Eight Ways of Plastic Forming

Plastics are ubiquitous in daily life. Whether daily necessities or industrial supplies has many different production modes. The below introduces eight common ways of plastic forming, helping to choose an appropriate one for you.

1. Injection molding

Approximately 80% plastics are manufactured by injection molding in daily life. It utilizes injection molding machine for production along with aluminum or steel molds which consist of cores and cavities. The injection molding machine heats resin raw material until it melts, using pressure to inject melted plastic into the cavity. The product is ejected from the mold after the core separates from the cavity.

The advantage of injection molding is large quantity, high speed, low cost and good surface effect. But mold structure complicacy relies on the geometry of product, the more complex, the higher costs. Besides, only by refining on engineering design can defects can be prevented and quality and speed be optimized.

2. Rational molding

Rational molding adopts molds made up of cores and cavities but the working principle is different. It adds plastic material to the mold which keeps revolving and heating along two vertical axes. Then, plastic material inside the mold, by gravity and thermal energy, can be smeared, melted and adhered to the cavity uniformly. The product will be taken out since the mold is unloaded, cooled and formed and the mold can be used for the next round of production.

3. Extrusion blow molding

Thin-wall and cheap containers, such as disposable cups and bottles, usually adopt extrusion blow molding. Despite high production speed and simple mold making, it's not suitable for complex and high-precision products.

The softened plastic forms parison and is placed in two open-close molds. After the mold is closed, compressed air is injected into the parison to make it inflated and stuck to the cavity wall. After the mold wall is cooled by water, the plastic parts are cured quickly, and then the mold is removed to get the finished product.

4. Injection blow molding

Injection blow molding makes use of pressure to inject melted resin into the cavity. The process can be controlled more easily and repeated. It is usually for the production of transparent plastic drink bottles which has good surface effect but it's not appropriate for those of thick wall.

PET and PEEK are common raw material for plastic bottles. It's because those two resins are clear and stable and easy to be recycled. Meanwhile, they are assessed as safety level as consumer goods.

5. Reaction injection molding (short for RIM)

RIM is often applied in automobile industry for the product has light weight and hard surface. Thus, body parts, dashboard and other parts can be made through paint spraying. RIM can only process thermosetting plastic material which extends and fulfills the whole cavity like foams after chemical reaction. Plastic is solidified to product as the chemical reaction stops.

The rapid tooling of RIM has relatively low costs but higher production mold costs. The main cost consists in raw material and extra steps, after production, like paint spraying to handle surface effect will increase costs.

6. Vacuum injection

It's a good choice of vacuum injection when investment in mold and material is limited but only few high-quality RT products are needed.

Prototype part or any solid models (usually 3D printed prototype part) are placed in a sealed box which is full of AQC and SIL later. The place where the prototype part is removed forms a mold cavity and restoring part can be produced when resin is poured in cavity. It's beneficial, in making molds, to avoid bubbles in mold using vacuum pressure to exhaust air. Products of vacuum injection has excellent surface effect and perfect details. Resins to be casted are able to imitate plastic goods of different engineering orders. The only bad thing is the short life that the mold will be degraded after using about 20 times.

7. Hot injection molding

Hot injection molding, placing plastic plates or sheets on die casting molds, is a sort of vacuum injection. It softens material by heating to enable plastic material to spread over the surface and utilizes vacuum pressure to bring form into being.

This method has simple molds and devices and usually produces hollow plastic samples of thin wall. In industrial use, hot injection molding often produces plastic cups, lids, boxes and open-close packing and thicker plastic plates are also used to manufacture vehicle parts. Hot injection molding is only allowed to adopt thermoplastic material.

8. Compression molding

Compression molding warms up material, puts it in the cavity of die casting and solidifies plastic by pressure and heat when the mold is closed. Thin-wall products easy to shape like plastic buttons, gaskets and O rings appear to this method.

The molding is comparatively cheap and less material waste but it's hard to control the stability of products which should be paid attention to during design.