Working Principle Of Ultrasonic Welding

The working principle of ultrasonic welding is to generate heat by friction between the contact surfaces of the welding materials through high-frequency mechanical vibration (usually 15-40kHz), which will fuse after reaching the melting point and form a strong connection after cooling. ‌This technology is applicable to plastics and metals, but the welding mechanisms of the two types of materials are different: plastics rely on local high-temperature melting, while metals achieve molecular bonding through solid-state plastic deformation‌
‌Overview of core principles‌
‌Energy conversion process‌:
Electric energy is converted into high-frequency mechanical vibration (ultrasound) by the transducer.
The vibration is amplified by the horn and transmitted to the welding head, focusing on the welding area. ‌‌
‌Material fusion mechanism‌:
Plastic welding: High-frequency vibration induces molecular friction, produces a local high-temperature melting interface, and forms a molecular chain after pressurized cooling. ‌‌
Metal welding: Vibration causes the oxide layer on the contact surface to break, and the metal lattice plastically deforms to form a micro weld without reaching the melting point. ‌‌
‌Detailed steps of plastic welding‌
‌Vibration transmission‌: The welding head transmits ultrasonic energy to the joint surface of the plastic workpiece, and the difference in acoustic impedance leads to energy concentration. ‌‌
‌Heat generation‌: The contact surface temperature rises suddenly due to high-frequency friction (poor thermal conductivity causes heat accumulation), reaching the melting point of the material. ‌‌
‌Pressure fusion‌: The molten interface penetrates each other under continuous pressure, and cools and solidifies after stopping vibration. ‌‌
‌Key features of metal welding‌
‌Cold welding characteristics‌: The temperature is only 1/3-1/2 of the metal melting point, avoiding defects in the heat-affected zone. ‌‌
‌Three-stage molecular bond formation‌:
Initial plastic deformation removes surface contaminants.
Micro welds expand the contact area through vibration.
Finally, a metallurgical bond is formed.