Vacuum forming is a plastic molding process in which heated plastic sheets are molded onto a die using vacuum suction. The process is used to manufacture various types of plastic items such as: storage trays, seed trays, plates, baths, and packaging, etc. Sheets made of thermo plastics like: acrylic, CPET (crystalline polyester), LDPE (low density polyethylene), HDPE (high density polyethylene), PP (polypropylene) are used in the vacuum forming process. Thermo setting plastics cannot be used in this process since they need very high temperatures to set. Vacuum forming is generally considered to be one of the easiest techniques used for creating plastic casings for almost anything. The process is ideal for producing odd shaped objects.
Vacuum forming is basically a simplified version of thermoforming and it can be used with plastic sheets of varying thickness. The plastic sheet needs to be preheated till it becomes malleable. A vacuum pump is then used to quickly suck out the air from the die. This causes the plastic sheet to collapse against the mold.
A typical set up will enable objects to be placed on a platform inside a chamber. A plastic sheet is then clamped in position above the object. A heater that is placed at the top of the chamber heats the sheet until it is soft enough for forming. The platform raises the object up to the plastic sheet. A vacuum pump is then used to pump air out from under the plastic and object. This makes the plastic mold itself around the object. After the part has cooled down, it can be either ejected automatically or removed manually and any excess is cut off.
The size of the component that can be produced depends on the machine tool that is used. The proper preparation of dies and molds is very important. Very intricate shapes with a range of cross sections or geometry and patterns are not vacuum formed. This is a high volume production process and should not be used for parts with thin walls or where great form accuracy is needed. Vacuum forming is used by many types of industries and hobbyists as it is a relatively, quick and inexpensive way of forming plastic items.