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.
Anvil Serration
Meaning
Teeth or ridges machined into the fixed base of an ultrasonic welding system provide the mechanical grip necessary to prevent material slippage. This surface geometry consists of a pattern of peaks and valleys that anchors the bottom layer of a workpiece against the vibrations of the welding horn. Proper anvil serration ensures that the energy from the transducer converts into internal friction at the weld interface rather than causing the entire stack to slide.
The dimensions of these features are tailored to the hardness and thickness of the metals being joined, such as the copper or aluminum foils used in battery electrode assembly. If the pattern is too aggressive, it risks piercing the material, while an overly smooth surface leads to poor bond quality.
Grip Pattern
Cross hatch or linear grooves define the contact area where the metal rests. Effective anvil serration distributes the clamping force across multiple contact points to prevent localized stress fractures in thin collectors.
Tooling Life
Wear on the sharp edges of the teeth eventually reduces the effectiveness of the mechanical coupling. Regular inspection of the anvil serration reveals when the tool requires replacement to maintain consistent electrical resistance across finished battery cells.
Material Interaction
Hardness values of the anvil must exceed those of the foils to maintain the integrity of the ridge profile over thousands of cycles. Soft materials like aluminum flow into the valleys of the anvil serration, creating a physical interlock that supports the development of a solid state bond. This interlocking prevents lateral movement during the high frequency oscillation phase of the welding process.