Aircraft quality

Denotes stock of sufficient quality to be forged into highly stressed parts for aircraft or other critical applications. Such materials are of extremely high quality, requiring closely controlled, restrictive practices in their manufacture in order that they may pass rigid requirements, such as magnetic particle inspection.

Alloy steel forging

One made from a steel containing additional alloying elements other than carbon (e.g., Ni, Cr, Mo) to enhance physical and mechanical properties and/or heat-treat response.


Aeronautical Materials Specification.

Auxiliary operations

Additional processing steps performed on forgings to obtain properties, such as surface conditions or shapes, not obtained in the regular processing operation.

Axial rolls

In ring rolling, vertically displaceable, tapered rolls, mounted in a horizontally displaceable frame opposite from but on the same centerline as the main roll and rolling mandrel. The axial rolls control the ring height during the rolling process.

Axisymmetric forging

A forging where metal flow, during deformation, is predominately in a direction away from a common axis in a radial direction.


A section hot rolled from a billet to a form, such as round, hexagonal, octagonal, square, or rectangular, with sharp or rounded corners or edges, with a cross-sectional area of less than 16 sq in. (A solid section that is long in relation to its cross-sectional dimensions, having a completely symmetrical cross section and whose width or greatest distance between parallel faces is 3/8 in. or more).


Convexity of the surfaces of cylindrical or conical bodies, often produced unintentionally during upsetting or as a natural consequence during compression testing. See also Compression Test.

Batch/batch-type furnace

A furnace for heating materials where all loading and unloading is done through a single door or slot.

Bend or twist (defect)

Distortion similar to warpage, but resulting from different causes; generally caused in the forging or trimming operations. When the distortion is along the length of the part, it is called “bend”; when across the width, it is called “twist.”


A preliminary forging operation to give the piece approximately the correct shape for subsequent forming.


A semifinished, cogged, hot-rolled, or continuous-cast metal product of uniform section, usually rectangular with radiused corners. Billets are relatively larger than bars. See Bloom.


Amount of the die in contact with the workpiece throughout one entire forging reduction, e.g., heavy bite is three-quarter to full width of the die.

Blast cleaning

A process for cleaning or finishing metal objects by use of an air jet or centrifugal wheel that propels abrasive particles (grit, sand, or shot) against the surfaces of the workpiece at high velocity.


The forging operation in which metal is progressively formed to general desired shape and contour by means of an impression die (used when only one block operation is scheduled).

Block and finish

The forging operation in which the part to be forged is blocked and finished in one heat through the use of a die having both a block impression and a finish impression in the same die. This also covers the case where two tools mounted in the same machine are used, as in the case of aircraft pistons. Only one heat is involved for both operations.

Block, first and second

Blocking operation performed in a die having two blocking cavities in the same die; the part being forged is successively blocked in each impression all in one heat. As many as three blocker dies are sometimes needed for some forgings and up to three operations are sometimes required in each die.

Blocker impression

The forging die impression which gives the forging its general shape, but omits any details that might restrict the metal flow; corners are well rounded. The primary purpose of the blocker is to enable the forming of shapes too complex to be finished after the preliminary operations; it also reduces die wear in the finishing impression.

Blocker-type forging

A forging that approximates the general shape of the final part with relatively generous finish allowance and radii. Such forgings are sometimes specified to reduce die costs where only a small number of forgings are desired and the cost of machining each part to its final shape is not exorbitant.


A semifinished product of square, rectangular, or even round cross section, hot rolled, or forged. For steel, the width of a bloom is not more than twice the thickness, and the cross sectional area is usually not less than about 36 sq. in. No invariable rule prevails for distinguishing between blooms and billets; the terms are frequently used interchangeably.

Board hammer

A type of gravity drop hammer where wood boards attached to the ram are raised vertically by action of contrarotating rolls, then released. Energy for forging is obtained by the mass and velocity of the freely falling ram and the attached upper die. See also Drop Hammer.


A relatively short protrusion or projection on the surface of a forging, often cylindrical in shape.


(1) An initial rolling or drawing operation, or a series of such operations, for reducing an ingot or extruded shape to desired size before the finish reduction. (2) A preliminary press-forging operation.

Brinell hardness

The hardness of a metal or part, as represented by the number obtained from the ratio between the load applied on and the spherical area of the impression made by a steel ball forced into the surface of the material tested. The Brinell Hardness Number (BHN) is determined by measuring the diameter of the impression using a low power microscope, then matching this diameter with the load on a standard table.


A bulge, bend, kink, or other wavy condition of the workpiece caused by compressive stresses. See also Compressive Stress.


Permanently damaging a metal or alloy by heating so as to cause either incipient melting or intergranular oxidation.


A thin ridge or roughness left on forgings by cutting operation such as slitting, shearing, trimming, blanking, or sawing.

Carbon steel

Steel containing carbon up to about 1.2%, and only residual amounts of other elements except for those added for composition control, with silicon usually limited to 0.60 % and manganese to 1.65%. Carbon steel forgings are forgings manufactured out of carbon steel.


Also known as sub-bolster, die assembly, trim and pierce assembly. An assembly of top and bottom dies and/or tools of each forming station assembled into one unit.


To break or remove sharp edges or corners of forging stock by means of straight angle tool or grinding wheel.

Charpy impact test

An impact test in which a specially V-notched specimen is broken by the impact of a falling pendulum. The energy absorbed in fracture is a measure of the impact strength or notch toughness of the sample.


A die forging defect; metal sheared from a vertical surface and spread by the die over an adjoining horizontal surface.

Chucking lug

A lug or boss to the forging so that “on center” machining and forming can be performed with one setting or chucking; this lug is machined or cut away on the finished item.

Closed die forging

The shaping of hot metal completely within the walls or cavities of two dies that come together to enclose the workpiece on all sides. The impression for the forging can be entirely in either die or divided between the top and bottom dies. Impression-die forging, often used interchangeably with the term closed die forging, refers to a closed-die operation in which the dies contain a provision for controlling the flow of excess material, or flash, that is generated. By contrast, in flashless forging, the material is deformed in a cavity that allows little or no escape of excess material. See Impression Die Forging.


The forging operation that locally reduces diameters in hollow forgings.


(1) A post-forging process—on hot or cold parts—used to attain closer tolerances or improved surfaces. (2) A closed-die squeezing operation in which all surfaces of a workpiece are confined or restrained, resulting in a well-defined imprint of the die on the work.

Cold heading

Plastically deforming metal at ambient temperatures to increase the cross-sectional area of the stock (either solid bar or tubing) at one or more points along the longitudinal axis. See also Heading and Upsetting.

Cold lap

A flaw that results when a workpiece fails to fill the die cavity during the first forging. A seam is formed as subsequent dies force metal over this gap to leave a seam on the workpiece surface. See also Cold Shut.

Cold saw

Mechanical sawing machine used to produce cut pieces prior to the forging operation. Sawing is carried out on the material at ambient temperature.

Cold shut

Also known as lap or fold. A defect such as lap that forms whenever metal folds over itself during forging. This can occur where vertical and horizontal surfaces intersect.

Cold-coined forging

A forging that has been restruck cold in order to hold closer face distance tolerances, sharpen corners or outlines, reduce section thickness, flatten some particular surface, or, in non-heat-treatable alloys, increase hardness.


A concave condition applicable to the width of any flat surface.

Counterblow forging

One made by equipment incorporating two opposed rams, which simultaneously strike repeated blows on the workpiece.

Counterblow forging equipment

A category of forging equipment in which two opposed rams are activated simultaneously, striking repeated blows on the workpiece at a midway point. Action is vertical or horizontal.

Cross forging

Preliminary working of forging stock in alternate planes, usually on flat dies, to develop mechanical properties, particularly in the center portions of heavy sections.


The removal of carbon from the surface of steel as a result of heating in a medium that reacts with the carbon. Decarburization is usually present to a slight extent in steel forgings. Excessive decarburization can result in defective products.

Die lubricant

A material sprayed, swabbed, or otherwise applied during forging to reduce friction and/or provide thermal insulation between the workpiece and the dies. Lubricants also facilitate release of the part from the dies and provide thermal insulation. See also Lubricant.

Die set

The assembly of the upper and lower die shoes (punch and die holders), usually including the guide pins, guide pin bushings, and heel blocks. This assembly takes many forms, shapes, and sizes and is frequently purchased as a commercially available unit. Also, two (or, for a mechanical upsetter, three) machined dies used together during the production of a die forging.

Die shift

The condition that occurs after the dies have been set up in a forging unit in which a portion of the impression of one die is not in perfect alignment with the corresponding portion of the other die. This results in a mismatch in the forging, a condition that must be held within the specified tolerance.

Dies, forging

Forms for the making of forgings; generally consist of a top and bottom die. The simplest will form a completed forging in a single impression; the most complex, made up of several die inserts, may have a number of impressions for the progressive working of complicated shapes. Forging dies are usually in pairs, with part of the impression in one of the blocks and the balance of the impression in the other block.

Directional properties

Properties whose magnitude varies depending on the relation of the test axis to a specific direction within the metal or alloy.

Disc (disk)

“Pancake” shaped forging (flat with a round cross-section); e.g., a blank for gears, rings and flanged hubs. Abbreviation is “D.”

Drawing out

The forging operation in which the length of a metal mass (stock) is increased at the expense of its cross section; no “upset” is involved. The operation covers converting ingot to pressed bar using “V,” round, or flat dies.


A condition where the dimensions of a part or forging are changed by local grinding or machining to remove one or more defects thereby causing a localized imperfection of a maximum depth. The depth is the dimension of the dressout.


In forging, the operation of forming or enlarging a hole by use of a tapered punch.


The property of a metal that enables it to stretch before rupturing.


Portion of a press cycle during which the movement of a member is zero or at least insignificant. Usually refers to the interval between the completion of the forging stroke and the retraction of the ram.

Dye-penetrant testing

Inspection procedures for detecting surface irregularities using penetrating liquids containing dyes or fluorescent substances.


The offset portion of the driveshaft that governs the stroke or distance the crosshead moves on a mechanical or manual shear.


The forging operation of working a bar between contoured dies while turning it 90° between blows to produce a varying rectangular cross section.

Efficiency (forging)

The amount of applied energy, in percentage, that is employed in deforming the workpiece to the total energy expended by the forging equipment.

Etch test

The process of revealing the macrostructure of metals by preferential attack of a prepared surface by a suitable reagent.


A hollow forging operation whereby the diameters are increased by reducing wall thickness with relatively little increase in length by working on a mandrel.

Extrusion pipe

A central oxide-lined discontinuity that occasionally occurs in the last 10% to 20% of an extruded bar. It is caused by the oxidized outer surface of the billet flowing around the end of the billet and into the center of the bar during the final stages of extrusion. Also called coring.