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When pressure forming is being utilized, product turn around can be as brief as a few seconds per part depending upon the specific materials and densities required. Common products produced in this economic way include shrouds, covers, equipment housings, bezels, bases, internal parts and components for computers and peripherals. Industries such as telecommunications, medicine, electronics, instruments, automotive and more frequently use this type of forming for small or medium production runs. Though pressure forming can be used in large runs, the molds are not as durable as those used in alternative methods. Nevertheless, pressure forming is a popular technique as it offers greater precision and improved retention and definition of shape in the mold. Pressure forming can be used to achieve undercuts when necessary as well as multiple textures in a single object making it ideal for complicated or multi-part assemblies.
The process behind pressure forming begins much like traditional thermoforming processes. A sheet of plastic, most commonly ABS, acrylic, PVC or polycarbonate, is attached to a frame or set of guiding chains which feed it into a heater. Using infrared, electric or natural gas the sheet is heated until it becomes soft and pliable. The time and temperature vary considerably based on the specific properties of a given polymer as well as the thickness of the sheet which ranges from 0.0375 inches to 0.093 inches. When thoroughly heated, the sheet is guided into a form station which holds the mold. The mold is usually female or concave in shape and is the inverse of the desired shale and detail of the final product. Similar to other vacuum forming processes vacuum pumps remove the air between the mold and the plastic, pulling the sheet into the mold. In pressure forming, compressed air is also directed at high pressures toward the side of the sheet opposite the mold. This creates up to five times the pressure of regular vacuum forming and creates a much better mold adherence, or the tightness of the mold to the sheet. Sheets take on the specific form of the mold as they are cooled and dried in place until rigid. Reverse airflow on the mold side of the form station is often needed to eject the finished part.
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Pressure Forming Image Provided by Engineered Plastic Products, Inc.
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