Vacuum forming

A simple visualization of the forming process

Vacuum forming, commonly known as vacuuforming, is a simplified version of thermoforming, whereby a sheet of plastic is heated to a forming temperature, stretched onto or into a single-surface mold (BrE, mould), and held against the mold by applying vacuum between the mold surface and the sheet. The vacuum forming process can be used to make most product packaging, speaker casings, and even car dashboards. The first commercial manufacturer of vacuum-formed plastics was Robinson Industries of Coleman, Michigan.

Normally, draft angles must be present in the design on the mold (a recommended minimum of 3°). Otherwise, release of the formed plastic and the mold will most likely be difficult.

Vacuum forming is usually, but not always, restricted to forming plastic parts that are rather shallow in depth. A thin sheet is formed into rigid cavities for unit doses of pharmaceuticals and for loose objects that are carded or presented as point-of-purchase items. Thick sheet is formed into permanent objects such as turnpike signs and protective covers.

Relatively deep parts can be formed if the form-able sheet is mechanically or pneumatically stretched prior to bringing it in contact with the mold surface and before vacuum is applied.

Suitable materials for use in vacuum forming are conventionally thermoplastics. The most common and easiest to use thermoplastic is High Impact Polystyrene Sheeting (HIPS). This is molded around a wood, structural foam or cast/machined aluminum mold and can form to almost any shape. Vacuum forming is also appropriate for transparent materials such as acrylic which are widely used in applications for aerospace such as passenger cabin window canopies for military fixed wing aircraft and "bubbles" for rotary wing aircraft.

Typical heavy gauge vacuum forming applications

Original equipment manufacturers (OEMs) utilize heavy gauge vacuum formed components for production quantities in the range of 250 - 3000 annual production volume. Vacuum-formed components can be used in place of complex fabricated sheet metal, fiberglass, or plastic injection molding. Typical industry examples include:

• Kiosks and automated teller machines
• Enclosures for medical imaging and diagnostic equipment such as magnetic resonance imaging (MRI) machines
• Engine covers in a truck cab
• Railcar interior trim and seat components

Common problems encountered with vacuum forming

• Moisture absorption: absorbed moisture expands forming bubbles within the plastic's inner layers. This will be solved by drying the plastic for an extended period at high but sub-melting temperature.
• Webs form around the mold, which is due to overheating the plastic and so must be carefully monitored. Webbing can also occur when a mold is too large or parts of the mold are too close together.
• Objects that are formed often stick to the mould, so make sure there is an angle of 3 degrees or more.

Types of Vacuum Forming Moulds

Vacuum forming tool

Wood Patterns - wood patterns are generally the first stage to a vacuum forming project. They are relatively inexpensive and allow the customer to makes changes to their design very easily. The number of samples that one is able to get from a wood pattern depends on the size of the part and the thickness of the material. Typically, wood patterns are used to gauge general functionality of both the part and the thickness of the material. Once the specifications of the part have been met, the wood pattern is then used to create a ceramic composite mould, or cast aluminum mould for regular production.

Cast aluminum Moulds - Cast aluminum moulds are cast at a foundry and typically have temperature control lines running through them. This helps to regulate the heat of the plastic being formed as well as speed up the production process. Aluminum molds can be male or female in nature and can also be used in pressure forming applications. The main drawback with this type of mould is cost.

Machined aluminum Moulds - Machined aluminum moulds are like cast aluminum except they are cut out of a solid block of aluminum using a CNC machine and some sort of CAD program. Typically machined aluminum is used for shallow draw parts out of thin gauge material. Applications may include packaging as well as trays. Again, cost is a significant factor with this type of tooling.

Composite Moulds - Composite moulds are a lower cost alternative to cast or machined aluminum moulds. Composite moulds are typically made from filled resins that start as a liquid and harden with time. Depending on the application, composite moulds can last a very long time producing high quality parts. Within the category of composite moulds, the subset of "Ceramic" moulds has consistently proven to be the most durable. While not temperature controlled, these moulds can run nearly as fast as Cast or Machined aluminium, yet at a substantially lower price point. Suitable for all but the highest volume production and strictest tolerances. Source: Composite Vacuum forming mould

See also

• Vac-u-form - a toy from the 1960s based on vacuum forming

Further reading

• D.E. Walsh, Do It Yourself Vacuum Forming for the Hobbyist, Workshop Publishing, Lake Orion, MI, 2002
• Soroka, W, "Fundamentals of Packaging Technology", IoPP, 2002, ISBN 1-930268-25-4
• Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6

External links

• A Vacuum Forming Guide
• Vacuum Forming Process Description