Process Advantages

In the mid-1960's, the appearance preferences of consumers began to change. Automobiles, refrigerators and typewriters began to give up their general rounded-off look. Clearly defined shapes with prominent lines and sharp, crisp corners began to be considered as the modern, contemporary styling for new products. Thermoforming's inability to provide these clearly defined details became a serious limitation to the further growth of the process into consumer oriented industrial product lines. The thermoforming industry responded to this changing marketplace with a new generation of improved plastic materials and refined processing techniques.

Among all of the thermoforming processes that were available, pressure forming offered the best chance of meeting the new design criteria. The higher forming pressures associated with pressure forming provided the capability of producing parts with sharp, well-defined details.

Whereas vacuum forming was limited to a theoretical maximum forming pressure of 14.7 psi, pressure forming, as the name implies, uses air or liquid pressure to push the softened sheet into a desired shape which is usually provided with a female die. The use of these higher forming pressures (in the ranges of 20 to 80, with an extreme of over 200 psi) made it possible to push the softened sheet into sharper, more clearly defined details.

The very rapid forming speeds that were possible with these increased pressures, coupled with hotter dies, minimized the thinning out problem in corners that was described earlier.

This was due to the fact that those portions of the hot sheet which first contacted the die did not have sufficient time to cool and thus regain the strength necessary to resist being stretched out toward the corners.

In some cases, the higher pressures and hotter dies actually allowed the plastic in the softened sheet to flow short distances. This also helps allow the plastic to conform to fine details on the surface of the die.

Thermoformed parts were no longer limited to the relatively large radii and the soft contours that had been thermoforming's hallmark prior to that time.

Thermo Pressure Forming's higher pressures made it an ideal process for producing the thicker walled business machine housings and other types of cabinetry which came into being at the same time. The simultaneous rapid increase in the cost and in the delivery schedules for the molds required for other more capital-intensive processes also helped establish the new pressure forming segment of the thermoforming industry. That situation has not changed. Today, pressure forming enjoys a significant share of the small-to-medium volume part of the housing and cabinetry market.

Thermoforming's primary advantage over other plastics processing techniques has always been its ability to produce very large, thin walled, lightweight, three-dimensional parts with a relatively low initial investment in time and cost for the dies and for the forming machines.

Thermo Pressure Forming retains all of these advantages while providing the added capability of being able to provide clearly defined surface details and excellent appearance qualities.

The appearance of Thermo Pressure Forming compares favorably with the older closed mold processes such as compression and injection molding.

The large sizes of parts which can be produced rival those now being made by newer processes such as injection molded structural foam and reaction injection molding.

The low initial investment in dies and machines brings Thermo Pressure Forming into the same range as that required for reinforced processes such as hand lay up or spray up and resin transfer molding.

Thermo Pressure Forming's ability to produce lightweight, non-corroding, pre-colored, complex shapes with low cost machines and dies far exceeds what can be achieved with sheet metal fabrication procedures.

Each of these other manufacturing techniques has its own unique advantages and disadvantages. However, none of the other processes offers the same favorable compromise between capability, limitations and cost considerations that are attainable with Thermo Pressure Forming.

Thermo Pressure Forming compares favorably in one area or another with each of these previously mentioned processes. However, Thermo Pressure Forming's primary rival is injection molding.

Most experienced design engineers are familiar with the widely used injection molding process which has been in existence since 1927.

The author assumes that the reader is familiar with the primary plastic materials and basic design requirements for injection molded parts, and will draw comparisons between Thermo Pressure Forming and injection molding in order to clearly define the differences between these two processes.

Space does not permit drawing comparisons with all of the competing processes mentioned above. However, the reader's attention is directed to Table 3 which rates the attributes of these other important manufacturing processes.