Softening of the heat-affected zone (HAZ) during gear shaft welding can weaken joint strength, and the key to controlling this issue lies in the precise matching of current and voltage. Considering the characteristics of commonly used quenched and tempered steel for gear shafts, a matching logic must be established from the perspectives of heat input control and arc stability. This is analyzed in detail below.
When selecting current for gear shaft welding, precise heat control is the core principle. Current directly determines the intensity of welding heat input. Excessive current can prolong the heating time of the HAZ, causing grain coarsening and destroying the original quenched and tempered structure, exacerbating softening. Therefore, current setting should be based on the properties of the base material. While ensuring weld penetration, current should be kept as low as possible to avoid excessive heat accumulation. This control strategy can reduce the Ac1-Ac3 temperature range in the HAZ, fundamentally reducing the risk of softening. This is a key prerequisite for parameter matching in gear shaft welding.
Voltage adjustment should work in synergy with current, prioritizing arc stability and uniform heat distribution. Excessively high voltage causes arc dispersion, expanding the heat diffusion range, blurring the boundaries of the heat-affected zone (HAZ) and widening the softening zone. Excessively low voltage causes arc contraction, which can easily lead to localized overheating and also softening. In gear shaft welding, voltage must be dynamically adjusted with current to ensure a concentrated and gentle arc shape, allowing heat to be precisely applied to the weld area and minimizing additional heating of the parent material's HAZ.
An imbalance between current and voltage can significantly exacerbate HAZ softening. If current is too high and voltage is insufficient, the arc's penetration is too strong but narrow, forming a localized high-temperature zone near the fusion line, leading to structural weakness in this area. If voltage is too high and current is too low, the arc covers a large area but has low energy density, requiring extended welding time to ensure deep penetration, which in turn increases overall heat accumulation in the HAZ. Gear shaft welding must avoid this imbalance by coordinating the ratio of the two to control the heat input rate.
The matching strategy must also be flexibly adjusted based on the actual working conditions of gear shaft welding. Welding requirements vary across different locations. For example, welding at the junction of a shaft journal and a gear requires fine-tuning the current and voltage ratio to accommodate structural constraints. The specific characteristics of the welding method must also be considered. Whether using argon arc welding or gas shielded welding, parameter matching must be performed with the goal of "low heat input and stable arc" to minimize microstructural changes in the heat-affected zone (HAZ). This is a crucial component of quality assurance in gear shaft welding.
In practice, test welds can be used to observe the optimal match between weld formation and HAZ conditions. If abnormal color is observed in the HAZ, it is likely due to excessive heat input caused by improper current and voltage matching. The current should be adjusted downwards and the voltage adjusted accordingly. This dynamic adjustment approach can compensate for discrepancies between theoretical parameters and actual operating conditions, effectively controlling the softening of the HAZ during gear shaft welding and ensuring the mechanical properties of the joint.
In short, the key to current and voltage matching in gear shaft welding lies in balancing heat input and arc stability. By employing the basic principle of "low current, appropriate voltage," combined with dynamic adjustments based on base material characteristics and operating conditions, thermal damage to the HAZ can be minimized and microstructural softening avoided. This matching strategy is not only the key to controlling welding defects, but also the core technical link to ensure the overall load-bearing capacity after gear shaft welding.
