Thermoforming Overview 260

A side

The side of a thermoformed part that touches the mold. The A side of the part has all of the features of the mold, including shape and surface finish.

additives

A substance that is added to a material during manufacturing in order to improve its properties. Additives perform a range of functions, from changing the color of plastic to improving its strength.

automated

A system or process that does not require human intervention to operate. Automated systems can increase the efficiency of industrial processes.

B side

The side of a thermoformed part that does not touch the mold. The B side of the part takes the shape of the mold but not the surface finish.

chemical resistance

The ability of a material to resist chemical changes. Chemical resistance prevents gradual degradation caused by the atmosphere, moisture, or other substances.

CNC machine

Computer numerical control machine. A machine controlled by a computer that runs special programs to manufacture a workpiece. CNC machines are very rigid and are capable of fast cutting speeds.

concave

Curving inward, like a bowl. Concave parts are made with female molds in thermoforming.

convex

Curving outward, like the exterior of a sphere. Convex parts are made with male molds in thermoforming.

cooling channels

A passage through which a cooling fluid is circulated to maintain a desired tool temperature. Cooling channels are sometimes referred to as cooling lines.

deburring

Removing sharp projections left on a workpiece after a machining operation. Deburring ensures that a workpiece has smooth, flat edges.

delamination

The separation of the surface of a plastic part from its inner structure. Delamination occurs when the melted plastic sticks to the mold in thermoforming.

drape forming

A thermoforming process in which plastic is placed over a male mold. Drape forming is used when the surface finish of the concave side of a part is important.

draw ratio

A measure of how much a plastic sheet can be stretched form its original surface area. The draw ratio of plastics used in thermoforming ranges form 1:1 to 4:1.

draw ratio

The ratio at which plastic can be stretched to fit a mold. The draw ratio for most thermoforming processes is 2:1, but can vary based on the specific process

duct holes

Openings in a thermoforming mold by which air is sucked out from between the part and the mold. Duct holes, also known as vacuum holes, are typically located in the lowest points of the mold.

ejector pins

A long pin that extends and retracts to force a solid, molded part out of a mold cavity. Ejector pins should only be activated after a part has completely cooled in order to prevent part deformation.

elongation

The ability of a material to be stretched. Elongation is a quality of low-density polyethylene (LDPE).

fasteners

A device that holds two or more objects together or locates them in relation to each other. Common fasteners include screws, bolts, rivets, and nails.

female mold

A mold that is concave. Female molds allow melted plastic to be molded inside of them.

finishing

A final process performed to complete a part. Finishing operations surface, condition, edge, and clean parts and are usually the last steps in the machining process, occurring before inspection and testing.

flame-retardant

A material that resists igniting when exposed to flame or elevated temperatures. Flame-retardant plastics, such as polyvinyl chloride, release gases when heated that suffocate flames.

flexibility

The ability of a material to be bent. Flexibility is a quality of low-density polyethylene (LDPE).

free forming

A thermoforming process that uses pressure to create a bubble-shaped part. Free forming is not used with a mold.

heating element

A device that heats a component when activated. Heating elements melt plastic to its sag point in thermoforming.

high-density polyethylene

HDPE. A common thermoplastic known for its high strength-to-density ratio. High-density polyethylene has a higher chemical resistance than low-density polyethylene.

high-impact polystyrene

HIPS. A form of polystyrene that has high durability and tensile strength. High impact polystyrene is created by adding materials to polystyrene.

impact resistance

The ability of a material to withstand sudden shock or impact without deforming or breaking. High impact resistance is a feature of polypropylene and high-impact polystyrene.

infrared lamps

A type of heating device that uses light radiation to produce heat. Infrared lamps are used in thermoforming to heat plastic to its sag point.

low-density polyethylene

LDPE. A translucent to opaque thermoplastic with loosely packed molecules. Low-density polyethylene has higher tensile strength than high-density polyethylene.

machined

A manufacturing process that uses cutting tools to remove material to form an object. Machining includes methods such as milling, turning, and drilling.

male mold

A mold that is convex. Male molds in thermoforming allow melted plastic to be stretched over them.

matched die thermoforming

A thermoforming process that uses male and female mold shells together. Matched die thermoforming is used when the surface finishes on both sides of a part are important.

mechanical thermoforming

A thermoforming process that shapes plastic around another part to create a housing. Mechanical thermoforming creates shapes such as plastic caps on metal screws.

mold

A device that plastic sheets are forced against to create plastic parts. Molds in thermoforming can be either male or female molds.

mold shell

A part of the mold containing all the mold cavities and features for a mold process. Mold shells in thermoforming can be either male or female.

molding area

The part of a thermoforming machine where the plastic is placed in the mold. The molding area may contain a pressure box, a plug, or it may just contain the mold.

MRI Machines

Magnetic Resonance Imaging. A medical device that uses a magnetic field and radio waves to produce a detailed image of the soft tissues and bones in the body. MRI machines typically include hard plastic casings.

multiple station

Performing more than one part of a manufacturing process. Multiple station machines may complete an entire manufacturing process, or they may complete several parts, leaving the other tasks to other machines.

negative pressure

Air pressure that is lower than the ambient air pressure. Negative pressure in the form of a vacuum is used to pull air from between a workpiece and the mold in thermoforming.

optical clarity

Allowing light to pass through. Optical clarity is important in parts such as headlight covers and windows.

plastic

A lightweight polymer material that has high corrosion resistance, a high strength-to-weight ratio, and a low melting point. Plastics are usually easy to shape and form.

plug

A component of a thermoforming machine that pushes the plastic into a mold. Plugs are generally made from metal or ceramic.

plug-assisted thermoforming

A thermoforming process that uses a hard device to push plastic into a mold. Plug-assisted thermoforming can create parts with greater depth than other thermoforming processes.

polyethylene

PE. A semicrystalline thermoplastic that is highly resistant to electricity and heat. Polyethylene is the most common commercial plastic.

polyethylene terephthalate

PET. A common synthetic thermoplastic that is highly resistant to electricity and heat. Polyethylene terephthalate is used in many products, including durable plastic bags and water bottles.

polypropylene

PP. A polymer that is tough, flexible, and resistant to fatigue. Polypropylene is commonly used to make translucent products such as food packaging.

polyvinyl chloride

PVC. A thermoplastic that can be manufactured to produce both rigid and flexible materials. Polyvinyl chloride is used to manufacture many common products such as corrosion-resistant pipes.

positive pressure

Physical force used to push on an object. Positive pressure in thermoforming comes from blown air or a plug.

pressure box

A component used in pressure thermoforming that encloses a plastic sheet in a mold and applies positive pressure to assist in forming. A pressure box is used in conjunction with vacuum force that sucks a thermoplastic sheet into the mold.

pressure forming

A thermoforming process that uses pressure, often through blown air, to push a part onto a mold. Pressure forming can shape thicker plastics than vacuum forming.

reverse-draw forming

A thermoforming process that uses blown air to stretch the plastic in the opposite direction of the mold. Reverse-draw forming uses a plug to push the stretched plastic back towards the mold.

rigidity

The measure of the ability of a material to resist bending or stretching. Rigidity is characterized by being stiff and inflexible.

sag point

The temperature at which plastic becomes malleable but remains solid. Plastic is heated to its sag point in thermoforming.

Sanding

A form of grinding that uses a fine-grain abrasive to remove small amounts of material. Sanding improves the finish of a surface.

single-station

Performing one part of the manufacturing process. Single-station machines are used along with other machines to complete a manufactured part.

snap-back forming

A thermoforming process in which a vacuum pulls plastic away from a mold, and the plastic springs back to the mold when the vacuum is released. Snap-back thermoforming is used with male molds.

tensile strength

The ability of a material to resist forces that attempt to pull it apart or stretch it. Materials with high tensile strength tend to deform, bend, or stretch before breaking.

thermoforming

A secondary plastic shaping process that forces heated plastic sheets around a mold. Thermoforming processes use mechanical, air, or vacuum pressure.

thermoplastics

A grouping of plastics that can be repeatedly reheated and re-shaped. Thermoplastics are the most commonly used plastics.

tolerances

A range of acceptable part dimensions. Tolerances indicate the allowable difference between a physical feature and its intended design.

twin sheet thermoforming

A thermoforming process that uses two female molds and two sheets of plastic. Thin sheet thermoforming creates two parts that are then welded together to create a single hollow part.

vacuum forming

A thermoforming process that uses negative pressure to pull the part onto the mold. Vacuum forming is one of the most common types of thermoforming.

vacuum holes

Openings in a thermoforming mold by which air is sucked out from between the part and the mold. Vacuum holes, also known as duct holes, are typically located in the lowest points of the mold.

warping

The deformation of a workpiece. Warping occurs when plastic heats unevenly in thermoforming.

wear

The erosion of material as a result of friction, use, or environmental conditions. Wear is often caused by two or more objects rubbing or sliding against each other.

webbing

The wrinkling of the surface of a plastic part. Webbing occurs when plastic is pulled unevenly across or into a mold in thermoforming.

welded

Permanently joined together through the use heat or pressure. Welded plastics can be made of the same material or from two compatible plastics.