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Electron beam (EB) welding is a keyhole welding process in which the kinetic energy of focused electrons is converted into the heat required for welding. When a full penetration weld is achieved in keyhole EB welding, a small part of the electrons from the electron beam pass through the workpiece via the open keyhole at the root side of the weld. These electrons provide a charge whose current value can be measured, namely, the through-current. The aim of this study was to develop and build a control system integrated in the EB welding machine that enables the maintenance of complete root penetration in EB welding by means of an adaptive control system. The adaptation was performed with closed-loop feedback equipment that simultaneously measures the electrons passing through the workpiece via the keyhole (transmitted through-current) and adjusts the required beam current parameter relative to the through-current measured during welding. The results of the welding tests demonstrated the functionality of the developed control system and the suitability of the concept itself. For example, in a welding test run in which the thickness of the test piece was linearly increased from 10 to 12 mm, the control system was able to react and regulate the welding power required for complete root penetration along the whole thickness range. In the above case, the test results showed that based on the measured through-current data, the control system instantaneously increased the amount of beam current required during welding linearly with increasing thickness of the plate to be welded.

Gas tungsten arc welding (GTAW) is a common joining method for austenitic stainless steel sheets. Edge joint is frequently used configuration when the aim is to produce weldments e.g., between the tube sheets and the tubes and to other hollow structures needing tight sealing welds and sound joints. In those applications all positions for welding is usually needed. Robotized welding is utilized, when manual welding is not possible, e.g., in maintenance for nuclear power applications. In automatic welding a strict control of location of arc and welding parameters are extremely important. In this work the aim was to find suitable welding parameters, as pulse parameters, welding speed and shielding gas composition and study their effects on weld joint penetration and weld quality in different welding positions. In addition, the inaccuracy in the alignment of the arc and its effects was tested in different cases. It was found that it was possible to find the optimal parameters in different positions, flat (PA), overhead (PE), and vertical-up position (PF). However, the vertical-down position (PG) was giving a lower joint penetration in the cases which allow sound welds. Therefore, it was considered that the fabrication of the circumferential joint was best done in two steps to avoid the PG position, which ensures that a sound weld with the set 2.6 mm penetration requirement is achieved over the entire circumference. The use of a shielding gas mixture containing argon and 2% hydrogen showed significant advantages over the other three shielding gas compositions tested, which was observed as deeper penetration of the welds. Post-print / Final draft

In thick section laser welding, filler metal addition is usually required to improve joint fit-up tolerances or to control the chemical composition of the weld metal. With deep and narrow welds produced using an over-alloyed filler metal, it may be challenging to ensure that the filler metal and its elements are homogeneously mixed and evenly distributed throughout the fusion zone. Inhomogeneous filler metal mixing can cause unfavourable changes to weld metal chemistry and microstructure. Filler metal mixing behaviour in laser-arc hybrid and laser cold-wire welding is studied in this work. Welding tests were conducted on 10 mm thick butt-welded joints of AISI 316L austenitic stainless steel. An overmatching type 2205 duplex stainless steel filler wire was used to obtain a composition contrast between the base metal and filler metal. Energy dispersive spectroscopy (EDS) with chromium as the trace element was used for element mapping and stepwise characterization of the weld cross-section samples. Optical metallography was used to observe possible inhomogeneous filler metal mixing behaviour like local acute changes in macro- and microstructural features. The results showed a clear difference in filler metal mixing between the weld surface part (upper half) of the weld and the weld root part (lower half) in 10 mm thick welded cross-sections for closed root gap of I-groove welds or when the gap was only 0.4 mm. In narrow I-groove preparations, inhomogeneous mixing phenomena were more pronounced in laser cold-wire welds than in laser-arc hybrid welds. In both welding processes, a combination of trailing wire feeding and the use of a wider groove enabled filler metal to be introduced deeper into the bottom of the groove and improved mixing in the root portion of the welds.

The welded lip seals form part of the torus primary vacuum boundary in between the port plugs and the vacuum vessel, and are classified as Protection Important Component. In order to refurbish the port plugs or the in-vessel components, port plugs have to be removed from the machine. The lip seal design must enable up to ten opening of the vacuum vessel during the life time operation of the ITER machine. Therefore proven, remote reliable cutting and re-welding are essential, as these operations need to be performed in the port cells in a nuclear environment, where human presence will be restricted. Moreover, the combination of size of the components to be welded (∼10 m long vacuum compatible thin welds) and the congested environment close to the core of the machine constraint the type and size of tools to be used. This paper describes the lip seal cutting and welding development programme performed at the VTT Technical Research Centre, Finland. Potential cutting and welding techniques are analyzed and compared. The development of the cutting, TIG and laser welding techniques on samples are presented. Effects of lip seal misalignments and optimization of the 2 welding processes are discussed. Finally, the manufacturing and test of the two 1.2 m × 1 m representative mock-ups are presented. The set-up and use of a robotic arm for the mock-up cutting and welding operations are also described.

This study introduces an experimental work carried out in multi-pass laser welding with cold filler wire and laser-arc hybrid welding of thick section austenitic stainless steel. As it has been demonstrated earlier, hybrid and cold wire welding with a keyhole-mode can offer very efficient way to produce multi-pass welds in narrow gap thick section joints. However, when multi-pass welding is applied to one pass per layer method without e.g. scanning or defocusing, the used groove width needs to be very narrow in order to ensure the proper melting of groove side walls and thus to avoid lack of fusion/cold-run defects. As a consequence of the narrow groove, particularly in thick section joints, the accessibility of an arc torch or a wire nozzle into the very bottom of a groove in root pass welding can be considerably restricted. In an alternative approach described in this paper, a power density of a laser beam spot was purposely dispersed by using a defocusing technique. In groove filling experiments, a power density of defocused laser beam was kept in the range, which led the welding process towards to conduction limited regime and thus enabled to achieve broader weld cross-sections. The object was to study the feasibility of defocusing as a way to fill and bridge wider groove geometries than what can be welded with focused keyhole-mode welding with filler addition. The paper covers the results of multi-pass welding of up to 60 mm thick joints with single side preparations.

Autogenous laser welding has shown many advantages over traditional welding methods in numerous applications. However, there could be even more applications, but due to the power levels of present high power lasers, depth of penetration is limited. One way to overcome this limitation is to use multipass laser welding, in which a narrow gap and a filler wire are applied. By this process thick sections can be welded with a smaller heat input and therefore with smaller distortions, and the process seems to be very effective compared to “traditional” welding methods. Another way to increase penetration and fill the groove is by using the so-called hybrid process, in which laser and GMAW are combined. In this study thick section austenitic stainless steel is welded using a multipass technique with filler wire, and also by utilizing a hybrid process. For narrow gap conditions, groove angles of 8°, 10°, and 12°, are used with a partially grooved V joint. Parameters (e.g, filler wire feeding, placement of wire, and arc) are varied. Results of the experiments are presented and phenomena of the process, as well as reasons for weld defects, are pointed out.

This study introduces an experimental work carried out in multi pass laser welding with cold filler wire and laser-arc hybrid welding of thick section austenitic stainless steel. As it has been demonstrated earlier, hybrid and cold wire welding with a keyhole-mode can offer very efficient way to produce multi pass welds in narrow gap thick section joints. However, when multi pass welding is applied to one pass per layer method without e.g. scanning or defocusing, the used groove width needs to be very narrow in order to ensure the proper melting of groove side walls and thus to avoid lack of fusion/cold-run defects. As a consequence of the narrow groove, particularly in thick section joints, the accessibility of an arc torch or a wire nozzle into the very bottom of a groove in root pass welding can be considerably restricted. In an alternative approach described in this paper, a power density of a laser beam spot was purposely dispersed by using a defocusing technique. In groove filling experiments, a power density of defocused laser beam was kept in the range, which led the welding process towards to conduction limited regime and thus enabled to achieve broader weld cross-sections. The object was to study the feasibility of defocusing as a way to fill and bridge wider groove geometries than what can be welded with focused keyhole-mode welding with filler addition. The paper covers the results of multi pass welding results of up to 60 mm thick joints with single side preparations. In order to reach final 60 mm joint thickness, it required the preliminary defocusing trials of bead-on plate samples, and tests of joint thicknesses of 10 mm and 20 mm with different groove openings.This study introduces an experimental work carried out in multi pass laser welding with cold filler wire and laser-arc hybrid welding of thick section austenitic stainless steel. As it has been demonstrated earlier, hybrid and cold wire welding with a keyhole-mode can offer very efficient way to produce multi pass welds in narrow gap thick section joints. However, when multi pass welding is applied to one pass per layer method without e.g. scanning or defocusing, the used groove width needs to be very narrow in order to ensure the proper melting of groove side walls and thus to avoid lack of fusion/cold-run defects. As a consequence of the narrow groove, particularly in thick section joints, the accessibility of an arc torch or a wire nozzle into the very bottom of a groove in root pass welding can be considerably restricted. In an alternative approach described in this paper, a power density of a laser beam spot was purposely dispersed by using a defocusing technique. In groove filling experiments, a pow...

An austenitic stainless steel AISI 316L grade base material with butt joint thickness of 15 mm and different root gap preparation was single pass welded using both laser-GMA hybrid and laser cold-wire feeding process. The aim was to be able to study the filler metal mixing in thick section laser welding and the effect of processing parameters on it. Particular interest was to examine how homogenous filler metal mixing is across the whole weld cross-section from the weld surface to the root portion. Avesta 2205 duplex stainless steel filler wire was used in order to produce an over-matched weld metal composition differing from the base metal. Chromium was used as a trace- element as its distribution and quantity within the weld cross-section was identified using SEM and EDS analysis. Moreover, micro- and macroscopic metallography was carried out to examine emerged weld microstructures and their features. In the technical paper the effect of influencing parameters on the amount and homogeneity of filler metal mixing such as root gap preparation, wire feeding orientation (leading vs. trailing) and welding process (hybrid vs. cold wire) are compared and discussed.An austenitic stainless steel AISI 316L grade base material with butt joint thickness of 15 mm and different root gap preparation was single pass welded using both laser-GMA hybrid and laser cold-wire feeding process. The aim was to be able to study the filler metal mixing in thick section laser welding and the effect of processing parameters on it. Particular interest was to examine how homogenous filler metal mixing is across the whole weld cross-section from the weld surface to the root portion. Avesta 2205 duplex stainless steel filler wire was used in order to produce an over-matched weld metal composition differing from the base metal. Chromium was used as a trace- element as its distribution and quantity within the weld cross-section was identified using SEM and EDS analysis. Moreover, micro- and macroscopic metallography was carried out to examine emerged weld microstructures and their features. In the technical paper the effect of influencing parameters on the amount and homogeneity of filler met...

Laser and laser-arc hybrid welding of duplex and ferritic stainless steels is demanding, because microstructure of the welds tends to be highly ferritic. Therefore, filler metal must be used for maintaining corrosion and mechanical properties of the welds. In this study, different filler metals including duplex, basic, and overalloyed austenitic grades were used with laser-arc hybrid method to weld lean duplex 1.4162 and novel ferritic stainless steels grades 1.4622 and 1.4509. Several sets of joint design and welding parameter combinations were used to adjust the amount of filler metal in the weld. The purpose of the trials was to evaluate whether weld metal microstructures (grain morphology, austenite/ferrite balance, etc.) can be modified by using an applicable joint preparation and an “overmatched” filler metal addition. Weld characterization included several research methods such as: Macro- and microscopic examination using light microscope¸ cross-sectional dilution ratio determination from the metallographic cross sections, electron backscatter diffraction method in order to assess austenite, and ferrite phase proportions in the test welds. The effects of used groove geometry, filler metal composition, and content on resulting metallurgical features of the welds are discussed in detail.

Although the austenitic stainless steel grades are commonly considered to be quite easily weldable, there are certain applications which make exception to the above statement. As an example, which has also attributed to this study, it could be mentioned a welded assembly which forms a very rigid structure. In above mentioned structure, a risk of solidification cracking (i.e. hot cracking) in produced welds could be a significant problem, if necessary precautions are not taken into account well in advance. It is generally known that hot cracking of austenitic stainless steel during welding is very much coupled to chemical composition and the strains formed during solidification stage of the weld. The level of strains is dependent on e.g. a groove design, used welding parameters and the rigidity of the structure to be welded. In this work the main objective was to find a method for studying hot cracking susceptibility when a thick section austenitic stainless steel is welded using laser hybrid welding process (3 kW Nd:YAG-laser + GMAW) and multi pass technique. The tested parent material was a specially customized heat: AISI 316L(N)-IG ITER-grade austenitic stainless steel. During this study the test system was first developed and tested. It consists of a very rigid clamping system and specially designed 60 mm thick test piece which was planned to be rigid as itself. The test welds were evaluated with macroscopic and microscopic examination. In addition NDT was used as well. The results of welding tests showed that the developed test set-up can produce strains high enough to promote hot cracking in produced test welds. According to welding test results, hot cracking occurred in these rigid weld arrangements. The test set-up is described and the results of hot cracking tests are reported. The effect of chemical composition of the used parent/filler material and prevailing micro structure of weld metal on the risk of hot cracking susceptibility is discussed as well.Although the austenitic stainless steel grades are commonly considered to be quite easily weldable, there are certain applications which make exception to the above statement. As an example, which has also attributed to this study, it could be mentioned a welded assembly which forms a very rigid structure. In above mentioned structure, a risk of solidification cracking (i.e. hot cracking) in produced welds could be a significant problem, if necessary precautions are not taken into account well in advance. It is generally known that hot cracking of austenitic stainless steel during welding is very much coupled to chemical composition and the strains formed during solidification stage of the weld. The level of strains is dependent on e.g. a groove design, used welding parameters and the rigidity of the structure to be welded. In this work the main objective was to find a method for studying hot cracking susceptibility when a thick section austenitic stainless steel is welded using laser hybrid welding proce...

Numerous advantages of hybrid welding, in which laser beam and arc has combined, over autogenous laser welding has been reported. Especially in case of inaccurate joint preparation or fixturing of the plates to be welded because of the filler metal added to the process through MIG-welding. Also additional heat, coming from the arc to the process, enables higher welding speed and deeper penetration. Aluminum alloy (AlMg3) was used in the experiments. Welding was carried out by using the hybrid process (combination of Nd:YAG- and MIG-welding) in the flat position. The joint preparation was carried out as shear cut and different gap widths were used. Welding experiments were made systematically using a statistical experiment procedure called TAGUCHI-method. Parameters, for example alignment of point of arc and laser, varied in experiments. Also characteristic parameters of both welding methods were changed according to the experimental procedure. In this paper results of welding experiments are reported as well as parameters used. A phenomenona of the hybrid process with aluminum is discussed and also reasons for weld defects occurred are pointed out.

Hybrid welding, in which laser and some arc welding method work together, has been introduced to be effective joining method. Hot spot, made by laser to the joint, has been reported to stablize the arc and change the way of material transfer in arc. Hot spot is also guiding the arc towards to it. This phenomenon has been utilized in this study in order to get the process to be happened inside a very narrow groove. In this way, together with multipass technique, the thickness of the parts to be welded can be increased. Welding still happens with quite low total heat input and according to that, method can be used for joining thick sections with very low distortions. Also phenomena of laser keyhole welding still take place, so method is very effective to joining thick sections.In this study thick section austenitic stainless steel has been welded using multipass technique and hybrid process; Nd:YAG -laser+GMAW. Welding has been done using partially grooved V joint geometry and narrow gap with groove angle of 10 degrees. Parameters, for example in filler wire feeding and placement of the wire and the arc are varied. Results of experiments are presented and a phenomenon of the process is discussed.Hybrid welding, in which laser and some arc welding method work together, has been introduced to be effective joining method. Hot spot, made by laser to the joint, has been reported to stablize the arc and change the way of material transfer in arc. Hot spot is also guiding the arc towards to it. This phenomenon has been utilized in this study in order to get the process to be happened inside a very narrow groove. In this way, together with multipass technique, the thickness of the parts to be welded can be increased. Welding still happens with quite low total heat input and according to that, method can be used for joining thick sections with very low distortions. Also phenomena of laser keyhole welding still take place, so method is very effective to joining thick sections.In this study thick section austenitic stainless steel has been welded using multipass technique and hybrid process; Nd:YAG -laser+GMAW. Welding has been done using partially grooved V joint geometry and narrow gap with groove angle o...

It is known that with electron beam welding produced in vacuum environment, deep and narrow welds with superior quality can be achieved. In some studies, this has inspired to use vacuum also with laser in order to improve already good performance achieved in atmospheric pressure. It has been reported that the use of vacuum increases penetration, change profile of weld cross-section and produce less porosity.In this study bead-on-plate Nd:YAG-laser welding experiments were carried out in vacuum and in atmospheric pressure in order to clarify the effect of vacuum on penetration and weld bead geometry. Materials used in the experiments were austenitic stainless steels AISI 304L, AISI 316LN and basic mild steel S235. Evaluations of the welds were done by visually and macroscopically from the macro cross-sections. Also occurrence of weld defects was taken into account.It is known that with electron beam welding produced in vacuum environment, deep and narrow welds with superior quality can be achieved. In some studies, this has inspired to use vacuum also with laser in order to improve already good performance achieved in atmospheric pressure. It has been reported that the use of vacuum increases penetration, change profile of weld cross-section and produce less porosity.In this study bead-on-plate Nd:YAG-laser welding experiments were carried out in vacuum and in atmospheric pressure in order to clarify the effect of vacuum on penetration and weld bead geometry. Materials used in the experiments were austenitic stainless steels AISI 304L, AISI 316LN and basic mild steel S235. Evaluations of the welds were done by visually and macroscopically from the macro cross-sections. Also occurrence of weld defects was taken into account.

Autogenous laser welding has shown many advantages over traditional welding methods in numerous applications. However, there could be even more applications but according to the power levels of present high power lasers depth of penetration is limited. One way to overcome this limitation is to use multipass laser welding, in which narrow gap and filler wire is applied. By this process thick sections can be welded with smaller heat input and then smaller distortions and process seem to be very effective comparing "traditional" welding methods not only according to the narrower gap. Another way to increase penetration and fill the groove is using so called hybrid process, in which laser and GMAW are combined.In this study thick section austenitic stainless steel is welded using multipass technique with filler wire and also hybrid process. For narrow gap, groove angles of 8, 10 and 12 degrees are used with partially grooved V joint. Parameters, for example in filler wire feeding and placement of wire and arc are varied. Results of experiments are presented and phenomena of the process as well as reasons for weld defects are pointed out.Autogenous laser welding has shown many advantages over traditional welding methods in numerous applications. However, there could be even more applications but according to the power levels of present high power lasers depth of penetration is limited. One way to overcome this limitation is to use multipass laser welding, in which narrow gap and filler wire is applied. By this process thick sections can be welded with smaller heat input and then smaller distortions and process seem to be very effective comparing "traditional" welding methods not only according to the narrower gap. Another way to increase penetration and fill the groove is using so called hybrid process, in which laser and GMAW are combined.In this study thick section austenitic stainless steel is welded using multipass technique with filler wire and also hybrid process. For narrow gap, groove angles of 8, 10 and 12 degrees are used with par...