Automatic Control System for Bodies of Revolution Processing

This research is related to metalworking processing of bodies of revolution with the help of universal lathe machines. The technology includes the application of two types of vibrations to the working tool and the processed surface error measurement. To increase the manufacturing accuracy, the workpiece processed surface error is measured while a workpiece is being rotated; this rotation is performed with the workpiece being rigidly fixed in end supports and at the same time being damped in the sections between these supports. Furthermore, the parameters of vibrations applied to the tool working travel are defined by the workpiece form error and the nature of distribution of stresses that appear when the workpiece is fixed; the nature of the workpiece processed surface form error is extrapolated from the data obtained in the workpiece sections between the supports. Before manufacturing, the workpiece is corrected while being fixed in rigid supports, and the correction itself is performed as the function of magnitude and vector of the workpiece maximum deflection plane. The workpiece may be fixed in rigid supports; steady rests with double rollers may be used as such supports. The workpiece dampening in its sections between end supports may be performed using self-centering steady rests.

Astigmatism correction of convex aspheres using the subaperture stitching Hindle test

We propose an astigmatism correction method for the subaperture stitching Hindle test to measure hyperbolic convex aspheres. Astigmatic wavefront errors arise from misaligned Hindle setups, mechanical runout errors of the rotational motion for stitching, and the surface error of the target itself. Because these errors are combined, they cannot be separated in the conventional subaperture stitching Hindle tests. We exploited the rotational periodicity of each error to distinguish the surface figure error from other astigmatic error sources and rectified the Hindle test results with a third-order astigmatism. Using the subaperture stitching Hindle test, we averaged two sets of measurement data with a 180° rotational phase difference between them to calculate the astigmatic surface error. The proposed method was verified experimentally by comparing it with the results from a commercial stitching interferometer from QED Technologies; only subnanometer differences in the root-mean-square values were obtained. Therefore, the proposed method calibrated the system errors from the test surface wedge and the rotational decenter easily, thereby reducing the mechanical costs and alignment efforts and making it more accessible than a sophisticated mechanism.

Parametric Mid-Spatial Frequency Surface Error Synthesis

Standard mid-spatial frequency tooling mark errors were parameterized into a series of characteristic features and systematically investigated. Diffraction encircled and ensquared energy radii at the 90% levels from an unpowered optical surface were determined as a function of the root-mean-square surface irregularity, characteristic tooling mark parameters, fold mirror rotation angle, and incident beam f-number. Tooling mark frequencies on the order of 20 cycles per aperture or less were considered. This subset encompasses small footprints on single-point diamond turned optics or large footprints on sub-aperture tool polished optics. Of the characteristic features, off-axis fabrication distance held the highest impact to encircled and ensquared energy radii. The transverse oscillation of a tooling path was found to be the second highest contributor. Both impacts increased with radial tooling mark frequency.

Precise Machining Based on Ritz Non-uniform Allowances for Titanium Blade Fabricated by Selective Laser Melting

Selective Laser Melting (SLM) is an increasingly concerned trend in Ti-6Al-4V blade manufacturing, while the SLMed Ti-6Al-4V blade cannot be used directly because of poor surface integrity and high residual stresses. Precise machining after SLM is a feasible solution but also a challenge. The low rigidity of the blade will lead to deformation when machining. The deformation can lead to surface error and may make defect parts. Two-steps machining processes to address the problems were proposed in this paper. First, a non-uniform allowance distribution was allocated and optimized in semi-finishing based on Ritz solution to elastic deformation. The blade was simplified as a cantilever thin plate with various thickness, and the thickness of finishing allowance was designed and optimized on the premise of ensuring the thin-wall stiffness of the blade, so as to realize the design of Ritz non-uniform allowance. Then, finishing machining was conducted to achieve precise parts. A blade deformation model was established to evaluate surface error with cutting force moving and changing. Finite element analysis and experimental validation in ball-end milling of a blade were conducted. FEA results and experimental results showed dimensional errors have been reduced up to 50%. Further surface tests demonstrated that the mean surface roughness reduced from 7.88 μm to 0.815 μm. And the residual surface stresses of the SLM samples changed after semi-finishing machining due to the residual stress relaxation and redistribution. The results demonstrated that the proposed method enhanced the surface quality of blade fabricated by SLM.

Topology Optimization Based Parametric Design of Balloon Borne Telescope’s Primary Mirror

For balloon-borne telescopes, the primary mirror is the most important optical element, but designing a primary mirror with an excellent overall performance is a challenge. To comprehensively consider the contradictory objectives of the root mean square (RMS) surface error under gravity in the X and Z directions, the mass and fundamental frequency of the primary mirror, a parametric primary mirror design using the compromise programming method based on topology optimization is proposed. The parametric design of the compromise programming method based on topology optimization is used to find the optimal solution for X-direction RMS (RMSx), Z-direction RMS (RMSz), mass, and fundamental frequency. Compared with the initial primary mirror structure designed according to traditional experience, the overall performance is improved. Results show that the respective mass of the primary mirror, the RMSx and the RMSz decreased by 8.5%, 14.3% and 10.5% compared to those before optimization. Comprehensive consideration can prove the effectiveness of parametric design based on the topology optimization of the primary mirror. This method provides a reference for the design of other primary mirrors for balloon-borne telescope and space cameras.