Visualization of laser back-reflection distribution during laser welding

There are several approaches to weld quality monitoring during laser welding. Reflected laser radiation carries partial information about the welding process. Fibre lasers has usually a built-in diode to detect excessive back-reflected laser radiation to protect the laser source from damage. Reflected laser radiation measured in the laser source is compared with reflected laser radiation measured in the welding head. Moreover, coaxial high-speed imaging with a narrow bandpass filter on laser wavelength is used to visualize the reflected laser radiation. The advantage of this solution is that no additional illumination is needed and the reflected laser intensity and spatial distribution can be obtained from the image. Keyhole inlet dimensions are measured and related to the laser power. The transition between laser welding modes is studied.

Investigating the Reproducibility of the Wire Arc Additive Manufacturing Process

Wire arc additive manufacturing (WAAM) of titanium parts shows promising potential for aerospace application due to its high deposition rates allowing a fast and economical production of large integral parts. However, due to the demands of aerospace industry an extensive qualification procedure is necessary to enable the parts as ready to fly. Nowadays, qualification for additive manufactured parts is a time-consuming process, so the advantages in additive manufacturing cannot be fully utilized. For this reason, a complete process qualification for WAAM would reduce the costs drastically in contrast to qualifying manufactured parts individually. As a first step the robustness and reproducibility of the energy reduced WAAM process was investigated. Thick-walled samples are manufactured layer by layer with an oscillating welding head motion. The mechanical properties of the samples are compared on an adequate statistical basis. Microstructural-and computer tomography analysis are conducted to comprehend shown interactions. The reproducibility is investigated in dependence of different heat treatment states, different directions of mechanical testing and two manufacturing systems of the same type.

Research on Technology of Welding Aluminum Foil in Pressure Vessel Based on Ultrasonic Rolling Welding

For solving the problems of low bonding strength of anticorrosive layer inside the pressure vessel, the technology of ultrasonic continuous welding applied in aluminum alloy foil is researched in this paper. The technological parameters which affect the welding quality most are analyzed. Through the finite element simulation, the stress and temperature distribution of metal layer and welding head during the welding process are analyzed. The influence of important parameters such as welding pressure and thickness of metal layer on welding quality are studied. The optimal combination of key process parameters such as welding speed, welding pressure and thickness of metal layer are discussed by orthogonal test. The results show that the bonding strength at the weld can reach the tensile strength of the metal itself, and is also qualified to the design expectation.

Dynamics Modeling and Optimization of a Wrapper Flow Pack Mechanism

This paper is about a mechanical solution to vibration problem of a wrapper flow pack mechanism, which is used in packaging industry. The target mechanism is the welding head of the machine where the vibration is generated, due to eccentric masses rotating with a cut-on-the-fly motion law. Consequently, production rate is limited by the vibration at 200 pieces per minute. To reduce the vibration so that the production rate can exceed over 200 ppm, two ways of improvements are considered. The first one is optimizing the motion law. The other one consists in mechanical modifications which eliminates or balance out the inertia forces derived from the eccentric rotating mass. This research implements the second way of adding balance weights and discusses the properties of it. During analysis, the software ADAMS which provides kinematic simulation is used as the analytical tool to test and examine the solutions proposed.

Railroad Rails Containing Electrode-Induced Pitting From Pressure Electric Welding

The Federal Railroad Administration (FRA) routinely conducts investigations of railroad accidents to determine causation and any contributing factors to help the railroad industry implement corrective measures that may prevent similar incidents in the future. Over the past decade, FRA has investigated multiple broken rail accidents in which fractures in the rail web were identified. The common features observed in the recovered rail fragments from these accidents included welds and spots or burn marks on the web, indicating that the rails were joined together by pressure electric welding. Pressure electric welding uses a welding head that clamps around two opposing rail ends, pressing an electrode on each rail, then hydraulically pulling the rail ends together while arcing current through the electrodes into the rails, causing them to essentially melt together to form a continuous rail. Based on the similarities observed in the web fractures, FRA rail integrity specialists hypothesized that stray (i.e. inadvertent and unwanted) arcing during pressure electric welding can result in the formation of burns or pits on the rail where it makes contact with the electrodes. Moreover, these electrode-induced pits behave as stress raisers (also referred to as stress concentrations). Fatigue cracks often develop at locations of stress concentration. Once a fatigue crack initiates, the localized stress encourages the growth of the crack, which may potentially lead to rail failure. This paper describes the forensic evaluations of three railroad rails containing electrode-induced pitting. These evaluations include: magnetic particle inspection to nondestructively detect cracks emanating from the pitting; fractography to study the fracture surfaces of the cracks; metallography to study the microstructure; analysis of chemical composition; and measurements of tensile mechanical properties and fracture toughness of rail steel. Moreover, the results of these evaluations confirm the hypothesis postulated by FRA that stray arcing during pressure electric welding can cause electrode-induced pitting.

Modified Twin-Spot Laser Welding of Complex Phase Steel

The work addresses modified methods of twin-spot laser welding of complex phase steel sheets and investigates the effects of laser beam distribution on the macrostructure, microstructure and hardness. The research-related results were obtained for the beam power distributions of 50%-50%, 60%-40% and 70%-30%. Test joints were made using a Yb:YAG disc laser with a maximum power of 12 kW and a welding head by means of which it was possible to focus a laser beam on two spots. It was found that the change in the laser beam distribution affects geometrical features of the joint. The application of the second beam of lower power enables obtaining tempering-like effects, which finally lead to the beneficial hardness reduction both in the fusion zone and in heat-affected zone. The identification of various microstructural constituents in different zones of the joint was performed using light microscopic micrographs and scanning electron images.

Microstructure of Fiber Laser Deposited WC-Co Cemented Carbide and Carbon Steel

Using a fiber laser welding head, crack-free WC-Co/Steel weld depositions are obtained with optimized welding parameters. The microstructure, composition, phase, structure, and bend strength are analyzed using optical metallography, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and bend test. The influence of the microstructure and WC/matrix interfaces in the vicinity of joint failure at the cemented carbide side is discussed. It is evident that the deposit consists of austenite dendrites and interdendritic eutectic carbides. The austenite further transforms to martensite on-cooling. The flexural bend strength and yield strength of the joints attained 970 MPa and 876 MPa, respectively. Bend fracture occurs at the HAZ in the cemented carbide side of the joint, characterized with cleavage fracture and quasi-cleavage fracture. TEM and HRTEM image of WC/Co interfaces verified the W2C and eta phase formation in the HAZ that contributed to the embrittlement.

Research on the Use of Robotized Tandem MAG Welding in Steel Plates Destined for the Manufacture of Pipelines

The performed research focuses on the complete replacement of the pipeline manufacturing process consisting in welding on SAW+MIG / MAG generators with the robotized Tandem MIG / MAG welding procedure, with low energy consumption.The Tandem MAG procedure was experimented on X52 MS steel plates destined for the manufacture of pipelines, measuring 400x150x12 mm, with Y-joints (30o).The welded joints were executed horizontally and unilaterally, with flux bed support, 3 welding seams, using for filler material two wires of the same quality, EN ISO 14341: G 42 4 M G3Si1 (Filcord C), measuring 1.2 mm in diameter, and shielding gas EN ISO 14175 (CORGON 18).The entire technological welding process was carried out in fully robotized, laboratory conditions, using the QIROX -315 welding robot, fitted with Tandem MIG/MAG welding equipment, type QUINTO-GLC 603.The welding seams were executed with the same Tandem MAG welding head, with two wires, taking advantage of the possibility to rotate the welding head so as to obtain welding seams with the wires either positioned one after the other (tandem), or transversally (perpendicular to the welding direction), obtaining, by correlation with the welding speed, optimal linear energies, implicitly, seams of various widths and penetrations.The results of the tests concerning the characterization of the obtained welded joints corresponded to the mechanical – metallographic tests, falling within the ranges provided by the applicable standards.The welding parameters used in the robotized Tandem MAG procedure may lead to remarkable advantages concerning the use of energy and filler metal. Thus, linear energies are about 40% - 45% smaller than in the case of the classical SAW+MIG / MAG process, with positive effects on the mechanical and metallographic characteristics of the welded joints, leading to significant reductions in energy consumption. Furthermore, the use of filler materials (wire, shielding gas) decreases by 10% - 15% as compared to the classical SAW+MIG / MAG process, leading, implicitly, to lower costs.As a consequence of the obtained results, MAG Tandem welding procedure may become an alternative to SAW submerged arc welding and combined SAW and MIG / MAG welding and a classical reference method for the manufacture of pipelines

Properties and Microstructure of Laser Welded VM12-SHC Steel Pipes Joints

Paper presents results of microstructure and tests of welded joints of new generation VM12-SHC martensitic steel using high power CO2 laser (LBW method) with bifocal welding head. VM12-SHC is dedicated to energetic installation material, designed to replace currently used. High content of chromium and others alloying elements improve its resistance and strength characteristic. Use of VM12-SHC steel for production of the superheaters, heating chambers and walls in steam boilers resulted in various weldability researches. In article are presented results of destructive and non-destructive tests. For destructive: static bending and Vickers hardness tests, and for non-destructive: VT, RT, UT, micro and macroscopic tests were performed.