Feather (Fin)

The thin projection formed on a forging by trimming or when the metal under pressure is forced into hairline cracks or die interfaces.


A characteristic of wrought metal, including forgings, indicated by a fibrous or woody structure of a polished and etched section, and indicating directional properties. Fiber is chiefly due to the extension of the constituents of the metal synonymous with flow lines and grain flow in the direction of working.


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


The thin projection formed on a forging by trimming or when metal is forced under pressure into hairline cracks or die interfaces.


(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 machined off the surface of a forging to produce the finish machine component.

Finish all over (F.A.O.)

A designation 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.

Finish trim

Flash removal from a forging; usually performed by trimming, but sometimes by band sawing or similar techniques.


Randomly oriented internal thermal cracks (“shatter cracks”) in steels resulting from critical combinations of stress and hydrogen content. In a fracture surface, flakes appear as bright silvery areas; on an etched surface they appear as short discontinuous cracks.

Flame straightening

The correction of distortion in metal structures by localized heating with a gas flame.


A projecting rim or edge of a part; usually narrow and of approximately constant width for stiffening or fastening. See Rib.


Metal in excess of that required to fill completely the blocking or finishing forging impression of a set of 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. Because it cools faster than the body of the component during forging, flash can serve to restrict metal flow at the line where dies meet, thus ensuring complete filling of the impression. See also Closed-Die Forging.

Flash, internal

That portion of the flash located entirely within a forging or enclosed by two or more forgings within a cluster of forgings.

Floating die

(1) A die mounted in a die holder or a punch mounted in its holder such that a slight amount of motion compensates for tolerance in the die parts, the work, or the press. (2) A die mounted on heavy springs to allow vertical motion in some trimming, shearing, and forming operations.

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 also Grain Flow.

Fluorescent magnetic particle inspection

Inspection with either dry magnetic particles or those in a liquid suspension, the particles being coated with a fluorescent substance to increase the visibility of the indications.


A forging defect caused by folding the metal back on its own surface during its flow in the die cavity. See Lap.


The relative ability of material to deform without fracturing, rupturing, or developing flaws. Also describes the resistance to flow from deformation. See also Formability.

Forging dies

Forms for making forgings; they generally consist of a top and bottom die. The simplest will form a completed forging in a single impression; the most complex, consisting 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 rest of the impression in the other block.

Forging quality

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

Forging reduction

Ratio of the cross-sectional areas before and after forging; sometimes refers to percentage reduction in thickness.

Forging roll

Also known as reducer roll. A machine situated alongside the forging machine for pre-forming. The operation is carried out by passing the work-piece between contra-rotating shafts, which carry appropriately shaped dies.

Form rolling

Hot rolling to produce bars having contoured cross sections; not to be confused with the roll forming of sheet metal or with roll forging.

Fracture toughness

The resistance of a given material to catastrophic failure in the presence of an existing sharp crack.


Guides or shoes that ensure the proper parallelism, squareness, and sliding fit between press components such as the ram and the frame. They are usually adjustable to compensate for wear and to establish operating clearance.


An individual crystal in a polycrystalline metal or alloy.

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 improves the mechanical properties of forgings.

Grain growth

An increase in the size of the grains of a metal with a proportional reduction of the number of grains.

Grain separation

In forging aluminum, rapid metal flow sometimes causes a separation or rupture of grain. Metal flow is affected by lubricant, die and metal temperature, part shape, alloy, and hammer operator technique; consequently, any one or combination of these factors can cause grain separation. The irregular crevices are seldom more than a few thousandths of an inch deep and can be removed by grinding or polishing.

Grain size

An expression that rates the number of grains per unit area of cross section as determined by metallographic examination.

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.

Hammer forging

The mechanical forming of metal by means of a hammer. The action of the hammer is that of an instantaneous application of pressure in the form of a sudden blow.

Hand forging

(See also Open Die Forging) (1) 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. (2) 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.

Hand straightening

A straightening operation performed on a surface plate to bring a forging within the straightness tolerance. Frequently, a bottom die from a set of finish dies is used instead of a surface plate. Hand tools used include mallets, sledges, blocks, jacks, and oil gear presses in addition to regular inspection tools.

Handling marks

Nicks and gouges formed on forgings if improperly handled; most prevalent for forgings in the as-forged condition prior to heat treatment.


The upsetting of wire, rod, or bar stock in dies to form parts that usually contain portions that are greater in cross-sectional area than the original wire, rod, or bar.


A term used to identify the material produced from a single melting operation. Different heats of the same material can vary in chemical composition within prescribed limits. Stock from a single heat will have a consistent analysis and more uniform properties. Also known in the U.K. as “Cast”.

Heat treatment

A sequence of controlled heating and cooling operations applied to a solid metal to impart desired properties.

Hot upset forging

A bulk forming process for enlarging and reshaping some of the cross-sectional area of a bar, tube, or other product form of uniform (usually round) section. It is accomplished by holding the heated forging stock between grooved dies and applying pressure to the end of the stock, in the direction of its axis, by the use of a heading tool, which spreads (upsets) the end by metal displacement. Also called hot heading or hot upsetting. See also Heading and Upsetting.

Impact test

Test to determine the energy absorbed in fracturing a notched test bar at high velocity. See also Charpy Test, Izod Test.


Particles of nonmetallic compounds of metals and impurity elements that are present in ingots and are carried over in wrought products. The shape and distribution of inclusions are changed by plastic deformation and contribute to directionality in metals.


A term used to describe the remnants of dendritic structure which may occasionally be found in forgings.


A piece of steel that is tightly fixed in a die. The insert may be used to fill a cavity, to replace a portion of the die with a grade of steel that is better suited for service at that point, or to function as a small die with the impression fastened to a master die.

Izod impact test

A pendulum-type impact test in which the specimen is supported at one end as a cantilever beam and the energy required to break off the free end by the impact of a falling pendulum is used as a measure of impact strength. See Charpy Impact Test.


A mechanism for releasing workpieces from a die.


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

Layout sample

A plaster, lead, or forged alloy sample taken from new dies to verify accuracy by layout and precise measurement. See also Cast.


In forging, a condition in which the flash line is not entirely in one plane. Where two or more plane changes occur, it is called compound lock. Where a lock is placed in the die to compensate for die shift caused by a steep lock, it is called a counterlock.


A material applied to dies, molds, plungers, or workpieces that promotes the flow of metal, reduces friction and wear, and aids in the release of the finished part.