Welding is a process that relies on precise control of heat input to melt and fuse materials, and current setting is one of the core parameters that determine heat input. Whether welding with 7018 rods or other types of electrodes, changing the current setting during a weld is strongly discouraged. This seemingly simple adjustment can have a series of negative impacts on weld quality, stability, and even equipment safety.
First and foremost, changing the current setting during a weld will directly lead to uneven heat input, which is a key factor in causing weld defects. The molten weld pool formed during welding has a specific temperature range to maintain its fluidity and fusion performance. If the current is suddenly increased, the heat input will rise sharply, causing the weld pool to overheat. This may lead to problems such as burn-through (especially for thin base metals), excessive penetration, or grain growth in the heat-affected zone (HAZ). Grain growth can reduce the toughness of the weld joint, making it more prone to cracking under stress. Conversely, if the current is suddenly reduced, the heat input will decrease, resulting in insufficient melting of the electrode and base metal. This can lead to incomplete fusion, cold laps, or a "ropey" weld bead with poor bonding, all of which significantly reduce the strength of the weld.
For 7018 rods, which are sensitive to heat input, the impact of current changes is more obvious. As a low-hydrogen rod, 7018 requires stable heat to ensure the proper decomposition of its coating and the formation of a protective gas shield. Sudden current changes will disrupt this process: too high a current may cause the coating to burn too quickly, losing its protective effect and increasing the risk of hydrogen absorption or oxidation; too low a current may prevent the coating from melting sufficiently, resulting in slag inclusions in the weld. These defects are particularly dangerous for 7018 applications, which often involve critical structures where weld reliability is paramount.
In addition to affecting the weld pool, changing the current during a weld will destabilize the arc. The arc is the energy source that melts the electrode and base metal, and its stability depends on a consistent current supply. A sudden increase in current can cause the arc to become violent, increasing spatter and making it difficult to control the weld pool. A sudden decrease in current can cause the arc to flicker, weaken, or even extinguish, leading to sticking of the electrode (a common problem with 7018 rods, as discussed earlier) or uneven deposition of filler metal. Once the arc is destabilized, it is difficult to restore a smooth welding process, and the resulting weld is almost certain to have defects.
Another important reason is that changing the current during a weld can damage the consistency of the weld bead shape and mechanical properties. A qualified weld bead should have uniform width, reinforcement, and penetration. Current changes will cause the weld bead to "bulge" or "narrow" at the point of adjustment, creating stress concentration points. These irregularities not only affect the appearance of the weld but also reduce its ability to withstand loads. In areas where current is increased, the weld may be too wide and weak; in areas where current is decreased, the weld may be too narrow and lack sufficient strength. For load-bearing structures, such inconsistencies can become potential failure points.
From the perspective of equipment and electrode performance, changing the current during a weld is also harmful. Welding machines are designed to operate stably within a set current range. Sudden current adjustments can cause voltage fluctuations inside the machine, increasing the load on internal components (such as transformers or inverters) and reducing their service life. For electrodes, especially those with specific coating requirements like 7018, stable current ensures that the coating melts and functions at a consistent rate. Current changes can cause the coating to melt unevenly, affecting its ability to provide shielding, deoxidation, or alloying elements, further compromising weld quality.
Moreover, changing the current during a weld increases the operational difficulty for the welder. Welders need to focus on maintaining a stable arc length, travel speed, and electrode angle to control the weld pool. Adjusting the current while welding distracts attention, making it impossible to respond in time to changes in the weld pool. This increases the risk of human error, such as improper manipulation of the electrode, which exacerbates weld defects.
It is worth noting that some welders may consider adjusting the current to compensate for other problems (such as uneven base metal thickness), but this is not a correct approach. Pre-weld preparation (such as grinding to uniform thickness) and selecting the appropriate current based on material thickness are better solutions. Current should be set correctly before welding starts, and tested on scrap metal if necessary to ensure it is suitable. Any adjustments to the current should be made between weld passes, not during a single weld.
In summary, changing the current setting during a weld disrupts the stability of heat input, arc, and weld pool formation, leading to a series of defects such as uneven penetration, incomplete fusion, spatter, and inconsistent bead shape. It also risks damaging equipment, reducing electrode performance, and increasing operational errors. For high-quality welds-especially those using 7018 rods in critical applications-current settings must be determined and locked in before welding begins. Maintaining a stable current throughout the weld is the foundation for achieving strong, reliable, and defect-free joints.
