The world of metal forging comes with its own specialized language. Understanding the terminology is essential for anyone working with forged components, whether you’re an engineer, buyer, or manufacturer. This glossary covers key forging terms used across different processes, materials, tolerances, and treatments to help you communicate clearly and make informed decisions about your product needs.
Alloy steel forging: alloy forging 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.
Aluminum precision forging: A process which plastically deforms an aluminum alloy to a finished part shape in special dies. Aluminum forging design considerations require little or no subsequent machining/processing, as a result of close forging tolerances, thin sections, small radii and minimum draft angles.
Bar: a section hot rolled from a billet to a round, square, rectangular, hexagonal or other shape with a cross-section less than 16 sq. in.
Billet: a semi-finished section (width <2X thickness), hot rolled from a metal ingot, generally having a cross-section ranging from 16 to 64 sq. in. Also applies to a hot-worked forged, rolled or extruded round or square.
Blank: raw material or forging stock from which a forging is made.
Bloom: same as a billet, but with a cross-sectional area greater than 36 sq. in.
Blocker-type forging: one with the general shape of the final configuration, but featuring a generous finish allowance, large radii, etc.
Carbon steel forging: forgings in carbon steel or a steel whose major alloying element, carbon, produces the resultant properties and hardness.
Close-tolerance forging: one held to closer-than-conventional dimensional tolerances.
Closed die forging: see impression die forging.
Coining: a post-forging process – on hot or cold parts – to attain closer tolerances or improved surfaces.
Cold-coined forging: one that is restruck cold to improve selected tolerances or reduce a specific section thickness.
Cold forging: various forging processes conducted at or near ambient temperatures to produce metal components to close tolerances and net shape. These include bending, cold drawing, cold heading, coining extrusion (forward or backward), punching, thread rolling and others.
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.
Cold working: imparting plastic deformation to a metal or alloy at a temperature below recrystallization to produce hardness and strength increases via strain hardening.
Controlled cooling of forgings: used to attain required properties and/or corresponding microstructural phase changes; applies to heat-treatable steels (e.g., quenching) and to microalloyed steels, which require no heat treatment, but only controlled cooling to attain final properties.
Conventional forging: one that, by design, requires a specified amount of finish (or machining) to reach the final dimensional requirements.
Counterblow forging: one made by equipment incorporating two opposed rams, which simultaneously strike repeated blows on the workpiece.
Cross forging: the practice of working stock in one or more directions to make resultant properties more isotropic (equal in three directions) – e.g., by upsetting and redrawing the material.
Directional properties: refers to the inherent directionality within a forging such that properties are optimally oriented to do the most good under in-service conditions. Typically, maximum strength is oriented along the axis that will experience the highest loads.
Disc: “pancake” shaped forging (flat with a round cross-section); e.g., a blank for gears, rings and flanged hubs.
Draft: the necessary taper on the side of a forging to allow removal from the dies; also applies to the die impression. Commonly expressed in degrees as the draft angle.
Draftless forging: a forging with zero draft on vertical walls.
Drawing: (1) reducing the cross-section of forging stock while simultaneously increasing the length; (2) in heat treating, the same as tempering.
Drop forging: one produced by hammering metal in a drop hammer between impression dies.
Extrusion: forcing metal through a die orifice in the same direction as the applied force (forward extrusion) or in the opposite direction (backward extrusion).
Finish: (1) the material remaining after forging that is machined away to produce the final part; (2) the surface condition of a forging after machining.
Finish all over (F.A.O.): designates that forgings be made sufficiently larger than dimensions shown to permit machining on all surfaces to given sizes.
Finish allowance: amount of stock left on the surface of a forging to be removed by subsequent machining.
Flash: excess metal that extends out from the body of the forging to ensure complete filling of the finishing impressions.
Flashless forging: “true” closed die forging in which metal deformed in a die cavity permits virtually no excess metal to escape.
Flow lines: patterns that reveal how the grain structure follows the direction of working in a forging.
Forgeability: relative ability of a material to deform without rupture.
Forging reduction: ratio of the cross-sectional area before and after forging; sometimes refers to percentage reduction in thickness.
Forging stock: wrought rod, bar, etc. used as the raw material or stock in forging.
Free-machining-steel forgings: those made from steels with special alloying-element additions to facilitate machining.
Grain flow: fiberlike lines that show (via macroscopic etching) the orientation of the microstructural grain pattern of forgings achieved by working during forging processes. Optimizing grain flow orientation maximizes mechanical properties.
Hammer forging: one produced on a forging hammer, usually between impression dies but sometimes flat dies; the process of forging in a drop hammer (see drop forging).
Hand forging: one made by manually controlled manipulation in a press without impression dies, usually between flat dies with progressive forging of the workpiece; also referred to as flat-die forging.
Heat treatment: heating or cooling operations, sometimes isothermal, to produce desired properties in forgings.
High-energy-rate forging: forgings made on equipment that utilizes very high ram velocities.
Hog-out: product machined from bar, plate, slab, etc.
Hollow forging: a cylindrical open die forging, e.g., thick-walled tubes or rings.
Hot-die forging: a process in which dies are heated close to the forging temperature of the alloy being forged/ used for difficult-to-forge alloys.
Hot forging: same as hot working – plastically deforming an alloy at a temperature above its recrystallization point, i.e., high enough to avoid strain hardening.
Hub: a boss in the center of a forging that forms an integral part of the body.
Iconel Alloy: a trademark of Special Metals Corporation that is a nickel-chromium-based superalloys.
Impact extrusion: a reverse extrusion process in which metal is displaced backwards between a punch and a die to form a hollow part.
Impression die forging: one formed to shape and size in die cavities or impressions; also commonly referred to as closed die forging.
Isothermal forging: is most commonly conducted at about 2000 degrees F under a controlled atmosphere or vacuum to prevent oxidation while forging superalloys.
Machine forging (upsetter forging): one made in a forging machine or upsetter, in which a horizontally moving die in the ram forces the alloy into the die cavities.
Mandrel forging: see saddle/mandrel forging.
Match: aligning a point in one die half with the corresponding point in the opposite die half.
Microalloyed-steel forging: one made from a mircroalloyed steel requiring only controlled cooling to reach optimum properties, which is in contrast to conventional quenched-and-tempered steels that require traditional heat treatments to achieve the same results.
Microstructure: the microscopic structure of metals/alloys as seen on a mounted, ground, polished and etched specimen to reveal grain size, constituent phases, etc.
Near-net-shape forging: forging components as close as possible to the required dimensions of the finished part.
Open die forging: one produced by working between flat or simply contoured dies by repetitive strokes and continuous manipulation of the workpiece; sometimes called hand forging.
Parting line: the plane that divides the two die halves used in forging; also applies to the resulting forging and impression dies.
Piercing: forming or enlarging a hole via a tapered or cylindrical punch.
Plastic deformation: permanent distortion of a material without fracturing it.
Plate: a flat, hot-rolled metal or alloy product whose thickness is much less than its width.
Precision forging: any forging process that produces parts to closer tolerances than conventional forging processes.
Preform: forging operation in which stock is preformed or shaped to a predetermined size and contour prior to subsequent die forging operations; also, ring blanks of a specific shape for profile (contour) ring.
Press forging: the shaping of metal between dies on a mechanical or hydraulic press.
Quenched-and-tempered steel forging: one that is quenched and tempered to produce the required forging hardness and properties; should more accurately be referred to as hardened-and-tempered. (Hardening and tempering are heat treatments that follow austenitizing, which is usually the first heat treatment performed on carbon- and alloy-steel forgings.
Restriking: a salvage operation following a primary forging operation – rehitting forgings in the same die in which they were last forged.
Rib: a forged wall or vertical section generally projecting in a direction parallel to the ram stroke.
Rib-and-web forging: one whose basic configuration consists of ribs and webs.
Rough machining: an initial machining operation that leaves adequate stock for subsequent finish machining.
Saddle/mandrel forging: rolling and forging a pierced disc over a mandrel to yield a seamless ring or tube.
Slab: a flat-shaped semifinished, rolled metal ingot with a width not less than 10 in. and a cross-sectional area not less than 16 sq. in.
Standard tolerance: an established tolerance for a certain class of product; preferred over “commercial” or “published” tolerance.
Straightening: a finishing operation for correcting misalignment in a forging or between different sections of a forging.
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.
Swaging: reducing the size of forging stock; alternately, forging in semicontoured dies to lengthen a blank.
Target machining: incorporating a “target” (benchmark or gage point) on a forging to facilitate machining; coined locating surfaces and drilled centers are commonly used.
Trimming: performed hot or cold, the mechanical shearing of flash or excess material from a forging by use of a trimmer in a trim press.
Upset forging: one made by upset of an appropriate length of bar, billet or bloom; working metal to increase the cross-sectional area of a portion or all of the stock.
Upsetter (forging machine): a machine with horizontal action used to produce upset forgings.
Warm forging: forging of steel at temperatures ranging from about 1000 degrees F to just below the normal hot working range of 1900 to 2300 degrees F.
Web: a relatively flat, thin portion of a forging – generally parallel to the forging plane – that connects ribs and bosses.
Wide tolerance: any special tolerance wider than “standard”.