What is injection moulding and how does it work?

                               

                                                                     Injection moulding

Injection moulding is a process that involves injecting molten plastic components into a mould, cooling them down, and hardening them.

Injection Molding is a procedure for mass-producing items in huge quantities. It's most commonly utilised in mass-production procedures when the identical part is made thousands, if not millions, of times in a row.

The injection moulding process isconsists major processes, as indicated below:

Injection moulding is the process of injecting a high-pressure polymer into a mould and shaping it. The steps in this method are all relatively quick. The entire injection moulding process usually takes between 2 and 2 minutes. The cycle is divided into four sections. Clamping, injection, cooling, and ejection are the stages involved.

Clamping

Both parts of the mould must be closed before material can be injected into it. A clamping unit holds them closed. After that, both sides are joined to an injection moulding machine, with one half being able to slide. As the clamping mechanism presses the halves together, material is injected, and both parts are held tightly together while material is injected. Closing and clamping the mould takes longer on larger machines (machines with more clamping power).

Injection

Plastic pellets are fed by means of a hopper into the injection moulding machine. These pellets move towards the mould by the injection unit. The heat surrounding the barrel and the pressure serve to melt the pellets.  The volume of material injected is called the ‘shot’. This injection time finished when 95%-99% or the mould is filled.  It is hard to calculate exactly the injection time because the flow of the plastic is always changing and dynamic.  Injection time can be estimated by other factors such as injection pressure,power and shot volume.  The injection pressure can range from 35-140 MPa. The rate of injection and the pressure which can be reached are determined and controlled by the hydraulic system in the machine.

Cooling

The cooling process involves the plastic inside the mould beginning to cool after it makes contact with the interior mould. As the plastic cools when it hardens it will take the desired shape.  The part may shrink slightly during cooling. Only when the cooling period has elapsed can the mould be opened.
It is from the wall thickness of the part and the thermodynamic properties of the plastic that the cooling time can be estimated.

Removal of part

The last stage is removal of part from the machine. This is done with an ejection system. When the mould opens the part is pushed out, Force must be used because the part shrinks and sticks to the mould. The mould can be shut again after ejection and another shot can be injected for the process to begin again.