Over the past few years, we’ve covered most of the common techniques for manufacturing plastics products. These include injection moulding, additive manufacturing, spin moulding, and 3d printing. However, to date we haven’t written about a technique that is becoming increasingly important to the medical device industry: thermoforming.
Thermoforming was first pioneered as early as the 1870’s by John Westley Hyatt, a mechanical engineer who some in the industry refer to as the father of modern plastics processing. Hyatt was trying to find innovative ways to use two newly available materials – celluloid and cellulose nitrate. With the help of fellow researcher Charles Burroughs, Hyatt developed the first thermoforming process. Hollow tubes of plastic were placed inside moulds made of steel and shaped like the desired product. Next, hot steam was used to soften the cellulose and force it to shrink around the inside of the mould. After cooling the cellulose and mould with water, the moulds could be opened and the products trimmed to eliminate any defects.
Unlike Hyatt’s technique, which depended on a chemical involving hot steam to soften and shape the feedstock, modern techniques depend solely upon heat and changes in pressure to achieve the same results. This produces end-products that are chemically inert.
Modern thermoforming takes two forms – pressure forming and vacuum forming. In pressure forming, compressed air is injected into the hot plastic film, forcing it to expand into the shape of the mould it is inside of. Vacuum forming, on the other hand, requires that a thin plastic sheet be stretched over the outside of a mould. Then, a vacuum is applied form within the mould, pulling the plastic sheet tightly around the outside of the mould.
Today, thermoforming has become a sophisticated technique for making high-quality, chemically inert, and customizable plastic products. It is this combination of attributes that has made thermoforming one of the most important technologies in the medical device industry, where consistency, safety, and customization are highly sought after.
As reported in Medical Plastics News, thermoforming often used in conjunction with innovative foam products – often, foam blown with an inert gas like nitrogen is enclosed within a thermoformed outer layer. This combination produces a product that can take advantage of the advantages of both types of technology while avoiding the disadvantages.