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Transfer Molding vs. Compression Molding

Join Date: 2022-08-08

When making a new part, you have to make a decision, or you just leave the decision to someone else. In either case, it's helpful to know the key differences between transfer molding and compression molding.

Transfer Molding

transfer-molding

Transfer molding processes use thermoset materials or preforms. There are two transfer molding processes: 1. Can transfer molding: The charge is injected from the "can" into the cavity through a vertical sprue channel. 2. Plunger transfer molding: The plunger is injected into the charge through a horizontal channel in the cavity. The mold remains closed during curing, then the plunger is lifted and the transfer material is removed. The mold is then opened and the part can be removed.

Transfer molding is capable of forming more complex part shapes than compression molding, but not as complex as injection molding. Transfer molding is very common in the production of electronic devices such as integrated circuits, capacitors and diodes.

Transfer molding offers several advantages, such as.

  • Minimal flutter formation at the mold parting line.
  • Faster set-up times.
  • Lower tooling costs.
  • Greater part design flexibility (and the ability for part complexity).
  • Transfer molding can be used for any industrial application.
  • Provides tight control over dimensional tolerances.

Compression Molding

compression-molding

Compression molding is a time-tested and widely used thermoset plastic molding process. It is used to mold automotive parts, electrical equipment, new bathrooms, etc. A precise amount of molding compound is loaded into the lower half of a heated mold, the compression mold is closed and heat and pressure are applied. As the cavity is filled, excess material fills the mold's overflow grooves. Afterwards, when curing is complete and the mold is opened, demolding is performed to remove any flying edges.

Compression molding is a good option for very hard or difficult-to-flow materials because it does not require pushing the plastic through a gate or runner. This molding technique is also used for very expensive materials, large parts and small batch applications, other uses include large cross-section parts that require long curing times.

Advantages of compression molding in their respective applications include

  • Simple mold construction
  • Molds require less maintenance
  • Reduced scrap
  • Low residual stress in molded parts (making the process ideal for flat, thin parts, such as automotive underbody guards)

The biggest disadvantage

  • Longer cycle times, which can lead to lower productivity

What are the similarities and differences between compression molding and transfer molding processes?

comrpression molding Transfer Molding
Feeding The mold is opened during feeding, and the material is placed in the proper position in the mold The mold is closed during feeding, and the heated blank is placed in the feeding chamber
The temperature of the material before molding Cold powder or blank, high frequency heating blank placed at 105~138°C High frequency heating blanks at 105~138°C
Mold temperature 130 ~ 200°C 140 ~ 180°C
Clamping pressure 15 ~ 70MPa, for every 1cm increase in product depth, increase by 2MPa Pressure injection plug 40~70MPa, the minimum tonnage of clamping injection plug should be equal to 75% of the pressure exerted by the pressure injection plug on the mold shell
Cure Time 30 ~ 300s 45 ~ 90s
Mold Exhaust Frequently used, outgassing to shorten curing time Neither feasible nor necessary
Moulded product size Depends on the capabilities of the press Up to about 0.5kg
Inlay Adoption Restricted, the inserts are easily displaced or deformed after the mold is closed Unlimited, easy to place complex inserts
Product Dimensional Accuracy Medium (depending on mold structure and molding direction) overflow mold is the worst; non-overflow mold is the best; semi-overflow mold is in the middle Good
Product Flash Thick Thin or None
Product shrinkage Small Larger than compression molding

Comparison table between compression molding and transfer molding processes

Before deciding on a molding process for your application, consult MDC to ensure that compression molding is the best fit for your production needs. MDC offers you excellent compression molded parts at competitive prices. Our experts are dedicated to managing your critical projects on-site and delivering parts or complementary lines at a lower price. Contact MDC today to learn more about our process. We'd love to hear about your project.

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