Manual Metal Arc Research Articles

Experimental investigation and modelling of WEDM process for machining nano-structured hardfacing material

In recent years, nano-structured hardfacing alloy constituting fine carbides, borides and boro-carbides have become pioneered in modern manufacturing industries due to their superior properties (excellent hardness, toughness and wear resistance) even at elevated temperatures. A nano-structured hardfacing alloy component was produced using manual metal arc welding process for making turning tool insert. The present paper investigates the effect of wire electrical discharge machining (WEDM) parameters such as discharge pulse time, discharge stop time, servo voltage, wire tension and wire feed rate on machining performances viz. material removal rate, machining time and surface roughness after proof-machining of welded nano-structured hardfacing material. Taguchi’s (L25) orthogonal array has been used to perform the experimental runs using conventional brass wire and zinc-coated wire electrodes, respectively. A combination of Taguchi’s robust design concept with principal component analysis has been applied to optimize the process parameters. For brass wire, the optimal settings of the input process parameters corresponds to discharge pulse time 0.45 µs, discharge stop time 8 µs, servo voltage 35 V, wire tension 800 g and wire feed rate 7 m/min, respectively. Similarly, for zinc-coated brass wire, the corresponding settings are discharge pulse time 0.5 µs, discharge stop time 11 µs, servo voltage 41 V, wire tension 600 g and wire feed rate 7 m/min. This paper also establishes the inter-relationships of various WEDM machining parameters and performances by employing response surface methodology-based approach. A confirmation test has also been carried out with the optimal process parameters to conform to the experimental result.

Technological Aspects Regarding Manual Metal Arc Welding Using Pulsed Current for Fillet Joints Applications

The idea of using electrical pulse current at manual arc welding with coated electrode starts from the observation of frequency influence, unchanging in manual TIG welding with filler materials, on weld pool volume, by partial solidification of the weld pool in base time of the pulse current, thus being able to control its volume.This paper presents for the first time this new challenge of inverter modern sources: manual metal arc welding using pulsed current.Experimental research findings highlight the technological aspects when using pulsed current in manual metal arc welding, using STEL welding equipment that has this option. The application - concerns the establishment the lack of fusion welded joints in fillet positions. It highlights the beneficial effect of pulsed current, in particular by the joint penetration.Experiments have pursued highlighting of welding pulsed current and frequency of the pulses by the appearance of the joint and the influence by weld geometry for lack of fusion fillet joint. Also, the influence of frequency pulsed current by arc stability, sprays, etc. compared with standard welding was observed.

Methodology for Estimating Thermal and Neutron Embrittlement of Austenitic Stainless Steel Welds During Service in Light Water Reactors

The effect of thermal aging on the degradation of fracture toughness and Charpy-impact properties of austenitic stainless steel (SS) welds has been characterized at reactor temperatures. The solidification behavior and the distribution and morphology of the ferrite phase in SS welds are described. Thermal aging of the welds results in moderate decreases in Charpy-impact strength and fracture toughness. The upper-shelf Charpy-impact energy of aged welds decreases by 50–80 J/cm2. The decrease in fracture-toughness J integral-resistance (J-R) curve or JIc is relatively small. Thermal aging has minimal effect and the welding process has a significant effect on the tensile strength. However, the existing data are inadequate to accurately establish the effect of the welding process on fracture properties of SS welds. Consequently, the approach used for evaluating thermal and neutron embrittlement of austenitic SS welds relies on establishing a lower-bound fracture-toughness J-R curve for unaged and aged and nonirradiated and irradiated SS welds. The existing fracture-toughness J-R curve data for SS welds have been reviewed and evaluated to define lower-bound J-R curves for submerged arc (SA)/shielded metal arc (SMA)/manual metal arc (MMA) welds and gas tungsten arc (GTA)/metal inert gas (MIG)/tungsten inert gas (TIG) welds in the unaged and aged conditions. At reactor temperatures, the fracture toughness of GTA/MIG/TIG welds is a factor of about 2.3 higher than that of SA/SMA/MMA welds. Thermal aging decreases the fracture toughness of all welds by about 20%. The potential combined effects of thermal and neutron embrittlement of austenitic SS welds are also described. Lower-bound curves are presented, which define the change in coefficient C and exponent n of the power-law J-R curve and the JIc value for SS welds as a function of neutron dose. The potential effects of reactor coolant environment on the fracture toughness of austenitic SS welds are also discussed.

RESEARCH OF TECHNOLOGICAL PROPERTIES OF STEEL X6CRNITI18-10 WELDED JOINTS EXPLOITED IN NITRIC ACID MEDIUM / PLIENO X6CRNITI18-10, EKSPLOATUOJAMO AZOTO RŪGŠTIES TERPĖJE, VIRINTINIŲ JUNGČIŲ TECHNOLOGINIŲ SAVYBIŲ TYRIMAS

The repair of chemical industry equipments often requires to replace long time operated pipes or welded inserts with the simi-lar chemical composition. During the study the joints from corro-sion resistant steel X6CrNiTi18-10 were welded by manual metal arc welding with covered electrodes (MMA process 111) and tungsten inert gas welding (TIG process 141) at different welding parameters. The visual, radiographic, penetrant control and ferrite content analysis were carried out. The transverse tensile and bending samples were produced from welded samples; also the macroscopic and microscopic analyse were carried out. Atliekant chemijos pramonės įrenginių remontą, dažnai tenka pakeisti ilgą laiką eksploatuotus vamzdžius ar įvirinti analogiškos cheminės sudėties intarpus. Tyrimo metu suvirintų jungčių bandomieji pavyzdžiai iš korozijai atsparaus plieno X6CrNiTi18-10 buvo suvirinti rankiniu lankiniu būdu glaistytaisiais elektrodais (111 MMA procesas) ir lankiniu suvirinimu volframo elektrodu inertinėse dujose (141 TIG procesas), esant skirtingiems suvirinimo režimų parametrams. Suvirintiems bandiniams buvo atlikta vizualinė, radiografinė, spalvinė kontrolė, nustatytas išsiskyrusio ferito kiekis. Iš suvirintų ruošinių buvo pagaminti skersinio tempimo, lenkimo bandiniai, taip pat atlikti virintinių jungčių makroskopinis ir mikroskopinis tyrimai.

Fatigue Life Evaluation of Fillet Welded Cruciform Joints with Load-Carrying Welds

Fatigue life of fillet welded cruciform joints with load-carrying welds conforming to Constructional Detail 26 (Detail Category 52) of IS 800: 2007 and made of IS 2062 Gr. E 300 steel plates of two different thicknesses was evaluated. The joints were formed by Manual Metal Arc welding conforming to IS 9595: 2003. The studies were carried out at various values of maximum stress which were decided as a percentage of the yield strength of the base material. The fatigue life values obtained were compared with the S–N data estimated based on the recommendations given in EN 1993-1-9 and IS 800: 2007. The effect of change in thickness of intermediate plate on the fatigue life of fillet welded cruciform joint with load-carrying welds was studied. Finite element analysis was also carried out using ABAQUS software; stress intensity factor range values were obtained and based on the principles of linear elastic fracture mechanics, fatigue life of the joint was predicted for different values of stress range.

Determination of the welding machine electromagnetic field effect on health safety and protection

In this paper the influence of the MMA welding machine based welding apparatus radiation on the welder's safety as well as the security and the protection measures have been presented. The influence of light, infrared and ultraviolet radiation as well as the impact of the electromagnetic radiation on the certain parts of the welder body during welding and idling have been considered where the different welding conditions in manual metal arc welding process with coated electrodes (111) on welding machine have been employed.

Restoration of Railway Turnout Elements with Manual Metal Arc Welding and Flux-Cored Arc Welding

The paper describes the experiment during which to evaluate potential time and material economy railway turnout element, in particular stock rail, was restored using two different welding methods – manual metal arc welding (MMA) currently used by Latvian Railway and flux-cored arc welding (FCAW). For quality control restored stock rails were further examined with metallographic examination. Performed experiment revealed that, if restoration is performed strictly following technical procedures, the restored elements are of equally high quality; however, FCAW has considerable time and material economy, consequently also cost economy in comparison with MMA.

Destructive Testing of the Weld Joints on Split Sleeve for Branch Connections Repairs

New type of repairing technology for branch connection defects on gas pipelines has been designed recently. Repairing technique is based on manufacturing of split sleeve and welding of its parts together and to the repaired pipes by manual metal arc welding technology. Appropriate testing has to be performed to ensure practical and permanent use of such kind of sleeve in commercial area. Destructive testing was performed to confirm quality of the welds on the prototype sleeve repair. Macrostructural and hardness evaluation showed inhomogeneity present in some welds. According to that, microstructure observations, spectral analysis and mechanical tests were performed on the base metal of the sleeve. It has been showed that even when some problems may be present, repairing technique by split sleeve can be still suitable for permanent repairs of the defects of the branch connections.

FINITE ELEMENT MODEL FOR PREDICTING RESIDUAL STRESSES IN SHIELDED MANUAL METAL ARC WELDING OF MILD STEEL PLATES

This paper investigates the prediction of residual stresses developed in shielded manual metal arc welding of mild steel plates through Finite Element Model simulation and experiments. The existence of residual stresses that cause fatigue and distortion in welded structures has been responsible for failure of machine parts in service. These stresses if not properly controlled can lead to loss of lives and property. The highlight is that various trial and error welding runs have to be carried out while hoping for the best performance during operation. This is wasteful of time, material and finance. Thus the need to incorporate Finite Element Analysis prediction of residual stresses by computational methods to first determine satisfactory welding conditions before actual production. The geometry of the butt welded Low Carbon (ASTM A36) steel plates was modeled and the residual stresses simulated using ANSYS Multiphysics V14. Three experimental samples of similar geometry were also produced using the shielded manual metal arc welding process to verify the result. Low carbon steel (ASTM A36) was used as the parent metal, E066 electrodes were used to complete the weld. The generated residual stresses were measured using an X-Ray Diffractometer (XRD 6000). From the Finite Element Model Simulation, the transverse residual stress in the x-direction (σ x ) had a maximum value of 375MPa (tensile) and minimum value of -183MPa (compressive) while in the y-direction (σ y ), the maximum value of 172MPa (tensile) and minimum value of zero. The longitudinal stress in the x-direction (σ x ) indicated a maximum value of 355MPa (tensile) and a minimum value of -10MPa (compressive) while in the y-direction (σ y ), the maximum value was 167MPa and the minimum value of the residual stress was -375MPa. The experimental values as measured by the X-Ray diffractometer were of reasonable correlation as transverse residual stress (σ x ) along the weld line in the transverse x-direction varied from 353MPa (tensile) to -209MPa (compressive) while in the y-direction, stress (σ y ) along the weld line varied from 177MPa (tensile) to zero. The longitudinal stress measured by the X-Ray diffractometer in the x-direction (σ x ) varied from 339MPa (tensile) to zero (compressive) while in the y-direction (σ y ) varied from 171MPa (tensile) to -366MPa (compressive). These results shows that the residual stresses obtained by prediction from the finite element method are in fair agreement with the experimental results. Based on this, it can be concluded that Finite Element Model can be used to replicate and determine the expected residual stresses that would be generated before an actual welding process is carried out. http://dx.doi.org/10.4314/njt.v35i1.14

The effects of Mn and Nb on the microstructure and mechanical properties of Alloy 152 welds

Abstract This study was to investigate the synergetic effects of Mn and Nb on the microstructure and mechanical properties of Ni-based welds. The dissimilar weldments of Alloy 690 and SUS 304 L were welded with a manual shielding metal arc welding (SMAW) process. The weld metals were made of a core wire of Alloy 52 coated with fluxes of various Mn and Nb additions. The results showed that an increase in Mn could induce finer grains and smaller Nb-rich phases in the welds, while the dendrites and Mn-oxides became larger. For the welds with 3.99 wt.% Mn and 1.82 wt.% Nb, Nb-rich precipitates and Mn-oxides became smaller, and dendrites grew denser concurrently. The elongation of the welds at room temperature increased with the addition of Mn, but, by contrast, their hardness decreased. High contents of Mn and Nb could improve the notch strength and ductility at 300 °C, while they had little effects on the tensile stress at room temperature. Ductile ridges were the dominant fracture feature of the welds with an addition of Mn. For the welds with 3.99 wt.% Mn and 1.82 wt.% Nb, ridges dotted with small and deep dimples became prevalent.

Effect of Electrode Types on the Solidification Cracking Susceptibility of Austenitic Stainless Steel Weld Metal

The effect of electrode types on the solidification cracking susceptibility of austenitic stainless steel weld metal was studied. Manual metal arc welding method was used to produce the joints with the tungsten inert gas welding serving as the control. Metallographic and chemical analyses of the fusion zones of the joints were conducted. Results indicate that weldments produced from E 308-16 (rutile coated), E 308-16(lime-titania coated) electrodes, and TIG welded joints fall within the range of 1.5≤Creq./Nieq.≤1.9 and solidified with a duplex mode and were found to be resistant to solidification cracking. The E 308-16 weld metal had the greatest resistance to solidification cracking. Joints produced from E 310-16 had Creq./Nieq. ratio < 1.5 and solidified with austenite mode. It was found to be susceptible to solidification cracking. E 312-16 produced joints having Creq./Nieq. ratio > 1.9 and solidified with ferrite mode. It had a low resistance to solidification cracking.

Assessment of the Biological Effects of Welding Fumes Emitted From Metal Active Gas and Manual Metal Arc Welding in Humans

Emissions from a particular welding process, metal inert gas brazing of zinc-coated steel, induce an increase in C-reactive protein. In this study, it was investigated whether inflammatory effects could also be observed for other welding procedures. Twelve male subjects were separately exposed to (1) manual metal arc welding fumes, (2) filtered air, and (3) metal active gas welding fumes for 6 hours. Inflammatory markers were measured in serum before, and directly, 1 and 7 days after exposure. Although C-reactive protein concentrations remained unchanged, neutrophil concentrations increased directly after exposure to manual metal arc welding fumes, and endothelin-1 concentrations increased directly and 24 hours after exposure. After exposure to metal active gas and filtered air, endothelin-1 concentrations decreased. The increase in the concentrations of neutrophils and endothelin-1 may characterize a subclinical inflammatory reaction, whereas the decrease of endothelin-1 may indicate stress reduction.

Life Cycle Assessment of welding technologies for thick metal plate welds

Life Cycle Assessment (LCA) is applied in evaluating environmental impacts of state-of-the-art welding technologies. Manual Metal Arc Welding (MMAW), Laser Arc-Hybrid Welding (LAHW) and two Gas Metal Arc Welding (GMAW) variants are used to join a plate of 20 mm thick structural steel. The LCA results indicate that for 1 m weld seam, MMAW causes the highest environmental impacts in global warming potential (GWP), eutrophication potential (EP), acidification potential (AP), and photochemical ozone creation potential (POCP) among the selected processes, and the LAHW variant performances the least. Filler material and electricity consumptions generally dominate the impacts and reach shares of up to 80% and 61% in the respective impact categories. However, electrode coating consumption in MMAW remarkably contributes impacts on AP and EP, for instance 52% of AP and 76% of EP. Strategies for improvement of the applied welding technologies are discussed.

Comprehensive study of structural integrity of non-load-carrying fillet-welded joint effect with large gap size

The structural integrity of the fillet-welded joint with large gap sizes made by semi-automatic CO2 gas shielded welding is investigated to suggest for the improvement of construction quality standards. An allowable limit on the gap size of welded joints is specified in many construction quality standards based on experimental and empirical results from the welded joints made by manual metal arc welding. Mechanical tests such as hardness, tensile, bending and fatigue were performed to confirm the welded specimen’s quality. Macro observation and dye penetrants inspection were performed on the welded specimen face and weld toe area to verify if any defects are present. Obtained S–N curves from experimental results for the welded specimen with large gap present higher performance compared to the fatigue design S–N curves proposed by the International Institute of Welding (IIW) and UK-HSE.

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.

Simultaneous speciation analysis of chromate, molybdate, tungstate and vanadate in welding fume alkaline extracts by HPLC–ICP-MS

A novel analytical procedure was developed for the simultaneous speciation analysis of chromate, molybdate, tungstate and vanadate by anion-exchange high performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (HPLC–ICP-MS). Linear gradient elution from 100% water to 100% 0.7M NaCl was applied for chromatographic separation of metal species. In standard aqueous solution at neutral pH molybdate, tungstate and vanadate exist in several aqueous species, while chromate is present as a single CrO42- species. Consequently, only chromate can be separated from this solution in a sharp chromatographic peak. For obtaining sharp chromatographic peaks for molybdate, tungstate and vanadate, the pH of aqueous standard solutions was raised to 12. At highly alkaline conditions single CrO42-, MoO42- and WO42- are present and were eluted in sharp chromatographic peaks, while VO43- species, which predominates at pH 12 was eluted in slightly broaden peak. In a mixture of aqueous standard solutions (pH 12) chromate, molybdate, tungstate and vanadate were eluted at retention times from 380 to 420s, 320 to 370s, 300 to 350s and 240 to 360s, respectively. Eluted species were simultaneously detected on-line by ICP-MS recording m/z 52, 95, 182 and 51. The developed procedure was successfully applied to the analysis of leachable concentrations of chromate, molybdate, tungstate and vanadate in alkaline extracts (2% NaOH+3% Na2CO3) of manual metal arc (MMA) welding fumes loaded on filters. Good repeatability and reproducibility of measurement (RSD±3.0%) for the investigated species were obtained in both aqueous standard solutions (pH 12) and in alkaline extracts of welding fumes. Low limits of detection (LODs) were found for chromate (0.02ngCrmL−1), molybdate (0.1ngMomL−1), tungstate (0.1ngWmL−1) and vanadate (0.2ngVmL−1). The accuracy of analytical procedure for the determination of chromate was checked by analysis of CRM 545, Cr(VI) in welding dust loaded on a filter. Good agreement between determined and reported certified values was obtained. For molybdate, tungstate and vanadate the assessment of accuracy was performed by spiking welding fume filters. Good recoveries for all investigated species (98–101%) confirmed the accuracy of the analytical procedure.

Influence of Power Supply Energy Characteristics upon the Stability of MMA Process

The paper provides the results of experimental study of how the technological characteristics (amount of spatter, stability of the welding process) of manual metal arc welding (MMA) depend upon power supplies providing various kinds of energetic impact upon the electrode metal (inverter power supply, diode rectifier). It was established that inverter power supplies (as they reduce peak loading) provide better quality of welds (more stable process, lower amount of spatter) and this reduces the fabrication cost due to the reduction of deseaming operations, lower welding material consumption as well as improving the service reliability of the welding constructions.

Calculation of the Heat Content of the Electrode Metal Droplet When Applying Power Supplies for Manual Arc Welding with Different Volt-Ampere Characteristic

In the paper the authors provide the method for calculating the heat content of the molten electrode metal droplets according to the energy parameters of the power supplies for manual metal arc welding. It was established that the type of the welding power supply has a significant impact upon the temperature, mass and active surface area of the electrode droplets.

Numerical simulation of side heating for controlling angular distortion in multipass MMAW butt welded plates

Distortion is a severe problem in weld products. It depends on various process parameters like plate thickness, current, voltage, type of weld joint and restraints put on. If distortion is not properly dealt during welding then the product may become useless from geometric accuracy point of view. In the present study, a 3-D coupled transient thermal analysis model with auxiliary side heating (parallel heating) is developed to control angular distortion. During analysis, parallel heating flames are placed at several locations from weld line in cross direction. A user defined subroutine is used to apply transient heat source and side heating flames. Element birth and death technique is used to simulate the filler material deposition. One side multipass ‘V’ butt weld configuration is used for this study. A series of observational tests are done with a special experimental fixture using Manual Metal Arc Welding (MMAW) to validate the proposed FEA model. It is found that the angular distortion has decreased from 2 mm to 0.4 mm with change in side heating distance from 50 to 90 mm from the weld line.

Human biomonitoring of aluminium after a single, controlled manual metal arc inert gas welding process of an aluminium-containing worksheet in nonwelders.

Several existing field studies evaluate aluminium welding works but no thoroughly controlled exposure scenario for welding fume has been described yet. This study provides information about the uptake and elimination of aluminium from welding fumes under controlled conditions. In the Aachen Workplace Simulation Laboratory, we are able to generate welding fumes of a defined particle mass concentration. We exposed 12, until then occupationally unexposed participants with aluminium-containing welding fumes of a metal inert gas (MIG) welding process of a total dust mass concentration of 2.5 mg/m(3) for 6 h. Room air filter samples were collected, and the aluminium concentration in air derived. Urine and plasma samples were collected directly before and after the 6-h lasting exposure, as well as after 1 and 7 days. Human biomonitoring methods were used to determine the aluminium content of the samples with high-resolution continuum source atomic absorption spectrometry. Urinary aluminium concentrations showed significant changes after exposure compared to preexposure levels (mean t(1) (0 h) 13.5 µg/L; mean t(2) (6 h) 23.5 µg/L). Plasma results showed the same pattern but pre-post comparison did not reach significance. We were able to detect a significant increase of the internal aluminium burden of a single MIG aluminium welding process in urine, while plasma failed significance. Biphasic elimination kinetic can be observed. The German BAT of 60 µg/g creatinine was not exceeded, and urinary aluminium returned nearly to baseline concentrations after 7 days.