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.
Different approaches may be used, depending the the size and shape of the items being molded, as well as the kind of plastic used, but the process follows the same basic principles in all of its forms. A plastic sheet is secured down and placed inside an industrial oven, where it is heated to a pre-determined temperature. When the plastic is soft, it is then stretched over the mold, cooled down using fans, and left to become rigid. There are several types of plastic that may be used, but the most common is HDPE, or "high density polyethylene".
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.
The mechanical technique involves a mold that consists of two halves, a positive upper half and a negative lower half. The sheet of plastic is draped over the bottom part, heated until it is pliable, then the upper part of the mold is lowered onto it, which in turn squeezes the plastic into shape. Air is forced out through vents in the lower half.
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.
This process is often preferred over injection molding by manufacturers since it provides several advantages. For one, thermoform equipment costs a fair deal less than that used for injection molding, and secondly it is much easier and cost efficient to design and build a suitable prototype for this kind of forming.
Different approaches may be used, depending the the size and shape of the items being molded, as well as the kind of plastic used, but the process follows the same basic principles in all of its forms. A plastic sheet is secured down and placed inside an industrial oven, where it is heated to a pre-determined temperature. When the plastic is soft, it is then stretched over the mold, cooled down using fans, and left to become rigid. There are several types of plastic that may be used, but the most common is HDPE, or "high density polyethylene".
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.
The mechanical technique involves a mold that consists of two halves, a positive upper half and a negative lower half. The sheet of plastic is draped over the bottom part, heated until it is pliable, then the upper part of the mold is lowered onto it, which in turn squeezes the plastic into shape. Air is forced out through vents in the lower half.
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.
This process is often preferred over injection molding by manufacturers since it provides several advantages. For one, thermoform equipment costs a fair deal less than that used for injection molding, and secondly it is much easier and cost efficient to design and build a suitable prototype for this kind of forming.
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 about custom plastic pallets then he recommends you visit his friends at PTM: Custom Plastics Injection Molding Company.
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