Low-Coherence Interferometry for Keyhole Weld Porosity Control
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Solution Overview
Problem
Current laser welding technologies face challenges in controlling the phase change region (PCR) during keyhole welding, leading to instability, internal voids, and high weld porosity due to the turbulent and stochastic nature of the light-matter interaction, which results in poor weld quality and requires expensive and destructive testing for verification.
Innovation Solution
The implementation of low-coherence interferometry to characterize the morphology of the keyhole and surrounding material by directing an interferometry measurement beam into the PCR, allowing for real-time monitoring of keyhole depth, width, and shape, and processing the interferometry output to determine critical characteristics, thereby enhancing control over the welding process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If keyhole welding is used to achieve deeper penetration and higher aspect ratio features, then the depth of the phase change region increases, but the process becomes more unstable and produces internal voids and high weld porosity
Solution Approach 1:
The patent implements real-time monitoring of keyhole dynamics using interferometry to provide feedback control. The system measures keyhole depth, width, and morphology continuously during welding, and uses this information to adjust welding parameters dynamically. This feedback mechanism allows the system to maintain stable keyhole formation at greater depths while preventing the instability that leads to voids and porosity.
Solution Approach 2:
The patent employs a multi-functional approach by using interferometry to simultaneously measure multiple keyhole characteristics (depth, width, shape, stability) with a single measurement system. This comprehensive monitoring capability enables the system to control various aspects of the welding process concurrently, ensuring both deep penetration and high weld quality without requiring separate measurement systems for each parameter.
2Loss of information
If conventional welding imaging solutions are used to monitor the weld joint, then the weld joint position can be tracked, but the phase change region dynamics cannot be characterized in real-time
Solution Approach 1:
The patent introduces interferometry as an intermediary measurement technique that bridges the gap between conventional imaging and direct PCR observation. The interferometric measurement beam acts as a mediator that can penetrate or reflect from the keyhole region to provide real-time information about PCR dynamics, while conventional imaging continues to track the weld joint position. This dual approach allows simultaneous acquisition of both positional and dynamic information.
Solution Approach 2:
The patent segments the measurement function into two distinct components: conventional imaging for weld joint tracking and interferometry for PCR dynamics characterization. This segmentation allows each measurement system to be optimized for its specific function without compromising the other, enabling simultaneous acquisition of weld position information and keyhole morphology data with appropriate precision for each purpose.
3Reliability
If destructive testing is used to verify weld quality, then accurate weld verification can be achieved, but the process is expensive and time-consuming
Solution Approach 1:
The patent performs preliminary assessment of weld quality by monitoring keyhole dynamics in real-time during the welding process itself. By measuring critical parameters such as keyhole stability, depth, and morphology continuously, the system can predict potential quality issues before they occur and adjust parameters preventively. This preliminary action reduces or eliminates the need for subsequent destructive testing, thereby maintaining high verification reliability while dramatically improving productivity.
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 enables dynamic and simultaneous tracking of the welding process, improving weld quality by reducing instability and porosity, and providing real-time feedback for process control, thus eliminating the need for destructive testing.
Implementation Method 1
an imaging light source that produces imaging light that is applied to a material processing system... at least one input-output port that outputs a first component of the imaging light to an optical access port of the material processing system and that receives a reflection component of the imaging light
Implementation Method 2
an optical combiner that combines the reflection component and at least another component of the imaging light to produce an interferometry output, the interferometry output based on a path length taken by the first component and the reflection component compared to a path length taken by the at least another component of the imaging light
Implementation Method 3
a material processing beam source that produces a material processing beam that is applied to the material in the material modification process wherein the material processing beam creates the phase change region (PCR) in the material
Implementation Method 4
the beam intensity is sufficient to melt the surface to open a vapor channel (also known as a capillary or 'the keyhole')
Implementation Method 5
the beam intensity is sufficient to melt the surface to open a vapor channel
Data Source
AI summary
A method, apparatus, and system are provided to monitor and characterize the dynamics of a phase change region (PCR) created during laser welding, specifically keyhole welding, and other material modification processes, using low-coherence interferometry. By directing a measurement beam to multiple locations within and overlapping with the PCR, the system, apparatus, and method are used to determine, in real time, spatial and temporal characteristics of the weld such as keyhole depth, length, width, shape and whether the keyhole is unstable, closes or collapses. This information is important in determining the quality and material properties of a completed finished weld. It can also be used with feedback to modify the material modification process in real time.