Principles of Thermoforming 265

amorphous polymer

Polymer whose molecular structure lacks a definite repeating form, shape, or structure.

CNC machine

A machine controlled by a computer that performs a series of operations by reading through a program and executing its instructions.

composite

A material made from combining two materials from the separate groups of polymers, metals, and ceramics. In a composite, all the materials retain their respective characteristics.

concave

Curving inward like the inside of a bowl.

convex

Curving outward like the exterior surface of a circle or sphere.

CT scan machine

A medical device that takes pictures all around the human body and uses a computer to generate a detailed 3D representation.

depth

The top-to-bottom measurement of a recess or relief.

depth of draw

The maximum vertical length that the plastic sheet is stretched.

drape forming

A thermoforming process that uses a male mold to produce deeply recessed, concave parts.

draw ratio

The distance the plastic sheet is stretched vertically divided by the distance it is stretched horizontally.

drawing

A forming operation that transforms a flat disc or sheet of stock into a hollow cup with an enclosed bottom. Drawing operations can also create boxes and more intricate shapes as well.

elastic

A material that has the ability to return to its original shape once it has been stretched or deformed.

extrusion

A plastic shaping process in which melted plastic resin is forced through an opening to produce a product that maintains a relatively consistent size and shape.

female mold

A forming device around which plastic is shaped during thermoforming. The female mold creates concave plastic parts.

free forming

A thermoforming method that uses force to shape a heated plastic sheet without a mold. Free forming produces a relatively limited range of part shapes.

infrared lamp

A lighting device that uses invisible electromagnetic radiation. Infrared lamps can be used to heat thermoplastic sheets for thermoforming operations.

injection molding

A molding process in which resin is heated in a barrel and then injected into a mold by a reciprocating screw.

male mold

A forming device around which plastic is shaped during thermoforming. The male mold creates convex plastic parts.

matched die thermoforming

A thermoforming method that uses both a female and male mold to create patterns on both sides of a plastic product.

mechanical thermoforming

A thermoforming method in which an object is pressed into hot plastic to create a housing for that object.

metal forming

The plastic deformation of a metal in order to produce a useful shape. Metal forming is done at elevated or hot-working temperatures with processes such as forging, or it is done at cold-working room temperatures with processes such as stamping or bending.

MRI scan machine

A medical device used to see the inside of a patient's body. MRI scanners are state-of-the art devices that allow doctors to diagnose the smallest of infractions on the body.

plug

A shaping tool that forces a heated plastic sheet into a female mold.

plug-assist forming

A thermoforming process that uses a plug to push a plastic sheet into a mold. Once the sheet is in the mold, vacuum pressure completes the molding process.

plug-assisted forming

A thermoforming method that combines either pressure or vacuum force with a mechanical device to force plastic material onto a mold.

pressure box

A component used in pressure forming that encloses the plastic sheet in the mold and applies positive pressure to assist in forming.

pressure forming

A thermoforming method that combines positive air pressure and negative air pressure to force plastic material around a mold. Pressure forming offers the highest degree of accuracy and detail in plastic parts.

quartz oven

A device that uses heated quartz to conduct heat. Quartz can conduct more heat than traditional oven heating elements such as tubes or bulbs, so it is used for high temperature applications.

reverse-draw forming

A thermoforming method during which a plastic sheet is thinned and pushed away from the mold by positive air pressure. When the sheet has thinned sufficiently, a plug pushes it into the mold to cool.

sag point

The temperature at which a given plastic sheet is able to be reshaped. The plastic sheet is not completely liquefied at the sag point, but merely softened.

semi-crystalline polymer

Polymers that have areas of crystalline molecular structure, but also having amorphous regions.

shearing

The cutting and separating of material through its cross section.

snap-back forming

A plastic shaping method that uses male molds to create plastic parts. The plastic sheet is lowered over an enclosed area with a vacuum. When the vacuum pressure is released, the plastic snaps onto the male mold.

springback

The tendency for a material to return to its original shape after deformation.

straight vacuum forming

A thermoforming method in which plastic is heated to its sag point and then placed over a mold. Straight vacuum forming is the simplest vacuum forming technique, as it is completed in one major step.

thermoforming

A plastic shaping process that shapes heated plastic sheets around a mold. Thermoforming is a lower-volume process that produces detailed parts with close tolerances.

thermoplastic

A polymer that is solid at room temperature and can be melted at high temperatures. Thermoplastics can be shaped by heat and pressure, cooled, and then reheated and reshaped.

thermoset

A liquid or malleable polymer. A thermoset is placed in a mold and cured with the addition of some type of energy, usually heat. Once a thermoset is cured, it cannot be re-heated and reshaped.

thick-gauge thermoforming

A sheet-fed thermoforming application. Thick-gauge thermoforming heats and forms thicker, plastic sheets into parts. Thick-gauge thermoforming is used to create coverings for large medical equipment.

thin-gauge thermoforming

A roll-fed thermoforming application. Thin-gauge thermoforming heats and forms thin plastic sheets into plastic parts. Thin-gauge thermoforming is often used for molding plastics used for packaging.

twin sheet thermoforming

A thermoforming method that heats and forms two separate plastic sheets, and then welds the sheets together to form a hollow part.

undercut

A recessed section of a molded part that helps keep the part secure within the mold.

vacuum forming

A thermoforming method that uses negative air pressure to force the plastic sheet against a mold. Vacuum forming is often used in the medical industry.

X-ray machine

A medical device that produces visual images generated by electromagnetic radiation.