Shielded Metal Arc Welding Process Research Articles

On the weldability of grey cast iron using nickel based filler metal

Shielded metal arc welding process using nickel based filler metal was used to join grey cast iron. The effect of post weld heat treatment (PWHT) on the microstructure and hardness was studied. PWHT included heating up to 870 °C, holding for 1 h at 870 °C and then furnace cooling. By using nickel based filler metal, formation of hard brittle phase (e.g. carbides and martensite) in the fusion zone is prevented. Before PWHT, heat affected zone exhibited martensitic structure and partially melted zone exhibited white cast iron structure plus martensite. Applied PWHT resulted in the dissolution of martensite in heat affected zone and graphitization and in turn the reduction of partially melted zone hardness. Results showed that welding of grey cast iron with nickel based filler metal and applying PWHT can serve as a solution for cast iron welding problems.

A comparative evaluation of ultrasonic testing of AISI 316L welds made by shielded metal arc welding and gas tungsten arc welding processes

Ultrasonic testing of austenitic welds prepared by two different welding processes is studied in this paper. The two welding processes considered are shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) and the ultrasonic testing technique used is time-of-flight diffraction (ToFD). Identical artificial flaws were implanted in both welds during the welding process. Austenitic characteristics consisting of grain orientation distribution and anisotropy show that the GTAW specimen is more isotropic than the SMAW due to the orientation of its grains. Moreover, comparison of echo amplitudes shows higher attenuation for the weld prepared by the GTAW process. The specimens were examined by the ultrasonic ToFD technique under identical conditions. B-scan images obtained from ToFD measurements of the two welds indicate that inspection of the specimen prepared by the SMAW process is easier than the one made by the GTAW process due to higher scattering of waves in the latter. The measurements also showed that the probe positioning is very important in the detection of diffracted echoes when using the ToFD technique.

English

Welding technique is one of the widely used permanent fastener techniques, where in different types of welding are used for different applications. Welding creates property changes in the welded location, so it is important to investigate the core mechanical properties after welding to create better designs using welding techniques. In this project the effect of the welding process of Shielded Metal Arc Welding (SMAW) and the relatively Tungsten inert gas welding (TIG) process on 304 Austenitic Stainless steel is studied. The welding process was carried out on 6mm thick plate of 304 Stainless Steel using SMAW and TIG welding processes The two set of plates having the single plate size of 200mmX150mmX6mm were welded using Tungsten Inert Gas welding And Shielded metal arc welding process. This project focuses on tensile property, toughness; micro hardness and micro structure of the each welding process of weld joints are studied and compared with those properties of each process related to the base metal, which shows the better welding process on Stainless Steel. The output variables of SMAW and TIG welding process on 6mm weld plate tensile strengths are compared. The studies indicated that the TIG joints were having better tensile strength than SMAW welded joints on 304stainless steel.

Weld surfacing of aluminium alloy by Ni—Cr base alloys

This article describes the microstructure, microhardness, and the abrasive wear behaviour of the Ni—Cr base alloy overlays deposited on the Al—Zn—Mg alloy (7039) substrate by the shielded metal arc welding process. The weld overlays were deposited by using four levels of the welding current in the range from 110 to 140A. Abrasive wear tests were carried out by using a pin-on-disc wear tester under a spiral wear track. Wear tests were carried out using three normal loads (5N, 10N, and 15N) and abrasives of three grit sizes (120, 320, and 600 grade). Scanning electron microscopy, X-ray diffraction, and the energy dispersive analysis of X-rays studies were performed on the weld overlay to characterize the microstructure, composition, and phase analysis. It was found that from the microstructure point of view, three different zones are formed in the weld overlays. These zones exhibited significant variation in terms of the nickel and the aluminium content in the micro-constituents. The microhardness has been found to decrease from the top surface of the weld overlays to the base metal.

Comportamiento del tiempo de duración, la frecuencia de los cortocircuitos y la conductividad eléctrica durante el reencendido del arco en la soldadura SMAW (AC) con electrodos E6013

El presente trabajo tiene como objetivo la evaluación del comportamiento del tiempo de duración, la frecuencia de los cortocircuitos y la conductividad durante el reencendido del arco en el proceso de soldadura SMAW (Shielded Metal Arc Welding), con corriente alterna y electrodos E6013. El análisis estadístico no-paramétrico garantiza un procesamiento robusto de los datos, atenuando la influencia de valores atípicos y errores derivados del empleo de aproximaciones a distribuciones continuas conocidas. La mediana y la mediana de la desviación absoluta (MAD), respecto a la mediana de los datos, constituyen los estimadores de localización y dispersión utilizados, respectivamente. El electrodo, en el régimen de 160 A, presenta una mayor estabilidad, en el aporte metálico, dada por el menor valor del MAD promedio del período de cortocircuito (39,36 ms) y de la duración del cortocircuito (1,43 ms), reafirmada con la presencia de una mayor conductividad eléctrica durante el reencendido (1766,17x10-3 S·s-1).

Effect of welding consumables and processes on dynamic fracture toughness (J1d) of armour grade Q&T steel joints

Austenitic stainless steel (ASS) welding consumables are being used for welding armour grade Q&T steels, as they have higher solubility for hydrogen in the austenitic phase, to avoid hydrogen induced cracking (HIC). Even with austenitic stainless steel consumables under high dilution, the risk of HIC prevailed. In recent years, the developments of low hydrogen ferritic steel (LHF) consumables that contain no hygroscopic compounds are utilised for welding Q&T steels. The use of ASS fillers for welding armour grade Q&T steels creates a duplex microstructure (austenite and δ ferrite) in the welds, which drastically reduces the joint efficiency (ratio of ultimate tensile strength of the joint and the base metal). On the other hand, the weld made using LHF fillers exhibited superior joint efficiency due to the preferential ferrite microstructure in the welds. The use of ASS and LHF consumables for armour grade Q&T steels will lead to formation of distinct microstructures in their respective welds. This microstructural heterogeneity will have a drastic influence on the dynamic fracture toughness of the armour grade Q&T steel welds. Hence, in this investigation an attempt has been made to study the influence on the welding consumables and processes on the dynamic fracture toughness properties of armour grade Q&T steel joints. Shielded metal arc welding (SMAW) and flux cored arc welding (FCAW) processes were used for fabrication of the joints using ASS and LHF welding consumables. The joints fabricated by SMAW process using ASS consumables exhibited superior dynamic fracture toughness values compared to all other joints.

The effect of thermal ageing on low cycle fatigue behaviour of 316 stainless steel welds

It is well known that welds are the weak links in any structure. Therefore, it is of out most importance to characterize the mechanical properties of welds. Moreover, the changes in the microstructure that occur in welds on exposure to high temperatures affect the mechanical properties and must be studied by ageing the welds at high temperature. In this paper the low cycle fatigue behaviour of thermally aged 316 stainless steel weld metal is presented. Weld pads with single V configuration were prepared by the shielded metal arc welding process using 316 electrodes. Thermal ageing was done for 10,000 h at 823 and 873 K. Total strain controlled low cycle fatigue tests were conducted at a constant strain rate of 3 × 10 −3 s −1 with strain amplitudes in the range ±0.25% to ±0.6% at 823 and 873 K. Weld metal exhibited initial hardening followed by cyclic softening prior to failure. The aged samples exhibited higher stress response as compared to the unaged samples. At both the temperatures and all strain amplitudes fatigue life was inferior to that of unaged samples. The metallography of the aged and tested material was studied through optical, scanning and transmission electron microscopy. The effect of transformation of δ-ferrite to sigma phase and carbides in the weld metal on low cycle fatigue behaviour was evaluated.

A microstructural and low-cycle fatigue investigation of weld-repaired heat-resistant cast steels

The multi-pass weld-repair of heat-resistant cast steels is carried out using an automated shielded metal arc welding (SMAW) process, with various filler materials and pre-heating at 400 °C. Specimens weld-repaired with a filler material more resistant than the heat-resistant cast steel (over-matching) generally crack within the base metal following the tenth filling pass, whereas specimens buttered with a soft alloy prior to welding remain free of cracks. The high temperature strain-controlled fatigue lifetime of material weld-repaired without buttering is lower than that of bulk initial material. This is due to an increase of the stress amplitude as a result of the so-called over-matching. In the case of material welded following a prior buttering, the fatigue lifetime is reduced because of the stress tri-axiality generated in the thin soft layer which prevents its plastic flow. As a consequence, it is concluded that even though buttering prevents cracking efficiently during welding, it is not acceptable as far as fatigue performance, especially lifetime, is concerned.

A Tribological Study for an Increased Coefficient of Friction in the Extraction of Sugarcane Juice

Historically, the roughening of the surface of sugarcane mill roller shells has been done by a shielded metal arc-welding process (SMAW), which is called “arcing” in the sugar industry. In this method, discrete weld globules are deposited on the grey cast iron mill roller shell surface, a process that has proven inefficient and expensive. In this investigation, the surface of the grey cast iron samples were sprayed using an electric wire arc-spraying machine. The coatings were characterized for their hardness, coefficient of friction, and corrosion resistance. A modified block and ring wear testing machine was used with bagasse as the counterface material to simulate the sucrose juice extraction process employed in the sugar cane industry. The results of the study indicated that an optimum coefficient of friction could be obtained while achieving satisfactory hardness and high corrosion resistance. Therefore, the results implied that arc spraying is a potential candidate to replace arcing in modifying the surface of the sugarcane mill roller shells.

Modeling of Molten Drop Oscillation in Gas Shielded Metal Arc Welding

In Gas shielded Metal Arc Welding process, the molten drop at the electrode wire tip is detached and transferred into the weld pool by various driving forces, which have been discussed mainly focusing on gravity force, electro-magnetic force, surface tension force and plasma drag force. In this paper the oscillation phenomena of metal drop and their numerical model are described. The numerical model developed is an axial symmetrical 2D model which enables to calculate and visualize time-change of the drop shape and the flow in the drop using VOF-CSF method. The validity of the model is verified through the comparison between calculations and experiments using waterdrop. It is shown that the natural frequency of the pendant drop decreases with increase of the drop size. And the numerical simulation predicts that it is possible to detach the molten drop from the electrode wire by exciting the forced oscillation around the natural frequency with pulsed current.

溶滴振動現象のモデル解析

In Gas shielded Metal Arc Welding process, the molten drop at the electrode wire tip is detached and transferred into the weld pool by various driving forces, which have been discussed mainly focusing on gravity force, electro-magnetic force, surface tension force and plasma drag force. In this paper modeling of the oscillation phenomena of molten drop at the wire tip are described. An analytical model evaluating natural frequency of liquid pendant drop was proposed on the basis of mass-spring model. The numerical model developed is an axial symmetrical 2D model which enables to calculate and visualize time-change of the drop shape and the flow in the drop using VOF-CSF method. It is shown that the natural frequency of the pendant drop decreases with increase of the drop size by both analytical and numerical models. And the natural frequency evaluated by analytical model is shown to be little higher than that by numerical model because of neglecting viscous resistance of liquid flow.

SOLDAGEM ROBOTIZADA COM ELETRODO REVESTIDO UTILIZANDO CONTROLE DE COMPRIMENTO DO ARCO ELÉTRICO COM COMPENSAÇÃO DA TEMPERATURA DO ELETRODO

The objective of this work is to show the results obtained with the shielded metal arc welding (SMAW) using an anthropomorphic robot. The procedure allies the robotization benefits such as quality, repeatability, traceability and flexibility to the ones inherent of the SMAW process, such as the chemical composition and microstructure control by using different electrodes and coatings. The diving movement must be done into the weld pool, maintaining the arc length constant, independently of the translation speed. To determine the arc length, the welding voltage and the electrode temperature are monitored, in order to compensate the melting rate and the material electric resistivity increase. It is observed that, controlling only the voltage, although the robot is able to keep it constant, the arc length significantly increases at the end of the weld bead, because the voltage drop on the electrode diminishes during electrode consumption. To compensate this effect, the voltage drop is modeled considering the electrode length reduction and the electric resistivity increase with the temperature. It is possible to keep the arc length constant during the entire welding.

Development of an automatic arc welding system using a variable structure model reference scheme

This paper presents an automatic welding control system for the alternating current shield metal arc welding process. A nominal nonlinear mathematical model containing uncertainties such as dead-zone, welding control system saturation, and the identified system parameters is derived. A novel variable structure model reference control scheme is designed to modulate the rate of the electrode feed mechanism, thereby regulating the arc current. The developed controller assures the global reaching condition of the sliding mode of the controlled welding system. In the sliding mode, the electric current error between the plant and the model asymptotically approaches zero. Moreover, the welding system remains insensitive to uncertainties and disturbance as the systems with friction. The simulation and experimental results confirm that the automatic welding control system, based on the proposed model-following variable structure controller, successfully maintains the magnitude of the arc current at the desired value and preserves the stability of the arc length, thereby ensuring excellent welding performance.

Effect of ultrasonic vibration on unmixed zone formation

Ultrasonic vibration was applied to molten super-austenitic stainless weld metal during the shielded metal arc–welding process. It was observed that the unmixed zone in the weld metal was completely eliminated by high-intensity ultrasonic vibrations. This is mainly due to a complete mixing of the molten filler metal and base metal, at the freezing front, caused by acoustically induced cavitation and streaming.

Three-Dimensional Finite Element Analysis to Predict the Effects of Shielded Metal Arc Welding Process Parameters on Temperature Distributions and Weldment Zones in Butt and One-Sided Fillet Welds

Temperature distribution patterns in any welding process control the microstructure, residual stress, and distortion. Welding process parameters can be optimized to obtain the desired microstructure and depth of penetration. In the present work, a three-dimensional finite element analysis was made to predict the different zones of microstructures for bead-on-plate and one-sided fillet welded joints using the shielded metal arc welding process. Some experiments were conducted to verify the model indirectly. Effects of welding process parameters such as electrode diameter, speed of travel, current, and voltage were considered in the finite element analysis. Various zones in the weldment were theoretically predicted from the finite element analysis and compared with the experimentally measured values.

Tuning PID control of an automatic arc welding system using a SMAW process

A new method to tune the gains of the proportional integral derivative (PID) controller for alternating current shield metal arc welding (SMAW) of automatic arc welding system using a SMAW process is presented in this paper. This method used the genetic algorithm (GA) approach to optimize the gains of the PID auto-tuner and considerably modulated the rate of an electrode feed mechanism that regulates arc current. The proposed controller was verified by simulation and experiments of the transient response in the automatic arc welding system. Finally, the performance indices of the proposed controller are compared with that based on Ziegler–Nichols tuning rules.

Evaluation of Mechanical Properties for Narrow-Gap Weld Zone in Reactor Coolant Loop

Conventionally, shield metal arc welding (SMAW) process was applied to join pipes of RCL, which caused lot of loss in time and cost due to excessive heat input and defects in joining section. Recently, narrow-gap welding (NGW) process was introduced to overcome the disadvantages of SMAW. However, the application of NGW to nuclear power plant is not yet common because safety of NGW process is not proven. In present paper, the welded coupons are manufactured under different welding processes in carbon steel. Then, microstructure observations and various mechanical tests are performed. It is verified that the mechanical properties of carbon steel are greatly changed after repair welding process due to applied heat flux, and that the effect of post-welding heat treatment is beneficial.

"The Role of Gases in Welding and Cutting Processes"

From the time that Edmond Fouche and Charles Picard developed the first oxy-acetylene torch, which gave a flame hot enough to melt steel in 1900, gases have played a very important role in the development of welding and cutting processes. In the early 1900s it was gas welding which laid the foundation for the commercial application of welding as a repair and joining process for steel and other metals, till the development of the coated electrode and shielded metal arc welding process by Oscar Kjellberg. Gas cutting, first introduced commercially in 1907, has however continued to be the backbone cutting process for the fabrication industry till today. Arc welding in a shielding gas atmosphere was patented by C.L.Coffin in 1890. However it was only in the 1940s that commercial use of inert gases Argon and Helium for shielding of the arc in the Gas Tungsten Arc and Gas Metal Arc welding processes was developed. The use of carbon dioxide and later argon based gas mixtures further enhanced the productivity and performance of Gas Metal Arc welding so that it has become the dominant welding process today. Gases and gas mixtures have also played a crucial role in the development of more advanced welding and cutting processes such as plasma and laser and today they play a very significant part in controlling the quality and cost effectiveness in any welded fabrication. The paper attempts to review the history and role of gases in the development of the welding and cutting processes through the years till the modern times.

Dry and wet abrasive resistance of Inconel 600 and stellite

This paper is a comparative study of the influence of different parameters in abrasive wear in dry and wet conditions of Inconel 600 and stellite. The parameters considered are chemical composition and microstructure characteristics. These alloys are deposited by the shield metal arc welding (SMAW) process, on ASTM A-36 steel. The abrasion tests were carried out using a dry sand/rubber wheel tribotester and a wet sand/rubber wheel tribotester. Tests were done following ASTM G 65–94 and ASTM G 105—89 standards, respectively. The results showed that the hardness and wear resistance of Inconel 600 and stellite coatings depend on the generated carbides. An austenitic matrix may be used to verify the behaviour of both coatings under dry and wet conditions.

An image-guided mobile robotic welding system for SMAW repair processes

Conventionally, shield metal arc welding (SMAW) has been performed by manual operator, and hence it is not easy to apply in hazardous areas such as in nuclear power plants. An image-guided mobile robotic welding system is developed in this study for the automation of the SMAW process. The position of cracks can also be determined by this image-guided mobile robotic welding system. We installed two CCD cameras, a five-axis SCORBOT-ER VII robot and SMAW equipment on a mobile vehicle. The cameras are installed in parallel and can be used to detect the position of any cracks beforehand; the robot is then driven at a constant welding speed along the welding path. Based on the binocular images captured by the CCD cameras, an on-line algorithm is used to compare the disparities between the two images and to obtain the welding paths for the cracks. Since the electrode is consumed during the SMAW process, the robotic joint trajectories need to be modified to keep the end of the electrode on tracking on the desired welding path. The control system determines the feeding velocity of the electrode from the measured welding current and joint positions and modifies the joint trajectories correspondingly. The experimental results show that our system can effectively perform SMAW operations resulting in good quality welding. Also, the variation of the welding current in our system is much smaller than that operated by even senior technicians.