Long Term Interconnect Creep and Weld Fatigue under Cyclic Thermal Load in Heavy Formats
Thermal expansion and cell swell induce cyclic shear stresses that trigger weld fatigue and interconnect creep, requiring compliance flexure loops.
Keyhole Porosity
Meaning
Structural defects occur during high energy density welding when a deep vapor cavity collapses prematurely. In the context of battery busbar joining, keyhole porosity reduces the mechanical strength and electrical conductivity of the weld bead. This condition results from an unstable metal vapor plume.
Formation Mechanism
Rapid cooling of the molten pool traps gas bubbles before they can escape to the surface. Fluctuations in laser power or travel speed contribute to the development of keyhole porosity in thin gauge copper and aluminum tabs.
Conductivity Impact
Internal voids increase the effective resistance of the joint, leading to localized heating under high current loads. Monitoring for keyhole porosity prevents the long term degradation of the battery interconnect system.
Welding Control
Optimizing the beam profile and the shielding gas flow helps maintain a stable vapor channel throughout the process. When keyhole porosity is detected through cross sectional analysis, engineers must adjust the pulse frequency and the focal position of the laser. Advanced real time monitoring systems use acoustic or optical sensors to identify the collapse of the keyhole during the weld event.
These systems allow for the immediate rejection of parts that do not meet the density requirements specified in the engineering standard. Continuous adjustment of the heat input maintains the integrity of the fused metal.