Thermoforming vacuum form

Film Processing Methods Fluorinated ethylene-propylene resins are processed by conventional melt-extrusion techniques. Films may be thermoformed, vacuum-formed, heat-sealed, heat-bonded, welded, metallized, or laminated. 

Processing methods extrusion, injection molding, blow molding, thermoforming, vacuum forming... 

Thermoforming vacuum forming, pressure forming Other processes... 

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

The chassis is made from a 1/4 in. sheet of either ABS or TPO vacuum formed into a tub and reinforced with reinforced pultruded glass fiber-TS polyester plastic tubing. The hood and other products are being made from a 20 mm thick sandwich of thermo-formed PPO-alloy skins, glass fabric infused with thermosetting vinyl ester, and a urethane foam core. The bumper and front fascia is thermoformed from a polyolefin elastomer sheet with an UV-resistant cap layer of DuPont s Tediar PVF film. The dash and... 

We use plug assisted thermoforming when we wish to make thick-walled products or thin-walled, deep draw products. The principal steps of the 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 thrust downwards into the cavity,... 

Food packaging, cups and dairy containers from thermoformed sheets, vacuum-formed packages... 

We can model the thermoforming process by examining a preheated sheet that is vacuum-formed directly onto the walls of a cavity. The softened sheet undergoes a... 

Figure 7.83 Schematic illustration of (a) vacuum-forming and (b) plug-forming variations of thermoforming. From Z. Tadmor and C. G. Gogos, Principles of Polymer Processing. Copyright 1979 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

The heat exchange function of the mold leads to a conflict of interest. Thermoforming is carried out at relatively low pressures, very low pressures in the case of vacuum forming, so molds can be constructed from light, inexpensive, easily shaped materials such as wood, plaster, or epoxy resins. However, these materials have poor thermal conductivity. Thus such molds do not function well as heat exchangers. 

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. 

Vacuum Forming - Vacuum forming is a type of thermoforming process consisting of preheating the plastic sheet prior to forming. The sheet is formed into the female mold by application of vacuum through holes in the mold. 

The choice of the process depends, inter alia, on the requirements of the end product with injection molding, narrower tolerances can be achieved than with thermoforming or rotomolding, for example. The nature of the polymer also plays a role it depends, for instance, on the stability of the polymer at the high temperatures in a process. The length of the rubbery region on the temperature scale determines the ease of vacuum forming too brittle a polymer is difficult to machine, for example. 

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