Why Is Sma Welding Current Referred To As Constant Current

Why is SMAW Welding Current Referred to as Constant Current?

Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), and Submerged Arc Welding (SAW) are all commonly referred to as constant voltage welding processes. In contrast, Shielded Metal Arc Welding (SMAW), often called stick welding, is known as a constant current process. But why? Understanding this difference hinges on how each process controls the arc and responds to changes in the arc length. This article delves deep into the electrical characteristics of SMAW, explaining why the current remains relatively constant despite variations in arc length and other factors.

The Basics of Arc Welding

Before diving into the specifics of SMAW, let's review the fundamental principles of arc welding. Arc welding relies on generating an extremely high temperature arc between an electrode and the workpiece. This arc melts the electrode and the base material, fusing them together. The process requires a power source, typically a welding machine, which provides the necessary electrical current to establish and sustain the arc.

The key components of an arc welding circuit include:

• Power Source: This provides the electrical energy to create the arc. Different power sources control voltage and current in different ways.
• Electrode: This is the consumable material that melts and forms part of the weld. In SMAW, it's a coated metal rod.
• Workpiece: This is the material being welded.
• Arc: This is the extremely hot, ionized gas column that forms between the electrode and the workpiece, carrying the electrical current.

Voltage and Current in Arc Welding: A Dynamic Duo

Two crucial parameters govern the arc welding process: voltage and current.

• Voltage (V): This represents the electrical potential difference between the electrode and the workpiece. It drives the current flow and influences the arc length. A higher voltage generally leads to a longer arc.
• Current (A): This represents the flow of electrons through the arc. It determines the amount of heat generated, directly affecting the weld bead size and penetration depth.

The relationship between voltage and current is complex and non-linear, influenced by factors like arc length, electrode type, and shielding gas. Understanding this relationship is crucial to achieving high-quality welds.

Constant Current vs. Constant Voltage Power Sources

Welding power sources are designed to control either current or voltage, leading to two distinct categories:

• Constant Current (CC) Power Sources: These maintain a relatively constant current despite changes in arc length. If the arc length increases (leading to higher voltage), the power source adjusts the voltage to keep the current stable. This is characteristic of SMAW.
• Constant Voltage (CV) Power Sources: These maintain a relatively constant voltage despite changes in arc length. If the arc length increases (requiring more voltage), the current drops. This is typical of GMAW, GTAW, and SAW.

Why SMAW is a Constant Current Process: A Deep Dive

The core reason why SMAW is a constant current process boils down to the characteristics of the electrode and its coating. Let's analyze the key factors:

1. The Electrode Coating's Role:

The electrode coating in SMAW plays a crucial role in arc stability and current control. It performs several vital functions:

• Shielding: The coating generates a protective gas shield around the arc, preventing atmospheric contamination of the weld.
• Fluxing: The coating provides fluxing agents that clean the weld zone and help to prevent porosity.
• Stabilizing the Arc: This is perhaps the most important function in relation to constant current. The coating's ionization properties help to maintain a relatively stable arc length and current despite minor fluctuations. The coating acts as a sort of buffer, smoothing out variations and preventing large current spikes.

2. The Nature of the SMAW Arc:

The SMAW arc is inherently less stable than the arcs in other welding processes like GMAW or GTAW. This inherent instability stems from several factors, including:

• Consumable Electrode: The electrode continually shortens as it melts, altering the arc length constantly.
• Coating Decomposition: The coating's decomposition during the welding process introduces variations in arc characteristics.
• Environmental Factors: Spatter, changes in electrode angle and speed, and other environmental factors also affect arc stability.

A constant voltage power source wouldn't be effective with SMAW due to this instability. If the voltage were held constant, any slight increase in arc length would drastically reduce the current, causing the arc to extinguish. The coating simply isn't equipped to continuously and precisely adjust for these variations.

3. Constant Current Power Source's Response:

A constant current power source automatically compensates for these fluctuations in arc length. If the arc length increases, the voltage increases to maintain a constant current. Conversely, if the arc length decreases, the voltage decreases to prevent excessive current flow and potential arc instability. This automatic feedback mechanism ensures a relatively stable arc and a consistent weld.

4. Practical Implications of Constant Current in SMAW:

The constant current characteristic of SMAW has significant implications for the welder's technique and the weld quality:

• Ease of Use: The relative arc stability enabled by a constant current power source makes SMAW easier to learn and master, especially for beginners.
• Consistent Weld Penetration: The consistent current ensures a consistent weld bead profile and penetration depth.
• Reduced Spatter: By stabilizing the arc, the constant current reduces spatter, enhancing weld quality and efficiency.

Comparison with Constant Voltage Processes

Let's compare SMAW with constant voltage processes to highlight the differences:

Conclusion: The Importance of Understanding SMAW's Constant Current Nature

Understanding why SMAW welding current is referred to as constant current is crucial for any welder. The constant current characteristic is not simply a label; it's a fundamental aspect of the process that directly influences its ease of use, weld quality, and the overall performance of the operation. The intricate interplay between the electrode coating, the arc's inherent instability, and the power source's feedback mechanism all contribute to this defining characteristic. By grasping these concepts, welders can better control the welding process, produce high-quality welds, and maximize their efficiency. This knowledge enhances both theoretical understanding and practical skills, making the welder more adept at troubleshooting and optimizing their welding techniques. The constant current nature isn't just a technicality; it’s the foundation upon which successful SMAW operation is built.