pad

“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.” (Eary, D. F., & Reed, E. A., 1958, p. 306-308).

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.

parting

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.

pedestal

See punch riser.

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.  Figure P1 illustrates the concept of percent strain safety.

percent total elongation

The amount of extension a material can withstand prior to fracture in a tensile test. Figure P2 shows the percent total elongation on a stress/strain curve of a tensile test.

percent uniform elongation

The amount of extension a material can withstand prior to necking in a tensile test. Figure P2 shows the percent uniform elongation on a stress/strain curve of a tensile test.

perforating

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.

perforator

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

permanent set

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

pick-&-place

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

pickoff

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

pickup

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

pick-up

See scoring.

pierce block

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

pierce button

See button.

pierce punch

See perforator and punch.

piercing

The general term for cutting (shearing or punching) openings, such as holes and slots, in sheet material, plate, or parts.  This operation is similar to blanking; the difference is that the slug or piece produced by piercing is scrap, while the blank produced by blanking is the useful part.

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.

pilot

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

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.

piobert lines

See Luders lines.

pitch

See progression.

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.

planar anisotropy

(See Figure P4)  

plane-strain

A deformation pattern which occurs when the minor strain is zero.  This is the most critical strain state of a material and is typically the lowest point on a forming limit curve as shown in Figure P3.

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. See Figure P4 for a schematic of plastic anisotropy in sheet material

plastic deformation

The permanent (inelastic) distortion of metals under applied stresses that strain the material beyond its elastic limit.  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.  Sometimes called shooting plastic.

plastic working

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

plasticity

The ability of a metal to undergo permanent deformation without rupture.

plasticity

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

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.

plunger

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.

pogo stick

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

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. (See Figure P5)

polishing bob or cone

See sanding bob.

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.

preheating

A general term used to describe heating applied as a preliminary to some further thermal or mechanical treatment.

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. (See Figure P6)

pre-hem face geometry

Angle of the pre-hem steel measured relative to the mating flange area. (See Figure P7)

pre-hem flange angle

Angle measured from the mating flange area to the pre-hemmed flange. (See Figure P8)

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 90⁰ flange to approximately a 45⁰ flange so the hem steel can finish hemming the flange.  Also called angle steel, starting steel, or starting ring.

press

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 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 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 or hydraulic press.

press hemmer

Ballscrew driven press hemmer. (See Figure P9)

press load

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

press ram

See press slide.

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.

pressure pad read through

It occurs in rare cases where the inner panel is held using excessive force on a pressure pad. (See Figure P10)

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.

pre-strain

It is a mathematical value in the generalized (Swift’s or Krupkowski’s) power law. (See Figure P11)

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.

profiling

Machining or grinding the outline of die members.

progression

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.

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.

proof

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

(1) The stress that will cause a specified small permanent set in a material. (2) 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.

puckering

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

punch

(1) 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).

(2) 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.

(3) The act of piercing or punching a hole.  Also referred to as punching.

punch line

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

punch or punch steel

“The male steel is referred to as the punch steel” (Eary, D. F., & Reed, E. A., 1958, p. 292).

punching

The die shearing of a closed contour in which the sheared out sheet metal part is scrap.

punch radii

• (1) punch corner radius  (2) punch nose radius.  (See Figure P12).

punch riser

(1) A block of steel or welded construction to which punch steels or punch retainers are mounted.  Also called stool, pedestal, or riser. (2) 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.