Uwe Reisgen

Joining properties of a composite glass-ceramic sealant

When assembling planar solid oxide fuel cell (SOFC) stacks, an electrically insulating and gas-tight sealing material is required. Glass-ceramic sealants have been shown to be an appropriate material for this application in the past. In the present study, the investigations are focused on a composite material consisting of zirconia in a glass matrix based on the system of BaO-CaO-SiO 2 (BCS). The joining behavior with ferritic stainless steel is macroscopically observed by so-called ‘sandwiched’ samples made out of two steel plates (size 50 × 50 mm 2 ) with the glass sealant in-between. Dilatometric measurements are carried out, and the coefficient of thermal expansion is taken for varying amounts of zirconia in the composite material. The crystallization behavior of the sealant is investigated by differential thermal analysis. The microstructure of joined samples, submitted to different scenarios of thermal treatment, is characterized by optical and scanning electron microscopy. The joining properties strongly depend on the amount of filler material. Additions of 20 wt% zirconia in the glass matrix prove to be the optimal composition. The glass matrix tends to crystallize very slowly, giving the prospect of an elastic seal during the initial operation of a stack.

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...

Hybrid laser welding in shipbuilding – Extension of the application range to vertical down welding

The Hybrid Laser Welding (HLW) has become one of the most important manufacturing technologies for an automated and efficient shipbuilding. The technology is successfully used since the early 2000s and mainly applied in the panel manufacturing (flat position groove weld 1G and fillet weld 2F). The target of the research work is to extend the range of application of the Hybrid Laser Welding in shipbuilding to the vertical welding positions 3G (groove weld) and 3F (fillet weld). The welds for wall structures are currently performed by manual vertical-up welding. The implementation of a fully mechanized vertical-down welding system, based on Laser Beam Welding (LBW) and Gas Metal Arc Welding (GMAW) processes will increase the productivity in a huge amount.The Hybrid Laser Welding (HLW) has become one of the most important manufacturing technologies for an automated and efficient shipbuilding. The technology is successfully used since the early 2000s and mainly applied in the panel manufacturing (flat position groove weld 1G and fillet weld 2F). The target of the research work is to extend the range of application of the Hybrid Laser Welding in shipbuilding to the vertical welding positions 3G (groove weld) and 3F (fillet weld). The welds for wall structures are currently performed by manual vertical-up welding. The implementation of a fully mechanized vertical-down welding system, based on Laser Beam Welding (LBW) and Gas Metal Arc Welding (GMAW) processes will increase the productivity in a huge amount.

Laser beam welding under vacuum of a fine-grained steel

Laser beam welding is an established method in the manufacturing industry. The method allows the achievement of a high aspect ratio (penetration depth to weld width) due to the deep penetration effect. The method is applied in different variations which comprise a wide spectre of materials and also a large field of applications, from the field of heavy machinery up to micro system technology. There are, however, some process-induced disadvantages which may force the user to compromise.Laser beam welding under vacuum is a new process variation with a clearly high potential. Particularly the further development in the field of solid-state lasers up to high powers and beam qualities increase the welding results, which can be achieved in the vacuum. First results made with solid-state lasers under vacuum show that the penetration depth can at least be doubled, compared to welding in atmosphere. The tendency to spatter formation to the upper surface is greatly reduced. The weld quality is, in the same turn, increased. Especially the formation of pores with increasing weld-in depths is practically non-existent.In this lecture, new results of laser beam vacuum welding of a fine-grained steel will be presented. This includes also the mechanical properties like hardness and toughness.Laser beam welding is an established method in the manufacturing industry. The method allows the achievement of a high aspect ratio (penetration depth to weld width) due to the deep penetration effect. The method is applied in different variations which comprise a wide spectre of materials and also a large field of applications, from the field of heavy machinery up to micro system technology. There are, however, some process-induced disadvantages which may force the user to compromise.Laser beam welding under vacuum is a new process variation with a clearly high potential. Particularly the further development in the field of solid-state lasers up to high powers and beam qualities increase the welding results, which can be achieved in the vacuum. First results made with solid-state lasers under vacuum show that the penetration depth can at least be doubled, compared to welding in atmosphere. The tendency to spatter formation to the upper surface is greatly reduced. The weld quality is, in the same turn, in...

Vertical-down hybrid welding in ship building - The next innovation step

The ever increasing competitive pressure caused by the worldwide development of ship building capacities requires the application of innovative and highly efficient production technologies in German shipyards. Due to the increase of welding speed and to the increased degree of mechanization, fully mechanised, sensor-supported vertical-down welding (FaSek) entails considerable economic advantages in the joining of vertical welds compared with the currently applied manual vertical-up welding. This is achieved by using the laser-beam GMA hybrid welding method with additional, oppositely arranged GMA torch.The ever increasing competitive pressure caused by the worldwide development of ship building capacities requires the application of innovative and highly efficient production technologies in German shipyards. Due to the increase of welding speed and to the increased degree of mechanization, fully mechanised, sensor-supported vertical-down welding (FaSek) entails considerable economic advantages in the joining of vertical welds compared with the currently applied manual vertical-up welding. This is achieved by using the laser-beam GMA hybrid welding method with additional, oppositely arranged GMA torch.

Micro-laser-GMA hybrid welding – The advancement from macro to micro range

Laser beam welding is characterized by high process speed and low energy input. A shorter processing time and also less distortion are the results.Expensive clamping and subassembly techniques are, how-ever, setting limits to the application scope of laser beam welding of thin sheets and foils (e.g. metal foils), particularly in the field of unit production and small-lot production. A gap of just 0.1u2005mm causes inadequate welding results, for example, root concavity and top bead sinkage, since a large part of the beam is streaming through the gap and, thus, the better part of its power remains unused. The quantity of molten material is, therefore, insufficient for the achievement of faultless welds.The application of micro-laser-GMA hybrid welding allows to expand the tolerance range and thus to considerably reduce work expenditure for the welding of fine sheets and/or metal foil joints. The hybrid technology also allows the reduction of cycle times through the increase of the travel speed and, moreover, the reduction of clamping expenditure which, again, results in enormous cost saving potential.In this publication, the successful implementation of the established laser-GMA hybrid welding from the macro-range to the micro-range is demonstrated.Laser beam welding is characterized by high process speed and low energy input. A shorter processing time and also less distortion are the results.Expensive clamping and subassembly techniques are, how-ever, setting limits to the application scope of laser beam welding of thin sheets and foils (e.g. metal foils), particularly in the field of unit production and small-lot production. A gap of just 0.1u2005mm causes inadequate welding results, for example, root concavity and top bead sinkage, since a large part of the beam is streaming through the gap and, thus, the better part of its power remains unused. The quantity of molten material is, therefore, insufficient for the achievement of faultless welds.The application of micro-laser-GMA hybrid welding allows to expand the tolerance range and thus to considerably reduce work expenditure for the welding of fine sheets and/or metal foil joints. The hybrid technology also allows the reduction of cycle times through the increase of the travel speed and, moreover, t...

Hybrid welding with controlled short arcs - A variation of the reduction of the energy-per-unit length

Laser beam welding is a fast, non-contact joining method. It is characterised by a high energy density which allows high process speed with, at the same time, low energy input into the joining zone. The weld seams which have been thus produced are very narrow and have a small heat affected zone. It is, however, not possible to exert metallurgical influence on the molten metal using the laser or to bridge gaps without weld sag or root collapse. There is the possibility to add cold wire where, however, comparatively expensive laser power for melting the wire must be used. Another approach is laser GMA hybrid welding with spray and/or pulsed arc. The energy-per-unit length is, however, strongly increased, thus problems caused by residual stresses and distortion in the component and also hot cracks in the weld may be developing. Conventional hybrid methods do, moreover, not permit the welding of plates with galvanised surfaces, since the GMA process shows instabilities caused by the explosive zinc burn-off. Due to this problem in laser beam GMA hybrid welding, the industry requires a joining method which combines the positive properties of laser beam GMA hybrid welding with a lower energy input. This method may be laser GMA hybrid welding with the addition of low-energy arc welding methods. The results of this project may, on the one hand, be beneficial for companies who apply laser GMA hybrid welding successfully already and who require a further minimisation of distortion. On the other hand, the process-oriented consequent further development of laser beam GMA hybrid welding allows the manufacturing of parts and components which have, so far, not been produced because of joining restrictions. It is, particularly with regard to the welding of coated materials, the distortion and the process stability, possible to generate advantages.Laser beam welding is a fast, non-contact joining method. It is characterised by a high energy density which allows high process speed with, at the same time, low energy input into the joining zone. The weld seams which have been thus produced are very narrow and have a small heat affected zone. It is, however, not possible to exert metallurgical influence on the molten metal using the laser or to bridge gaps without weld sag or root collapse. There is the possibility to add cold wire where, however, comparatively expensive laser power for melting the wire must be used. Another approach is laser GMA hybrid welding with spray and/or pulsed arc. The energy-per-unit length is, however, strongly increased, thus problems caused by residual stresses and distortion in the component and also hot cracks in the weld may be developing. Conventional hybrid methods do, moreover, not permit the welding of plates with galvanised surfaces, since the GMA process shows instabilities caused by the explosive zinc burn-off. D...