Plastics no doubt have become part of our daily life. You cannot go a day without encountering an object that is not made of plastic. From your cellphone case, food packaging, and make-up containers, they come in various forms. But, have you ever wonder how they are made?
Thermoforming is a plastic fabrication technique using a heated sheet of plastic and a mold to form the desired geometry of the output. One kind of thermoforming is called plastic vacuum forming.
Plastic vacuum forming uses vacuum technology where its name is derived. This is not a new technology since we started using this process since the 1930s. But due to continuous advancement, modifications have been added to improve the quality of plastics made from vacuum forming.
This process offers low-cost production, ease of tooling, and speed of replication. The economic value plastic vacuum forming provides makes it popular and the most preferred type of thermoforming.
Read on to find out more about vacuum thermoforming- the process, and its benefits and limitations.
PROCESS IN PLASTIC VACUUM FORMING
Since vacuum forming uses a different range of high temperatures depending on the nature of the plastic resin, the machine operator must wear protective gear for safety purposes.
A sheet of plastic is secured between the clamp and the open frame. The plastic sheet can be loaded manually but for automatically operated machines, moving parts must be guarded and interlocked to avoid accidents. Most machines can handle the thickness from 6mm for a single heater to 10 mm for a twin heater.
The plastic is heated with heaters that use infra-red elements. Pyrometer is used to accurately measure the temperature to achieve the melting point. The plastic material then begins to sag. Sometimes machine operators preferred uneven sag that concentrates above the mold to thicken the output.
The heated plastic is lowered to mold and a vacuum allows the sheets to stick on its surface. Mold can be classified as a female (concave) and a male mold (convex). When a female mold is used, tiny holes are drilled to introduce the vacuum.
Vacuum refers to a process where the air is removed. The uneven atmospheric pressure allows the plastic sheet to adhere to the mold.
After the vacuum process, the plastic needs to cool before dismounting. Early removal can result in accidental damage to the product. Since most mold used is made of aluminum which is an excellent conductor of heat, the plastic cools easily. For larger output, a fan or cool mist is used to speed up the process.
After cooling, the mold and the plastic is removed from the machine. This process should be done gradually to avoid damaging the thinnest portions of the output.
To complete the plastic vacuum forming, the plastic should be trimmed and smoothen to achieve the desired look of the newly produced material.
These are the general steps in plastic vacuum forming but they can differ with added procedures depending on the complexity of the product that will be manufactured.
Benefits of Plastic Vacuum Forming
The advantages of plastics vacuum forming include:
Vacuum forming allows designers to customize and test different prototypes in a short time. The molds can be made of wood, aluminum, or plastic itself. If product alterations are needed, new mold can be produced immediately at a low cost.
This technique allows the customization of shapes, colors, and sizes to suit the needs of the customers. With the simple steps in operating the machine and low investment cost, it becomes ideal to use for customized products like dental retainers.
Vacuum forming costs twice less than injection molding. The materials needed for molding and plastic resin are readily available in the market at a low price.
Small capital for manufacturing results in low cost but with high-quality products. Vacuum forming is even ideal for large and small production. The machines used and the price of cost differs with the complexity of the desired product.
The trimmed excess parts of the product can be melted and flattened into sheets for use in the next process.
Vacuum forming can produce a large number of products faster than other thermoforming methods. Manufacturers use 3D design to further expedite the process without compromising quality. Businesses can then think of new products and make them readily available to customers.
This is ideal for products that are consumed at a higher rate like food packaging, cosmetics, and medical and pharmaceutical kits.
Limitations of Plastic Vacuum Forming
Vacuum forming is like any other method of plastic forming which has its drawbacks. Though cost-effective this method is not ideal for all molds with complex geometry. Shapes with deep and different small indentations may not be fully covered by this process. Hence, the prototype may be less the same as the expected output.
Vacuum forming can result in an uneven thickness of the products if other techniques like drape and plug assist are not applied. Since the heated plastic comes in contact with the mold at different rates, it results in thickness inconsistency. A female mold is often thick on the upper parts and thinner on the bottom parts. Male mold is the reverse; it’s thicker at the bottom and thinner at the upper parts.
Bubbles can also form in the plastic reducing its quality. It happens during the cooling process when bubbles are trapped inside that weaken the structure. But this can be avoided by gradually cooling the product in sub-melting temperature.
If the plastic resin is overheated, webbing can form around the plastic. Therefore, the temperature during the heating stage should be monitored.
Remember that these disadvantages of plastic vacuum forming can be avoided if additional machines or methods are added in the process. This would not be the preferred thermoforming method if the cons outweigh the pros.
Thoughts on Do-It-Yourself Vacuum Forming
Various sites on the web offer various steps in making your vacuum forming device. The materials used mostly involved household tools like a vacuum cleaner. The safety of this material depends on the size, quality of materials, and how parts are put together. Though not advisable, if you want to make your own, make sure it comes from a trusted source then follow the directions without taking shortcuts.
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