Didier Perret, global business development manager, medical segment, Emerson, talks about how to choose the right technology for medical devices.
There are always new challenges that demand new designs, new features, new capabilities, greater complexity and higher standards as a result of the fast-growing medical device industry. Many medical devices are too complex to mold as single pieces, and so optimal assembly methods are essential for the successful delivery of reliable products. In order to select an assembly method and supplier for your assembly needs it is imperative to examine and compare all of the options to understand the advantages and limitations of each process, and to leverage assembly system providers that can offer the greatest technical expertise for your application.
The best way to get the optimal process for your application is to go into the decision-making process with a ‘process-neutral’ mindset. Working with suppliers that can help you explore a range of assembly technology is often the best way to achieve the benefits of reduced time to market, lower costs, and improved product reliability.
A wide range of technologies to consider
Many joining technologies exist for medical device applications, ranging from fasteners to adhesives to various forms of plastic welding. Plastic welding methods are popular because they can join a range of thermoformed plastic assemblies while eliminating the biocompatibility concerns associated with chemical solvents and adhesives, and the design complexities of incorporating mechanical fasteners.
In addition to traditional welding with heated plates, there are a variety of plastic welding approaches available, including ultrasonic welding, vibration welding, spin welding, and ‘clean’ methods with laser, infrared, and ‘pulse staking.’ ‘Clean’ welding methods are specially designed to produce plastic welds with a minimum of flash and particulates - a critical factor for success in any medical device or product application, and for many applications, utilizing a combination of techniques provides the best solution. In nearly all cases, clean plastic joining methods integrate easily into high-volume part production and automation processes, thanks to rapid process cycles, data-driven quality assurance, and high energy-efficiency.
Application examples
Ultrasonic welding
Ultrasonic plastic welding is an extremely cost-effective and popular technique whose benefits include speed, no consumables, minimal or no setup time, low cost of capital equipment, and easy integration into automation. It utilizes a series of components to deliver mechanical vibration and force to the parts, which generates heat at the interface of the mating surfaces, melting the plastic and creating a strong bond.
In medical devices, reliable, repeatable, high-precision, and perfectly clean joining processes are typical requirements. As medical devices and their component parts continue to miniaturize, device makers face the challenge of joining thinner, lighter, and more intricate plastic components that may also contain embedded electronics. Successful welding processes therefore demand an increasingly difficult balance of precision positioning, low trigger force, and exceptional control over the weld that conventional ultrasonic welders cannot provide.
To meet this challenge, Emerson recently introduced the Branson GSX ultrasonic welding platform. This new product incorporates an advanced electro-mechanical actuation system (patents pending) that combines software, servo controls, and a proprietary ‘dynamic follow-through’ feature that can provide instantaneous weld adjustments based on real-time feedback. With it, the Branson GSX platform provides control and position accuracy, and delivers and controls ultra-low weld actuation forces. This enables consistency across multiple welders in the same line, with post-weld tolerances and part variabilities measured in microns.
Thanks to technical advances like this, ultrasonic welding continues to provide significant advantages for the assembly of wearable and implantable medical devices, minimally invasive surgical instruments, as well as catheters, cannulas, luers, and trocars and other important medical products.
Laser technology
Laser welding of plastics is an innovative welding technique based on the principle of passing laser energy through one plastic component (transmissive part) and absorbing it in the second component (the absorptive part). This absorption results in heating and melting of the component interface, and the parts are joined with the application of a controlled clamp force.
Laser welding is a gentle and clean joining process that enables welding of complex geometries and materials that are difficult to bond with other techniques. Laser welding can ensure attractive, reliable hermetic sealing in a single step that only takes a few seconds.
The new Branson GLX-Micro Laser Welder can control clamping forces as low as 1N, enabling repeatable, flash-free welding of small parts and complex geometries without the risk of deflection, bending, or cracking essential components. Its cleanroom-ready design and customizable data outputs were developed to meet the needs of medical device manufacturers.
Infrared technology
Clean Infrared Technology (CIT) can be used for clean joining of small, medium, and large parts. Precise plasticization occurs using noncontact heat input by medium-wave, metal-foil emitters that emit the same wavelength spectrum as the absorption range of most common thermoplastics. During the CIT process, the two-part halves to be joined are held in position a few millimeters from the metal-foil-emitter platen that follows the contoured profile of the weld seam. The platen uniformly preheats the weld area without damaging pre-assembled inner parts. Once plasticization has occurred, the platen is removed, and the halves are brought together under pressure and allowed to re-solidify, producing a clean, clear, weld that is virtually particle-free.
Vibration and clean vibration technology
Vibration has been used for many years to weld large parts. Clean vibration technology combines infrared and vibration processes. An infrared source preheats the part surfaces to minimize particle generation during the subsequent vibration welding process. This approach produces clean, high-strength joints with low residual stresses, low material-specific friction, and shorter welding times.
The major application benefit of clean vibration joining lies in its ability to join large (up to 1500 mm long and 700 mm wide) and intricately shaped plastic parts. The process works with multi-plane and curved surfaces and is capable of sealing even internal cross ribs in parts to create separate fluid compartments. This technology is typically used to assemble large two-part systems such as patient monitors, infusion pumps, or fluid collection vessels. Clean vibration processes often are set up to weld multiple assemblies at one time as part of automated production.
Key considerations for process selection
- Material
- Part geometry
- The complexity of the part and weld profile
- Wall thickness and internal walls
- Production volumes
- Capital equipment cost
For new or modified medical devices, all parameters should be evaluated with a ‘process-neutral’ approach to ensure the appropriate joining technique is chosen.