Plastic thermoforming

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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.

Contents 1 Types of thermoforming 2 History 3 Engineering 4 Applications 5 Industry 6 References 7 External links 8 See also

Types of thermoforming

Main article: Types of thermoforming

There are several categories of thermoforming, including vacuum forming, pressure forming, twin-sheet forming, drape forming, free blowing, and simple sheet bending.

History

Historically, thermoforming is one of the oldest plastics processes. Baby rattles and teething rings were formed of camphorated cellulose nitrate or celluloidTM in the 1890s. The industry did not grow substantially until the 1930s, until the development of cellulose acetate and acrylic provided the industry with formable sheet. The earliest roll-fed thermoforming machines were developed in the late 1930s in Europe.

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 ^[3]. 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.

Industry

The more than USD10 billion North American market has traditionally been ¾ thin-gauge and ¼ heavy-gauge. In 2003, there were about 150 thin-gauge thermoformers in North America. Sixty percent formed proprietary products. Thirty percent were custom formers and 10 percent were OEMs with in-house forming capability. There were nearly a dozen thin-gauge formers having annual sales of at least USD100 million. The largest had annual sales in excess of USD1,000 million. There were about 250 heavy-gauge formers in North America. Nearly all were custom formers. Only two or three heavy-gauge formers had annual sales of more than USD100million. The largest had annual sales of about USD140 million ^[2].

References

1. J.L. Throne, Understanding Thermoforming, Hanser Gardner Publications, Inc., Cincinnati OH, 1999.
2. The Industrial Thermoforming Business: Review and Outlook, Plastics Custom Research Services, Advance NC, 2004.
3. J.L. Throne, Technology of Thermoforming, Hanser Verlag, Munich, 1996.

External links

• The guide to Thermoforming Process & Troubleshooting
• Plastic Thermoforming Process vs. Injection Molding - How to Choose?

See also

• Thermoplastic
• Vacuum forming
• Injection moulding