Thermoforming operations are a very important part of plastic shaping processes. There are lots of kinds of parts are produced with thermoforming processes. Actually, general types of thermoforming processes include two steps: Heating the plastic sheet or film and thermoform it.
The three types of thermoforming processes are most common;
- Mechanical thermoforming processes,
- Vacuum thermoforming processes,
- Pressure thermoforming processes.
How The Plastic Sheets Are Heated?
In general, heat radiators are used to heat the plastic sheet. Sufficient heat must be provided to make plastic sheets can be formed. Actually, the thermoforming process is secondary right after the production of plastic sheets and films. After the production of sheets and films, the thermoforming process is applied.
To decrease the costs of heating and production time, plastic films and sheets can be produced at the temperature that they can be formed right after the production.
Mechanical Thermoforming Processes
The application of the mechanical thermoforming process is very simple. As we stated above, heating of plastic sheet must be accomplished. After the heating, the plastic sheet is clamped from both sides, and pair of negative and positive molds are drawn on a plastic sheet.
In this method, the surface characteristics of produced parts are superior compared with others. But the main downside of mechanical thermoforming is the requirement of two halves of molds.
Pressure Thermoforming Process
In pressure thermoforming, the pressure is used to stretch the plastic sheet upon mold. At the upper side of the mechanism that sheet plastic is stretched, the air is blown to obtain pressure effect.
This pressure stretches the heated plastic sheet on negative or positive molds. Yes, there are generally two types of molds are used; negative molds which are concave in shape, and positive molds which are convex in shape.
At the first sight, you may not see any differences in the application of positive and negative molds. But there is a very important difference in the contacting surfaces with mold, in positive and negative molds.
In negative molds, the surface contacts with mold will that the exact shape of the mold. In positive molds, the situation is also like that. So in terms of the shape and thickness characteristics of produced plastic parts, this is a very important consideration.
Thinning is another important parameter of the pressure thermoforming process. When a specific thickness of the plastic sheet is stretched on mold, the surface area of the plastic sheet will increase. This means that the thickness will decrease. This phenomenon is called thinning.
Thinning can be compensated with the pre-stretching of the plastic sheet with the application of vacuum.
Vacuum Thermoforming Process
In the vacuum thermoforming process, the vacuum is used to stretch plastic sheets on molds. The other parameters are completely the same with the pressure thermoforming process.
There are small orifices beneath the mold that air is evacuated to obtain the vacuum effect. This vacuum stretches the plastic part on molds.
The main disadvantage of the vacuum thermoforming process is that the only negative pressures up to 1 atm can be obtained in theory. But in pressure thermoforming processes, 3-4 atm of pressures can be applied.
What Kinds Of Products Are Produced With Thermoforming Processes?
The packaging industry is the most important industry that thermoforming processes are used. Thermoforming processes can be used to produces packages right after the production of consumer products that are produced. Produced plastic parts with thermoforming can be used to package these consumer products in the same production site.
Blister and skin packs are the most important applications of thermoforming processes. These packs can be very useful packs to pack different kinds of products starting from cosmetics to toys.
Also, big, thick, and hollow parts can be produced with thermoforming processes. Bathtubs, door coatings, advertisement panes, machinery coverings, etc.
What Kinds Of Materials Are Used In Thermoforming Processes?
In thermoforming processes, only thermoplastic polymers can be used. Thermosetting polymers are not proper for thermoforming processes because of the cross-linking occurrence. After the sheets and films are formed with thermosetting, cross-linking between molecules are occurred. Because of this reason, they can not be used for re-heating, softening, and re-shaping after the formation of thin sheets or films.
The most common thermoplastics that are used in thermoforming operations;
- Polyethylene and polypropylene,
- Cellulose acetate,
- PVC and acrylics.
Conclusion For Thermoforming Processes
Thermoforming processes are very important secondary processes that are generally applied in different sub-industries such as packaging industries.
This article can be a summary of information about thermoforming processes. Do not forget to leave your comments and questions below about the thermoforming processes.
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