Differences Between Liquid Injection Molding (LIM), Compression Molding, and Transfer Molding

Liquid injection molding, compression molding, and transfer molding are characterized by a number of both shared and unique qualities. The following blog post explores each of these three molding techniques, outlining their similarities and differences, pros and cons, and applications.

Liquid Injection Molding (LIM)

Liquid injection molding (LIM) utilizes liquid silicone rubber (LSR) or similar elastomeric material to create a range of products that demonstrate excellent durability and flexibility. Some of the typical products produced by LIM are:

  • Seals and sealing membranes
  • Electrical and electronic components, such as connectors and cables
  • Medical and sterile devices
  • Kitchen goods
  • Infant care products

Due to its use of LSR, liquid injection molding relies on a more streamlined and consistent mechanical mixing process rather than a labor-intensive one (such as is used in compression molding). The closed-loop process employs a pump and mixing unit to mix and dispense the liquid material into a molding press. Once the curing stage is complete, the press opens and ejects the finished component, allowing it to be manually or robotically removed.

Liquid injection molding is one of the most cost-effective and versatile manufacturing methods currently available. It is applied towards any industry or market, including:

  • Aerospace and aviation
  • Automotive
  • Electronics
  • Food and beverage
  • Medical and dental

When implemented correctly, LIM consistently produces high-quality molded components in large quantities. However, it is not always the most optimal choice. For example, it is important to consider whether silicone would be the best material to choose. Silicone tends to react with certain environmental and chemical conditions, such as pressurized steam at temperatures above 150°C, which breaks down the material’s siloxane polymer and degrades its material properties.

For a more detailed explanation of when you should and should not choose the liquid injection molding process, download our new eBook, “5 Common Liquid Injection Molding Mistakes (And How to Avoid Them)”.

Compression Molding

Compression molding involves placing thermosetting resins into a heated mold cavity and applying pressure to force it down and compress it in the mold. Throughout the entire process—from distribution to curing—the material is regulated for temperature and pressure level to facilitate accurate part production.

Compression molding is highly flexible and versatile. It is suitable for producing parts with a variety of sizes, thicknesses, and complexities and addresses certain manufacturing challenges, such as production operations that require special materials, difficult-to-manage inserts, or unique part shapes.

Due to its flexibility and versatility, compression molding is advantageous for any industry that requires:

  • Versatile compound requirements to meet part performance criteria.
  • Parts with difficult to mold geometry.
  • Prototype parts that require the material of choice.
  • Insert molding.
  • Dual material molding.

Compression molded parts can exhibit environmental versatility and high chemical resistance. Parts that can be produced by compression molding process include buttons, gaskets, respirator masks, spatulas, and syringe stoppers.

Although compression molding is suitable for high volume production, liquid injection molding offers faster processing and is more repetitive and consistent requiring little if any labor. Compression molding offer faster production changeover times, in some cases less expensive tooling, lower up front material costs and greater production flexibility (as tooling and materials can be relatively quickly changed to meet production demands).

With these considerations in mind, before deciding on a molding process for your application, consult with your molding service provider to make sure that compression molding is most suitable for your production needs.

Compression Molding - Services & Capabilities

Transfer Molding

Despite its similarity to compression molding, the key distinctions of transfer molding lie in its specific tools and unique benefits.

Similarly to injection molding, transfer molding pushes the material into a mold through a sprue. However, a plunger—rather than a screw, barrel and complex injection system—is also employed to transfer the material.

Both injection and transfer molding are efficient methods of producing high-quality, durable, and lightweight products in large volumes. However, injection molding generally allows for faster production cycles than transfer molding, making it more suitable for certain projects.

Transfer molding offers several advantages over other molding processes, such as:

  • Minimal flash formation at parting lines of molds.
  • Faster setup times.
  • Lower tooling costs.
  • Greater part design flexibility (and capacity for part complexity).

Any industrial application can employ transfer molding.

LIM, Compression Molding, and Transfer Molding Services at ETI

As outlined above, the ideal molding process largely depends on your production specifications and requirements. For assistance determining the optimal material and molding process to use for your part, fill out and submit our Design analysis form.

For over 30 years, ETI has stood by the same guiding principle: create a way to achieve every customer’s goal. To help deliver on this promise, we are always looking for ways to improve the quality of our service. Most recently, we invested in a new and larger facility that allows us to have better material control and improved workflow while allowing for future technological improvements.

To learn more about the liquid injection molding, compression molding, or transfer molding services we offer at ETI, reach out to us today.

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