Ultrasound Tab Welding Microstructure and Joint Resistance Limits
Ultrasonic tab welding balances acoustic softening and static clamp force to break interfacial oxides, yielding sub-5-micro-ohm joints without foil cutting.
Acoustic Softening
Meaning
Reduction of flow stress in metallic materials occurs during the application of high frequency mechanical vibrations. This physical phenomenon characterizes the decrease in resistance to plastic deformation when ultrasonic energy enters a workpiece. Manufacturers utilize acoustic softening to facilitate the bonding of thin foils in battery tab welding without requiring the heat levels associated with traditional laser or resistance methods.
It acts on the crystalline lattice by increasing dislocation mobility, which allows the metal to yield at lower static pressures. The effect ceases immediately when the ultrasonic generator stops, ensuring that the finished joint retains its mechanical strength.
Deformation Mechanism
High frequency oscillations provide kinetic energy that lowers the external force needed for grain boundary sliding. While acoustic softening assists the initial phase of metal joining, the process eventually transitions to hardening as the lattice structure stabilizes. This transition determines the optimal dwell time for a weld cycle.
Yield Reduction
Stress levels drop precipitously when the ultrasonic amplitude reaches a specific threshold relative to the material thickness. Because acoustic softening operates at the molecular level, it prevents the macro scale melting that often compromises the structural integrity of thin copper or aluminum collectors.
Manufacturing Application
Equipment settings for ultrasonic welders rely on this property to achieve hermetic seals on pouch cell tabs. By modulating the power delivery, a technician controls how acoustic softening influences the flow of metal around the horn teeth. Consistent control prevents excessive thinning of the foil stack during the assembly of high density battery packs, which protects the integrity of the power path.