Transfer Molding of Polymers (Its Process, Examples & More)

Transfer molding process

What is transfer molding?
Transfer molding is a process in which a polymer is preheated and loaded into a holding chamber (called pot) and then it is forced into a preheated mold cavity to get the desired shape.

Transfer molding process is similar to the compression molding process, but the difference is that in compression molding, the raw material is placed in an open mold. While in transfer molding, the raw material is kept in a closed holding chamber.

Well, there are a lot more things regarding the transfer molding of polymers like, transfer molding process, advantages and disadvantages of transfer molding, examples of transfer molding, etc, which I have discussed below.

So let’s dive right into it!

Transfer molding process

Transfer molding process of polymers
  • In the Transfer molding process, the polymer is first preheated and it is loaded into a holding chamber. This holding chamber is known as a pot.
  • Now with the help of a hydraulic plunger, this raw material (or polymer) is forced into the preheated mold cavity through a sprue.
  • The mold is kept closed until the plastic material solidifies inside the mold cavity.
  • The flash (i.e excess material produced along the parting line) produced in transfer molding is very less compared to that in compression molding.
  • But since there is a sprue, air holes, and overflow grooves present in the transfer molding process, the wastage of material is more.
  • The main advantage of using transfer molding is that you can place different inserts like metal prongs, dry fibers, ceramics, etc in the mold cavity before the injection of a raw material in the mold cavity.
  • Because of this advantage, the transfer molding process is used to manufacture integrated circuit packaging with molded terminals, studs, pins, connectors, etc.

Advantages of transfer molding

Advantages of transfer molding process are mentioned below.

  • Maintenance cost of a machine is generally less because the gates and runners are subjected to less wear.
  • In this process, longer core pins can be used and supported on both the ends, allowing the smaller diameters.
  • Very delicate inserts and sections can also be molded by using a transfer molding process.
  • The molded plastic possesses higher tensile strength and flexural strength.

Disadvantages of transfer molding

Disadvantages of transfer molding process are mentioned below.

  • After the transfer molding process, the molded plastic may contain knit lines in the back of the pins and inserts.
  • The runner and sprue system causes a waste of raw material, but this can be reduced by using injection molding process.
  • The fibre degradation of orientation that occurs in the gate and runner system reduced the impact strength of the molded polymer.
  • The molding pressure required in transfer molding is higher than that required in the compression molding process.

Applications/Examples of transfer molding products

The examples of transfer molding products are mentioned below.

  • Spark plugs with wires
  • Pins
  • Studs
  • Connectors
  • Circuit with molded terminal, etc.

External links:
Transfer molding: Image by Mark.subbotin, CC BY-SA 4.0, via Wikimedia Commons

Leave a Comment