Plastics are generally manufactured using non-machining processes, resulting in a fully finished product that requires no further processing other than deburring.
The most commonly used forming methods are: pressing, injection molding, thermoforming (transfer), and blow molding.
■ Pressing
The powdered material in granule form (granza), to which filler and additives have been added, is fed into the bottom of the mold (1). It is then compressed and heated until it becomes plastic and flows, filling the cavities of the mold (2) completely. Once the part has hardened, it is removed (3).
■ Injection
The raw material (granules) is placed in a container where, under the effect of heat and pressure, it becomes highly malleable. A plunger compresses the mass and forces it into the mold through one or more nozzles. After it has hardened, the mold is opened and the part is removed.
■ Thermoforming
The parts are manufactured from films or rigid sheets using thermoforming (hot forming); the film or sheet is placed on the appropriate mold so that it rests securely against the edges.
Once the seal is applied, it is heated to the required temperature—depending on the type of material—and then vacuum, pressure, or both are applied. Once it has cooled, it is removed from the mold, yielding the finished products.
■ Extrusion Blow Molding
The thermoplastic material exits in a molten state through a conduit (a), taking on a tubular shape as it exits.
Hot air is immediately blown into the mold under pressure, causing the material to conform to the inner walls of the mold and cool as it comes into contact with the metal of the cooled mold.
Next, the two halves of the mold open, and the part falls out.
