The welding process around the top cover of a square aluminum battery often results in inward deformation of the aluminum casing after welding. Today, we will conduct a simple analysis.
Root cause analysis
The main causes of welding deformation in aluminum shells are as follows:
Uneven heat input: Welding heat accumulation leads to differences in temperature contraction in the fusion zone between the cover plate and the shell;
Material properties: Aluminum alloys have a large coefficient of linear expansion, and the release of residual stress in the weld zone induces plastic strain;
Insufficient clamping of the fixture: Excessive gap or step value in the shell cover leads to inconsistent shrinkage after welding.
Specific solutions
1. Precise optimization of welding process parameters: Power reduction-speed increase strategy: Power adjustment: Appropriately reduce power but avoid incomplete welding and excessive penetration; Speed increase: Increase welding speed and reduce heat input; Defocus optimization: Adjust negative defocus to positive defocus, expand the spot size and reduce heat concentration at the bottom of the molten pool; Composite spot/oscillating welding: Use fiber-semiconductor composite laser or ring spot to balance the stability of the molten pool; Increase beam oscillation (oscillation spacing 0.5-0.7mm, frequency ≥200Hz) to disperse heat input.
2. Fixture and Press-fit Control (Key Measures) Step and Clearance Calibration: Use a 3D profiler to ensure that the step value between the cover plate and the housing is ≤0.2mm and the clearance is ≤0.05mm; add suction cup clamps to tighten the large surface of the housing and suppress welding shrinkage and inward concavity; Hydraulic clamping optimization: increase the press-fitting pressure, increase clamping rigidity, and reduce the misalignment of the cover and housing during welding.
3. Protective gas and plasma control: Protective gas parameters: Nitrogen (purity ≥99.999%) coaxial blowing, flow rate 15-25L/min, angle 30°-45° (to avoid turbulence forming pores and molten pool fluctuations); add side blowing auxiliary gas (inert gas) to further suppress plasma interference.
Post-weld straightening and process verification
1. Roll forming: Roll forming is used for long-side welds to eliminate post-weld shrinkage stress;
2. Metallographic inspection: Randomly check whether the maximum weld depth (0.8~1.3mm), weld width (≥1.0mm), and flange allowance (≤60μm) meet the standards;
3. Online monitoring: An OCT melt depth monitoring system (250kHz sampling) is introduced to provide real-time feedback on keyhole depth fluctuations and dynamically adjust power and speed.
Emergency adjustment of implementation path priority: Prioritize optimization of welding parameters (power-speed-decoking amount) and preheating process to reduce heat input; Fixture upgrade: Simultaneously improve press-fit fixtures (suction cup design + pressure calibration) to ensure that the step value meets the standard; Long-term solution: Introduce oscillating welding or composite light source equipment to enhance heat distribution control capabilities.
