Welding Tests Research Articles

Computer Aided Design of Ultrasonic Test by Numerical Simulation

Ultrasonic tests of dissimilar metal welds require extremely sophisticated technology. The complexity of the test is caused by the grain orientation and difficult accessibility of the weld and it is therefore necessary to redound the examinations by simulation. This study details some application possibilities of CIVA software and presents an example of the evaluation of the procedure used for the given test method with probability of detection curves.

Neutron and gamma radiation shielding Ni based new type super alloys development and production by Monte Carlo Simulation technique

In the present study, five different type of new super alloys have been developed and produced which have high temperature resistance for both gamma and fast neutron radiation shielding. These super alloys have been produced with powder methodology by using the materials such as iron (Fe), rhenium (Re), boron carbide (B4C), nickel (Ni), chromium (Cr), boron (B), copper (Cu), tungsten (W), tantalum (Ta). Gamma-ray Mass attenuation coefficients, half value layer effective atom number, mean free path and fast neutron total macroscopic cross section, transmission number values have been theoretically calculated by using Geant 4 code, WinXCom and Phy-X / PSD software. In addition, experimentally equivalent dose measurements have been carried out by using 241Am-Be fast neutron source. Sulfuric acid abrasion, compressive strength, temperature resistance and weldability tests have been made. The results are compared with 316LN nuclear stainless steel because of its common use in nuclear shielding applications and all new type super alloy samples have shown better radiation absorption ability for both gamma and fast neutron. It has been determined that these new type super alloys can be used in nuclear applications for better shielding.

Metallurgical Modelling of Ti-6Al-4V for Welding Applications

Manufacturing processes such as welding subject the α/β titanium alloy Ti-6Al-4V to a wide range of temperatures and temperature rates, generating microstructure variations in the phases and in the precipitate dimensions. In this study, the metallurgical and numerical modelling of Ti-6Al-4V when subjected to a high energy density welding process was affected by a series of analytical equations coded in Sysweld commercial specialist FE welding software. Numerical predictions were compared with experimental results from laser welding tests on plates with different thicknesses, initial microstructural morphologies, and operating conditions. The evolution of the microstructure was described by using a diffusion-based approach when the material was operating in the α + β field, whilst empirical equations were used for temperatures above the β-transus temperature. Predictions made by the subroutines within the FE model were shown to match with reasonable trends when validated using experimental characterisation methods for various metallurgical features, including the α particle size, β grain size, martensitic needle thickness, and relative phase volume fractions.

Mobile parallel robot machine for heavy-duty double-walled vacuum vessel assembly

Purpose This paper aims to present a detailed mechanical design of a seven-degrees-of-freedom mobile parallel robot for the tungsten inert gas (TIG) welding and machining processes in fusion reactor. Detailed mechanical design of the robot is presented and both the kinematic and dynamic behaviors are studied. Design/methodology/approach First, the model of the mobile parallel robot was created in computer-aided design (CAD) software, then the simulation and optimization of the robot were completed to meet the design requirements. Then the robot was manufactured and assembled. Finally, the machining and tungsten inert gas (TIG) welding tests were performed for validation. Findings Currently, the implementation of the robot system has been successfully carried out in the laboratory. The excellent performance has indicated that the robot’s mechanical and software designs are suitable for the given tasks. The quality and accuracy of welding and machining has reached the requirements. Originality/value This mobile parallel industrial robot is particularly used in fusion reactor. Furthermore, the structure of the mobile parallel robot can be optimized for different applications.

New Weldable Steel for Rebars

A new steel grade, developed at the CELSA steelworks in Ostrowiec Świętokrzyski and used in the production of rebars, contributes greatly to the development of industrial and civil engineering. Steel B600B is characterised by yield point fyk = 600 MPa and immediate tensile strength ftk = 700 MPa. Tests revealed that the steel satisfies all requirements of related standards, both in terms of strength and processing properties. The mechanical properties of the new steel grade are higher by 20% than those of currently produced steels characterised by the highest mechanical properties (characteristic yield point Re= 500 MPa). As a result, the application of the new steel provides notable technical and economic advantages. The new steel grade meets requirements concerning technical class C in accordance with PN-EN 1992-1-1, which indicates that the steel has a significant yield point margin (being an important advantage in terms of limit state design). Plastic steels are easier to weld and less susceptible to welding crack formation. Technological (research-related) tests revealed the favourable welding properties of the new steel. Welding tests were performed using the manual metal arc welding method, i.e. the most common welding process used when making structural reinforcements. The welding tests involved the making of butt, overlap and cruciform joints. The strength and technological tests revealed that the steel satisfied the requirements specified in the PN-EN ISO 17660-1 standard.

Laser Welding of Laser Powder Bed Fusion (LPBF) Manufactured 316L Stainless Steel Lap Joint

The aim of the study was to determine the static strength of laser welded lap joint in laser powder bed fusion (LPBF) printed stainless steel material and also a joint formed of printed and commercial sheet metal. Printed 316L test pieces with a thickness of 2 mm and a similar commercial 2 mm thin plate were used as test material. A laser welded lap joint made of a commercial sheet metal was used as a reference. Yb:YAG disk laser with wavelength 1030 nm and maximum output power 4 kW was used in welding tests. All test sets were welded with the same welding parameters and argon shielding gas. One fully penetrated keyhole weld was made to the lap joint. The static strength of the lap joints was determined by tensile tests. The measured shear strength was highest in the reference joint. In other cases, shear strength was only 8-11% lower compared to the reference joint. The cross-sections of the welds were analyzed on the basis of images taken with an optical microscope. Based on the results, the printed 316L is highly laser weldable material.

Joining of dissimilar metals between magnesium AZ31B and aluminum A6061-T6 using galvanized steel as a transition joining layer

A galvanized steel is used to join Mg AZ31B alloy and Al A6061-T6 alloy as a joining transition layer by cold metal transfer (CMT) method. Firstly, to optimize the process variables, extensive welding tests were performed by a design of experiment method. Then, microstructures, joining mechanisms and tensile properties were characterized and analyzed. Results indicated that Mg and Al alloys can be joined by using galvanized steel as a joining transition layer and cold metal transfer welding method. The formed joint is called as a Mg–steel–Al CMT joint. By using galvanized steel transition joining layer, Mg–Al brittle intermetallics Al12Mg17 and Al3Mg2 were inhibited. The properties of Mg–steel–Al CMT joints have been improved after optimizing the welding variables. The strength of Mg–steel–Al CMT joint is comparable to those of Al–Al joint and Mg–Mg joint. The strength of Mg–steel–Al CMT joint can reach 100% that of Al–Al joint and Al–steel joint, and reach 90% that of Mg–Mg joint and Mg–steel joint. The optimized Mg–steel–Al CMT welded joint with galvanized steel transition layer is fractured at the heat affected zone of Al base metal rather than at the weld-brazed interface, due to softening of Al base metal.

Droplet transfer behavior and weld formation of gas metal arc welding for high nitrogen austenitic stainless steel

Abstract High nitrogen austenitic stainless steel (HNASS) wire with 0.78 wt.% nitrogen content was used for gas metal arc welding (GMAW) test. The characteristics of droplet transfer and weld formation in different welding parameters were investigated. There were three typical metal transfer modes in GMAW of HNASS, namely in terms of stable short circuit transfer, unstable short circuit transfer and spray transfer. With wire feed speed (WFS) of 3 m/min∼8 m/min and moderate arc voltage, the droplet transfer was stable short-circuiting transition mode. The transfer period and waveform of electrical parameters were regular and the weld formation was satisfactory with few spatters. With the increasing of arc voltage or WFS, the droplet grew up to abnormal large size due to the expansion of supersaturated nitrogen. The electric parameters were more disordered and the metal transfer became unstable with spatter. When wire feed speed was over 10 m/min with high arc voltage, the droplet transfer became spray transfer accompanied by numerous welding fumes. The weld formation of HNASS for unstable short circuit and spray transfer mode was inferior with serious spatters.

Оценка параметров сварки промышленных соединений из толстых листов из алюминия 6082-T6 по европейским стандартам

Tungsten inert gas (TIG) welding had been applied to produce four double-V butt welded joints performed on thick plates made from 6082-T6 aluminum alloy. The thicknesses of the plates are 18, 45, 60, and 80mm.This type of aluminum alloy is very sensitive to heat due to its high conductivity and high thermal expansion coefficient. Heat from TIG welding reduces the strength of the cited welded plates in the welding zone and in the heat affected zone (HAZ) and favorites the formation of porosities and solidification cracks in the welded joints. Porosities and solidification cracks are the most frequent imperfection that appear in this type of welded joints and they are often the reason which prevent them to comply with the requirements of the BS EN ISO 10675-2: 2017 Non destructive testing of welds: Acceptance levels for radiography testing-Aluminium and its alloys, and of the BS EN ISO 23277: 2015 penetrant testing of welds –Acceptance levels. This article represents the type of the filler metal that used and the welding parameters that applied to perform TIG welding of the cited thick plates in order to get welded joints that are free from porosities and solidification cracks as confirmed by X-ray radiography and by red dye penetrant testing of these welded joints.

Numerical Simulation of Temperature Distribution in Robotic Arc welding by ARISTOTM Robot

The present analyses also studied a numerical simulation on the specimen of mild steel weld by robotic welding. A conical moving temperature source from Gaussian was applied to the current numerical simulation. ANSYS is also used for thermally mechanical weld tests by the ARISTO robot, with some variations. Taking into consideration the thermal and physical properties of mild steel that affect the welding thermal conductivity. The analysis of temperature distribution was defined according to robotic arc welding process parameters, such as welding temperature, welding current, and welding speed impact on the geometry of the weld bead was investigated. The temperature distribution based on numerical observations is associated with experiment results. This form is well in line with the results obtained by numerical simulation of the weld zone profile.

Influence of Activated Fluxes on the Bead Shape of A-TIG Welds on Carbon and Low-Alloy Steels in Comparison with Stainless Steel AISI 304L

The article presents results of comparative A-TIG welding tests involving selected unalloyed and fine-grained steels, as well as high-strength steel WELDOX 1300 and austenitic stainless steel AISI 304L. The tests involved the use of single ingredient activated fluxes (Cr2O3, TiO2, SiO2, Fe2O3, NaF, and AlF3). In cases of carbon and low-alloy steels, the tests revealed that the greatest increase in penetration depth was observed in the steels which had been well deoxidized and purified during their production in steelworks. The tests revealed that among the activated fluxes, the TiO2 and SiO2 oxides always led to an increase in penetration depth during A-TIG welding, regardless of the type and grade of steel. The degree of the aforesaid increase was restricted within the range of 30% to more than 200%.

Nano Identification and Tribo Testing of Explosive Welding Copper/Brass

Nano Identification and Tribo Testing of Explosive Welding Copper/Brass

The role of liquid feeding in nugget-edge cracking in resistance spot welding of dissimilar magnesium alloys

In fusion welding, cast magnesium alloys typically present higher sensitivity to liquation cracking than wrought alloys. In this study, a fluid-mechanics-based analytical model was established to investigate an unusual phenomenon: a lack of cracking in cast magnesium alloy while cracking took place in wrought magnesium alloy. This was observed in resistance spot welding, in which the pressure within the molten nugget allows the liquid to feed through the interface between the fusion zone and the partial melting zone, an aspect which is not generally considered in the typical criteria for liquation cracking. The analytical model shows that the liquid is easy to feed into the inter-grain zone of a cast coarse-grained metal but difficult to feed into wrought metal. The liquid feeding effect changes the composition of the inter-grain region, causing the semi-solid grains to bond to each other tightly in the cast magnesium alloy. Electro-probe microanalysis illustrates the mass transfer pattern of liquid feeding at the interface between the fusion zone and the partial melting zone. Magnesium alloys AZ31, AZ91, and ZK61 were selected to carry out resistance spot welding tests of which results match the theory raised in this work well.

Weldability Evaluation of Alloy 718 Investment Castings with Different Si Contents and Thermal Stories and Hot Cracking Mechanism in Their Laser Beam Welds

In this work, weldability and hot cracking susceptibility of five alloy 718 investment castings in laser beam welding (LBW) were investigated. Influence of chemical composition, with varying Si contents from 0.05 to 0.17 wt %, solidification rate, and pre-weld heat treatment were studied by carrying out three different weldability tests, i.e., hot ductility, Varestraint, and bead-on-plate tests, after hot isostatic pressing (HIP) and solution annealing treatment. Onset of hot ductility drop was directly related to the presence of residual Laves phase, whereas the hot ductility recovery behaviour was connected to the Si content and γ grain size. LBW Varestraint tests gave rise to enhanced fusion zone (FZ) cracking with much more reduced heat-affected zone (HAZ) cracking that was mostly independent of Si content and residual Laves phase. Microstructural characterisation of bead-on-plate welding samples showed that HAZ cracking susceptibility was closely related to welding morphology. Multiple HAZ cracks were detected in nail or mushroom welding shapes, typical in keyhole mode LBW, irrespective of the chemical composition and thermal story of castings. In all LBW welds, Laves phase with a composition similar to the eutectic of the pseudo-binary equilibrium diagram of alloy 718 was formed in the FZ. The composition of this regenerated Laves phase matched with the continuous Laves phase film observed along HAZ cracks. This was strong evidence of backfilling mechanism, which is described as wetting and infiltration of terminal liquid along γ grain boundaries of parent material. The current results suggest that this cracking mechanism was activated in three-point intersections resulting from perpendicular crossing of columnar grain boundaries with fusion line and was enhanced by nail or mushroom weld shapes and narrow and columnar γ grain characteristics of castings. Neither Varestraint nor hot ductility weldability tests can reproduce this particular cracking mechanism.

Badania możliwości łączenia kompozytów metalowych odlewanych odśrodkowo

Centrifugal composite castings based on aluminium alloys belong to a group of materials with high potential for application in the automotive and aerospace industries. Their use is limited by the lack of a technology enabling the obtainment of a permanent joint ensuring safe operation. The article presents the results of preliminary surfacing and welding tests of a hybrid centrifugal composite casting based on the AlSi12 alloy and reinforced with silicon carbide (5 % by weight) and glassy carbon (5 % by weight) particles. Structural tests and the quantitative evaluation of the distribution of structural constituents indicated the possibility of the joining of such composites using the TIG welding process. It was found that overlay welds made using the filler metal having a chemical composition similar to that of the matrix could be treated as a buffer layer. The aforesaid approach should enable the joining of composite castings. The structure of the weld revealed the presence of heterogeneously distributed reinforcing phases, which was related to the gradient structure of centrifugal composite castings. The presence of the Al4C3 phase at the interface between the glassy carbon and the matrix could result in the reduction of corrosion resistance in a humid environment. The structural tests discussed in the article should be supplemented with the assessment of the mechanical properties of the joint. As a result, it will be possible to implement the technology for the welding of composite castings on an industrial scale.

Improving mechanical properties and electrode life for joining aluminum alloys with innovatively designated Newton ring electrode

Abstract Aluminum alloys are critical lightweight materials in the automotive industry, which can significantly reduce vehicle weight and improve vehicle fuel efficiency. However, resistance spot welding, as one of key joining approaches, faces the challenges of short electrode life and unstable weld quality when welding aluminum alloy. A novel electrode named as Newton Ring (NTR) electrode was developed to address these issues. The mechanical property, nugget evolution and electrode degradation during continuous welding of aluminum alloy with NTR electrode were investigated and compared with the typical spherical electrode. Results indicate that the mechanical property, electrode life and surface quality of the weld fabricated by NTR electrode were much better than typical one. The improvement in the weld quality with NTR electrode stems from its unique surface morphology, which changes the current density distribution during welding and creates a ring-shaped nucleation process of the nugget. Therefore, the shape and size of the nugget are more stable, and the nugget does not cause serious offset in the continuous welding test. Additionally, the wear of the NTR electrode gradually grows from concentric rings to the base ring, avoiding the random and rapid wear on the electrode weld face, thus improving the surface quality of the weld.

Understanding mechanisms of shape memory function deterioration for nitinol alloy during non-equilibrium solidification by electron beam

IntroductionAs an important advanced functional material, the memory effect of nitinol shape memory alloy (SMA) is the focus of research. According to the current research, the memory function of the alloy decreases after welding, and there is no sufficient explanation for the phenomenon. ObjectivesFor the problem, this research is to explore the underlying causes of the decrease of shape memory function after welding by analyzing the microstructure and micro defects. MethodsThe vacuum electron beam welding tests of 1 mm thick Ni50Ti50 alloy plate was carried out to determine the appropriate welding process parameter. And the shape memory function of the welded joint was compared with that of the base metal to analyze the change of memory function. ResultsIt was found that the shape memory function of the welded joint decreased significantly under different strain variables. And the phase transition temperature also changed. ConclusionsThis was due to the micro stress field produced by non-equilibrium solidification in molten pool promoted the formation and propagation of dislocations, increasing the dislocation density in the martensite. Dislocations entangled with each other in the martensite, showing a grid-like distribution, which destroyed the integrity of martensite substructure. At the same time, the twin substructure of martensite was often accompanied by vacancies, dislocations, stacking faults, and a consequently large stress field formed between twin planes due to lattice distortion. Secondary twin was identified inside martensite under micro shear stress, where the martensite showed the bending state. The habitual relationship between martensite phase and parent phase was destroyed, resulting in the decrease of shape memory function.

Development of ferrous-based weldable seismic damping alloy with prolonged plastic fatigue life

A new weldable Fe-Mn-Cr-Ni-Si seismic damping alloy with high fatigue resistance was developed by controlling phase transformation behaviour during both solidification and fatigue deformation. The solidification phase transformation was controlled by changing the Cr/Ni ratio to induce ferrite-austenite transformation and thus reduce the solidification cracking susceptibility. The Gibbs free energy difference between the austenite and ε-martensite was optimized to exhibit reversible transformation during fatigue deformation. The resultant alloy exhibited a prolonged fatigue life, and no solidification cracking was observed in a melt-run welding test. By using the newly developed alloy, a weld damper with excellent fatigue resistance can be fabricated.

The effect of flux chemistry on element transfer in Submerged Arc Welding: application of thermochemical modelling

Post-weld slag and weld metal analyses were used to interpret the effects of different commercial flux compositions on element transfer between molten flux (slag) and weld metal in Submerged Arc Welding (SAW). Selected fluoride based flux compositions cover a wide range of basicity index (BI) values of 0.5–3.0. Thermochemical modelling in FactSage software is used to simulate the welding process in terms of gas-slag-metal equilibria. The importance of the gas phase in SAW element transfer is illustrated. The model provides improved accuracy in predicted weld metal oxygen values (ppm O) compared to the generally used empirical relationship of weld metal ppm O vs. flux BI. Model predicted oxygen values are within 150 ppm of the analysed values, compared to the empirical relationship values which are within 240 ppm from the analysed values. The model provides resolution in ppm O values at BI > 1.8. This information is lacking in the empirical relationship with constant ppm O of 250 ppm at BI > 1.8. The measured ppm O values follow the Fe–FeO equilibrium trend with a positive offset. The relative level of oxygen to deoxidation elements (Ti, Al, Mn, Si) in the weld metal is an important factor in oxide inclusion engineering. This model will aid in the specification of flux formulations to attain specific weld metal compositions for maximum acicular ferrite formation. In this way the weld metal mechanical properties can be improved. This model will reduce the number of welding tests required to develop new flux formulations.

Shielded Active Gas Forge Welding of an L80 Steel in a Small Scale Shielded Active Gas Forge Welding Machine

The Shielded Active Gas Forge Welding (SAG-FW) method is a solid-state welding technique in which the mating surfaces are heated by induction heating or direct electrical heating before being forged together to form a weld. In this article, an API 5CT L80 grade carbon steel alloy has been welded using the SAG-FW method. A small-scale forge welding machine has been used to join miniature pipes extracted from a large pipe wall. The welding was performed at three different forging temperatures, i.e., 1300 °C, 1150 °C and 950 °C, in some cases followed by one or two post weld heat treatment cycles. In order to qualify the welds, mechanical and corrosion testing was performed on miniature samples extracted from the welded pipes. In addition, the microstructure of the welds was analysed, and electron probe microanalysis was carried out to control that no oxide film had formed along the weld line. Based on the complete set of experimental results, promising parameters for SAG-FW welding of the API 5CT L80 grade steel are suggested. The most promising procedure includes forging at relative high temperature (1150 °C) followed by rapid cooling and a short temper. This procedure was found to give a weld zone microstructure dominated by tempered martensite with promising mechanical and corrosion properties. The investigation confirmed that small scale forge welding testing is a useful tool in the development of welding parameters for full size SAG-FW welding.