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Z94.12.1 - Forging


AIR-LIFT HAMMER. A type of gravity drop hammer where the ram is raised for each stroke by an air cylinder. Since length of strike may be controlled, ram velocity and thus energy delivered to the workpiece may be varied.

ANISOTROPY. The characteristic of exhibiting different values of a property in different directions with respect to a fixed reference system in the material.

ANVIL (BASE). Extremely large, heavy block of metal which supports entire structure of conventional gravity or steam driven forging hammers. Also, the block of metal on which hand (or smith) forgings are made.

BARK. The decarburized layer just beneath the scale produced by heating steel in an oxidizing atmosphere.

BATCH-TYPE FURNACE. A furnace for heating materials in which the loading and unloading is done through a single door or slot.

BENDER. Term denoting a die impression, tool, or mechanical device designed to bend forging stock to conform to the general configuration of die impressions subsequently to be used.

BILLET. A semi-finished, cogged, hot-rolled, or continuous-cast metal product of uniform section, usually rectangular with radiused comers. 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.

BLISTER. A defect caused by gas bubbles either on the surface or beneath the surface of the metal.

BLOCKER (BLOCKING IMPRESSION). The impression in the dies (often one of a series of impressions in a single die set) which imparts to the forging an intermediate shape, preparatory to forging of the final shape.

BLOCKER DIES. Blocker dies are characterized by generous contours, large radii, draft angles of 7° or more, and liberal finish allowances.

BLOCKER-TYPE FORGING. A forging which approximates the general shape of the final part with relatively generous finish allowance and radii. Such forgings are sometimes specified to reduce die casts where only a small number of forgings are desired and the cost of machining each part to its final shape is not excessive.

BLOCKING. A forging operation often used to impart an intermediate shape in the finishing impression of the dies. Blocking can ensure proper “working” of the material and contribute to great die life.

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

BLOWHOLE. A cavity produced by gas evolved during solidification of metal.

BOARD HAMMER. A type of gravity drop hammer where wood boards attached to the ram are raised vertically by action of contra-rotating rolls, then released. Energy for forging is obtained by the mass and velocity of the freely falling ram and the attached upper die.

BOLSTER. The plate secured to the bed of a press for locating and supporting the die assembly.

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

BURNT. Permanently damaged metal caused by heating conditions producing incipient melting or intergranular oxidation.

BURST. An internal discontinuity caused by improper  forging.

BUSTER (PRE-BLOCKING IMPRESSION). A type of die impression sometimes used to combine preliminary forging operations such as edging and fullering with the blocking operation to eliminate blows.

CAMBER. Deviation from edge straitness, usually referring to the greatest deviation of side edge from a straight line. Sometimes used to indicate crown on flat rolls.

CHECK. Crack in a die impression, generally due to forging pressure and/or excessive die temperature. Die blocks too hard for the depth of the die impression have a tendency to check or develop cracks in impression corners.


CLOSE-TOLERANCE DESIGN. A forging designed with commercially recommended draft radii and finish allowances, but with dimensional tolerances of less than one-half the commercial tolerances recommended for otherwise similar parts. Often little or no machining is required after forging.

COGGING. The process of forging ingots to produce blooms or billets.

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

COLD HEADING. Working metal at room temperature in such a manner that the cross-sectional area of a portion or all of the stock is increased.

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 nondestructive tests such as a magnetic particle, dye penetrant, and sonic inspection.

COLD LAP. A flaw caused when a workpiece fails to fill the die cavity during first forging. A seam is formed as subsequent dies force metal over this gap to leave a seam on the workpiece surface.

COLD TRIMMING. Removing flash or excess metal from the forging in a trimming press when the forging is at room temperature.

COLD WORKING. Permanent plastic deformation of a metal at a temperature below its recrystallization point — low enough to produce strain hardening.

COMPRESSIVE STRENGTH. The maximum stress that a material subjected to compression can withstand when loaded without deformation or fracture.

CORE FORGING. The process of displacing metal with a punch to fill a die cavity.

COUNTERBLOW FORGING EQUIPMENT. A category of forging equipment wherein two opposed rams are activated simultaneously, striking repeated blows on the workpiece of a midway point. Action may be vertical, as in the case of counterblow forging hammers, or horizontal as with the “Impacter.”

COUNTERLOCK. A jog in mating surfaces of dies to prevent lateral die shifting from side thrust developed in forging irregular shaped pieces.

CREEP. Time-dependent strain occurring under stress. The resistance to creep, or creep strength, decreases with increasing temperature.

CRITICAL (TEMPERATURES). Temperatures at which phase changes take place in metals.

Cross FORGING. Preliminary working of forging stock in flat dies so that the principal increase in dimension is in the transverse direction with respect to the original axis of the ingot.

DIE BLOCK. A block (usually) of heat-treated steel into which desired impressions are machined or sunk and from which closed-die forgings are produced on hammers or presses. Die blocks are usually used in pairs with part of the impression in one of the blocks and the balance of the impression in the other.

DIE FORGING. (l) Compression in a closed impression die. (2) A product of such an operation.

DIE LUBRICANT. A compound sprayed, swabbed or otherwise applied on die surfaces of forgings during forging to reduce friction between the forging and the dies. Lubricants may also ease release of forgings from the dies and provide thermal insulation.

DIE MATCH. The condition where dies, after having been set up in the forging equipment, are in proper alignment relative to each other.

DIES (DIE BLOCKS). The metal blocks into which forging impressions are machined and from which forgings are produced.

DIE SHIFT. A condition requiring correction where, after dies have been set up in the forging equipment, displacement of a point in one die from the corresponding point in the opposite die occurs in a direction parallel to the fundamental parting line of the dies.

DIRECTIONAL PROPERTIES. Anisotropic values. Physical or mechanical properties varying with the relation to a specific direction, resulting from structural fibering and preferred orientation.

DOWEL. A metal insert placed between mating surfaces of the die shank and die holder in the forging equipment to assure lengthwise die match.

DRAFT. The amount of taper on the sides of the forging necessary for removal of the workpiece from the dies. Also the corresponding taper on the side walls of the die impressions.

DRAFT ANGLE. The angle of taper, expressed in degrees, given to the sides of the forging and the side walls of the die impression.

DRAWING. A forging operation in which the cross section of forging stock is reduced and the stock lengthened between flat or simple contour dies. (See FULLER.)

DROP FORGING. A forging produced by hammering metal in a drop hammer between dies containing impressions designed to produce the desired shape. (See IMPRESSION DIE FORGING.)

DROP HAMMER. A term generally applied to forging hammers wherein energy for forging is provided by gravity, steam, or compressed air. (See AIR-LIFT HAMMER, BOARD HAMMER, STEAM HAMMER.)

EDGER (EDGING IMPRESSION). The portion of the die impression which distributes metal during forging into areas where it is most needed to facilitate filling the cavities of subsequent impressions to be used in the forging sequence. (See FULLER.)

EXTRUSION. The process of forcing metal to flow through a die orifice in the same direction in which energy is being applied (forward extrusion); or in the reverse direction (backward extrusion) in which case the metal usually follows the contour of the punch or moving forming tool. The extrusion principle is used in many impression die forging applications.

EXTRUSION FORGING. (l) Forcing metal into or through a die opening by restricting flow in other directions. (2) A part made by the operation.

FILLET. The concave intersection of two surfaces. In forging, the desired radius at the concave intersection of two surfaces is usually specified.

FINISH ALLOWANCE. The amount of excess metal surrounding the intended final shape. Sometimes called clean-up allowance, forging envelope, or machining allowance.

FLAKES. Short, discontinuous, internal fissures in ferrous metals attributed to stresses caused by localized transformation and decreased solubility of hydrogen during cooling after hot working.

FLASH. Necessary metal in excess of that required to completely fill the finishing impression of the dies. Flash extends out from the body of the forging as a thin plate at the line where the dies meet and is subsequently removed by trimming. Cooling faster than the body of the component during forging, flash can serve to restrict metal flow at the line where dies meet, thus assuring complete filling of the finishing impression.

FLASH GUTTER. An additional cavity machined along the parting line of the die cavity to receive the excess metal as it flows out of the die cavity through the flash gap.

FLASH LAND. Configuration in the finishing impression of the dies designed either to restrict or to encourage growth of flash at the parting line, whichever may be required in a particular instance to ensure complete filling of the finishing impression.

FLAT DIES 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.

FLOW LINES. Patterns in a forging resulting from the elongation of nonhomogeneous constituents and the grain structure of the material in the direction of working during forging; usually revealed by macroetching. (See GRAIN FLOW.)

FLOW STRESS. (l) The shear stress required to cause plastic deformation of solid metals. (2) The uniaxial true stress required to cause flow at a particular value of strain.

FORGEABILITY. Term used to describe the relative ability of material to deform without rupture.

FORGING. The product of work on metal formed to a desired shape by impact or pressure in hammers, forging machines (upsetters), presses, rolls, and related forming equipment Forging hammers, counterblow equipment, and high-energy-rate forging machines impart impact to the workpiece, while most other types of forging equipment impart squeeze, but the majority of metals are made more plastic for forging by heating.

FORGING MACHINE (UPSETTER OR HEADER). A type of forging equipment, related to the mechanical press, in which the main forming energy is applied horizontally to the work-piece which is gripped and held by prior action of the dies.

FORGING ROLLS. Rolling mills that forge comparatively uniform shapes by using variable radii around the circumference of rolls that rotate in the opposite direction from those ordinarily used for rolling.

FORGING STRAINS. Differential strains that result from forging or from cooling from the forging temperature, and that are accompanied by residual stresses.

FORGING STRESSES. Elastic stresses induced by forging or cooling from the forging temperature; sometimes erroneously referred to as forging strains.

FULLER (FULLER IMPRESSION). Portion of the dies which 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).

GATE (SPRUE). A portion of the die which has been removed by machining to permit a connection between multiple impressions or between an impression and the bar of stock.

GATHERING. An operation which increases the cross section of part of the stock above its original size.

GATHERING STOCK. Any operation whereby the cross section of a portion of the forging stock is increased above its original size.

GRAIN FLOW. Fiber-like lines appearing on polished and etched sections of forgings which 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: board hammers and air-lift hammers.

GUTTER. A slight depression machined around the periphery of an impression in the die which allows space for the excess metal (flash during forging).

HAMMER FORGING. Shaping of metal by impact between dies in one of several types of equipment known as forging hammers. (See AIR-LIFT HAMMER, BOARD HAMMER, COUNTERBLOW FORGING EQUIPMENT, STEAM HAMMER.)

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

HEAT OF METAL. The quantity of material manufactured from one melt at the metal producer’s facility. Metal from a single heat is extremely uniform in chemical analysis.

HIGH-ENERGY-RATE FORGING (HIGH VELOCITY OR HIGH SPEED FORGING). The process of producing forgings on equipment capable of extremely high ram velocities resulting from the sudden release of a compressed gas against a free piston.

HOT STAMP. Impressing markings in a forging while the forging is in the heated, plastic condition.

HOT TRIM. Removing flash or excess metal from the forging in a trimming press while the forging is in the heated state.

HOT WORKING. The mechanical working of metal at a temperature above its recrystallization point — a temperature high enough to prevent strain hardening.

HYDRAULIC HAMMER. A gravity drop forging hammer which uses hydraulic pressure to lift the hammer between strokes.

IMPRESSION. A cavity machined into a forging die to produce a desired configuration in the workpiece during forging.

IMPRESSION DIE FORGING. A forging that is formed to the required shape and size by machined impressions in specially prepared dies which exert 3-dimensional control on the workpiece.

INSERT. A component which is removable from a die. An insert can be used to fill a cavity or to replace a portion of the die with a material which gives better service.

IRONING. (l) A press operation used to obtain a more exact alignment of the various parts of a forging, or to obtain a better surface condition. (2) An operation to increase the length of a tube by reduction of wall thickness and outside diameter. (See COINING) (SWAGING.)

ISOTHERMAL FORGING. A forging operation performed on a workpiece during which the temperature remains constant and uniform. Generally used when aluminum, nickel, or titanium is being forged.

LAP. A surface irregularity appearing as a seam, caused by the folding over of hot metal, fins, or sharp comers and by subsequent rolling or forging (but not welding) of these into the surface.

LOCKS. Changes in the plane of the mating faces of the dies. Locks aid in holding die alignment during forging by counteracting lateral thrust which is present to an extent dependent on the shape of the workpiece.


MANIPULATOR. A mechanical device for handling an ingot or billet during forging.

MATCH. 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.

MATCHED EDGES (MATCH LINES). Two edges of the die face which are machined exactly at 90° to each other, and from which all dimensions are taken in laying out the die impress and aligning the dies in the forging equipment.

MATCHING DRAFT. When unsymmetrical ribs and side walls meet at the parting line it is standard practice to provide greater draft on the shallower die to make the forging’s surface meet at the parting line. This is called matching draft.

MECHANICAL WORKING. Subjecting metal to pressure, exerted by rolls, hammers, or presses, in order to change the metal’s shape or physical properties.

NATURAL DRAFT. After the parting line has been established and a machining allowance is provided, a shape may have what is called natural draft.

NO-DRAFT FORGING. A forging 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 closer control of grain flow and retention of surface material in the final component.

OPEN-DIE FORGING. Hot mechanical forming of metals between flat or shaped dies where metal flow is not completely restricted. Also known as hand or smith forging.

PARTING LINE. The line along the surface of a forging where the dies meet, or the line along the corresponding edge of the die impression.

PARTING PLANE. The plane which includes the fundamental parting line of the dies; the dividing plane between dies.

PLATTER. The entire workpiece upon which the forging equipment performs work, including the flash, sprue, tonghold, and as many forgings as are made at one time.

PRESS FORGING. The shaping of metal between dies by mechanical or hydraulic pressure. Usually this is accomplished with a single workstroke of the press for each die station.

PROOF. Any reproduction of a die impression in any material, frequently a lead or plaster cast.

PUNCH. (l) The movable die in a trimming press or forging machine. (2) A tool used in punching holes in metal.

PUSHER FURNACE. A continuous type furnace where stock to be heated is charged at one end, carried through one or more heating zones, and discharged at the opposite end.

QUANTITY TOLERANCE. Allowable variation of quantity to be shipped on a purchase order. This tolerance is properly agreed to by forging producer and purchaser when order is placed.

RAM. The moving part of a forging hammer, forging machine, or press, to which one of the tools is fastened.                

RESTRIKING. Striking a trimmed forging in order to align or size its several components or sections. The operation can be performed hot or cold.

RING ROLLING. The process of shaping weldless rings from pierced discs or thick-walled, ring-shaped blanks, between rolls which control wall thickness, ring diameter, height, and contour.

ROLLER (ROLLING IMPRESSION). The portion of a forging die where cross sections are altered by hammering or pressing while the workpiece is being rotated.

ROLL FORGING. The process of shaping stock between power driven rolls bearing contoured dies. The workpiece is introduced from the delivery side of the rolls, and is reinserted for each succeeding pass. Usually used for pre-forming, roll forging is often employed to reduce thickness and increase length of stock.               

ROTARY FURNACE. A circular furnace constructed so that the hearth and workpieces rotate around the furnace’s axis during heating.

SADDLING (MANDREL FORGING). The process of rolling and forging a pierced disc of stock over a mandrel in order to produce a weldless ring.

SCALE. The oxide film that is formed on forgings, or other heated metal, by chemical action of the surface metal with the oxygen in the air.

SCALE PIT. A surface depression formed on the forging operation.

SEAM. A crack or inclusion on the surface of forging stock which may carry through forging and appear on the finished product.

SEMI-FINISHER (SEMI-FINISHING IMPRESSION). An impression in the forging die which only approximates the finish dimensions of the forging. Semi-finishers are often used to extend die life of the finishing impression, to assure proper control of grain flow during forging, and to assist in obtaining desired tolerances.

SHANK. The portion of the die or tool by which it is held in position in the forging unit.

SHOE. A holder used as a support for the stationary portions of trimming and forming dies; sometimes termed sow block.

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.

SHRINK SCALE. A measuring scale or rule, used in die layout, on which graduations are expanded to compensate for thermal contraction (shrinkage) of the forging during cooling.

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

SLUG. (l) Metal removed when punching a hole in a forging. Also termed “punch out’.’ (2) Forging stock for one workpiece cut to length. (See BLANK.)

SNAG GRINDING (SNAGGING). The process of removing portions of forgings not desired in the finished product, by grinding.

SOW BLOCK. Metal die holder employed in a forging hammer to protect the hammer anvil from shock and wear. Also called anvil cap or shoe.

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.

SWAGE (SWEDGE). Operation of reducing or changing the cross sectional area by revolving the stock under rapid impact blows.

TONGHOLD. The portion of the stock by which the operator grips the stock with tongs during forging.

TRIMMING. The process of removing flash or excess metal from a forging.

UPSETTING. Working metal in such a manner that the cross-sectional area of a portion of all of the stock is increased.

VENT. A small hole in a punch or die which permits the passage of air or gas. Venting prevents trapping air that interferes with forming of a vacuum, which interferes with stripping.


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