Plastic Thermoforming

Thermoforming is a manufacturing process for thermoplastic sheet or film. The sheet or film is heated between infrared natural gas or other heaters to its forming temperature. Then it is stretched over or into a temperature-controlled, single-surface mold. Cast or machined aluminum is the most common mold material, although epoxy and wood tooling are sometime used for low volume production. The sheet is held against the mold surface unit until cooled. The formed part is then trimmed from the sheet. The sheet trim is usually reground, mixed with virgin plastic, and reprocessed into usable sheet.

Engineering

Thermoforming has the ability to fabricate thin-walled parts with large areas, using relatively inexpensive, single-sided tooling. Its deficiencies – variable wall thickness, added cost of sheet and trim regrind, and extensive trimming – have been offset by the ability to economically produce a few, thick-walled parts or very many thin-walled parts.

Thermoforming has benefited from applications of engineering technology. Infrared radiation is the primary method of heating sheet. The softened sheet is arithmetically treated as a rubbery elastic membrane as it stretched mechanically or pneumatically into or onto a cooled single-surface rigid mold. Finite element analysis is used to predict local wall thickness of the formed sheet. Heavy-gauge sheet is trimmed with multiaxis routers adapted from the woodworking industry.

Applications

Elastomers and Thermosets can not be formed by the Thermoforming methods because of their cross-linked structure – they do not soften when heated.

Thermoplastics which may be processed by the thermoforming method are:

• Polypropylene (PP)
• Polystyrene (PS)
• Polyvinyl Chloride (PVC)
• Low Density Polyethylene (LDPE)
• High Density Polyethylene (HDPE)
• Cellulose Acetate
• Polymethylmethacrylate (PMMA)
• Acrylonitrile-Butadiene-Styrene (ABS)

Thermoforming is widely used in the food packaging industry for manufacturing ice cream and margarine tubs, meat trays microwave containers, snack tubs sandwich packs etc.

Thermoforming is also used for manufacturing some pharmaceutical and electronic articles, small tools, fasteners, toys, boat hulls, blister and skin packs.