Root cause analysis
The main causes of welding deformation in aluminum shells are as follows:
Uneven heat input: Welding heat accumulation leads to temperature difference and shrinkage differences in the fusion zone between the cover plate and the shell; Material properties: Aluminum alloy has a large coefficient of linear expansion, and residual stress release in the weld zone triggers plastic strain; Insufficient clamping of fixtures: Excessive gap or step value between the shell and cover leads to inconsistent shrinkage after welding. Specific solutions: 1. Precisely optimize welding process parameters.
Power reduction-increase strategy:
Power adjustment: Reduce the power appropriately, but avoid incomplete welding and excessive penetration;
Speed Enhancement: Increase welding speed and reduce heat input;
Defocusing optimization: Negative defocusing was adjusted to positive defocusing, expanding the light spot and reducing heat concentration at the bottom of the molten pool;
Composite spot/oscillating welding:
Fiber-semiconductor composite lasers or ring-shaped laser beams are used 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 gap calibration:
Use a 3D profilometer to ensure that the step value between the cover plate and the housing is ≤0.2mm and the gap is ≤0.05mm;
Adding suction cup clamps to tighten the large surface of the housing helps suppress weld shrinkage and inward concavity.
Hydraulic clamping optimization:
Increase the pressing pressure, increase clamping rigidity, and reduce misalignment of the cover during welding.
3. Protective gas and plasma control
Protective gas parameters:
Nitrogen gas (purity ≥99.999%) is purged coaxially at a flow rate of 15-25 L/min and an angle of 30°-45° (to avoid turbulence that could cause porosity and molten pool fluctuations).
Adding side-blowing auxiliary gas (inert gas) further suppresses plasma interference.
Post-weld straightening and process verification
1. Roller straightening:
Rolling edge process is used for long side welds to eliminate post-weld shrinkage stress;
2. Metallographic testing:
The maximum melt depth (0.8~1.3mm), melt width (≥1.0mm), and flange allowance (≤60μm) were randomly inspected to ensure they met 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.
