At present, there are two main ways to study the lightweight technology of mirror: casting forming method, high temperature welding or welding sealing method, and mechanical drill weight reduction method. Each of these three methods has its own advantages. The first two methods of processing the structure stiffness is relatively large, light weight, light weight rate can reach more than 70%, can ensure a higher surface accuracy of the mirror. Some oversized mirrors basically use the first two lightweight methods. For most mirrors of conventional caliber, the light weight of mirror structure is generally carried out by machining method. Mechanical drilling is an earlier method of mirror lightweight, which is achieved by mechanical drilling to remove the material on the mirror that does not participate in the imaging part of the optical system. At present, the commonly used methods include milling and drilling, ultra-Luo drilling, etc. The milling and drilling method controlled by computer can obtain the mirror with higher processing efficiency, higher lightweight degree and higher precision.
The shapes of the lightweight cells of the mirror mainly include triangular cells, quadrilateral cells, hexagonal cells, honeycomb cells, sector cells and circular cells, etc. The density and layout of the lightweight cells should be considered according to the requirements of the optical system on the surface shape of the primary mirror. Its form is shown in the figure.
The circular cells has good technological performance and is easy to process, but the lightweight rate is low. The fan-shaped lightweight cells is generally used for the lightweight of the circular mirror with a central cells. According to the different reinforcement arrangement is divided into continuous reinforcement type and intermittent reinforcement type of lightweight cells. In terms of machinability and structural rigidity, the structural rigidity of honeycomb cells is the best, and the technological performance of circular cells is the best. The technological properties of triangular cells, quadrilateral cells and fan-shaped cells are not much different. The structural stiffness of triangular cells and hexagonal cells is better, among which triangular cells are the best, but it is easy to form hot junction at the joint of triangular cells. Therefore, the thermal performance of triangular cells is not as good as that of hexagonal cells.