What are the main methods of plastic molding process


The plastic Home Appliance Mould molding process involv […]

The plastic Home Appliance Mould molding process involves flowing polymer through a mold to form the desired shape.
Plastic extrusion
Various plastic products are made from extruded parts, such as curtain railings, household gutters, window frames, polyethylene bags and films. Extrusion involves forcing molten thermoplastic polymer through a die. The polymer is fed into a screw mechanism, which passes the polymer through the heating zone and forces it out through the die. For extruded products such as curtains, the extruded material is simply cooled.
If a film or sheet is required, a die can be used, which provides an extruded cylinder of material. This cylindrical extruded material is inflated by compressed air while still hot, forming a tubular film sleeve. The expansion of the material is accompanied by a decrease in thickness. Such films can be easily converted into bags.
It is easy to process polyethylene into a tubular sleeve with this method, but polypropylene has a problem in that the cooling rate is insufficient to prevent crystallization, so the film is opaque and very brittle. A slit die can be used to produce flat film extrusions. By using rollers, the cooling rate can be made fast enough to prevent crystallization of polypropylene. The extrusion process can be used for most thermoplastics and produces continuous length products. Complicated shapes can be produced, and high output rates can be achieved.

Blow molding
Blow molding is a method widely used to produce hollow articles such as plastic bottles made of thermoplastics. Can produce containers of various sizes. For extrusion blow molding, the method involves the extrusion of a hollow thick-walled tube, which is then clamped in a mold. Pressure is applied to the inside of the tube to expand it to fill the mold. Blow molding can also be used with injection molding.
Plastic vacuum forming
Vacuum forming is a common method of thermoforming. It uses a vacuum on one side of a sheet of thermally softened thermoplastic to press it against a cooled mold to produce the desired shape. Plates such as 6 mm thick acrylic plates may be preheated in the oven before being clamped, but thinner plates may be heated by a radiant heater placed above the mold. Vacuum forming can have a higher output rate, but the dimensional accuracy is not very good, and it cannot produce objects such as holes, threads and closed shapes.
Calendering is a process used to form thermoplastic films, sheets and coated fabrics. The most common use is for plasticized PVC. Calendering involves feeding a heated pasty plastic block into the gap between two rollers, which are called nip rollers. It is squeezed into a film, then passed through a cooling roll, and then wound on a winding roll. This method can also be used to coat fabrics with polymers.
Plastic processing
The processes used to shape polymers generally require no or hardly any machining or any other processes to produce finished products. For injection molding, compression molding and blow molding, gates and flash must be cut off. When squeezing, the length must be cut off. As with metals, single-point and multi-point cutting tools can be used with polymers. In the case of discontinuous rather than continuous chips, the machined surface becomes excessively rough due to the chips being cut away. Therefore, it is desirable to select cutting conditions that result in continuous chip formation.