I. Welding Current 1. Welding Current The selection of appropriate welding current is critical in CO2 welding and is determined by various welding parameters, including plate thickness, welding position, welding speed, and material properties. In CO2 welding machines, adjusting the current effectively means modifying the wire feed speed, highlighting the intricate relationship between these two […]
The selection of appropriate welding current is critical in CO2 welding and is determined by various welding parameters, including plate thickness, welding position, welding speed, and material properties. In CO2 welding machines, adjusting the current effectively means modifying the wire feed speed, highlighting the intricate relationship between these two parameters.
It is crucial to maintain a precise balance between welding current and voltage. This equilibrium ensures that the wire feed speed aligns perfectly with the melting rate of the welding wire at the set voltage, thereby maintaining a stable arc length. This synchronization is fundamental for achieving high-quality welds and optimal process efficiency.
The Relationship between Welding Current and Wire Feed Speed:
Understanding and optimizing this relationship is essential for achieving superior weld quality, minimizing defects, and maximizing productivity in CO2 welding applications across various industries.
Welding voltage, also known as arc voltage, is a critical parameter that provides the energy for the welding process. It directly influences the arc characteristics, heat input, and overall weld quality. The relationship between arc voltage and welding energy is proportional: higher arc voltage results in greater welding energy, faster melting of the welding wire, and increased welding current.
The effective arc voltage can be expressed by the following equation:
Arc Voltage = Output Voltage – Voltage Drop
Where:
The voltage drop primarily occurs due to resistance in the welding cables, connections, and the arc itself. When a welding machine is installed according to manufacturer specifications, the most significant source of voltage drop is often the extension of welding cables.
For optimal welding performance, it’s crucial to compensate for voltage drops, especially when using extended welding cables. The following table provides guidelines for adjusting the output voltage based on cable length extensions:
| 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 |
Note: These values are general guidelines. Actual voltage adjustments may vary based on factors such as cable gauge, material, and specific welding application requirements.
When adjusting welding voltage, it’s important to consider its effects on:
Proper voltage selection and compensation are essential for achieving high-quality welds and maintaining process efficiency in various welding applications.
Select the welding current based on the specific welding conditions and workpiece thickness. Calculate the appropriate welding voltage using the following empirical formulas:
These formulas provide a starting point for voltage selection, which may require fine-tuning based on factors such as material composition, joint configuration, and desired weld characteristics.
Example 1: For a selected welding current of 200A (< 300A):
Welding Voltage = (0.05 × 200 + 14 ± 2) Volts
= (10 + 14 ± 2) Volts
= 24 ± 2 Volts
Recommended voltage range: 22 – 26 Volts
Example 2: For a selected welding current of 400A (≥ 300A):
Welding Voltage = (0.05 × 400 + 14 ± 3) Volts
= (20 + 14 ± 3) Volts
= 34 ± 3 Volts
Recommended voltage range: 31 – 37 Volts
Note: Always consult the welding equipment manufacturer’s guidelines and perform test welds to optimize voltage settings for specific applications. Factors such as shielding gas composition, wire feed speed, and travel speed may influence the optimal voltage selection.
Welding voltage provides the energy necessary for the melting of the welding wire. Higher voltages result in a faster melting speed of the wire. Welding current, on the other hand, is essentially the balanced outcome of wire feeding 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 the type of welding rod, plate thickness, and rod diameter.
The current is proportional to both plate thickness and wire diameter. 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) Welding current is selected according to the welding position:
140A for overhead welding seams; between 140-160A for vertical and horizontal butt welding; over 180A for flat butt welding. For all-position welding (inclusive of flat, horizontal, vertical, and overhead positions), the selected welding current should be universal, usually taking the value of vertical welding current. When welding a horizontally fixed pipe for butt joint, the all-position welding current is used, generally taking the value of 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 one for the filling layer, and the current value for the cover layer is relatively reduced. For example, in flat butt welding, a multi-layer, multi-pass welding approach is usually used.
The root layer is welded with a 150A current, while the filling layer can use a current value between 180-200A. The cover layer uses a reduced current value by 10-15A, to ensure an aesthetically pleasing result and avoid welding defects such as undercut.
4) Choosing welding current based on the type of welding rod and the method of manipulation:
1. According to the type of welding rod: Iacid > Ialkaline > Istainless 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 less, i.e., a welding current of 160A. If welding is done with A137 stainless steel electrode, the current should be 20% less, approximately 140A. Otherwise, the welding rod may turn red and the flux layer may peel off halfway through the welding process.
2. Choosing based on manipulation method: Small current values are generally used for drag arc method, while slightly higher current values are used for lift arc method. When doing vertical butt welding or vertical angle welding with a Ф4 alkaline electrode, a drag arc method with 120A may be used, whereas the lift arc method can utilize 135A.
5) Choosing welding current based on production experience:
Look at the spatter, the welding current roughly decides the arc force, more spatter means more arc force; less welding current means less arc force, making it hard to distinguish between slag and molten metal.
Look at the weld formation: higher welding current is likely to cause undercutting, with less reinforcement; lower welding current results in a narrow but high weld. Observe the melting state of the electrode: a higher welding current melts the electrode faster, turning it red; a lower welding current might cause sticking.
When the voltage is too high:
The arc length increases, spatter particles grow larger, porosity is more likely to occur, the weld bead widens, while the penetration depth and reinforcement decrease.
When the voltage is too low:
The welding wire dips into the base material, spattering increases, the weld bead narrows, while the penetration depth and reinforcement increase.
As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.
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