Indian Welding Journal

Pawan Kumar ¹, Kishor P. Kolhe ², Som Ashutosh ¹, C. K. Datta ¹

Affiliations
1 Department of Mechanical Engineering, Delhi College of Engineering, Delhi, IN
2 Department of Mechanical Engineering, Agricultural University, Dapoli - Ratnagiri, IN

Abstract

The present paper depicts the application of pulsed gas tungsten arc welding (pulsed GTAW) for aluminium alloy (AA7039) using various Ar + He (Argon + Helium) mixtures as a shielding gas with sinusoidal AC wave. In this investigation, Taguchi method is used to formulate the experimental layout, to analyse the effect of each process parameter on the bead geometry, and to predict the optimum setting for each welding process parameter. The pulsed GTAW process is employed for a high rate of current rise and decay at a high pulse repetitive rate, which is widely used in the joining of precision parts. Zinc is usually added to improve mechanical properties through formation of hard intermediate phase, such as Mg₂Zn. The main aim of pulsing is to achieve maximum penetration without excessive heat built-up. The use of high current pulses is to penetrate deeply and allow the weld pool to dissipate some of the heat during a proportionately of longer arc period at a lower current. AA7039 is employed in aircraft, automobiles, high-speed trains and high-speed ships due to their low density, high specific strength and excellent corrosion resistance.

Keywords

Pulsed GTA Welding, Aluminum Alloy 7039, Bead Geometry.

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Kishor P. Kolhe ¹, C. K. Datta ²

Affiliations
1 College of Agril. Engg. & Tech, Dapoli, IN
2 Delhi College of Engineering, Delhi, IN

Abstract

The wear characteristics of a multi-pass weld-joint, of a low carbon- manganese structural steel has been studied together with the characteristics of its varying microstructure and hardness at different locations. Attempts have been made to correlate the wear characteristics with the varying microstructure and the varying hardness values in the weld-joint. It is observed that the wear characteristics, e.g. wear rate and coefficient o f wear resistance are considerably dependent only on the microstructure. The various sub zone microstructures observed in the weld metal and HAZ on a SA weld are spherodized, partially transformed; grain refined and grain coarsened area exhibiting predominantly Widmanstatten ferrite with pearlite, with the others sub zones of HAZ reveal polygonal ferrite and pearlite. Depending on the number, size and distribution of inclusions, the weld microstructure varies because of the prevalence of varying cooling rates in weld metal, a wide range of microstructures such as periodic pearlite, grain boundary ferrite with pearlite and side place with cementite along the side plate boundaries. This study has been performed to investigation on the wear of a weld joint of a structural steel and variations in the microstructure at various regions of heat affected zone base metal and a weld metal.

Keywords

Weld, HAZ, Wear, Weld Microstructure, HAZ Microstructure, Hardness.

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Kishor P. Kolhe ¹, C. K. Datta ²

Affiliations
1 Department of Mechanical Engineering, College of Agricultural Engineering & Technology, Dapoli, IN
2 Department of Mechanical Engineering, Delhi College of Engineering, Bawana Road, Delhi - 42, IN

Abstract

The use of arc welding for fabrication, repair, hard facing and erection has resulted in increase in productivity and quality. Quality of welding largely depends on the bead the characteristics, penetration, mechanical properties, HAZ dimensions and microstructures of weld metal and HAZ. The micro structural sub zones in the heat-affected zone of a weld are spheroidised zone, partially transformed zone, grain refined zone and grain-coarsened zone. Welding parameters has a direct effect on the microstructure and the bead characteristics of a base metal. The typical microstructure formed in the HAZ of mild steel consists of grain boundary ferrite, Widmanstaten ferrite, pearlite, banite, acicular ferrite and martensite depending upon the cooling rate below critical temperature. In submerged arc welding (SAW), selecting appropriate values for process variables is essential in order to control heat-affected zone dimensions and get the required bead size and quality. Also, conditions must be selected that will ensure a predictable and reproducible weld bead, which is critical for obtaining high quality. Present study was conducted to observe the bead geometry and microstructures of weld zone and heat affected zone of submerged arc welding. The experiments were performed on 13 mm thick mild steel plate and single pass submerged arc weld was carried out by varying welding parameters, metallurgical tests where performed using inverted binocular optical metallurgical microscope fitted with digital camera which is connected to a computer. The effects of welding variables on bead geometry and microstructure of weld metal and heat affected zone were experimentally studied using suitable wire flux combination and finally the results were analyzed.

Keywords

Submerged Arc Welding, Heat Affected Zone, Heat Input, Weld Penetration, Weld Hardness.

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C. K. Datta ¹

Affiliations
1 Mechanical Engineering Department, Jalpaiguri Government Engineering College, Jalpaiguri, West Bengal., IN

Abstract

Resistance welding involves complex interactions between material characteristics, thermal mechanical and electromagnetic phenomena. The occuring during spot weld formation (break down of surface asperities, molten nugget formation negget growth and mechanical collapse) can be understood through dynamic resistance curves. In seam welding speed and current are very improtant the limiting factor of welding speed is the surface splash. In practical terms, the significance of dynamic resistance curves lies in their possible use in monitoring weld quality. These can be very effectively utilised for the initial selection of the welding variables. In a welding such curve is characterised by initial peak of resistance followed by resistance drop, secondary peak, and ultimately stable condition. Studies are made in mild steel

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