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Is it time to inject more accuracy, versatility, quality, and cost-efficiency into your medical manufacturing project? Then injection molding might be just what the doctor ordered. This proven production method can create high volumes of tight-tolerance parts from a wide variety of polymers, including medical-grade plastics that meet tough regulatory requirements and testing standards.
Whether for single-use products, repeated use devices, or durable medical equipment, injection molding can speed production after alpha, beta, and pilot prototyping is complete. That’s why so many engineers and designers in the medical industry mold their parts instead of using other techniques.
If you’re looking to understand medical device injection molding, start with these four questions.
- Why does the medical industry use injection molding?
- How is the injection molding process different when used for medical applications?
- Which types of injection molding are used for which types of medical products?
- Who understands injection molding for the medical industry?
Why does the medical industry use injection molding?
Injection molding isn’t the only plastics manufacturing process, but it’s a cost-effective choice for high volume production. Although the cost of an injection mold may seem expensive, this amount can be amortized, or spread out, across many parts to get a low cost-per-part. For example, if a $10,000 mold is amortized across 100,000 parts, the tooling cost is just ten cents per part.
Injection molding also supports the use of materials ranging from lower-cost commodity plastics to high-performance engineering resins. Designers and engineers can choose polymers with specific properties, from thermoplastics that melt at high temperatures to thermosets that don’t. Different plastics also come in different grades, such as medical-grade plastics that are made of ingredients with demonstrated histories of biocompatibility. Plus, injection molding can produce parts in various shapes and sizes.
Perhaps most importantly, injection molding supports the tight tolerances required by the medical industry. Often, injection molded parts are installed within larger assemblies. In medical device design, tolerance stack analysis is used to ensure that these parts fit, or stack up, correctly. If misalignments occur, a part redesign may be required. Production rework also adds costs and can result in new product introduction (NPI) delays.
Although injection molding has many advantages, it’s not the right choice for every plastics project. For example, 3D printing is more cost-effective at low volumes, especially for prototypes, because it doesn’t require tooling. Yet 3D printing doesn’t offer the same broad selection of specialized polymers as injection molding, and 3D printing materials don’t have the same end-use properties.
How is the injection molding process different when used for medical applications?
Injection molding isn’t just used by the medical industry, but there are special considerations for medical applications. For example, the plastic that you select may need to meet requirements set by the U.S. Food and Drug Administration (FDA). When determining whether a medical device is safe and effective, the FDA reviews information about the device’s constituent materials, including polymers.
For injected molded products that contact living tissue, USP Class VI or ISO 10993 testing requirements may apply. Although these are not regulatory requirements, they are used to determine the biocompatibility of plastic materials. Neither standards are synonymous with biocompatibility testing, however, so it’s not enough to just specify a “biocompatible plastic” during material selection.
The plastics for medical injection molding may also require a certificate of analysis (COA) from the material supplier or a certificate of conformance (COC) from a third-party testing laboratory. This is an important distinction because some suppliers claim to use USP Class VI compliant ingredients but may not be able to ensure the compliance of the end product, especially if they make an ingredient substitution.
Finally, medical injected molded parts need to have a high degree of accuracy while meeting tight tolerances. Parts must pass dimensional inspections and may be subject to traceability requirements. Although the European Union Medical Regulation (EU MDR) applies to only finished medical devices, component-level traceability can help medical manufacturers with their EU MDR compliance efforts.
Which types of injection molding are used for which types of medical products?
The medical industry uses different injection molding techniques. Conventional injection molding melts solid thermoplastic pellets so that the liquid material flows into and fills the mold’s cavities. Pressure is applied directly to the mold and the part or product takes on the mold’s shape. Dwelling, cooling, mold opening, and ejection are all part of this manufacturing process.
The medical industry also uses insert molding and overmolding to mold plastic onto other materials. With insert molding, a pre-formed part is placed into the mold and plastic is shot, or injected, directly over it. Overmolding also uses a pre-formed part but injects two separate shots instead. Thin wall molding, a variant of the conventional injection molding process, is used to produce thin, lightweight parts without a preform.
Medical injection molding can be used to produce high volumes of disposable single-use consumables that, in the case of thermoplastics, are also recyclable — the plastic can be reheated and then remolded. Medical injection molders can also make products for repeated use, such as surgical instruments, where a polymer that withstands sterilization is molded over a preformed part like a metal scalpel.
Although conventional injection molding is used widely, liquid injection molding (LIM) has important healthcare applications such as spacers for asthma inhalers. Reaction injection molding (RIM) is used to produce parts ranging from medical equipment enclosures and housings to trays and covers. Injection molding processes for implantables, orthotics, and prosthetics use more expensive resins and must meet especially demanding requirements.
Who understands injection molding for the medical industry?
Without injection molding, some of the medical products that we depend upon might still be nothing more than a CAD model. There’s a place for other manufacturing methods in the medical field, of course, and injection molding might not always be the right choice for prototyping or low-volume production. Yet, it’s often what’s prescribed for accurate, versatile, quality-driven, and cost-efficient manufacturing at scale.
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