Deterministic polishing is critical to the fabrication of ultra-precision aspheric optics, where precise dwell time algorithms are used to remove surface material. However, the sub-aperture polish removal function introduces surface ripple characteristics and degrades optical performance due to its narrow full width at half maximum and mismatched spatial wavelengths, reducing volume removal rate and introducing high and medium spatial frequency errors on the surface. Therefore, there is an urgent need to introduce pre-processing and post-processing to improve flexibility control in deterministic small tool polishing, enhance the adaptability of the tool to the workpiece surface with changing curvature, and obtain a stable Gaussian-like tool influence function. This paper explores the surface finishing removal mechanism based on the compliant figuring process and verifies the robustness and machining accuracy of the tool influence function for plane and variable curvature Nickel-phosphorous alloy machined surfaces. Firstly, based on the removal mechanism of the figuring process, the relative velocity and contact pressure models were established. Secondly, the influence of the radius of curvature and the amount of offset on the removal function is discussed. Finally, the high frequency band and middle frequency band of the one-dimensional power spectral density curve are analyzed in detail, and the reliability and modification ability of the compliant figuring process are verified according to the amplitude spectrum image.
The removal function in machining is not an ideal impulse function, and the material removal at any point on the workpiece is a superposition of the removal at that point from the distribution of removal at surrounding points. When the residence time suddenly jumped to zero at the edge, the removal function and the residence time convolution results will gradually decrease at the edge, the removal matrix at the edge of the formation of the "collapse", after many convolution iterations, the edge of the face shape of the error convergence rate is lower than the other positions, resulting in edge effects. This paper firstly put forward an iterative algorithm based on the residence time of the cylindrical projection, and then analyze the edge effect in the iterative algorithm, and put forward two methods to suppress the edge effect, and select different removal functions and the form error on the algorithm to carry on the simulation calculation. Finally, the results of machining of mold #54 verifies the effective suppression of edge effect error by the method in this paper.
Temporary sources and explosive celestial bodies in the universe can only be observed through their high-energy radiation, for example X-rays. The multilayer nested Wolter-I type focusing mirror is widely used in X-ray astronomical telescopes. The electroforming replication process can achieve batch high-precision production of Wolter-I type focusing mirrors, with the process flow of mold ultra-precision turning, ultra-smooth, coating, electroforming, and demolding. The fabrication of molds accounts for a large proportion in the process, and the molds accuracy and surface quality directly determine the optical performance of the mirrors. We built the DRL2000 ultra-precision lathe for mold turning of mission EP (Einstein Probe) and eXTP (enhanced X-ray Timing and Polarimetry mission). The swing straightness error of the guide rail was separated and compensated through trial cutting and reverse measurement methods to achieve a turning generatrix accuracy of peak-to-valley (PV)<0.2μm. An in-situ measurement device has been built based on the ultra-precision lathe. After adjustment the system measurement error can be controlled within 0.1μm. The corresponding spiral measurement path and coaxiality error separation method were studied and verified through experiments. An offline measurement device was built and based on it, an optical lever measurement method was preliminarily validated. Finally, a division method of medium-low frequency error and medium-high frequency error was proposed.
Based on chemical-mechanical polishing and combining mechanical and tribochemical polishing techniques, a precision lapping method suitable for parabolic polishing specified by grazing incident X-rays is introduced. Various factors affecting the polishing process are analyzed, and the results show that the proposed method is consistent with Preston's equation and Hertz contact principle. Therefore, this paper proposes a general material removal model based on the above two methods. The mid and high-spatial frequency errors are demanded to reach the requirements with an angular resolution consistently < 6 arcsec HEW and a roughness of 0.3 nm rms (between 1 mm and 0.002 mm spatial frequency range). To achieve the conformal ultra-smooth polishing of focusing mirrors, the process of full-aperture super-smooth pitch polishing is investigated. The influences of key polishing parameters are revealed. The evolution of the surface topology has been studied. A polishing setup is established to carry out experimental polishing to verify the optimum processing parameters obtained by simulations and previous polishing tests. Besides, the effect of abrasive particle size on the roughness is also verified. The roughness of the polished mandrel is measured at different positions, and the optimum roughness reaches Ra 0.359 nm. The polishing approach can significantly reduce the surface roughness of the replication mandrel, satisfying the low energy band focusing requirement of grazing incidence X-ray mirrors.
Electroless nickel is an excellent material for making optical molding dies, because of its machinability with both single-point diamond turning and polishing, as well as its suitable hardness and durability. This paper deals with the ultra-precision polishing of molding dies for telescope mirrors with a super smooth surface with a roughness below 1 nm root-mean- square (rms). According to the probability density distribution function of different sizes of abrasive grains cut into the workpiece, a surface roughness model combining the micro contact model and the force balance principle was established. A surface roughness of 0.316 nm Ra was obtained on slab molding dies of 30 mm in diameter.
In recent years, major projects, such as National Ignition Facility and Laser Mégajoule, have generated great demands for large aperture optics with high surface accuracy and low Subsurface Damage (SSD) at the mean time. In order to remove SSD and improve surface quality, optics is fabricated by sub-aperture polishing. However, the efficiency of the sub-aperture polishing has been a bottleneck step for the optics manufacturing. Atmospheric Pressure Plasma Processing (APPP) as an alternate method offers high potential for speeding up the polishing process. This technique is based on chemical etching, hence there is no physical contact and no damage is induced. In this paper, a fast polishing machine tool is presented which is designed for fast polishing of the large aperture optics using APPP. This machine tool employs 3PRS-XY hybrid structure as its framework. There is a platform in the 3PRS parallel module to support the plasma generating system. And the large work piece is placed on the XY stage. In order to realize the complex motion trajectory for polishing the freeform optics, five axis of the tool operate simultaneously. To overcome the complexity of inverse kinematics calculation, a dedicated motion control system is also designed for speeding up the motion response. For high removal rate, the individual influence of several key processing parameters is investigated. And under specific production condition, this machine tool offers a high material over 30mm3/min for fused silica substrates. This results shows that APPP machine tool has a strong potential for fast polishing large optics without introducing SSD.
Hydrostatic guideway has been widely used for ultra-precision machine tools due to its high stiffness and motion accuracy. In order to optimize the stiffness and motion accuracy of hydrostatic guideway, the effect of different diameters orifice restrictors on the stiffness and deformation of hydrostatic guideway is investigated in detail in this paper. The theoretically optimal structural coefficient is verified through the experiments. Hydrostatic guideway can obtain the maximum stiffness when the value of optimal structural coefficient is 0.707. And changing the diameter of orifice restrictors is an effective method to adjusting the structural coefficient. Due to the error caused by manufacture and assembly of hydrostatic guideway, the optimal structural coefficient is hard to be obtained accurately. Based on this condition, a larger structural coefficient is adopted to reduce the oil pressure in the pocket of hydrostatic guideway effectively, so that the deformation of guideway can be reduced. And finally, the stiffness loss caused by the deformation decreased. In addition, the experimental results show that the maximum deformation of hydrostatic guideway can be reduced from 2.06μm to 1.82μm and the stiffness arise from 1453N/μm to 1855N/μm when orifice restrictors with 0.15mm diameter are used rather than 0.2mm diameter.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.