Keyhole mapping to enable closed-loop weld penetration depth control for remote laser welding of aluminum components using optical coherence tomography

Abstract

Remote laser welding (RLW) combines the positive features of tactile laser welding with additional benefits such as increased processing speed, reduced operational cost and service, and higher process flexibility. A leading challenge preventing the full uptake of RLW technology in industry is the lack of efficient closed loop in-process (CLIP) monitoring and weld quality control solutions. This underpins the need to fuse multiple sensor technologies and data analytics with predictive engineering simulations. Although the development and integration of a variety of sensors covers the radiation spectrum from ultraviolet to farinfrared, the flawless deployment of CLIP solutions is still challenged by the need for the following: signal denoising in the case of process instability; real-time data analytics; and adaptive control engineering architecture to cope with process variations induced by manufacturing tolerances. This paper focuses on the aspect of weld penetration depth control using optical coherence tomography (OCT) as a necessary step to enable adaptive penetration depth control during RLW of aluminum components in the fillet lap joint configuration with consideration to part-to-part gap variation. The approach entails decoupling the welding process parameters in two subsets: (1) in-plane control of the heat input on the upper part to facilitate the droplet formation; and (2) out-of-plane heat management to achieve the desired level of penetration control in the keyhole mode. This paper presents the results of finding the optimal placement of the OCT beam with variable part-to-part gap conditions. Results have shown that statistical signal processing of the raw OCT signal gives insight not only into the depth of the keyhole but can infer the shape of the keyhole itself. Current limitations and next phases of research and development are highlighted based on the experimental study.

Applying optical coherence tomography for weld depth monitoring in remote laser welding of automotive battery tab connectors

“… Measured WPD, PW,Q. A previous study [20] evaluated the sensitivity of percentile on the accuracy of the output OCT signal and showed that the 80th percentile results in the highest accuracy, i.e. minimal deviation between PW,Q and the actual penetration depth, PW,C, as measured by metallographic analysis of cross-sections.…”

“…Higher values of PW,M corresponds to higher probability of obtaining single-modal distribution. Higher values of the normalized modality index are expected when the OCT measuring beam is positioned closer to the bottom of the keyhole [20].…”

“…Research conducted in [20] concluded that the cumulative effect of those variations leads to the fact that the position of the OCT measuring beam is not universal and has to be adjusted for every specific welding setup. This paper aims at studying the impact of process variation on the WPD measurements during RLW of Al-Cu thin foil lap joint (Al 1050 foil 450 μm and Ni-plated Cu foil 300 μm) using the OCT technology in conjunction with the ARM laser.…”

“…This paper aims at studying the impact of process variation on the WPD measurements during RLW of Al-Cu thin foil lap joint (Al 1050 foil 450 μm and Ni-plated Cu foil 300 μm) using the OCT technology in conjunction with the ARM laser. It builds upon the "Keyhole Mapping" approach [20] which focused on finding the optimal position of the OCT measuring beam and was tested for fillet lap joint configuration of similar Al-Al sheet metal parts. The extension of this work to dissimilar metal welding of thin foil Al and Cu components brings the following technical challenges which will be discussed throughout the paper:…”

Algorithms for Weld Depth Measurement in Laser Welding of Copper with Scanning Optical Coherence Tomography

“…One solution to observe the weld penetration depth inline is optical coherence tomography (OCT). OCT is an interferometric measurement technology that enables the measurement of weld penetration depth coaxially to the processing laser in a fixed optic [5][6][7][8][9][10][11][12] or scanning optic [13][14][15].…”