High-power Fiber Laser Welding Research Articles

Effect of plume on weld penetration during high-power fiber laser welding

To clarify the effect of the laser-induced plume on weld penetration during high-power fiber laser welding, this paper investigates the change in weld penetration, plume behavior and temperature, particles present in the plume, and the attenuation of the horizontal probe laser. Results show that the weld penetration had an improvement of about 20% as the plume was blown away by using a supersonic cross jet. The plume temperature at a height of 5 mm was approximately 5078 K. The weld penetration, plume temperature, and plume attenuation to a probe laser decreased as plume height increased. A plume height of approximately 80 mm resulted in a shape similar to that of a focused laser beam; a cone of white smoke composed of numerous particles appeared around the plume. Calculated and measured results indicate that the interaction of laser particles in the plume accounts for the primary impact on laser-plume interaction. It is found that, if the plume height increases, the weld penetration decreases correspondingly due to the increasing attenuation of the high-power fiber laser beam by the particles in the plume.

Distinct morphology of keyhole wall during high power fibre laser deep penetration welding

The keyhole wall is the interaction interface between the laser and the material during the laser deep penetration welding. Measuring the morphology of the keyhole wall is thus of significance for understanding the high power fibre laser deep penetration welding process. In this paper, the clear keyhole wall was reserved by suddenly closing laser during high power fibre laser welding of copper alloy. The results indicate that the keyhole can be divided into laser action region and metallic vapour pressure maintenance region. The laser action region is on the front wall of keyhole, and a series of concentric elliptical rings are observed in this region. In another region, its diameter is significantly larger than the spot diameter and the keyhole wall is basically smooth. The results are different from those generally accepted viewpoints, which clarify the flowing law of molten fluid in the keyhole and are thus of great guiding significance for optimising the welding technology.

A novel method for observing the micro-morphology of keyhole wall during high-power fiber laser welding

Most of the laser welding defects are likely to be related to the welding process transport phenomena induced by the energy conversion process in the keyhole. The keyhole wall is the interaction interface between the laser and welded material, and studying its micro-morphology is significant for understanding the energy conversion process. Because the current measuring methods are limited, observation of keyhole wall micro-morphology is still a challenge. In this paper, a novel method was designed. The keyhole wall was preserved as the high-power fiber laser was suddenly shut off during welding process, and then it was measured by using a scanning electron microscopy (SEM). The results show that the laser beam directly acted on the keyhole front wall during welding. The concentric elliptical rings, wrinkles, and ripples were found on the laser-action region. These micro-morphologies indicate that the energy coupling is mainly the absorption of the keyhole front wall, and the keyhole formation is similar to a laser drilling on the keyhole front wall during welding. The novel method can be used to investigate on the formation of the welding defects during high-power fiber laser welding in the future study.

Effects of a paraxial TIG arc on high-power fiber laser welding

Abstract In this study, the effects of a paraxial tungsten-inert gas (TIG) arc on the high-power fiber laser welding process were investigated by measuring plume behavior, plume temperature, weld depth, and the particles in the plume. The experimental results indicated that when DLA (i.e. the distance between the laser beam and arc) was less than 8 mm, the slender plume similar to the shape of the focused laser beam was eliminated, and the weld depth was increased by around 20%. Moreover, both the vertical and horizontal temperatures of the hybrid welding plasma were much higher than that of the plume. In addition, in the space near the laser beam, the size and density of the particles were significantly reduced. Further analysis indicated that the paraxial TIG arc could eliminate the slender plume by reducing the density and size of particles in the plume during high-power fiber laser–arc hybrid welding; therefore, it can reduce the negative effects of the plume on the welding process while improving laser energy utilization and the weld depth.

Numerical investigation of energy input characteristics for high-power fiber laser welding at different positions

Partial penetration welding with a fiber laser at a 9-kW laser power was carried out on 20-mm-thick plates at different positions and analyzed by both experimental and numerical methods. Experiments were carried out for four different angular positions at 1.5 m/min welding speed. All four cases showed a tail-like structure of molten pool on the top surface. The in-depth mechanisms of the energy input characteristics in fiber laser position welding for eight different positions were studied by numerical simulation using the volume-of-fluid (VOF) method. Experimental and numerical results were compared for four cases and showed fair agreement. Observation of flow pattern and bead shape revealed that gravity had little influence on bead shape and flow structure, but changed the pore structure considerably. Flow structure showed a periodic behavior which probably nullified the effect of gravity in position welding. Most of the laser rays reached the bottom of the keyhole without interruption and then multiple reflections started within the keyhole. The first five reflections inside the keyhole delivered around 70 % of the total energy.

Control of the plume induced during high-power fiber laser welding with a transverse arc

In this letter, the addition of the transverse arc into high-power fiber welding is proposed. The effects of the transverse arc on the laser-induced plume, the morphology of the weld, and the stability of the welding process are investigated. The experimental results indicate that, by introducing the transverse arc, the slender plume disappears, the temperature of the plasma plume increases then decreases with the rise in height, the weld width is reduced by around 42%, and the weld depth and the melting area are enhanced by about 28 and 12%, respectively. Moreover, the stability of the welding process is improved remarkably. As concluded from further analysis, the Mie scattering of the incident laser, induced by the particles in the plume, is responsible for the adverse effects induced by the plume. With the addition of the transverse arc, the particles in the plume are gasified and, thus, do not impact the energy transmission of the fiber laser. Consequently, the adverse effects induced by the plume can be significantly suppressed while the laser energy utilization efficiency and the stability of the welding process are improved.

Plume temperature diagnosis with the continuous spectrum and Wien’s displacement law during high power fiber laser welding

The laser-induced plume is an essential physical phenomenon during high power fiber laser welding. Its physical nature can be investigated by diagnosing its temperature. In order to overcome the lack of sufficient line spectra in the temperature diagnosis, the continuous spectrum method (based on the continuous spectrum and Wien’s displacement law) is thus developed in this research. The optical spectra emitted by the plume or plasma were detected by using a SP-2500i spectrometer during bead-on-plate welding with an IPG YLS-6000 fiber laser or fiber laser-arc hybrid. The rationality of the continuous spectrum method was evaluated by comparing the plasma temperatures diagnosed by applying the continuous spectrum and line spectra. The results reveal that the continuous spectrum method used in temperature diagnosis is rational. When the line spectra cannot be detected due to an increase in detected height, the plume temperature can be still obtained by using the continuous spectrum method.

Investigation of keyhole plasma during 10 kW high power fiber laser welding

During high power fiber laser deep penetration welding, the laser induced plasma/vapor has a great effect on the weld pool flow and keyhole stability. In this paper, experiments on 10 kW fiber laser welding of stainless steel have been carried out. A long keyhole and keyhole plasma have been observed. The distinct spectral lines of the keyhole plasma induced by the high power fiber laser were measured and used to calculate the parameters of the plasma. The pressure of the plasma was investigated experimentally. The welding images showed a clear long keyhole and uneven distribution of the keyhole plasma. The data demonstrated that, compared with the results during CO2 laser welding, the electron temperature was lower during fiber laser welding, while the electron density remained at a similar level. The ionization degree was found to be low. The pressure of the plasma was found to be much higher than atmospheric pressure. The results revealed that the low fiber laser absorptivity of the plasma and the high atomic density of the vapor induced by the high power fiber laser were the factors that dominated the values of the plasma parameters. In particular, the high pressure plasma was ascribed to the high atomic density of the metallic vapor.

Detection of weld pool width using infrared imaging during high-power fiber laser welding of type 304 austenitic stainless steel

Thermal radiation of a weld pool contains plenty of welding quality information in a high-power fiber laser welding process, in which the weld pool width can reflect the welding stability. Thus, extracting the weld pool width characters of high-power fiber laser welding based on infrared imaging is an important method for monitoring the welding status. In this paper, the type 304 austenitic stainless steel is welded by a 10-kW high-power fiber laser continuously. A high-speed infrared video camera is employed to capture the infrared images of weld pools and their surroundings in the laser welding process. The infrared image characteristics of a weld pool are analyzed, and the improved homomorphic filtering algorithm based on Fourier transform is used to extract weld pool width which depends on the characteristic variation of weld pool images. And the comparison between improved homomorphic filtering algorithm and traditional homomorphic filtering algorithm is also discussed. Welding experimental results show that the proposed improved homomorphic filtering algorithm can extract the weld pool width and reflect the status of high-power fiber laser welding process accurately.

高功率光纤激光焊接羽辉对焊接过程的影响

高功率光纤激光焊接羽辉对焊接过程的影响

Monitoring of high-power fiber laser welding based on principal component analysis of a molten pool configuration

There exists plenty of welding quality information on a molten pool during high-power fiber laser welding. An approach for monitoring the high-power fiber laser welding status based on the principal component analysis (PCA) of a molten pool configuration is investigated. An infrared-sensitive high-speed camera was used to capture the molten pool images during laser butt-joint welding of Type 304 austenitic stainless steel plates with a high-power (10 kW) continuous wave fiber laser. In order to study the relationship between the molten pool configuration and the welding status, a new method based on PCA is proposed to analyze the welding stability by comparing the situation when the laser beam spot moves along, and when it deviates from the weld seam. Image processing techniques were applied to process the molten pool images and extract five characteristic parameters. Moreover, the PCA method was used to extract a composite indicator which is the linear combination of the five original characteristics to analyze the different status during welding. Experimental results showed that the extracted composite indicator had a close relationship with the actual welding results and it could be used to evaluate the status of the high-power fiber laser welding, providing a theoretical basis for the monitoring of laser welding quality.

Optimization of deep penetration laser welding of thick stainless steel with a 10 kW fiber laser

Deep penetration laser welding of 12mm thick stainless steel plates was conducted using a 10kW high-power fiber laser. The effect of the processing parameters on the weld bead geometry was examined, and the microstructure and mechanical properties of the optimal joint were investigated. The results show that the focal position is a key parameter in high-power fiber laser welding of thick plates. There is a critical range of welding speed for achieving good full penetration joint. The type of top shielding gas influences the weld depth. The application of a bottom shielding gas improves the stability of the entire welding process and yields good weld appearances at both the top and bottom surfaces. The maximum tensile stress of the joint is 809MPa. The joint fails at the base metal far from the weld seam with a typical cup–cone-shaped fracture surface. The excellent welding appearance and mechanical properties indicate that high-power fiber laser welding of a 304 stainless steel thick plate is feasible.

Observation of spatter formation mechanisms in high-power fiber laser welding of thick plate

This paper aims to present the dynamic behaviors of spatter formation, and to clarify the spatter formation mechanisms in the high-power fiber laser welding of a thick plate at low welding speeds. We used a modified “sandwich” specimen to directly observe the geometry of the longitudinal keyhole wall. The dynamic behaviors of the keyhole, vapor plume, and melt pool with the formation of spatters were observed using high-speed imaging. The mechanisms of the formation of the spatter ejected from the top and bottom surfaces were analyzed. The recoil momentum associated with the energized vapor plume jet acts on the tips of the gauffers on the front keyhole wall and micro-droplets inside the keyhole, thereby resulting in the formation of high-speed micro-spatter. At partial penetration, the spatter ejected from the keyhole inlet is influenced mainly by the upward melt flow above the keyhole, melt displacement around the keyhole, and the strong shear stream of the directed vapor plume force. Moreover, some spatter droplets are accelerated through the vapor plume outside the keyhole. At full penetration of the melt, spatters are generated when the downward momentum of the melt due to downward flow and gravity, or vapor burst with an open keyhole, exceeds the surface tension forces. At full penetration of the keyhole, the crucial driving force for spatter generation is the viscous friction drag associated with high-speed motion of the energized vapor plume through the open keyhole. The welding process evolves into almost a cutting process at a lower welding speed.

Weld Seam Deviation Detection Base on Laser Welding Pool’s Centroid

For detecting weld seams deviation during the industrial actual welding process, IPG YLR-10000 high power fiber laser welding equipment was used during laser welding experiments. A high-speed near-infrared camera was used to capture the dynamic welding pool image sequences. Through studying the change of the features of near-infrared images of the weld pool when the laser beam deviated the weld seam, the centroid of the welding pool could be used as the deviated parameter of the weld seam. The welding pool images coordinates were established, and the ways of rotating and shifting the coordinates were used to build a model to test the welding spots deviation. Finally, the model of the relationship of the actual weld seam deviation and the tested weld seam deviation had been set up by using the regression analysis method. Its validity and feasibility had been tested by analyzing the models correlation R parameters.

Laser absorption characteristics in high-power fibre laser welding of stainless steel

A tightly focused high-power fibre laser beam can produce a narrower and deeper penetration weld than a conventional laser weld of wine cup shape, which is expected to improve laser absorption. The objective of this research was to assess laser absorption in a wide range of conditions such as laser powers of 2–10 kW or welding speeds of 17–250 mm/s in bead-on-plate welding of Type 304 austenitic stainless steel with a laser beam of 200 μm spot diameter by water-calorimetric method. Furthermore, the relationship between the laser absorption and the keyhole formation location to a focused laser beam was revealed by using X-ray transmission in-site observation system and high-speed video camera with diode-laser illumination. It was found that the absorption at 10 kW laser power and 17 mm/s welding speed was 89% high. Compared X-ray transmission observation images of the keyhole with the focusing feature of the fibre laser beam and the centre part of the incident beam with a bell-shaped profile were delivered directly to the tip of a keyhole. Moreover, the increase in the welding speed from 17 to 250 mm/s reduced the absorption from 89 to 65%. The high-speed observation pictures indicated that the incident fibre laser beam was partially exposed out of the keyhole inlet at higher welding speed, which led to the decrease in the laser absorption. Consequently, it was confirmed that the tightly focused high-power fibre laser welding was high-efficiency process at the maximum of about 90% in laser absorption at low welding speeds, owing to the irradiation of almost all the incident laser beam into the keyhole inlet. It was also assessed that the energy loss due to vapourization was smaller than 1%.

大功率光纤激光焊接过程中工艺参数对熔深和气孔的影响

大功率光纤激光焊接过程中工艺参数对熔深和气孔的影响

高功率光纤激光和CO2激光焊接熔化效率对比

高功率光纤激光和CO2激光焊接熔化效率对比

Vapor–plasma plume investigation during high-power fiber laser welding

This work is devoted to the investigation of the laser–matter interaction during up to 20 kW ytterbium fiber laser welding of thick mild steel plates. The plume attenuation of a probe 1.3 μm wavelength diode laser beam as well as of continuous radiation in the 250–600 nm wavelength range was measured during welding with and without Ar shielding gas supply. The measured results allow the calculation of the average size and concentration of fine condensed metal particles in different plume areas using the multi-wavelength method and the Mie scattering theory. The plume temperature, which determines the condensation conditions, was measured by means of Fe I atom spectral line emission registration. The spatial distribution of the extinction coefficient in the welding plume was measured and the plume attenuation of the high-power fiber laser beam during the welding process was estimated.

Seam Tracking Monitoring Based on Adaptive Kalman Filter Embedded Elman Neural Network During High-Power Fiber Laser Welding

This paper proposes a method of seam tracking monitoring during high-power fiber laser welding. A visual sensor system was employed to capture the infrared images of molten pools and the surroundings in the laser welding process. A weld seam position variable was extracted by the image difference and centroid algorithms. The state and measurement equations for weld seam position were established based on an eigenvector derived from the weld seam position variable. A Sage-Husa adaptive Kalman filter (AKF), as an estimator of the noise statistical characteristics, was applied in order to enhance the filtering precision. By embedding an Elman neural network into the AKF, an error estimator was used to compensate for the filtering errors. The results of the welding experiments have demonstrated the effectiveness of the proposed method to improve the accuracy of weld detection.

Extraction of Characteristic Parameters of Keyhole during High Power Fiber Laser Welding

During deep penetration laser welding, a keyhole is formed in the molten pool. The characteristics of keyhole are related to the welding quality and stability. Analyzing the characteristic parameters of a keyhole during high power fiber laser welding is one of effective measures to control the welding quality and improve the welding stability. This paper studies a fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 10 kW continuous wave fiber laser, and an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. A combination filtering system with a filter length of 960-990nm in front of the vision sensor was used to obtain the near infrared image and eliminate other light disturbances. The width, the area, the leftmost point, the rightmost point, the upmost point and the bottommost point of a keyhole were defined as the keyhole characteristic parameters. By using the image preprocessing method, such as median filtering, Wiener filtering, threshold segmentation and Canny edge detection methods, the characteristic parameters of a keyhole were obtained. By analyzing the change of the keyhole characteristic parameters during welding process, it was found that these parameters could reflect the quality and stability of laser welding effectively.