Valtair Antonio Ferraresi

Identification and control of metal transfer in pulsed GMAW using optical sensor

Abstract The aim of the present work was to design and develop an identification device for droplet detachments during pulsed GMAW and to assess the possibility of implementing a metal transfer control system. The developed identification device was based on a luminescence sensor and an electronic interface, capable of sensing the arc light flux. A basic control system for the pulse parameters was implemented using an A/D–D/A board for receiving signals from the sensor and sending instructions to an electronic power source and a trained neural network for the metal transfer recognition. Alternatively, the signal from the electronic interface could be directed to a microcomputer with a dedicated monitoring program. Automated pulsed welding was carried out on plain carbon steel, aluminium and stainless steel plates in the flat position. The metal transfers were recorded using a high speed camera and applying the shadowgraphy technique to validate the device performance. The results showed that the detachment device was efficient and consistent for aluminium (best results), stainless steel and low carbon welding. Moreover, the control system was capable of setting parameters that provided stable transfer at one drop per pulse rate, from welds starting at inadequate pulse parameter levels.

Metal transfer in the aluminum gas metal arc welding

Among the aluminum welding processes, the GMAW (Gas Metal Arc Welding) process can be easily made automatic, has high productivity and great versatility regarding the type and thickness of material used in welding. The possibility of changing the transfer mode to adapt to different thickness, joint types, among other aspects, is another important and attractive feature. However, little is known about the transfer modes in aluminum GMAW process. For this reason, in this study an analysis of the metal transfer modes in the aluminum welding was made, and the objective was to generate maps that could identify the metal transfer modes and their regions in relation to the shielding gas and the wire diameter. The experimental procedure was the execution of weld on aluminum plate in a flat position with a constant voltage power source. The methodology used was laser Shadowgraphy combined with a high-speed movie camera. Therefore, it was possible to design the maps in which four metal transfer modes and their respective transition zones were determined. The maps also permit determination of the transition current zone between the globular and the spray mode, and modeling of the melting rate.

Análise da microestrutura e da resistência ao desgaste de revestimento duro utilizado pela indústria sucroalcooleira

O setor sucroalcooleiro tem apresentado um expressivo crescimento nos ultimos anos no Brasil, entretanto, a manutencao das industrias apresenta um elevado custo devido a perda de metal dos equipamentos por mecanismos de desgaste. O objetivo deste trabalho e avaliar a resistencia ao desgaste abrasivo e a microestrutura de revestimentos duros depositados em camada unica. Foram utilizados quatro tipos de consumiveis utilizados na industria sucroalcooleira: um eletrodo revestido da liga FeCrC de 4,0 mm de diâmetro e tres arames tubulares autoprotegidos de 1,6 mm de diâmetro, de ligas FeCrC, FeCrCNb, FeCrCTiMo. O metal de base utilizado foi um aco SAE 1020. As soldagens com os arames tubulares foram efetuadas no modo de transferencia por curto-circuito, com mesmos valores de corrente e tensao de soldagem. Para o ensaio de desgaste utilizou-se o abrasometro Roda de Borracha, segundo a norma ASTM G65-91. Os corpos de prova de desgaste foram retirados da regiao central das chapas de testes e da mesma regiao retirou-se dois conjuntos de amostras para analise microestrutural (microscopia otica). Os resultados dos ensaios com a roda de borracha mostrou que a liga FeCrCNb apresenta maior resistencia ao desgaste, seguida do eletrodo revestido e com pior desempenho a liga FeCrCMoTi e a liga FeCrC. A liga FeCrC (tanto para o eletrodo revestido como para o arame tubular) apresentou microestrutura formada por carbonetos primarios M7C3 distribuidos em uma matriz de menor dureza; a liga contendo Nb apresentou microestrutura similar alem da presenca de carbonetos NbC; por sua vez, a liga com adicao de Ti e Mo apresentou a presenca de grandes carbonetos primarios de titânio.The Brazilian sugar/alcohol sector presented expressive growth in recent years. However, maintenance cost is high due to metallic losses by wear. This paper studies the application of hardfacing by flux cored arc welding on the wear resistance and microstructure of single layer weld beads. Four types of consumable were used: three selfshielded flux cored wires of 1.6 mm diameter of alloys FeCrC, FeCrCNb, FeCrCMoTi and a covered electrode of FeCrC alloy of 4 mm diameter. The base metal was SAE 1020 steel. Test specimens were evaluated using Rubber Wheel Abrasion Test (ASTM G65). The selfshielded flux cored wires were welded in short-circuit transfer mode with the same current and voltage values. Wear evaluation was by mass loss and microstructure analysis by optic microscopy. The results of the trials with Rubber Wheel Test showed that the FeCrCNb alloy presented the largest wear resistance, followed by the covered electrode. The FeCrC+Ti alloy and the FeCrC alloy presented the worst performance. The FeCrC alloy (for both covered electrode and tubular wire) presented microstructure formatted by primary M7C3 carbides distributed in a smaller hardness matrix; the alloy containing Nb presented a similar microstructure apart from its carbides that were mainly NbC. The alloy with Ti and Mo addition presented large titanium primary carbides.

A quality and cost approach for welding process selection

The aim of this work was to propose, apply and evaluate a methodical approach to select welding processes in a productive environment based on market requirements of Quality and Costs. A case study was used. The welds were carried out in laboratory, simulating the joint conditions of a manufacturer and using several welding processes: SMAW, GTAW, pulsed GTAW, GMAW with CO2 and Ar based shielding gases and pulsed GMAW. For Quality analysis geometrical aspects of the beads were considered and for Cost analysis, welding parameters and consumable prices. Quantitative indices were proposed and evaluated. After that, evaluation of both Quality and Costs was done, showing to be possible to select the most suitable welding process to a specific application, taking into account the market conditions of a company.

Influence of welding current in plasma–MIG weld process on the bead weld geometry and wire fusion rate

One of the versions of the plasma–metal inert gas (MIG) process is basically a combination of a plasma arc with a MIG/metal active gas (MAG) arc in a single torch. With this association, the advantages of each arc are combined. The main characteristic of this is the independence between the heat input by the process and the deposited material, resulting in greater facility to control bead weld geometry. In the current literature, there is a shortage of information related to the process, and most of this goes back to the 1970s and 1980s when the technology available was not able to make the process viable for industry. However, in recent years, the use of the diffusion of new electronic power sources used in welding has sparked up again the interest in plasma–MIG process. In this context, this paper aims to contribute to the studies related to the influence of the MIG and plasma current balance on the geometry of the bead weld and wire fusion rate. Bead-on-plate welds were carried out with plasma and MIG/MAG current combinations at three levels each, keeping, by welding speed corrections, the bead volume the same. It was observed that the introduction of the plasma current over the MIG/MAG current reduces penetration and dilution and leads to convex beads. On the other hand, the use of plasma current increases the MIG/MAG wire fusion rate. However, it seems that the intensity of the plasma current is not the governing parameter of those changes.

Ferritic stainless steel welding with the A-TIG process

The main advantage of the TIG with flux process (A-TIG welding) is the possibility of obtaining greater penetration of the weld bead while employing the same welding parameters as conventional TIG welding. Various studies have shown the influence of active fluxes on the geometric characteristics of stainless steel austenitic welds. However, little is known about the influence of this process on the geometric and metallurgical characteristics of the weld beads in ferritic stainless steels. In this work, different types of flux are applied when welding ferritic stainless steel with the objective of verifying possible influences on the weld beads profile, on its visual appearance, on the microstructure, on the hardness of the welded zone and on the impact resistance (Charpy test). The bead-on-plate welds were produced without using any addition metal. Six types of flux were used – one being an oxide produced in a laboratory (TiO2) and five commercial fluxes. The results showed that use of the flux allows an increase in penetration with significant changes in the appearance of the weld bead. It was also confirmed that the microstructure and the hardness of the weld bead for the steel studied were not affected by the type of flux used, with the microstructure analysed under an optical microscope. The steel in the study showed a high degree of fragility at ambient temperature.

Soldagem de um aço inoxidável ferrítico com o processo A-TIG

The A-TIG welding process presents as main advantage the possibility of increase in the penetration depth using the same parameters as conventional TIG welding. Many researchers show the influence of the active flux on the weld geometry in austenitic stainless steel, however little it is known of the influence of this process in the weld fillet shape and metallurgic characteristics of the weld fillet in ferritic stainless steel. In this work different types of flux are applied with the objective to verify possible influences on the weld fillet in ferritic stainless steel welding, such its visual aspect, the microstructure, the hardness and resistance to the impact of the fusion zone. Bead on plate welds were made without metal filler. Six types of flux had been used, and one flux was prepared in laboratory (TiO2) and the others five were commercial flux. The results indicate that the use of the flux allows increase in the penetration with significant changes in the aspect of the weld fillet. It was verified that the microstructure and the hardness of the weld fillet of this ferritic stainless steel was not been affected by the flux type. The result of the Charpy test in the metal base it was batter in the fusion zone.

The influence of parameter settings on cathodic self-etching during aluminum welding

Abstract Cathodic self-etching is a mechanism that has been used for a long time to make feasible the GTA welding of aluminum, by cleaning the metal surface in real time. The use of power supplies with rectangular wave AC output has extended the efficiency of the phenomenon. The objective of this work is to gain further insight into this matter. A study of the influence of the power source output parameters and travel speed on cathodic etching and, consequently, on welding geometry and arc stability is presented. An experimental design based in the robust design technique was applied to make the number of experiments affordable. The obtained tendencies were confirmed by validation experiments and comparison with the results of other authors: The results suggest the beneficial effect of a short electrode positive duration and increasing travel speed on oxide cleaning. Too effective cathodic etching leads to arc instability during polarity reversal. The negative electrode amplitude and duration does not govern this aspect, yet they govern the bead geometry. Finally, a theoretical explanation of the phenomena is proposed.

Análise da resistência ao desgaste de revestimento duro aplicado por soldagem em facas picadoras de cana-de-açúcar

The Brazilian sugar/alcohol sector presented expressive growth in recent years. However maintenance cost is high due to metallic losses by wear. This paper studies the application of hardfacings by flux cored arc welding on the wear resistance of sugarcane shredder knives comparing laboratory and field-test results. Four types of consumable were used: three selfshielded flux cored wires of diameter 1.6 mm of alloys FeCrC, FeCrC+Nb and FeCrC+Ti and a covered electrode of FeCrC alloy of diameter 4.0 mm. The base metal is SAE 1020 steel. Test specimens were evaluated using rubber wheel abrasion tests (ASTM G65). Sugarcane shredder knives hardfaced in the same welding conditions were also tested on a shredder in an alcohol distillery. Wear evaluation is by mass loss. The flux cored wires were welded in short-circuit transfer mode with the same current and voltage values. The wire with Nb had the highest wear resistance in laboratory test but due to cracks and spalling had the least wear resistance in field test. The FeCrC and FeCrC+Ti wires presented the worst results in laboratory tests and the best results in field test, respectively. In comparison with the covered electrode, the FeCrC+Nb wire presented similar performance in laboratory and the FeCrC+Ti wire presented similar performance in field tests.

Shielding gas influence on the ferritic stainless steel weldability

Abstract Ferritic stainless steels are not characterized by good weldability. Wires made of austenitic stainless steels are usually applied to join ferritic materials because of the good mechanical resistance, tenacity, and ductility reached by austenitic weld metal. However, novel ferritic stainless steel wires, stabilized with niobium and titanium, have been developed to tackle the target of matching the required mechanical properties and keeping the costs lower by using ferritic stainless steels. The characterization of these wires concerning weldability aspects (operational and metallurgical) has not been accomplished yet. The aim of the present study was to investigate the influence of the shielding gas composition (pure argon and mixtures with O2 or CO2) on the chemical composition and microstructure of weld deposits obtained with gas metal arc welding using stabilized ferritic wires (ER430Ti and ER430LNb). The study was made comparatively to a non-stabilized wire (ER430). For each combination gas/wire, three layers of beads were deposited. To prevent interference from base metal dilution, a UNS 43932 was used as support for the layers and only the last layer was analysed. A special experimental approach was applied to permit more reliable comparison among different combinations of wire-shielding gas. Predicted equations for the demanded level of stabilizers in the wire were successfully applied. The results showed that the shielding gas composition played an important role in determining the final chemical composition and microstructure of the deposits, but its effect was dependent on the chemical composition of the deposit as a rule. In general, it was confirmed that the increase in CO2 in the shielding gas augmented the carbon content (and martensite formation) in the weld metal, but wire stabilized with niobium could prevent this detrimental effect but was not able to arrest grain coarsening. There were always losses of alloying elements due to the presence of O2/CO2, but the intensity depended on the amount of titanium/niobium.