Laser Weld Defect Detection via Thermal Radiation Analysis
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Solution Overview
Problem
Lack of fusion defects in laser welding of galvanized steel sheets are difficult to detect due to their internal nature and variable gap dimensions, which can lead to 'false friend' weld seams appearing defect-free despite incomplete fusion.
Innovation Solution
A method involving two-dimensionally locally resolved detection of radiation from the solidified molten mass and liquid melting bath to determine characteristic values for heat dissipation, comparing these with reference values to detect defects such as lack of fusion and through penetration, using thermal imaging and mathematical models to assess weld seam quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If gap dimension between metal sheets is increased to allow zinc vapor dissipation, then harmful vapor emission is reduced, but weld seam quality deteriorates due to lack of fusion
Solution Approach 1:
The patent implements real-time monitoring of the liquid melting bath during laser welding using a CCD camera to detect the position of the rear boundary face. This feedback mechanism allows dynamic adjustment of welding parameters to maintain proper fusion despite gap variations, resolving the contradiction between vapor dissipation and weld quality
Solution Approach 2:
The patent monitors and adjusts welding parameters (such as laser power and welding speed) based on the detected position of the melting bath boundary. By dynamically changing these parameters in response to gap variations, the system maintains reliable fusion while allowing sufficient gap for zinc vapor dissipation
2Difficulty of detecting and measuring
If indirect assessment variables are used to detect lack of fusion, then defect detection capability is improved, but measurement precision deteriorates due to false friend weld seams
Solution Approach 1:
The patent uses the liquid melting bath as an intermediary to detect fusion status. By monitoring the position and behavior of the melting bath boundary during welding, the system can directly assess fusion quality without relying on indirect post-weld measurements that are prone to false negatives
Solution Approach 2:
The patent performs defect detection during the welding process itself by monitoring the melting bath, rather than after welding is complete. This preliminary detection allows for immediate identification of fusion problems while the melting bath is still visible and characteristic
3Measurement precision
If two-dimensionally locally resolved detection of radiation is performed, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent uses a CCD camera to create an optical copy or image of the liquid melting bath and solidified molten mass. This optical copying approach enables two-dimensional locally resolved detection without requiring complex physical probes or sensors in the weld zone
Solution Approach 2:
The patent replaces complex mechanical measurement systems with optical detection using a CCD camera. By substituting mechanical probes with optical imaging, the system achieves high measurement precision while reducing mechanical complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for reliable detection of defects by evaluating thermal gradients and radiation patterns, providing real-time monitoring and enabling interventions to improve welding quality by adjusting parameters like welding speed and radiation intensity.
Implementation Method 1
performing a two-dimensionally locally resolved detection of radiation that is emitted by a solidified molten mass
Data Source
AI summary
A method for detecting defect in a weld seam during laser welding. The method includes performing a two-dimensionally locally resolved detection of radiation that is emitted by a solidified molten mass that is adjacent to a liquid melting bath. The method also includes determining at least one characteristic value for heat dissipation in the solidified molten mass by evaluating the detected radiation along at least one profile-section of the solidified molten mass, and detecting a defect in the weld seam by comparing the at least one characteristic value with at least one reference value.