Forgings Glossaryforging_glossary

ForgeLog – a Forging Glossary, is a dictionary of several hundred terms used in the forging and metalworking industries. Click on a letter of the alphabet to view all the terms in a specific section. This content is protected by copyright but is available for your own personal use.

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Age – An operation in which forgings are subjected to low temperature treatment for specific periods of time to effect the complete or partial precipitation of the solutes in the alloy, resulting in controlled hardening of the metal.

Age hardening (aging) – The latter part of a two-step heat treating operating applied to certain alloys for strengthening and hardening (See also Solution heat treatment). Aging involves heating to a relatively low temperature for a specified period of time, and results in controlled precipitation of the constituent dissolved during the solution heating treatment.

Aging – The change in the properties of a metal that occurs at relatively low temperature following a final heat treatment or a final cold working operation: aging tends to restore equilibrium in the metal and eliminate any unstable condition induced by a prior operation.

Aircraft quality – Denotes stock of sufficient quality to be forged into highly stressed parts for aircraft or other critical applications. Suchmaterials 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 (Ref: Aerospace Material Specification 2301).

Air-lift hammer – A type of gravity drop hammer where the ram is raised for each stroke by an air cylinder. Because length of stroke can be controlled, ram velocity and thus energy delivered to the workplace can be varied.

Alloy – A material having metallic properties and composed of two or more chemical elements of which at least one is a metal. In practice, the word is commonly used to denote relatively high-alloy grade of material – for example, “alloy” steels as differentiated from “carbon” steels. Materials are alloyed to enhance physical and mechanical properties such as strength, ductility, and hardenability.

Annealing – full-A heat-treating operation wherein metal is heated to a temperature above its critical range, held at the temperature long enough to allow full recrystallization, then slowly cooled through the critical range. Annealing removes working strains, reduces hardness, and increases ductility.

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 from 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.

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Backward extrusion – Forcing metal to flow in a direction opposite to the motion of a punch or die.

Backing arm – A device for supporting the ring rolling mill mandrel from above during the roll process.

Bar – 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″; 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″ or more.

Bed – Stationary platen of a press to which the lower die assembly is attached.

Bend – Operation to preform (bend) stock to approximate shape of die impression for subsequent forging; also includes final forming. 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”. Low-draft and no-draft forgings are more susceptible to bending, as they must be removed from the dies by some form of mechanical ejection. Dull trimming tools and improper nesting will cause bending in the trimming operation. When bend or twist exceeds tolerances, it is considered a defect. Corrective action entails either hand straightening, machine straightening, or cold restriking.

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

Billet – (1) A semi-finished section hot rolled from a metal ingot, with a rectangular cross section usually ranging from 16-36″, the width being less than twice the thickness. Where the cross section exceeds 36″, the term “bloom” is properly but not universally used. Sizes smaller than 16″ are usually termed”bars”; a solid semi-finished round or square product which has been hot worked by forging, or extrusion. (2) A semi-finished, cogged, hot-rolled, or continuous-cast metal product of uniform section, usually rectangular with radiused corners. Billets are relatively larger than bars.

Blank – A piece of stock (also called a “slug” or “multiple”) from which a forging is to be made.

Blast cleaning (blasting) – 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.

Block – 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).

Blow – The impact or force delivered by one workstroke of the forging equipment.

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

Box annealing – A heat-treating 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.

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.

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 (10mm ball, 500kg load for aluminum alloys). 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 routine inspection of forgings, and as a heat treat control function.

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

Case – The surface layer of an alloy that has been made substantially harder than the interior by some form of hardening operation.

Case hardening – A heat treatment or combination of processes in which the surface layer of a ferrous alloy is made substantially harder than the interior. Carburizing, cyaniding, nitriding, and heating and quenching techniques are commonly used. Case hardening can provide a hard, wear-resistant surface on a forging, while retaining a softer, tougher core.

Centering arm – in ring rolling, externally mounted rolls, adjusted to the outside diameter of the ring during rolling. The rolls maintain and guide the ring in a centerline position to achieve roundness.

Charpy test – A pendulum type impact test where the specimen is supported as a simple beam and is notched opposite the point of impact. The energy required to break the beam is used as an index of impact strength measurement.

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

Cleaning-The process of removing scale, oxides, or lubricant acquired during heating for forging or heat treating from the surface of the forging. (See also Blasting, Pickling, Tumbling).

Cogging – The reducing operation in working the ingot into a billet by the use of a forging hammer or a forging press.

Coining – The process of applying necessary pressure to all or some portion of the surface of a forging to obtain closer tolerances or smoother surfaces or to eliminate draft. Coining can be done while forgings are hot or cold and is usually performed on surfaces parallel to the parting line of the forging.

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 on-heat-treatable alloys, increase hardness.

Cold inspection – A visual (usually final) inspection of the forgings for visible defects, dimensions, weight, and surface condition at room temperature. The term may also be used to describe certain non destructive tests, such as magnetic particle, dye penetrant, and sonic inspection.

Cold shut – A defect characterized by a fissure or lap on the surface of a forging that has been closed without fusion during the forging operation.

Conventional forging – A forging characterized by design complexity and tolerances that fall within the broad range of general forging practice.

Core – The softer interior portion of an alloy piece that has been surface (case) hardened; or, that portion of a forging removed by trepanning or punching.

Critical point – The temperature in metal at which recrystallization or other phase transformation takes place.

Critical (temperature) range – Temperatures at which changes in the phase of a metal take place. Changes are determined by absorption of heat when the metal is heated, and liberation of heat when it is cooled.

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Decarburization – The loss of carbon from the surface of steel by heating above lower critical temperature or by chemical action. Decarburization is usually present to a slight extent in steel forgings. Excessive decarburization can result in defective products.

Descaling – The process of removing oxide scale from heated stock prior to or during forging operations, using such means as extra blows, wire brushes, scraping devices, or water spray.

Drawing – A forging operation in which the cross section of a forging stock is reduced and the stock lengthened between flat or simple contour dies. (See also Fuller).

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F.A.O. – An abbreviation of “finish all over”, it designates that a forging must have sufficient size over the dimensions given on the drawing so that all surfaces may be machined in order to obtain the dimensions shown on the drawing. The amount of additional stock necessary for machining allowance depends on the size and shape of the part, and is agreed on by the vendor and the user.

Flat die forging (open-die forging) – Forging worked between flat or simple contour dies by repeated strokes and manipulation of the workpiece. Also known as “hand” or “smith” forging.

Forging quality – Term describing stock of sufficiently superior quality to make it suitable for commercially satisfactory forgings.

Fuller (fullering impression) – Portion of the die that is used in hammer forging primarily to reduce the cross section and lengthen a portion of the forging stock. The fullering impression is often used in conjunction with an edger (or edging impression).

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Grain – The characteristic crystalline structural unit or metals and alloys.

Grain flow – Fiber-like lines appearing on polished and etched sections of forgings that are caused by orientation of the constituents of the metal in the direction of working during forging. Grain flow produced by proper die design can improve required mechanical properties of forgings.

Grain size – The average size of the crystals or grains in a metal as measured against an accepted standard.

Gravity hammer – A class of forging hammer wherein energy for forging is obtained by the mass and velocity of a freely falling ram and the attached upper die. Examples are board hammers and air-lift hammers.

Grinding – Process of removing metal by abrasion from bar or billet stock to prepare stock surfaces for forging. Occasionally used to remove surface
irregularities and flash from forgings.

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Hammer forging – A forging that is made on the flat die of a steam hammer. A forged piece produced in a forging hammer, or the process of forming such a piece. (See also Board hammer, Power-drive hammer, Rope hammer).

Hand forge (smith forge) – The forging operation in which the forming is accomplished on dies that are generally flat. The piece is shaped roughly to the required contour with little or no lateral confinement; operations involving mandrels are included.

Hand forging – A forging made by hand on an anvil or under a power hammer without dies containing an exact finishing impression of the part. Such forgings approximate each other in size and shape but do not have the commercial exactness of production die forgings. Used where the quantity of forgings required does not warrant expenditure for special dies, or where the size or shape of the piece is such as to require means other than die forging. A forging worked between flat or simply shaped dies by repeated strokes and manipulation of the piece. Also known as smith forging or flat die forging.

Hardening – A heat treatment consisting of heating an alloy to a temperature within or above the critical range, maintaining that temperature for the prescribed time (usually 15-30 min.), then quenching or otherwise rapidly cooling. For age-hardening alloys, a two-stage process consisting of solution heat treatment and aging.

Heat (forging) – Amount of forging stock placed in a batch-type furnace at one time.

Heat treatment – A combination of heating, holding, and cooling operations applied to a metal or alloy in the solid state to produce desired properties.

Hub – A boss that is in the center of the forging and forms a part of the body of the forging.

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Impact testing – Tests that determine the energy absorbed in fracturing a test bar at high velocity. (See also Charpy test, Izod test).

Impression die forging – A forging that is formed to the required shape and size by machined impressions in specially prepared dies that exert three-dimensional control on the workpiece.

Inclusion – Impurities in metal, usually in the form of particles in mechanical mixture.

Izod test – A pendulum-type impact test in which the specimen is upported at one end as a cantilever beam and the energy required to break off the free end is used as a measure of impact strength.

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

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Lap – A surface defect appearing in a seam, caused by the folding over of hot metal, fins, or sharp corners and by subsequent rolling for forging (but not welding) of these into the surface.

Loose material – During forging operations, pieces of flash often break loose necessitating cleaning of the dies between forging blows; this is usually accomplished by lubricating the die while air is blown on it. Insufficient cleaning results in pieces of flash becoming imbedded in the surface of the forging. Such forgings are often salvaged by removing the loose pieces and hot reforging to fill out the depressions.

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Macrotech – A testing procedure for conditions such as porosity, inclusions, segregations, caburization, and flow lines from hot working. After applying a suitable etching solution to the polished metal surface, the structure revealed by the action fo the reagent can be observed visually.

Magnetic particle testing – A non-destructive test method of inspecting areas on or near the surface of ferromagnetic materials. The metal is magnetized, then iron powder is applied. The powder adheres to lines of flux leakage, revealing surface and near surface discontinuities. Magnetic particle testing is used for both raw material acceptance testing and product inspection. Quality levels are usually agreed on in advance by the producer and purchaser.

Magnaglo© – A type of magnetic particle testing where the magnetic powder is fluorescent and the inspection is performed under black light. (See also Magnetic particle testing). Trade name of Magnaflux Corp.

Mandrel forging – The process of rolling and forging a hollow blank over a mandrel in order to produce a weldless, seamless ring or tube.

Mechanical properties – Those properties of a material that reveal the elastic and inelastic reaction when force is applied, or that involve the relationship between stress and strain; for example, the modulus are dependent on chemical composition, forging, and heat treatment.

Microstructure – 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).

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

Normalizing – A heat treatment in which ferrous alloys are heated to approximately 100�F above the critical range, holding that temperature for the required time, and cooling to room temperature in air.

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Overheating – Can occur in preheat furnaces prior to forging or in the heat-treating operation. The condition results when metal temperature exceeds the critical temperature of the alloy involved and a change in phase occurs; this is also known as the transformation temperature. Externally, overheated material will often form blisters or a web of fine cracks; internally, overheating causes precipitation of melted constituents around grain boundaries and the formation of rounded pools of melted constituents often called “rosettes”.

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

Pierce – In ring rolling, the process of providing a through hole in the center of an upset forging as applied to ring blank preparation.

Plane, forging – The plane that includes the principal die face and that is perpendicular to the direction of the ram stroke; when the parting is flat, the forging plane coincides with the parting line.

Power-driven hammer – A forging hammer with a steam or air-cylinder for raising the ram and augmenting its downward blow.

Precision forging – A forging produced to closer tolerances than normally considered standard by the industry.

Preform – The forging operation in which stock is preformed or shaped to a predetermined size and contour prior to subsequent die forging operations; the operation may involve drawing, bending, flattening, edging, fullering, rolling, or upsetting. The preform operation is not considered to be scheduled operation unless a separate heat is required; usually, 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. In ring rolling, a term generally applied to rind blanks of a specific shape to be used for profile (contour) ring rolling.

Preheating – A high-temperature soaking treatment used to change the metallurgical structure in preparation for a subsequent operation, usually applied to the ingot.

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

Press forging – The shaping of metal between dies by mechanical or hydraulic pressure. Usually this is accomplished with a single work stroke of the press for each die station.

Punch – A shearing operation to remove a section of metal as outlined by the inner parting line in a blocked or finished forging; the operation is generally performed on a trim press using a punch die, a tool used in punching holes in metal. The movable die in a press or forging machine.

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Radial ring rolling mill (RW) – A type of ring forging equipment for producing seamless rolled rings by controlling only the outside and inside diameters.

Radial roll (main roll, king roll) – The primary driven roll of the rolling mill for rolling rings in the radial pass. Roll supported at both ends.

Radial rolling force – The action produced by the horizontal pressing force of the rolling mandrel acting against the ring and the main roll. Usually expressed in metric tons.

Ram – The moving or falling part of a drop hammer or press to which one of the dies is attached; sometimes applied to the upper flat die of a steam hammer.

Reduction of area (contraction of area) – The difference in a tension specimen, between the size of the original sectional area and that of the area at the point of rupture. It is generally stated as the percentage of decrease of cross sectional area of a tension specimen after rupture.

Ring rolling – The process of shaping weldless rings from pierced disks or thick-walled, ring-shaped blanks between rolls that control wall thickness, ring diameter, height, and contour.

Rockwell hardness testing – A method of determining the relative hardness value of a material by measuring the depth of residual penetration by a steel ball or diamond point under controlled loading.

Roller (roller impression) – The portion of a forging die where cross sections are altered by hammering or pressing while the workpiece is being rotated.

Rolling – The forging operation of working a bar between contoured dies while turning it between blows to produce a varying circular cross section.

Rolling mandrel – In ring rolling, a vertical roll of sufficient diameter to accept various sized of ring blanks and exert rolling force on an axis parallel to the main roll.

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Sand blasting – The process of cleaning forgings by propelling sand against them at high velocity. (See also Blast cleaning).

Shearing – A process of mechanically cutting metal bars to the proper stock length necessary for forging the desired product.

Shoe – A holder used as a support for the stationary portions fo forging and trimming dies.

Shot blasting – A process of cleaning forgings by propelling metal shot at a high velocity by air pressure or centrifugal force at the surface of the forgings. (See also Blast cleaning).

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

Sizing – A process employed to control precisely a diameter of rings or tubular components.

Smith hammer – Any power hammer where impression dies are not used for the reproduction of commercially exact forging.

Solution heat treatment – A process in which an alloy is heated to a suitable temperature, held at this temperature long enough to allow a certain constituent to enter into solid solution, then cooled rapidly to hold the constituent in solution. The metal is left in a supersaturated, unstable state and may exhibit age hardening.

Spheroidizing – A form of annealing consisting of prolonged heating of iron base alloys at a temperature generally slightly below the critical range, followed by a relatively slow cooling. Causes the graphite to assume a spheroidal shape.

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.

Stress relieving – A process of reducing residual stresses in a metal object by heating it to a suitable temperature and holding for a sufficient time. This treatment may be applied to relieve stresses induced by quenching, normalizing, machining, cold working, or welding.

Swage – operation of reducing or changing the cross-sectional area by revolving the stock under fast impact of blows. Finishing tool with concave working surface; useful for rounding out work after its preliminary drawing to size.

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Table mill – In ring rolling, a type of ring forging equipment employing multiple mandrels with a common main roll. Usually used in high volume production of small-diameter rolled rings.

Tensile properties – The property data obtained from tensile test on a specimen, including tensile strength, elongation, reduction of area, and yield strength.

Tensile strength – The maximum load per unit of initial cross-sectional area obtained before rupture in a tension test.

Tonghold – The portion of the stock by which the operator grips the stock with tongs. A small portion of metal projecting from the forging used to manipulate the piece, usually trimmed off.

Tongs – Metal holder used to handle metal pieces.

Tumbling – The process for removing scale from forgings in a rotating container by means of impact with each other and abrasive particles and small bits of metal. A process for removing scale and roughness from forgings by impact with each other, together with abrasive material in a rotating container.

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Ultrasonic testing – A non-destructive test applied to sound-conductive materials having elastic properties for the purpose of locating inhomogeneties or structural discontinuities within a material by means of an ultrasonic beam.

Upend forging – A forging in which the metal is placed in the die so that the direction of the fiber structure is at right angles to the faces of the die.

Upset – Working metal in such a manner that the cross-sectional area is increased, and length is decreased.

Upset forging – A forging obtained by upset of a suitable length of bar, billet, or bloom; formed by heading or gathering the material by pressure upon hot or cold metal between dies operated in a horizontal plane.

Upsetter (forging machine) – A machine with horizontal action, used for making upset forgings.

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Warpage – Term generally applied to distortion that results during quenching from the heat-treating temperature; 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 a defect and cause for rejection.

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Yield point – The load per unit of original cross section at which a marked increase in the deformation of the specimen occurs without increase of load. It is usually calculated from the load determined by the drop of the beam of the testing machine or by the use of dividers. The stress in material at which there occurs a marked increase in strain without an increase in stress.

Yield strength – Stess corresponding to some fixed permanent deformation, such as 0.1 or 2.0% offset from the modulus slope.

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Zyglo© – A method for nondestructive surface inspection of primarily nonmagnetic materials using fluorescent penetrants. Trade name of Magnaflux Corp.

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