The core technology of hydrodynamic mechanical seals, represented by a dry gas seal and an upstream pumping mechanical seal, is the precision machining of hydrodynamic grooves. Laser ablation has gradually become the main machining method for hydrodynamic grooves, and the accuracy of the groove depth can generally be controlled on the order of magnitude of microns, while the hydrodynamic groove depth is usually set to 5-10 μm. For hydrodynamic mechanical seals, the insufficient stiffness and opening force may be caused by small variations in the groove depth, leading to instability or failure of the sealing operation. Thus, there is a strict requirement of accuracy for the groove depth and achieving dynamic groove precision machining with high efficiency and at a low cost remains a challenge. Taking hydrodynamic mechanical seals as an example, a novel theoretical calculation model for hydrodynamic groove depth is proposed based on laser energy density and actuation duration in this study. The influence of the process parameters on the groove depth is fully investigated by calculating the groove depth and comparing it with the experimental value, which provides a reference for the laser processing of hydrodynamic grooves of mechanical seals and microgroove processing in other fields.

A novel theoretical calculation model for hydrodynamic groove depth was established based on the relationship among the groove depth, laser energy density, and actuation duration. For a silicon carbide (SiC) sealing ring, a theoretical analysis on the laser machining of square hydrodynamic grooves was carried out by the control variable method. Moreover, an experimental comparison investigation was implemented by employing a fiber laser marking machine and a surface roughness profile shape measuring machine to explore the influence of the process parameters (e.g., laser power, repetition rate, scanning speed, filling spacing, and number of marking) on the hydrodynamic groove depth.

The depth of the hydrodynamic groove depends on the laser energy intensity acting on the material surface; that is, the groove depth is related to the laser energy density and actuation duration. According to the theoretical calculation model of the hydrodynamic groove depth, the laser energy density increases as the laser power increases. The groove depth calculation values are in good agreement with the experimental data, and they follow a linearly increasing trend with an increasing laser power value (Fig. 6). The higher the repetition rate, the lower is the laser energy density. The calculated and experimental groove depths decrease as the repetition rate increases and are consistent with each other (Fig. 7). With an increase in the scanning speed, the actuation duration shows a decreasing trend, resulting in both the calculated and experimental values of the groove depth decreasing inversely (Fig. 8). Similarly, the actuation duration decreases as the filling spacing increases, resulting in the calculation and experimental values of the groove depth decreasing. This reduction variation is found to be approximately inverse in proportion to the increase in the filling spacing (Fig. 9). With an increase in the number of markings, the actuation duration increases, and the calculated and experimental values of the groove depth increase linearly (Fig. 10). Within the range of the investigated process parameters, the maximum relative errors between the calculated and experimental groove depths are 7.25%, 5.83%, 15.07%, 7.81%, and 2.89% for the five process parameters of laser power, repetition frequency, scanning speed, filling spacing, and number of marking, respectively, indicating that the groove depth calculation model proposed in this study has a high calculation accuracy.

Theoretical and experimental investigations on the hydrodynamic groove depth of mechanical seals were conducted in this study. The influence of the process parameters (e.g., laser power, repetition rate, scanning speed, filling spacing and number of marking) on the hydrodynamic groove depth were explored and a comparison with the experimental data was done, which indicates that the variation trend in the calculation and experiment results is similar and their values are close to each other, the maximum deviation between both results is 15.07%. Laser power and repetition rate are usually utilized to adjust the laser energy density, and the actuation duration depends on the scanning speed, filling spacing, and number of marking. The law according to which the process parameters affect the hydrodynamic groove depth can be revealed by looking at the laser energy density and actuation duration; that is, the higher the laser energy density, the longer the laser acts on the material, leading to a deeper hydrodynamic groove. During the laser machining process, increasing the laser power, scanning speed, and filling spacing, and lowering the number of marking and repetition rate can effectively contribute to an improvement in the processing efficiency of hydrodynamic grooves. The groove depth calculation method proposed in this study has a high adaptability for hydrodynamic groove depth calculations for different materials and design depths, which provides theoretical and engineering guidance for various types of hydrodynamic grooves of mechanical seals or the laser precision machining of microgrooves in other fields.