut impression of the desired part shape. The workpiece is fully constrained within the die cavity. Also called Impression-Die Forging.

Roll Forging

A process where a bar stock is passed between two contoured rolls that progressively reduce its cross-section and increase its length to form a part (e.g., a tapered lever).

Upset Forging

A process that increases the diameter of a stock by compressing its length. Performed horizontally in a specialized machine.

Isothermal Forging

A specialized process where the die is heated to the same temperature as the workpiece. Used for superalloys and other difficult-to-work materials to minimize cooling and reduce forging pressure.

Hammer (Drop Hammer)

Equipment that deforms the workpiece by the impact energy of a falling ram. Can be gravity-driven (drop hammers) or power-assisted.

Press (Forging Press)

Equipment that applies a slow, controlled, compressive force to deform the workpiece.

Mechanical Press

A press that uses a motor and a mechanical mechanism (e.g., crank, eccentric) to move the ram.

Hydraulic Press

A press that uses hydraulic cylinders to move the ram. Capable of the highest forces and full-tonnage at any stroke position.

Die

A hardened tool steel block that contains the impression of the part to be forged. It is the core tooling in forging.

Die Holder / Bolster

A heavy block that holds and supports the die assembly in the press or hammer.

Punch

The male part of a die set that performs operations like piercing.

Ingot

A large, cast metal block that is the initial product of a primary metal facility. Often used as the starting stock for large open-die forgings.

Billet / Bloom

A semi-finished product of a square or rectangular cross-section, typically produced by rolling an ingot. A common starting stock for forging.

Bar Stock

Long, straight lengths of metal of a specific cross-section (round, square, hexagonal), used as feedstock for many forging processes.

Blank

A pre-cut piece of stock (from a billet or bar) that is ready to be placed into the forging die.

Preform

A preliminary forged shape, often from an earlier forging operation, that is designed to distribute metal optimally before the final forging blow.

Parting Line (P/L)

The plane where the two die halves meet. It is often visible as a line on the finished forging.

Draft Angle

A taper applied to the vertical walls of the forging to allow for its ejection from the die cavity. Essential for part removal.

Flash

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

Flash Land

The narrow, flat surface on the die that forms the flash and creates the resistance necessary to ensure the die cavity is completely filled.

Gutter

The recess in the die outside the flash land that allows space for the excess flash to flow.

Rib

A thin, raised wall on a forging.

Web

A thin, flat section of a forging that connects ribs and other features.

Die Cavity

The hollow impression in the die that gives the forging its shape.

Shut-off

A sealing surface within the dies that prevents metal from flowing into certain areas, often used to create internal passages.

Grain Flow

The directional pattern of the metal's grain structure that is aligned along the contours of the forging during plastic deformation. This is the primary reason for the superior mechanical properties of forgings.

Recrystallization

The formation of a new, strain-free grain structure within a deformed metal when heated above its recrystallization temperature. This occurs during hot forging.

Strain Hardening (Work Hardening)

The increase in hardness and strength of a metal caused by plastic deformation at temperatures below its recrystallization point (i.e., during cold forging).

Forging Laps

A defect caused when a surface fold of metal is forged into the surface of the part. Often a result of improper die design or technique.

Die Shift

A defect where the two halves of the die are misaligned, causing a mismatch at the parting line on the forging.

Scale

The layer of oxide that forms on the surface of the metal when heated in the presence of air. It must be removed to avoid being forged into the part surface.

Trimming

The operation of removing the flash from the forged part, typically done in a press with a trimming die while the part is still hot.

Heat Treatment

A process of heating and cooling the forging (e.g., annealing, normalizing, quenching & tempering) to achieve the desired mechanical properties (strength, hardness, toughness).

Shot Blasting

Propelling a stream of abrasive material (shot) at the forging to remove scale and clean the surface.

Shot Peening

A similar process to shot blasting, but controlled to impart compressive stresses on the surface of the part, improving its fatigue life.

Coining

A final precision forging operation performed in a special die under high pressure to improve surface finish and hold critical dimensions.

Machining

Removing material from the forging (e.g., turning, drilling, milling) to achieve final dimensions and tolerances that cannot be achieved by forging alone.