MECHANICAL THEORY Production

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

4 Types of Molding Processes: The types of molding processes are 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, molding process is divided into 4 types.

Types of Molding Process
Types of Molding Process

The 4 Types of Molding Processes are as follows:

1.Compression Molding

2.Injection Molding

3.Transfer Molding

4.Blow Molding

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

4 Types of Molding Processes:

1.Compression Molding:

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 mold of the required shape of the component and subjected to compression followed by a cooling process of the mold.
  • 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 Molding:
  • 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 molds.
  • The liquid will fill the mold with uniform compaction among the atoms and that implies the density is uniform.
  • After filling the liquid in the mold 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.
Types of Molding Processes-Injection Molding
Types of Molding Processes-Injection Molding

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 Molding Process-Machine, Applications or Products and Defects

3.Transfer Molding:
    • One of the types of the molding process is Transfer Molding and is applicable only for thermoset plastics.
    • Thermoset liquid is pressurized at outside the mold assembly and transferred into the space between the molds 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 mold 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 Molding:
  • It is applicable for thermoplastics only.
  • Thermoplastic sheet or film of a thickness(t)will be kept at the entrance of the mold in a soft condition.
  • By blowing high pressure on the soft sheet, it will bend according to the internal shape of the mold and deposits on the internal surface of the mold and achieve the shape of the component.
Types of Molding Processes-Blow Molding Process
Types of Molding Processes-Blow Molding Process
  • By the 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 mold 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 Molding Process-Pressure Distribution, Applications, Differences, etc.

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

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