Z94.12.4 Metal Forming

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SCALING. Surface oxidation caused on metals by heating in air or in other oxidizing atmospheres.

SEAM. (1) The fold or ridge formed at the juncture of two pieces of sheet material. (2) An extended, narrow defect on the metal surface, resulting from a blow hole or inclusion which has been stretched during processing.

SEAMING. The process of joining two edges of sheet material to produce a seam. Machines that do this work are referred to as seaming machines or seamers.

SEIZING. Welding of metal from the workpiece to a die member under the combined action of pressure and sliding friction.

SHAVING. Trimming heavy-gauge blanks to remove uneven sheared edges.

SHEAR. (1) A type of cutting operation in which the metal object (sheet, wire, rod, or such) is cut by means of a moving blade and fixed edge or by a pair of moving blades that may be either flat or curved. (2) A type of deformation in which parallel planes in metal crystals slide so as to retain their parallel relation to one another, resulting in block movement.

SHEAR STRENGTH. The maximum stress that a metal can withstand before fracturing when the load is applied parallel to the plane of stress; contrasted with tensile or compressive force, which is applied perpendicular to the plane of stress. Under shear stress, adjacent planes of metal tend to slide over each other.

SHEET. Any material or piece of uniform thickness and of considerable length and breadth as compared to its thickness is called a sheet or plate. In reference to metal, such pieces under 1/4" thick are called sheets and those 1/4" thick and over are called plates. Occasionally, the limiting thickness for steel to be designated as "sheet steel'' is number ten Manufacturer's Standard Gage for sheet steel, which is 0.1345" (3.42 mm) thick.

SHUT HEIGHT. The distance from the top of the bed to the bottom of the slide of a vertical press, with stroke down and adjustment up. On moving bolster presses, the shutheight is measured from the top of the bolster (when the bolster is integral with the carriage) or the top of the carriage (when the bolster is separate).

SINGLE-ACTING HAMMER. A forging hammer in which the head is raised by a steam cylinder and piston and the blow is delivered by the free fall of the head.

SINGLE-ACTION PRESS. A forming press that operates with a single function, such as moving a punch into a die with no simultaneous action or holding down the blank or ejecting the formed work.

SINGLE-STROKE MECHANISM. A mechanical arrangement used on a full-revolution clutch to limit the travel of the slide to one complete stroke at each engagement of the clutch.

SIZING. A final pressing of a sintered compact to secure the desired size.

SKELP. A plate of steel or wrought iron from which pipe or tubing is made by rolling the skelp into shape longitudinally and welding the edges together.

SLIDE. The main reciprocating member of a press, guided in the press frame, to which the punch or upper die is fastened. Sometimes called the ram. The inner slide of a double-action press is called the plunger or punch-holder slide; the outer slide of a double-action press is called the blankholder slide; the third slide of a trip-action press is called the lower slide; and the slide of a hydraulic press is often called the platen.

SLITTING. Cutting or shearing along single lines either to cut strips from a sheet or to cut along lines of a given length or contour in a sheet or workpiece.

SLUG. Small pieces of material (usually scrap) which are produced in punching holes in sheet material.

SPINNING. The procedure of making sheet metal disks into hollow shapes by pressing a tool against a rotating form (spinning chuck).

SPRINGBACK. An indicator of elastic stresses, frequently measured as the increase in diameter of a curved strip after removing it from the mandrel about which it was held. The measurement is employed as an indicator of the extent of recovery or relief of residual stresses that has been achieved by the transformation of elastic strain to plastic strain during heating or stress relieving.

STAMP. (1) The act of impressing by pressure (sink in) lettering or designs in the surface of sheet material or parts. (2) The act of forming or drawing by pressworking. (3) The general term used to denote all pressworking.

STAMPING. A process used to cut lines of letters, figures and decorations on smooth metal surface. The impact of a punch with comparatively sharp projecting outlines impresses the characters into the surface of the metal.

STEEL RULE DIE. A metal cutting die employing a thin strip of steel (printer's rule) formed to the outline of a part and a thin steel punch mounted to a suitable die set.

STOP. A device for positioning stock or dies in a die.

STOP CONTROL. An operator control designed to immediately deactivate the clutch control and activate the brake to stop slide motion. (Explanation: The term Emergency Stop is sometimes used to refer to this control, even though its use is most commonly not on an emergency basis. Sometimes, the control causes motor shutdown, in addition to clutch disengagement. Also, quite commonly, a top stop control is used to stop continuous stroking at top of stroke or at another predetermined point in stroke. A top stop control action is delayed, after actuation of the operating means, to cause stopping at the predetermined point in stroke.)

STRAIN. A measure of the change in size or shape of a body, due to force, in reference to its original size or shape. Tensile or compressive strain is the change, due to force, per unit of length in an original linear dimension, in the direction of the force.

STRAIN HARDENING. An increase in hardness and strength caused by plastic deformation at temperatures lower than the recrystallization range.

STRESS. The intensity of force within a body which resists a change in shape. It is measured in pounds per square inch or pascals. Stress is normally calculated on the basis of the original cross-sectional dimensions. The three kinds of stresses are tensile, compressive, and shearing.

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

STRETCH FORMING. A process of forming panels and cowls of large curvature by stretching sheet over a form of the desired shape. This method is more rapid than hammering and beating.

STRETCHING. Stretching is defined as an extension of the surface of the sheet in all directions. In stretching, the flange of the flat blank is securely clamped. Deformation is restricted to the area initially within the die. The stretching limit is the onset of metal failure.

STRIPPER. A plate designed to surround the piercing punch steels or the piercing punches. Its purpose, quite literally, is to strip the sheet metal stock from the punching members during the withdrawal cycle. Strippers are also employed for the purpose of guiding small precision punches in close toleration dies, to guide scrap away from dies, and to assist in the cutting action. Strippers are made in two types, fixed and movable.

STROKE. The distance between the terminal points of the reciprocating motion of a press slide.

STROKES PER MINUTE (SPM). The specified continuous running speed of a press. It is not the number of permissible single trippings of a press and consequently does not measure the possible production per minute, except when a press is run continuously. The number of single trippings per minute varies with different types and makes of clutches as well as with the dexterity of the operator.

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