Plastics play a significant role in the design of medical products because of their
versatility and reduced weight compared to metals. However, there are times when a
metal component is necessary. While there are different methods for connecting a metal
and plastic component, insert molding is often chosen for its efficiency and durability –
two attributes that are crucial to medical product manufacturers.
What is Insert Molding?
Insert molding is a common injection molding process to “insert” a prefabricated
substrate into a plastic component. The plastic is generally molded over part of the
substrate but can be molded under or to the side of it. The substrate is often a metal
component but can be ceramic or another material.
To be a suitable candidate for insert molding, the component must be able to handle the
heat and pressure of injection molding. Inserts should be smaller than the plastic part
they are embedded in to maintain part strength. Metal inserts do not chemically bond to
plastic and instead rely on mechanical bonding. This means that the design needs
physical interlocks, such as a knurled, ribbed, or abraded surface on the metal part or
undercuts in the design, to ensure a robust and permanent attachment between metal
and plastic.
Before molding, the insert may be cleaned, roughened, or have open ends sealed to
prep it for the process. The insert is placed in the mold, and thermoplastic is injected
into the mold to surround the appropriate area of the insert. The part is allowed to cool
before moving on to any other operations that may be required.
What Medical Products Have Insert Molded Components?
Insert molding is used for components in numerous medical products because of its
versatility and ability to create complex, durable components. Some uses include:
- Instruments that require handles, such as scalpels, forceps, scissors, and dental
drills, benefit from insert molding. The plastic handle provides a more
comfortable grip than metal alone. - Medical and surgical devices, including catheters, drug delivery systems, IV
systems, obturators, or other devices incorporating ports, valves, needles,
connectors, hubs, or other parts with plastic components. - Laboratory equipment, including centrifuges, where plastic housings are insert
molded with metal parts to secure components like motor shafts or rotor mounts. - Connectors for power and signal cables used in patient monitors, imaging
devices or dialysis machines. Also, electrical switches and control panels in
medical equipment. - Medical carts and other equipment with wheels might use insert molding to
create the wheel assemblies. - Plastic products requiring fasteners, hardware, or threaded components for
assembly - Products that require attaching two load-bearing parts
- Medical equipment with plastic housing that needs to be dissembled or requires
maintenance access
Alternatives to Insert Molding
As mentioned, insert molding is not the only process for securing a substrate to a plastic
component. Other options are adhesive bonding, ultrasonic welding, and heat staking.
Adhesive bonding uses specialized adhesives to attach the metal and plastic. The
adhesive requires a significant curing time to create a strong bond. Adhesives can be
sensitive to environmental conditions, like temperature and humidity, and the bond may
degrade over time.
Ultrasonic welding involves using high-frequency ultrasonic vibrations to bond plastic to
metal. An insertion hole smaller than the insert is included in the part design to guide
the insert into place. This vibration travels through the driven part until it meets the
plastic. It generates localized heat that softens the plastic, allowing the driven
component to be inserted. The ultrasonic vibrations can damage some electrical
components, so another method must be used.
A third alternative is heat staking. Heat staking mechanically bonds the metal into the
plastic using controlled heat and pressure. The thermoplastic part is molded with a hole
or recess where the metal component will be placed. A heat staking machine with a
heated tool or staking head contacts and heats the metal component, which causes the
thermoplastic around it to soften. A controlled amount of pressure is applied to allow the
metal component to be embedded into the plastic.
Choosing Insert Molding for Medical Products
Choosing insert molding over other methods of joining metal and plastic components of
medical parts will depend on your application and needs. Medical products inherently
strive for reduced risk, material compatibility, and manufacturing efficiency – all benefits
of insert molding. The resulting product is more robust, reliable, and suitable for
demanding medical applications where safety and reliability are essential.
Insert molding provides a highly robust mechanical bond since the insert is
encapsulated directly by plastic during molding. This creates a connection that is
generally more reliable and long-lasting compared to bonding with adhesives or other
post-assembly methods. Medical devices must often be durable and resistant to
stresses such as pulling, twisting, or exposure to bodily fluids and chemicals. Insert
molding reduces potential failure points because the insert and plastic become one
integrated part, minimizing the risk of component detachment over time.
Contamination prevention is important for many medical products. Adhesives can pose
a contamination risk if they degrade over time or leach chemicals into surrounding
areas, which is particularly problematic for medical applications. Insert molding is an
adhesive-free process, ensuring a clean and stable bond.
Medical parts often need to undergo sterilization processes like gamma irradiation,
ethylene oxide (EtO) gas, or autoclaving. Adhesives can degrade or weaken during
these processes, whereas parts produced with insert molding maintain their integrity.
Insert-molded parts generally have higher heat stability since the bond is created during
the molding process, making them more suitable for autoclaving or other high-
temperature sterilization techniques compared to parts that are assembled using
adhesives or heat staking.
Another advantage of insert molding is design flexibility. It allows for integrating multiple
functions into one component, such as incorporating metal fittings, sensors, or
connectors within a plastic housing. This capability is valuable in medical parts where
space is limited, and combining multiple functions can reduce overall part count and
potential failure points. Additionally, insert molding can embed complex shapes, which
can be challenging with heat staking or ultrasonic welding. This allows manufacturers to
produce parts with intricate designs customized for specific medical device applications.
Efficiency is another benefit. Insert molding is a one-step process that combines
molding the plastic part and integrating the insert into a single operation. This is more
efficient than the multiple steps required for adhesive bonding, ultrasonic welding, or
heat staking, each of which is a separate post-molding operation. By combining insert
integration with molding, manufacturers can significantly reduce assembly time and the
risk of inconsistencies that may come with multi-step assembly processes.
Finally, since insert molding is a single-step process, the risk of surface defects such as
warping, burns, or weld marks during the other secondary operations is minimized. This
is important for maintaining the quality and functionality of medical devices, especially
those that come in direct contact with patients.
Get High-Quality Insert Molded Medical Products With Advantech Plastics
As an ISO 13485:2016 certified medical/dental components and disposables
manufacturer, we have the experience to deliver insert molded products that meet your
exact specifications. We frequently work with aluminum, brass, copper, plastics, rare
earth metals, and stainless steel, but we will discuss whatever material needs you have.
If you have an application that is more suitable for ultrasonic welding, we also offer that.
Contact us so we can work with you to determine the best processes to bring your
product to market quickly.