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.
Shear Strength Limit
Meaning
Mechanical force thresholds define the maximum parallel load a welded or bonded battery connection can withstand before failing. Exceeding the shear strength limit leads to the separation of tabs, foils, or busbars, causing an open circuit or high-resistance failure. Design engineers use this metric to evaluate the physical durability of cell connections.
Mechanical Testing
Destruction tests are executed on sample joints during production to measure the maximum force required to tear the connection apart. A joint that fails below the specified shear strength limit indicates a sub-optimal welding process, such as incorrect ultrasonic power or laser focus. These tests are performed using specialized tensile pull testers equipped with custom grips.
Structural Integrity
Vibration and thermal expansion put continuous mechanical stress on battery joints during their field life in electric vehicles. If the joints are engineered too close to their shear strength limit, the cyclic stresses can cause fatigue and lead to sudden joint failure under road shocks. High-quality packs are designed with a safety margin that lies well above this mechanical threshold.
Material Selection
Different metals and alloy combinations exhibit varying levels of joint toughness. Selecting the right metal foil thickness ensures that the finished joint does not fail below the required shear strength limit.