Laser Welding Defects Research Articles

Color Image Segmentation of Plume for Monitoring Disk Laser Welding Process

During deep penetration laser welding, changes in the metal vapor plume contain information about the stability of welding process. A high-speed camera was used to online monitor the welding process in order to detect the laser welding defects. A color segmentation clustering algorithm based on HSI color space was proposed for processing the recorded welding sequences. The effectiveness of algorithms based on different model is discussed, welding experimental results showed that the proposed algorithm could achieve better image segmentation, and it highlighted the edge of the metal vapor details in the image.

Laser welding defects detection in automotive industry based on radiation and spectroscopical measurements

Laser welding is a common technique in the automotive industry. For economic reasons, it is of great importance to detect the defects that can appear. The CO2 penetration laser welding process is characterized by the formation of an electron-free plasma whose radiation can be measured to detect the defects. This paper presents two different approaches to defect detection. The first is based on the correlation between the power spectrum of a photodiode-generated signal and the defects. The second approach is based on the plasma electronic temperature, which is correlated to the presence of defects. Results obtained in an industrial facility under production conditions are presented.

FPGA implementation of time–frequency analysis algorithms for laser welding monitoring

The on-line monitoring and detection of defects in laser welding is a basic manufacturing requirement in several applicative contexts, as vehicle assembly in automotive production. This work presents the FPGA implementation of time–frequency analysis algorithms as an effective solution compared with pure software implementation based on different modern processors. In particular the proposed FPGA based approach not only satisfies the processing constraints of the considered application, but still offers a high degree of flexibility and modularity.

Theoretical analysis of photodiode monitoring of laser welding defects by imaging combined with modelling

On-line process monitoring of laser welding defects by detecting characteristic changes of the process emissions via photodiodes has high potential but, due to the complex process, lack of directly interpretable and thus controllable correlations. Deep analysis of the process by high speed imaging in combination with modelling enables one to discuss the correlations between the signal and the process, as was demonstrated for quasi-steady state conditions and for transient phenomena. Despite improved knowledge through the study, several uncertainties like the emissivity, the keyhole radiation characteristics and the temperature field need to be identified more accurately for a complete theoretical description of the signal causes.

パルス波形制御によるレーザ溶接欠陥の防止_-_突合せ溶接について_-_

パルス波形制御によるレーザ溶接欠陥の防止_-_突合せ溶接について_-_

In-process Monitoring and Adaptive Control for Laser Spot and Seam Welding of Pure Titanium

In-process monitoring and adaptive control is increasingly expected for the decisive detection of laser welding defects and for the stable formation of sound welds since laser welding has been applied in several industries. The objective of this research is to obtain a fundamental knowledge of in-process monitoring and availability of adaptive control for laser spot and seam welding of pure titanium with a pulsed Nd:YAG laser beam. The reflected light and heat radiation from the laser-irradiated area were monitored in synchronism with 20,000 F/s high-speed video observation of a molten pool. With respect to in-process monitoring, it was found that the reflected light was sensitive to the molten area formation and the heat radiation had clear correlation to the molten pool sizes for respective laser powers. Moreover, the heat radiation intesity had a quick response to the rapid change of laser peak power, and then the correlation between the heat radiation and the molten pool size was maitained in the designed laser power. As for adaptive control, spatters and pores were drastically reduced by controlling laser peak power and pulse duration according to the obtained features of the heat radiation-monitoring signal.

パルス波形制御によるレーザ溶接欠陥の防止_-_キーホール挙動とポロシティーの発生_-_

パルス波形制御によるレーザ溶接欠陥の防止_-_キーホール挙動とポロシティーの発生_-_

Behaviour of monitoring signals during detection of welding defects in YAG laser welding. Study of monitoring technology for YAG laser welding (Report 2)

Behaviour of monitoring signals during detection of welding defects in YAG laser welding. Study of monitoring technology for YAG laser welding (Report 2)

ＹＡＧレーザ溶接におけるモニタリング技術の研究 ２ ＹＡＧレーザ溶接における溶接異常時のモニタリング信号挙動

In our first paper, we have proposed the monitoring method using reflected Ar+ laser beam in YAG laser welding. It has been shown that this method was effective to monitor the changes of the welding conditions in YAG laser welding. It is also very important to detect the welding defects in YAG laser welding. In this paper, signals of the light and acoustic emission in addition to that of reflected Ar+ laser were measured at the same time. We investigated changes of these monitoring signals due to welding defects, such as lack of penetration, underfill by a wide gap and misalignment in butt joints. Main results are as follows; 1) The signal of the light emission was suitable to detect the penetration was full or partial. 2) The reflected Ar+ laser signal was suitable to detect the underfill due to a wide gap and the misalignment. 3) Only one signal was changed when these welding defects were occurred. While various signals were altered at same time when the welding conditions were varied. 4) The signal of the acoustic emission was not changed by these welding defects.

Effect of vacuum on penetration and defects in laser welding

The effect of vacuum on weld penetration and porosity formation was investigated in high-power cw CO2 and YAG laser welding. It was consequently confirmed in welding with both lasers that the penetration was slightly deeper in aluminum alloys and austenitic stainless steel with a decrease in the ambient pressure. It was also revealed that no porosity was present in the materials welded at lower pressures. The reason for no porosity formation in vacuum was examined by observing keyhole behavior, bubble and porosity formation situation, and liquid flow in the molten pool during high-power YAG laser welding under various conditions through the microfocused x-ray real-time observation system. It was confirmed in the coaxial Ar or He shielding gas that a lot of bubbles were generated near the bottom part of the molten pool from the tip of a fluctuated keyhole and resulted in large pores. On the other hand, under the vacuum conditions, no bubbles were formed in the melt pool from the keyhole, although the middle and bottom parts of the keyhole swelled up in the molten pool probably because the evaporation of metals was so intense. Moreover, opposite liquid flows as well as different molten pool geometry were observed between the normal atmospheric pressure welding with a coaxial shielding gas and the vacuum welding. Namely, during normal welding in a gas, the circulation of a strong molten flow was observed downward along the keyhole, from the keyhole tip along the bottom molten pool to the upper rear, and subsequently below the surface to the forward keyhole. On the other hand, in vacuum welding, the liquid flowed upwards along the rear keyhole wall, but there was no such strong flow near the bottom and the rear parts of the molten pool. It is considered in vacuum welding that the liquid flow into the bottom part of the molten pool from the keyhole tip does not occur because of the direction of evaporated metals toward the upper keyhole outlet. This may exert a beneficial effect on the reduction or prevention of pores or porosity.

Spectroscopic diagnostics on CW-laser welding plasmas of aluminum alloys

In-process diagnostics intended to correlate spectrometric measurements to the occurrence of laser welding defects such as notches and blowholes have been carried out. The plasma light emitted during high-power CO 2 laser welding of a 6013 aluminum alloy was guided to an imaging spectrograph and the dispersed light was detected with a CCD system. A transient recorder was used to record the signal from a fast laser-power monitor and the sync signals from the CCD and a fast speed video camera. Accuracy of the measurements are discussed in relation to the low and fast acquisition rate approaches (58 spectra s −1 and 4×10 3 spectra s −1, respectively) used in the experiments. Spectroscopic measurements at fast acquisition rates showed both an increase in the intensity of the overall spectral emission and the growth of lines corresponding to ionic aluminum species taking place right before the occurrence of weld defects.

A system for on line monitoring of pulsed laser welding processes

In the field of laser welding, the lack of suited inspection means generally leads users to develop their own systems. From this observation, an adaptable system to all welding conditions, dedicated to on line inspection of pulsed laser welding operations, has been devised. Its principle is very close to Quality Control by Artificial Vision systems. It is based on the recording and the treatment of signals resulting from laser–material interaction. The use of classification techniques and signal processing tools such as the wavelet transform, introduce an innovating approach of on line inspection. Thus, defects detection by discriminant parameters determination becomes automatic and nonsubjective. The presented method allows to determine the weld spot position (pulse number) and the type of defects and to estimate the reliability of the detection. This article presents the principle of the system and its validation on some classical defects in laser welding. The final objective is, in particular, to detect penetration variations during welding hollow parts, at the Valduc center of the French Atomic Energy Agency. In most cases penetration can be easily estimated by observing (with a photodiode or charge-coupled camera for example) the heating of the back of the welded part. Unfortunately in case of hollow parts, the sensors can only be placed at the outside!

Laser welding of thin-sheet carbon and zinc-coated steels

Summary The results of research on CO2 laser welding of thin-sheet carbon steels (zinc-coated and uncoated) in several thickness combinations, are presented. Laser welding has a high potential for application to welding of sub-assemblies prior to forming (consisting of various parts of different materials and thicknesses), known as tailored blanks, for the automotive industry. The welding process is studied by analysing parameter optimisation, metallurgical quality and the distortions induced by welding. The clamping and gas shielding systems are described in detail, in order to minimise common defects in thin-sheet laser welding, such as misalignment and in zinc-coated laser welding, such as porosity and zinc vaporisation. Finally, weld quality is assessed using DIN standard 8563 and assessed quantitatively by tensile, micro-hardness and corrosion tests.

Soldadura laser de chapa fina de aço carbono e aço galvanizado

This paper describes the results of a research on CO 2 laser welding of thin-sheet carbon steels (zinccoated and uncoated), at several thicknesses combinations. Laser welding has an high potential to be applied on sub-assemblies welding before forming to the automotive industry-tailored blanks. The welding process is studied through the analysis of parameters optimization, metallurgical quality and induced distortions by the welding process. The clamping system and the gas protection system developed are fully described. These systems allow the minimization of common thin-sheet laser welding defects like misalignement, and zinc-coated laser welding defects like porous and zinc volatilization. The laser welding quality is accessed by DIN 8563 standard, and by tensile, microhardness and corrosion tests.