What is metal transfer in welding?
Metal transfer refers to how the filler metal is deposited to the parent metal in order to form a weld bead.
There are 3 modes/types of metal transfer in welding.
Let me tell you few important things about each mode/type of metal transfer used in the welding process.
Modes/Types of metal transfer in welding
Before discussing the modes of metal transfer, one thing is important for you to know that there are various factors that determine the modes of metal transfer in welding. These factors are mentioned below.
- Type of base metal,
- Diameter of electrode,
- Arc voltage,
- Arc length,
- Arc current,
- Composition of filler metal,
- Composition of shielding gas,
- Welding position, etc.
#1) Short circuit transfer
In welding, the short circuit transfer occurs when the filler material is deposited from the electrode by short circuiting to the workpiece surface.
From the above diagram, you can easily understand the short circuit transfer mode in welding process.
You might be knowing that in an electric bulb, if the higher current is passed through the circuit, then the fuse overheats and blows.
The exact principle is used in the short circuit transfer mode of welding.
The only difference here is that the fuse (i.e electrode) is fed continuously and the short circuit keeps on occurring over and over again.
Because of this, the filler material is deposited continuously on the workpiece.
In simple words, when the electrode strikes the weld surface, the heat is generated which melts the filler rod, and finally the filler metal is deposited on the workpiece.
Short circuit transfer in welding operates at relatively lower voltage and current ranges.
As the heat input is less in short circuit transfer method, it is not preferred for plate materials. This is because the penetration as well as fusion capability of the weld are limited in this type of metal transfer mode.
For using short circuit transfer mode, a skilled welder is required for producing sound welds.
Unskilled welder may produce poor quality weld (with poor penetration or incomplete fusion).
The weld puddles formed by short circuiting transfer method are small and they are fast freezing.
They are generally used for welding roof passes, gap filling, etc.
#2) Spray transfer
In welding, the spray transfer mode occurs at higher current and higher voltage, but it requires an inert gas shield.
If spray transfer mode is to be used for steels, then around 80% of argon is recommended as shielding gas. And for welding aluminum, 100% argon is common.
The higher current used in the spray transfer method induces a magnetic field at the end of the wire to pinch off the molten drops.
Also the magnetic field produces radial inward force on the ionized gas in the weld zone that makes the narrow cone shaped arc (see above image).
The rate of metal deposition is higher which ultimately leads to high quality weld without spatter.
The main disadvantage of spray transfer is that it is not suitable for overhead weldings as well as it is also not suitable for ferrous metals thinner than ⅛ inches.
#3) Globular transfer
Globular transfer takes place when the arc voltage is kept higher.
In Globular transfer mode, the electrode forms the balled end which is approximately twice that of the electrode’s diameter.
The molten drop falls to the weld surface due to the gravity acting on it.
In the globular type metal transfer, you may see the gap between the electrode and the weld surface.
Also the irregular shaped globules result in the spatter around the weld.
Globular transfer welding is suitable for horizontal or flat type welding only. It is not suitable for vertical or overhead weldings.
The main disadvantage with globular transfer welding is that it causes the welding defect called spatter.
And because of the more spatter formation, this mode of metal transfer is generally avoided.