Medical Design Briefs - May 2021 - 17

TECHNOLOGY LEADERS Materials/Coatings/Adhesives

Using Dynamic Weld Mode Welder to Tackle
Hard-to-Handle Plastic Part Applications

T

hanks to computerized weld
modes, medical manufacturers
routinely use ultrasonics to weld,
insert, or stake plastics and other
parts into a wide range of medical device
assemblies with the expectation of high
consistency and quality. Popular weld
modes optimize welder performance
around a single factor critical to part
quality, such as energy (joules per weld),
peak power, distance (part collapse
depth), or total weld time. These modes,
along with increasingly precise digital
control of actuator force and downspeed, weld amplitude, and other parameters, make real-time performance monitoring and quality tracking possible.
Yet, for all of the advancements available in ultrasonic technology, there are
certain component, material, or application characteristics that can make
assembly quality very difficult to control using single-factor weld modes.
Examples of such hard-to-handle applications include:
* Welding parts atop plastic assemblies
containing compressible internal elements, such as elastomeric seals or cores.
* Welding small, thin, or complex plastic
parts onto plastic structures directly
atop sensors or delicate electronics.
* Ultrasonically swaging or inserting
posts or other structural elements into
substrates that vary in hardness or structural consistency, such as composites.
To solve assembly problems like these,
ultrasonic suppliers and manufacturers
often choose to augment single-factor
weld mode controls with additional
information collected during the welding process, such as external measurements, data points, or signals.
These data, collected before or during the weld process, can be used to
assist a single-factor weld mode in
achieving a more precise, consistent
result in such areas as weld or insertion
depth, insert pull strength, or part
dimensional stability. However, the cost
and complexity of developing and using
external measurement or sensing
devices to augment weld mode controls

To achieve fluid-tight ultrasonic welds of thin plastics over delicate electronics used in wearable medical
devices, a new dynamic welding mode uses material and device characteristics to optimize weld depth and
sealing quality without putting undue pressure on sensitive electronics. (Credit: iStock)

can be significant, especially when mass
production is required.
To overcome the limitations of singlefactor weld modes and eliminate the
need for external measuring devices, a
new patent-pending dynamic mode has
been developed by Emerson and is now
available in its most advanced ultrasonic
welder, the BransonTM GSX-E1 2.0
welder. Dynamic mode leverages the
welder's advanced electromechanical
actuation system, combining computing
power and cutting-edge algorithms with
high-speed data communications to
monitor, recalculate, and adjust the weld
process in real time and achieve an optimized target result.
To use the welder with dynamic mode,
the user selects a single-factor weld
mode, such as energy, distance, or time
that is providing the best application
results so far. Then, the user enters two
additional scores, which act as limits for
dynamic mode activity. The first is a
material density score that, essentially,

Medical Design Briefs, May 2021

www.medicaldesignbriefs.com

Cov

ToC

characterizes the hardness or resistance
of the material that is to receive the
welded, staked, or inserted part (e.g., a
low density score equates to a harder,
more resistant material). The second is a
weld reactivity score, which is used to
adjust the degree of variability allowed
in the target result (e.g., a low reactivity
score equals a more homogenous
result).
In operation, dynamic mode monitors
each weld cycle, using the density and
reactivity limits to adjust the cycle in
response to specific part-to-part variabilities throughout the production run. To
get a better sense of how dynamic mode
works, consider the following application examples.
Sealing a Fluid-Proof Cover over Medical
Electronics
Imagine the need to weld a watertight
plastic cover onto the shell of a very
small medical device. The cover is contoured to fit around sensitive electronic

17
http://www.medicaldesignbriefs.com
Medical Design Briefs - May 2021

Table of Contents for the Digital Edition of Medical Design Briefs - May 2021
