As described by The Open University in their article, “Vacuum Forming (Thermoforming),” vacuum forming is a widely used technique for shaping thermoplastic materials into a variety of products. This process involves heating a thermoplastic sheet, softening it, and then using a vacuum to force it against the contours of a cooled mold.
In traditional vacuum forming, a thermoplastic sheet ranging from 0.60 to 13 mm in thickness is clamped over a female die impression. The sheet is then heated to temperatures between 115˚C and 165˚C using infrared heaters, quartz lamps, or resistance heaters. Once the sheet reaches the desired temperature, a vacuum is created below it, pulling the softened sheet down into the mold. The areas of the sheet that contact the mold last are typically the thinnest, allowing for excellent detail reproduction from the mold.
In plug-assisted vacuum forming, the process is enhanced by the use of a plug or plunger, which helps to shape the material before the vacuum is applied. This method, along with plug-assisted pressure forming, allows for greater control over the material’s thickness and ensures more uniformity in the final product. The process can be automated using microprocessor control systems, enabling high output rates of up to 1,500 parts per minute on multi-cavity dies.
A wide range of thermoplastic materials can be used in vacuum forming, including polystyrene, ABS, PVC, acrylic, polycarbonate, and polyethylene. These materials are chosen for their good “hot melt strength” and ability to be easily formed just above their glass transition temperature.
Vacuum forming is utilized in the production of many everyday items, such as disposable drinking cups, meat trays, and even large components like canoe hulls. The process is especially well-suited for creating large, thin-walled parts with generous radii and flowing contours. While the process allows for considerable flexibility in design, secondary operations like drilling or sawing may be required for features such as holes or openings.
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Article with all rights reserved, courtesy of open.edu
