Thermoforming

Pressure Forming

What is Pressure Forming for Plastics?

Plastic pressure forming starts with an extruded sheet of plastic secured in a clamp frame. Next, the plastic moves into an oven and heated until it reaches a malleable temperature.
Afterward, we removed the clamped sheet from the oven. It is then sandwiched between a pressure box and the forming tool.

Preventing Thinning

To reduce the amount of material thinning in parts with a deep draw, plug assists are often used. This pre-stretches the plastic sheet and reduces the amount of material thinning that can occur.

A Plug Assist is called for when using a negative mold with pre-stretching. The mold is pushed into the heated plastic sheet to create a seal on the edge. At the same time, the plastic sheet pushes into the mold using the plug assist.

As it enters the hot sheet, air between the sheet and the mold is compressed, causing the sheet to undulate around the plug. The hot plastic sheeting is prevented from directly contacting the cooler mold as the sheet stretches. This ensures maintaining a consistent material dimension.

Providien uses a thinner starting gauge plastic, which reduces both raw material and processing cost.

Forming the Part

With the sheet secured, a strong vacuum applies up to 85 PSI pressure to the back of the sheet. The suction pulls the sheet over the tool and formed.

The vacuum pressure forces the part to match the contours of the tool. Following forming, the part cools on the tool. The part is free of molded stress and ready for finishing.

Trimming the Part

The newly pressure formed part gets processed through a 5-axis CNC trimming station. In the CNC station, it is expertly trimmed to its final dimensions. Further fabrication steps may be performed at this point before the final product is ready for release.

Advantages of Pressure Formed Parts

The best features of pressure formed parts include:
– tight tolerances
– crisp detail
– formed-in texture
– formed-in threaded inserts
– custom color parts without the need for paint.

Pressure formed parts have aesthetics that rival injection molded parts at a fraction of the tooling cost.

The Value of Undercuts

Undercuts are another benefit of pressure formed parts. This allows the attaching of parts to mated pieces. Undercut parts can also be more easily attached to a chassis or frame. When compared to traditional vacuum forming techniques, this reduces costs and increase repeatability.

This provides a cost great advantage when compared to traditional vacuum forming techniques.

Great Results for Less

Pressure formed parts provide cosmetically similar parts that are on par with injection molded parts. Pressure formed tooling is 60%-80% less expensive than injection mold tooling. Of course, this depends on the part geometry and size of the parts.

Pressure forming competes well against other large part processes such as reaction injection molding (RIM) and structural foam molding.

Total program cost including both tooling and unit cost are typically favorable for pressure forming.

Another value to pressure forming is that it does not require paint. This feature makes it more environmentally friendly. And at the same time, it provides for better cosmetics when compared to reaction injection molding (RIM) and structural foam.

A vacuum formed gray plastic medical device cover.