Laser-arc Hybrid Welding Research Articles

Lean Methodology to Transform Shipbuilding Panel Assembly

The core competence of any medium-to-large sized shipyard includes the panel assembly line. Ship panels are the basic building blocks of well over 60% of the interim products of typical commercial ships. Therefore the improvement of the panel assembly process could greatly reduce the number of man-hours of all assembled panels, thereby yielding significant savings to the shipyard. Using a lean methodology to make kaizen improvements to traditional panel assembly lines will greatly reduce the costs in ship production. This means that shipyards, which are barely keeping earnings above costs, will be able to increase profits. Value stream mapping is a key way of determining how lean a production process is. The wastes in production assembly are readily identified as well as the takt time and the areas where there is push as opposed to pull. In this paper, a case study of a typical commercial shipyard, which builds a product mix of vessels is analyzed. The present state panel assembly line is mapped and then using lean tools and avantgarde technologies, such as hybrid laser arc welding, the new transformed panel assembly line is demonstrated to bring man-hour reductions of over 80%, so that a typical panel is assembled using 12 man-hours as opposed to the present 72 man-hours. 1. Introduction The core competence of virtually any medium-to-large sized shipyard includes a panel assembly line. Many times shipyard management takes for granted that the panel assembly line is just fine as is and therefore it is not necessary to make analysis to improve this core shipbuilding assembly process any further. However, since flat panels make up well over 60% of the building blocks of most commercial ships, any type of significant improvement to the panel assembly line will result in important cost savings for the shipyard.

Factors affecting weld root morphology in laser keyhole welding

Welding production efficiency is usually optimised if full penetration can be achieved in a single pass. Techniques such as electron and laser beam welding offer deep high speed keyhole welding, especially since multi-kilowatt lasers became available. However, there are limitations for these techniques when considering weld imperfections such as weld cap undercuts, interior porosity or humps at the root. The thickness of sheets during full penetration welding is practically limited by these root humps. The mechanisms behind root morphology formation are not yet satisfactory understood. In this paper root humping is studied by reviewing previous studies and findings and also by sample examination and process observation by high speed imaging. Different process regimes governing root quality are presented, categorized and explained. Even though this study mainly covers laser beam and laser arc hybrid welding, the presented findings can generally be applied full penetration welding in medium to thick sheets, especially the discussion of surface tension effects. As a final result of this analysis, a map of methods to optimise weld root topology is presented.

Study of microstructural inhomogeneity and its effects on mechanical properties of multi-layer laser welded joint

Hybrid laser-arc welding is an emerging joining technology which has a promising prospect in thick plate manufacturing. In this paper, the thick plate butt joint of 16MnDR with 20 mm was successfully connected by using multi-layer laser welding technology. On this basis, the microstructural inhomogeneity and its influences on mechanical properties of the multi-layer welded joint were further investigated. The results indicated that microstructure of the multi-layer welded joint is inhomogeneous for two reasons: firstly, different heat inputs and cooling rates caused the microstructural inhomogeneity of different layers; secondly, different thermal cycles at different locations within inter-laminar zones led to disparate microstructure transformation and further intensified the microstructural inhomogeneity of the multi-layer welded joint. As a result, mechanical properties of the welded joint are obviously influenced by the microstructural inhomogeneity. From layer 1 to layer 4, the hardness distribution showed an overall downward trend and fluctuated obviously in inter-laminar zones. Besides, ductile fracture happened in all impact specimens, and the impact toughness decreased from layer 1 to layer 4 owing to the microstructural inhomogeneity and increasing microvoids. In addition, the uncleaned contamination between layers weakened the tensile strength of the welded joint. Thus, it is necessary for the multi-layer welding procedure to clear up former welds effectively before latter welding.

Effect of laser pulse on alternative current arc discharge during laser-arc hybrid welding of magnesium alloy

The coupling effect between a laser and arc plasma was studied in situations in which the laser acts at the positive and negative waveforms of the arc discharge during the laser-arc hybrid welding of magnesium alloy. Using the methods of direct observation, high speed imaging, and spectral analysis, the surface status of weld seams, weld penetration depths, plasma behavior, and spectral characteristics of welding plasma were investigated, respectively. Results show that, as compared with the laser pulse acting at the negative waveform of the arc plasma discharge, a better weld seam formation can be achieved when the laser pulse acts at the positive waveform of the arc discharge. At the same time, the radiation intensity of Mg atoms in the arc plasma increases significantly. However, the weld penetration depth is weaker. The findings show that when the laser pulse is acting at the negative waveform of the arc plasma discharge, the position of the arc plasma discharge on the workpiece can be restrained by the laser action point, which improves the energy density of the welding arc.

Laser–arc hybrid welding of high-strength steel and aluminum alloy joints with brass filler

ABSTRACTThe laser–tungsten inert gas hybrid welding method was adopted to realize the welding process between Q460 high-strength steel and 6061 aluminum alloy. The influence of the dual heat source on the mechanical properties and microstructure of the welded joints are discussed. In addition, the effects of including a copper–zinc interlayer on the microstructure, elemental distribution, and mechanical properties of welded joints are also studied. The results show that the mechanical properties of the welded joints are influenced by the relative heat inputs of the two heat sources and the Cu-Zn interlayer. The braze welded joint fabricated without a Cu-Zn interlayer fractured at an Al-Fe intermetallic compound (IMC) layer formed at the interface, whereas the braze welded joint fabricated with a Cu-Zn interlayer fractured at an Al-Cu IMC layer formed at the interface. Comparisons show that the maximum tensile shear load of the brazed welded joint with the Cu-Zn interlayer was increased by about 20% relative to that formed without the interlayer. The formation of Al-Fe IMC layer in the deep penetration joint was inhibited by the combined effect of the dual heating sources and the Cu-Zn interlayer.

Effect of Ni content on rolling toughness of laser-arc hybrid welded martensitic stainless steel

Laser-arc hybrid welding of AISI 420 martensitic stainless steel (MSS) was studied by employing three types of commercial filling wires with different Ni content. Weld toughness is dependent on the contents of retained austenite (CRA) and high-misorientation (>15°) martensite (CHM) in the lower part of the weld (LaserZ). As the Ni content of filling wire increases from 13% to 20%, the CRA and the CHM increase to about 4% and 57%, respectively. It increases the weld toughness. The crack location of Erichsen sample changes from the fusion line to the BM, but the crack in the LaserZ is not suppressed thoroughly during the rolling with 45% reduction. As the Ni content increases to 66%, the CRA and CHM increase to about 12% and 60% respectively. It further increases the weld toughness, and the rolling crack in the LaserZ is suppressed. The general criterion, which only employs Erichsen result to predict whether the weld meets the rolling requirement or not, is not suitable for the MSS, both the CRA and the CHM must be taken into account. The toughness improvement was discussed according to crack propagation behavior.

Effect of magnetic field applied during laser-arc hybrid welding in improving the pitting resistance of the welded zone in austenitic stainless steel

Pitting corrosion resistance of austenitic stainless steel welded zone is improved with an external magnetic field applied during laser-arc hybrid welding. Analysis of the microstructure indicates that welding with an external magnetic field homogenizes distribution of δ-ferrite in austenite matrix by weakening δ-ferrite texture intensity and promoting growth of uniform skeletal morphology. The improved pitting corrosion resistance is characterized by a higher pitting potential with smaller passivation current density, which is attributed to the uniform Cr diffusion resulting from homogeneous distribution of δ-ferrite.

Elements loss analysis based on spectral diagnosis in laser-arc hybrid welding of aluminum alloy

Aluminum alloy has been widely used in automobiles, high-speed trains, aerospace and many other fields. The loss of elements during welding process causes welding defects and affects the microstructure and properties of the joints. This paper discusses the correlation between welding process, spectral intensity and loss of elements in laser-arc hybrid welding of Al alloys. The results show that laser power and arc current have a significant impact on the spectral intensity and loss of elements. Compared with the base metal, the contents of alloying elements in the weld area are lower. The burning losses of alloy elements increase with the welding heat input.

Dynamic compressive behaviour of weld joints

Materials used in military applications have to withstand multiple threats like ballistics and explosions. Thus, high-strength low alloyed (HSLA) steels are used. The main joining technique for metals is welding. Therefore, analysing the dynamic impact behaviour of high-strength welds is very important to fulfil these demands. Investigation of welds at high strain rates has rarely been conducted in the past. To determine the dynamic impact behaviour of hybrid laser-arc welds, the Split Hopkinson Pressure Bar (SHPB) technique was used. The base material was a quenched and tempered fine-grained armour steel with yield strength of 1100MPa.First, a full hybrid laser-arc weld was investigated by extracting specimens consisting of weld metal and heat affected base material. The influence of two variables, the cooling time between 800°C and 500°C (t8/5) and strength of filler material, on the impact behaviour was studied. The cooling time t8/5 was varied by preheating to influence the microstructure in the HAZ and to analyse the effect on the hardness and dynamic compressive strength.Subsequent analysis to detail the original investigation was carried out by dilatometer heat treatment of specimens to create homogenous subzones of the weld. These specimens have a homogenous microstructure of HAZ and were tested by SHPB to determine the stress-strain characteristics for the different microstructures of HAZ.The results of the weld specimen showed the effect of preheating and filler material strength on the dynamic compressive behaviour. The analysis of the different microstructures of the HAZ indicated that especially the tempered microstructure caused a reduction in dynamic compressive strength.

Toughness assessments of laser arc-hybrid welds of ultra high strength steel

This paper investigates the toughness properties of laser arc hybrid welds of HT980 (980 N/mm2 class) and HT780 (780 N/mm2 class) steels. In the Charpy tests, a side groove specimen, along with the standard V-notch specimen, is employed to try prevention of fracture path deviation. A three-point bending test, a double-edge notch tensile (DENT) test, and a deep notch (DN) test are performed to measure the critical crack tip opening displacement (CTOD) at brittle fracture initiation. It is demonstrated that the critical CTOD is affected by the loading mode; critical CTOD by tension test is apparently higher than that by bending test. Nevertheless, three-point bend critical CTOD has exceeded the CTOD required value evaluated by WES2805 (“Method of Assessment for Flaws in Fusion Welded Joints with Respect to Brittle Fracture and Fatigue Crack Growth”) design curve with the allowable stress designed for an assumed crack. It has been observed that even though fracture pass deviation (FPD) occurred in a Charpy impact test, a straight brittle crack propagated throughout welded metal in a notched wide plate tensile test that was conducted at the same testing temperature as that of the Charpy impact test.

Stabilization mechanism and weld morphological features of fiber laser-arc hybrid welding of pure copper

Process characterization of laser-arc hybrid welding of pure copper was studied. The morphological features and the porosity of the welds were measured by optical microscope and X-ray non-destructive test, respectively. Process stability was characterized by the numbers in interruption and short circuit of the arc, which were counted from the waveform of arc current. The dynamic behaviors of molten pool, keyhole and droplet transfer were observed by high speed video camera. The results showed that the process was unstable in single laser welding and single arc welding, but could be easily stabilized by hybrid welding. Accepted weld and stable process could be obtained under the optimized parameters, which were the laser power around 4kW, the arc current higher than 120A and the welding speed lower than 1.5m/min. The process stabilization was attributed to two reasons. Firstly, laser keyhole was stabilized by homogenizing and decreasing of dynamic vapor pressure on keyhole rear wall. Secondly, the arc wandering was avoided by keyhole fixation. Both of the reasons prevented the fast heat loss caused by the high heat conductivity of pure copper.

A study on the angular distortion in tee type full penetrated welded joint fabricated by the laser-arc hybrid welding

The reducing effect of the angular distortion in T-type full penetrated welded joints fabricated by laser-arc hybrid welding was investigated. The angular distortion caused by the laser-arc hybrid welding were measured and compared with one caused by CO2 gas shielded-arc welding. As a result, the amount of angular distortion by laser-arc hybrid welding was the same level as one in the case of forming a leg size of F1 grade regulated by the Common Structural Rules for Bulk Carriers by applying arc welding. In addition, numerical analysis of the welding deformation was carried out by thermal elastic–plastic finite element analysis and these results were generally consistent with the measured results. Moreover, the effect on the FE result of the penetrated shape is discussed.

Optimization of hybrid laser arc welding of 42CrMo steel to suppress pore formation

The hybrid laser arc welding (HLAW) of 42CrMo quenched and tempered steel was conducted. The effect of the processing parameters, such as the relative positions of the laser and the arc, the shielding gas flow rate, the defocusing distance, the laser power, the wire feed rate and the welding speed, on the pore formation was analyzed, the morphological characteristics of the pores were analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the majority of the pores were invasive. The pores formed at the leading a laser (LA) welding process were fewer than those at the leading a arc (AL) welding process. Increasing the shielding gas flow rate could also facilitate the reduction of pores. The laser power and the welding speed were two key process parameters to reduce the pores. The flow of the molten pool, the weld cooling rate and the pore escaping rate as a result of different parameters could all affect pore formation. An ideal pore-free weld was obtained for the optimal welding process parameters.

Multipass laser hot-wire welding: Morphology and process robustness

There are great prospects for utilizing multipass laser hot-wire welding to join thick steel sheets, especially for techniques commonly performed in single passes, e.g., laser arc hybrid welding, fall short, presenting great opportunities for vehicle industries and offshore applications. Many modern approaches for applying these techniques rely on customized wire feeding nozzles or special scanner optics to ensure proper laser–wire interactions and, in turn, robust process behavior, making them less accessible to many industries. Here, we present a modified adaption of laser hot-wire welding, utilizing more readily available equipment, including an unmodified welding source and a nozzle, presented and evaluated through means of, e.g., high speed imaging and macroscopy. This technique was found to have high process robustness, especially for sealing passes, if wire resistance heating is kept within suitable levels. It is able to both maintain proper laser–wire interaction and produce close to net-shape weld caps. Also, recommended process parameters are presented, together with a description of a potential method for suppressing solidification cracking.

An investigation on capability of hybrid Nd:YAG laser-TIG welding technology for AA2198 Al-Li alloy

This paper surveys the capability of the hybrid laser-arc welding in comparison with lone laser welding for AA2198 aluminum alloy experimentally. In the present research, a continuous Nd:YAG laser with a maximum power of 2000W and a 350A electric arc were used as two combined welding heat sources. In addition to the lone laser welding experiments, two strategies were examined for hybrid welding; the first one was low laser power (100W) accompanied by high arc energy, and the second one was high laser power (2000W) with low arc energy. Welding speed and arc current varied in the experiments. The influence of heat input on weld pool geometry was surveyed. The macrosection, microhardness profile and microstructure of the welded joints were studied and compared. The results indicated that in lone laser welding, conduction mode occurred and keyhole was not formed even in low welding speeds and thus the penetration depth was so low. It was also found that the second approach (high laser power accompanied with low arc energy) is superior to the first one (low laser power accompanied with high arc energy) in hybrid laser-arc welding of Al2198, since lower heat input was needed for full penetration weld and as a result a smaller HAZ was created.

Investigation on microstructure and mechanical properties of NV E690 steel joint by laser-MIG hybrid welding

Hybrid laser-arc welding (HLAW) was carried out on 690MPa high strength NV E690 steel plates of 15mm thickness using single-pass and double-pass welding processes. Fine weld joints with good performance were successfully obtained by double-pass HLAW. The weld bead characteristics, microstructure and mechanical properties (hardness, tensile strength, low-temperature impact toughness) were investigated. The porosity morphology and distribution were detected by the micro-CT. The results showed that the fusion zone was composed of martensite and ferrite. The average hardness value of the fusion zone was higher than that of the base material, but lower than that of the heat affect zone. The tensile strength of the welded specimens matched the strength of the BM. The ultimate tensile strength of the fusion zone exceeded 1100MPa. The fracture mode of the welded specimens was ductile fracture. The average absorbed energy in the fusion zone at −40°C reached 46.02% that of the base material, higher than the industrial standard (35.8%). The fracture surface of double-pass HLAW specimens presented a typical brittle fracture mechanism. The correlation between the microstructure features and mechanical properties of the weld bead was analyzed.

Stabilization effect of space constraint in narrow gap laser-arc hybrid welding analyzed by approximate entropy

Approximate entropy (ApEn) was developed to quantify the effects of welding parameters on the process stability of narrow gap laser-arc hybrid welding (NGHW). The smaller the ApEn of arc current, the higher the welding stability. A dimensionless parameter, η A, which was the ApEn increment of the NGHW to the hybrid welding without narrow gap, was proposed to quantitatively characterize the effects of space constraint on the process stability. All the η A were negative. It had a good agreement with the experimental values and demonstrated that the process could be stabilized by space constraint. The η A was minimized to be −16.7%, but usually at the range from −8 to −1%. Increasing arc current, laser-arc distance, and welding speed, or decreasing laser power, all increased the η A by weakening the space constraint. Finally, the stabilization mechanism was discussed in terms of the effects of space constraint on the behaviors of laser keyhole and arc droplet transfer.

Effects of laser-arc distance on corrosion behavior of single-pass hybrid welded stainless clad steel plate

Single pass laser-arc hybrid welding of stainless clad steel plate was first carried out to develop alternatives to multi-pass welding with low efficient or single pass welding with poor corrosion resistance. The results demonstrated that the weld corrosion resistance increased with the increase of laser-arc distance (DLA), and the corrosion morphologies changed from big and deep ‘nail’ pits to small and shallow hemispherical pits. The weld with nearly equal corrosion resistance to the base metal (BM) could be obtained at the DLA of 9mm, where the charge transfer resistance increased to 89% of the BM and the corrosion current density decreased by ten times to close to the BM, only 0.13μA·cm−2 lower. The corrosion resistance improvement had a good agreement with the microstructure homogenization and the increase of Cr content. The microstructure formation was discussed by the molten pool behavior and the laser-arc interaction. The corrosion resistance improvement was explained by the formation and damage mechanism of the passive film.

ГИБРИДНАЯ ЛАЗЕРНО-ДУГОВАЯ СВАРКА ВЫСОКОПРОЧНЫХ ТРУБНЫХ СТАЛЕЙ КЛАССОВ ПРОЧНОСТИ API X80 И X120

The aim of the present work was to investigate the possibilities of hybrid laser arc welding regarding reliable production of longitudinal welds of high strength pipe steels X80 and X120 and to evaluate achievable mechanical properties of laser hybrid welds. The study focused on weld toughness examination in low temperature range up to -60 °C. SЮТЭКЛХО ПТХХОЫ ЦКЭОЫТКХЬ were identified in the context of this task. It could be shown that metal cored electrodes guaranteed sufficient Charpy impact toughness at low temperature for both investigated materials. Modern arc welding technologies such as modified pulsed spray arc were used to promote deeper Penetration of the filler material into the narrow laser welding gap. Edge preparation with a 14 mm deep root face was considered as optimum, because no penetration of the filler material could be detected beyond this depth limit and therefore any metallurgical influences on the weld metal properties through the welding wire could be excluded.

Weld characterization of laser arc hybrid welding of pure copper

A series of experiments of high-power fiber laser-arc hybrid welding of pure copper was carried out. It could be seen that the microstructure of weld metal was obviously coarsened, and the columnar grain spacing at fusion zone and the massive grain size at heat-affected zone were both linearly increased with the increase of heat input. The weld conductivity decreased with the increase of heat input because the widening weld increased the microstructure nonuniformity of test samples. The heat input as well as welding parameter has no obvious effect on the ultimate tensile strength (UTS) of cross-weld but has obvious effect on the elongation. The UTS of all the welds was 200 MPa or so. The elongation was bigger than 20% when the heat input was in the optimization range from 250 to 380 J/cm. The decrease of the elongation was attributed to either high porosity at insufficient heat input or coarser grain at excessive heat input.