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Home > Metal Forming and Welding Glossary > P

Metal forming and welding glossary - P

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The pad is a spring or air operated plate used in forming dies. The pad is used to grip the sheet metal against the punch or die steel. The functions of the pad are as follows: (1) To hold the sheet metal in proper location during forming. (2) To hold the sheet metal flat. During forming, the areas not being formed tend to bow or otherwise distort. Therefore, these areas are held in their original contour by pad pressure. (3) The pad acts as a hold-down.

Pad drivers

Blocks used to compress the pad ahead of the stock while blanking or trimming. Also to equalize pressure on the pad to eliminate the cocking of the pad.

Pad retainer pins

The pins that go in the side of a stripper plate or pad to retain it for the designed range of travel.

Pad window

See window.

Pancake die

Simple push through die for blanking or piercing.


Defining a feature's size by establishing a geometric relationship between it and other features, instead of defining it with a dimension.


A specific kind of cutting operation in which complete severance of the stock strip is achieved by punching out a piece of stock material (scrap) from between the piece parts.


The weld metal deposited in one general progression along the axis of the weld.

Pattern direction

Orientation of features or surface patterns on sheets and coils.

Patterned or embossed sheet

A sheet product on which a raised or indented pattern has been impressed on either one or both surfaces by the use of rolls.


A block of steel or welded construction to which punch steels or punch retainers are mounted. Also called a punch rise or riser.

Pem fastener

Self-clinching inserted fastener (nut, stud, standoff, pin. blind stand off, etc.) made by Penn Engineering & Manufacturing Corp.


Depth of a cutting operation before breakout occurs. In welding, the depth of material through which fusion occurs.

Percent strain safety

This is a measure of how close a strain state is to failure with regards to a forming limit diagram. Percent strain safety is calculated by dividing the difference between the major strain to failure and the actual major strain by the major strain to failure. Thus, a zero percent strain safety indicates material failure.

Percent total elongation

The amount of extension a material can withstand prior to fracture in a tensile test.

Percent uniform elongation

The amount of extension a material can withstand prior to necking in a tensile test.

Percussive welding

A resistance welding process in which a discharge of electrical energy and the application of high pressure occurs simultaneously, or with the electrical discharge occurring slightly before the application of pressure.


The punching of many holes, usually identical and arranged in a regular pattern, in a sheet, workplace blank, or previously formed part. The holes are usually round, but may be any shape. The operation is also called multiple punching. See also piercing.


A specific name for a punch that falls in the cutting punch category. See punch. Also called a pierce punch.


The extreme outer edge of part or drawing.

Permanent set

The deformation or strain remaining in a previously stressed body after release of the load.


Dimensional relationship of a part or datum located at right angles (90°) to a given feature.

Phosphor bronze

Copper base alloy with 3.5 10 % of tin to which phosphorus has been added in a molten state in varying amounts of less than 1% for deoxidizing and strengthening purposes.


An electrically or mechanically driven mechanism, attached to and, controlled by a press, for loading and removing a part from a die.

Pickled and oiled

Hot rolled steel with the scale removed through immersion in acid and a follow up rinsing and oiling process for oxidation protection. Also referred to as P&O and HRPO.


An automatic device for removing the finished part from a die after it has been stripped or released from the die.


See scoring.


Small particles of oxidized metal adhering to the surface of a mill product.



To cut, shear, or punch anopening in sheet metal, strip, plate or parts such as a slot or a hole.

Pierce block

An individual die part that contains one or more pierce holes or die buttons.

Pierce button

A small cylindrical die steel with an opening larger than the punch point size, generally by a percentage of the thickness of the material being pierced. It is also called a button or a die button.

Pierce punch

A specific name for a punch that falls in the cutting punch category. It is also referred to as a perforator.


The general term for cutting (shearing or punching) openings, such as holes and slots, in sheet material, plate, or parts.

Piercing die

A die which cuts out a slug, which is usually scrap, in sheet or plate material.

Piggy back cam

A cam which is actually two cams. The bottom cam is normally a dwell cam and the top cam is normally a straight cam.


A pin or projection provided for locating work in a die from a previously punched hole. Also called locating pin or pilot pin.

Pinch pass

A term applied when, after annealing, sheet or strip is lightly rolled with the object of preventing stretcher lines or kinks on subsequent cold working.

Pinch trim

Trimming excess material from a drawn part at the bottom of the stroke. Leaves drawn shell without an inside burr, but with an outside burr and a thinned edge.

Pinch trimming

Trimming the edge of a part by punching or pushing the flange or lip of the part over the cutting edge of a draw or stationary punch.


Long fern like creases usually diagonal to the direction of rolling.


A coating defect consisting of the randomly spaced small round holes (as a straight pin would make in the cured film) which quite often occur in large numbers. The open area (pinhole) usually exposes bare substrate. Contaminated substrate or improperly dispersed lubricant or additive may cause pinholes. Pinholes are typically caused by laminations, inclusions, scratches or gouges.

Piobert lines

Elongated surface markings or depressions caused by localized plastic deformation that results from discontinuous (in homogeneous) yielding. Also known as Luders lines, Hartmann lines, or stretcher strains.


See progression.

Pitch (for welding)

The center to center spacing of welds.

Pitch notch

A notch usually cut on one side of a stock strip in a progressive die to control stock width and progression of the stock. Also called French cut and French notch.


A coating defect consisting of randomly spaced small depressions in the cured film. Pitting is similar to pinholing, except that pits do not expose the bare substrate.

Plasma Arc Welding (PAW)

Specialized process utilizing a non-consumable electrode ionizing an inert gas and increasing temperature to melt the material being welded.


Plastic anisotropy

This is the concept that a material has a preferred strain direction. In sheet material, plastic anisotropy is measured as the ratio of width strain to thickness strain. This value is called the r-value and measures the tendency of the sheet to thin under deformation. It also is an indicator of the directional differences in a rolled material like sheet.

Plastic deformation

Permanent deformation occurring in forming of metal after elastic limits have been exceeded under the action of applied stresses. The ability of metals to flow in a plastic manner without fracture is the fundamental basis for all metalforming processes.

Plastic flow

The phenomenon that takes place when metals or other substances are stretched or compressed permanently without rupture.

Plastic hit

A method of determining the cutting edge of a steel from the mating steel by assembling the die so the trim steels are just short of entering. Then applying epoxy plastic to the top of the steel and against the mating steel which has a parting agent on it and allowing it to harden before disassembling. This is sometimes called shooting plastic.

Plastic working

The processing of a substance by causing a permanent change in its shape without rupture. See plastic deformation.


The property of a substance that permits it to undergo a permanent change in shape without rupture. See plastic deformation.

Plastic-strain ratio (revalue)

The ratio of the true width strain to the true thickness strain in a sheet tensile test. A formability parameter that relates to drawing, it is also known as the anisotropy factor. A high revalue indicates a material with good drawing properties.


A flat-rolled metal product of some minimum thickness and width arbitrarily dependent on the type of metal. Sheet steel thicker than 7 gauge 0.179 in. (4.55 mm) or sheet aluminum thicker than 3/16 in. (4.76 mm).


See plate.


A thin coating of metal laid on another metal.


See press slide.


Pneumatic spring

A one way air cylinder having a large hollow shaft and a check valve on the air supply at the cylinder which eliminates the need for a surge tank.


If energy transfer is in the form of compressed airflow then it is known as pneumatics. In industry compressed air is generated by using a machine called a compressor, which draws in normal air, squeezes it to increase its pressure and then passes it through a moisture separator and stores it in the reservoir for later use in the factory.

Pogo stick

An adjustable rod which holds an indicator for checking the level of a press ram.


A piece of geometry at an exact location. Polishing Abrasive process in which the surface created takes on a bright reflective finish, scratch free to the unaided eye.

Point of origin

A point from which other dimensions are taken. See also construction hole.

Poisson's ratio

The ratio of the second principal strain 2 in the transverse direction to the principal strain 1 in the axial direction when a uniaxial tension or compression is applied.

Polishing bob or cone

See sanding bob.


The presence of gas pockets or inclusions in welding.

Positions of welding

All welding is accomplished in one of four positions - flat, horizontal, overhead, and vertical. The limiting angles of the various positions depend somewhat as to whether the weld is a fillet or groove weld.


To paint a manufactured part after at it has been formed.

Postcut roll forming

A process whereby the raw material is fed into the roll forming mill in coil form with the formed part cut to length. This is the most common roll forming material feeding process. See precut roll forming.

Powder coating

100% solids coating applied as a dry powder and subsequently converted into a film with heal.

Power spinning

The art of forming metal over a mold in one pass using hand or hydraulic pressure.

Precision lead screw

See lead screw.

Precut roll forming

A process whereby the raw material is cut to length prior to entering the roll forming mill and fed into the mill as blanks. It is primarily used for low-volume applications. See postcut roll forming.

Prefinished material

Stock which has been painted or plated prior to fabrication or stamping.

Prenotch/prepunch press

A device used to stamp a hole or notch pattern in incoming material on a roll forming line prior to roll forming.

Preformed part

A partially formed part which will be subjected to one or more subsequent operations. Usually done after a blank die and prior to going into a draw die.

Pre-hem contact path

Angle between a line (formed by a point on the pre-hem steel at first contact with flange to the same point at end of pre-hem) and the mating surface.

Pre-hem face geometry

Angle of the pre-hem steel measured relative to the mating flange area.

Pre-hem flange angle

Angle measured from the mating flange area to the pre-hemmed flange.

Pre-hem force

Maximum force required to bend flange to pre-hem position.

Pre-hem springback

Elastic recovery that follows plastic deformation when the pre-hem load is removed.

Pre-hem steel

The steel in a hem die that bends the 90° flange to approximately a 45° flange so the hem steel can finish hemming the flange. Also called angle steel, starting steel, or starting ring.



A machine having a stationary bed or anvil and a slide (ram or hammer) which has a controlled reciprocating motion toward and away from the bed surface and at right angle to it. The slide is guided in the frame of the machine to give a definite path of motion.

Press attachment

A bed mounted device on a slide forming machine used for punching, piercing and other press operations.

Press bed

The stationary and usually horizontal part of a press that serves as a table to which a bolster plate or lower die assembly is mounted.

Press brake

An open-frame single-action press used to bend, blank, corrugate, curl, notch, perforate, pierce, or punch sheet metal or plate.

Press brake machine - illustration

Press capacity

The rated force a press is designed to exert at a predetermined distance above the bottom of the stroke of the slide.

Press forming

Any sheet metal forming operation performed with tooling by means of a mechanical press or hydraulic press.

Press hemmer

Ballscrew driven press hemmer.

Press load

The amount of force exerted in a given forging or forming operation.

Press ram

See press slide.

Press section

A device that is built into a slide forming machine used for punching, piercing and other press operations.

Press 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, press ram, slide, plunger, or platen. See slide.

Press tool (metal stamping die)

A piece of precision-made, mass production, tooling used to cut, bend and shape metal components from flat, strip, coil or sheet material. The components produced could range in size from car roof panels, door skins or bonnets, to small clockwork gears in mechanical watches and timepieces.

Pressure pad read through

It occurs in rare cases where the inner panel is held using excessive force on a pressure pad.

Pressure pin

A pin used in conjunction with a die cushion to transfer pressure from the cushion to the bottom of a die pad. Also called cushion pins, air pins, and transfer pins.

Pressure plate

A plate located beneath the bolster that acts against the resistance of a group of cylinders mounted to the pressure plate to provide uniform pressure throughout the press stroke when the press is symmetrically loaded.

Pressure welding

Any welding process or method in which pressure is used to complete the weld.

Prime coil

Any coil produced by the line that is not held for any out-of-spec or quality reasons.


Metal products, such as sheet and plate, of the highest quality and free from visible surface defects.


Procedure certification

A demonstration that welds made by a specific procedure can meet prescribed standards.

Process class

Each process is assigned a group of process classes. Primary processes take unshaped material (liquid metal, a powder or a solid ingot) and give it shape. Thus casting processes are primary, though they can be discrete or continuous. Secondary processes modify, refine or add features to an already-shaped body. As an example: fine machining is a secondary process, and it is one that can modify, refine and add features.


The object or material that has had an operation of the class type performed upon it.

Production jigs and fixtures

Precision-made mass production tooling used to safely and accurately position and hold components during a production line process, to allow follow-on operations such as machining, welding, painting, assembly and/or packaging to be undertaken on the component.

Production rate

Units: kg/hr (SI), lb/hr (Imperial); or m/min (SI), ft/min (Imperial). The production rate is the output-rate of the process. For batch processes, it is measured in number of units per hour, or in total mass per hour of product. For continuous processes, it is measured in total mass or length per hour. Automated processes have higher output rates than their manual counterparts.

Profile grinder

A machine used to grind contour on a steel. Can be used with mounted wheels or carburrs. Also called a diemaker's friend or helper.


Machining or grinding the outline of die members.

Programmable back gauges

Stops on metalforming machines which can be adjusted during and between cycles by computer numeric control. Progressive Tool-Die using multiple stations or operations to produce a variety of options that can incorporate piercing, forming, extruding and drawing, and is usually applied to high quantity production runs.


The precise linear travel of the stock strip at each press stroke and is equal to the interstation distance. Also called pitch, advance, or feed.

Progressive die

A die with two or more stations arranged in line for performing two or more operations on a part one operation usually being performed at each station. The parts are connected by a carrier strip until final parting or cutoff operation.

Progressive forming

Sequential forming at consecutive stations with a single die or separate dies.

Progressive tool

Die using multiple stations or operations to produce a variety of options. Can incorporate piercing, forming, extruding and drawing, and is usually applied to high quantity production runs.

Project number

Numbers used to identify special accounts to cover the cost of new work, engineering changes, and service work on past model dies. Numbers can be found in books in supervisor's office.

Projection welding

Using protrusions on one of the two parts to be resistance welded, creating a positive conductance path.


Any reproduction of a die impression in any material; often a lead or plaster cast. See also die proof.

Proof load

A predetermined load, generally some multiple of the service load, to which a specimen or structure is submitted before acceptance for use.

Proof stress

The stress that will cause a specified small permanent set in a material. A specified stress to be applied to a member or structure to indicate its ability to withstand service loads.

Proportional limit

The greatest stress a material is capable of developing without a deviation from straight-line proportionality between stress and strain. See also elastic limit and Hooke's law.


First part of a design which is made to test tolerance capability, tooling concepts and manufacturability.


A wavy condition in the walls of a deep drawn part.

Pull down

Area of material next to the penetrating edge of a piercing punch, or die edge of the blanking station, where the material yields, i.e. flows in the direction of the applied force, creating a rounded edge. Also known as roll-over.

Pulsation welding

A spot, projection, or seam welding process in which the welding current is interrupted one or more times without the release of pressure or change of location of electrodes.

Pulse mode

Intermittant surging of laser cutting power action.


The male part of a die-as distinguished from the female part, which is called the die. The punch is usually the upper member of the complete die assembly and is mounted on the slide or in a die set for alignment (except in the inverted die). In double-action draw dies, the punch is the inner portion of the upper die, which is mounted on the plunger (inner slide) and does the drawing. The act of piercing or punching a hole. Also referred to as punching. The punch is the movable part that forces the metal into the die in equipment for sheet drawing, blanking, coining, embossing and the like.

Punch direction

The direction from which a tool or punch enters the workpiece.

Punch line

The outline of the draw punch in the plan view of a blueprint

Punch press

Machine supplying compression force for reshaping materials.

Punch radii

The punch corner radius and/or the punch nose radius.

Punch riser

A block of steel or welded construction to which punch steels or punch retainers are mounted. Also called stool, pedestal, or riser. A cast spacer between the inner ram and the draw punch in a toggle draw die. Also called a riser.

Punch shoe

The upper section of a die set. Bushings and punch steels are usually mounted to this section.

Punch side

Opposite side from burr side for pierced features; side on which the punch enters the material. The punch side is the burr side for blanked outside contours.

Punch steel (or punch)

The male steel is commonly called the punch steel.


(1) Shearing holes in sheet metal with punch and die. (2) The die shearing of a closed contour in which the sheared out sheet metal part is scrap. (3) Forming metal components using a punch.

Punching process - illustration


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