Glossary of Forging Terms

7. A GLOSSARY OF FORGING TERMS Air-lift hammer — A type of gravity-drop ham- Backward extrusion — Forcing metal to flow in mer in which the ram is raised for each stroke by a direction opposite to the motion of a punch or an air cylinder. Because the length of stroke can die. be controlled, ram velocity and therefore the energy delivered to the workpiece can be varied. Bar — A section hot rolled from a billet to a form, See also Drop Hammer and Gravity Hammer. such as round, hexagonal, octagonal, square, or rectangular, with sharp or rounded corners or Aircraft quality — Denotes stock of sufficient edges, with a cross-sectional area of less than 16 quality to be forged into highly stressed parts for sq in. (A solid section that is long in relation to its aircraft or other critical applications. Such materi- cross-sectional dimensions, having a completely als are of extremely high quality, requiring closely symmetrical cross section and whose width or controlled, restrictive practices in their manufac- greatest distance between parallel faces is 3/8 in. ture in order that they may pass rigid require- or more). ments, such as magnetic particle inspection. Bar end — See End Loss. Alloy steel forging — One made from a steel containing additional alloying elements other than Barreling — Convexity of the surfaces of cylin- carbon (e.g., Ni, Cr, Mo) to enhance physical and drical or conical bodies, often produced uninten- mechanical properties and/or heat-treat re- tionally during upsetting or as a natural conse- sponse. quence during compression testing. See also Compression Test. AMS — Aeronautical Materials Specification Batch/batch-type furnace — A furnace for As forged — The condition of a forging as it heating materials where all loading and unload- comes out of the finisher cavity without any ing is done through a single door or slot. subsequent operations. Bend or twist (defect) — Distortion similar to ASTM (Specifications) — The American Society warpage, but resulting from different causes; for Testing and Materials. generally caused in the forging or trimming operations. When the distortion is along the Auxiliary operations — Additional processing length of the part, it is called “bend”; when across steps performed on forgings to obtain properties, the width, it is called “twist.” such as surface conditions or shapes, not obtained in the regular processing operation. Bender — A die impression, tool, or mechanical device designed to bend forging stock to conform Axial rolls — In ring rolling, vertically to the general configuration of die impressions displaceable, tapered rolls, mounted in a horizon- subsequently to be used. tally displaceable frame opposite from but on the same centerline as the main roll and rolling Bending — A preliminary forging operation to mandrel. The axial rolls control the ring height give the piece approximately the correct shape during the rolling process. for subsequent forming. Axisymmetric forging — A forging where metal Billet — A semifinished, cogged, hot-rolled, or flow, during deformation, is predominately in a continuous-cast metal product of uniform section, direction away from a common axis in a radial usually rectangular with radiused corners. Billets direction. are relatively larger than bars. See Bloom. 137 Bite — Amount of the die in contact with the preliminary operations; it also reduces die wear workpiece throughout one entire forging reduc- in the finishing impression. tion, e.g., heavy bite is three-quarter to full width of the die. Blocker-type forging — A forging that approxi- mates the general shape of the final part with Blank — Raw material or forging stock (also relatively generous finish allowance and radii. called a “slug” or “multiple”) from which a forging Such forgings are sometimes specified to reduce is made. die costs where only a small number of forgings are desired and the cost of machining each part Blast cleaning — A process for cleaning or to its final shape is not exorbitant. finishing metal objects by use of an air jet or centrifugal wheel that propels abrasive particles Bloom — A semifinished product of square, (grit, sand, or shot) against the surfaces of the rectangular, or even round cross section, hot workpiece at high velocity. rolled, or forged. For steel, the width of a bloom is not more than twice the thickness, and the Block — The forging operation in which metal is cross sectional area is usually not less than progressively formed to general desired shape about 36 sq. in. No invariable rule prevails for and contour by means of an impression die (used distinguishing between blooms and billets; the when only one block operation is scheduled). terms are frequently used interchangeably. Block and finish — The forging operation in Board hammer — A type of gravity drop hammer which the part to be forged is blocked and fin- where wood boards attached to the ram are ished in one heat through the use of a die having raised vertically by action of contrarotating rolls, both a block impression and a finish impression then released. Energy for forging is obtained by in the same die. This also covers the case where the mass and velocity of the freely falling ram two tools mounted in the same machine are and the attached upper die. See also Drop used, as in the case of aircraft pistons. Only one Hammer. heat is involved for both operations. Bolster plate — A plate to which dies can be Block, first and second — Blocking operation fastened; the assembly is secured to the top performed in a die having two blocking cavities in surface of a press bed. In press forging, such a the same die; the part being forged is succes- plate may also be attached to the ram. sively blocked in each impression all in one heat. As many as three blocker dies are sometimes Boss — A relatively short protrusion or projection needed for some forgings and up to three opera- on the surface of a forging, often cylindrical in tions are sometimes required in each die. shape. Block, first, second, and finish — The forging Breakdown — (1) An initial rolling or drawing operation in which the part to be forged is passed operation, or a series of such operations, for in progressive order through three tools mounted reducing an ingot or extruded shape to desired in one forging machine; only one heat is involved size before the finish reduction. (2) A preliminary for all three operations. press-forging operation. Blocker impression — The forging die impres- Brinell hardness — The hardness of a metal or sion which gives the forging its general shape, part, as represented by the number obtained but omits any details that might restrict the metal from the ratio between the load applied on and flow; corners are well rounded. The primary the spherical area of the impression made by a purpose of the blocker is to enable the forming of steel ball forced into the surface of the material shapes too complex to be finished after the tested. The Brinell Hardness Number (BHN) is 138 determined by measuring the diameter of the Chamfer — To break or remove sharp edges or impression using a low power microscope, then corners of forging stock by means of straight matching this diameter with the load on a stan- angle tool or grinding wheel. dard table. Charpy impact test — An impact test in which a Buckling — A bulge, bend, kink, or other wavy specially V-notched specimen is broken by the condition of the workpiece caused by compres- impact of a falling pendulum. The energy ab- sive stresses. See also Compressive Stress. sorbed in fracture is a measure of the impact strength or notch toughness of the sample. Burning — Permanently damaging a metal or alloy by heating so as to cause either incipient Check — Crack in a die impression, generally melting or intergranular oxidation. due to forging pressure and/or excessive die temperature. Die blocks too hard for the depth of Burr — A thin ridge or roughness left on forgings the die impression have a tendency to check or by cutting operation such as slitting, shearing, develop cracks in impression corners. trimming, blanking, or sawing. Chop — A die forging defect; metal sheared from Buster (rougher) — An impression employed in a vertical surface and spread by the die over an a die when considerable metal movement is adjoining horizontal surface. required and which precedes a blocker cavity and a finisher cavity. Also known as breakdown/ Chucking lug — A lug or boss to the forging so pancake, scalebreak, cheese. that “on center” machining and forming can be performed with one setting or chucking; this lug is Buster (preblocking impression) — A type of machined or cut away on the finished item. die impression sometimes used to combine preliminary forging operations such as edging Cleaning — The process of removing scale, and fullering with the blocking operation to elimi- oxides, or lubricant—acquired during heating for nate blows. forging or heat treating—from the surface of the forging. (See also Blasting, Pickling, Tumbling.) Carbon steel — Steel containing carbon up to about 1.2%, and only residual amounts of other Close-tolerance forging — One held to closer- elements except for those added for composition than-conventional dimensional tolerances so that control, with silicon usually limited to 0.60 % and little or no machining is required after forging. manganese to 1.65%. See also Precision Forging. Cassette — Also known as sub-bolster, die Closed die forging — The shaping of hot metal assembly, trim and pierce assembly. An assembly completely within the walls or cavities of two dies of top and bottom dies and/or tools of each that come together to enclose the workpiece on forming station assembled into one unit.

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