Thermoforming is a generic term that refers to a process that begins with an extruded sheet of plastic. The process involves heating the plastic sheet to a temperature range where it is soft or malleable. Thermoforming represents a group of sheet-forming processes that includes vacuum forming, drape forming, billow of free bubble forming, mechanical bending, matched mold forming, billet molding, pressure forming, and twinsheet forming. The thermoforming process is usually segmented into thin-gauge and thick-gauge markets. Thin-gauge markets tend toward disposable products such as rigid packaging. Thick-gauge markets tend toward permanent or industrial products. Thermoforming is a low-temperature, low-pressure process in which the sheet is handled as a rubbery solid or elastic liquid. Molds are usually single-surfaced. Mold materials are relatively inexpensive and are often fabricated in relatively short times. Thick-gauge thermoforming produces a limited number of products at production costs below those produced by other processes such as injection molding. In contrast the advantages thermoforming has several disadvantages. The incoming material is an extruded sheet, with the extrusion process adding 50% or more to the cost of the formed product. Thermoforming generates substantially more trim than other processes and that trim must be ground and re-extruded at additional cost.
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