RESOURCE GUIDE

THE ULTIMATE GUIDE TO PLASTIC INJECTION MOLDING TERMINOLOGY

FIRST EDITION

1 The GreenLeaf Industries team is passionate about integrating Engineered Quality, Reliable Delivery and Cost Containment into every design and project. We are a family owned, made in America manufacturer that is committed to supporting our clients and the Plastic Injection Molding Industry. It is our pleasure to introduce our latest resource guide to help designers, engineers and purchasing professionals navigate the world of plastic injection molding.

A

ADDITIVE MANUFACTURING – This is actually the technical term for 3-D printing. It is the process of manufacturing a three-dimensional object by placing layer on top of layer based on a specific CAD model.

AGING – Refers to the change of a material with time under defined environmental conditions, leading to either improvement, or the deterioration of certain properties.

ALLOY – A composite material made by blending polymers (or copolymers) with other polymers or elastomers under predetermined conditions.

ANGLE PINS – Pins that are placed at an angle and fit freely into a slide. Because the pins are at an angle, a cam action is created as the mold opens, and this moves the slide out of the way prior to part ejection. Angle pins may be called “horn pins.”

ANNEALING – The process of heating a molded plastic article to a predetermined temperature and slowly cooling it to relieve stresses caused by the manufacturing process. This secondary process is occasionally required for injection molded parts.

ANTISTATIC AGENT – An agent added to the molding material (or applied on the surface of the molded object) to make it less conductive, whereby hindering the fixation of dust.

AUTOMATIC MOLDING – Repeatedly going through the entire injection molding cycle, including the ejection process, without human assistance. B

BACK TAPER – A reverse draft used in a mold to prevent molded articles from drawing freely.

BACKING PLATE – A plate used in mold construction, as a support for the cavity blocks, guide pins, bushings, etc.

BLISTER – A raised area on the surface of a molded part that is caused by the pressure of gases inside it on its incompletely hardened surface.

BLUSH – Is simply a clouded discoloration of plastic in areas that come under high stress. When located at the gate (a high stress location) it is called “gate blush.”

2 BOSS – A projection on a plastic part designed to add strength, facilitate alignment during assembly, or provide strength in an area where fasteners are installed.

BUBBLE – An internal pocket (void) of air or other gas trapped within a space of plastic due to poor part design, poor mold design, or poor processing.

BURN – When the air temperature inside the mold exceeds the flash point of the plastic, a “burn mark” is made. If something is “burned” in molding, it shows evidence of thermal decomposition through some discoloration, distortion and localized destruction of the surface of the plastic. C

CARBON BLACK – Is a black pigment produced by the incomplete burning of natural gas or oil. It is widely used as filler… particularly in the rubber industry. Because it possesses useful ultraviolet protective properties, it is also used for injection molding compounds where the item is intended for outside weathering applications.

CASE HARDEN – It is a term used when hardening the surface of a piece of steel to a relatively shallow depth.

CAST – To form a “plastic” object by pouring a fluid monomer-polymer solution into an open mold where it finishes polymerizing.

CAVITY – A depression in a mold, which usually forms the outer surface of the molded part. Depending on the number of such depressions, molds can be designated as single cavity or multi- cavity.

CENTER GATED MOLD – An injection mold wherein the cavity is filled with molding material through a “sprue”, or gate, directly into the center of the part.

CHALKING – This term represents a dry, chalk-like appearance or deposit on the surface of a plastic. It is sometimes known as a “haze”

CHROME PLATING – An electrolytic process that deposits a hard film of chromium metal onto working surfaces of other metals in the event that resistance to corrosion, abrasion or erosion is required.

CLAMPING PLATE – A plate fitted to a mold and then used to fasten the mold to a molding machine.

CLAMPING FORCE – In injection molding, it is the pressure that is applied to the mold to keep it closed while molten plastic is injected at very high pressures.

COLD SLUG – This is what we call the first material to enter an injection mold. It gets its name from the fact that when it passes through the sprue orifice, it is cooled below the effective molding temperature.

COLD SLUG WELL – It is the space directly opposite of the sprue opening, inside an injection mold,

3 to trap the cold slug.

COMPRESSIVE STRENGTH – The crushing load (at failure) divided by the original sectional area of the specimen.

CONDUCTIVE PLASTICS – Materials that allow a current or charge to travel through it. Conductive plastics are hybrid polymers that are electrically conductive or static dissipative. These plastics are engineered, using additives such as copper, silver, aluminum, carbon black and carbon fibers, to have conductivity characteristics.

CONTINUOUS SERVICE TEMPERATURE – The maximum temperature above which mechanical and electrical properties are degraded over the lifetime of the item.

COOLING CHANNELS – Channels or passageways located within the body of a mold through which a cooling medium can be circulated to control the mold temperature and remove heat as the molten plastic cools.

COOLING FIXTURE – A fixture holding the shape of a molded piece to maintain the proper shape, or dimension, of a molded part after it is removed from the mold. It is used until the part is cool enough to retain its shape without appreciable distortion.

CORE – A term describing a male element within a die, which produces a hole or recess inside the part. It also refers to a part of a more complex mold, used to mold undercut parts.

CORE PIN – A pin that is being used to mold a hole.

CORING – The process of removing excess material from the cross section of a molded part to attain a more uniform wall thickness.

CRAZING – The small “hair-like” cracks on or beneath the surface of a plastic part. It sometimes is an indicator of imminent material fracture.

CREEP – The tendency of a plastic material to move slowly, at the molecular level, over a period of time under the influence of stresses. Over long periods of time these tiny movements add up, changing part dimensions. Manufacturing engineers designing parts for applications having a consistent high pressure will consider creep when choosing their materials.

CRYSTALLINITY – A state of molecular structure in resins which denotes uniformity and compactness of the molecular chains that form the polymer. Normally the condition can be attributed to the formation of solid crystals with a definite geometric form.

CURE – To change the physical properties of a material by chemical reaction to make it more stable & functional. The process may include condensation, polymerization, or vulcanization.

CURING TEMPERATURE – The proper temperature at which a molded product is subjected to curing.

CYCLE – The complete sequence of operations involved in a process, or part of a process, is a cycle. In molding, the cycle time is the period, or elapsed time, between a certain point in one cycle and the same point in the next.

4 D

DAYLIGHT OPENING – Clearance between two plates of a press in the open position.

DECORATION (OF PARTS) – After injection molding, a secondary operation where the part is printed (decorated) by screen printing, pad printing, heat transfer, or similar methods.

DEFLASHING – Covers the range of finishing techniques used to remove the flash (excess, unwanted material) that occurs on plastic parts such as cutting, scraping, filing, sanding, milling or tumbling.

DEGRADATION – A damaging change in the chemical structure of a plastic resulting from such things as heat, light exposure, and general weathering.

DELAMINTATION – The splitting of a plastic material along the plane of its layers. It is the condition of physical separation, or loss of bond, between laminate plies.

DENSITY – Weight per unit volume of a substance, expressed in units such as grams per cubic centimeter or pounds per cubic foot.

DESSICANT – A substance that can be used for drying plastic pellets because of its affinity for water.

DESTATICIZATION – Is the act of treating plastic materials to minimize their accumulation of static electricity.

DETERIORATION – A permanent change in the physical properties of a plastic evidenced by impairment of these properties.

DIMENSIONAL STABILITY – The ability of a plastic part to retain its precise shape over time. Different plastic materials have different dimensional stability characteristics, and the dimensional stability of some plastics are even affected by moisture.

DISCOLORATION – Any change that occurs from the original color that likely has resulted from overheating, light exposure or chemical exposure.

DISHED – Showing a symmetrical distortion of a flat, or curved, section of a plastic object.As normally viewed, it now appears concave, or more concave than intended.

DISPERSION – Finely divided particles of a material, that is in suspension inside another substance.

DOMED – A symmetrical distortion of a flat, or curved, section of a plastic object. As normally viewed, it now appears convex, or more convex than intended.

DOWEL – A pin used to maintain alignment between two or more parts of a mold.

DRAFT – The degree of taper of a sidewall or the angle of clearance designed to facilitate removal of parts from a mold.

DRY COLORING – A method occasionally used by fabricators for coloring plastic by tumble blending

5 uncolored particles of plastic material with selected dyes and pigments.

DUROMETER HARDNESS – The hardness of a plastic material, as measured by the Shore Durometer.

DWELL – A pause in the application of pressure to a mold… made just before the mold is completely closed. It allows the escape of gas from the molding material. E

EDM (ELECTRIC DISCHARGE MACHINING) – A metal working process applicable to mold construction in which controlled sparking is used to erode away the metal, usually to create a complicated shape.

EJECTOR CONFIRMATION SWITCH – A switch used to prevent mold damage by detecting if the ejector plate does not fully return to home position.

EJECTOR PIN – Steel pins used to eject parts and runners from the mold. When the ejector system of a mold is actuated by the molding machine, ejector pins will move forward and thereby remove parts.

EJECTOR PIN RETAINER PLATE – The retainer into which ejector pins are assembled.

EJECTOR RETURN PINS – Projections that push the ejector assembly back as the mold closes.

EJECTOR ROD & BAR – The bar that moves the ejector assembly after the mold is opened.

ELASTICITY – The property of a material by virtue of which it tends to “recover” to its original size and shape… after deformation.

ELASTOMER – A material which stretches under low stress to at least twice its length, and snaps back to the original length upon release of stress.

ELECTRONIC TREATING – When plastic parts are made of a material that does not naturally adhere to inks, the part surface is subjected to a high voltage corona discharge. Once treated, the plastic will be rendered “printable.”

ELECTROPLATING – The accumulation of metals on certain plastics and molds for finishing.

ELONGATION – The fractional increase in length of a material stressed under a tensile load.

ENCAPSULATING – When an article is covered in a closed, envelope of plastic… by immersing the object in a casting resin and allowing the resin to polymerize or to cool.

ENVIRONMENTAL STRESS CRACKING – The susceptibility of a thermoplastic part to crack (or craze) under the influence of certain chemicals, aging, weather or stress.

6 F

FABRICATE – To work a material into a finished form by various manufacturing methods.

FABRICATING – The use of various manufacturing methods to create plastic products. Examples of fabrication processes include: cutting, tapping, fastening and punching such plastics as sheets, tubes, rods and more.

FAMILY MOLD – A multi-cavity mold where the various cavities form different parts in a single shot using the same material.

FAN GATE – A shallow gate somewhat wider than the runner from which it extends. The gate is fan- shaped with the widest part of the gate touching the plastic part.

FIBER – This term usually refers to thin fibers of glass, which are used to reinforce plastic materials. The fiberglass is incorporated into the plastic pellets prior to the injection molding process.

FILLER – An additive to resins for the purpose of modifying physical properties (for example: impact resistance, hardness or dimensional stability). It can also be used to reduce the expense of resin.

FILLET – A small radius added to replace a sharp interior corner… usually for reducing a stress concentration, and thereby making the part stronger.

FINISH – To complete the secondary work on a molded part so that it is ready for use. Operations such as filing, de-flashing, buffing, drilling, tapping and de-gating are commonly called “finishing operations.”

FIXTURE – The means of holding a part, or parts, during a manufacturing operation.

FLAME RATING – An internationally accepted plastics “flammability” testing standard created by Underwriters Laboratories.

FLASH – Extra plastic attached to a molded part along the parting line or other shut-off locations in the mold.

FLASH GATE – Usually a long gate extending from a runner, which runs parallel to an edge of a molded part… along the flash or parting line of the mold.

FLEXURAL STRENGTH – The ability of a material to flex without permanent distortion or breaking.

FLOW – A qualitative description of the fluidity of a plastic material during the process of molding.

FLOW MARKS – Visible indications on the surface of a part that show how the plastic flowed into the mold. G

GATE – In injection molding, the orifice through which the melt enters the cavity is called the gate.

7 GLOSS – The shine or luster that appears on the material surface.

GUIDE PINS – Devices that maintain proper alignment of the core and cavity while the mold closes. These are also called “leader pins.” H

HARDNESS – The resistance of a material to compression and indentation. Among the more important methods of testing this property are Brinell hardness and Rockwell hardness.

HAZE – The degree of cloudiness in a plastic material.

HEAT TRANSFER – The transfer of thermal energy across a boundary. Molds and their cooling systems are designed to effectively and efficiently transfer heat, allowing the molten plastic to solidify.

HEAT TRANSFER PRINTING – A part decoration process using heat to transfer an image from a printed roll of film onto a plastic part.

HOT MANIFOLD MOLD – A thermoplastic injection mold in which the portion of the mold, which contains the runner system, has its own heating elements. The molding material is kept in a molten state ready for injection into the cavities, from which the manifold is insulated.

HOT STAMPING – A secondary engraving operation for decorating (or marking) plastics in which the roll leaf is stamped with heated metal dies onto a plastic part.

HYGROSCOPY – Is the ability of a substance to attract and hold water molecules from the surrounding environment. I

IMPACT RESISTANCE – The measure of how much a plastic item can withstand high-speed stress.

IMPACT STRENGTH – The ability of a material to withstand shock loading. Molded plastics are usually given a value on an izod scale. An izod impact test is designed to determine the resistance of a plastic material to a shock loading.

IN-MOLD LABELLING (IML) – A form of insert molding where a pre-printed label is installed into the mold, the mold is closed, and then plastic is injected into the cavity. The label will be “permanently” attached to the plastic part.

INJECTION MOLDING – The process of creating plastic parts and components by melting plastic; forcing (injecting) the molten plastic into a mold; allowing the plastic to solidify in the mold; and finally, removing the solid plastic parts from the mold.

INJECTION BLOW MOLDING – A blow molding process in which the item to be blown is first formed by the injection molding process.

INSERT – An integral part of a plastic molding consisting of metal, or other material, which may be

8 molded into position or may be pressed into the molding after the molding is completed. J

JETTING – A turbulent flow of resin from an undersized gate, or thin section, into a thicker mold section. This is opposed to a laminar flow of material progressing radially from a gate to the extremities of the cavity.

JIG – A means of holding a part and guiding a tool during a machining or assembly operation. K

KNIT LINE – A mark on a molded piece made by the meeting of two flow fronts during molding. It can also be called a “weld line.” L

LIM (LIQUID INJECTION MOLDING) – A process used to produce silicone parts using an injection molding machine. The silicone is a thermoset resin, and is injected as a two-part liquid into a heated mold where the silicone rubber is solidified (vulcanized).

LIFTER – A moving part of the mold used to release parts that will not eject normally because the part has an undercut feature. Lifters are part of the ejector system of a mold.

LIGHT RESISTANCE – The ability of plastic materials to resist fading after exposure to sunlight or ultraviolet light.

LIVING HINGE – A thin section between two thicker parts that is flexible and acts like a hinge. Using the correct plastic material allows the hinge to be “living” which means it can open and close repeatedly without the plastic cracking.

LOW TEMPERATURE FLEXIBILTY – The ability of plastic to withstand fracturing at low temperatures. M

MAR RESISTANCE – A glossy plastic’s resistance to damage caused by abrasion.

MASTERBATCH – An off-the-shelf combination of pigments, fillers, additives and other substances within a polymer base.

MATTE FINISH – A dull, non-reflective finish on a molded part.

MELT FLOW – The viscosity of a polymer based on the polymer’s weight when extruded under certain pressure and temperature.

9 MELT FLOW INDEX – A scientific measure of how easily molten plastic will flow during the injection molding process. Various grades of the same material may have different melt flow index numbers.

MEMORY – A plastic article’s tendency to revert to previous dimensions.

METALIZING – Covering or coating any plastic item with metal.

MINERAL REINFORCEMENTS – Are inorganic substances such as clay, mica or talc used as filler in plastics.

MOLDING MATERIAL – Plastic material, in varying stages of granulation, often comprised of resin, filler, pigments, plasticizers and other ingredients. It is used in the molding operation and also referred to as the molding compound.

MOLDING PRESSURE – The pressure applied directly, or indirectly, on the molten plastic in the mold to allow the complete transformation to a solid, dense part.

MOLDING SHRINKAGE – The difference in dimensions between a molding and the mold cavity in which it was molded.

MOLD PARTING LINE – A mark (sometimes called a “witness line”) on a molded part where the halves of a mold come together.

MOLD RELEASE – A lubricant used to coat a mold cavity to prevent the molded piece from sticking to it, thus facilitating its removal from the mold.

MONOMER – A relatively simple compound, which can react to form a polymer.

MOVABLE PLATEN – The platen of a molding machine that moves, thereby opening and closing a plastic injection mold. This platen is moved either by an electric motor, a hydraulic ram or a toggle mechanism.

MUD FRAME (MASTER UNIT DIE) – A mold frame that remains in the molding machine and works with multiple mold units to save tooling costs and reduce mold changeover times. N

NOTCH SENSITIVITY – The extent to which the sensitivity of a material to fracture is increased by the presence of a surface in homogeneity such as a notch, a sudden change in section, a crack, or a scratch. Low notch sensitivity is usually associated with ductile materials, and high notch sensitivity with brittle materials.

NOZZLE – The hollow cored metal nose screwed into the end of the heating cylinder of an injection machine. Molten plastic flows through the nozzle and into the mold.

NOZZLE TIP (REMOVABLE) – A replaceable tip that installs into the end of the molding machine’s nozzle. Nozzle tips must be matched to the mold surface (for sealing off high injection pressures), and to the orifice of the mold sprue.

10 O

ORIENTATION – The alignment of the crystalline structure in polymeric materials so as to produce a highly uniform structure.

OUT-OF-ROUND – When an item has a non-uniform radius or diameter. P

PERMANENT SET – The increase in length, expressed in a % of the original length, by which an elastic material fails to return to original length… after being stressed for a standard period of time.

PINPOINT GATE – A restricted orifice through which molten resin flows into a mold cavity.

PLASTIC – A moldable polymer made of natural and synthetic material and chemicals that can be transformed into a solid.

PLASTIC DEFORMATION – A change in dimensions of an object under load that is not recovered when the load is removed. (If it is recovered, you have elastic deformation.)

PLASTICITY – A property of plastics which allows the material to be deformed continuously and permanently without rupture upon the application of a force that exceeds the yield value of the material.

PLASTICIZE – To soften a material and make it plastic or moldable either by means of a plasticizer or the application of heat.

PLASTICIZER – A material incorporated in a plastic to increase its workability and its flexibility.

PLUNGER – The part of an older injection press that applies pressure on the unmelted plastic material to push it into the chamber. It forces plastic melt at the front of the chamber out through the nozzle.

POLYMER – A compound of high molecular weight derived either by the addition of many smaller molecules, as polyethylene, or by the condensation of many smaller molecules with the elimination of water, alcohol, or the like, as nylon. If two or more monomers are involved, a copolymer is obtained. Some polymers are elastomers, some plastics.

POLYMERIZATION – A chemical reaction in which the molecules of a monomer are linked together to form large molecules whose molecular weight is a multiple of that of the original substance.

PREHEATING – The heating of a compound prior to molding or casting in order to facilitate the operation, reduce cycle time, and improve the product.

PREMIX – A molding compound prepared, prior to and apart from the molding operations, and containing all components required for molding (resin, fillers, catalysts, release agents, and other compounds).

11 PROTOTYPE MOLD – A simplified mold construction often made from a light metal casting alloy or from an epoxy resin, in order to obtain information for the final mold and/or part design.

PURGING – Cleaning one color or type of material from the cylinder of an injection molding machine by forcing it out with a “purge compound,” or with the new color/material to be used in subsequent production. R

RECIPROCATING SCREW – In injection molding machines, a combination device that 1) melts (by friction heat) and mixes the plastic resin by rotating the screw, and 2) injects the plastic into the mold as it acts like a plunger (reciprocating action).

REINFORCED MOLDING COMPOUND – A material reinforced with special fillers to meet specific requirements.

REINFORCEMENT – A strong inert material bound into a plastic to improve its strength, stiffness, and impact resistance.

RESIN – Another name for plastic, as in “plastic resin.”

RIB – A reinforcing member of a fabricated or molded part.

ROCKWELL HARDNESS – A common method of testing material for resistance to indentation in which a diamond or steel ball, under pressure, is used to pierce the test specimen.

RUBBER – Is an elastomer capable of rapid elastic recovery after being stretched to at least twice its length… at temperatures from 0 to 150°F and at any humidity.

RUNNER – In an injection mold, the channel that connects the sprue with the gate to the cavity is the runner.

RUNNER SYSTEM – The term applied to all the material (sprues, runners and gates) which lead material from the nozzle of an injection machine to the mold cavity. S

SHELF LIFE – An expression to describe the time a molding compound can be stored without losing any of its original physical or molding properties.

SHORT SHOT – A molded part produced when the mold has not been filled completely.

SHOT – The yield from one complete molding cycle, including sprue, runner, and parts.

SHOT CAPACITY – The maximum volume/weight of material which a machine can inject from one forward motion of the screw.

SHUT OFF – Where pieces of metal in an injection mold come together (touch off). If the area of

12 “shut off” has a gap, excess plastic material will fill the gap and create a defect condition called “flash.”

SIDE CORING OR SIDE DRAW PINS – Projections used to core a hole in a direction other than the line of closing of a mold and which it must be withdrawn before the part is ejected from the mold.

SILICONE – A chemical derived from silica used in molding as a release agent and a general lubricant.

SILK SCREEN PRINTING –The laying of a pattern of insoluble material on a finely woven fabric, so that ink drawn across it is able to pass through the screen only in the desired areas.

SINK MARK – A depression or dimple on the surface of an injection molded part due to collapsing of the surface following local internal shrinkage after the gate seals.

SLIDES – Parts of injection molds that form undercuts (e.g., a hole) in the part, and are designed to move out of the way to allow the part to eject.

SOLVENT – Any substance, usually a liquid, which dissolves other substances.

SPECIFIC GRAVITY – The density (mass per unit volume) of any material divided by the density of water.

SPIDER GATE – Multi-gating of a part through a system of radial runners from the sprue.

SPIN WELDING – A process of fusing two objects together by forcing them together while one of the pair is spinning until frictional heat melts the interface. Upon melting, spinning is then stopped and pressure held until they are frozen together.

SPLAY – Streaks occurring as the result of moisture in the resin.

SPRUE – The plastic part formed by the opening/passageway from the molding machine’s nozzle tip to the runner system. The sprue hole is tapered so that the sprue will easily release from the sprue bushing.

SPRUE BUSHING – A hardened steel insert in an injection mold which contains the tapered sprue hole and has a suitable seat for the nozzle of the injection cylinder.

SPRUE GATE – A passageway through which molten resin flows from the nozzle to the mold cavity.

SPRUE LOCK OR PULLER – A portion of the sprue which is held in the cold slug well by an undercut. It is used to pull the sprue out of the sprue bushing as the mold is opened.

STABILIZER – An ingredient used in the formulation of some plastics to assist in maintaining the physical and chemical properties of the compounded materials at their initial values throughout the processing and service life of the material.

STATIONARY PLATEN – The plate of an injection molding machine, to which the front plate of the mold is secured during operation. This plate does not move (see “moving platen” definition).

13 STICKING – A complication during ejection… when a part does not release from the mold as intended.

STRESS CRACK – An internal or external crack in a solid plastic part caused by tensile, compressive, or in some cases shear force.

STRIPPER PLATE – A plate that strips a molded piece from core pins or the core. It performs the same function as “ejector pins.”

SUBMARINE GATE – A type of gate where the opening from the runner into the mold is located below the parting line. With submarine gates, the parts are automatically cut from the runner system as the parts/runner are ejected from the mold.

SURFACE FINISH – The roughness of a plastic part’s surface. For plastic, this is usually measured by visually comparing the part’s surface to a surface finish standard.

SURFACE TREATING – Any method of treating a material so as to alter the surface and render it receptive to inks, paints, lacquers, and adhesives. T

TAB GATE – A small, removable tab of approximately the same thickness as the molded part, usually located perpendicular to the part.

TENSILE STRENGTH – The pulling pressure required to break a given plastic specimen.

THERMAL CONDUCTIVITY – The ability of a material to conduct heat.

THERMAL STRESS CRACKING – Crazing and cracking of thermoplastic resins, which results from over-exposure to elevated temperatures.

THERMOPLASTIC – A material that will repeatedly soften when heated and harden when cooled.

THERMOSET RESIN – A material that, unlike a thermoplastic, can only be molded one time.

THREAD PLUG – A part of a mold that shapes a thread and must be unscrewed from the finished piece.

TIE BARS – Are “bars” which provide structural rigidity to the clamping mechanism of a press used to guide platen movement.

TOGGLE ACTION – Pressure exerted by the application of force on a knee joint. It is often used as a method of closing presses.

TOLERANCE – A specified allowance for deviations from the standard dimensions or weight.

14 U

ULTRASONIC INSERTION – The inserting of a metal insert into a thermoplastic part by the application of vibratory mechanical pressure at ultrasonic frequencies.

ULTRASONIC WELDING – The application of vibratory mechanical pressure at ultrasonic frequencies (20 to 40 kc.) to melt the material between two surfaces that forms a weld as the plastic solidifies.

UNDERCUT – Having a protrusion, or indentation, that impedes withdrawal from a two-piece, rigid mold. It should be noted that flexible materials can be ejected intact, even with slight undercuts.

UV STABALIZER – Any chemical compound which, when admixed with a thermoplastic resin, selectively absorbs UV or ultra violet rays to reduce degradation due to UV light. V

VACUUM METALIZING – The process in which surfaces are thinly coated with metal by exposing them to the vapor of metal that has been evaporated under vacuum.

VENT – In a mold, a very shallow channel or minute hole cut in the cavity to allow air to escape as the material enters.

VISCOSITY – The measure of a melted plastic’s ability to resist flow. In fluids, high viscosity may be thought of as “thickness,” and low viscosity as “runniness.”

VOID – A void or bubble occurring in the center of a heavy thermoplastic part. W

WARP (WARPAGE) – A curving or bending that results as a part cools and shrinks at varying rates along a surface.

WATER ABSORPTION – The ability of a thermoplastic material to absorb water from an environment.

WELDING – The act of joining thermoplastic pieces by one of several heat-softening processes (spin welding, butt fusion, or ultrasonic welding).

WELD LINE – A mark on a molded piece made by the meeting of two flow fronts during molding. It can also be called a “knit line.” Y

YIELD VALUE – The lowest stress at which a material undergoes plastic deformation.

15 About GreenLeaf: GreenLeaf Industries is an ISO 9001 registered manufacturer that con- sistently adheres to all its standards to provide our clients with consistent, reliable, quality automotive and industrial plastic parts. We are an American company, unafraid to compete in the world market and determined to succeed. Established in 1999, we take pride in our high-quality craftsmanship and superior customer service.

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