Industries which produce items such as packaging, automobile and aircraft parts, toys, and electronic components often employ a manufacturing process that consists of heating thin sheets of plastic and applying them to molds to form numerous shapes. This method is called thermoforming, and it can be done in several ways which all produce molded plastic objects.
Although there are some variations in method, the basic process is the same. The plastic sheet is clamped down and heated in an industrial oven to a specific temperature, once pliable, it is stretched over the mold, cooled down with fans, and left to harden. The method used depends on the type of plastic and the size and shape of the object being formed. Several plastics may be used for this purpose, but the most common one is "high density polyethylene" or HDPE.
When a vacuum thermoform method is applied, the sheet plastic and mold are put into a temperature-controlled vacuum unit, the former over top of the latter. Heat softens the plastic, then the waiting mold is raised up until it presses into it, as air is drawn out from beneath, producing a vacuum and airtight seal between the two surfaces which molds the 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.
Mechanical forming is that which uses a double-mold that has a negative bottom half and positive top half. The plastic sheet is placed over the bottom of the mold, heated until it is pliable, and then covered with the top half of the form which squeezes the softened plastic in the particular shape being made. Air vents in the bottom piece provide ventilation.
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.
Many manufacturing companies prefer the thermoform approach over injection molding because it offers several advantages. The biggest benefit is that it costs much less for the equipment than it does for injection molding machines, in particular for larger sized objects. Developing a suitable prototype is also more easily facilitated and affordable for thermoform processes.
Although there are some variations in method, the basic process is the same. The plastic sheet is clamped down and heated in an industrial oven to a specific temperature, once pliable, it is stretched over the mold, cooled down with fans, and left to harden. The method used depends on the type of plastic and the size and shape of the object being formed. Several plastics may be used for this purpose, but the most common one is "high density polyethylene" or HDPE.
When a vacuum thermoform method is applied, the sheet plastic and mold are put into a temperature-controlled vacuum unit, the former over top of the latter. Heat softens the plastic, then the waiting mold is raised up until it presses into it, as air is drawn out from beneath, producing a vacuum and airtight seal between the two surfaces which molds the 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.
Mechanical forming is that which uses a double-mold that has a negative bottom half and positive top half. The plastic sheet is placed over the bottom of the mold, heated until it is pliable, and then covered with the top half of the form which squeezes the softened plastic in the particular shape being made. Air vents in the bottom piece provide ventilation.
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.
Many manufacturing companies prefer the thermoform approach over injection molding because it offers several advantages. The biggest benefit is that it costs much less for the equipment than it does for injection molding machines, in particular for larger sized objects. Developing a suitable prototype is also more easily facilitated and affordable for thermoform processes.
About the Author:
Genevive B. Mata has over 20 years of professional sales experience, 10 of them directly in the plastic pallets and materials handling industry. On her spare time she works on applied-sustainability projects. If you are interested in plastic pallet suppliers, she suggests you check out her friends www.ptm.com/global.
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