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.
Pressure forming is a method which implements the use of compressed air that forces the heated plastic sheet onto or into the mold. The air pressure released can range from 15 to 300 pounds per square inch, depending on how large the molded forms used are. The plastic is pressed into the shape of the mold, forming the desired object.
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.
Pressure diaphragm forming can be used to produce plastic parts by means of pressurized fluid and a vacuum. Twin sheet forming is useful for joining two plastic parts divided by a empty space, it works by melting the parts, and then attaching them to each other.
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.
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 plastic injection molding services then he recommends you visit his friends at PTM: Custom Plastics Injection Molding Company.