Plug assisted thermoforming

We use plug assisted thermoforming when we wish to make thick-walled products or thin-walled, deep draw products. The principal steps of die process are illustrated in Fig. 16.2. The first two stages are similar to those of vacuum forming. Once the sheet has been clamped, a plug made from a material with low heat conductivity is dirust downwards into the cavity, 

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Figure 3.62 Plug-assist thermoforming using vacuum.

In plug-assist thermoforming, a mechanical device is used to help stretch the sheet Into the mold, as shown in Fig. 10.6. Where the plug touches the material, it is cooled, and the material does not stretch much more. The optimal shape for the... 

FIGURE 18.14 Steps in plug-assisted vacuum thermoforming. Initially vacuum is applied and the plug is pulled into the sheet pushing it into the mold. Further vacuum pulls the sheet against the walls of the mold. Finally, vacuum is turned off and the plum and formed product removed. 

Figure 3.63 Reverse draw thermoforming with plug-assist and vacuum.

Thermoformed (Coextruded Plug-Assisted Twin-Sheet) Fuel Tanks Show Promise, MP, Apr. 2000. 

Thermoforming has close similarities with vacuum forming, except that greater use is made of air pressure and plug assisted forming of the softened sheet. The process is invariably automated and faster cycle times are achieved than in the vacuum forming process. Only thermoplastic sheet can be processed by this method. 

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). 

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