Coaxial Laser Interferometry for In-Situ 3D Melt Pool Measurement
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Solution Overview
Problem
Current LPBF AM processes face challenges in in-situ online monitoring of melt pool 3D morphology due to high temperatures and small areas, leading to poor accuracy in morphology measurement.
Innovation Solution
An in-situ measurement device and system that uses a measurement laser device, beam splitter, processing laser device, galvanometer, field lens, and image acquisition unit to capture interference images of melt pools, processed by an image processing unit comprising a GAN, wrapped phase retrieval module, and absolute phase retrieval module to obtain accurate 3D morphology information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-speed cameras are used to capture melt pool surface morphology, then two-dimensional surface information can be obtained, but the true three-dimensional morphology cannot be accurately measured
Solution Approach 1:
The patent introduces a measurement laser beam as an intermediary to probe the melt pool surface. The laser beam interacts with the melt pool surface to create interference patterns that encode three-dimensional topography information, which is then captured by the camera system. This intermediary approach enables 3D measurement without requiring complex multi-camera setups.
Solution Approach 2:
The patent replaces traditional mechanical 3D scanning systems with an optical interference-based measurement system. By using laser interference patterns instead of mechanical profilometers or structured light scanners, the system achieves 3D morphology measurement with reduced complexity and higher temporal resolution suitable for dynamic melt pool monitoring.
2Measurement precision
If high-speed cameras directly capture melt pools at high temperatures, then in-situ monitoring is achieved, but thermal radiation interferes with image quality and measurement accuracy
Solution Approach 1:
The patent applies a short-pass filter before the camera detector to block thermal radiation in advance. This preliminary filtering action removes the harmful thermal radiation components from the optical path before they can interfere with the measurement, allowing clear capture of the laser-induced interference patterns from the hot melt pool surface.
Solution Approach 2:
The patent utilizes wavelength-selective filtering to isolate the measurement laser wavelength from the broad-spectrum thermal radiation. By selectively transmitting only the measurement laser wavelength range and blocking other wavelengths including thermal radiation, the system achieves thermal radiation rejection while maintaining measurement signal integrity.
3Area of stationary object
If the measurement area is increased to improve signal capture, then more morphology information is obtained, but the small melt pool area makes accurate measurement difficult
Solution Approach 1:
The patent transitions from direct spatial magnification to optical path length modulation for measurement. By encoding height information into the optical path length of the laser beam through interference patterns, the system achieves high-resolution 3D measurement of small features without requiring large physical measurement areas or high-magnification optics.
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
Achieves high-precision, in-situ monitoring of melt pool 3D morphology with micrometer-level accuracy, overcoming the limitations of two-dimensional surface morphology capture and high-temperature interference.
Implementation Method 1
a light beam formed by the reference laser beam interfered with the measurement laser beam reflected by the melt pool is directed to the image acquisition unit
Implementation Method 2
the filter eliminates a high-temperature thermal radiation emitted from the melt pool
Implementation Method 3
the filter eliminates a high-temperature thermal radiation emitted from the melt pool
Implementation Method 4
the processing laser beam melts the metal powder to form melt pool
Implementation Method 5
the processing laser beam melts the metal powder to form melt pool
Data Source
AI summary
The disclosure aligns a processing laser beam and a measurement laser beam coaxially, and directs the processing laser beam and the measurement laser beam respectively onto the metal powder and melt pool surface for manufacturing and measuring the 3D of melt pool. A light beam is formed by the reference laser beam interfered with the measurement laser beam reflected by the melt pool, and is directed to the image acquisition unit to obtain an interference image of the melt pool surface. The contour accuracy was proved to be 15 nm under case of lateral resolution of 15.63 μm by the resolution board. The experiment of 3D melt pool was performed. This disclosure enables in-situ measurement of the 3D morphology of the melt pool during additive manufacturing. The disclosure is to incorporate a filter to eliminate high-temperature thermal radiation emitted from the melt pool, significantly enhancing the accuracy of morphology measurements.