In order to improve the processing efficiency on the basis of obtaining good surface quality for aluminum alloy mirror with the chemical mechanical polishing(CMP) method, the status between abrasives and workpiece surface is researched adopting the elastic plastic deformation and nano indentation theory. The material removal mechanism is revealed through the CMP material removal model which is established on the analysis of surface topography, particle force and removal efficiency. It is found that the discontinuous down pressure which is related to surface morphology of the polished pad has a serious influence upon removal efficiency as well as the original pressure and the rotate speed of pad. With the support of these results, a variable parameter polishing method is proposed. The actual experiment result shows that the processing time is shortened by about 64% compared with the original method on a Φ100mm plane sample in the process of roughness improvement from Ra 5.03nm to Ra 2.95nm. The validation of variable parameter CMP method is certificated.
A Lap-MRF process is proposed for large aperture mirrors. In Lap-MRF, a lap is used to expand the polishing area, which improves the material removal rate. Moreover, the MR fluid can be renewed continuously to ensure the stability of the material removal rate, which improves the convergence efficiency of the surface profile error. In this paper, the figuring ability of the Lap-MRF removal function is analyzed. The Lap-MRF process, which is based on surface profile filtering, is presented. Finally, a series of figuring experiments on a Φ350 mm K9 mirror are carried out. For the Lap-MRF removal function, the volume removal rate is up to 0.48 mm3 /min and the cut-off frequency is about 0.03 mm-1 . After four times figuring using Lap-MRF, the surface profile error throughout the whole surface is improved to 4.84 λ (λ= 632.8 nm) PV (Peak-to-Valley), 0.69 λ RMS (Root Mean Square) from 25.24 λ PV, 4.31 λ RMS and its total convergence ratio of the RMS error is up to 6.32. These results verify the validity of the proposed method for large aperture mirrors.
Complex surface optical components have been widely used in the forefront of aerospace, space exploration, military reconnaissance and modern information technology due to their advantages in improving aberrations, improving imaging quality, reducing system unit quantity and weight, reducing power loss, improving accuracy and stability. As one of the main methods to process high precision optical component, Computer controlled optical surfacing (CCOS) has also been applied in the processing of complex surfaces. However, due to the incompletely contact between the polishing pad and the surface of the workpiece especially the high-steepness and large curvature area during processing, the phenomenon of unstable removal function is generated, which leads to deterioration of surface accuracy and even flaws..In this paper, the elastic fiber modeling theory derivation, ABAQUS finite element simulation and experimental verification method are used to study the contact problem between the polishing disc and the workpiece surface and the stress distribution when processing complex curved surfaces, and the deformation layer of the polishing pad is optimized. An improved semiflexible polishing disc was used to machine a complex curved aluminum alloy mirror, which improved the surface quality while controlling the change in surface accuracy (PV value) within 10%, verifying the improved polishing disc processing. The effectiveness of complex surfaces.