Experimental study on nanosecond laser controlled cutting of polycrystalline diamond (<italic>invited</italic>)

ObjectiveDiamond has excellent thermal conductivity, ranging from 2 000 to 2600 W·m−1·K−1 at room temperature. It has a relatively low dielectric constant and dielectric loss, and is insulating at room temperature, which gives it a significant advantage in the field of thermal management of electronic devices. However, the high hardness, brittleness, and extremely high chemical stability of diamonds make it difficult to process and shape them using traditional mechanical or chemical methods, which seriously hinders their widespread application. Laser processing, as a non-contact process, effectively avoids direct impact and hard contact, making it a highly effective method for diamond processing. Nanosecond lasers, with their short pulse width and high peak energy, effectively overcome the thermal effects of long-pulse laser processing, making them particularly advantageous for high-precision processing of high-melting-point and ultrahard materials. Therefore, this study experimentally investigated the process of ultraviolet nanosecond laser cutting polycrystalline diamond.MethodsThis study investigated the slitting of thick diamond using an ultraviolet nanosecond laser, discussing the effects of laser and scanning parameters on the diamond surface quality and the taper of the kerf sidewalls. The processing results were observed and analyzed using scanning electron microscopy, Raman spectroscopy, and confocal microscopy. After parameter optimization, a focal plane array layer-by-layer feeding method was employed to process the thick samples.Results and DiscussionsExperiments show that a laser power of 10 W achieves both high processing efficiency and high kerf quality. The S-shaped fill process produces smoother kerf sidewalls, with no noticeable taper at the lower end. The kerf sidewalls maintain good perpendicularity to the upper surface of the diamond sample. When the fill spacing is 20 μm, the lower portion of the kerf is severely curved, with only a small portion of the sidewall perpendicular to the upper surface of the diamond sample. When the filling spacing is 1 μm, the side wall taper is the smallest. While processing without focal plane feed can ensure no taper, it can only cut diamond samples ranging from 500 μm to 1 mm, making it difficult to achieve the desired slicing goal. After line scanning to create a rectangular outer frame, an S-shaped reciprocating filling scan method is used. To ensure that the focal plane is as close as possible to the bottom surface of the material being processed, the number of single-layer scans is set to 10, and the focal plane layer-by-layer feed method is used three times until the kerf completely penetrates the entire diamond sample. This method maximizes the laser energy used to remove material and minimizes the effects of defocus. Finally, high-quality taper-free controllable slitting of 2 mm thick polycrystalline diamond was successfully achieved, with the diamond sidewall roughness reaching 2.65 μm.ConclusionsThrough systematic experimental research, this paper identified the key process principles for UV nanosecond laser cutting of thick polycrystalline diamond (PCD) and successfully achieved high-quality, low-damage slicing of 2 mm thick samples. The main conclusions are as follows: 1) Laser power is a key parameter influencing kerf morphology and the degree of graphitization. A power of 10 W achieves a high material removal rate while achieving smooth kerfs and a relatively thin graphite layer on the machined surface, achieving a balance between processing efficiency and surface quality. 2) The scanning path has a decisive influence on processing stability and sidewall quality. Compared with the Z-type path, the S-type reciprocating filling scan avoids frequent jumping processes, improves processing continuity, thereby obtaining a smoother side wall and effectively suppressing the generation of taper in the early stage of processing. 3) The number of scans and the fill spacing jointly determine the kerf depth and taper. As the number of scans increases, the slit depth tends to be saturated due to the limitation of the laser Rayleigh length and energy loss, and the taper increases accordingly. When the scanning interval is 1 μm, combined with the optimized number of scans, the sidewall taper can be minimized and the platform structure at the bottom of the kerf can be maintained. 4) The rectangular frame scanning strategy is an effective means to control the taper of deep cutting slits. A combined process of "first scanning the rectangular frame to define the outline, then performing S-shaped fill to remove the inner material" significantly improves sidewall taper, resulting in a nearly taper-free vertical sidewall. 5) For thick samples, this study proposed a "focal plane layer-by-layer feed" processing method. Under the optimal parameter combination (power 10 W, frequency 50 kHz, speed 300 mm/s, width 100 μm, S-type fill, 1 μm spacing, and 10 single-layer scans), a complete kerf section of 2 mm thick polycrystalline diamond was successfully achieved after three passes. The final kerf sidewall roughness (Sa) was 2.65 μm, with no macroscopic defects such as chipping or cracks.