The Liquid Injection Molding Process for Medical Parts: Precision and Sterility in One Solution

Medical device manufacturing requires precision, attention to detail, and safeguards to prevent contamination. A variety of techniques and materials are used for different device components, including liquid injection molding (LIM) with platinum-cured liquid silicone rubber, or LSR. This material is valuable in medical applications due to its high tensile and tear strength, biocompatibility, temperature and chemical resistance, and durability.

LIM is an efficient, cost-effective, and low-waste method for medium to high-volume manufacturing. LSR is injected into the cavity of a mold, then the mold is clamped closed while the material cures. Molds are opened after curing and finished parts are ejected. It’s also possible to mold LSR over or around other metal or plastic components in a process called overmolding. LIM is largely automated, limiting human error and accidental contamination.

Learn more about the process and its use in the medical device manufacturing industry.

Liquid Injection Molding Process

The basic steps in the LIM process are:

1. CAD Design

Part drawings created with CAD tools make it possible to assess part manufacturability, feature dimensions, and tolerances with virtual modeling and testing. The drawings are also used to manufacture the molds that are used to create finished parts.

2. Mold Production

Molds are made from steel or aluminum, depending on the complexity of the part and volume of production. CNC machining or EDM tools are used to create the hollow mold cavity that will hold the LSR as it cures. Another mold component called a core pushes on the finished part to eject it from the mold automatically without human assistance. Molds can also incorporate vents, sensors, and other components to achieve complex or intricate shapes.

3. Liquid Injection Molding

LSR material is a thermoset that is often made from a mixture of platinum catalyst and crosslinking methyl hydrogen siloxane. These two components are held separately in tanks and mix when injected into a hot mold. Injection pressure is high enough that the material fills the mold cavity completely. Pigments can also be added to color the part. The mold is clamped shut to apply pressure as the thermoset LSR cures.

In contrast to thermoset LSR, which forms a shape permanently and cannot be melted again, thermoplastics are melted prior to being injected into the mold, and can be remelted and reformed repeatedly.

After parts are ejected, any excess material, called flash, is trimmed and any additional finishing or assembly is performed.

Medical Injection Mold Benefits and Applications

Injection-molded goods have several advantages over goods produced through other processes. In medical device and healthcare manufacturing, it is critical to achieve consistent parts without defects or contamination.

At Jefferson Rubber Works, Inc., we use medical-grade materials and maintain a Class 8 cleanroom for producing medical devices. We also have experience with many biocompatible and FDA-compliant materials, including LSR.

Additional benefits of medical injection mold manufacturing are:

  • Durability. Injection molds are machined to the exact dimensions and geometry of the parts being made. As a result, they make contiguous parts with few or no joints or points of assembly. This improves durability and helps maintain tolerances.
  • Precision Manufacturing. Injection molds are machined to match the tight tolerances of medical parts for accuracy and minimal variation between parts and batches.
  • Automation. LIM processes are automated and largely hands-free, meaning there is less contact with humans and potential contaminants during manufacturing.
  • Versatility. LIM can be used for both prototyping and large-scale production once revisions are finalized. Pre-formed components made from metal or plastic can also be overmolded with this process as well.
  • Superior Mechanical Properties. Injection molded silicones like LSR are strong, resist tearing, and withstand extreme temperatures. They also return to their original shape after compression and are chemical resistant. As a result, they can be used for sealing applications and exposure to body fluids and pharmaceuticals.

Injection Molded Medical Components From Jefferson Rubber Works, Inc.

At Jefferson Rubber Works, Inc. we serve the medical industry with high-quality liquid injection mold manufacturing, outperforming compression molding in terms of both speed and accuracy. Our facility includes a Class 8 cleanroom for molding, and we are ISO 13485:2016 and ISO 9002:2015 certified.