The Thermo Pressure Forming Process

A step-by-step review of the Thermo Pressure Forming process is as shown here. There are many variations of the process, however the technique described here is common.

The precut sheet stock is clamped into a frame that will carry it through the process. The clamp frame carries the sheet into the oven (Fig. A) where it is heated to the forming temperature.

The frame moves the sheet from the oven to a sealing position on the top of the forming die & the pressure chamber moves into position and seals the softened sheet against the top of the die. (Fig. B)

Low air pressure is introduced under the sheet to blow a billow and prestretch the softened sheet. (Fig. C)

The low pressure air under the sheet is released and a vacuum is drawn to reverse the billow and pull the sheet into the die. (Fig. D) Air pressure is introduced above the sheet to finish the forming process.

A common variation of this process is the addition of a plug assist as shown in Fig. E . In this case the plug descends from above to reverse the billow and push the softened sheet into the die.

In either case pressure is maintained and the formed sheet is held in contact with the die until it cools sufficiently to retain its shape. (Fig. F)

The clamping frame lifts the formed part out of the die and the clamps open. (Fig. G)

The part is removed from the frame and trimmed to its final size. (Fig. H)

With the exception of the dwell times required to heat and cool the sheet, all of these individual steps take place in a smoothly blended sequence. Accurate time, temperature and pressure sequencing is mandatory and the importance of good equipment, especially good controls, cannot be overemphasized.