Quantitative evaluation of keyhole stability during laser welding using optical coherence tomography

Abstract

Online monitoring of keyhole during laser welding is of great importance to evaluate the stability of the live process and the final quality of the weld. Indirect methods based on visual imaging and thermal radiation are lack of strong correlations with keyhole behavior, resulting in a low accuracy. Optical coherence tomography (OCT) shoots beam coaxially with the processing beam into the bottom of the keyhole, enabling direct monitoring of keyhole behavior. However, current OCT keyhole monitoring systems suffer from the harsh noise and are limited to only evaluating the keyhole depth through statistical analysis. In this paper, an enhanced OCT system was built with a capacity of capturing keyhole open/collapse behavior, opening a way of quantitatively evaluating the keyhole behavior. First, the signal was denoised and filled given the nature of fluid dynamics in time domain. Then an algorithm was developed to automatically detect the keyhole open/collapse behavior, based on which the weld status (heat conduction mode and keyhole mode) is determined, and the metrics of interests are characterized quantitatively. The proposed method provides a solid method to quantitatively evaluate the keyhole stability, which is well suited for developing new laser welding process and monitoring laser involved high volume manufacturing.

Keywords:

• Laser welding
• optical coherence tomography
• keyhole
• weld status
• quantitative evaluation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The financial support of National Natural Science Foundation of China under Grant 62003075, 62303093, U2030205, 61903065, 62003074, the New Cornerstone Science Foundation through the XPLORER PRIZE and Sichuan Science and Technology Planning Project 2022JDJQ00400, 2023YFG0044 is acknowledged.