Thermoforming pressure forming

The term thermoforming incoroporates a wide range of possibilities for sheet forming but basically there are two sub-divisions - vacuum forming and pressure forming. 

Polypropylene can be extruded into sheets and thermoformed by solid-phase pressure forming into thin-walled containers. Due to its light weight and toughness, polypropylene and its copolymers are extensively used in automobile parts. 

Products are affected dimensionally by the difference between their forming temperature and their product-use temperature. Thus, a plastic s coefficient of thermal expansion and contraction has a significant effect on service conditions. The thermoforming pressure, time, and temperature variations that can exist will affect the final dimensions. Of these factors, evenness in heating throughout the sheet thickness before forming is usually the most important control. Type of heater has a direct effect on obtaining uniform heat... 

Leading the processing growth was the expansion of twin-sheet and pressure-formed plastic products. Fueled mostly by advances in mold technology, material developments, and thermoforming machinery capabilities, technology improvements in the form of machine controls have led to machine designs that are faster and more consistent than was previously possible. As an example advanced materials and... 

Freeman, R., Pressure Forming with Style, SPE Thermoforming Quarterly, Spring 1999. 

Figure 7.10 Thermoforming (1) female mould, vacuum, no prestretching (2) female mould, pressure forming with male or plug, prestretching (3) male mould, vacuum, with pressurised air prestretch...

In general only the simpler materials can be thermoformed on cylinders using vacuum (e.g. PVC, polystyrene, PVdC coated PVC). Platens using pressure forming, particularly with plug assistance, not only offer more uniform blisters but can utilise the more complex materials, e.g. Aclar/PVC, polypropylene, coextrusions (Figure 13.4). 

There are many methods for molding the sheet of plastic, once it has been softened by heat. The simplest are drape forming, vacuum forming, and pressure forming. Other thermoforming techniques are modifications or combinations of these basic methods. 

This term refers to the normal method of most thermoforming processes in which a material is formed at a temperature above the melting point in semicrystalline polymers or above the softening point in amorphous polymers. See Pressure Forming, Vacuum Forming and Thermoforming,... 

Pressure forming refers to a type of thermoforming process in which pressures greater than atmospheric are used to force material against the contours of a mold. Deep draw PS deli containers and PP barrier food containers are product examples. See Thermoforming and Vacuum Forming. 

The types of thermoforming processes are vacuum forming, pressure forming, melt phase thermoforming, and matched mold forming. Examples of applications of thermoformed parts are ... 

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