In the medical device industry, the success of a lifesaving operation may depend on the integrity of a bond between components of varying materials. For instance, an overmolded luer hub on a catheter must have a strong bond with its shaft to ensure that fluids may be successfully transferred into or out of a patient’s body without risk of leakage or contamination. In this scenario and many others, it is crucial that the device manufacturers understand the advantages and disadvantages that accompany different bonding processes.

Typically, when a part is overmolded, the substrate is made up of a more rigid plastic or metal, while the overmolded material is softer and provides additional function to the part. (Credit: Pelham Plastics)

Overmolding. Overmolding is a process by which plastic is injection molded on top of a prefabricated component of similar or different material type. Typically, the substrate is made up of a more rigid plastic or metal, while the overmolded material is softer and provides additional function to the part. There are two main overmolding methods: pick and overmolding and two-shot overmolding. Both methods accomplish the same task.

In pick and place overmolding, the substrate is manufactured as part of a subassembly process (either using a different machine/mold or by a third-party supplier) and is manually loaded into the mold by an operator or automation. Plastic resin is then melted and injected into the mold, where it adheres to the substrate. The substrate can also be strategically designed so that it creates a mechanical interlock with the overmolded component, allowing for even greater bond strength. In two-shot overmolding, the substrate is manufactured and then immediately moved to a separate mold or another injection station within the same mold, where overmolding occurs. This transfer is completed mechanically by the machine itself, without the need for operators to intervene between shots.

Gluing. Gluing, a simpler and more traditional method of bonding components, requires a manual application of adhesive followed by curing through heat and light. In many cases, this can be just as effective as overmolding, and many manufacturers might choose gluing methods for several reasons.

For instance, an injection molding machine is expensive; not every company can afford to make this kind of investment, even if it may increase profits down the road. These are also complex pieces of equipment, and with this comes great responsibility for engineering and maintenance personnel. Molding is a more niche area of expertise, and companies interested in overmolding may have trouble finding a team of personnel who are not only capable of designing and overseeing processes, but also troubleshooting and repairing machinery.

Why Overmolding?

Safety of patients is the most crucial goal for any medical device manufacturer. There is perhaps no better way to ensure success of equipment than by minimizing the opportunity for human error during manufacturing. Overmolding requires operators to load and remove components, at least during the pick and place method; however, if process parameters are tested and in place, the bond itself will have a level of strength and consistency that is nearly impossible to achieve through gluing.

Gluing procedures, by contrast, require operator attention and manipulation of parts throughout the entire process. Several factors such as amount of adhesive applied, application location, and cure time are subject to operator error and could result in a medical device failing in the field. For example, if too much adhesive is applied to a catheter extrusion, the glue may migrate inside the extrusion or into the tip of the catheter. These critical variables are not present during overmolding.

In addition to the increased integrity of components, overmolding is a more efficient and cost-effective bonding option. Not only are fewer operators (if any) required to run an overmolding process, but the process itself is quicker. Despite the initial expenses incurred by owning injection molding machines, the savings achieved through minimizing labor hours ultimately justify these costs. Further, the rapid production of overmolded parts makes meeting delivery deadlines more manageable, to the point where it may be possible to take on larger lot sizes if desired by the customer.

For medical device manufacturers, there are certainly risks to choosing overmolding over gluing, with the added difficulty of finding competent personnel to keep processes running smoothly. Because of these factors, gluing tends to be used more often than overmolding to bond medical devices. However, overmolding offers a number of advantages from providing a more secure bond of components to an increasing process efficiency. Manufacturers, customers, and most importantly patients, can all benefit greatly from these advantages.

This article was written by Kevin Crowell, Technical Writer, Pelham Plastics, Pelham, NH. For more information, contact This email address is being protected from spambots. You need JavaScript enabled to view it. or visit here .