Commonly, there are two main types of plastic molding, such as thermosets and thermoplastics. The main difference between those two types of plastics is that the thermoplastics are meltable at high temperature while thermosets will harden at high temperature.
The difference above is mainly caused by the polymers which form those two plastics. Thermoplastics have polymer which look like a chain of atom in one dimensional string. Since they are melted at high temperature, it can be reshaped. On the other hand, thermosets are formed from a polymer with three-dimensional chains so that they are able to keep their shape. There are a lot of processes which are used for shaping or molding plastic using either thermopastics or thermosets. It is also possible to use the combination of those two types.
There are a lot of types of molding process such as extrusion, injection molding, and the combination of the two processes which is known as blowing molding.
Extrusion molding process starts with raw plastics like powder, pellets, and beads. Firstly, the plastic will be fed to a revolving chamber. The chamber which is also known as the extruder will turn and melt the plastic. The melted plastic can be formed to the shape you want. Then, the finished product is dropped on the conveyor belt to be cooled with water. The next step is cutting and finishing touch. The items which are commonly made through extrusion are films, sheets, and also pipes.
Injection molding is another process of molding. The principle used for this process is typically the same as the extrusion. The raw plastic will be fed into the melting chamber through a hopper. The difference is that the melted plastic is put into cold mold with high pressure. If the mold is cool, the product will be cleaned and finished. The items which are commonly made through injection molding are bottle caps, butter containers, lawn furniture, and also toys.
Blow molding is another type of plastic molding process which uses a blowing method after the extrusion or injection molding. The melted plastic in the extrusion process uses a die to create the heated plastic tube with the cool mold around it. In the extrusion blowing, the compressed air will be blown through the tube so that it will force the plastic to make a hallow shape inside. With this method, the manufacturer does not need to attach different injection-molded parts. On the other hand, injection blowing method blows the melted mold into the final shape in different cold.