A testing procedure for conditions such as porosity, inclusions, segregation, carburization, and flow lines from hot working. After applying a suitable etching solution to the polished metal surface, the structure revealed by the action of the reagent can be observed visually. See Etch test.


The structure and condition of metals as revealed on a suitably prepared and etched sample, and visible without the use of a microscope or under low magnification (up to 10 diameters).

Magnetic-particle inspection (testing)

A nondestructive method of inspection/testing for determining the existence and extent of possible defects in ferro-magnetic materials. The metal is magnetized, then iron powder is applied. The powder adheres to lines of flux leakage, revealing surface and near-surface discontinuities.


A blunt-ended tool or rod used to retain or enlarge the cavity in a hollow metal product during forging.


Wood, metal or plastic reproduction of a proposed forged shape, used to control cutters on tracer-controlled die sinking equipment.


A condition in which a point in one die half is aligned properly with the corresponding point in the opposite die half within specified tolerance.

Microalloyed-steel forging

One made from a microalloyed steel requiring only controlled cooling to reach optimum properties, in contrast to conventional quenched-and-tempered steels that require traditional heat treatments to achieve the same results.


The structure and internal condition of metals as revealed on a ground and polished (and sometimes etched) surface when observed at high magnification (over 10 diameters).


(1) Term used to describe a die impression designed to produce more than a single piece at a time. (2) A piece of stock for forging that is cut from bar or billet lengths to provide the exact amount of material needed for a single workpiece.

No-draft forging

A forged shape with extremely close tolerances and little or no draft, requiring a minimum of machining to produce the final part. Mechanical properties can be enhanced by this closer control of grain flow and retention of surface material in the final component.

Nondestructive inspection

Any method of detection or measurement of the properties or performance capabilities of materials, parts, assemblies, or structures that does not impair the surface or internal integrity of the part.


Metals or alloys that contain no appreciable quantity of iron; applied to such metals as aluminum, copper, magnesium, and their alloys.

Open die forging

Forging produced by working between flat or simply contoured dies with unrestricted metal flow using repetitive strokes and continuous manipulation of the workpiece; sometimes called hand forging. Read more about open die forging vs closed die forging.

Open dies

Dies with flat surfaces that are used for preforming stock or producing hand forgings.


In the normal processing of aluminum forgings, a caustic etch operation is employed for the dual purpose of cleaning parts and emphasizing defects to facilitate visual inspection. Immersion of parts for too long or use of too concentrated a solution will produce a rough, slightly pitted surface.

Overheated metal

Metal with an undesirable coarse grain structure due to exposure to an excessively high temperature. Unlike a “burnt” structure, the metal is not permanently damaged but can be corrected by mechanical working.

Pancake forging

A rough forged shape, usually flat, that can be obtained quickly with minimal tooling. Considerable machining is usually required to attain the finish size.


Small particles of oxidized metal adhering to the surface of a mill product.


The process of removing oxide scale from forgings by treating in a heated acid bath.


In ring rolling, the process of providing a through hole in the center of an upset forging using a tapered or cylindrical punch. See Drifting.


A finishing operation for the purpose of removing the trim line of forgings or of obtaining closer tolerances. Usually done by rolling, pressing or hammering, hot or cold.


The entire mass of metal upon which the hammer performs work, including the flash, sprue, tonghold, and as many forgings as are made at one time.

Poisson’s ratio

The ratio of strain in the longitudinal direction to that in the transverse direction. Typical values range from 0.28 to 0.33 for most forging alloys.

Powder forging

The plastic deformation of a powder metallurgy compact or preform into a fully dense finished shape by using compressive force; usually done hot and within closed dies.

Power rolls

Power-driven rolls used in preforming bar or billet stock that have shaped contours and notches for introduction of the work.


(1) In ring rolling, a vertically mounted piercing (punching) tool used for preparation of ring blanks on the ring blank press. (2) A tapered tool of various diameters and lengths.


(1) The forging operation in which stock is preformed or shaped to a predetermined size and contour prior to subsequent die forging operations. When a preform operation is required, it will precede a forging operation and will be performed in conjunction with the forging operation and in the same heat. (2) Ring blanks of a specific shape for profile (contour) ring rolling. (3) The initially pressed powder metallurgy compact to be subjected to repressing.


(1) A preliminary heating of ingots, billets, or forgings to reduce the hazards of thermal shock upon subsequent heating to higher temperatures. (2) A high-temperature soaking treatment used to change the metallurgical structure in preparation for a subsequent operation, usually applied to the ingot.

Preparation charge

A one-time charge covering the cost of sinking dies and preparing required auxiliary tooling for producing forgings to a particular design. In usual practice, this charge conveys to the customer the exclusive right to purchase forgings produced on this tooling. The dies themselves are the property of the forger, who also has the responsibility for maintaining and replacing the dies as required for satisfactory production of forgings.


A machine tool with a stationary bed and a slide or ram that has reciprocating motion at right angles to the bed surface; the ram is guided in the frame of the machine.

Press forging

The shaping of metal between dies on a mechanical or hydraulic press. The action is that of kneading the metal by relatively slow application of force as compared with the action of hammering.

Profile (contour) rolling

In ring rolling a process to produce seamless rolled rings with a predesigned shape either on the outside or the inside diameter, requiring less volume of material and less machining to produce finished parts.


A collection of sample forgings taken following the first and subsequent blows of the forging sequence. Also known as a progression.


An extra portion of metal added in a mutually agreeable location of a forging to permit removal and subsequent testing without destroying the forging. Generally applies to open die and some large rolled rings.


The main reciprocating member of a press, guided in the press frame, to which the punch or upper die is fastened.


To forge an ingot lightly in the initial forging operation in order to break up and refine coarse, as-cast structure at the surface.


A holder used as a support for the stationary portions of forging and trimming dies.

Shot blasting

A process of cleaning forgings by propelling metal shot at high velocity by air pressure or centrifugal force at the surface of the forgings. See also Blast cleaning.


The contraction of metal during cooling after hot forging. Die impressions are made oversize according to precise shrinkage scales to allow the forgings to shrink to design dimensions and tolerances.

Shut height

For a press, the distance from the top of the bed to the bottom of the ram with the stroke down and adjustment up. In general, it is the maximum die height that can be accommodated for normal operation, taking the bolster plate into consideration.

Shuts (cold)

Faults produced in a forging by incorrect tool design or incorrect flow of steel that results in the formation of a crack in the forging surface.

Side thrust

Lateral force exerted between the dies by reaction of the forged piece on the die impressions.

Side thrust

Lateral force exerted between the dies by reaction of the forged piece on the die impressions.


Secondary forming or squeezing operations needed to square up, set down, flatten, or otherwise correct surfaces to produce specified dimensions and tolerances. Often accomplished with a coining press. See Coining.


A slender fragment or splinter that is a part of the material, but that is incompletely attached. A torn fiber of metal forced into the surface of a forging.

Slot furnace

A common batch-type forge furnace where stock is charged and removed through a slot or opening.


(1) Forging stock for one workpiece cut to length. See also Blank. (2) Metal removed when punching a hole in a forging (also termed “punchout”).


The blacksmith, forger, or pressman.

Snag grinding (snagging)

The process of removing portions of forgings not desired in the finished product, by grinding.

Sow block

A block of heat-treated steel placed between a hammer anvil and a forging die to prevent undue wear to the anvil. Sow blocks are occasionally used to hold insert dies. Also called Anvil cap.

Split die

A die made of parts that can be separated for ready removal of the workpiece. Also known as segment die.


(1) The elastic recovery of metal after stressing. (2) The extent to which metal tends to return to its original shape or contour after undergoing a forming operation. This is compensated for by overbending or by a secondary operation of restriking.

Stainless steels

Steels that are corrosion and heat resistant and contain a minimum of 10% to 12% chromium. Other alloying elements are often present.

Stamp (marking)

An operation performed to identify the particular forgings as specified or requested by the customer.

Steam hammer

A type of drop hammer where the ram is raised for each stroke by a double-action steam cylinder and the energy delivered to the workpiece is supplied by the velocity and weight of the ram and attached upper die driven downward by steam pressure. Energy delivered during each stroke may be varied.


The material to be forged regardless of form. Also, an individual piece of metal used to produce a single forging.

Stock marks

In cutting forging stock to specified length for a die-forged part, the ends of the bar always contain surface imperfections caused by the cutting tool; these are often retained on the surface of the finished part. If pronounced, such marks are removed by light grinding. On parts where repeated indications of stock marks are encountered, efforts are usually made to eliminate them by conditioning the stock ends prior to forging by polishing the cut ends and beveling the edge of the cut.


Finishing operation for correcting misalignment in a forging or between different sections of a forging. Straightening may be done by hand, with simple tools, or in a die in forging equipment.

Straighten, hand

A straightening operation performed on a surface plate to bring a forging within straightness tolerance. Frequently, a bottom die from a set of finish dies is used instead of a surface plate; hand tools used include mallets, sledges, blocks, jacks, and oil gear presses, in addition to regular inspection tools.

Strain hardening

An increase in hardness and strength caused by plastic deformation at temperatures below the recrystallization range. Also known as work hardening.

Stroke (up or down)

The vertical movement of a ram during half of the cycle, from the full open to the full closed position or vice versa.

Structural integrity

Inherent microstructural soundness of forgings as a result of achieving 100% density, uniform metallurgical structure and grain size, as well as the absence of porosity, segregation, large inclusions, and other non-forged part defects.

Sub-sow block (die holder)

A block used as an adapter in order to permit the use of forging dies that otherwise would not have sufficient height to be used in the particular unit or to permit the use of dies in a unit where the shank sizes are different.


A defect caused by the “sucking in” of one face of a forging to fill a projection on the opposite side.


A term broadly applied to iron-base, nickel-base, and cobalt-base alloys, often quite complex, that exhibit high elevated-temperature mechanical properties and oxidation resistance.


The ability of certain metals to develop extremely high tensile elongations at elevated temperatures and under controlled rates of deformation.


(1) Reducing the diameter of or rounding out a section of a forging by a series of blows, tapering the forging lengthwise until the entire section attains the smaller dimension of the taper. (2) Tapering forging stock by forging, hammering, or squeezing.