Laser Welding Penetration Monitoring Based on Time-Frequency Characterization of Acoustic Emission and CNN-LSTM Hybrid Network

Abstract

In-process penetration monitoring of the pulsed laser welding process remains a great challenge for achieving uniform and reproducible products due to the highly complex nature of the keyhole dynamics within the intense laser-metal interactions. The main purpose of this study is to investigate the feasibility of acoustic emission (AE) measurement for penetration monitoring based on acoustic wave characteristics and deep learning. Firstly, a series of laser welding experiments on aluminum alloys were conducted using high-speed photography and AE techniques. This allowed us to in-situ visualize the complete keyhole dynamics and elucidate the generation mechanism of acoustic waves originating from pressure fluctuations at the keyhole wall. Then, an adaptive time-frequency technique namely VMD (Variational Mode Decomposition) was proposed to characterize the acoustic energy distribution among the nine subsignals with low-frequency and high-frequency components under different welding penetrations. Lastly, a novel hybrid model combing CNN (Convolutional Neural Network) and LSTM (Long Short Term Memory) was designed to deeply mine the spatial and temporal acoustic features from the extracted frequency components. Extensive experiments demonstrate that our proposed approach yields a remarkable classification performance with a test accuracy of 99.8% and a standard deviation of 0.21, which obtains a high recognition rate. This work is a new paradigm in the digitization and intelligence of the laser welding process and contributes to an alternative way of developing an efficient end-to-end penetration monitoring system.

LSTM Modeling for Improved Laser Welding of AISI 904 L Stainless Steel for optimal Parameter Selection

“…In 2023, Luo et al [20], addressed the persistent challenge of in-process penetration monitoring in pulsed laser welding, crucial for achieving uniform and reproducible products amidst the intricate dynamics of keyhole formation during intense laser-metal interactions. This study aimed to explore the viability of acoustic emission measurement for penetration monitoring through an innovative combination of acoustic wave characteristics and deep learning.…”

Virtual Sensor for On-Line Hardness Assessment in TIG Welding of Inconel 600 Alloy Thin Plates

“…This high workload cannot be omitted by sample generation using, e.g., finite-elementmethod simulation. This is the case because in simulations for fixed sets of parameters, the same results will always be obtained [26][27][28]. During welding for the same set of parameters, slightly different results are gathered due to differences in the material structure or temporary changes in process conditions [29][30][31].…”

Temporal Resolution of Acoustic Process Emissions for Monitoring Joint Gap Formation in Laser Beam Butt Welding

“…Yet, as the authors of [17][18][19] suggest, relying on statistical measures alone is not sufficient for classifying different weld characteristics. On the other hand, the emerging number of machine learning approaches [20][21][22] utilize signal structure, yielding higher classification accuracy than solely based on signal energy or statistical measures. However, the correlation of acoustic emissions and weld-relevant parameters is imperceptible for human visual inspection [12].…”