What is plastic injection moulding?

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Injection moulding is a process in which moulds are used. Synthetic resins, also known as plastics, are first heated and after melting, they are sent to the mould and then cooled to form the designed shape. Resembling the process of injecting fluids with a syringe, it is called injection moulding.

It was invented as far back as the 19th century, but is still one of the best ways to produce complex parts at low cost, which is why it is considered one of the most widely used methods.

moldeo por inyeccion del plastico

How does plastic injection moulding work?

The injection moulding machine uses custom moulds to fill them to specification, creating identical copies that can be customised in a variety of ways.

With injection moulding, parts of various shapes, including complex ones, can be produced quickly and continuously in large volumes. So what do we use injection moulding for? To manufacture raw materials and products in a very wide range of industries.

Plastic injection moulding is a process that has been making its way into industry, both for economic and technical benefits. It has displaced traditional materials such as bronze, steel, aluminium, etc. in industrial applications. The level of complexity, the number of cavities and the quality of the materials have an impact on costs. If we have to establish an adequate relationship between production costs and the mould, the figure to be injected, the number of parts and the cost of the moulds must be well defined.

The process can be subdivided as follows

  • Mould closing: We supply the polymer into the injection unit and close the mould.
  • Injection:
  1. The plastic is injected into the mould cavity through the nozzle of the injection unit.
  2. Maintaining the pressure so that the part reaches the desired dimensions.
  • Cooling and hardening of the part inside the mould.
  • Opening of the mould to release the part.

The manufacture of parts by injection moulding uses plastic, usually in the form of granules, which is melted inside the machine and then injected into a mould under high pressure. The material is then cooled, solidifies and is released by opening the two halves of the mould.
To build a mould, there are 4 main phases: design, prototyping, prototype testing – and the implementation of corrections and readjustments to the mould.
Thanks to this process, a pre-defined and fixed size plastic product can be produced, thus reducing costs and making the whole process more cost-effective.
It should be noted that the parts to be used in the injection moulding technique have to be carefully designed, as it is necessary to create the corresponding mould, usually using materials such as aluminium or steel, so that the plastic parts can then be mass-produced.
Plastic moulded parts are made from thermoplastics, which are composed of polymers capable of melting at high temperatures and solidifying at low temperatures. Thermoplastics can be heated and cooled several times before being lowered. Unlike thermosetting plastic material, which burns if heated several times.
Thermoplastics in pellet form are most commonly used for injection moulding. However, in order to give the parts a more specific, more concrete colour, the plastic pellets can be mixed with recycled material and even glitter or other special additives.

Types of injection moulding processes.

The following are examples of plastic injection moulding:

  • Thin-wall injection moulding
  • Gas-assisted injection moulding
  • Gas reaction assisted injection moulding
  • Water-assisted injection moulding
  • Cast-core injection moulding
  • Co-injection moulding
  • Structural foam moulding
  • Microcellular foam moulding
  • Multi-component injection moulding
  • Interval moulding
  • Insert moulding
  • Outsert technology
  • Layer moulding
  • Encapsulation under injection moulding
  • Finishing of metal profiles
  • Moulding of interconnected devices
  • Resin transfer moulding
  • Reinforced reaction injection moulding
  • Reactive gas assisted injection moulding
  • Liquid silicone moulding
  • Vibration-assisted injection moulding
  • Clean room injection moulding

All in all, plastic injection moulding is a frequently used, efficient, environmentally friendly and economical technique.
The disadvantage it can have is that since plastic injection moulding is based on heating and cooling the plastic, if the shape of the mould causes the plastic to cool unconsciously, the part will be weak to defects. However, this risk can be limited by ensuring that the mould walls are homogeneous in size, so that the part is optimally strengthened.

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