High-power Laser Welding Process Research Articles

Weld bead characteristics for full-penetration laser welding of aluminum alloy under electromagnetic field support

An oscillating electromagnetic field weld pool support system combined with a welding sample travel mechanism was designed for improving the weld bead formation in full-penetration laser welding of A5083 aluminum alloy. The experimental results show that a proper oscillating electromagnetic field can effectively reduce the weld root sagging. When the root mean square of magnetic induction intensity on the back surface Brms0 = 80 m T and its electromagnetic frequency f = 400 Hz, the weld root sagging for the joint of aluminum alloy plate with thickness of 10 mm can be almost eliminated. The electromagnetic frequency and the laser power have a great impact on the weld root sagging height and the weld back surface roughness, while the influence of magnetic induction intensity is relatively small within its variable range in this study. The analysis of welding joint microstructure shows that the electromagnetic field can also refine the grains to some extent and decrease the width of columnar grain zone, decreasing the cracking susceptibility and improving the mechanical properties of the welding joint. However, the undercut defects are inevitable in full-penetration laser welding of aluminum alloy unless filler wire is used, because the metallic evaporation and splash are unavoidable during the high-power laser welding process.

Investigations on in-process control of penetration depth for high-power laser welding of thick steel-aluminum joints

Over the last few decades, the demand for lightweight constructions has been increased continuously for several industrial applications, like automotive and ship building, to reduce the weight of vessels in order to minimize the CO2 emissions as a result of a lower fuel consumption. Lightweight construction is almost applied for ship applications, especially for yachts, which are designed by using aluminum for the deck constructions and steel for the ship hull. For joining these parts, a high-power laser welding process shall be developed. However, the welding of these dissimilar materials is associated with great challenges, due to the different physical properties and the formation of hard and brittle intermetallic phases, which may influence negatively the properties of the weld seam. The quality of dissimilar joints depends strongly on the mixture ratio between the molten amount of steel and aluminum. However, the mixture ratio varies over the weld seam length due to a high dynamic of the keyhole resulted by welding of this material combination. Furthermore, different batches of materials and varied sheet thicknesses t may influence the mixture ratio. In this study, a high-power laser welding process is developed with in-process control of the penetration depth tP by analyzing the spectral process emissions for dissimilar lap joints of aluminum alloy EN AW-6082 (t = 8 mm) and steel S355 (t = 5–7 mm). In the context of these investigations, an increase of occurring cracks within the weld seam and ejections of molten material with increasing penetration depth tP can be observed. To achieve a relative high joint strength, the penetration depth tP must be kept constant at a value of 1.4 mm. In case of varied batch of material, thickness t of the used sheets, welding speed vS, and leap of the steel sheet thickness t, the penetration depth tP requested cannot be achieved. Using the in-process control of the penetration depth tP, the weld seam quality remains almost constantly over the weld seam length, as shown in visual inspections, metallographic analyses, profiles of the penetration depth tP, and tensile shear testing. Among other things, the appearance of ejections of molten material can be avoided by using the in-process control of the penetration depth tP.

Investigations on laser welding of dissimilar joints of steel and aluminum using a high-power diode laser

Lightweight construction is currently of high interest, not only for the automotive sector, but also for the maritime industry, due to various benefits. On the one hand, CO2 emissions can be reduced as a result of lower fuel consumption, and on the other hand a higher speed can be achieved, especially for yachts. Hence, hybrid joints of steel and aluminum parts are in great demand for yachts. Presently, these parts are joined using explosive welding adapters, which are complex, time-consuming, and costly to manufacture. For efficient manufacturing of such adapters, a high-power laser welding process is predestined. Aluminum alloy EN AW-6082 (t = 8 mm) and steel S355 (t = 5 mm) are welded in a lap joint configuration using a diode laser with a laser beam power of 10.4 kW. The challenge of welding this dissimilar material combination is the formation of hard and brittle intermetallic compounds within the weld seam, which may lead to cracks and negative effects on mechanical properties of the joint. To meet the required mechanical properties, the mixing ratio of the intermetallic compounds can be limited, as determined in the context of the presented welding process development. Using suitable mixing ratios, the weld seam quality can be increased as shown in metallography analysis, hardness tests, and tensile shear tests. Among other things, the welded samples provide a shear force of approximately 9 kN.

Online detection method of weld penetration based on molten pool morphology and metallic vapor radiation for fiber laser welding

A novel detection method of penetration status was presented for a high-power fiber laser welding. The metallic vapor and molten pool was recorded by a high-speed camera during welding process. The radiation intensity of metallic vapor, as well as the morphology of molten pool end, was calculated by image processing algorithm as image features. Four image features, the radiation intensity of metallic vapor (RIMV), the area of molten pool end (AMPE), the rear angle of molten pool end (RAMPE), and the aspect ratio of molten pool end (ARMPE), were extracted. The mean value, relative range, variation coefficient, and frequency ratio were computed for the four features to obtain the 16 characteristic parameters. Aiming at penetration status, the characteristic parameters were reorganized to form two complex indicators by the principal component analysis. Experimental results showed that the detection method was potential for online detection on the penetration status in a high-power laser welding process.

A Study on Optimization for Galvanized Iron Sheet Using a High Power Laser Welding Process

A Study on Optimization for Galvanized Iron Sheet Using a High Power Laser Welding Process

Investigation of Image Characteristics of Plume and Spatters during High-Power Disk Laser Welding

During high-power laser welding process, the workpiece produces metal vapor because of the laser irradiation. The characteristics of metal vapor are related to the quality and stability of welding and the utilization of the laser power. An approach of analyzing the characteristics of metal vapor was researched during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW. A high-speed photography was used to capture metal vapor dynamic images. Metal vapor area, beam path, swing angle are calculated by image processing, which is the foundation for monitoring and control of welding quality in real time.

Analysis of characteristics of spatters during high-power disk laser welding

Real-time monitoring and control of welding process is important for laser welding quality. Therefore, the variation rule of sensing characteristics of welding process and their relations to weld quality should be known. Spatter is one of the most important phenomena in high-power laser welding process. The characteristics of spatters are related to the quality and stability of welding and the utilization of the laser power. An approach to analyze the characteristics of spatters is investigated during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW. An ultraviolet and visible sensitive high-speed video camera is used to capture the dynamic images of the laser welding spatters. The number, area, and ejecting distance of spatters and the centroid height of spatter images are calculated as the characteristic parameters of spatters by using the image processing technology. The weld bead width is considered as a parameter reflecting the quality and stability of welding process. The linear and the higher order polynomial curve fitting for the data of the characteristic parameters are used to study the variation rule of the characteristic parameters of spatters. In comparison of the fluctuation of the weld bead width, the correlation between the spatter characteristics and the quality and stability of welding is studied. The experimental results of actual laser welding show that the quality and stability of a high-power disk laser welding of Type 304 austenitic stainless steel plates could be monitored and estimated by analyzing the characteristic parameters of spatters, which is the foundation for monitoring and control of welding quality in real time.