Shielding gas

About: Shielding gas is a research topic. Over the lifetime, 6697 publications have been published within this topic receiving 58668 citations.

Formation mechanism of porosity in high power YAG laser welding

Abstract: With the objectives of clarifying the formation mechanism of porosity and producing a sound weld bead, welding conditions of porosity formation were investigated in A5083 alloy and Type 304 steel welded with a high power YAG laser, and the behavior of a keyhole, bubbles and porosity as well as liquid flows were observed during laser welding through X-ray transmission imaging system using markers. It was confirmed that a lot of bubbles and pores were formed in 3.5 kW YAG laser weld beads produced in Ar, He and N2 gases except Type 304 in N2 gas. Porosity was reduced at high welding speed in Type 304 steel even in He and Ar gases. A lot of bubbles were formed by the evaporation of metals from the bottom tip of the keyhole and flowed upwards in front of the solid-liquid interface. Some bubbles disappeared out of the molten surface especially in A5083 alloy welded at low welding speed, but the majority of bubbles were trapped at the solidifying front of the weld beads in most cases. The shielding gas was also included in the porosity. This mechanism is similar to that in high power CO2 laser welding. Fast liquid flows occurred circularly from the bottom keyhole to the rear upper part of the molten pool, from the rear to the front near the pool surface, and from the top to the bottom behind the keyhole in weld molten pools of both A5083 alloy and Type 304 steel in He, Ar or N2 shielding gas. Slightly different flows were noticed in the molten pool of Type 304 steel between YAG and CO2 lasers.With the objectives of clarifying the formation mechanism of porosity and producing a sound weld bead, welding conditions of porosity formation were investigated in A5083 alloy and Type 304 steel welded with a high power YAG laser, and the behavior of a keyhole, bubbles and porosity as well as liquid flows were observed during laser welding through X-ray transmission imaging system using markers. It was confirmed that a lot of bubbles and pores were formed in 3.5 kW YAG laser weld beads produced in Ar, He and N2 gases except Type 304 in N2 gas. Porosity was reduced at high welding speed in Type 304 steel even in He and Ar gases. A lot of bubbles were formed by the evaporation of metals from the bottom tip of the keyhole and flowed upwards in front of the solid-liquid interface. Some bubbles disappeared out of the molten surface especially in A5083 alloy welded at low welding speed, but the majority of bubbles were trapped at the solidifying front of the weld beads in most cases. The shielding gas was also...

Effect of vacuum on penetration and defects in laser welding

Abstract: The effect of vacuum on weld penetration and porosity formation was investigated in high-power CW CO2 and YAG laser welding. It was consequently confirmed in welding with both lasers that the penetration was slightly deeper in aluminum alloys and was improved in austenitic stainless steel with a decrease in the ambient pressure. It was also revealed that no porosity was present in the materials welded at lower pressures. The reason for no porosity formation in vacuum was examined by observing keyhole behavior, bubble and porosity formation situation and liquid flow in the molten pool during high power YAG laser welding under various conditions through the microfocused X-ray real-time observation system. It was confirmed in the coaxial Ar or He shielding gas that a lot of bubbles were generated near the bottom part of molten pool from the tip of a fluctuated keyhole and resulted in large pores. On the other hand, under the vacuum conditions, no bubbles were formed in the melt pool from the keyhole, although the middle and bottom parts of the keyhole swelled in the molten pool probably because the evaporation of metals was so intense. Moreover, quite different liquid flows were observed between the normal and vacuum welding. Namely, there was a strong molten flow from the bottom of molten pool near the keyhole tip along the solidification interface to the upper rear part in the normal welding, while the liquid flowed upwards along the rear keyhole wall probably due to the strong stream of metallic vapors in vacuum. It is considered in vacuum welding that the liquid flow into the bottom part of the molten pool from the keyhole does not occur because of the direction of evaporated metals toward the upper keyhole outlet. This may exert a beneficial effect on the reduction or prevention of pores or porosity.The effect of vacuum on weld penetration and porosity formation was investigated in high-power CW CO2 and YAG laser welding. It was consequently confirmed in welding with both lasers that the penetration was slightly deeper in aluminum alloys and was improved in austenitic stainless steel with a decrease in the ambient pressure. It was also revealed that no porosity was present in the materials welded at lower pressures. The reason for no porosity formation in vacuum was examined by observing keyhole behavior, bubble and porosity formation situation and liquid flow in the molten pool during high power YAG laser welding under various conditions through the microfocused X-ray real-time observation system. It was confirmed in the coaxial Ar or He shielding gas that a lot of bubbles were generated near the bottom part of molten pool from the tip of a fluctuated keyhole and resulted in large pores. On the other hand, under the vacuum conditions, no bubbles were formed in the melt pool from the keyhole, althoug...

Touchwork system for a MIG arc welding apparatus

Abstract: A touchwork system for use in conjunction with a MIG arc welding apparatus comprising a sensing circuit operating at very low output voltages, e.g. 6-8 volts, which senses the touch of the consumable wire electrode to the workpiece when the welding process is started. A control circuit energizes the welding contactor in response to a signal from the sensing circuit and turns on the power supply. At the same time, the control circuit starts the wire feeder motor and also the flow of shielding gas to the torch. A detector circuit detects the flow of welding current and feeds a signal to the control circuit to keep the welding contactor energized and the power supply in circuit and also to maintain operation of the wire feeder motor and the flow of shielding gas to the torch.