One common manufacturing process that can be used to make a wide range of products such as toys, parts for cars and aircraft, electronic components, and packaging, involves using a thin sheet of heated plastic and forming it into various shapes. Known as thermoforming, there are several different techniques, but all result in producing items made from molded plastic.
There are multiple ways to thermoform plastic, but the general process is similar. A plastic sheet is held in place firmly as it's heated to the point of pliability in an industrial oven, it is then stretched over a mold, and cooled down with fans until it is firm. While there are multiple types of plastic that can be used, HDPE or "high density polyethylene" is the most popular. The technique used depends on the type of plastic and size of the mold.
A vacuum thermoform process involves the use of a temperature-controlled vacuum unit in which both the mold and the sheet of plastic are placed, with the latter positioned above the former. The plastic is heated until soft, then the mold is raised to contact it, while air is suctioned out from underneath, creating an airtight fit which forms the desired shape.
The pressure method relies on air pressure to force the heated sheet of plastic into or around the mold. Compressed air is delivered from the top of the machine with a pressure that ranges from 15 to 300 pounds per square inch, depending on the size of the molded forms. The object forms as the plastic is pressed into the mold.
A mechanical process uses a two-piece mold that has a top and bottom part. The plastic sheet is laid on top of the bottom, or negative half of the mold, and is then heated until soft, at which point the top or positive mold is lowered onto it, squeezing the plastic into the desired shape, and allowing air to escape through vents in the bottom piece.
Other methods of forming are used as well in certain instances. A technique known as twin sheet forming that involves melting and fusing pieces to each other, is used to join together components separated by an empty space. Some plastic parts are formed by way of pressure diaphragm forming which uses pressurized fluid and a vacuum.
Manufacturers utilize this process because it has numerous advantages over other techniques, namely injection molding. The equipment required for injection molding costs considerably more, especially that used to produce large objects. It is also challenging to construct a suitable prototype for this method of molding, whereas with the thermoform method, this can be done simply and cost effectively.
There are multiple ways to thermoform plastic, but the general process is similar. A plastic sheet is held in place firmly as it's heated to the point of pliability in an industrial oven, it is then stretched over a mold, and cooled down with fans until it is firm. While there are multiple types of plastic that can be used, HDPE or "high density polyethylene" is the most popular. The technique used depends on the type of plastic and size of the mold.
A vacuum thermoform process involves the use of a temperature-controlled vacuum unit in which both the mold and the sheet of plastic are placed, with the latter positioned above the former. The plastic is heated until soft, then the mold is raised to contact it, while air is suctioned out from underneath, creating an airtight fit which forms the desired shape.
The pressure method relies on air pressure to force the heated sheet of plastic into or around the mold. Compressed air is delivered from the top of the machine with a pressure that ranges from 15 to 300 pounds per square inch, depending on the size of the molded forms. The object forms as the plastic is pressed into the mold.
A mechanical process uses a two-piece mold that has a top and bottom part. The plastic sheet is laid on top of the bottom, or negative half of the mold, and is then heated until soft, at which point the top or positive mold is lowered onto it, squeezing the plastic into the desired shape, and allowing air to escape through vents in the bottom piece.
Other methods of forming are used as well in certain instances. A technique known as twin sheet forming that involves melting and fusing pieces to each other, is used to join together components separated by an empty space. Some plastic parts are formed by way of pressure diaphragm forming which uses pressurized fluid and a vacuum.
Manufacturers utilize this process because it has numerous advantages over other techniques, namely injection molding. The equipment required for injection molding costs considerably more, especially that used to produce large objects. It is also challenging to construct a suitable prototype for this method of molding, whereas with the thermoform method, this can be done simply and cost effectively.
About the Author:
Genevive B. Mata has taught plastics molding techniques for over 15 years. He specializes in injection molding and thermoforming. If you are interested in learning more plastic solutions then he recommends you visit his friends at PTM: Plastic Injection Molding Services.
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