CO2 mig welding Common defects and failures—Operational defects
Common defects in CO2 mig welding are mainly caused by improper operation. There are many common faults in CO2 mig welding, mainly including faults caused by improper adjustment and wear of the mechanical parts of the equipment.
CO2 mig welding Operational defects
There are many operational defects in CO2 mig welding, mainly including porosity and lack of penetration.
Stomata of CO2 mig welding
Before the start of CO2 mig welding, the flow rate of the shielding gas must be adjusted correctly, so that the shielding gas can evenly and fully protect the welding pool and prevent air from infiltrating. Poor protection will create pores in the weld. The main reasons for poor protection are as follows:
Low CO2 gas purity
CO2 gas contains a lot of water or nitrogen, especially when the water content is too high, there will be pores of different sizes on the entire weld.
Water-cooled welding gun leaks
In many special places of welding, a water-cooled welding torch needs to be used, but there is water leakage in the welding torch, so pores are most likely to be generated during the welding process.
No protective gas
Before welding, the high pressure valve on the CO2 gas cylinder was not opened at all due to negligence or the preheater was not connected to the power supply, and the welding started. Because there is no shielding gas during welding, the entire weld is full of pores.
Wind speed is too high
When the CO2 mig welding shielding gas flow rate is suitable, the wind speed is large due to the influence of the weather and the welding environment, so that the shielding gas cannot normally achieve the rated range of protection. Form effective maximum protection, even without protection, causing porosity during welding, as shown in Figure The effect of wind on shielding gas.
Inappropriate gas flow
If the flow rate of CO2 shielding gas is too small, the protection range will also decrease. Due to the reduction of the protection range, the welding pool cannot be completely and reliably protected (Fig. shielding gas flow-a); however, the flow rate of CO2 shielding gas should not be too large, and the The assembly generates a vortex, and the air is also drawn into the protection zone (Fig. shielding gas flow-b), resulting in the failure of the protection. Therefore, the unsuitable gas flow will cause pores in the weld.
CO2 mig welding Nozzle clogged with splash
Different degrees of spatter may be generated during CO2 shielded gas welding. When the spatter is too much, the gas port will be blocked, resulting in the attenuation of gas flow and the reduction of the protected area, as shown in Figure Nozzle clogged with splash. Therefore, during the welding process, if the spatter sprayed on the nozzle is not removed in time, it will cause eddy currents in the shielding gas, and it will also suck in air, causing pores in the weld. Therefore, the spatter on the nozzle must be removed frequently during the welding process, and the surface roughness of the inner circle of the nozzle must be prevented from being damaged. In order to facilitate the removal of spatter, it is best to spray a layer of anti-spatter spray or a layer of silicone oil on the inner and outer surfaces of the nozzle before welding.
Anti-spatter spray is a high-tech water-based lubricant. Before welding, spray a layer on the inner and outer surfaces of the nozzle to form a thin film to prevent spatter from adhering to the metal surface during welding, and it is easy to clean after welding. In the welding process, it can protect the welding tip, the welding surface and prevent the welding tip from sticking. Its main features are to prevent the welding slag from sticking and burning the metal surface, preventing the welding torch from depositing carbon, no flash point and fire point, no burning Special formula ,Suitable for welding all kinds of non-silicon, non-oily mucosa materials, no need to grind, knock, smooth after welding, the welding slag is easy to remove, convenient for secondary processing, no solvent-based cleaning agent.
Anti-spatter silicone oil is a kind of organosilicon non-ionic surfactant with unique properties. Various organosilicon surfactants with different properties can be obtained during production to meet the needs of preventing welding spatter. The product is characterized by lower surface tension, better softness and strong antistatic properties, suitable for preventing welding spatter.
CO2 mig welding Torch angle is too large
If the inclination angle of the welding torch is too large during welding (Figure Welding torch angle is too large), air will also be sucked in, which will cause pores in the weld.
CO2 mig welding The wire sticks out too much or the nozzle is too high
When welding, when the length of the welding wire is too large or the height of the nozzle is too large, the protective effect of the shielding gas is not good, and it is easy to cause pores, as shown in Figure The wire sticks out too long and the nozzle is too high.
The inner hole of the spring hose is blocked
The inner hole of the spring hose is blocked by oxide skin or other dirt, the first half of the sealing plastic tube is broken or the sealing ring at the wire inlet is leaking, and the shielding gas leaks from the inlet of the welding torch, reducing the shielding gas flow at the nozzle. Small, which is one of the important reasons for the generation of stomata. In this case, you can often hear the “hissing” sound of air leakage at the connection of the wire feeder welding gun, usually there are air holes in the entire weld, and bubbles in the molten pool can be seen during welding. The phenomenon.
In addition, the oil, rust or scale in the welding area is too thick and not cleaned, which is also the reason for the porosity of the weld.
CO2 mig welding Not penetrated
Improper beveling or assembly
Bevel processing before welding is also an important part of welding. If the bevel angle is too small, the blunt edge is too large, the gap is too small, and the misalignment is too large, it will cause incomplete penetration defects, as shown in Figure Incomplete penetration due to improper bevel preparation or assembly. In order to prevent non-fusion, the groove angle should be 40°~60°.
Poor bottom weld bead
During welding, because the bottom bead is too high, it is easy to cause unfused, as shown in Figure Incomplete penetration caused by bottom bead. Therefore, when welding the bottom layer, the swing range of the welding torch should be controlled to ensure that the bottom layer weld bead and the groove surfaces on both sides should be well fused, the surface of the weld seam is concave, and there should be no grooves on both sides to cover the upper layer weld seam.
Bad weld joints
If the joints are not ground, or arc ignition is improper, the joints are likely to be unfused, as shown in Figure Lack of fusion at the joint. In order to ensure that the welding seam is well connected, it is required to grind the joint into an inclined plane during welding, start the arc at the highest point, and continue welding.
Inappropriate welding parameters
During flat welding, the welding speed is too low, the welding current is too large, the deposition coefficient is too large or the inclination angle α of the welding torch is too large, which will cause incomplete penetration, as shown in Figure Incomplete penetration due to inappropriate welding parameters. Therefore, in order to prevent incomplete penetration during the welding process, the welding speed must be adjusted according to the fusion situation to ensure that the arc is located in the front of the molten pool.
The arc position is wrong
When welding, the arc of the welding torch is not aligned with the center of the groove, and the arc deviates to one side of the groove when the welding torch swings, and the dwell time of the arc on the groove surface is too short, which will cause incomplete penetration, as shown in Figure Incomplete penetration caused by incorrect arc position.
Welding position restrictions
During the welding process, due to the structural limitation of the weldment, the arc cannot be centered or the edge of the groove cannot be reached, which will also lead to the phenomenon of incomplete penetration, as shown in Figure Incomplete penetration caused by improper welding position.
