Simon Olschok

Welding Thick Steel Plates with Fibre Lasers and GMAW

The results of a collaborative research project on laser beam weldability of carbon steels of high sheet thickness are presented. That includes single and multiple pass welding of 16 mm and 20 mm thick plates, as well as the investigation of acceptable tolerances i.e. gap bridgeability and edge misalignment. For the welding experiments fibre lasers with 8 kW, 20 kW laser power and different GMAW-techniques were used in various applications. With the 20 kW fibre laser 16 mm plates could be welded with a single pass, 20 mm required a seam preparation or alternatively preheating of the material. For multi pass welding with 8 kW laser power a joint preparation with a single V-butt joint with a broad root face (Y-groove) was applied. The root pass was always welded with a hybrid process, the filler passes with a hybrid process as well as a GMAW process which produced the best results.

Laser Beam Welding of Open-Porous Metallic Foams for Application in Cooling Structures of Combined Cycle Power Plants

Within the Collaborative Research Centre 561, “Thermally highly loaded, porous and cooled multilayer systems for combined cycle power plants,” open-porous and high-temperature stable Ni-based structures are being developed for the requirements of effusion cooling. A two-dimensional cooling strategy for the walls of combustion chambers, which allows the outflow of the cooling medium over the complete wall area of the combustion chamber, could be realized by an open-porous metallic foam structure. The open-porous metallic foam is produced by the “slip reaction foam sintering” process, a powder metallurgical process. To join several foams to assemble structural elements, laser beam welding has been used. Different joining strategies have been examined to find out the most suitable method to join these foams. In this paper, the process setups, settings of the different strategies, and results of trials (seam geometry and strength tests) are discussed. The need for graded structures to combine the essential permeability and adequate weldability is also shown.

Laser Beam Submerged Arc Hybrid Welding

The laser beam-submerged arc hybrid welding method originates from the knowledge that, with increasing penetration depth, the laser beam process has a tendency to pore formation in the lower weld regions. The coupling with the energy-efficient submerged-arc process improves degassing and reduces the tendency to pore formation. The high deposition rate of the SA process in combination with the laser beam process offers, providing the appropriate choice of weld preparation, the possibility of welding plates with a thickness larger than 20° mm in a single pass, and also of welding thicker plates with the double-sided single pass technique.

Laser beam welding under vacuum of high grade materials

Currently, three welding processes are used in the manufacturing of large scale work pieces with high weld seam depths. The gas metal arc welding and the submerged arc welding processes are characterized by a comparatively low penetration depth and welding speed, the use of welding consumables and a high energy input per length. Electron beam welding is suitable for single pass welding of high wall thicknesses, but a fine vacuum is needed, x-ray radiation is generated, the process is prone to magnetic fields, and the technology has to face a low market penetration. Laser beam welding under vacuum (“LaVa”) is on its way to become a new and superb option for these welding tasks. The paper at hand presents the latest results of a research project which targets the qualification of LaVa for the welding of heavy-walled steel structures made of unalloyed steel or duplex stainless steel. The achieved results demonstrate that, in comparison to laser beam welding at atmospheric pressure, an increase of the penetration depth and a high process stability can be achieved, whereby economic advantages and a high weld seam quality are realized. On the other hand, the latest results of the application of LaVa for the welding of nickel-base alloys, copper, and titanium are presented. It is shown that LaVa is suitable for the welding of these materials. A high process stability is achieved; spattering is minimized; and high penetration depths are achieved.

Laser beam welding in vacuum – A process variation in comparison with electron beam welding

This article gives a comparison between laser beam welding and electron beam welding. In a first step, the basic principles and properties of both methods and/or the resulting weld joints are specified, afterwards the research results from laser beam welding in vacuum are presented.Thanks to modern laser systems (fibre laser and/or disk laser) and their excellent beam quality, laser beam welding in vacuum allows a direct comparison of the process behaviour, the development of the keyhole and the respective welding results from both beam welding methods.The welding possibilities of this process variation are demonstrated, the advantages with regard to electron beam welding and/or the disadvantages compared to laser beam welding in atmosphere are discussed and the need for future research are specified.This article gives a comparison between laser beam welding and electron beam welding. In a first step, the basic principles and properties of both methods and/or the resulting weld joints are specified, afterwards the research results from laser beam welding in vacuum are presented.Thanks to modern laser systems (fibre laser and/or disk laser) and their excellent beam quality, laser beam welding in vacuum allows a direct comparison of the process behaviour, the development of the keyhole and the respective welding results from both beam welding methods.The welding possibilities of this process variation are demonstrated, the advantages with regard to electron beam welding and/or the disadvantages compared to laser beam welding in atmosphere are discussed and the need for future research are specified.

Welding of thick plate copper with laser beam welding under vacuum

Today, copper is one of the most important materials and will become even more important in the future. It is used in a wide range of products, industry sectors, and plate thicknesses. The beam welding technologies laser beam welding and electron beam welding achieve high intensities and are thereby suitable to overcome the difficulties in the welding of copper, which are caused by properties such as high thermal conductivity. There is a high demand for the application of the laser beam in the welding of copper, but in industrial applications, a sufficient process capability is currently only achieved with a high welding speed and a high laser power level. At low welding speeds, process instabilities such as weld metal ejections occur. These ejections can cause critical welding defects which have to be prevented. At high welding speeds, the penetration depth decreases dramatically even if a high laser power is applied. In addition, the process control is hampered and the investment costs increase. By laser beam welding in vacuum, the process capability can be increased significantly. Weld metal ejections at low welding speeds are prevented. This increase in process stability can be transferred in a high penetration depth at a comparatively low laser power level. Sound welding of copper at a power level between 4 and 8 kW (intensity level 50–80 kW/mm2) of a multimode solid state laser becomes possible without weld metal ejections. A penetration depth of 3–8 mm is achieved.Today, copper is one of the most important materials and will become even more important in the future. It is used in a wide range of products, industry sectors, and plate thicknesses. The beam welding technologies laser beam welding and electron beam welding achieve high intensities and are thereby suitable to overcome the difficulties in the welding of copper, which are caused by properties such as high thermal conductivity. There is a high demand for the application of the laser beam in the welding of copper, but in industrial applications, a sufficient process capability is currently only achieved with a high welding speed and a high laser power level. At low welding speeds, process instabilities such as weld metal ejections occur. These ejections can cause critical welding defects which have to be prevented. At high welding speeds, the penetration depth decreases dramatically even if a high laser power is applied. In addition, the process control is hampered and the investment costs increase. By lase...

Laser beam welding in vacuum of thick plate structural steel

Laser beam and electron beam welding methods are well established in the manufacturing industry. Each of the methods has specific advantages which are used for a large variety of application cases.For some time now, laser beam welding in vacuum has experienced a renaissance. First tests about the topic were made in Japan as early as in the Eighties. The brilliant solid-state laser beam sources available today offer many advantages compared to the previously used CO2 laser beam sources. Higher power and beam quality is available, the interface for getting the laser into the vacuum can be designed simpler and the welding heads have a compact design. Compared with electron beam welding, laser beam welding in large vacuum chambers can be carried out with simpler means.This article covers a spotlight on the main aspects of lower pressure on the laser beam welding process and the specific advantages of laser beam welding in vacuum. Moreover it shows the recent progress made from the early phenomenological examination of the process variation to the use as welding process for connection welds on thick plate steel up to (and over) 70mm wall thickness.Laser beam and electron beam welding methods are well established in the manufacturing industry. Each of the methods has specific advantages which are used for a large variety of application cases.For some time now, laser beam welding in vacuum has experienced a renaissance. First tests about the topic were made in Japan as early as in the Eighties. The brilliant solid-state laser beam sources available today offer many advantages compared to the previously used CO2 laser beam sources. Higher power and beam quality is available, the interface for getting the laser into the vacuum can be designed simpler and the welding heads have a compact design. Compared with electron beam welding, laser beam welding in large vacuum chambers can be carried out with simpler means.This article covers a spotlight on the main aspects of lower pressure on the laser beam welding process and the specific advantages of laser beam welding in vacuum. Moreover it shows the recent progress made from the early phenomenological exami...

Confirmation of tensile residual stress reduction in electron beam welding using low transformation temperature materials (LTT) as localized metallurgical injection – Part 1: Metallographic analysis

Abstract For the reduction of the distortion and the residual tensile stresses in welded seams on carbon manganese steels, low transformation temperature materials (LTT) were developed. These materials use the volume expansion effect during martensitic transformation. The volume expansion counteracts volume shrinkage during cooling. The positive effects of the low transformation temperature alloys on the residual tensile stresses were demonstrated in various investigations. The low transformation temperature materials were, so far, used as filler material in arc welding processes in large volumes. The use of modular thermal fields of the electron beam welding processes offers the potential of a temporally activated use of compressive stress induction by phase transformation of the low transformation temperature alloys. The aim is to exert influence in situ on the welding residual stress state and thus on the distortion of complex parts. The metallographic analysis of an electron beam welded seam in unalloyed steel with low transformation temperature filler material is demonstrated. The evaluation is made via electron backscatter diffraction (EBSD) and is shown in the first part. The second part will show the effect on near surface residual stresses examined by hole-drilling method in combination with an optical evaluation by electronic speckle pattern interferometry.

Innovative hybrid welding process for structural steelwork engineering—Laser submerged arc hybrid welding

The welding of thick metal sheets has become increasingly important for structural steelwork engineering applications (e.g., pipe- or crane building). Nowadays, welding tasks are performed using a time-consuming conventional submerged arc welding process. Here, a large number of welding passes are necessary, which leads to a thermally induced distortion. Therefore, there is a high demand for a welding process which allows a cost-effective welding of thick metal sheets. By the development of a laser beam submerged-arc hybrid welding process (LUPuS), a technique is created which combines the high penetration depth of the laser with the high thermal efficiency of the submerged arc process. This leads to synergy effects which predestine LUPuS for the given welding task. Earlier projects have shown a general feasibility of LUPuS. Steel plates with thicknesses of up to 50 mm have been joined without any welding issues using the double-sided single pass technique. However, different results of the notch impact t...

Robot application for laser-GMA hybrid welding in shipbuilding

The research project „Development of a three-dimensional laser hybrid welding system for increasing the efficiency and quality of works in the panel line of a shipyard (PaLas)“ which is funded by the BMWi (Federal Ministry of Economics and Technology) is supposed to contribute towards solving the problems of vertical-down and corner welds by applying a robot during fibre laser GMA hybrid welding. The research project comprises the manufacturing of the welds and the development of an in-process sensor system which is based on the arc sensor principles.The research project „Development of a three-dimensional laser hybrid welding system for increasing the efficiency and quality of works in the panel line of a shipyard (PaLas)“ which is funded by the BMWi (Federal Ministry of Economics and Technology) is supposed to contribute towards solving the problems of vertical-down and corner welds by applying a robot during fibre laser GMA hybrid welding. The research project comprises the manufacturing of the welds and the development of an in-process sensor system which is based on the arc sensor principles.