Vacuum forming process

Why would we use a plug assist process instead of a vacuum forming process ... 

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. 

During stretching flow, material is drawn from one cross-sectional area to another. This type of flow dominates fibre, film, blow molding, and vacuum forming processes (57). Let us assume that a filament of a molten polymer is hauled off under a force F (see Fig. 13.40). Taking the die of the extruder as the origin of the reference frame, the cross-sectional area A of the filament... 

Figure 5. Vacuum forming process for preparing thermal insulation.

The vacuum forming process is shown schematically in Figure 11.12. The plastic sheet is clamped in place mechanically and heated. A vacuum is then placed beneath the hot elastic sheet, and this makes atmospheric pressure push the sheet down onto the contours of the cold mold. The plastic material cools down, and after an appropriate time the cooled part is removed. 

Vacuum Forming n (straight vacuum forming) Process in which heated thermoplastic sheets are converted to other configurations by causing them to flow into molds with application of a vacuum. The simplest, original technique of Sheet Thermoforming. 

Inflation of a sheet clamped over a circular hole suffers the same difficulty. More work has been done with this method (see Dealy, 1982). Inflation has been done with both liquid and gas. The stress and deformation equations are treated in Chapter 1, Exercise 1.10.8, andby Dealy (1982). The results can give the biaxial viscosity function and e up to 2 has been achieved (Rhi-Sausi and Dealy, 1981 Yang and Dealy, 1987). But results so far have been limited to relatively low extension rates. The method requires photography and a somewhat complex apparatus. Inflation tests, however, are similar to the vacuum forming process for making shaped plastic items (Schmidt and Carley, 1975 DeVries and Bonnebat, 1976). Thus there is motivation to continue this work. 

Acceleration of fusion (gelation) AAA Vacuum forming processability AAA-AA Draw-down resistance AAA-AA Long run processability A Processability in foaming extrusion AAA-AA Flexible purpose AA... 

There are of course many applications in which plastics sheet is used in its original flat form, but the fact that it can be heated and shaped makes it of considerable additional interest and this chapter sets out to describe the main thermoplastic sheeting materials available, the facility with which they can be vacuum formed, the nature of the vacuum forming process and the equipment currently in use. 

The vacuum forming process is fairly safe, but in all things, there are dangers both hidden and realized. Proceed carefully and think through each move until you become familiar with the process. 

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