Hybrid laser welding offers promising advantages over the traditional arc-based welding processes... more Hybrid laser welding offers promising advantages over the traditional arc-based welding processes. The high penetration ability of lasers and the filler wire delivery of gas metal arc welding enable joining of thick section materials without the need of multipass. The output power of modern solid state lasers provides enough energy to penetrate thicknesses exceeding 20 mm in steel. However, the high aspect ratio fusion zone with the rapid solidification does not always provide beneficial conditions for achieving good weld profiles. Distribution of the liquid metal between the top and root sides of a joint, and hence the weld profile, is determined by a complex balance between the vaporization pressure of a laser, the electromagnetic force of an arc, and the surface tension of a meltpool. In this work, the stability of the root profile and all the aspects related to the achievement of acceptable roots in pipeline welding have been investigated. It has been found that in order to achi...
Science and Technology of Welding and Joining, 2004
The present paper reports on weld penetration control based on weld pool oscillation during gas t... more The present paper reports on weld penetration control based on weld pool oscillation during gas tungsten arc welding (GTAW) with cold filler wire addition (cold wire GTAW). Experiments were carried out in which the weld pool was brought into oscillation by applying short pulses on the welding current. The frequency of the weld pool oscillation was obtained from the arc voltage variation via fast Fourier transform analysis. It was found that the weld pool oscillation approach is suitable for penetration control during cold wire GTAW when the metal transfer occurs in an uninterrupted bridging manner. Interrupted bridging transfer results in a disturbed oscillation signal due to agitation of the weld pool by mass transfer and/or oscillation of the pendant droplet. STWJ/378
The infl uence of the oscillation behaviour of the weld pool and the pendant droplet on the elect... more The infl uence of the oscillation behaviour of the weld pool and the pendant droplet on the electric arc in pulsed GMA welding has been studied. High speed video images are related to measurements of the voltage. It is found that the weld pool is triggered into motion by the impact of the transferred liquid droplet. The increase of the current in the peak pulse period hardly affects the weld pool. The remaining liquid at the electrode tip may start to oscillate by the action of surface tension and gravity after the droplet is detached. It appears that the oscillation pendant droplet changes the structure of the arc. A conceptual model is derived to explain the observed behaviour: visual observations and voltage measurements. Two different regions can be distinguished in the arc, a bright region and a normal region. The bright arc region surrounds the droplet and shrinks and expands with the up and down movement of the droplet. The behaviour of the bright arc region can be correlated with the measured arc voltage. The shape of the droplet has a negligible effect on the measured voltage, it only initiates the changes occurring in the arc. The periodical release of additional metal vapour in the arc affects the arc voltage considerably. The results of the experimental work presented here cannot yet explain the mechanism behind the alteration of the arc structure and further research is required to elucidate these phenomena. The results presented in this paper focus on bead on plate-pulsed GMA welding in partial penetration conditions.
This paper gives an historic overview and new developments of research activities in the field of... more This paper gives an historic overview and new developments of research activities in the field of the oscillatory behaviour of liquid metal in arc welding. Early work focused on the oscillation behaviour of the weld pool in Gas Tungsten Arc Welding (GTAW). Agitated weld pools exhibit specific modes of oscillation, the frequency of which can be measured from the arc voltage data and is conditioned by the geometry of the weld pool and the properties of the liquid metal. Of technological interest is the alteration of the oscillation behaviour for partially and fully penetrated situations, which can be used for penetration control during welding. A logical extension of the research activities was related to the influence of filler wire addition on the oscillation behaviour. An intermediate step towards the description of Gas Metal Arc Welding (GMAW), is the situation of GTAW with cold filler wire supply. It was found that both the liquid weld pool and the pendant liquid droplet at the tip of the filler wire experience an oscillation, which obscures the influence of the individual contributions of both liquid masses on the voltage data. It was shown that online penetration control is still possible, provided that the metal is transferred in an uninterrupted way, i.e. the filler wire flows smoothly into the weld pool. For GMAW, in which detached droplets collide with the weld pool surface, the difficulties are even more prominent. Recent work is related to this issue. Monitoring of the phenomena occurring at the weld pool and the pendant droplet become problematic by means of the voltage data. Observations by means of high-speed video imaging will be discussed. Apart from the experimental studies, efforts are undertaken in numerical simulations of the processes. A good correlation is obtained between experimental data and the results of the numerical models.
The purpose of this research is to obtain insight into the oscillation behaviour of the liquid me... more The purpose of this research is to obtain insight into the oscillation behaviour of the liquid metal and the arc behaviour during GMA welding. Observations of the weld pool and the arc were undertaken by visual means using a high-speed video and by analysis of the voltage. To deal with the complex phenomena that take place, the research is performed in two steps; firstly, with cold-wire GTA welding on stainless steel AISI 316L tubes where a filler wire is introduced into the weld pool without being preheated, and secondly with pulsed-current GMA (P-GMA) welding on mild steel S235JR plate. The results of the cold-wire GTA experiments showed that for the same penetration state the oscillation modes of the cold-wire and the autogenous GTA weld pools are similar. The partially and the fully penetrated welds oscillate in a sloshy mode and frequencies can be predicted from relatively simple analytical expressions based on weld pool length rather than an equivalent weld pool diameter. When...
Modern lasers allow achievement of full penetration single pass welds in steel plates with thickn... more Modern lasers allow achievement of full penetration single pass welds in steel plates with thicknesses exceeding 20 mm, at welding speeds much greater than any traditional arc-based process. However, the addition of filler wire, which in most structural welds is required to ensure good mechanical properties, is more challenging. Most welds from laser and hybrid welding with filler feeding start to exhibit inhomogeneous fusion zones above a particular joint thickness. The filler consumable segregates near the top section of the joint, while the bottom forms by the re-melted parent metal, which negatively affects mechanical properties. In this work, the homogeneity of laser-arc hybrid welds was investigated experimentally, using a filler wire with a signature element, whose distribution was measured. Three different bevels with different geometry were used to study the flow of liquid filler wire across the joint. The laser and arc parameters were varied to establish the dominant forces responsible for the transport of filler wire and weld homogeneity. The results indicate that hybrid welds are susceptible to form inhomogeneous fusion zones and to achieve acceptable welds, two aspects need to be controlled. The first one is the average content of an alloying element in the meltpool, which is mainly controlled by the wire composition, its deposition rate and dilution with the parent metal. Whilst the second aspect being the weld homogeneity. It has been found that the laser power density is predominantly responsible for the transport of the consumable metal across the material. Furthermore, most processing parameters, such as the arc power or laser power, play contradicting roles, improving one aspect and simultaneously hindering another. The best way of achieving fully homogenous welds with known composition is by applying sufficient wire deposition, to satisfy the compositional requirement, and then provide enough laser power density to transport it across the full thickness.
Science and Technology of Welding and Joining, 2006
This paper deals with pendant droplet oscillation in pulsed current gas metal arc welding (GMAW).... more This paper deals with pendant droplet oscillation in pulsed current gas metal arc welding (GMAW). Using a constant current power source, bead on plate welds were made on mild steel plates. The frequency of the pendant droplet oscillation was monitored visually (using a high speed video camera) and electronically (by analysis of the voltage signals). The results obtained are compared with the results predicted by a model based on a mass spring system. It was found that the oscillation frequency of small droplets revealed by both monitoring techniques matches that predicted by the model. For larger droplets, the oscillation frequency measured by voltage signal analysis tends to be higher than that revealed by video analysis and that predicted by the model. This implies that during droplet oscillation in (GMAW) the arc behaviour may change and as a result the arc voltage is not any more proportionally related to the arc length.
Hybrid laser welding offers promising advantages over the traditional arc-based welding processes... more Hybrid laser welding offers promising advantages over the traditional arc-based welding processes. The high penetration ability of lasers and the filler wire delivery of gas metal arc welding enable joining of thick section materials without the need of multipass. The output power of modern solid state lasers provides enough energy to penetrate thicknesses exceeding 20 mm in steel. However, the high aspect ratio fusion zone with the rapid solidification does not always provide beneficial conditions for achieving good weld profiles. Distribution of the liquid metal between the top and root sides of a joint, and hence the weld profile, is determined by a complex balance between the vaporization pressure of a laser, the electromagnetic force of an arc, and the surface tension of a meltpool. In this work, the stability of the root profile and all the aspects related to the achievement of acceptable roots in pipeline welding have been investigated. It has been found that in order to achi...
Science and Technology of Welding and Joining, 2004
The present paper reports on weld penetration control based on weld pool oscillation during gas t... more The present paper reports on weld penetration control based on weld pool oscillation during gas tungsten arc welding (GTAW) with cold filler wire addition (cold wire GTAW). Experiments were carried out in which the weld pool was brought into oscillation by applying short pulses on the welding current. The frequency of the weld pool oscillation was obtained from the arc voltage variation via fast Fourier transform analysis. It was found that the weld pool oscillation approach is suitable for penetration control during cold wire GTAW when the metal transfer occurs in an uninterrupted bridging manner. Interrupted bridging transfer results in a disturbed oscillation signal due to agitation of the weld pool by mass transfer and/or oscillation of the pendant droplet. STWJ/378
The infl uence of the oscillation behaviour of the weld pool and the pendant droplet on the elect... more The infl uence of the oscillation behaviour of the weld pool and the pendant droplet on the electric arc in pulsed GMA welding has been studied. High speed video images are related to measurements of the voltage. It is found that the weld pool is triggered into motion by the impact of the transferred liquid droplet. The increase of the current in the peak pulse period hardly affects the weld pool. The remaining liquid at the electrode tip may start to oscillate by the action of surface tension and gravity after the droplet is detached. It appears that the oscillation pendant droplet changes the structure of the arc. A conceptual model is derived to explain the observed behaviour: visual observations and voltage measurements. Two different regions can be distinguished in the arc, a bright region and a normal region. The bright arc region surrounds the droplet and shrinks and expands with the up and down movement of the droplet. The behaviour of the bright arc region can be correlated with the measured arc voltage. The shape of the droplet has a negligible effect on the measured voltage, it only initiates the changes occurring in the arc. The periodical release of additional metal vapour in the arc affects the arc voltage considerably. The results of the experimental work presented here cannot yet explain the mechanism behind the alteration of the arc structure and further research is required to elucidate these phenomena. The results presented in this paper focus on bead on plate-pulsed GMA welding in partial penetration conditions.
This paper gives an historic overview and new developments of research activities in the field of... more This paper gives an historic overview and new developments of research activities in the field of the oscillatory behaviour of liquid metal in arc welding. Early work focused on the oscillation behaviour of the weld pool in Gas Tungsten Arc Welding (GTAW). Agitated weld pools exhibit specific modes of oscillation, the frequency of which can be measured from the arc voltage data and is conditioned by the geometry of the weld pool and the properties of the liquid metal. Of technological interest is the alteration of the oscillation behaviour for partially and fully penetrated situations, which can be used for penetration control during welding. A logical extension of the research activities was related to the influence of filler wire addition on the oscillation behaviour. An intermediate step towards the description of Gas Metal Arc Welding (GMAW), is the situation of GTAW with cold filler wire supply. It was found that both the liquid weld pool and the pendant liquid droplet at the tip of the filler wire experience an oscillation, which obscures the influence of the individual contributions of both liquid masses on the voltage data. It was shown that online penetration control is still possible, provided that the metal is transferred in an uninterrupted way, i.e. the filler wire flows smoothly into the weld pool. For GMAW, in which detached droplets collide with the weld pool surface, the difficulties are even more prominent. Recent work is related to this issue. Monitoring of the phenomena occurring at the weld pool and the pendant droplet become problematic by means of the voltage data. Observations by means of high-speed video imaging will be discussed. Apart from the experimental studies, efforts are undertaken in numerical simulations of the processes. A good correlation is obtained between experimental data and the results of the numerical models.
The purpose of this research is to obtain insight into the oscillation behaviour of the liquid me... more The purpose of this research is to obtain insight into the oscillation behaviour of the liquid metal and the arc behaviour during GMA welding. Observations of the weld pool and the arc were undertaken by visual means using a high-speed video and by analysis of the voltage. To deal with the complex phenomena that take place, the research is performed in two steps; firstly, with cold-wire GTA welding on stainless steel AISI 316L tubes where a filler wire is introduced into the weld pool without being preheated, and secondly with pulsed-current GMA (P-GMA) welding on mild steel S235JR plate. The results of the cold-wire GTA experiments showed that for the same penetration state the oscillation modes of the cold-wire and the autogenous GTA weld pools are similar. The partially and the fully penetrated welds oscillate in a sloshy mode and frequencies can be predicted from relatively simple analytical expressions based on weld pool length rather than an equivalent weld pool diameter. When...
Modern lasers allow achievement of full penetration single pass welds in steel plates with thickn... more Modern lasers allow achievement of full penetration single pass welds in steel plates with thicknesses exceeding 20 mm, at welding speeds much greater than any traditional arc-based process. However, the addition of filler wire, which in most structural welds is required to ensure good mechanical properties, is more challenging. Most welds from laser and hybrid welding with filler feeding start to exhibit inhomogeneous fusion zones above a particular joint thickness. The filler consumable segregates near the top section of the joint, while the bottom forms by the re-melted parent metal, which negatively affects mechanical properties. In this work, the homogeneity of laser-arc hybrid welds was investigated experimentally, using a filler wire with a signature element, whose distribution was measured. Three different bevels with different geometry were used to study the flow of liquid filler wire across the joint. The laser and arc parameters were varied to establish the dominant forces responsible for the transport of filler wire and weld homogeneity. The results indicate that hybrid welds are susceptible to form inhomogeneous fusion zones and to achieve acceptable welds, two aspects need to be controlled. The first one is the average content of an alloying element in the meltpool, which is mainly controlled by the wire composition, its deposition rate and dilution with the parent metal. Whilst the second aspect being the weld homogeneity. It has been found that the laser power density is predominantly responsible for the transport of the consumable metal across the material. Furthermore, most processing parameters, such as the arc power or laser power, play contradicting roles, improving one aspect and simultaneously hindering another. The best way of achieving fully homogenous welds with known composition is by applying sufficient wire deposition, to satisfy the compositional requirement, and then provide enough laser power density to transport it across the full thickness.
Science and Technology of Welding and Joining, 2006
This paper deals with pendant droplet oscillation in pulsed current gas metal arc welding (GMAW).... more This paper deals with pendant droplet oscillation in pulsed current gas metal arc welding (GMAW). Using a constant current power source, bead on plate welds were made on mild steel plates. The frequency of the pendant droplet oscillation was monitored visually (using a high speed video camera) and electronically (by analysis of the voltage signals). The results obtained are compared with the results predicted by a model based on a mass spring system. It was found that the oscillation frequency of small droplets revealed by both monitoring techniques matches that predicted by the model. For larger droplets, the oscillation frequency measured by voltage signal analysis tends to be higher than that revealed by video analysis and that predicted by the model. This implies that during droplet oscillation in (GMAW) the arc behaviour may change and as a result the arc voltage is not any more proportionally related to the arc length.
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