Current status of ul-tra-precision manufacturing of complex curved aluminum mirrors

Complex optical surfaces can simplify the structure of the optical system, reduce the quality of the system, provide more flexible system layout, and have a higher degree of design freedom. A few complex curved components can replace multiple traditional rotationally symmetric optical curved components, so the complex curved surface becomes an important direction for the development of reflection mirror shapes. Compared with traditional optical materials such as fused silica, optical glass, single crystal silicon and silicon carbide, aluminum and its alloys used as optical components have many advantages: (1) The material has good machinability and is easy to realize complex curved surface manufacturing. The aluminum reflector can use the existing mature manufacturing techniques such as turning and milling to quickly process the matrix structure of the mirror body, giving full play to the advantages of aluminum material's easy molding. (2) High weight reduction rate can be achieved. Aluminum alloy materials not only have low density, but also have good workability. Turning and milling can quickly and accurately complete the processing and manufacturing of conventional weight-reducing holes, achieving high weight reduction. (3) Non-heating optical and mechanical integrated structure design. The installation support structure of the optical system and the mirror body can be made of the same aluminum alloy material, which avoids the thermal stress and strain caused by the inconsistent expansion coefficient of the material caused by the use of multiple materials in the traditional opto-mechanical system, which is important for maintaining the long-term performance of the optical system. Stability is of great significance, and it is especially suitable for optical systems that work in environments with large temperature differences. Therefore, the complex curved aluminum mirror has a very broad prospect in the application of optical systems.

A research team from the Precision Engineering Laboratory of the National University of Defense Technology published a review article in the "Optical Engineering" titled "The Status of Ultra-precision Manufacturing of Complex Curved Aluminum Mirrors". This article was subject to the National Defense Fundamental Scientific Research Challenge (TZ2018006) and National Natural Science The key project of the Fund (51835013) is funded to show the current research status of manufacturing and testing of complex curved aluminum mirrors. The main contents are:

1. Single-point diamond turning (SPDT) turning technology for complex curved aluminum mirrors

SPDT processing can directly process complex surface-shaped optical elements, and a nano-level smooth surface can be obtained in one processing. The processed mirror can directly meet the needs of infrared wave band. In addition, SPDT has good processing repeatability, high production efficiency, high enough assembly precision of processed optical components and mounting brackets, simple assembly and adjustment, and convenient calibration. The combination of SPDT turning technology and other processing technologies to form a combined process can also obtain better performance optical components, which has an extremely important position in the manufacture of advanced optical systems.

2. Polishing technology of complex curved aluminum mirror

At present, the finished optical components processed by SPDT technology can only meet the application requirements in the infrared spectral region. If you want to obtain a complex curved aluminum reflector that meets higher use requirements, you must use subsequent polishing to form a combination process to improve the aluminum reflector Surface shape accuracy and improve its surface quality. This article introduces the Magnetorheological Finishing (MRF) technology used in the polishing of complex curved aluminum mirrors and the conformal smoothing polishing technology based on Computer Controlled Optical Surfacing (CCOS). These two polishing technologies When polishing a complex curved mirror surface, it can adapt to the change of local curvature, and a high-quality optical surface can be obtained.

3. Complex surface CGH detection

The detection technology of complex curved surfaces is an important step in the manufacturing process of complex curved optical elements,and is one of the most critical factors restricting the development of complex curved optical elements in a higher direction. Computer Generated Hologram (CGH) detection method has unique application advantages in the detection of complex curved optical parts. It can generate reference wavefronts of any shape and compensate for various types of aberrations. Its design is flexible and adaptable. The range is wide, and the measurement uncertainty can reach the nanometer level.

Fig.1 Free Form Surface Aluminum Mirror

Fig.2 Schematic Diagram of CGH Detection

About The Group

The precision engineering research team of National University of Defense Technology is an innovative group in Hunan Province. It has been engaged in ultra-precision processing technology research for a long time. As the chief unit, it has completed the military and civilian optical manufacturing 973 projects, and has systematically established an Ultra-precision optical manufacturing theory based on controllable flexible body, developed magnetorheological and ion beam polishing digital optical manufacturing equipment with independent intellectual property rights, and formed new theories and new methods for deterministic manufacturing of optical mirrors, including lithography objective lenses, space cameras and strong light systems, etc. The development of major optical systems provides manufacturing technical support. Won 1 second prize of National Technological Invention Award, 1 first prize and 1 second prize of Military Science and Technology Progress Award, 1 first prize of Science and Technology Progress Award of the National Defense Science and Technology Commission, 1 first prize and 1 second prize of Hunan Science and Technology Progress Award each He has obtained more than 100 national invention patents, published more than 10 monographs, and published more than 400 SCI/EI search papers.

Article

Xu Chao, Peng Xiaoqiang, Dai Yifan. Current status of ultra-precision manufacturing of complex curved aluminum reflectors.[J]. Opto-Electronic Engineering, 2020, 47(8): 200147.

DOI:10.12086/oee.2020.200147