Page 168 - C:\Users\Adik\Documents\Flip PDF Professional\Marketer PPT LR\

while the softened plastic cools. Joint strength is very near that of the parent
material. Cycle time including manual loading and unloading ranges between 5 and
8 sec for most parts. The process is adaptable to fully automated systems. This
technique is particularly useful for joining linear objects that are too large for
ultrasonic welding or where hotplate welding would take too long. Vibration welding
accommodates large parts that are impossible or impractical to weld by other
methods. Parts can be rectangular or irregular, as long as the weld joint is in a single
plane and a small amount of motion (at least 0.12 in.) in that plane is possible.
Components with weld surfaces as long as 20 in. have been successfully joined
Ultrasonic Welding: Ultrasonic welding is another frictional process that can be
used on many thermoplastic parts. Frictional heat in this form of welding is
generated by high-frequency vibration. The key component is a transducer or
converter where electrical energy is transformed into mechanical vibrational energy
with the same frequency.
The horn vibrates the substrate sufficiently fast relative to a fixed substrate that
significant heat is generated at the interface. With pressure and subsequent
cooling, a strong bond can be obtained. The frequency generally used in ultrasonic
assembly is 20 kHz, because the vibration amplitude and power necessary to melt
thermoplastics are easy to achieve. However, this power can produce a great deal
of mechanical vibration, which is difficult to control, and tooling becomes large.
Higher frequencies (40 kHz) that produce less vibration are possible and are
generally used for welding the engineering thermoplastics and reinforced polymers.
Higher frequencies are also more appropriate for smaller parts and for parts where
less material degradation is required. The Ultrasonic Welder comprises of two
devices to increase the amplitude - of the vibrations sufficient enough to melt the
material to be welded. The first is known as a booster and is an integral component
of the ultrasonic welder that typically doubles the amplitude. The second is the horn,
also known as a sonotrode. This is not a part of the machine and must designed
specifically to suit the individual welding task. The horn is in contact with the parts to
be joined, and is contoured to fit the joint. Its function is to transfer both vibration and
pressure to the joint while further increasing the amplitude of vibration at the tip.
Horn design is a complex affair and is best left in the hands of Machine supplier. The
suitability of a thermoplastic for ultrasonic welding depends on its ability to transmit
high frequency vibration. This means that rigid materials are better than flexible
ones. Melting behaviour is also important. Materials that melt over a broad
temperature range and resolidify gradually work best. This is why amorphous
plastics are better for ultrasonic welding than semicrystalline plastics.
Important parameters for welding - TEMPERATURE, PRESSURE, TIME
Temperature is the set welding temperature for the plastic that you are welding. It is
crucial to be able to adjust the temperature on the tool according to the plastic and to
maintain the set temperature throughout the welding process.
Pressure is very important. Without it you cannot get plastics to join together.
Pressure is applied by pushing down on the welding rod while welding or, if butt
welding, on the two edges that are being overlap welded together.
Time is critical because if you move too fast or too slow, the quality of the weld will be
compromised.

DAVE TECHNICAL SERVICES 168