Showing papers on "Arc welding published in 2017"

Recent developments in joining of aluminum alloys

Abstract: The mass saving potential of light-weight materials, such as Al alloys, is beneficial for fuel economy and reducing CO2 emissions. However, the wide-spread use of these alloys has been long hindered due to the difficulty in fusion joining as well as their high cost. Welding of Al alloys, which are considered to be difficult to weld through conventional arc welding, is now possible by either of low heat input arc welding, high-power density fusion joining, such as laser beam welding and electron beam welding, or friction stir welding. Particularly, friction stir welding can be successfully applied to these materials owing to the fact that no melting takes place in the weld nugget. The aim of this overview is to summarize the developments in the joining of Al alloys over the recent years. This study is also intended to provide guidance for the industry and researchers dealing with joining of these alloys.

Material properties of CMT—metal additive manufactured duplex stainless steel blade-like geometries

Abstract: Impeller blades are often individual and complex-shaped components made of challenging metals. As the manufacturing of such blades is highly sophisticated, only a few companies worldwide possess the necessary processing knowledge and that is why long production times have to be accepted by customers. To overcome this economic disadvantage, manufacturing technologies are permanent under supervision and it seems that metal additive manufacturing could thereby play an important role in future. In this paper, wire arc additive manufacturing (WAAM) based on gas metal arc welding (GMAW) is considered. Shape-giving GMAW is well known in industrial manufacturing, but its application is limited due to restrictions by the welding process itself: For thinner wall thicknesses, a significant reduction of the weld process energy is required which increases the risk of process instabilities and spatter formation. Extensive welding process-related efforts have been undertaken to overcome this fact and a new GMAW process, called CMT (Cold Metal Transfer) was introduced. CMT is based on a high-frequency forward and backward movement of the welding wire electrode and provides an almost spatter-free and absolute precise, periodic detachment of accurately defined droplets from the filler wire at very low process energies. In combination with an accurate robotic movement of the CMT welding torch, geometries with minimum thicknesses in the range of 2–4 mm can be build up layer by layer. Additionally, a broad range of different, well established and third party-approved GMAW filler metals for joining is available. In this work, an impeller blade-like geometry out of duplex stainless steel has been manufactured by CMT using a filler wire type G 22 9 3 N L. The investigations have shown that the achieved surface roughness is comparable to sand casting and the microstructure is without any evidence for porosity and lack of fusion. Furthermore, an austenite/δ-ferrite weld microstructure with partly preferred grain orientations and a δ-ferrite content of around 30FN exists. The measured mechanical properties, especially strength and toughness, are comparable to data provided by the filler metal data sheet.

Real-time seam penetration identification in arc welding based on fusion of sound, voltage and spectrum signals

Abstract: Sensor technology application is the key for intelligent welding process. Multiple sensors fusion has shown their significant advantages over single sensor which can only provide limited information. In this paper, a feature-level data fusion methodology was presented to automatically evaluate seam quality in real time for Al alloy in gas tungsten arc welding by means of online arc sound, voltage and spectrum signals. Based on the developed algorithms in time and frequency domain, multiple feature parameters were successively extracted and selected from sound and voltage signals, while spectrum distribution of argon atoms related to seam penetration were carefully analyzed before feature parameters selection. After the synchronization of heterogeneous feature parameters, the feature-level-based data fusion was conducted by establishing a classifier using support vector machine and 10-fold cross validation. The test results indicate that multisensory-based classifier has higher accuracy i.e., 96.5873 %, than single sensor-based one in term of recognizing seam defects, like under penetration and burn through from normal penetration.

Effect of A-TIG Welding Process on the Weld Attributes of Type 304LN and 316LN Stainless Steels

Abstract: The specific activated flux has been developed for enhancing the penetration performance of TIG welding process for autogenous welding of type 304LN and 316LN stainless steels through systematic study. Initially single-component fluxes were used to study their effect on depth of penetration and tensile properties. Then multi-component activated flux was developed which was found to produce a significant increase in penetration of 10-12 mm in single-pass TIG welding of type 304LN and 316LN stainless steels. The significant improvement in penetration achieved using the activated flux developed in the present work has been attributed to the constriction of the arc and as well as reversal of Marangoni flow in the molten weld pool. The use of activated flux has been found to overcome the variable weld penetration observed in 316LN stainless steel with <50 ppm of sulfur. There was no degradation in the microstructure and mechanical properties of the A-TIG welds compared to that of the welds produced by conventional TIG welding on the contrary the transverse strength properties of the 304LN and 316LN stainless steel welds produced by A-TIG welding exceeded the minimum specified strength values of the base metals. Improvement in toughness values were observed in 316LN stainless steel produced by A-TIG welding due to refinement in the weld microstructure in the region close to the weld center. Thus, activated flux developed in the present work has greater potential for use during the TIG welding of structural components made of type 304LN and 316LN stainless steels.

Review on magnetically controlled arc welding process

Abstract: External magnetic field (EMF) has a strong effect on the welding arc shape, droplet transfer, weld forming, microstructure, and properties of joint metal. This paper defines the types of external magnetic field and reviews the development of magnetically controlled arc welding process, particularly, the effect of external magnetic field parameters on the welding process. It is found that the welding productivity, the weld formation, the ductility, and toughness of welded metal can be improved; and the welding residual stresses, the chemical inhomogeneity, and the welding defects can be reduced. Finally, the development trend is discussed in the later sections of the paper.

Additive Manufacturing Based on Welding Arc: A low-Cost Method

Abstract: The objective of this paper is to present a review of a new developing manufacturing technology based on welding of metallic materials. Additive manufacturing (AM) is based on robot welding and it has showed the high flexibility, efficiency, fast output, good quality and low cost. This paper explores several common welding materials and manufacturing technologies include the shield gas, materials engineering, processes and most concerned commercial interests. AM has the potential to revolutionize the global parts manufacturing and industrial tendencies with the rapid development of increasing material manufacturing technology. AM based on arc welding has the big advantages of high efficiency and low cost, which makes it possible to use in many industries although it has a little bit poor surface qualities compare to AM based on laser and electron beam manufacturing.

Hardfacing of AISI H13 tool steel with Stellite 21 alloy using cold metal transfer welding process

Abstract: Cold metal transfer (CMT) welding is a new gas metal arc welding process having several advantages such as low heat input and spatter free welding. This makes it of great advantage in weld cladding applications. In this study, hardfacing of AISI H13 die steel with Stellite 21 alloy has been carried using CMT process. Coatings were deposited on H13 substrate in annealed as well as quenched & tempered (Q&T) condition at room temperature as well as with a preheat of 400 °C. The Q&T substrate with and without preheat and the annealed substrate without preheat were found to be susceptible to underbead cracking upon Stellite deposition. The cracking in the heat affected zone (HAZ) was due to formation of brittle martensite upon rapid cooling which is associated with formation of high tensile residual stresses at the bead toe. The annealed substrate with preheat of 400 °C showed the least cracking tendency. The cracking tendency was investigated by studying the variation of the microstructure and microhardness along the depth of HAZ. The dilution levels based on Fe content was found to be 3–4%, which was considerably lower than that of conventional arc welding deposits. The Stellite coated H13 plate (annealed with preheat) could be successfully subjected to quenching & tempering heat treatment to restore the properties of the substrate without introducing any defects.

Initiation and growth kinetics of solidification cracking during welding of steel.

Abstract: Solidification cracking is a key phenomenon associated with defect formation during welding. To elucidate the failure mechanisms, solidification cracking during arc welding of steel are investigated in situ with high-speed, high-energy synchrotron X-ray radiography. Damage initiates at relatively low true strain of about 3.1% in the form of micro-cavities at the weld subsurface where peak volumetric strain and triaxiality are localised. The initial micro-cavities, with sizes from 10 × 10−6 m to 27 × 10−6m, are mostly formed in isolation as revealed by synchrotron X-ray micro-tomography. The growth of micro-cavities is driven by increasing strain induced to the solidifying steel. Cavities grow through coalescence of micro-cavities to form micro-cracks first and then through the propagation of micro-cracks. Cracks propagate from the core of the weld towards the free surface along the solidifying grain boundaries at a speed of 2–3 × 10−3 m s−1.

Effect of Continuous and Pulsed Current Gas Tungsten Arc Welding on Dissimilar Weldments Between Hastelloy C-276/AISI 321 Austenitic Stainless Steel

Abstract: In the present investigation, an attempt has been made to join Hastelloy C-276 nickel-based superalloy and AISI 321 austenitic stainless steel using ERNiCrMo-4 filler. The joints were fabricated by continuous and pulsed current gas tungsten arc welding processes. Experimental studies to ascertain the structure-property co-relationship with or without pulsed current mode were carried out using an optical microscope and scanning electron microscope. Further, the energy-dispersive spectroscope was used to evaluate the extent of microsegregation. The microstructure of fusion zone was obtained as finer cellular dendritic structure for pulsed current mode, whereas columnar structure was formed with small amount of cellular structure for continuous current mode. The scanning electron microscope examination witnessed the existence of migrated grain boundaries at the weld interfaces. Moreover, the presence of secondary phases such as P and μ was observed in continuous current weld joints, whereas they were absent in pulsed current weld joints, which needs to be further characterized. Moreover, pulsed current joints resulted in narrower weld bead, refined morphology, reduced elemental segregation and improved strength of the welded joints. The outcomes of the present investigation would help in obtaining good quality dissimilar joints for industrial applications and AISI 321 ASS being cheaper consequently led to cost-effective design also.

Development of welding technology for improving the metallurgical and mechanical properties of 21st century nickel based superalloy 686

Abstract: Alloy 686 is a highly corrosion resistant 21st-Century Nickel based superalloy derived from Ni-Cr-Mo ternary system. The alloying elements chromium (Cr) and molybdenum (Mo) are added to improve the resistance to corrosion in the broad range of service environment. The presence of a higher percentage of alloying elements Cr and Mo lead to microsegregation and end up with hot cracking in the fusion zone of Nickel-based superalloys. However, there is scanty of information regarding the welding of alloy 686 with respect to the microsegregation of alloying elements. The present study investigates the possibility of bringing down the microsegregation to cut down the formation of secondary phases in the fusion zone. The weld joints were fabricated by Gas Tungsten Arc Welding (GTAW) and Pulsed current gas tungsten arc welding (PCGTAW) with ERNiCrMo-10 filler and without filler wire (autogenous) mode. The microstructural properties of the weld joints were studied with optical and Scanning Electron Microscope (SEM). The joints fabricated by pulsed current (PC) technique shows refined microstructure, narrower weld bead and practically no heat affected zone (HAZ). Scanning Electron Microscope demonstrates the presence of secondary phases in the interdendritic regions of GTAW case. Energy Dispersive X-ray Spectroscopy (EDS) analysis was carried out to evaluate the microsegregation of alloying element. The results show that the segregation of Mo noticed in the interdendritic zone of GTAW both autogenous and filler wire. Tensile and Impact tests were done to evaluate the strength, ductility, and toughness of the weld joints. The results show that the PCGTA helps to obtain improved strength, ductility and toughness of the weld joints compared to their respective GTAW. Bend test did not lead to cracking irrespective of the type of welding adopted in the present study.

Wrought aluminium alloys

Abstract: Approximately 70% of aluminum produced globally is cast and fabricated into wrought alloy products by processes that are briefly described. These alloys are divided into two groups depending on whether or not they respond to heat treatment. The mechanical properties of the non-heat-treatable alloys are controlled by work hardening and annealing, whereas the heat-treatable groups are strengthened by age hardening. Temper designations are listed and described. Compositions and tensile properties of many of the commercial alloys are summarized in tables and their individual characteristics are discussed in some detail. Joining processes involving arc welding, friction stir welding, laser welding, brazing, diffusion bonding, and soldering are described. Attention is then directed to the commercial applications of the wrought aluminum alloys in the aerospace, automotive, shipping, packaging, and building industries. Reference is also made to lighter weight lithium-containing alloys that are finding structural applications in modern aircraft. Other more specialized topics include powder metallurgy products, aluminum alloy bearings, superplastic alloys, and aluminum-ion storage batteries.