Precision hole-machining of SiCf/SiC composite using single-layer brazed diamond core drill dressed by pulsed laser

ObjectivesThe single-layer brazed diamond core drill generally exhibits poor protrusion height uniformity of grains, making it difficult to control the hole diameter and the accuracy when machining SiCf/SiC composites. Pulsed laser is used to dress the core drill to improve grain height uniformity, thereby enhancing hole accuracy on SiCf/SiC composite.MethodsFirstly, a pulsed laser dressing platform for the single-layer brazed diamond core drill is developed, and the influence of laser dressing parameters on grain height uniformity and morphology is revealed. Then, the aperture accuracy of the core drill before and after dressing is compared and analyzed to verify the benefits of laser dressing in improving hole accuracy. Finally, high-quality processing of SiCf/SiC composite holes is achieved using the dressed drill. During the process, the total cutting depth of the pulsed laser is determined by dressing a standard rod to the target aperture size and then replacing it with the core drill for further dressing. The relative distance between the abrasive grains and the laser beam is adjusted, and the laser beam focus is aligned with the cutting point. The laser beam is reciprocally scanned along the tool axis to remove the protruding diamond grains and improve core drill height uniformity.ResultsThe experiments show that pulsed laser dressing can effectively enhance the height uniformity of the side grains on the single-layer brazed diamond core drill. The discrete coefficient of grain height after dressing is reduced by 64%, from 0.11 to 0.04. Following pulsed laser dressing, the contour lines of side grains on the core drill become smoother, indicating improved height uniformity. The surface of diamond grains after pulsed laser ablation appears black due to a graphitization reaction, forming a thin black metamorphic layer that does not affect diamond grain performance. The laser-dressed single-layer brazed diamond core drill exhibits improved hole-making performance with a smaller variation range in hole diameter (4.00 - 4.02 mm) and higher hole-making accuracy. In contrast, the untrimmed core drill shows a larger variation range in hole diameter (4.06 - 3.98 mm) during the hole-making process. Furthermore, pulsed laser dressing has no negative impact on the grinding ability of the core drill. The average drilling force is 13.72 N before dressing and 12.43 N after dressing, with a difference of 1.29 N consistent with the change trend of the drilling force during the entry stage. The laser-dressed core drill maintains aperture accuracy better throughout its lifespan, with aperture deviation being only 0.02 mm, meeting the requirements on hole accuracy and showing a 75% reduction compared to the undressed condition.ConclusionsThe study applies pulsed laser dressing to enhance the protrusion height uniformity of grains on single-layer brazed diamond core drills. A laser dressing device is constructed, and a method is proposed. Using a graphite rod as the standard rod for determining the laser dressing depth reduces the diameter deviation. Pulsed laser dressing effectively improves grain height uniformity, with the discrete coefficient reduced by 64%. The dressed core drill demonstrates smaller aperture deviation (0.02 mm), meeting accuracy requirements without adversely affecting grinding ability or service life. This verifies the advantage of laser-dressed core drills in improving hole-making accuracy.