Como os parâmetros e processos de soldagem afetam a costura de solda?

How do welding parameters and processes affect the weld seam?

1. Influence of welding current, arc voltage and welding speed on the weld seam

1. Welding current

When the welding current increases (under other constant conditions), the weld penetration and reinforcement also increase, while the fusion width remains unchanged or increases slightly. The reasons for these changes are as follows:

① Increasing current leads to an increase in arc strength and heat input into the workpiece, causing the position of the heat source to move downward and resulting in an increase in penetration. Penetration is almost proportional to current.

② The increase in current results in a proportional increase in the amount of welding wire fusion, leading to an increase in reinforcement since the fusion width remains almost constant.

③ The increase in current causes the diameter of the arc column to increase, but also results in an increase in the depth of the arc in the workpiece, with the moving range of the arc point being limited. As a result, the melt width remains virtually unchanged.

2. Arc Voltage

As the arc voltage increases, the arc power and heat input to the workpiece also increase. This leads to an increase in arc length and distribution radius, resulting in a slight decrease in penetration and an increase in melt width.

However, the increase in fusion width results in a decrease in reinforcement and a slight decrease in the amount of fusion of the welding wire.

3. Welding speed

As welding speed increases, linear energy decreases and the result is a decrease in penetration, width and reinforcement. This occurs because the amount of welding wire metal deposited per unit length of weld decreases as the welding speed increases. Furthermore, the fusion width decreases proportionally to the square of the welding speed.

2. Connection method

DC positive connection: The workpiece is connected to the positive terminal of the welding machine, and the welding torch is connected to the negative terminal of the machine.

DC reverse connection: The workpiece is connected to the negative terminal of the welding machine, and the welding torch is connected to the positive terminal.

In general, the depth and width of penetration in DC reverse welding are greater than that in positive DC welding. This is due to the high energy release of the part, which acts as a cathode.

When using positive DC connection, the welding wire acts as the cathode, resulting in a high melting rate of the wire.

In TIG welding, the penetration depth is greater with positive DC connection and smaller with reverse DC connection.

Welding aluminum, magnesium and alloys requires removing the oxide film on the surface of the weld pool, making AC welding a better option. The reverse DC connection is suitable for welding thin plates, while the positive DC connection is typically used for welding other materials.

3. Weld formation defects and causes of defects

1. Incomplete penetration

In fusion welding, incomplete penetration into the joint root is called “incomplete penetration”.

Reasons for this defect include low welding current, high welding speed, inadequate slot size and misalignment of the welding wire with the center of the weld.

This defect is commonly seen in short-circuit transition CO2 welding with a thin wire due to low heat input to the workpiece.

Incomplete penetration

2. Burn

In fusion welding, when molten metal flows down the back of the weld and creates a hole, it is called a “burn.”

This defect may occur due to an excessive welding current, a welding speed that is too low or a gap groove that is too large.

Burn

3. Undercut

In the base metal near the weld, a depression or groove created by burning is called an “undercut.” This defect may occur during high current and high speed welding.

If the vertical web fillet weld is welded with too large a weld leg or with too high tension, undercutting may also occur. Improper operation when welding butt joints can also result in undercuts.

Undercut

4. Weld bead

In fusion welding, when molten metal flows into the unmolten base metal outside the weld and forms a protrusion, this is called a “weld bead”.

Weld beads can be caused by an excessive amount of filler metal, which is often associated with small gaps and grooves, slow welding speed, low voltage, or large welding wire extension length.

Weld bead

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