Injection molding has allowed many life-enhancing and life-saving medical devices to be within reach of millions of people, by making it possible to produce plastic medical products in large volumes and at competitive cost.

Although the basic injection molding process is relatively simple—squeeze hot, molten thermoplastic into a metal mold, then let that mold cool and harden the plastic, and finally open the mold and eject the solid part out—there are many variations, and some of those have proved particularly useful for medical contract manufacturers. In this post, we’ll discuss four of them.

Clean Room Molding

Products such as implantables, dental products, and catheters, require sterility, absence of contaminants like dust and chemical vapors, as well as consistent quality. All three of these can be provided by performing the injection molding process in a clean room.  For class I, II, and & III medical devices, performing the injection molding in an ISO 8 (100K) clean room can greatly reduce infection and other risks to the patient. After the part is molded, secondary operations like assembly and packaging can occur in an ISO 7 (10K) clean room before the packaged finished devices are shipped to the end customer. If the molded parts are destined for final assembly elsewhere, packaging inside the ISO 7 clean room can protect the part from contaminants until it reaches the OEMs clean rooms for final assembly.

Together with advanced injection molding machines and automated quality inspection equipment, clean room molding safeguards patient safety by ensuring a clean environment and consistent molding process.


Overmolding is a great way to have one device that combines the strengths of two or more different materials. This technique is often used when manufacturing medical devices that require a stiff durable plastic housing or handle, and a soft-touch grip thermoplastic like TPE to ensure the device doesn’t slip from the doctor or nurses’ hands. Overmolding can form a strong mechanical bond between these and other materials, without mechanical fasteners or adhesives, saving an OEM extra labor and assembly costs.

Insert Molding

An injection molding technique that is closely related to overmolding is insert molding, where a plastic material bonds to a metal insert (like a threaded fastener) inside the mold as it cools. It can even bond one plastic to another plastic used as an insert, often called a “first shot”.  Insert molding can combine metal and plastics or multiple combinations of materials and components into a single part, and thus allows OEMs to minimize labor-intensive assembly steps by effectively “pre-assembling” the product during molding operations.

Insert molding is commonly used for medical instruments, like the addition of soft grips to steel surgical instruments. It’s also very popular for manufacturing the knobs used on medical diagnostic equipment, and can mold threaded inserts into plastic equipment enclosures, to facilitate easier assembly in a later process.

Family Molding

A single mold can contain multiple cavities, and those cavities can be slightly different sizes and shapes. This offers “family molding”, and is able to make several different parts at the same time with the same resin (think multiple pieces of a medical device enclosure). This process offers a decrease in projected tooling costs, piece price and lead times, versus creating multiple single cavity tools.

However, with different cavity volumes and geometries, there can be an inherent imbalance of resin flow and cooling times. Here at Crescent, we use mold fill simulation software to help our customers determine the best family mold design that mitigates the risk of bad parts from short shots or flash, and can be implemented in the mold design phase, before a mold is even machined. This crucial design for manufacturing (DFM) step, combined with a method called sequential valve gating, helps us improve mold performance, reduce process variation and improve balance during the injection molding process.

Whether its instruments or insulin pumps, medical contract manufacturers have many molding techniques at their disposal for producing today’s medical products, as well as the next breakthrough device. By leveraging years of expertise, rigorous quality standards, and the economies of scale, medical contract manufacturers continue to play a vital part in the delivery of healthcare.

Crescent Industries has been in the injection molding business for over 70 years. We are a full-service medical contract manufacturer with on-site Class 10,000 and Class 100,000 cleanrooms that can employ all three of these techniques—and many others—for your next innovative project.

Topics: clean room injection molding, custom injection molding, injection mold building