The effect of alternate supply of shielding gases in austenite stainless steel GTA welding

PROBLEM TO BE SOLVED: To provide a gas shielded arc welding method where the generation of spatters can be suppressed even in high speed welding without depending on welding speed, further, the uniformization of the shape of toes is satisfactory, a wide and flat bead shape can be obtained, and cracking resistance, blow hole resistance or the like are excellent as well. SOLUTION: In the gas shielded arc welding method where pulse welding is performed using a solid wire, the solid wire comprises S, Si, Mn, C and P each by prescribed quantity, and the balance Fe with inevitable impurities, and in which pulse peak current (Ip) in a pulse P of pulse welding is ≥350 A, a pulse peak period (Tp) is 0.5 to 2.0 msec, and further, as a shielding gas, a gaseous mixture composed of, by volume, 75 to 98% Ar, and the balance one or more selected from CO 2 and O 2 is used. COPYRIGHT: (C)2008,JPO&INPIT

Gas-shielded arc welding method

An ultranarrow gap GMA welding (UNGW) process with less than 5 mm gap width has been developed in which the arc pole is strongly oscillated over the groove wall in the thickness direction. A simulation model for wire melting tip behaviour with dc pulse current has been proposed and verified by observation of the tip motion in the UNGW groove. This simulation can define the optimum welding conditions to avoid welding defects. A synchronised control system consisting of a pulsed arc current waveform with cyclical variation of wire feed rate has been successfully developed on the base of the computer simulation. The newly developed UNGW system makes it possible to reduce arc heat input density sufficiently to produce an excellent weld joint with a narrow (1–2 mm) HAZ. Penetration shape control can also be achieved by this control method.

Ultranarrow GMAW process with newly developed wire melting control system

Ar-MIG Arc Behavior in Local Addition of Small Amount of Oxygen into Shielding Gas

Purpose: Generally discrete alternate supply of shielding gas is a new technology which alternately supplies the different kinds of shielding gases in weld zone. In this study, welding characteristics under variation of alternate supply method of shielding gases in austenite stainless steel using a GTA welding process have been investigated and found the relationship between different types of shielding gas and shielding gas supply. Design/methodology/approach: 2-D axisymmetric heat and fluid mathematical model about weld pool has been developed for verifying the effect of alternate supply of shielding gas. The developed models were solved using a general thermofluid-mechanics computer program, PHOENICS code, which is based on SIMPLE algorithm. Findings: The computed results showed that the developed computational models are very adequate to predict in the weld pool and bead geometry, and the technique of alternate supply of shielding gas should be useful to increase higher productivity, cost savings and better quality in arc welding. Research limitations/implications: The effect of alternate supply of shielding gas should be useful to apply for a narrow-gap welding process. Originality/value: The range of molten metal at the top of weld pool for supply of He shielding gas became wider than that for supply of Ar shielding gas. The developed computational models are very adequate to predict in the weld pool and bead geometry.

Development of a mathematical model to study on variation of shielding gas in GTA welding

In previous reports, an ultra-narrow gap CO2 gas metal arc welding process has been developed in order to produce excellent welded joints. In the ultra-narrow gap (less than 5 mm gap) welding process, as the welding wire melting behavior was controlled by low frequency pulsated arc current waveform, the arc generating at the wire tip was widely oscillated in the direction of thickness and a good weld bead with large throat thickness was formed. In such a higher efficient welding process, the strong arc force of CO2 arc is essential to obtain sound beads without lack of fusion at a groove bottom, however, the oxygen content of weld metal in CO2 arc welding has to be reduced to obtain high-toughness at weld metal. In this report, a newly welding process is proposed in which an arc is widely oscillated along groove walls and oxygen content of welded metal is reduced as periodically controlling composition of CO2 gas in shielding gas. As an arc length between the wire tip and groove wall is held constant in ultra-narrow I type gap joint, arc current at stable operating point of CO2 arc essentially decreases less than that at stable operating point of Ar arc in constant potential characteristics of power source. It was confirmed from the numerical simulations on both wire melting and electric welding circuit that pulsated current waveform was produced as periodically alternating CO2 arc with MIG arc. Using the developed welding torch locally introducing CO2 gas into Ar+2%O2 shielding gas, the welding was carried out under V-type groove with less than 30 degree in the bevel angle. It was shown that the arc was widely oscillated along V groove walls and sound bead was formed in one side welding. Furthermore, it was confirmed that the oxygen content of weld metal in the proposed process was reduced to the level of that in MIG arc welding, and absorbed energy of weld metal was the same level as the MIG arc welding.

シールドガス組成制御によるgma溶接プロセスの開発 : 超狭開先gma溶接プロセスの開発(第3報)

Narrow gap welding (NGW) joints offers many advantages over conventional welding methods, such as good mechanical properties of joints, high welding efficiency and low residual stress. As the groove gap width becomes narrower, the arc heat input can be reduced and the merits in narrow gap welding increases more.Generally, GMA welding method has been never applied to less than 5 mm groove gap, because it is guessed that it is arc instability and lack of fusion at the groove bottom area occur.In this paper, first of all, arc behavior under narrower gap joints is discussed, and it was concluded that the arc in MIG arc welding irregularly perturbates up-to-downwards along the groove wall under less than 5 mm gap, but CO2 arc was stable under narrower gap.Next, penetrations at the groove bottom area in CO2 arc welding were discussed. Characteristics of bead formation phenomena in CO2 buried arc welding of bead-on-plate were analyzed. From the results, the relationship between hydrostatic potential of molten metal and arc force corresponding with welding current was estimated. Furthermore, the width of gauging region of penetration by arc force was measured and the relationship between the melting width at groove bottom and welding conditions (welding current and welding speed) can be suggested.With these results, numerical simulation model was proposed and the optimum welding conditions to melt the groove bottom area sufficiently and to minimize heat input were searched by numerical simulation. And then narrow gap welding with 5 mm groove gap was carried out using these simulated welding conditions. In the experimental results, the weld bead was obtained without lack of fusion at groove bottom, but the convex surface bead was formed which is disagreeable in multi-pass welding.The new welding process was proposed from numerical simulations in order to prevent this convex bead and to obtain sufficient melting at bottom area. In the new process, the wire extension can be controlled by welding current waveform and then arc regularly oscillated up-to-downwards along the groove wall. In this arc oscillation, arc heating distribution along groove wall led to both sufficient penetration at groove bottom and concave surface bead shape.

超狭開先ｇｍａ溶接プロセスの開発 １ 狭開先化に伴うアーク溶接現象の基本的な特性把握と溶接安定化の提案:超狭開先gma溶接プロセスの開発(第1報)

PROBLEM TO BE SOLVED: To enable dissolved oxygen concentration to be ≤100 ppm in a weld metal and to enable superior bead formation to be obtained while maintaining arc stability, in welding steel by GMA welding method. SOLUTION: This welding torch comprises a case 1, a tip body 2 installed in this case, a tip 4 attached to the tip end of the tip body, and a nozzle 9 surrounding this tip. A gap 2 is formed between the case and the tip body, with the tip end of this gap made an injection port 11 of a shielding gas. Also, in the welding torch, there are radially provided a plurality of additive gas injection holes 8 at the tip end of the case and inside the nozzle. Using this welding torch, a shielding gas composed of inert gases is supplied to a wire 5 that becomes a consumable electrode, and the additive gas composed of a mixture of oxidizing gases and the inert gases is supplied to the outer edge of a molten pool. COPYRIGHT: (C)2007,JPO&INPIT

照美中村

Papers

シールドガス組成制御によるgma溶接プロセスの開発 : 超狭開先gma溶接プロセスの開発(第3報)

超狭開先ｇｍａ溶接プロセスの開発１狭開先化に伴うアーク溶接現象の基本的な特性把握と溶接安定化の提案:超狭開先gma溶接プロセスの開発(第1報)

Consumable electrode type gas shielded arc welding method and welding torch used therefor

照美 中村

Papers

シールドガス組成制御によるgma溶接プロセスの開発 : 超狭開先gma溶接プロセスの開発(第3報)

超狭開先ｇｍａ溶接プロセスの開発 １ 狭開先化に伴うアーク溶接現象の基本的な特性把握と溶接安定化の提案:超狭開先gma溶接プロセスの開発(第1報)

Consumable electrode type gas shielded arc welding method and welding torch used therefor

照美中村

超狭開先ｇｍａ溶接プロセスの開発１狭開先化に伴うアーク溶接現象の基本的な特性把握と溶接安定化の提案:超狭開先gma溶接プロセスの開発(第1報)