Laser Welding OCT Depth Measurement Under Varying Keyhole States
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Solution Overview
Problem
Existing laser welding apparatuses face challenges in accurately measuring the penetration depth of a welding portion due to variations in material, temperature, and keyhole formation state, leading to insufficient measurement accuracy and quality evaluation.
Innovation Solution
A laser welding apparatus and method utilizing a swept source optical coherence tomography (SS-OCT) system that generates an interference signal to create two-dimensional tomographic image data, allowing for the extraction of specified depth data and derivation of accurate penetration depth even when the keyhole formation state is not constant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If beam emission intensity correlation method is used to measure penetration depth, then measurement can be performed indirectly based on molten metal emission, but measurement accuracy deteriorates when keyhole formation state varies
Solution Approach 1:
The patent replaces the indirect optical emission correlation method with direct optical coherence tomography (OCT) measurement. The OCT system uses low-coherence interferometry to directly measure the depth of the keyhole bottom, substituting the mechanical/optical emission correlation approach with an optical interferometric measurement system that provides direct geometric measurement independent of keyhole formation state
Solution Approach 2:
The patent introduces an optical interferometer as an intermediary measurement system. The interferometer generates reference and measurement beams that interfere to produce depth information, acting as a mediator between the welding process and the measurement system. This intermediary approach allows direct measurement of keyhole depth without relying on correlations with molten metal emission characteristics
2Measurement precision
If optical interferometer measurement beam is used to directly measure keyhole depth, then direct measurement is achieved, but measurement accuracy deteriorates when keyhole formation state is not constant
Solution Approach 1:
The patent applies preliminary action by measuring the keyhole depth during the welding process itself rather than after welding completes. The OCT measurement system operates concurrently with the welding, capturing depth information at various stages of keyhole formation. This real-time measurement approach allows the system to track depth variations and identify the maximum penetration depth achieved, improving reliability under varying conditions
Solution Approach 2:
The patent transitions from indirect one-dimensional emission intensity measurement to direct depth measurement by introducing the depth dimension through optical path difference measurement. The OCT system measures the optical path difference between reference and measurement beams, converting this into direct depth information in the vertical dimension, providing accurate penetration depth measurement independent of keyhole formation state variations
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
Enables precise measurement and evaluation of penetration depth, ensuring high accuracy in assessing the quality of the welding portion regardless of keyhole formation variations.
Implementation Method 1
an optical interferometer configured to generate an interference signal that indicates an intensity of an interference beam including a measurement beam reflected by the welding portion and a reference beam
Implementation Method 2
The laser beam is transmitted to a beam condensing optical system 13 via a laser beam transmitting optical system 12, and is condensed on a welding portion 2 of a welded material 1 by the beam condensing optical system 13
Implementation Method 3
a laser beam... condensed on a welding portion... enabling localized heating and welding
Implementation Method 4
During welding, a molten metal of the welding portion 2 emits a beam. The beam emitted from the molten metal is condensed by the beam condensing optical system 13 and transmitted to an interference filter 15
Data Source
AI summary
A laser welding apparatus includes: a laser oscillator configured to emit a laser beam toward a welding portion of a welded material; an optical interferometer configured to generate an interference signal that indicates an intensity of an interference beam of a measurement beam reflected by the welding portion and a reference beam; and a derivation unit configured to generate, based on the interference signal, two-dimensional tomographic image data indicating a correlation among a distance in a proceeding direction of welding of the welding portion, a depth of the welding, and an intensity of the interference signal, to extract specified depth tomographic image data within a specified range from the two-dimensional tomographic image data, and to derive a depth for each distance based on the intensity of the interference signal in the specified depth tomographic image data.