Chapter 2: LSR 2-Shot & Overmolding Innovative Technology

Our 2-Shot Solutions at SIMTEC Silicone Parts

Injection molding for the medical industry with SIMTEC’s LSR 2-Shot technology provides incomparable benefits to medical professionals. Our 2-Shot solutions are also known as multi-component, double-shot, twin-shot, and 2K molding. The process is where we integrate several materials, parts, and functions into one piece, using one machine that has two injection units. If we didn’t use 2-Shot techniques, we would need different materials for various functions which would increase costs for assembly and material.

But with the multi-component solution, the injection process occurs in a single machine. The first area holds the initial material. Before inserting the second, we modify the mold to have channels and cavities for both elements. The piece with the lowest melting point is usually injected first. The 2K molding process is where we can integrate functions into a plastic component which makes it more complicated compared to conventional molds. However, material and assembly costs decrease because no additional assembly is necessary despite its complexities.

2k Molding Process

SIMTEC can fuse together parts in various sizes and configurations to suit the medical industry in thousands of ways. Using the same injection molding machine and mold, the 2-Shot process combines features of two materials. Benefits of 2K injection molding include:

  • Better appearance
  • Greater integrity
  • More ergonomic
  • Quality control

Our solution results in more complex designs, multiple material integration, part weight optimization, and various functions in one piece. With modern technology and skilled technicians, we can produce repeatable solutions for high-volume requests. The 2-Shot process decreases the need for further assembly which makes it an economical choice. It also provides dimensional control and forms a stronger bond between parts. Working with LSR often involves a combination of hard and soft elements.

What Is Overmolding and How Is It Used in the Healthcare System?

Overmolding is the third method we conduct at SIMTEC with injection molding and 2-Shot molding as the initial two techniques. With overmolding, we take a completed object — often plastic or metal — and place it into the LSR mold. We overmold a new part onto the existing which results in benefits such as:

  • Alignment of medical gaskets, seals, etc.
  • Integrated bonding and non-bonding materials
  • Consistent thickness and clean surfaces
  • Ability to mold complex designs
  • Design flexibility
  • Quality control
  • Superior surface finish
  • Save time and money with reduction of assembly steps, material waste, and production time

The procedure includes the addition of an extra layer of LSR to an existing part which can have a positive impact on medical tools and devices.

For example, soft-touch handles are a significant product of the overmolding procedure which creates softer handles on silicone medical products for comfort. LSR overmolding can improve the grip of specific tools and form ergonomic shapes that fit the hands of doctors and nurses. We first overmold the shaft of metal with LSR. The thermoplastic makes a soft-touch handle with a seamless surface and no gaps, which limits the potential for contaminants getting trapped.

How the Overmolding Method Works for Medical Silicone Molding

Medical device injection molding from SIMTEC using the overmolding process is when we apply uncured LSR to another base material. We then cure it into a new shape where the liquid silicone rubber adheres to the surface through chemical or mechanical bonding or both. Chemical bonding is the most reliable because it takes place on a molecular level. Mechanical requires various undercuts and interlocks. Aggressive undercuts on LSR products form positive retention between both of the materials.

Overmolding Process

Types of Materials You Can Overmold

Three common materials you can overmold using liquid silicone rubber are silicone, metal, and thermoplastics. Silicone on silicone is the easiest and most popular technique that can achieve multiple colors at once and various durometers, which is the degree of hardness for an LSR object. It’s ideal if you want to combine a less expensive silicone with a more expensive LSR.

If you want to incorporate LSR onto a metal, most require a barrier or primer which promotes the solution’s chemical adhesive properties and prevents the leaching of chemicals like sulfur. Sulfur acts as an inhibitor to the cross-linking. SIMTEC professionals can sandblast, texturize, or peen metal products to generate more surface area bonding.

Using overmolding technology on a thermoplastic is one of the fastest growing segments in the industry. It takes the properties of silicone — like compression set, temperature, and biocompatibility — and combines it with properties of the engineered resins. However, overmolding LSR onto other thermoplastics is the most challenging because not all thermoplastics bond to silicone. It’s also difficult because the thermoplastic glass transition temperature is lower than what’s required to cure LSR.

The Advantages of Using 2K and Overmolding LSR

Not only does the LSR 2K and overmolding technology from SIMTEC give you the freedom to design various devices with soft-grip rubber and other characteristics, but it also costs less and improves the quality of the solution. Multi-component liquid silicone molding has a flexible design where you can combine unique materials to craft more projects and higher performance abilities.

Because silicone parts have a tacky surface, they are more difficult to assemble, so by molding LSR onto another part, it’s quicker and easier. Our solutions also offer fewer material costs. Using a less expensive substrate in combination with LSR, you can receive the pieces you need at a more cost-effective rate. Improved quality is another advantage because overmolding forms a greater bond between the two materials as opposed to other methods.

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