Powder Bed Fusion Laser Alignment Using Isotropic Spot Detection
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Solution Overview
Problem
Existing methods for aligning laser scanners in powder bed fusion apparatuses are prone to inaccuracies due to thermal expansion and contraction, which affect the alignment of optical modules, and rely on assumptions about the position of laser beams within the field of view of on-axis detectors, leading to issues like multiple images from back-reflections and obscured melt pools.
Innovation Solution
The use of isotropic position sensitive detectors to determine the centroid of laser spots or melt pools without relying on the focus of the image, and positioning these detectors after movable focussing optics to avoid interference, allowing for faster and more accurate alignment of laser beams by comparing recorded positions with expected positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If on-axis detectors are used to determine laser beam position, then alignment can be performed, but multiple images from back-reflections and obscured melt pools cause measurement inaccuracies
Solution Approach 1:
The patent introduces a separate detection optical path that acts as an intermediary between the laser beam and the detector. This separate path captures the laser beam position without being affected by back-reflections from the powder bed or obscured views of the melt pool, thereby resolving the measurement accuracy issue while maintaining the ability to perform alignment.
Solution Approach 2:
The patent segments the optical paths into separate channels: one for laser beam delivery and another for position detection. This segmentation allows the detection system to independently measure laser spot position without interference from the melting process, eliminating the harmful effects of back-reflections and obscured views.
2Manufacturing precision
If calibration is performed multiple times during build to account for thermal expansion, then alignment accuracy is maintained, but build time increases
Solution Approach 1:
The patent implements continuous feedback by monitoring laser spot position throughout the build process using the separate detection optical path. This real-time feedback allows the system to detect and compensate for thermal expansion effects without stopping the build, thereby maintaining alignment accuracy while avoiding build time penalties.
Solution Approach 2:
The patent ensures continuous alignment monitoring and correction during the entire build process rather than performing discrete calibration stops. This continuity maintains manufacturing precision while maximizing productivity by eliminating interruptions to the additive manufacturing process.
3Measurement precision
If dedicated calibration areas or material consolidation is used for alignment, then scanner positioning can be determined, but system footprint increases and material is consumed
Solution Approach 1:
The patent enables the system to perform self-calibration by using the laser beam itself as the calibration target. The detection optical path monitors the laser spot position directly on the powder bed, allowing the system to determine scanner positioning without requiring separate calibration objects or dedicated calibration areas, thereby eliminating material consumption for calibration purposes.
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 method provides precise and efficient alignment of laser beams in powder bed fusion, reducing system footprint and minimizing errors from thermal changes and optical interference, enabling faster and more accurate calibration without the need for dedicated calibration areas or material consolidation.
Implementation Method 1
position sensitive detectors to determine the centroid of laser spots or melt pools without relying on the focus of the image
Implementation Method 2
a laser beam is scanned across portions of the powder layer that correspond to a cross-section (slice) of the workpiece being constructed. The laser beam melts or sinters the powder to form a solidified layer
Implementation Method 3
The laser beam melts or sinters the powder to form a solidified layer
Implementation Method 4
optical modules, each optical module for directing a corresponding laser beam to the powder bed
Data Source
AI summary
A method includes a plurality of scanners, each scanner directing a corresponding laser beam to different positions on a powder bed, an isotropic position sensitive detector arranged to detect electromagnetic radiation arising from interaction of the laser beams with the powder bed and a movable optical component for moving a field of view of the isotropic position sensitive detector to different positions on the powder bed. The method includes positioning the movable optical component and/or a first or second scanner of the plurality of scanners such that a first or second point irradiated by a first or second laser beam of the first or second scanner within the field of view of the isotropic position sensitive detector and recording a first or second position of an image on the isotropic position sensitive detector generated during irradiation of the first or second point by the first or second laser beam.