Plastic pressure forming starts with an extruded sheet of plastic that is secured in a clamp frame and then brought into an oven to be heated to a formable temperature. The clamped sheet is then removed from the oven and brought between a pressure box and the forming tool. A plug assist may be utilized to pre-stretch the plastic sheet for parts with a deep draw. This is done to reduce the amount of material thinning that can occur. The plug assist also ensures the part will have a more uniform wall thickness in the finished part and can drive cost savings. By reducing the amount of thinning in the material, Providien Thermoforming will start with a thinner starting gauge of material, which reduces both raw material cost , and processing cost.
A strong vacuum then pulls the sheet into or over the tool and pressure at up 85 PSI is applied to the backside of the sheet. Afterward, the part is cooled, and then unrestrained in the tool, (leaving a part that is free of molded in stress). The pressure formed part is then placed into a 5-axis CNC trimming station where it is trimmed to its final dimensions.
Advantages of Pressure Forming Parts
The best characteristics of pressure formed parts include tight tolerances, crisp detail, formed-in texture, formed-in threaded inserts and 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.
An additional benefit of the pressure forming process is the use of undercuts which can allow for parts to be attached to mating parts as well as to the chassis or frame in ways that can reduce cost and increase repeatability as compared to traditional vacuum forming techniques.
Pressure formed parts provide cosmetics that are on par with injection molded parts. Pressure formed tooling is typically 60%-80% less expensive than injection mold tooling depending on the part geometry and size of the parts. Pressure forming can also compete favorable against other large part processes such as reaction injection molding or RIM and structural foam. Total program cost when both tooling and unit cost are included are typically favorable for pressure forming. Additionally, pressure forming does not require paint and is therefore more environmentally friendly while simultaneously providing better cosmetics when compared to reaction injection molding (RIM) and structural foam.