Minimum Voltage Principle
Welding is a complex process which requires an understanding of the science underlying it in order to create sound, reliable joints. To create a high-quality weld, engineers and welders must select and control different variables, such as amperage, the type of electrode, the welding technique and shielding gas. One of the control variables employed in the welding process is the minimum voltage principle.
The minimum voltage principle states that, in order to achieve a consistent, superior quality weld, the welding voltage must be set above a specific level. The voltage level is determined by the combination of the electrode diameter, material thickness, and the current type (DC or AC). If the voltage is set below this minimum level, the metal can’t be fused together, because the heat being generated from the arc is insufficient to melt the base material.
The arc involves the transfer of heat energy from the electrode to the base material, and the temperature of the metal must reach and exceed the melting point -- or fusion point -- before the two materials can be joined and fuse together. The heat energy is generated by electrons that flow through the arc. The amperage, coupled with the length of the arc, directly control the temperatures, and the arc length is determined by the voltage.
The voltage is the pressure difference between the electrode and the workpiece, driving the electrons toward the base material. If the voltage is too low, the electrons can’t travel the required distance, resulting in a weak, unstable arc and an insufficient amount of heat to melt the weld zone. When the voltage is set too low, more amperage needs to be delivered in order to compress the arc, build a dependable connection, and generate elevated temperatures for a stable and effective arc.
The voltage set-point, determined by studying charts with the exact specifications of the electrode diameter, material thickness and current type, is the minimum point necessary to form and sustain an effective, stable arc, while still delivering an adequate level of heat to melt the base material
The minimum voltage principle is a critical factor in ensuring weld quality, and it must be applied to ensure sound, reliable welds. Setting the correct voltage not only ensures that the arc length is correct and that a sufficient amount of heat is delivered to the weld zone, but it also helps reduce the risk of excessive distortion or shrinkage of the material due to over-penetration. In addition, using the proper voltage reduces arc blow and undercut, minimizes welding spatter, and leads to an overall more effective, efficient and consistent welding process.
