Objective Bronze-based diamond grinding wheels have been widely used, and their applications have increased sharply. However, they are difficult to dress after being blunt. Traditional dressing methods, such as mechanical and electrical dressing, have the disadvantages of large loss of dressing tools, low dressing efficiency, and serious environmental pollution. The laser dressing method has significant advantages such as high efficiency, environmental protection, controllability, and wide applicability. However, if using traditional long-wavelength continuous, millisecond, or nanosecond infrared lasers, their melting/vaporization ablation mechanism can easily cause carbonization damage of the diamond abrasive grains on the surface of the grinding wheel. The short-wavelength picosecond laser has the technical advantage of “electronic state” cold processing, which can simultaneously ensure the sharpening effect and inhibit the carbonization damage of diamond abrasive grains due to high temperatures. It has significant technical advantages when dressing the grinding wheel. In this paper, the picosecond green laser was used to radially sharpen the bronze-based diamond grinding wheel. The protocols of using a picosecond green laser to sharpen the bronze-based diamond grinding wheel were explored. Moreover, selectively and quantitatively removing of the bronze matrix at the grinding wheel was achieved.
Methods Firstly, a 10 ps green laser was focused on the bronze/diamond surface, and the damage thresholds were calibrated by the S-on-1 damage measurement method. This method allowed to determine the suitable working conditions for picosecond green laser to sharpen the bronze/diamond grinding wheels. Secondly, a picosecond green laser was used to sharpen the surface of the bronze/diamond grinding wheel. Thirdly, the surface morphology and roughness were characterized using the laser confocal microscope. Finally, the effects of laser peak power density, repetition frequency, and scanning times on the sharpening effect were studied.
Results and Discussions 1) The damage thresholds of the bronze matrix and the diamond abrasive grains differed in two orders of magnitude and amounted to 1.23×10 9 W/cm 2 and 3.71×10 11 W/cm 2, respectively (Fig. 4). The difference in damage threshold was conducive to the selective micro-removal of the bronze matrix and the selection of the sharpening process parameters. 2) The picosecond laser damage characteristics of bronze diamond grinding wheels were studied. Next, these characteristics are compared with the traditional approach using a continuous or short-pulse laser. Picosecond laser has greatly reduced the carbonization of diamond abrasive grains. If the appropriate peak power density was selected, the diamond abrasive grains were not easy to be carbonized even at high repetition frequency, there was no obvious heat trace. 3) The laser power density played a major role in the sharpening effect (Fig. 7). When the laser power was constant, adjusting the number of scans quantitatively removed the bronze matrix at the surface of the grinding wheel (Fig. 9). When the power density was constant, a proportional increase in both the laser power and repetition frequency achieved a good sharpening effect. However, the gradual accumulation of heat has increased the chances of carbonization (Fig. 8).
Conclusions In this study, the damage rules and mechanisms of bronze-based diamond grinding wheels sharpening with picosecond laser were studied. Moreover, the damage threshold of the picosecond laser ablation of the bronze matrix/diamond was quantified, and the laws of different process parameters acting at the surface of the grinding wheel were analyzed. The removal mechanism of the picosecond green laser on the bronze matrix is mainly vaporization. It allowed avoiding the carbonization of diamond abrasive grains. Even at high repetition frequencies, there was no obvious heat accumulation. The study shows that the damage threshold of the bronze matrix and diamond abrasive grains are different in two orders of magnitude. The bronze matrix can be selectively removed by adjusting the peak power density and quantitatively removed by adjusting the number of scans. Moreover, the picosecond green laser is capable of ensuring the integrity of the diamond abrasive grains by selectively and quantitatively removing the bronze matrix.
