Study on Porosity Defect Detection in Narrow Gap Laser Welding Based on Spectral Diagnosis

Area of Science:

• Materials Science
• Manufacturing Engineering
• Plasma Physics

Background:

• Narrow gap laser welding offers high efficiency for thick components but suffers from porosity defects.
• The complex welding environment, including contaminants, exacerbates porosity issues.

Purpose of the Study:

• To investigate the impact of process parameters and contaminants (water, oil) on porosity in narrow gap laser welding.
• To analyze the mechanism of water's effect on laser-induced plasma characteristics.
• To establish a method for identifying porosity defects using spectral analysis.

Main Methods:

• Experimental narrow gap laser welding (self-fusion and wire filling).
• Plasma diagnostics using optical emission spectroscopy (OES) and Boltzmann plot method.
• X-ray detection for porosity assessment.
• Analysis of spectral intensity variations under different conditions.

Main Results:

• Spectral intensity in narrow gap welding is lower than in flat plate welding.
• Optimal conditions yielded electron temperature of 7413.3 K and density of 5.6714 × 10^15 cm^-3 with minimal porosity.
• Water contamination drastically increased porosity and altered plasma properties (reduced temperature, increased density).
• Fe I spectral line intensity effectively differentiates between normal and contaminated welding conditions.

Conclusions:

• Water and oil pollutants significantly increase porosity defects in narrow gap laser welding.
• Plasma spectral analysis, particularly Fe I line intensity, provides a reliable method for detecting these defects.
• Understanding plasma behavior under contamination is crucial for controlling weld quality.