MECHANICAL THEORY Production

4 Types of Moulding Processes-Compression Moulding,Transfer,Injection & Blow Moulding

4 Types of Moulding Process: The types of moulding process is based on the type of plastics we use. As we know that there are two types of plastics, one is Thermoplastics and the other is Thermosetting plastics and depending upon the nature of plastics, moulding process is divided into 4 types.

Types of Moulding Process
Types of Moulding Process

The 4 Types of Moulding Process are as follows:

1.Compression Moulding

2.Injection Moulding

3.Transfer Moulding

4.Blow Moulding

The detailed explanation of the above-mentioned types of moulding processes is as follows.

1.Compression Moulding:

It is used for both thermoplastics as well as thermosetting plastics.

Case 1:(For Thermosetting Plastics)

  • Thermoset liquid will be kept in the mould of the required shape of the component and subjected to the heating process.
  • During heating, the liquid will undergo the following changes i.e. liquid will undergo in the form of gel and by the application of pressure, it turns to solid.
  • Compression load is applied at the gel condition of the liquid so that shaping of the component can be done.
  • Heating converts the liquid into solid whereas, compression load will give the shape to the component.

Case 2:(For ThermoPlastics)

  • A thermoplastic molten liquid will be kept in the mould of the required shape of the component and subjected to compression followed by a cooling process of the mould.
  • Compression gives the shape of the component whereas cooling converts the molten liquid into solid.
  • Thanks, density and the Strength of the plastic can be controlled by varying the compression load “P”.
  • Small and simple shapes of the component can be produced with uniform density.
  • Larger and complex shapes of the components are difficult to produce with uniform density
  • Difficult to insert metal pieces in the plastic part during the production of the component.
  • Ex: outer envelopes of a washing machine, refrigerators, gaskets, helmets, automobile auto parts etc.

 

2.Injection Moulding:
  • It is applicable for thermoplastics only.
  • Thermoplastic molten liquid is pressurized at outside the assembly and allowed to travel through a nozzle of small Dia with high velocity and high pressure into the space between the moulds.
  • The liquid will fill the mould with uniform compaction among the atoms and that implies the density is uniform.
  • After filling the liquid in the mould by cooling process, it will be solidified.
  • Any shape and any size of the component can be produced with uniform density.
  • Density can be controlled by varying the pressure in the pressure line and thereby the production rate is high and the wastage is recyclable.
  • The component can be produced any number of times till it achieves the required shape.
Injection Moulding Process-Machine, Applications or Products and Defects
Injection Moulding Process-Machine, Applications or Products and Defects

Note:

  • Thermoplastic molten liquid possesses low viscosity that implies it can flow easily and thereby the diameter at the nozzle is small.
  • In the case of thermoset liquids, the viscosity is high and it implies difficult to flow and thereby we can say that the diameter at the nozzle is large so as to avoid the obstruction.

Read: Injection Moulding Process-Machine, Applications or Products and Defects

3.Transfer Moulding:
    • One of the types of moulding process is Transfer Moulding and is applicable only for thermoset plastics.
    • Thermoset liquid is pressurized at outside the mould assembly and transferred into the space between the moulds with uniform pressure and velocity and that indicates compaction among the atoms will be uniform and that implies density is uniform and that implies the strength is uniform.
    • After filling the liquid in the mould by the heating process, it will be converted into solid.
    • The density and the strength of the plastic can be controlled by varying pressure “P”.
    • Any shape and any size of the components can be produced with uniform density.
    • Metal pieces can be inserted in the plastic part easily during production.

Ex: Electrical switches, plugs, sockets etc.

4.Blow Moulding:
  • It is applicable for thermoplastics only.
  • Thermoplastic sheet or film of thickness(t)will be kept at the entrance of the mould in a soft condition.
  • By blowing high pressure on the soft sheet, it will bend according to the internal shape of the mould and deposits on the internal surface of the mould and achieve the shape of the component.
Blow Moulding Process-Pressure Distribution,Applications,Differences etc.
Blow Moulding Process-Pressure Distribution, Applications, Differences etc.
  • By cooling process, the sheet will regain its hardness.
  • It is simple and any size of the component can be produced with the good dimensional accuracy of the product.
  • Difficult to produce Complex geometry of the components with good dimensional accuracy.
  • To produce high thickness plastic parts, high blowing pressure is required.
  • If the shape of the mould is complex implies the pressure distribution is non-uniform and thereby compaction of the film is non-uniform and it indicates that the thickness is non-uniform and obviously it indicates that the dimensional accuracy is low.

Ex: Water bottles, plastic buckets, liquid containers, mugs, plastic cups etc.

Read: Blow Moulding Process-Pressure Distribution, Applications, Differences etc.

This is the explanation of 4 Types of Moulding Processes-Compression Moulding, Transfer, Injection & Blow Moulding which was explained in a detailed manner.

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