How Does Ultrasonic Welding Melt Materials
Ultrasonic is used in welding to provide small but rapid vibrations. When the horn or sonotrode is attached to materials, the ultrasonic vibrations will cause the materials to vibrate about half a millimeter or so in to and fro motion.
Such a minute motion is enough to melt the material because the rate of vibration is quite high. These vibrations cause the materials to rub against each other, and the resulting friction between them generates heat.
You can reenact a similar environment by rubbing your hands together rapidly. You will feel the heat being generated between your palms.
And if you continue rubbing rapidly, it gets quite uncomfortable. Imagine the heat generated within the materials when they rub against each other with speeds that are hard to pick up by the human eye!
The friction raises the temperature to such a degree that the contact points between the materials melt, paving the way for molecular bonding. This is how ultrasonic welding welds plastics.
However, there is a slight difference when it comes to welding metals. Ultrasonic welding is used to heat the metal to one-third of its melting point temperature.
At this point, the molecules between the two metals will travel across each other, creating a strong molecular bond. There is no melting in metals.