AbstractNowadays, functional surfaces play an increasingly important role in optics and electronics, biomedicine, and the energy field due to their novel properties such as super-hydrophobic, optical tuning, antifouling and drag reduction. Grinding with laser profiled wheels is a promising method to efficiently generate micro and macro features on brittle materials. However, the difficulties in precisely texturing the diamond grinding wheels and the lack of an on-machine surface measurement system (OMSM) impose challenges on grinding functional surfaces in a controllable manner. In this thesis, a deterministic surface structuring technique using laser textured wheels is developed with the assistance of an embedded surface metrology system.
Firstly, a nanosecond pulse laser is integrated into the grinding environment to investigate the feasibility of laser truing, dressing, and shaping the diamond grinding wheels. An orthogonal test was performed to characterise the effect of pulse energy, pulse overlap, and line overlap on the graphitization degree and material removal rate. Then an offset compensation method considering the shifting depth of focus is proposed to take full advantage of the beam energy. Moreover, an optimised laser texturing path was proposed to improve the sidewall straightness of laser profiled rectangle grooves. Results show that the nanosecond pulse laser is competent in the whole conditioning process of diamond grinding wheels. The runout of less than 10 μm and the abrasive protrusion height of 𝑆𝑝𝑘 5.3 μm were achieved after laser truing and dressing, respectively. The rectangle and trapezoid shapes were textured on the wheel after profiling. Using the improved laser profiling method, grooves with a straight sidewall can be generated on the wheel and the minimum groove width and spacing that were fabricated on the grinding wheel were 150 μm and 160 μm, respectively.
The performance of laser conditioned diamond grinding wheels was investigated through a series of grinding experiments. Three types of microstructures including riblets, rectangle groove and pillar arrays were ground on the glass-ceramic with good shape transferability. The surface roughness 𝑆𝑎 of the ground microstructures increased with the growth of the feedrate and depth of cut (DoC). The minimum surface roughness of 𝑆𝑎 1.06±0.217 μm was achieved when grinding with feedrate 0.25 μm/revolution and DoC 3 μm. The macro wear of the grinding wheel was about 10 μm.
To improve the machining accuracy, a chromatic confocal displacement sensor was integrated into the grinding environment for OMSM. A general routine was developed to calibrate the ultra-precision machine tool (UPMT) used in this research. Key geometric errors of the XZC type UPMT were identified by Monte Carlo simulation considering the characterization of the on-machine sampling path. An error measurement platform using the self-turned brass bar was then constructed to measure the straightness of linear slides and axial/radial errors of the spindle. Results showed that the slide straightness was less than 70 nm, and the spindle axial and radial errors were within 20 nm. The measurement result of ground microstructures showed the effectiveness of integrated OMSM.
Based on the developed grinding and OMSM system, a deterministic microstructure grinding technique was developed to structure the brittle materials. The shape transferability of the developed grinding technique was evaluated by generating micro-grooves and pillar arrays with different geometries. Results show that the inclination between the grinding wheel and the sample can be controlled at less than 0.1°, and the height deviation of ground microstructures was less than 2 μm after compensation grinding. Micro grooves and pillar arrays with varying spacing (180-230 μm) and height (20-120 μm) can be ground in a highly controllable manner.
|Date of Award
|9 Sep 2022
|Zhen Tong (Main Supervisor) & Jane Jiang (Co-Supervisor)