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Ultrasonic Welding, the most widely used welding
method, is quite often the joining method of choice for
design engineers due to its simplicity of use and rapid
joining potential. The process utilizes ultrasonic energy
at high frequencies to produce mechanical vibration
causing slight melting of the substrate surfaces. There
are, however, a number of drawbacks that limit the
usefulness of ultrasonic welding. Like solvent welding,
ultrasonic welding cannot be used on thermoset plastics
and is sensitive to bondline configuration. Large gaps
and/or minimal contact areas pose problems for ultrasonic
welding processes. In the case where dissimilar plastics
are used, similar melting points and chemical
compatibility of the two substrates must be considered.
Ultrasonic welding requires significant investment for
capital equipment as well as special tooling for each
unique assembly. |
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Vibration welding involves the melting of the joint of
an assembly via friction caused by the vibration of two
substrates in contact with each other. For such a process
to work, the materials selected must be thermoplastics,
must be somewhat rigid and must have either flat or
slightly curved interfaces. As with various other welding
processes, capital expenditure as well as special tooling
is required. In addition, vibration welding of substrates
that contain high levels of moisture may result in bubble
formation during processing which, in turn, may result in
poor aesthetic appearance and/or weak interfacial bonds.
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BENEFITS & LIMITATIONS OF MEDICAL DEVICE ASSEMBLY
METHODS |
|
Solvent Welding |
Ultrasonic
Welding |
Vibration
Welding |
Adhesive Welding |
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Benefits:
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Benefits:
-
Easily automated
-
Simple
-
Fast
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Benefits:
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Benefits:
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Limitations:
-
Not usable on thermoset
plastics
-
Can cause stress
cracking
-
Health & safety issues
Poor gap filling
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Limitations:
-
Not usable on thermoset
plastics
-
Plastics must be
compatible
-
Poor gap filling
-
Capital cost
-
Must remove or hide weld
flash
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Limitations:
-
Not usable on thermoset
plastics
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Plastics must be rigid /
flat
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Capital cost
-
Must remove or hide weld
flash
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Limitations:
-
Requires cure
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Requires fixture time
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Adhesives for the Assembly of Medical Devices
In general,
adhesives offer several benefits over other medical device
assembly methods including ability to fill large gaps,
ability to bond dissimilar materials, ability to
distribute stress evenly across a bondline, and ability to
form a hermetic seal when confined between two substrates.
The variety
of adhesives which currently meet biocompatibility
requirements ensure that the majority of device assembly
applications can be quickly and effectively completed.
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Adhesive Type (Chemistry) |
Characteristics |
Typical Applications |
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Cyanoacrylates |
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Catheter
components
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Tubeset
bonding
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Polyolefin bonding
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Light Curing Acrylics |
|
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Needle
assembly
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Anathesia
masks
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Heat
exchangers
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Oxygenators
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Tubeset
bonding
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Epoxies |
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Needle
assembly
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Deep
section potting
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Polyurethanes |
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Regulatory Issues:
Along with
performance issues, medical device manufacturers must also
consider regulatory issues. Device manufacturers rely on
their component suppliers for assurance that the substrate
and/or adhesive will not cause problems with the
biocompatibility of the device. In an effort to address
such issues, substrate suppliers and adhesive
manufacturers began testing their components using testing
similar to that used to qualify an end-use device.
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