Cícero Murta Diniz Starling

Statistical modelling of narrow-gap GTA welding with magnetic arc oscillation

Abstract Statistical experimental design and linear-regression modelling were used to study the effect of the welding parameters on the bead shape in a narrow gap-GTAW process with magnetic are oscillation. It was shown that, for the conditions studied, are oscillation has little influence on the lateral fusion of the joint, although it favourably influences the shape of the bead. The undercutting level tended to increase rapidly when the gap width was reduced. Optimized welding conditions are presented, based on models calculated from the experimental data.

Bead characterization on FCAW welding of a basic tubular wire

This work aimed to study the effect of some operational conditions on the characteristics of beads produced by a Brazilian-made basic tubular wire (ASME SFA-5.20: E71T-5/E71T-5M), 1.2 mm in diameter, intended for welding common structural carbon steels with low and medium levels of carbon. Welding tests were carried out, in a flat position, on thick plates (12 mm thick) of common low-carbon steel using a source operating in constant voltage mode and with continuous monitoring of the arc current, arc voltage, and feed speed (fusion) values for the wire. The composition of the shielding gas (75%Ar–25%CO2 and 100%CO2), the electrode polarity (positive and negative), and the wire feed speed (7 and 9 m/min) were varied. The other welding parameters were kept fixed, including the energized lengths of the electrode (16 mm) and the arc (3.5 mm). The effects of the operational conditions on the main characteristics of the bead were evaluated including its geometry (penetration, reinforcement, width, welded area, deposited area and dilution), presence of discontinuities, microstructure, and hardness. For the basic wire, the operational conditions with the highest productivity (the highest deposit rate) associated with a bead with suitable characteristics for welding thick plates of structural steels were assessed.

Comparison of operational performance and bead characteristics when welding with different tubular wires

The aim of this work was to make a comparative study of the characteristics of the weld bead produced by nationally manufactured tubular wires; all rutilic (ASME SFA-5.20: E71T-1/E71T-9/E71T-9M), basic (ASME SFA-5.20: E71T-5/E71T-5M) and ‘metal cored’ (ASME SFA-5.18: E70C-3M), 1.2 mm in diameter, intended for the welding of structural steels with low and medium levels of carbon. Welding tests were carried out, in the flat position, on thick plates (with a thickness of 12 mm) of common low-carbon steel using a source operating in ‘constant voltage’ mode, with monitoring of the current and voltage signals of the arc and feed speed (fusion) of the wire. The following were varied in welding with each type of tubular wire: the composition of the shielding gas (75%Ar–25%CO2 and 100%CO2) and the feed speed of the wire (7 and 9 m/min). The other parameters were kept fixed, including the polarity of the electrode (DC+) and the energized lengths of the electrode (16 mm) and of the arcs (3.5 mm). For the different tubular wires, there was a comparative analysis of the principal weld bead characteristics, including its geometry (penetration, reinforcement, width, fused area, deposited area and dilution), presence of weld discontinuities, microstructure and hardness. Operational conditions that yielded weld bead characteristics that favoured the welding of thick plates of structural steels were determined.

Characterization of GMAW arc instability phenomena related to low oxidation potential shielding gases

Characterizing instability phenomena in arc welding may be a complex task, since they depend on a number of interrelated factors. Such phenomena may manifest themselves in various ways, acting on the characteristics of the arc, the metal transfer, the amount of splatter and fumes formed, the arc format, the geometry of the bead and other aspects of welding. The literature on the subject reports diverse forms of instability associated with arc welding with solid wire and gas shielding (GMAW). This work aimed to define the instability phenomena associated with the GMAW process in welding with gases with a low oxidation potential. To do so, the welding current and voltages were monitored and metal transfer was filmed at high speed. The welding tests were carried out on plates of common carbon steel with a source operating at a constant current and an electrode with positive polarity. By synchronizing the filming with the welding current and voltage signals, the results showed that, during the periods of highest voltage, the transfer tended to be globular repulsive, as opposed to spray transfer during the lowest voltage periods. The synchronization of the electrical signals with the optical sensor indicates that, during periods of unstable operation, the arc is more luminous. It also showed that more fumes were generated during these periods.

Bead characterization of FCAW of a rutilic fluxed core wire

This paper studies the effect of operational conditions on bead shape characteristics in fluxed core arc welding with a Brazilian-made wire with rutilic flux (ASME SFA-5.20: E71T-1/E71T-9/E71t-9M) of 1.2 mm in diameter. Bead-on-plate downhand welding trails were performed on 12 mm-thick low-carbon steel plates with a constant voltage power supply. A digital data logging system was used to measure the welding current and voltage, and wire feed rate. While the shielding gas composition (75% Ar–25% CO2 and 100% CO2), wire polarity, and feed rate (7 and 9 m/min) were varied during the trials, the electrode voltage (16 mm) and arc length (3.5 mm) were not changed. Weld bead characteristics (penetration depth, width, and fused and deposited areas), the presence of discontinuities, bead microstructure, and hardness were evaluated. Welding conditions of high productivity (high deposition rate) associated with adequate bead characteristics were determined for the wire.

Metal transfer evaluation of tubular wires

Arc welding with tubular wire (FCAW) is a process that combines the principle advantages of welding with solid wire and shielding gases (GMAW), with a high work rate by the welder, high rate of deposit, and high returns, resulting in high productivity and quality of the weld produced. It also includes the advantages of manual welding with clad electrodes (SMAW), such as high versatility, the opportunity to adjust the chemical composition of the weld bead and ease of operations in the field. The shielding of the arc and of the weld bead is made by the welding flux being contained within the electrode, which may be supplemented by a gas flow supplied by an external source. In FCAW welding, as in other welding processes with a consumable electrode, the electrode material needs to be heated from its initial temperature up to its melting temperature and then fused and separated (transferred) from the electrode to the weld pool. The way in which the fused metal transfers from the electrode to the weld pool influences various operational aspects of the welding, particularly the level of splashes and fumes, the capacity of the process to be used outside the flat position, the format of the bead and, finally, the stability and the operational design of the process. Various techniques can be used to study the transfer of the addition metal. However, the techniques most commonly used can be grouped into three basic categories: mechanical methods, cinematic methods (using profilographs) and indirect methods (measurement of secondary effects). Mechanical techniques are based on the collection, by means of some device (for example, a rotating disc and solid cover when the arc is open) of the individual drops of additional metal. Indirect methods include the measurement and analysis of a parameter related to the transfer process, for example, the current and / or voltage of welding, light, sound, etc. The profilograph technique is considered to be the most suitable for the study of metal transfer in welding, being used in various works and revised extensively by Vilarinho and Scotti. This technique consists of casting the shadow projected by various elements (such as the electrode, drops and plate) onto a photographic film or directly onto the lens of a film camera. As the light of the arc is very intense and radiates in all directions, it is not possible to utilise it to produce this shade, and therefore a source of additional light is needed, which is normally produced by a He–Ne laser. By using special optical filters that only allow the light of the laser through (and block, almost totally, the light of the arc) it is possible to obtain the shadow of the elements intercepted by the laser. To study adequately the rapid events that occur during the metallic transfer in welding, it is necessary to film or photograph the shadow of the drops transferred at very high speed. With the use of a high-speed camera (with the capacity to film 1000 frames per second or more), it is possible to make a better evaluation of the metallic transfer, as well as to measure with greater precision the average size of the drops and the frequency of transfer of the same. Due to the development of the GMAW process, the major part of the investigations were conducted using this process, partially due to its optimal characteristics for observing the transfer of metal (it allows operations with an open arc, without slag, and with a lower level of fumes or smoke). Modenesi carried out an extensive review of the principal characteristics of metal transfer in this process. In the FCAW process, the form of metal transfer depends particularly on the characteristics of the flux in the nucleus of the wire, since, up to the moment, these were not sufficiently established. According to Norrish, basic tubular wires operate normally with non-axial transference globular for high currents and short-circuits for lower currents. In this case, the non-fused flux forms a clear column, which projects away from the wire in the direction of the arc. Again, according to Norrish, rutile tubular wires operate normally at high currents by projecting a non-axial transfer spray. Part of the flux forms a layer of slag on the surface of the drop, a small quantity decomposes to form shielding gases and the remaining part of the flux is transferred to the weld pool where it is fused and produces a layer of protective slag. According to Bracarense et al. who studied the transfer of metal in welding a tubular rutile wire using 75 % Ar–25 % CO 2 , the flux forms a column that touches the weld pool and Metal transfer evaluation of tubular wires

Comparação do desempenho operacional e das características do cordão na soldagem com diferentes arames tubulares em polaridade negativa

This paper compares the bead characteristics of welds deposited of carbon steel tubular wires. Three tubular wires of 1.2mm produced in Brazil were used: rutilic (ASME SFA-5.20: E71T-1/E71T-9/E71T-9M), basic (ASME SFA-5.20: E71T-5/E71T-5M) and metal cored (ASME SFA-5.18: E70C-3M). Welding trials were performed in downhand position on thick (12 mm) low-carbon steel plates using a constant voltage power supply in negative wire polarity (CC-). Welding current and voltage, and wire feed rate were monitored in all trials. For each tubular wire type, the shielding gas composition (75%Ar-25%CO2 and 100%CO2) and wire feed rate (7 and 9 m/min) were changed, and other process variables, including electrode and arc lengths (16 mm and 3.5 mm, respectively) were kept constant throughout the experimental program. Weld bead geometry parameters (penetration depth, reinforcement, width, fused and deposited areas, and weld dilution), presence of weld discontinuities, fusion zone microstructure and hardness were measured and compared for the different tubular wires. Operational conditions that yielded weld bead characteristics favored for the welding of thick plates of structural steels on negative wire polarity were determined.

Comparação do desempenho operacional e das características do cordão na soldagem com diferentes arames tubulares

This paper compares the bead characteristics of welds deposited of carbon steel tubular wires. Three tubular wires of 1.2 mm produced in Brazil were used: rutilic (ASME SFA-5.20: E71T-1/E71T-9/E71T-9M), basic (ASME SFA-5.20: E71T-5/E71T-5M) and metal cored (ASME SFA-5.18: E70C-3M). Welding trials were performed in downhand position on thick (12 mm) low-carbon steel plates using a constant voltage power supply. Welding current and voltage, and wire feed rate were monitored in all trials. For each tubular wire type, the shielding gas composition (75%Ar-25%CO2 and 100%CO2) and wire feed rate (7 and 9 m/min) were changed, and other process variables, including electrode polarity (CC+), electrode and arc lengths (16 mm and 3.5 mm, respectively) were kept constant throughout the experimental program. Weld bead geometry parameters (penetration depth, reinforcement, width, fused and deposited areas, and weld dilution), presence of weld discontinuities, fusion zone microstructure and hardness were measured and compared for the different tubular wires. Operational conditions that yielded weld bead characteristics favored for the welding of thick plates of structural steels were determined.

Proposed model for the fusion of tubular wires

Arc welding with tubular wire (FCAW) is a process that combines the principle advantages of welding with solid wire and shielding gases (GMAW), with a high work rate by the welder, high rate of deposit, and high returns, resulting in high productivity and quality of the weld produced. It also includes the advantages of manual welding with clad electrodes (SMAW), such as high versatility, the opportunity to adjust the chemical composition of the weld bead and ease of operations in the field. The shielding of the arc and of the weld bead is made by the welding flux being contained within the electrode, which may be supplemented by a gas flow supplied by an external source. In the FCAW process, the metallic part of the wire is principally responsible for conducting the electrical current to the arc. The arc occurs outside the flux and, therefore, the conditions for fusion of the flux are less favourable than in the submerged arc welding (SAW) process. In GMAW welding, as in other welding processes with a consumable electrode, the electrode material needs to be heated from its initial temperature, around room temperature, up to its melting temperature and then fused and separated from the electrode. The speed with which the electrode is fused must be, on average, the same as the speed at which it is supplied in order to keep a relatively constant arc length. In these conditions, for GMAW, FCAW and SAW processes operating in conditions in which only a few short circuits occur, it can be considered that a stationary state has been achieved when the energized length of the electrode – the stick out – is kept relatively constant if the distance from the contact tip to the part does not alter. Therefore, the temperature distribution in the electrode must be kept approximately constant during welding. On the other hand, in the SMAW process, since the length of the electrode varies continuously to the extent that it is consumed, the temperature distribution in the electrode changed continuously during welding. 1.1 Fusion of solid wires

Análise do processo de projeto em obras de readequação predial em instituição universitária pública

The present paper aims to develop an exploratory analysis of the design process for building retrofitting construction in public university institution. The method employed is the multiple case studies, one of them presented here. Firstly, it is presented a theoretical background for the study. From methodological procedures described in the study, through case studies from sources of evidence such as document analysis, direct observation of work routines, interviews and visits to constructions, the functional structure of the Institution and its relation to the design process is characterizes, as well as the workflows of the design process that characterizes the cases studied. One of the three designs studied is characterized, presented the flow of information throughout the design process, and relevant aspects of it, such as programming, detailing the phases, monitoring and coordination. The main problems of the projects are identified from the visit to the constructions and documentary analysis, and an analysis of these problems is made in light of the design process. Guidelines for the improvement of the design process are briefly outlined, taking into account the particularities of the designs in public university institutions.