Exploring Overmolding vs. Gluing for Bonding Medical ...

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.

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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 .

Low-pressure overmolding stands as an immensely advantageous process with diverse applications across various industries, particularly in the realm of encapsulation using different rim applications. For those seeking a deeper understanding of this method, a comprehensive guide to low-pressure overmolding can offer invaluable insights. Below, we delve into what low-pressure overmolding entails, its primary advantages, the types of items it can mold, and more.

 

WHAT IS LOW-PRESSURE OVERMOLDING?

Low-pressure overmolding involves molding a component directly into a polyurethane part under relatively low temperatures and pressures. Depending on the desired appearance and application of the final product, the molded-in component can be fully or partially enclosed by the molded part. This method obviates the necessity for primers or adhesives for bonding, as the component chemically adheres to the polyurethane part, resulting in an exceptionally robust bond.

 

This process owes its feasibility to reaction injection molding. The blend of polyol and isocyanate used in reaction injection molding generates a low-viscosity substance akin to motor oil. This motor oil-like material can be easily injected into a tool without requiring high temperatures or pressures to ensure it fills every nook and cranny.

 

ADVANTAGES OF LOW-PRESSURE OVERMOLDING

Low-pressure overmolding offers a host of benefits, serving functional and aesthetic purposes. These advantages encompass:

 

Enhanced protection for delicate items: 

The low-pressure nature of this process enables the overmolding of delicate components like antennas or circuit boards without causing damage. Once integrated into the part, these fragile elements benefit from added protection provided by the resilient polyurethane layer. This shielding allows the components to operate safely even in challenging conditions such as wind, water, and vibrations.

Reduced visibility of parting lines: 

Unlike traditional methods involving primers and adhesives to fuse parts, low-pressure overmolding eliminates unsightly seams and parting lines. This technique ensures a seamless and polished appearance for the molded part.

Improved wireless capabilities: 

Overmolding can enhance wireless functionality in parts. The lower density of overmolded materials can amplify the radio signal strength of wireless components compared to alternative encapsulation techniques like potting.

Deterrence against theft and tampering: 

Low-pressure overmolding acts as a deterrent against both physical and intellectual property theft. The seamless integration of an item into the part makes extraction or tampering significantly more challenging. Accessing the overmolded item typically requires breaking it, providing greater protection for sensitive electronics or valuable intellectual property against theft and malicious tampering.

 

WHAT CAN UNDERGO LOW-PRESSURE OVERMOLDING?

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The application of reduced pressure in low-pressure overmolding enables the molding of delicate components from items like electronics or medical devices into a single part. Various scenarios utilize low-pressure overmolding, including:

 

Antennas: The low-pressure, low-temperature process ensures sensitive antennas remain undamaged and can even experience improved radio signal strength due to the protective overmolding material's low density.

Circuit boards: Fragile electronic components like circuit boards can seamlessly integrate into a part through low-pressure overmolding, safeguarded by the low-viscosity material that flows into the mold, shielding against external elements.

Magnets: The low density of materials used in low-pressure overmolding, such as polyurethane, allows for the molding of magnets into a part without significant loss in magnetic capabilities.

Batteries: Low-pressure overmolding enables the molding of batteries into parts without compromising their capacity. The surrounding material acts as a protective casing, enhancing shock, vibration, moisture, and corrosion resistance to prolong battery lifespan.

Threaded inserts: Parts requiring attachments or assembly benefit from threaded inserts molded directly into the part through low-pressure overmolding, ensuring easier and stronger attachment.

Metal rods, bolts, and clips: For augmented structure and stability, components like metal rods, bolts, and clips can be directly molded into a part using low-pressure overmolding.

 

FACTORS TO CONSIDER WHEN UTILIZING LOW-PRESSURE OVERMOLDING FOR YOUR PROJECT

When contemplating the integration of low-pressure overmolding into your project, several crucial considerations merit attention.

 

DEGREE OF REQUIRED PROTECTION

The sensitivity of the components within your project serves as a pivotal factor in determining the viability of implementing a low-pressure overmolding process. Assess whether your equipment is susceptible to dirt, oil, chemicals, or grease.

 

Upon gauging the sensitivity of your equipment, deliberate on the potential operating environment for your final product. Will users employ the product in wet, moist, or underwater conditions? Is the intended use in a rugged environment where exposure to dirt, wind, or impacts is probable?

 

Should your equipment display sensitivity or foresee use in harsh or moist surroundings, the seamless and protective layer formed through the low-pressure overmolding process is likely to offer substantial benefits.

 

INTEGRATING ADDITIONAL FUNCTIONS INTO YOUR PART

Another critical aspect to consider when contemplating the adoption of low-pressure overmolding in your part production process is the integration of additional functions. If you anticipate the need for extra functionalities within your part, opting for low-pressure overmolding can eliminate the necessity for a lengthy and potentially expensive secondary assembly process. This approach could significantly reduce overall manufacturing costs by streamlining production steps and minimizing the number of vendors in the supply chain.

 

STREAMLINING YOUR MANUFACTURING PROCESS

Moreover, assessing the desired simplicity of your manufacturing process is crucial in determining the suitability of employing low-pressure overmolding. This method has the potential to eliminate the requirement for supplementary steps in the secondary assembly process. Those seeking a streamlined, single-piece manufacturing solution should seriously consider the benefits offered by low-pressure overmolding.

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