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.
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 types include pressure diaphragm forming which fabricates plastic parts using a vacuum and pressurized fluid. Also, twin sheet forming is used particularly for joining two parts that are separated by a hollow space, and it involves first melting two sheets of plastic then joining them together.
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.
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 types include pressure diaphragm forming which fabricates plastic parts using a vacuum and pressurized fluid. Also, twin sheet forming is used particularly for joining two parts that are separated by a hollow space, and it involves first melting two sheets of plastic then joining them together.
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 taught plastics molding techniques for over 15 years. He specializes in injection molding and thermoforming. If you are interested in learning more about buy plastic pallets then he recommends you visit his friends at PTM: Custom Plastics Injection Molding Company.
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