Publisher Correction: Process comparison of laser deep penetration welding in pure nickel using blue and infrared wavelengths

Adopting coaxial and side blown protective gas to control plasma, many experiments of CO2 laser deep penetration welding on the stainless steel are finished. Considering the protective gas effect of melten characteristics on laser welding,the experiments choose the gas species and composition to promote the collision and energy exchange of gas and plasma; The laminar flow state is holded by controlling the gas runoff, the angle and direction, increaseing the gas stiffness to prevent plasma punctured, and the plasma energy exchange range is close on the surface of the workpiece so that the energy of laser beam is less absorbed by plasma than the workpiece.The experiments indicate that shielding gas suppression are adverse factors on plasma to use alone Ar, He and N2. Adopting He-Ar-N2 and the ratio of 7:4:l as a protective gas when gas flow rate is about 30L/min, the deep and wide ratio is large,the deep penetration welding seam surfaces obtained are smooth,the defects aren't obvious;the protective effect is poor if the gas flow is too large or too small.

Laser welding offers advantages like high speed, narrow seams, and reduced heat-affected zones, but is limited when joining dissimilar materials such as aluminum (Al) and low-carbon steel (Fe) due to differences in physical properties and the formation of brittle intermetallic compounds (IMCs), including FeAl 2 and Fe 2 Al 5 . To address this, cold spray technology propels Fe powder at high velocity to create mechanical bonding, suppress IMC formation, and enhance interface stability. In this study, laser welding was applied to overlapped joints of stainless steel, a cold-sprayed Fe layer, and aluminum. Mechanical and microstructural properties were evaluated under varying welding parameters and corrosive environments. Additionally, a CNN-based model using thermal and molten pool images from CMOS and IR cameras was developed to classify weld penetration states. The findings confirm cold spray’s effectiveness as an interlayer method and show that AI enables process control over weld penetration.

Underfill defect in welding affects not only the surface integrity but also the mechanical properties of workpiece. In this paper, the effects of the process parameters on underfill defects were investigated, and the deep penetration welding by a 10-kW fiber laser on 12-mm-thick stainless steel plates was used as the case study. The correlation of the processing parameters with the formation and elimination of underfill defects was analyzed and discussed. It was found that during the autogenous laser welding of thick plates, the direction of laser beam relative to gravity has a significant effect on the formation of underfill defects, and the preferable direction was an inclination angle of 60° with respect to the gravity. A negative defocus tended to obtain a full penetration weld with underfill and undercut defects. The higher the welding speed was, the lower the underfill depth was on the top surface. This phenomenon was observed on the full penetration welds at a defocus of − 10 mm. With a negative defocus, it became feasible to optimize the combination of the focal position and the welding speed to achieve a satisfactory appearance of welds. In addition, a bottom-shielding ambience helped the full penetration in the laser welding process positively.

A mathematical model that is capable of simulating the fluid flow and heat transfer during fully penetration laser welding is developed to study: the shape of the keyhole and its stability; velocity vectors and distribution in the weld pool. Firstly, a new combination heat source model consisting of a rotary Gaussian volumetric heat source and a double ellipsoidal volumetric heat source during laser keyhole welding is developed. It represents substantial characteristic of heat transfer of the keyhole. Secondly, A mathematical model for the simulation of heat transfer and fluid flow in weld pool phenomena during deep penetration laser beam welding based on a numerical solution of the conservation equations of energy, momentum and mass is presented. and verification and validation tests were carried out.A mathematical model that is capable of simulating the fluid flow and heat transfer during fully penetration laser welding is developed to study: the shape of the keyhole and its stability; velocity vectors and distribution in the weld pool. Firstly, a new combination heat source model consisting of a rotary Gaussian volumetric heat source and a double ellipsoidal volumetric heat source during laser keyhole welding is developed. It represents substantial characteristic of heat transfer of the keyhole. Secondly, A mathematical model for the simulation of heat transfer and fluid flow in weld pool phenomena during deep penetration laser beam welding based on a numerical solution of the conservation equations of energy, momentum and mass is presented. and verification and validation tests were carried out.

During laser deep penetration welding process, defects cannot be completely avoided yet. Due to the dynamic process, especially process pores and spatters occur. Keyhole dynamics are assumed to be responsible for the initiation of both pores and spatters. However, it is not completely clear yet how spatters and pores are formed. A semianalytical model of a keyhole is used to simulate dynamic keyhole properties of laser beam welding of aluminum. These are related to characteristics of spatters and pores occurring during laser deep penetration welding recorded using high-speed-imaging technique and x-ray analysis, respectively. Correlations of keyhole shapes and pore formation show that the volume underneath a keyhole collapse can be sufficient to capture the gas that is necessary for the formation of a pore and a keyhole expansion is not necessarily needed to produce the pores found in the weld seam. Calculated keyhole wall fluctuations are found to be not sufficient to detach spatters from the keyhole wall without additional forces from the melt pool.

A computational analysis is achieved during laser deep penetration welding. Multiple reflection and absorption are implemented simultaneously with the ray tracing technique in the keyhole. With all the governing equations including continuity, momentum and energy equation, the VOF method is adopted to trace the free surface of the molten pool. Temperature field is achieved by numerical simulation. The laser keyhole welding experiments on 304 stainless steel sheet showed that the computational results agree well with experimental results.

The melt bath movements induced during deep penetration laser welding can be controlled by external effects that can lead to more uniform flow. By directing an inert gas jet towards the keyhole aperture under a given angle and height of the gas delivering nozzle, a laminar flow is observed, allowing the reduction of porosity formation, and the obtaining of smoother and narrower weld seams. In this paper, the effect of a supplied inert gas jet on the liquid movements during deep penetration laser welding is investigated in 3D modelling.The melt bath movements induced during deep penetration laser welding can be controlled by external effects that can lead to more uniform flow. By directing an inert gas jet towards the keyhole aperture under a given angle and height of the gas delivering nozzle, a laminar flow is observed, allowing the reduction of porosity formation, and the obtaining of smoother and narrower weld seams. In this paper, the effect of a supplied inert gas jet on the liquid movements during deep penetration laser welding is investigated in 3D modelling.

The authors have examined proper welding condition which enclosed good weld beads in terms of welding appearance for full penetration welding. For CO2 laser welding of large output, it is generally known that porosity may occur in the weld bead when a deep penetration welding in single pass is performed in the ambient atmosphere. Welding defects mainly including porosity also occur more frequently with increase of plate thickness even though in the case of using proper welding condition.In order to spread laser welding generally, porosity is one of the most important problems to be solved. It is thought that formation mechanism of porosity is expressed as follows. Bubbles are generated mainly at the bottom of keyhole, which are trapped in molten metal during floating up and remain as porosity in metal.In this context, to reduce welding defects in welded bead, the authors paid attention to the following two conceptions; the first is that long heat input time would enable to delay beginning of molten metal solidification; the second is that molten metal could be fluidified smoothly by changing direction of recoil pressure. The authors adopted use of twin spot condensing system and improvement for the radiation angle of laser to test piece to accomplish these conception. Twin spot welding was the method of welding with two spot lasers which were condensed two laser beams which were divided from an uncondensed laser beam so that heat input increased in spite of decrease of penetration depth. Forehand welding was performed using a method of inclined laser radiation so that molten metal could be fluidified smoothly by changing direction of recoil pressure.In this report, the authors discuss in detail the prevention of welding defects which are generated by mainly porosity for thick plates.The authors have examined proper welding condition which enclosed good weld beads in terms of welding appearance for full penetration welding. For CO2 laser welding of large output, it is generally known that porosity may occur in the weld bead when a deep penetration welding in single pass is performed in the ambient atmosphere. Welding defects mainly including porosity also occur more frequently with increase of plate thickness even though in the case of using proper welding condition.In order to spread laser welding generally, porosity is one of the most important problems to be solved. It is thought that formation mechanism of porosity is expressed as follows. Bubbles are generated mainly at the bottom of keyhole, which are trapped in molten metal during floating up and remain as porosity in metal.In this context, to reduce welding defects in welded bead, the authors paid attention to the following two conceptions; the first is that long heat input time would enable to delay beginning of molten metal ...

Machine learning-based in-process monitoring for laser deep penetration welding: A survey

Keyhole stability during laser welding—Part II: process pores and spatters

In aluminum welding, the grain structure of produced seams is an essential factor with respect to the seam properties. In the casting technology the effect of mechanical vibrations on the grain growth during the solidification of liquid metals is known as a refinement method. In this paper, the transferability of this approach from comparatively long-time processes in the field of casting to the short-time process of laser deep penetration welding is investigated. Therefore, specimens were sinusoidal vibrated with frequencies up to 4 kHz during bead-on-plate full-penetration welding experiments. The resulting grain size was determined by applying the circular intercept procedure on the center of a cross-section micrograph of each weld. The results show that grain refinement is in general achievable by mechanical vibrations in the audible frequency range during laser full penetration keyhole welding of the aluminum alloy EN AW-5083.

A laser remote cutting process is analyzed, which differs significantly from established laser cutting processes. On the one hand, no cutting gas is needed and a high working distance is realized. On the other hand—in opposite to conventional laser remote cutting—sheets of metal with thicknesses above 1 mm can be cut in one step. Examinations were carried out at the martensitic boron steel 22MnB5 due to its interesting applications at automotive industry and significant advantages of the presented cutting process. Large focal spots and low cutting velocities are needed when moving the laser beam over the surface of the work-piece. Mainly, the material is melted besides a little fraction of vapor, which forms a keyhole, comparable with laser deep penetration welding. Besides typical parameters, the behavior of the ejection of melt is presented. The melt exits the kerf characteristically in beam direction at the bottom of the work-piece but changes its axial direction. Therefore, two subprocesses are defined and examined separately: Subprocess A can be observed at low cutting velocities and is characterized by a pushing melt ejection, whereas subprocess B needs significantly higher velocities and results in dragging melt ejection.

Laser deep penetration welding is characterized by the formation of a vapor capillary (keyhole) and a high overall absorption (coupling rate) of the laser radiation in comparison to heat conduction welding. Due to multiple reflexions within the highly dynamic keyhole, the absorption mechanisms are very complex. The questions, how a laser beam interacts with the existing keyhole, and, if shadowing effects occur, are a matter of concern for several researchers. In this study, the hypothesis that the beam of a laser source can be transmitted to a significant extent through an existing keyhole and acts predominantly at the keyhole bottom was investigated. Experiments were carried out on mild steel and technical pure aluminum, using a specially designed optical system, which allows to coaxially combine two laser beams and to adjust their settings like the energy and the focal plane individually. A combination of a disk laser with a focal diameter of 390 µm and a single-mode fiber laser with a focal diameter of 30 µm was used. Weld depths and seam shapes were analyzed in cross and longitudinal sections. Based on the results, it is shown that the much smaller focal diameter of the single-mode laser beam acted at the bottom of the keyhole and caused a kind of “keyhole-in-keyhole formation” in the form of a local maximum in weld depth whose expression depended on the focal plane of the single-mode laser beam.

Spatter formation is a major issue in deep penetration welding with solid-state lasers at high welding speeds above 8 m/min. In order to limit spatter formation, the use of local gas flows represents a technically feasible solution. By using the gas flow, the pressure balance inside the keyhole, and therefore the keyhole stability, is affected. Existing investigations demonstrate a reduction in spatter and pore formation for partial penetration welding up to a welding speed of 5 m/min. However, the effect of the gas flow is not yet clarified for full penetration welding at welding speeds above 8 m/min. By using a precisely adjustable shielding gas supply, the effect of a local gas flow of argon was characterized by welding stainless steel AISI304 (1.4301/X5CrNi18-10). The influence of the gas flow on the melt pool dynamics and spatter formation was recorded by means of high-speed videography and subsequently analyzed by image processing. Schlieren videography was used to visualize the forming flow flied. By the use of the gas, a change in melt pool dynamics and gas flow conditions was observed, correlating to a reduction in loss of mass up to 70%. Based on the investigations, a model of the acting effect mechanism was given.

Analysis of droplet transfer, weld formation and microstructure in Al-Cu alloy bead welding joint with pulsed ultrasonic-GMAW method