Forgings Guide – Glossary of Terms

AGE HARDENING: A process of increasing the hardness and strength of an alloy by the precipitation of particles of a phase from a supersaturated solid solution alloy. The hardening cycle usually consists of heating or annealing at a temperature sufficiently high to maintain solid solution; rapid cooling or quenching to retain the supersaturated solid solution, and subsequent heating at a temperature lower than the solution anneal to effect the precipitation.

ALLOY: A substance having metallic properties composed of two or more elements, at least one of which is a metal.

ANNEALING: A process involving heating and cooling designed to effect: (1) softening of a cold worked structure by recrystallization or grain growth or both; (2) softening of an age hardened alloy by causing a nearly complete precipitation of the second phase in relatively coarse form; (3) softening of certain hardenable alloys by dissolving the second phase and cooling rapidly enough to obtain a supersaturated solution; (4) relief of residual stress.

AS EXTRUDED: The condition of a metal mill product resulting from hot extrusion-soft, not cleaned nor drawn or rolled to size. See “EXTRUSION”

BAKED ON: The condition of the forging where lubrication has been carbonized on the surface of the forging.


BILLET: A slug cut from rod to be heated and forged.

BLANK WEIGHT: Weight of the finished, sawed and deburred slug or blank cut from wrought material.

BLOCKER: Preform die or impression, used when part cannot be made in a single operation.

BOSS: A projection extending from the main body of the forging.

BOTTOM DIE: The stationary half-die.

BREAKDOWN: Preliminary forging operation.


BROACH: A method of removing metal by planing it with a series of teeth moving in a straight line so that each tooth as it progresses removes a definite amount of metal.

BUFFING: A finishing of metal surfaces by a compound applied to a flexible wheel which rotates at high speed. Coloring and cutting are two types of buffing procedures.

BURR: A thin ridge or roughness left by a cutting operation such as slitting, shearing, blanking or sawing.

CARBON: As applied to forgings, the carbonaceous residue resulting from lubricant burned on the surface of the slug, cut from wrought material, or pressed part.

CAST: Pouring molten lead or sulphur into the die cavity to indicate the shape of the forging.

CAVITY: The impression in either the upper or lower die.

CHAMFER: The beveled surface, usually at a 150 to 450 angle, to break a sharp corner or edge.

CHOKE: The reduction in area to retard the flow of metal.

CHOPPER OR CHOPPING PRESS: A machine used to shear rather than saw slugs cut from wrought material.

CHUCKING LUG: A lug or boss added to the forging so that "on center" machining and forming may be performed with one setting or chucking. This lug is machined or cut away on the finished item.

CLIP: To remove flash.

CLIP AND SHAVE: A dual operation in which one cutting surface in the clipping die removes the flash, and then the forging is pushed further past another edge which shaves and sizes the entire contour or outside surface of the forging.

CLIPPING EDGE: Where the flash is trimmed or clipped off.


COLD SHUT: On a forging, a portion of the surface that is separated by oxide from the main body of the metal.

COLD STAMP: To restrike a forging cold in order to hold to closer tolerance, sharpen corners or outlines, reduce section thickness, flatten some particular surface, increase hardness, or add lettering.

CORED FORGING: Regular die forging produced by a special technique which introduces a horizontal punch action in combination with the vertical action of a forging press. This produces cavities not possible with standard forging procedures.

COUNTERSINK: Beveling the mouth of a hole or cavity so that when it is drilled through no burr will be left, or to enlarge a portion of a hole tapered at a specific angle and to a certain diameter.

DEBURRED SLUG: One from which the burrs have been removed.

DENSITY: Weight per unit volume.

DIES: Metal blocks having cavities so shaped as to impart the desired shape to a metal workpiece when the dies are brought together.

DIE BLOCK: The steel block into which the impression is cut or sunk.

DIE HOLDERS: Steel blocks used for holding the punch or die.

DIE SET: The holders for a self-contained set-of dies, where punch and die alignment is maintained without the aid of the press.

DIE SHIFT: The impression of the top die not being in alignment with the impression of the bottom die, also, the amount of misalignment.

DRAFT: The taper on a vertical surface to facilitate the removal of the forging from the die or punch.

DRAWN SHAPE: Stock brought to final dimensions by cold drawing through a die, regardless of temper or prior operations.

DRILL CENTER: A depression forged to aid the starting of a drill.

ECCENTRIC: A cavity or any portion of forging with a center that does not coincide with the center of the main piece.

ELONGATION: The permanent extension of a specimen which has been stretched to rupture in a tension test. The percentage elongation is an indication of ductility. See “TEST, TENSION”

END PERCENTAGE: The allowance made for loss of rod ends.

(1) As applied to mill products and forgings, an attack by corrosive media resulting in pitting, meatiness or outline of structural details of the metal
(2) In metallography, the process of revealing structural details by the preferential attack of reagents on a metal surface.

EXTRUDED BAR: Stock brought to final

EXTRUDED ROD: Dimensions by extrusion.


EXTRUSION: The process of shaping metal into a chosen continuous form by forcing it through a die of appropriate shape. See “AS EXTRUDED”

FEATHER OR FIN: The thin projection formed on a forging when the metal under pressure goes into hairline cracks caused by the heat and wear of dies or formed by clipping.

FILLET: A curved inside corner to increase the strength of an object at the corner and to improve appearance. Also important as it increases forging die life.

FINISH: The condition of the surface of the product, produced by normal or special mill procedures. Several types of finishes can be produced, including:
(1) Bichromate Dipped Finish – A semi-matte finish approaching the true color of the metal, obtained by immersion in an aqueous solution of sodium bichromate and sulphuric acid to remove scale and oxide.
(2) Bright Dipped Finish – A bright finish having the true color of the metal, obtained by immersion in an aqueous solution of sulphuric acid and nitric acid.

FINISH WEIGHT: The weight of the trimmed or machined forging.

FIXTURE: A device used for holding work while machining.

FLANGE: A projecting rim for fastening or stiffening.

FLASH: The excess metal that flows out between the upper and lower dies which is required to accomplish a desired forging shape.

FLASH EXTENSION: The amount of metal extending beyond the part at the flash line.

FLASH LINE: The line where the flash occurs.

FLATTENING: A preliminary operation performed on a slug cut from wrought material to position the metal for final forging, or performed on the finished forging to remove the effects of warping.

FLOATING DIE: A type of construction where the die is supported on springs. Generally used in forming deep cavities.

FLOW LINES: The pattern of metal grain structure revealed on a polished and etched section of a hot or cold formed piece which discloses the manner in which the metal has been deformed to fill and follow a die contour.


FORGING: The production of semi-finished forms from wrought metal blanks hot or cold in closed dies by a sudden, sharp impact. See “HAMMER FORGING” and “HOT PRESS FORGING”

FORGING RANGE: Temperature range within which the slug cut from wrought material should be heated to give optimum forging conditions.

GRAIN SIZE: The average diameter of grains, usually determined microscopically, on an etched plane surface of the metal as described in ASTM Standard Method E112.

GRIND: A process for rough finishing parts by means of a revolving abrasive wheel.

GUTTER: A slight depression surrounding the cavity in the die to relieve pressure and control flash flow.

HAMMER FORGING: A forging process in which the piece is deformed by repeated blows.

HARDNESS: The resistance of a metal to plastic deformation by indentation. Common methods of measurement are Rockwell, Brinell, Scleroscope and Vickers.

HEAT CHECK: Fine cracks in the forging dies caused by excessive heat or extended use without polishing. The pattern of these “heat checks” is reproduced on the forged part.

HEAT TREATMENT: A combination of heating and cooling operations, applied to a metal or alloy in the solid state to produce desired properties. See also “AGE HARDENING,” “ANNEALING,” and “QUENCHING”

HOT PRESS FORGING: A method of forming parts by pressing a heated slug, cut from wrought material, in a closed – impression die.

IMPACT: The blow of two dies coming together.

IMPACT EXTRUSION: The formation of a tubular closure by the rapid application of force through a punch on a metal blank, the metal flowing up around the punch to form the tubular section.

IMPRESSION: The cavity in the die which forms the shape of the forging.

INCLUSIONS: Particles of foreign material (usually chips, dirt, carbon, oxides) that are held mechanically on or within the metal.

INSERT: Built up section which saves the use of expensive steel except at the point where actually needed.

KEY. A pin generally of a square tapered cross section used to lock dies into die blocks, etc.

KEY WAY: A recess where a key is inserted to lock two members together.

LAP: A surface defect appearing as a seam, caused by folding over hot metal, fins or sharp corners and then rolling or forging, but not welding them into the surface.

LOCK: A condition where the flash line is not all in one plane.

LUBRICATE: Swabbing or spraying the dies with lubricant to assist in initial flow and to facilitate ejection of the forging.

MASTER: A standard mold or pattern used for duplicating die cavities.

MISMATCH: Misalignment of forging at flash line caused by die or cavity positioning. (Mismatch should not exceed allowable tolerances.)

MODEL: Brass, wood, plaster, etc., form which serves as a pattern for cutting the die.

OPEN DIES: Metal is not confined.

PARTING LINE: The line where the dies come together and the flash is removed.

PICKLING: The liquid process of removing surface oxide and scale from metal which has been hot worked.

PILLAR SET: A self-contained set of dies; one that does not depend upon the press for proper alignment.

PILLARS: Guide posts used in a pillar set.

POLISHING: The finishing of metal surfaces with a compound impregnated in the surfaces of a hard fabric faced wheel which rotates at high speed. Also see “BUFFING”



PRESSURE LOAD: Pressure necessary to produce a forging, generally expressed in tons.

PUNCH: Generally the upper member of a tool set which develops the design of the top side of the forging.

QUENCHING: A process of rapid cooling from an elevated temperature by contact with low temperature liquids, gases or solids.


RELIEVE: Process of reducing dimensions so that one part will fit another.

ROUGH WEIGHT: Gross Weight.

SCALING: Heavy surface oxidation on metals caused by heating in air or in other oxidizing atmospheres.

SCALE DIPPING: The process of removing scale prior to a “Bright Dip.”

SHAVE: The process of pushing a forging through a cuffing die to form or size some dimension more accurately.

SHRINKAGE: The contraction that occurs when a forging cools.

SINK: To cut an impression in a die.

SLUG: The blank, cut from wrought material, from which a forging is made, see “BILLET.”

SPLIT DIE: A type of die construction where the two pieces are split vertically to make possible the forging of shapes with cavities or undercut details.

STRESS: The applied force per unit area, usually expressed as pounds per square inch (psi).
(1) Applied Stress – Stresses that are set up and exist in a body during application of an external load.
(2) Residual Stress – Stresses that remain within a body as the result of plastic deformation.

TENSILE STRENGTH: The value obtained by dividing the maximum load observed during tensile straining by the specimen cross-sectional area before straining. Also called “Ultimate Strength.”

(1) Impact – A test made to determine the resistance of metals to failure by sudden shock load. (See ASTM E23.)
(2) Tension – A test to determine one or more of the following: tensile strength, yield strength, elongation and reduction of area. (See ASTM E8.)

TOLERANCE: The amount by which any characteristic, such as dimensional, chemical, physical or mechanical properties, may vary from that specified.



TUMBLING: Rolling in a revolving container to remove sharp edges and improve finish.

WASH OUT: Wear of dies caused by metal flow.

WEB: The thin section of metal remaining at bottom of a cavity or depression in a forging. The web may be removed by piercing or machining.

YIELD STRENGTH: As commonly applied to copper and copper-base alloys, yield strength is the stress which will produce a .5 percent extension under load. It is known as “Yield Strength” (.5 percent extension) See “TEST, TENSION” and ASTM E8.