Methods and systems for characterizing laser machining properties by measuring keyhole dynamics using interferometry
Inventors
Assignees
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Publication Number
US-10654126-B2
Publication Date
2020-05-19
Expiration Date
Abstract
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.
Core Innovation
The disclosed invention relates to low-coherence interferometry systems and methods for in-real-time characterization of a laser-created phase change region (PCR), including keyhole welding. A laser head forms a keyhole in a workpiece by focusing a laser beam, and an imaging system generates at least first and second imaging beams. The first imaging beam is directed to an imaging beam position inside the keyhole or PCR, and the second imaging beam is directed to an imaging beam position outside the keyhole or PCR.
Interferometry is used to generate a first measurement from the imaging beam inside the keyhole or PCR and a second measurement from the imaging beam outside the keyhole or PCR. The system determines keyhole depth or penetration depth into the PCR from the first measurement and the second measurement. The disclosed approach uses a reference arm and interferometer output processing to determine depth relative to top-surface reference points (TSRPs), including simultaneous TSRP tracking via a secondary reflected path from the combining optic.
The disclosed apparatus architectures include an imaging light source, beam directing optics/scanners, an optical combiner, and interferometry output processing, with optional gas/protection and auxiliary sensors. Tracking is supported using lead/lag offsets between imaging and processing beams, and compensation techniques include gas pressure path-length compensation and scanning-induced path-length distortion correction with reference delay synchronization. Experimental results are reported showing improved signal-to-noise ratio (SNR) and stability, and the ability to detect instability, spiking, and other quality indicators, with feedback/control use described for compensation.
Claims Coverage
The partial content includes four independent claims. Each independent claim is directed to measuring a penetration depth using two imaging beams with interferometry, where one imaging beam is directed inside the keyhole or PCR and the other is directed outside the keyhole or PCR.
Two-position interferometric depth measurement using imaging beams inside and outside the keyhole
Directing a focused laser beam using a focusing optic to form a keyhole for keyhole welding; generating at least first and second imaging beams; directing the first imaging beam to a first imaging beam position inside the keyhole to generate a first measurement using interferometry; directing the second imaging beam to a second imaging beam position outside the keyhole to generate a second measurement using interferometry; and determining keyhole depth from the first measurement and the second measurement.
Apparatus with dual interferometric imaging beams for keyhole depth
Providing a laser head configured to focus a laser beam onto a workpiece to form a keyhole for keyhole welding; and an imaging system configured to produce at least first and second imaging beams directed to at least first and second imaging beam positions, where the first imaging beam is directed inside the keyhole to generate a first measurement using interferometry and the second imaging beam is directed outside the keyhole to generate a second measurement using interferometry, and where the first and second measurements provide a keyhole depth measurement.
Two-position interferometric penetration depth measurement for a phase change region (PCR)
Directing a processing beam onto a workpiece using a processing beam head to form a phase change region (PCR) for achieving welding; generating at least first and second imaging beams; directing the first imaging beam to a first imaging beam position inside the PCR to generate a first measurement using interferometry; directing the second imaging beam to a second imaging beam position outside the PCR to generate a second measurement using interferometry; and determining penetration depth into the PCR from the first measurement and the second measurement.
Apparatus with low-coherence interferometry dual imaging beams for PCR depth
Providing a processing beam head configured to shape and direct a processing beam onto a workpiece to form a phase change region (PCR) for achieving welding; and an imaging system configured to produce at least first and second imaging beams directed to at least first and second imaging beam positions, where the first imaging beam is directed inside the PCR to generate a first measurement using low coherence interferometry and the second imaging beam is directed outside the PCR to generate a second measurement using low coherence interferometry, where the first and second measurements provide a depth measurement in the PCR.
Across the independent claims, the claimed inventive concept centers on generating two imaging beams for interferometry-based depth measurement, with one measurement obtained from an inside-keyhole or inside-PCR imaging position and a second measurement obtained from an outside-keyhole or outside-PCR imaging position, and then determining depth from the two measurements.
Stated Advantages
Improved signal-to-noise ratio (SNR) and stability.
Ability to detect instability, spiking, and other quality indicators.
Feedback/control use described for compensation.
Documented Applications
Keyhole welding.
Welding by forming a phase change region (PCR).
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