Weld Deposits Research Articles

Towards an automated robotic arc-welding-based additive manufacturing system from CAD to finished part

Arc welding has been widely explored for additive manufacturing of large metal components over the last three decades due to its lower capital cost, an unlimited build envelope, and higher deposition rates. Although significant improvements have been made, an arc welding process has yet to be incorporated in a commercially available additive manufacturing system. The next step in exploiting “true” arc-welding-based additive manufacturing is to develop the automation software required to produce CAD-to-part capability. This study focuses on developing a fully automated system using robotic gas metal arc welding to additively manufacture metal components. The system contains several modules, including bead modelling, slicing, deposition path planning, weld setting, and post-process machining. Among these modules, bead modelling provides the essential database for process control, and an innovative path planning strategy fulfils the requirements of the automated system. A user friendly interface has been developed for non-experts to operate the developed system. Finally, a thin-walled aluminium structure has been fabricated automatically using only a CAD model as the informational input to the system. This exercise demonstrates that the developed system is a significant contribution towards the ultimate goal of producing a practical and highly automated arc-welding-based additive manufacturing system for industrial application.

Determination of parameters of mechanical pulse action on the weld pool for the metal structuring in automatic arc deposition welding

The strength and other operational characteristics of the metal during arc deposition welding processes are determined by the presence of columnar crystals, the growth of which occurs as a result of metal overheating in the molten bath. To control the columnar crystals growth, a variety of methods are used, including pulse impacts on the weld pool or creating mechanical vibrations of the part during deposition welding. In the latter case, the periodic removal of the heat source from the point of the weld pool overheating prevents the growth of columnar crystallites and thus improves the weld metal structure. The developed engineering method for calculating the effective parameters of the mechanical vibrations of the weld pool during automatic deposition welding of cylindrical parts in CO2 is based on the theory of heat transfer at welding. It is shown that deposit welding on the mild steel St.3 with the Sv08G2C wire of the 1.2 mm diameter should be carried out with the 1...12 Hz vibration frequency at the amplitude equal to 1/2 of the deposition welding step. Experimental verification of various mode parameters showed that, compared to the welding performed without vibration of the weld pool, the weld bead width is increased by 16...23% in the deposited layer, there are no cracks, and its durability improved by 1.3...1.7 times. The improvement of mechanical properties of the deposited layer is due to grinding of metal grains exposed to the controlled vibrations of the part. At that, there are hardly any weld metal columnar structures, which are observed at conventional deposition welding.

Plasma Transferred Arc Welding of Stellite 6 Alloy on Stainless Steel for Wear Resistance

Austenitic stainless steel was deposited on 9Cr-1Mo steel (ASME Grade 91) by flux cored arc welding process and above that Stellite 6 (Co-Cr alloy) was coated by plasma transferred arc welding process to improve wear resistance for high temperature valves applications. Microstructural characterization was carried out on Stellite 6 coatings and hardness and chemical composition were measured by vicker's hardness tester and optical emission spectrometer respectively. The impact of alloying elements in Stellite 6 deposits and fusion line of Stellite 6 and stainless steel were analyzed by electron dispersive spectroscopy line scan. It was observed that dilution of Iron in PTA welding deposit in Stellite 6 is below 2% and hardness of more than 600 HV0.3 was obtained. Microstructure of Stellite 6 consisted of Co - solid solution matrix with dendritic structure and interdendritic eutectic carbides which provides the hardness. Pin-on-disc tests were carried out at 400°C and characterized using scanning electron microscope of worn out surfaces. The wear mechanism was identified as delamination and abrasive wear in the worn-out surfaces as observed. Abrasive form of wear was reported due to the presence of alloying elements such as Co, Cr & W.

Influence of Process Parameters on the Process Efficiency in Laser Metal Deposition Welding

Conventionally manufactured tools are often completely constructed of a high-alloyed, expensive tool steel. An alternative way to manufacture tools is the combination of a cost-efficient, mild steel and a functional coating in the interaction zone of the tool. Thermal processing methods, like laser metal deposition, are always characterized by thermal distortion. The resistance against the thermal distortion decreases with the reduction of the material thickness. As a consequence, there is a necessity of a special process management for the laser based coating of thin parts or tools. The experimental approach in the present paper is to keep the energy and the mass per unit length constant by varying the laser power, the feed rate and the powder mass flow. The typical seam parameters are measured in order to characterize the cladding process, define process limits and evaluate the process efficiency. Ways to optimize dilution, angular distortion and clad height are presented.

Arrested diatreme development: Standing Rocks East, Hopi Buttes, Navajo Nation, USA

Maar–diatreme volcanoes, defined by their relatively large pyroclastic debris-filled subsurface structures and craters that cut into the pre-eruptive land surface, are typically found in small-volume mafic to ultramafic monogenetic volcanic fields. Diatremes are associated with strong explosions throughout most of their development, focused along feeder dikes and generally attributed to magma–water interaction, or high magmatic volatiles. Detailed mapping of the magnificently exposed Standing Rocks East (SRE) diatreme shows evidence of additional eruptive complexity, and offers new insights into how the plumbing and vent structures of small-volume volcanoes evolve during an eruption.SRE is part of a larger, basanitic volcanic complex that includes several diatremes formed along a series of irregular, offset NW–SE trending dikes exposed 300m below the pre-eruptive land surface. Its similarly oriented elliptical-shaped diatreme structure comprises predominantly country rock lithic-rich breccia of coarse inhomogeneously mixed wall-rock blocks sourced from above and below the current surface, plus sparse juvenile material. Domains of pyroclastic deposits crosscut the country rock breccia deposits, and the best exposed is the NW massif rising 35m above the current erosional surface. It represents a cross-section of an evolving crater floor, and comprises matrix-rich lapilli tuff and spatter deposits cut by irregularly distributed dikes, some with very complex textures. The most significant deposit, in terms of volume, is an unbedded lapilli tuff that is poorly sorted and has a well-mixed population of wall-rock and juvenile clast varieties, thus resembling deposits typical of diatremes. It is overlain by and locally intercalated with spatter deposits, and this irregular contact demarcates the base of what was during eruption an uneven, evolving crater floor. The generally massive, variably welded spatter deposits constitute mostly lapilli-sized juvenile clasts with fluidal, folded-over shapes and ropy surfaces, subordinate thermally altered wall-rock and variegated domains of lapilli tuff.SRE shows a progressive transition from fissure to diatreme, and overall evolution from more explosive to weakly explosive eruption styles recorded at the conduit-crater transition. Diatreme development was initiated by deep-quarrying explosive eruptions along a fissure to form the country rock-rich breccia. Only parts of the fissure remained active as magma feeding the highly explosive eruptions along the fissure localized into discrete point sources forming the matrix-rich lapilli tuff deposits. These superimposed deposits record the passage of multiple debris-jets and subvertical fallback from shallow cratering arising from explosions triggered by magma–water interaction at numerous, discrete sites. However, instead of continuing to build a well-formed diatreme, the system switched to weak spattering with intermittent explosive activity and near-surface dike emplacement into the unconsolidated anisotropic, pyroclastic debris of the crater floor. Dominant spatter from strombolian-style bursts accumulated on the topographically varied, evolving unstable syn-eruptive crater floor, and led to local failure and remobilization. This study demonstrates how the combination of fissure behavior and sensitivity of the shallow plumbing system to local conditions during an eruption can lead to a decrease in eruptive footprint within the diatreme structure, and an overall decrease in explosivity resulting in the arrested development of an immature diatreme.

Desenvolvimento e Validação de Algoritmos para Emprego de Sensores na Soldagem Robótica Orbital do Passe de Raiz de Tubulações

Resumo Os sistemas comerciais destinados à automação da soldagem orbital enfrentam desafios perante o controle da trajetória e a parametrização do processo. Os tubos e dutos do setor de Petróleo e Gás apresentam descontinuidades, advindas de sua fabricação, críticas para o processo de soldagem. Para superar isto, o presente trabalho investiga a utilização de sensores para correção em tempo real da soldagem orbital. Um robô antropomórfico atua na condução da tocha. Um sensor a arco para seguimento de junta e um sensor baseado no contato elétrico para procura da junta foram empregados. Um programa em forma de algoritmos para geração de uma trajetória orbital automática e alocação dos parâmetros de soldagem foi desenvolvido. A validação da estratégia proposta e do controle da tocha pelo sensor a arco foi realizada com depósitos em corpos de prova de tubos. A soldagem do passe de raiz com um processo MIG/MAG com controle de corrente no curto-circuito também foi executada em conjunto com o sensor a arco.

Pulsed current gas metal arc welding of P91 steels using metal cored wires

A detailed experimental study was undertaken to examine the suitability of pulsed current gas metal arc welding of 12mm thick P91 steels in groove joint configurations with metal cored filler wire. Both the single and multipass welds showed satisfactory bead morphology, tensile strength and toughness especially at higher groove angles of 60° and 75° for the selected range of welding current and speeds. The weld metal compositions showed considerably high presence of Ni, Mn and Si with little loss of other alloying elements. The weld properties were primarily affected by the heat input per unit length of weld and the groove angle. The maximum ultimate tensile strength and toughness of the welds were found to be around 845MPa and 125J, respectively, for a heat input of 1.38kJ/mm and a groove angle of 75°. The use of metal cored filler wires could enhance the welding speed by 20% and filler wire deposition rate by 42% compared to that with the solid wires. Overall, the present study showed that the pulsed current gas metal arc welding of medium to high thickness P91 steels using metal cored filler wires could provide higher deposition rate and welding speed, and enhanced weld bead properties in comparison to solid wires.

Effect of Post Weld Heat Treatment on Weld Hardness Quality of P91 Welded Pipes

Quality of a weld produced is generally evaluated by different parameters such as weld size, bead geometry, deposition rate, hardness and strength. A common problem that has been faced at the construction sites is to obtain a good welded joint having the required strength with minimal detrimental residual stresses to avoid any premature cracking due to high variation of hardness. In order to address this issue and to attain good weld quality, this study has been made to comprehend the effect of the post weld heat treatment on P91 material welds produced by TIG welding. Findings from the studies indicate that the PWHT has significant influence on the weld hardness of Alloy Steel-A335 P91 pipes. It is eminent that during cooling, after welding of P91, quenched martensite was formed in the HAZ that results in an increased hardness to an undesirable level of more than 250HB. PWHT at temperature of 760°C for 2 hours has good influence on mechanical properties as the hardness decreases and turns out to be uniformly distributed. If the PWHT is correctly carried out, the hardness of parent metals, heat affected zones and weld metal can be brought into the required limits to avoid any premature cracking due to high variation of hardness.

Some Aspects on the Welding Characteristics and Formation of Microstructures in a Newly Developed Coated Electrode for Austempered Ductile Iron (ADI)

In this study, six different coated electrodes were manufactured to select compatible one for ADI and only two electrodes were further studied (Trial 3 and Trial 4) to check their compatibility. Welding conditions were established to obtain crack free weld deposit on DI plate by varying preheat (200°C, 300°C and 400°C for lhour) as well as PWHT (maintaining same preheat temperature) at constant heat input using two selected electrodes. Only preheating at 300°C was possible to obtain sound weld for Trial 3, whereasboth preheat (300°C) and PWHT (300°C) were required for Trial 4. Although the as-deposited microstructures of FZ and PMZ consisting of ledeburitic carbide and alloyed pearlite in both the electrodes were same, the amount of microstructural constituents varied significantly. More ledeburitic carbide and less alloyed pearlite were observed in Trial 3 compared to Trial 4. However, microstructures of HAZ for both the electrodes showed bainitic and pearlite. Austempering heat treatment comprising of austenitization at 900°C for 2 hr and austempering at two different temperatures (300°C and 350°C) for different holding time was carried out for both the weld deposits. Interestingly, for both the weld deposits austempered microstructures show bainitic ferrite and retained austenite with graphite nodules. Increasing austempering temperature from 300°C and 350°C the lower bainite transformed to upper bainite and vol. % of retained austenite was also increased.

Effect of SMAW manufacturing process in high-cycle fatigue of AISI 304 base metal using AISI 308L filler metal

The shielded metal arc welding (SMAW) process is commonly used in many applications due to its high versatility in the manufacturing of industrial parts, components and assemblies. This paper is about the effect SMAW process on the high-cycle fatigue of austenitic stainless steel AISI 304 using AISI 308L filler metal. Two different parameters (factors) of the manufacturing process were evaluated: type of electrode coating and heat input in the welding process. Three different electrode coating were compared: E308L-15, E308L-16 and E318L-16 Premium. Additionally, three different heat inputs levels were used in the welding process for each electrode covering (“low”, “medium” and “high”). For this welding application, cold rolled plates 300mm length, 76.2mm wide, 6.4mm thick of AISI/SAE 304 were used as base material, making up V-groove type joints on them. After welding, microstructure characterization using optical and scanning electron microscopy; chemical analysis composition; HRB hardness test; tensile test and ferrite number (FN) of the welded joints were evaluated. Fatigue tests were conducted in the INSTRON 8872 machine. To analyze the fatigue results, Quantitative Analysis Accelerated Life Testing was used, wherewith Smax-N graphs were plotted among all the experimental factors (as a factorial experiment). It was found that solidification of weld shows dendrite growth with both ventricular and lathy morphologies. The E308L-15 electrode deposits have better resistance to high cycle axial fatigue than the other electrode deposits. Furthermore, we found that the high-cycle fatigue resistance of the deposits is enhanced at lower heat inputs of welding process and greater FN. Material failures were localized among the weld deposit, through the dendrite orientation on microstructure that also led the growth of the crack.

Stainless Steel Bismuth Free Flux-cored Wires for High Temperature Applications

Since the 1970s, bismuth has been widely used as an auxiliary ingredient in stainless steel flux-cored wires to improve slag detachability. But for components subject to post weld heat treatment (PWHT) and/or applications at high temperature, bismuth has been confirmed to have a negative effect on weld metal ductility. There are also reports on cracks found in such weldments after service at elevated temperatures. For this reason, specifications recently started limiting the weld metal bismuth content. API RP 582, for instance, has included a maximum bismuth content of 20 ppm in the weld deposit when welding with austenitic stainless steel flux-cored wires for applications above 538 °C, including PWHT. This new demand required development of a new range of flux-cored wires intended for overlay welding (cladding) of creep resistant steels and joining stainless steels for high temperature applications. The fillers that have been developed include the alloys E347, E309 L, and E308H. Two types for each alloy are available: One is optimized for welding in flat/horizontal position, and the other features a fast-freezing slag system supporting the weld pool when welding in other positions. The mechanical properties obtained in all-weld metal, V joints, and weld overlay applications with the newly developed wires are compared with standard wires. The effect of the chemical composition on welding behavior and slag detachability is discussed and some examples are given where these specific flux-cored wires can be used in the oil and gas industry.

Effects of filling status of cold wire on the welding process stability in twin-arc integrated cold wire hybrid welding

Twin-wire metal inert gas/metal active gas (MIG/MAG) arc welding is one typical type of the high-efficient welding technologies. In order to further improve the welding efficiency without increasing the welding heat input, a novel welding technology entitled twin-arc integrated cold wire hybrid welding was developed. The addition of cold wire not only increased the welding deposition rate but also improved the welding stability. In this paper, the influential mechanism of cold wire on welding stability was studied by the high-speed photography and electrical signal acquisition. It was found that the cathode spot could be stabilized on the surface of the weld pool by increasing the cold wire feed speed, which significantly improved the welding stability. The main reasons are as follows: the addition of cold wire significantly decreased the temperature of the liquid weld pool metal around the cold wire. This led to increasing the electron emission difficulty and reducing the gradient distribution of surface tension. Therefore, the cathode spot would be more likely to stabilize in the high temperature zone instead of drifting with the rear flow of the liquid weld pool metal. Besides, the cathode spot could also be stabilized because of the less dramatic fluid flow of the liquid metal. Finally, the welding stability was evaluated by a mathematical statistic method, which further verified that the welding stability could be improved with the increase of cold wire feed speed to a proper range.

Wear and Grip Loss Evaluation of High Chromium Welding Deposits Applied on Sugar Cane Rolls1

Wear on sugar cane rolls is an expensive maintenance problem for the sugar cane industry. Wear produces loss of sucrose extraction and loss of grip of the roll on the bagasse. This paper presents the evaluation of wear and loss of grip of hypoeutectic and hypereutectic high chromium welding deposits applied on ASTM A-36 steel and gray cast iron. A modified ASTM G-65 standard test was used. Wear was produced by the abrasive action of wet bagasse with three levels of mineral extraneous matter. Silica grains with sizes in the range of 0.212-0.300 mm (AFS 50/70) were used as mineral extraneous matter. Grip was evaluated by measuring the torque on the power transmission shaft that moves the specimens. Worn surfaces were characterized by using scanning electron microscopy. Wear was found to increase proportionally related to the mineral extraneous matter content. Geometric changes of the weld deposits related to wear caused grip loss. For low mineral extraneous matter level, wear resistance of carbon steel was greater than that of gray cast iron; whereas the opposite was found for high mineral extraneous matter level.

Quantification of residual stresses in multi-pass welds using neutron diffraction

Neutron diffraction results highlighted the effect of heat input through changes of travel speed and welding sequence (direction) on the residual stresses in multi-pass weldments of high strength low alloy steel. Residual stresses in excess of yield strength were developed in the weld metal and HAZ particularly for the upper-layers of welds which were not affected by the tempering of the subsequent weld layers. The magnitude of the residual stresses was significantly reduced by increasing the heat input. There was no substantial difference in the magnitude of the residual stresses when the direction of weld deposition was varied but the distribution was more uniform.

First Experimental and Numerical Study on the Use of Sheet Metal Die Covers for Wear Protection in Closed-Die Forging

To reduce the failure of dies by abrasive wear, mechanical fatigue and thermal fatigue in closed-die forging usually measures like nitriding, deposition of ceramic layers by Physical Vapour Deposition (PVD), Chemical Vapour Deposition (CVD) or deposition welding are used. However, after some time wear appears and the dies have to be replaced. A new concept implements sheet metal die covers, which are placed on the die engraving during forging and will absorb abrasive wear, thermal and mechanical load. The inexpensive cover will be replaced quickly by a new one after it is worn-out. This concept is regarded in a first numerical and experimental study by comparing a covered die (C) and an uncovered die (U) for the production of the same part. A one-time use of the die cover showed a reduction of the peak temperature by 140 K and of the temperature amplitude by 37 %. The temperature reduction and the increase of inner radii of the engraving to fit the 1mm thick die cover doubled the expected die life time. The experiment showed that the soft deep drawing steel DC04 is not suitable in the current case for a die cover and a higher strength sheet metal should be applied.

Stress corrosion cracking of austenitic weld deposits in a salt spray environment

ER 308L and 309LMo were utilized as the filler metals for the groove and overlay welds of a 304L stainless steel substrate, which was prepared via a gas tungsten arc-welding process in multiple passes. U-bend and weight-loss tests were conducted by testing the welds in a salt spray containing 10 wt% NaCl at 120 °C. The dissolution of the skeletal structure in the fusion zone (FZ) caused the stress corrosion cracking (SCC) of the weld. The FZ in the cold-rolled condition showed the longest single crack length in the U-bend tests. Moreover, sensitization treatment at 650 °C for 10 h promoted the formation of numerous fine cracks, which resulted in a high SCC susceptibility. The weight loss of the deposits was consistent with the SCC susceptibility of the welds in a salt spray. The 309LMo deposit was superior to the 308L deposit in the salt spray.

Influence of Particle Fracture on the Slurry Abrasion Behavior of Weld Deposited Martensitic Steel

The life of the components used under slurry abrasion conditions is governed by the process variables, properties of the abrasive materials in the slurry and the material properties. Slurry wear, abrasion occurs in Extruders, pumps and pipe transport slurry of minerals and ores in mineral processing industries. In the present research, the effect of operating variables such as abrasive particle size and shape, slurry concentration and normal load on the abrasive slurry wear behavior of the weld deposit martensitic steel surface produced by the Manual Metal Arc Welding Hard facing process was conceded out. The testing was conceded out using the slurry abrasion test rig. The silica sand particles were used as the abrasive medium. The qualitative nature of wear pattern and morphology of the worn out surface was examined under scanning electron microscope (SEM). These features were correlated with operating parameters.

Microstructure and Tribological Properties of Weld Deposited Co-Cr-Mo Alloy

AbstractCo-Cr-Mo alloy samples were deposited using arc welding process with optimum parameters of deposition. The samples were tested for their hardness, XRF, wear resistance and microstructures. The results were compared with the laser deposited samples and cast samples from literature. The experimental results revealed that the hardness of the weld deposits was inferior to as-cast samples as well as the laser deposited samples. But the wear resistance of the weld deposited samples was compatible with laser deposited samples. Metal to metal contact Pin on Disc wear resistance test was conducted. The XRF results were in agreement with results of as-cast samples. Scanning electron microscopy was used for microstructure analysis. Thorough investigation was made to compare the microstructures of the weld deposits with laser deposited and as-cast Co-Cr-Mo alloy samples.

Structure Analyses of Experimental Welds Designed for Repair Welding of VVER 1000 Presssure Vessel

Microstructural analysis and microhardness measurement of experimental repair weld joints were carried out in heat affected zone (HAZ) of the base material (BM) – steel 15Ch2NMFA after weld deposition of several layers by welding metal of Inconel FM 52. A temper bead welding (TBW) technique was used. Required microhardness up to 350 HV0.1 in heat affected zone of base material in distance 0.5 mm from fusion line was exceeded in all three experimental blocks with various welding energy inputs during deposition of three or five weld layers. Metallography showed reaustenitization and structure transformation in HAZ after the deposit of first layer in all three blocks. After deposit of the last layer the structure of HAZ in two blocks was tempered only and one variant of them have been recommended for futher technological tests. Structure of HAZ of the third block was not full tempered even after the last layer deposit.

Stereo vision based measuring system for online welding path inspection

A welding path measuring system (WPMS) is developed in order to achieve better understanding of the welding execution of the critical welds or weld deposits in multi-pass and repair welding. The developed WPMS system measures the arc position in 3D space based on the stereo vision principle. The time sequence of arc positions shows a 3D welding path in time, which bears information on how the weld or deposit was welded. Test welding was carried out in order to validate the developed system and to demonstrate how the welding path reveals simulated irregularities in the groove shape and in the electrode motion. The simulated irregularities are visible as anomalies in the welding path. A method for their automatic detection based on the welding path distribution along the weld was proposed.