December 29, 2022 in blog posts

Pressure forming vs Vacuum Forming

Prestige Tooling, LLC: pressure and vacuum forming molds.

Vacuum forming is a method of transforming plastic sheet into finished parts through heat and vacuum pressure. The plastic sheet is heated to its particular thermoforming temperature and immediately shaped into the desired configuration. At processing temperatures, the sheet is very pliable, enabling it to be formed rapidly with great detail and minimum force. Pressure is maintained until the part has cooled.

Our vacuum forming molds are primarily used in two separate, but similar processes to achieve the desired outcome of the end user.

1. Vacuum Forming: With vacuum forming, a positive or negative mold (male or female) of the desired part is created and mounted into a vacuum forming machine. A sheet of plastic (a blank) is clamped into the clamp frame of the vacuum forming machine to make sure that the sheet is held firmly in place during the vacuum forming process. The plastic sheet is moved into the vacuum forming oven, where it is heated to the desired level of flexibility. Once heated, the plastic blank is moved out of the oven and over the vacuum forming mold. The plastic sheet is then draped over the mold and a vacuum is applied to quickly remove the air between the two. Removing the air between the mold and the plastic blank allows atmospheric pressure to press (form) the now pliable plastic to the mold. Cooling fans are applied once the plastic is formed to the shape. When the part has cooled, it is removed from the mold.

2. Pressure Forming: To thermoform plastic parts that require more design detail such as sharp edges, close dimensional tolerances, and detailed surface shapes, pressure forming would be used over vacuum forming. Pressure forming applies high pressure to the plastic blank along with the vacuum to form the desired part. Common pressures are 35 to 60 PSI, however, higher pressures may be required for large parts of higher hot strength materials. The heated plastic sheet is draped into a negative mold and a pressure plate is clamped on top of the negative mold. Vacuum is applied to remove the ambient air between the mold and the plastic sheet, and compressed air is used to pressurize the empty space in the mold cavity. The added pressure literally pushes (forces) the pliable plastic into the negative mold shape forcing sharp edges, undercuts, and other high tolerance design shapes. The vacuum and pressure are applied until the part cools and can be removed from the mold.

As with vacuum forming, there are several pressure forming techniques used depending on the design of the part being formed.

Feel free to contact Prestige Tooling with any questions or feedback and stay tuned for more vacuum forming mold information.

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