Machining Aspheric Surface by Vacuum Coating
The hollow coating method is one of the additional processing methods. Its essence is to use vacuum plating on polished spherical surface or plane (substrate) to coat variable thickness film that is clear or not. On the different zones of the surface to be asphericized, the change of film thickness is ensured by the baffle (screen with circular holes). Obviously, the aspheric surface processed by vacuum coating method is different from that processed by mechanical method, because the latter is based on removing the remaining data, while the former is attached with certain data. In some cases, the vacuum coating process has certain advantages. For example, it is possible to select different coating materials, whether they are clear or not. When the waste product is produced, the film layer can be removed without harming the substrate.
The main advantage of this method is that it can process arbitrary aspherical surfaces, including asymmetric aspherical surfaces (obtained by non-uniform rotating baffles), and has high repeatability. The error is about 1% e. This means that when the technology of vacuum coating equipment is determined, the error of film thickness from one production cycle to another is not more than 1%, and when the film thickness is 20 um, the error is 0.2 um, It is equivalent to the difference of one aperture when checking the aspheric surface with a glass template. Therefore, the vacuum coating process is completely suitable for making high-precision aspherical surfaces.
The vacuum coating of optical parts makes them aspherical. The general vacuum coating machine can be used to make the transmission organization of parts rotate and the equipment to check the film thickness.
This method was proposed in the mid-1930s. At that time, a spherical surface was made into a paraboloid by vacuum aluminum plating. At that time, light scattering was found at the beginning of the mirror. In some cases, when the film exceeded 5 wavelengths, the film appeared cracks and fell off in layers. Later, it was proved that the thickness of zinc sulfide coating can be greatly increased to 30-40A on the condition that the quality of the coating is not harmed. In the early 1960s, the Soviet Union had successfully plated a diameter of 140mm, a relative diameter of 1:1.4, and a maximum deviation of 10um. Then it proves the possibility of using vacuum method to make high precision reflecting non spherical mirror. At present, the method of vacuum coating asphericalization is still developing and improving.
Hangzhou Datian CNC Machine Tool Co., Ltd. focuses on efficient processing and is the navigator of efficient processing machine tools. Its efficient machining center machine tools have the most obvious advantages and are welcomed by users. This article is supported by Datian CNC website www.hzdtsk.com.
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