Forging Glossary

A B C D E F G H I J K L M N O P Q R S T U V W Y 

Aerospace Quality: Indicates a level of quality required of forgings that are designed for use in aircraft or other critical applications. Such parts are forged from extremely high-quality materials and require strictly controlled and restrictive manufacturing practices to meet stringent requirements such as magnetic particle inspection (MPI).

Alloy: A metal formed by combining two or more metallic elements, specifically to give greater strength or resistance to corrosion to each forging.

Alloy Steel: Steel containing small amounts of one or more non-carbon elements, including manganese, silicon, nickel, titanium, copper, chromium or aluminum added.

Annealing: A heat treatment process whereby a metal is heated to a specific temperature and then allowed to cool slowly. This softens the metal which means it can be cut and shaped more easily.

Anvil: A block of metal with a hard surface on which another object is shaped. In closed die forging, an anvil provides the resting surface upon which a forging die is placed.

ASTM: The American Society for Testing and Materials.

AS9100: A quality system with standard requirements which specifies additional requirements for the quality system of the aerospace industry.

Artificial Aging (Aging): Artificial aging is the heat treatment of an alloy at elevated temperatures in order to accelerate changes in the chemical properties of an alloy as a result of forging. Generally, the chemical properties of newly forged metals naturally change and settle very slowly at room temperatures. Aging accelerates this change more rapidly at higher temperatures. This process also ensures quality and accuracy in parts with close tolerance specifications.

Assembly: Fitting together the separate component parts of a part, machine, or tool.

Axisymmetric Forging: A forging where the flow of the metal during deformation is in a direction predominantly away from a common axis in a radial direction.

Bead Blast: A process of cleaning a metal part whereby excess metal or scale is removed from a raw forging by means of shooting an abrasive substance, such as sand or glass beads against a part.

Bender: A die impression, tool, or mechanical device used to bend metal stock to conform to the general configuration of die impressions prior to forging.

Bending: A preliminary forging operation used to give the piece to be forged approximately the correct shape prior to its primary deformation.

Bite: The portion of the die in contact with the workpiece during one entire forging reduction, e.g., the heavy bite is three-quarters to the full width of the die.

Blank: Raw material or forging stock (also called a multiple) from which a forging is made.

Block: The forging operation in which metal is progressively formed to the general desired shape and contoured utilizing an impression die (used when only one block operation is scheduled).

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 allow the forming of shapes too complex to be finished after the preliminary operations; it also reduces die wear in the finishing impression.

Blow: The force delivered by one work-stroke of the forging equipment.

Bolt: A threaded fastener with an external male thread.

Box Annealing: A heat treatment process whereby metal to be annealed is packed in a closed container to protect its surfaces from oxidation. Sometimes used to describe the process of placing forgings in a closed container immediately after forging operations are completed, permitting forgings to cool slowly.

Brass: A metal alloy comprised of copper and zinc.

Brittleness: The relative ease or amount of energy needed for a metal piece to break without deformation: the inability of a metal piece to bend or absorb energy without losing its structural integrity.

Brinell Hardness Testing: Method of determining the hardness of materials; involves impressing a hardened ball of specified diameter into the material surface at a known pressure. The Brinell hardness number results from calculations involving the load and the spherical area of the ball impression. Direct-reading testing machines designed for rapid testing are generally used for the routine inspection of forgings, and as a heat treat control function.

Bushing: A metal lining for a circular projection, especially one in which an axle revolves.

Camshaft: A shaft having at least one cam attached to it, especially one used to operate the valves of an internal-combustion engine.

Carbon Steel: Steel in which carbon is the main element in the alloy, and whose properties are primarily dependent upon the amount of carbon present.

Carbonitriding: A process of case hardening a ferrous material in a gaseous atmosphere containing both carbon and nitrogen.

Cleaning: Removing of scale, oxides, or lubricant from the surface of the forging acquired during heating, forging, or heat treating.

Closed-Die Forging: A forging process involving placing the workpiece between two shaped dies and compressing the workpiece by mechanical or gravitational pressure.

CMM (Coordinate Measuring Machine): a device for measuring the geometrical characteristics of an object that may either be manually controlled or via a computer. Measurements are defined by a probe attached to the third moving axis of the machine.

CNC Computer Numerical Control Machining: A type of machining process that involves the use of computers to control machine tools including lathes, mills, routers, and grinders.

Coating: covering that is applied to the surface of a forging. The purpose of applying the coating may be functional, aesthetic, or both.

Cobalt: An element used in combination with chromium and tungsten, to form alloys for use in aerospace applications, gas turbines, and some stainless steel.

Coining: A process whereby pressure is applied on the surface of the forging in order to obtain closer tolerances, smoother surfaces, and eliminate drafts.

Connecting Rod: A forged engine component that connects the piston to the crank or crankshaft in an alternating piston engine. Together with the crankshaft, it converts the reciprocating motion into a rotating motion. The connecting rods can also convert the rotary motion into reciprocating motion.

Copper: A soft, malleable, and ductile metal with very high thermal and electrical conductivity.

Crankshaft: An elongated forged metal component in certain machines that transforms rectilinear movement into circular or inverse movement.

Destructive Testing: An evaluation technique used to analyze the properties of forged materials or components that verifies the stress resistance limits until damage occurs.

Die: A specialized impression tool used to shape material using the force of a mechanical press or hammer.

Die Impression: The portion of the die surface that shapes the forging.

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 the release of the part from the dies and provide thermal insulation.

Discontinuities: Includes cracks, folds, cold shuts, and flow-through, as well as internal defects such as inclusion, segregation, and porosity; internal discontinuities can be detected and evaluated using ultrasonic testing equipment.

Double forging: A forging designed to be cut apart and used as two separate pieces.

Ductility: The relative ability of a metal to undergo permanent deformation through elongation (reduction in cross-sectional area) or bending at room temperature without fracturing. Opposite of brittleness.

Electrical Conductivity: Rate at which electrons move through atoms causing current to flow.

Elongation: The amount of permanent stretch in a tensile test specimen before rupture.

Ferrous Metals: Metal alloys that contain iron and other elements which depending on their concentrations and composition give specific properties.

Finish: (1) The forging operation in which the part is forged into its final shape in the finish die. If only one finish operation is scheduled to be performed in the finish die, this operation will be identified simply as finish; first, second, or third finish designations are so termed when one or more finish operations are to be performed in the same finish die. (2) The surface condition of a forging after machining. (3) The material is machined off the surface of a forging to produce the finish machine component.

Flange: A flat rim, collar, or rib projecting from an object, serving to strengthen or attach to another component or to maintain position on a rail.

Flashing: The excess material ejected from the closed die due to the force of the impression.

Forging: A manufacturing process of shaping a malleable metal part, known as a blank, billet, or workpiece, is worked to a predetermined shape by one or more processes such as hammering, upsetting, pressing, rolling metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die.

Galvanizing:  A layering process used to apply a protective coating of zinc to a forging.

Gear: A machine component having cut teeth or cogs, which mesh with another toothed or cogged part to transmit torque. Geared devices can change the speed, torque, and direction of input. Gears usually produce a change in torque, creating a mechanical advantage, determined by the relative number of teeth or cogs between two individual gears.

Grain: The basic crystalline structural unit of metals and alloys.

Grain Flow: Lines appearing on polished and etched sections of forgings indicating the orientation and direction of the metallic structural units due to working during the forging process. Grain flow produced by proper die design produces the enhanced mechanical properties of forgings.

Grain Size: The average size of the crystals or grains in a metal relative to accepted standards.

Gravity Hammer: A type of forging hammer wherein energy for forging is obtained by the mass and velocity of a freely falling ram and the attached upper die.

Grinding: Process of removing metal by abrasion from bar or billet stock to prepare stock surfaces for forging. It can also be used to remove surface irregularities and flash from forgings.

Hammer: A large, heavy piece of metal used to deliver blows to a surface or workpiece.

Hardened Steel: A steel that has been annealed and quenched to achieve a certain metal density.

Heat treating: The heating and cooling of metals to change their physical and mechanical properties, without letting them change their shape.

Hot Forging: A metal forming process whereby the workpiece is heated above 1200 Centigrade of its melting temperature and then shaped by the hammer, upsetter, press, or ring roller according to the process required for the individual piece.

Hub: Center part of a wheel, rotating on or with the axle, and from which the spokes radiates.

ISO 9001: A quality management system (QMS) certification that assures a company is continually monitoring, managing, and improving quality across all operations.

Jominy: A hardenability test for steel to determine the depth of hardening obtainable by a specified heat treatment.


Knockout mark: A small protrusion, such as a button or ring of flash, resulting from the depression of a knockout pin from the forging pressure, or the entrance of metal between the knockout pin and the die.

Knockout pin: A power-operated plunger installed in a die to aid the removal of the finished forging.

Liquid Penetrant Inspection: Also known as a dye penetrant inspection (DPI) or penetrant testing (PT), it was first developed in the early 1940s to detect flaws on the surface of materials. Liquid penetrant inspection is a non-destructive test method that does not harm the samples or parts being inspected. It effectively detects porosity, cracks, fractures, laps, seams, and other flaws that are open to the surface of the test piece and may be caused by fatigue, impact, quenching, machining, grinding, forging, bursts, shrinkage, or overload.

Machining: A manufacturing process such as abrading, cutting, drilling, forming, grinding, and or shaping of a piece of metal or other material performed by machine tools such as lathes, power saws, and presses.

Magnesium: A common metal often used to form an alloy with aluminum for the aerospace industry.

MPI Magnetic Particle Inspection: a method for detecting cracks or other imperfections in ferromagnetic materials such as iron and steel by applying magnetic particles upon a piece and measuring the magnetic flow. A discontinuity is indicated by a distortion in the distribution of the magnetic particles.

Nickel: A ductile and malleable metallic element, alloyed to iron and cobalt, not readily oxidized: used chiefly in alloys.

Non-Destructive Testing: analysis techniques used to evaluate the properties of a material, component, or system without causing damage.

Non-Ferrous Metals: Metals that do not contain iron or iron alloys. Examples include aluminum, aluminum alloys, brass, bronze, and zinc.

Normalizing: A process of heat treating steel by warming it above the critical temperature, holding for a period of time until transformation occurs, and air cooling.

Open Die Forging: The mechanical forming of metals between flat or shaped dies, where the flow of the metal is not completely restricted.

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.

Painting: The practice of applying a coating, pigment, color, or another medium to a solid surface to cover a part of surfaces and to provide improved durability for a forging yield improved longevity in harsh environments.

Powder Coating: A process that consists of applying a non-solvent-based coat of paint that is applied in powder form: it does not require a solvent to keep the binder and filler parts in a liquid suspension form as does a liquid paint.

Press: A method of forging using closed impression dies by a single continuous squeezing action, in contrast to a series of blows as in drop forging. This squeezing is obtained by means of hydraulic or mechanical presses.

Punching: Process of removing material from a forging by using a protruding tool called a punch to pierce or puncture the workpiece while it is still hot.

Quench: A heat treatment process involving rapid cooling of a workpiece to obtain certain material properties

Ring Rolling: A forging process in which a ring of smaller diameter is rolled into a precise ring of larger diameter and a reduced cross-section. This is accomplished by the use of two rollers, one driven and one idle, acting on either side of the ring’s cross-section.

Rod: A thin straight bar of metal.

Shaft: An elongated, narrow part or section forming the handle of a tool or other implement.

Shotblast: The process of shooting small metal beads against a part at high velocity to remove impurities.

Super-alloy: A metallic alloy that can be used at high temperatures, often in excess of 0.7 of the absolute melting temperature. Creep (cold-flow) and oxidation resistance are the prime design criteria. Superalloys can be based on iron, cobalt, or nickel.

Temper: Reheating the hardened steel to the tempering temperature in order to relieve stress-induced in the hardening process and remove some of the hardness in exchange for toughness.

Tensile Test: a procedure that measures the overall strength of an object fitted between two grips at both ends, then slowly pulled apart until it breaks, which provides vital information related to a product’s yield point, tensile strength, and proof stress.

Threaded Rod: Also known as a stud and is a relatively long rod threaded on both ends; the thread may extend along only a portion or along the complete length of the rod. Designed to be used in tension.

Trimming: A cleaning process that is used as a finishing operation for forged parts, in order to remove the excess material surrounding the forged part.

Trunnion: A forged pin or forged pivot on which something can be rotated or tilted.

Upsetting: A forging process that increases the diameter of a workpiece by compressing its length.

Vent: A small hole in a punch or die for admitting air to avoid suction holding or for relieving pockets of trapped air that would prevent die closure or action.

Vent mark: small protrusion resulting from the entrance of metal into die vent holes.

Warm forging: Deformation at elevated temperatures below the recrystallization temperature. The flow stress and rate of strain hardening are reduced with increasing temperature; thus, lower forces are required than in cold working. For steel, the temperatures range from about 1000° F to just below the normal hot working range of 1900 to 2300° F.

Warpage: Term generally applied to distortion that results during quenching from heat-treating temperatures; hand straightening, press straightening, or cold restriking is employed, depending on the configuration of the part and the amount of warpage involved. The condition is governed by applicable straightness tolerances; beyond tolerances, warpage is defect and cause for rejection. The term is not to be confused with “bend” or “twist.”

Ways: The fitted V-shaped grooves in the ram and columns of a hammer or press that guide the descent and ascent of the ram.

Web: A relatively flat, thin portion of a forging, generally parallel to the forging plane—that connects ribs and bosses.

Wrought steel: A descriptive term for any particle of steel that has been produced by hot mechanical working.

Yoke: A coupling component used in heavy industry applications.

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