I. Welding current
1. Welding current
The appropriate welding current is selected based on welding conditions such as plate thickness, welding position, welding speed and material parameters. In reality, adjusting the current on a CO2 welding machine means adjusting the wire feed speed.
Therefore, the welding current of the CO2 welding machine must match the welding voltage, ensuring that the wire feed speed is in line with the melting ability of the welding wire to the voltage, to maintain a stable arc length .
For the same welding wire, the higher the current, the higher the wire feeding speed. With the same current, the thinner the wire, the faster the wire feed speed.
two . Welding voltage
Welding voltage, also known as arc voltage, provides the energy for welding. The higher the arc voltage, the greater the welding energy, the faster the welding wire melts and the greater the welding current.
The arc voltage is equal to the output voltage of the welding machine minus the voltage loss in the welding circuit, which can be represented by the following formula:
Arc Voltage = Output Voltage – Voltage Loss
If the welding machine is installed in accordance with the installation requirements, voltage loss mainly refers to the voltage loss caused by the extension of the welding cable. If your welding cable needs to be extended, you can refer to the following table when adjusting the output voltage of the welding machine.
| Welding current cable length | 100A | 200A | 300A | 400A | 500A |
| 10m | Approximately 1V | Approximately 1.5V | Approximately 1V | Approximately 1.5V | Approximately 2V |
| 15m | Approximately 1V | Approximately 2.5V | Approximately 2V | Approximately 2.5V | Approximately 3V |
| 20m | Approximately 1.5V | Approximately 3V | Approximately 2.5V | Approximately 3V | Approximately 4V |
| 25m | Approximately 2V | Approximately 4V | Approximately 3V | Approximately 4V | Approximately 5V |
II. Setting the welding voltage
Select the welding current according to the welding conditions for the corresponding plate thickness, and then calculate the welding voltage using the following formulas:
- For <300A: Welding Voltage = (0.05 × Welding Current + 14 ± 2) Volts
- For > 300A: Welding voltage = (0.05 × Welding current + 14 ± 3) Volts
Example 1: Given a selected welding current of 200A, the welding voltage is calculated as follows:
Welding voltage = (0.05 × 200 + 14 ± 2) Volts
= (10 + 14 ± 2) Volts
= (24 ± 2) Volts
Example 2: Given a selected welding current of 400A, the welding voltage is calculated as follows:
Welding voltage = (0.05 × 400 + 14 ± 3) Volts
= (20 + 14 ± 3) Volts
= (34 ± 2) Volts
III. Welding Current Selection
The welding voltage provides the energy required to melt the welding wire. Higher tensions result in a faster melting speed of the wire. Welding current, on the other hand, is essentially the balanced result of wire feed speed and melting speed. So how should we choose the appropriate welding current?
1) The appropriate welding current value is selected based on factors such as welding rod type, plate thickness and rod diameter.
The current is proportional to the thickness of the plate and the diameter of the wire. The current (I) can be calculated using the formula I=(35-55)d, where 'd' is the rod diameter. For example, if the rod diameter is 4mm, the welding current value is selected between 140-220A.
2) The welding current is selected according to the welding position:
140A for overhead welding seams; between 140-160A for vertical and horizontal butt welding; above 180A for flat butt welding. For welding in all positions (including flat, horizontal, vertical and overhead positions), the selected welding current must be universal, generally taking the value of the vertical welding current. When welding a pipe fixed horizontally to butt joint, the welding current of all positions is used, generally taking the value of the vertical butt welding current.
3) The current value is selected according to the welding layers:
A smaller current value is generally used for the root layer, a larger value for the filling layer, and the current value for the capping layer is relatively reduced. For example, in flat butt welding, a multi-layer, multi-pass welding approach is generally used.
The root layer is welded with a current of 150A, while the filler layer can use a current value between 180-200A. The cover layer uses a current value reduced by 10-15A, to ensure an aesthetically pleasing result and avoid welding defects such as undercuts.
4) Choice of welding current based on the type of welding rod and method of manipulation:
1. According to the type of welding rod: Acid > Alkaline > Stainless steel. Acidic electrodes use the highest current value. When the electrode diameter is 4mm, the filler layer of flat butt welding can use a current of 180A.
However, with the same electrode diameter using an alkaline electrode, the welding current needs to be 20A lower, that is, a welding current of 160A. If welding is done with an A137 stainless steel electrode, the current must be 20% lower, approximately 140A. Otherwise, the welding rod may turn red and the flux layer may peel off in the middle of the welding process.
2. Choose based on manipulation method: Small current values are generally used for the drag arc method, while slightly higher current values are used for the lift arc method. When doing vertical butt welding or vertical fillet welding with an F4 alkaline electrode, a drag arc method with 120A can be used, while the lift arc method can use 135A.
5) Choosing welding current based on production experience:
Look at the spatter, the welding current roughly decides the arc strength, more spatter means more arc strength; Less welding current means less arc strength, making it difficult to distinguish between slag and molten metal.
Observe weld formation: higher welding current will likely cause undercuts with less reinforcement; Lower welding current results in a narrow but tall weld. Observe the melting state of the electrode: a higher welding current melts the electrode more quickly, turning it red; lower welding current may cause sticking.
4. Impact of welding voltage on welding performance
When the voltage is too high:
Arc length increases, spatter particles grow, porosity is more likely to occur, the weld bead widens, while penetration depth and reinforcement decrease.
When the voltage is too low:
The welding wire plunges into the base material, spatter increases, the weld bead narrows, while the penetration depth and reinforcement increase.
V. Standard Adjustment
- Prefabrication is carried out according to the reference formula before welding.
- Test welding
- Initially, the current is determined.
- The voltage level is evaluated based on the tactile response, sound and stability of the arc.
- Fine adjustment of tension is performed.
