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It requires many years of industry experience and hard work to become a true thermoforming expert. However, a few minutes with our glossary of thermoforming and plastics manufacturing terms will at least help you sound like one.


A substance which applied as an intermediate is capable of holding materials together by surface attachment.

The change of material with time under defined environmental conditions, leading to improvement or deterioration of properties.

Air-Assist Forming
A method of thermoforming in which air flow or air pressure is employed to partially preform the heated sheet immediately prior to the final pulldown onto the mold using vacuum.

Composite material made by blending polymers or copolymers with other polymer or elastomers under selected conditions.

A process of holding a material at a temperature near, but below its melting point, the objective being to permit stress relaxation without distortion of shape.

Antistatic Agents
Methods of minimizing static electricity in plastic materials.

Artificial Weathering
Exposure to cyclic laboratory conditions involving changes in temperature, relative humidity and radiant energy, with or without direct water spray, an attempt to produce changes in the material similar to those observed after long-term continuous outdoor exposure.

Protuberance on a plastic part designed to add strength; to facilitate alignment during assembly; to provide for fastening.

Carbon Black
A black pigment produced by the incomplete burning of natural gas or oil. It is widely used as a filler, particularly in the rubber industry. Because it possesses useful ultraviolet protective properties, it is also used in polyethylene compounds intended for such applications as cold water piping, black agricultural sheet and many other outdoor products.

Depression in a mold made by casting or machining, or a combination of these methods; depending on the number of such depressions, molds are designed as Single-Cavity or Multi-Cavity.

A powdery residue on the surface of a material often resulting from degradation.

Chill Mark
A surface blemish on a formed part.

An additive that increases the transparency of a material.

Coefficient of Expansion
The fractional change in length of a material for a unit change in temperature.

Computer-Aided Design
Computer design of part wall thickness using geometry of FEM. Also shown as CAD.

Cooling Channels
Channels or passageways located within the body of a mold through which a cooling medium can be circulated to control temperature on the mold surface.

Cooling Fixture
A framework used to hold the shape of a formed part. Used to maintain the proper shape or dimensional accuracy of a part after it is removed from the mold until it is cool enough to retain its shape without further appreciable distortion. Also known as a Shrink Fixture.

A small, shallow surface imperfection.

Fine cracks which may extend in a network or under the surface or through a layer of a plastic material.

The dimensional change with time of a material under load, following the initial instantaneous eleastic deformation. Creep at room temperature is sometimes called Cold Flow.

Cut Sheet
Usually refers to heavy gauge sheet, fed one at a time, into a rotary or shuttle thermoformer. Normally .060 inches thick and above.

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

Daylight Opening
Clearance between two platens of the forming station in the open position.

An indent or cut in design or lettering of a surface.

Covers the range of finishing techniques used to remove the trim burrs (excess, unwanted material) on a trimmed thermoformed part.

Decorative Sheet
A laminated plastic sheet used for decorative purposes in which the color and/or surface pattern is an integral part of the sheet.

A deterioration in the chemical structure of plastic.

The separation of the layers in a laminate caused by the failure of the bond between layers.

Weight per unit volume of a substance, expressed in grams per cubic centimeter, pounds per cubic foot, etc.

Die Cutting
Cutting shapes from sheet stock or trimming formed parts by striking them sharply with a shaped knife edge known as a steel rule die.

Die Lines
Marks or lines in the extrusion direction on sheet caused by damage of die parts or contamination.

Dimensional Stability
Ability of a plastic part to retain the precise shape in which it was formed, fabricated, or cast.

Any change from the original color, often caused by overheating, light exposure, irradiation, chemical attack, or bad sheet extrusion.

The degrees of taper of a side wall or the angle of clearance designed to facilitate removal of parts from a mold.

The process of stretching a thermoplastic sheet to reduce its cross-sectional area.

Techniques used to create depressions of a specific pattern in plastic film and sheet.

Environmental Stress Cracking
The susceptibility of a thermoplastic article to crack or craze formation under the influence of certain chemicals, UV and stress.

The compacting of a plastic material and the forcing of it through a die in a more continuous fashion.

To work a material into a finished form by machining, forming, bonding, welding or other operation.

Family Mold
A multi-cavity mold where each section forms one of the component parts of the assembled finished object.

In thermoforming, the indented, recessed part of a mold.

A cheap, inert substance added to a plastic to make it less costly. Fillers may also improve physical properties, particularly hardness, stiffness and impact strength.

A rounded filling of the internal angle between two surfaces of a mold.

Finite Element (FEM)
A computer technique for predicting how a sheet of plastic deforms under load.

Fish Eye
A fault in transparent, translucent, and opaque plastic materials, such as film or sheet, appearing as a small globular mass and caused by incomplete blending of the mass with surrounding material.

Flame Retardant Resin
A resin which is compounded with certain chemicals to reduce or eliminate its tendency to burn.

Measure of the extent to which a material will support combustion.

Flexural Modulus
A measure of the strain imposed in the outermost fibers of a bent specimen.

A small resin particle which differs from its surroundings by being of higher molecular weight, so that its processing characteristics differ from the surrounding resin making it difficult to disperse in the surrounding resin.

The shine or luster of the surface of a material.

Grit Blasted
A surface treatment of a mold in which steel grit or sand materials are blown against the surfaces of a mold to produce a matte finish. During thermoforming air escape between the hot sheet and the mold is greatly improved. Often a special appearance on the formed article can be obtained.

The resistance of plastic material to compression and indentation. Among the most important methods of testing this property are Brinell Hardness, Rockwell Hardness, and Shore Hardness.

The degree of cloudiness in a plastic material.

Heat Deflection Temperature
The temperature at which a standard test bar deflects .010 inch under a stated load of either 66 or 264 p.s.i.

Tending to absorb moisture.

Impact Resistance
Relative susceptibility of plastics to fracture by shock.

Impact Strength
The ability of a material to withstand shock loading.

To move a sheet forward or rotate a fixed length.

Part of the electromagnetic spectrum between the visible light range and the radar range. Radiant heat is in this range, and infrared heaters are commonly used in sheet thermoforming.

A substance that slows down chemical reaction. Inhibitors are sometimes used in certain types of monomers and resins to prolong storage life.

Injection Molding
A molding process whereby a heat softened plastic material is forced from a cylinder into a relatively cool cavity which gives the article the desired shape.

An integral part of a thermoformed part consisting of metal or other material which may be thermoformed into position or may be pressed into the molded part after forming.

International Organization of Standardization.

Izod Impact Test
A test designed to determine the resistance of a plastic material to a shock loading. It involves the notching of a specimen, which is then placed in the jaws of a machine and struck with a weighted pendulum.

Tool for holding component parts of an assembly during the manufacturing process, or for holding other tools. Also called a fixture.

A product made by bonding together two or more layers of material or materials. Bonding can be done by extrusion laminating, pressing or autoclave.

The ability of a plastic material to resist fading or degradation after exposure to sunlight or ultra-violet light. Nearly all plastics tend to darken under these conditions.

Melt Strength
The strength of plastic while in the molten state.

Applying a thin coating of metal to a nonmetallic surface. May be done by chemical deposition or by exposing the surface to vaporized metal in a vacuum chamber.

Mold Shrinkage
The difference in dimensions, expressed in inches per inch, between a part and the mold surface in which it was shaped, with the mold at forming temperature and the part at normal room temperature.

Mounting Plate
The part of a thermoforming machine to which a mold is attached.

Moveable Platen
The structure to which the mold, plug assist, pressure box or pre-draw box is secured during operation. The platen is moved by air cylinders, hydraulic rams or servo motors.

Descriptive of a material or substance which will not transmit light. Opposite of transparent.

Orange Peel
Sheet or parts that have unintentionally rough surfaces.

Stresses put into sheet and film when it is produced.

A plastic part manufacturing variance in which a round part, when formed, does not remain round.

Parting Line
Mark on a formed part where halves or parts of a mold meet.

Any colorant, usually a powdered substance, used to produce a desired color or hue.

An imperfection, a small, sharp, or conical elevation on the surface of a plastic part or sheet.

A very small hole in the extruded resin coating, sheet, film or formed part.

An imperfection, a small crater in the surface of the plastic, with the width of approximately the same order of magnitude as its depth.

One of many high-polymeric substances, including both natural and synthetic products, but excluding the rubbers. At some stage in its manufacture, every plastic is capable of flowing, under heat and pressure, if necessary, into the desired final shape.

Plastic Deformation
A change in dimensions of an object under load that is not recovered when the load is removed.

Plastic Memory
A phenomenon of processed plastics to return to its original form. Different plastics posses varying degrees of this characteristic.

Chemical agent added to plastic compositions to make them softer and more flexible.

The mounting plates of a forming station to which the entire mold assembly is bolted.

Pressure Forming
A thermoforming process where compressed air is used to push the sheet to be formed against the mold surface as opposed to using vacuum to form the sheet.

Pressure Sensitive Adhesive
An adhesive which develops maximum bonding power by applying only a light pressure.

Profile Heating
Adjustment of radiant heating elements to obtain uniform sheet temperature or to achieve special temperatures in a given area.

Recessed Panel
A part design in which the flat area for labeling is indented or recessed.

Recycled Plastic
Plastic prepared from used articles which have been cleaned and reground.

Reformulated Plastic
Recycled plastic that has been upgraded to alter or improve performance capability or to change characteristics through use of plasticizers, fillers, stabilizers, pigments, etc.

Recyclable granulated resin from trim, salvage and drop off, cut from thermoformed parts or clean non-degraded parts or sheet.

Any of a class of solid or semi-solid organic products of natural or synthetic origin, generally of high molecular weight with no definite melting point. Most resins are polymers.

A reinforcing, stiffening member of a fabricated or thermoformed part.

The flow of a molten sheet in a thermoforming operations, the amount of droop.

Contraction of a formed part upon cooling.

Stress Crack
An external or internal crack in plastic caused by tensile stresses.

Thermal Expansion
The fractional change in length of a material for a unit change in temperature.

Thermal Stress Cracking
Crazing and cracking of some thermoplastic resins which results from over exposure to elevated temperatures.

Any process of forming thermoplastic sheet which consists of heating the sheet and forcing it onto a mold surface.

Capable of being repeatedly softened by heat and hardened by cooling.

Stress caused by twisting a material.

Descriptive of material capable of transmitting some light, but not clear enough to be seen through.

Descriptive of material capable of a high degree of light transmission.

Portion of the sheet that is not part of the final product.

Having a protuberance or indention that impedes withdrawal from a rigid mold. Some flexible materials can be ejected intact even with slight undercuts.

UV Stabilizer
Any chemical compound which, when mixed with a thermoplastic resin, selectively absorbs UV rays.

Vacuum Forming
Method of shaping a sheet by use of vacuum to enable atmospheric pressure to form a part.

Dimensional distortion in a plastic object after forming.

During forming, a fold of plastic that cannot be stretched flat against a mold surface.

Definitions courtesy of:

McConnell, William K. Ten Fundamentals of Thermoforming: 2 Video Series & Companion Volume. Brookfield, CT: Society of Plastics Engineers, 2001. Print.

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