Wojciech Suder

Welding process impact on residual stress and distortion

Abstract Residual stress and distortion continue to be important issues in shipbuilding and are still subject to large amounts of research. This paper demonstrates how the type of welding process influences the amount of distortion. Many shipyards currently use submerged arc welding (SAW) as their welding process of choice. In this manuscript, the authors compare welds made by SAW with DC gas metal arc welding, pulsed gas metal arc welding, Fronius cold metal transfer (CMT), autogenous laser and laser hybrid welding on butt welds in 4 mm thick DH36 ship plate. Laser and laser hybrid welding were found to produce the lowest distortion. Nevertheless, a considerable improvement can be achieved with the pulsed gas metal arc welding and CMT processes. The paper seeks to understand the relationship between heat input, fusion area, measured distortion and the residual stress predicted from a simple numerical model, and the residual stresses validated with experimental data.

Investigation of the effects of basic laser material interaction parameters in laser welding

The depth of penetration achieved in continuous wave (CW) laser welding results from a balance of many complicated phenomena, which are linked with the characteristics of the heat source. In this work, the laser welding process has been investigated in terms of basic laser material interaction parameters: power density and interaction time. It has been shown that these two parameters are insufficient to characterize the laser welding process. Thus, a third parameter, specific point energy, has been introduced, which along with the power density and the interaction time allowed the welding process to be uniquely defined. It has been shown that the depth of penetration is mainly controlled by the power density and the specific point energy, whilst the weld width is controlled by the interaction time.

Comparison of joining efficiency and residual stresses in laser and laser hybrid welding

Abstract Laser welding is a high energy density process, which can produce welds with less energy input and thereby lower residual stress generation compared to arc welding processes. However, the narrow beam dimension makes it extremely sensitive in terms of fit up tolerance. This causes a problem in achieving high quality welds. Laser with arc hybrid process overcomes such issues. In this paper, longitudinal residual strains were compared for autogenous laser welding and laser/TIG hybrid processes. Joining efficiency, which is defined by the penetration depth achieved per unit of energy input, was correlated with the residual strain generation. It has been shown that to achieve a specific penetration depth, there is an optimum welding condition for each of the welding processes, which will give minimum tensile residual stress generation. The results imply that for the same penetration depth, hybrid process resulted in ∼50% higher tensile longitudinal domain compared to autogenous laser.

Use of fundamental laser material interaction parameters in laser welding

By using material interaction parameters in laser welding improvements in process phenomenological understanding and transferability are obtained. Using a new parameter, power factor, a more systematic method for specifying laser welding parameters has been developed.

Neutron Diffraction Residual Stress Measurements in Key-Hole Laser Formed Weldments

There is a new generation of lasers available for materials processing. The new lasers include fibre and disc laser are characterized by very high beam quality at very high power levels providing extremely high energy density. In general laser welding is selected over other welding processes because of the minimisation of the heat input, residual stresses and distortion, for this reason they are increasingly popular over a wide range of industries. The narrowness of the welds makes it challenging to resolve the details of the residual stresses produced by the welding process. Residual strain/stress measurements of two specimens produced using the fibre laser were performed on Engin-X. Across the weld and through thickness distributions are reported in this paper.

Parameter selection in laser welding using the power factor concept

To achieve specific penetration depths in laser welding particular combinations of laser power and travel speed are required. Different combinations of power and travel speed can be used to obtain the same penetration depth. Further, for a given combination a different penetration depth occurs if a different beam diameter is used. Beam diameter is controlled by the laser properties and the optical system, and varies between laser systems. This causes difficulties in both selecting optimum laser parameters for a given application and in transferring parameters between laser systems. This can be greatly simplified using the power factor concept. Power factor is defined as the product of intensity and beam diameter. Plots of constant penetration depth as a function of power factor and interaction time can be generated and these are independent of beam diameter. Using this concept, system parameters can be selected based on criteria defined by users, such as productivity, process efficiency or heat input. A suitable laser system for that application can then be specified. It also allows transfer of laser parameters between systems. This approach will be illustrated by the use of some specific examples.To achieve specific penetration depths in laser welding particular combinations of laser power and travel speed are required. Different combinations of power and travel speed can be used to obtain the same penetration depth. Further, for a given combination a different penetration depth occurs if a different beam diameter is used. Beam diameter is controlled by the laser properties and the optical system, and varies between laser systems. This causes difficulties in both selecting optimum laser parameters for a given application and in transferring parameters between laser systems. This can be greatly simplified using the power factor concept. Power factor is defined as the product of intensity and beam diameter. Plots of constant penetration depth as a function of power factor and interaction time can be generated and these are independent of beam diameter. Using this concept, system parameters can be selected based on criteria defined by users, such as productivity, process efficiency or heat input. A s...

Root stability in hybrid laser welding

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 achieve a smooth root profi...

Hybrid laser welding of single sided fully penetrated fillet welds

Fillet welds are inherent part of large structures in the shipbuilding industry, where distortion is a major issue. Hybrid laser welding enables fully penetrated fillet welds to be achieved with a lower energy than arc-based welding processes. This provides an increase in productivity, decrease in distortion and reduction of weight. To achieve defect-free welds with good fatigue life it is necessary to control the weld profile, particularly in fully penetrated welds. In this work a detailed study of the key forces determining the profile and the fatigue life of hybrid fillet welds has been carried out. The effect of laser and Metal Inert Gas (MIG) parameters, such as the laser power density, MIG current and voltage and processing angles of both sources on the weld bead profile has been investigated. The results indicate that the weld profile in fully penetrated fillet joints is a net result of the amount of deposited material by the MIG source, the energy distribution of the laser and the pressure of the laser- induced vapour and the electromagnetic force of the MIG. By changing the balance between the deposited material and the net pressure that transports it to the back side, the weld profile can be tailored to a particular application.Fillet welds are inherent part of large structures in the shipbuilding industry, where distortion is a major issue. Hybrid laser welding enables fully penetrated fillet welds to be achieved with a lower energy than arc-based welding processes. This provides an increase in productivity, decrease in distortion and reduction of weight. To achieve defect-free welds with good fatigue life it is necessary to control the weld profile, particularly in fully penetrated welds. In this work a detailed study of the key forces determining the profile and the fatigue life of hybrid fillet welds has been carried out. The effect of laser and Metal Inert Gas (MIG) parameters, such as the laser power density, MIG current and voltage and processing angles of both sources on the weld bead profile has been investigated. The results indicate that the weld profile in fully penetrated fillet joints is a net result of the amount of deposited material by the MIG source, the energy distribution of the laser and the pressure of the ...