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.
Proc. SPIE. 9685, 8th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Micro- and Nano-Optical Devices and Systems; and Smart Structures and Materials
KEYWORDS: Thin films, Data modeling, Manufacturing, Resistance, Head, Inductance, Smart materials, Liquids, Absorption, Design for manufacturability
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.