How Do Welding Parameters and Processes Affect the Weld Seam?

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

1. Welding current

When the welding current increases (other conditions remain unchanged), the weld penetration and reinforcement increase, and the melting width does not change (or slightly increase). The reasons are as follows:

① after the current increases, the arc force and heat input on the workpiece increase, the heat source position moves down, and the penetration increases. The penetration is nearly proportional to the current.

② When the current increases, the melting amount of welding wire increases in proportion, and the reinforcement increases because the melting width is nearly constant.

③ When the current increases, the diameter of the arc column increases, but the depth of the arc into the workpiece increases, and the moving range of the arc spot is limited, so the melting width is nearly unchanged.

2. Arc voltage

When the arc voltage increases, the arc power increases, the workpiece heat input increases, the arc length lengthens and the distribution radius increases, so the penetration decreases slightly and the melting width increases;

The reinforcement decreases because the melting width increases, but the melting amount of welding wire decreases slightly.

3. Welding speed

When the welding speed increases, the linear energy decreases, and the penetration, width and reinforcement decrease.

This is because the deposited amount of welding wire metal on the unit length weld is inversely proportional to the welding speed, and the melting width is inversely proportional to the square of the welding speed.

2. Connection method

DC positive connection: the workpiece is connected to the positive electrode of the welding machine, and the welding gun is connected to the negative electrode 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, the penetration depth and width of DC reverse welding are larger than that of DC Positive welding, which is due to the large energy released by the workpiece (cathode).

When DC positive connection, the welding wire is the cathode, and the melting rate of the welding wire is large.

During TIG welding, the penetration depth of DC positive connection is the largest and the reverse connection is the smallest.

Welding aluminum, magnesium and alloys have the problem of removing the oxide film on the surface of the molten pool.

It is better to use AC. and the reverse connection can also be used when welding thin plates. DC positive connection is generally used for welding other materials.

3. Weld forming defects and causes of defects

1. Incomplete penetration

During fusion welding, the phenomenon of incomplete penetration at the root of the joint is called incomplete penetration.

The causes are low welding current, high welding speed, improper groove size and misalignment of welding wire to the weld center.

This defect is easy to occur due to low heat input of workpiece during short-circuit transition CO2 welding with fine wire.

Incomplete penetration

2. Burn through

During fusion welding, molten metal flows out from the back of the weld to form perforation, which is called burn through.

This defect may be caused by excessive welding current, too small welding speed or too large gap groove size.

Burn through

3. Undercut

In the base metal part along the weld, the phenomenon of depression or groove formed by burning is called undercut. Defects may occur during high current and high speed welding.

When the fillet weld with the web in the vertical position is welded, undercut will also occur if the weld leg of one welding is too large or the voltage is too high, and improper operation during butt joint welding will also occur.


4. Weld bead

During fusion welding, the molten metal flows to the unfused base metal outside the weld to form a metal tumor, which is called weld bead.

Weld bead is caused by too much filler metal, which is related to small gap and groove size, low welding speed, low voltage or large extension length of welding wire.

Weld bead

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