Application
The influence of welding parameters and processes on weld seams
Release time:
2016-08-10
When the welding current increases (other conditions remain unchanged), the penetration depth and residual height of the weld increase, while the melt width remains unchanged (or slightly increases), for the following reasons:
1、 The influence of welding current, arc voltage, and welding speed on the weld seam
1. Connect current
When the welding current increases (other conditions remain unchanged), the penetration depth and residual height of the weld increase, while the melt width remains unchanged (or slightly increases), for the following reasons:
① After the current increases, both the arc force and heat input on the workpiece increase, the position of the heat source moves downwards, and the melting depth increases. The depth of fusion is approximately proportional to the current.
② After the current increases, the melting amount of the welding wire increases almost proportionally, and due to the almost constant melting width, the excess height increases.
③ After the current increases, the diameter of the arc column increases, but the depth of the arc penetrating into the workpiece increases, and the range of arc spot movement is limited, so the melting width remains almost unchanged.
2. Arc voltage
After the arc voltage increases, the arc power increases, and the heat input to the workpiece increases. At the same time, the arc length lengthens and the distribution radius increases, resulting in a slight decrease in melting depth and an increase in melting width; The decrease in excess height is due to the increase in melting width, but the amount of melted wire slightly decreases.
3. Welding speed
As the welding speed increases, the line energy decreases, and the depth of fusion, width of fusion, and excess height all decrease. This is because the deposition of welding wire metal on a unit length weld seam is inversely proportional to the welding speed, and the melting width is inversely proportional to the square root of the welding speed.
2、 Connection method
DC positive connection: the workpiece is connected to the positive pole of the welding machine, and the welding gun is connected to the negative pole of the welding machine;
DC reverse connection: the workpiece is connected to the negative pole of the welding machine, and the welding gun is connected to the positive pole of the welding machine.
In general, during melting electrode arc welding, the melting depth and melting width are greater when the DC is reversed than when the DC is reversed, because the energy released by the workpiece (cathode) is greater. When connected in a DC positive direction, the welding wire serves as the cathode and has a higher melting rate.
During tungsten inert gas welding, the DC positive connection has the highest penetration depth and the reverse connection has the lowest. Welding aluminum, magnesium, and alloys has the problem of removing the oxide film on the surface of the molten pool. It is better to use alternating current, and reverse welding can also be used when welding thin plates. Welding other materials generally uses DC positive connection.
3、 Defects in weld formation and their causes
1. Incomplete penetration: The phenomenon of incomplete penetration at the root of the joint during fusion welding is called incomplete penetration. The reasons for the formation are low welding current, high welding speed, inappropriate groove size, and misalignment of welding wire with the center of the weld seam. During CO2 welding with thin wire short-circuit transition, this defect is prone to occur due to the low heat input of the workpiece.
2. Burn through: The phenomenon of molten metal flowing out from the back of the weld seam during fusion welding, forming a perforation, is called burn through. Excessive welding current, low welding speed, or large gap groove size may form this defect.
3. Bite edge: The phenomenon of forming a depression or groove by melting along the base metal of the weld seam is called bite edge. Defects may occur during high current high-speed welding. When welding the fillet weld with the belly plate in a vertical position, if the welding foot is too large or the voltage is too high, undercutting will also occur. Improper operation during welding of the butt joint can also result in undercutting.
4. Weld bead: The phenomenon of molten metal flowing onto the base metal outside the weld seam and forming a metal bead during fusion welding is called weld bead. Weld bead is caused by excessive filler metal, which is related to small gap and groove sizes, low welding speed, low voltage, or long wire extension.
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