For thermoplastic welding applications, the mechanical oscillations are transmitted under pressure to the plastic piece to be welded. These oscillations generate molecular agitation in the thermoplastic, due to its high degree of absorption; in turn it generates a suitable local temperature. The temperature rising causes even more heating by vibration, which accelerates the process. The result is clean, quick welding, typically less than one second.
In ultrasonic welding usually we find two types of applications:
• Welding using an energy director. This type of welding is used to join a wide variety of parts given its excellent appearance, high mechanical strength and even sealing, if required. The energy director provides a specific volume of material to melt, so as to provide good strength without excessive burr, also due to its design it impedes the passage of energy from the top to the bottom piece causing heating in the contact zone between both and thereby producing the fusion and welding of the two parts.
• Spot welding. This type of welding is used for joining flat surfaces and is based on the penetration of the horn by the lower part, both being joined at the penetration zone.