Study on the fabrication of a high precision aluminum alloy cylindrical mirror with combined process

With the excellent optical performance especially some aspherical surfaces enhanced, aluminum alloy mirrors are widely used in many optical systems. The technique of Single-point diamond turning (SPDT) applied in the IR optical application directly. However, it is difficult to obtain higher precision for some complex mirrors and the remaining periodic diamond turning structure can cause scatter losses for shorter wavelengths. Hence, additional polishing steps are necessary. In this paper, a process chain contains SPDT and Magnetorheological finishing (MRF), is put forward for machining an aluminum alloy cylindrical mirror. A high accurate measurement setup, composed of an interferometer and an advanced Computer generated hologram (CGH) is built, and the data distortion is analyzed and corrected. Additionally, normal positioning error caused by tool setting is analyzed and simulated, and a workpiece self-localization system in MRF is used to control the error. The experimental result shows that the surface texture converges to PV 0.233. (lambda=632.8nm, 90% aperture), rms 0.040 lambda (90% aperture). It is concluded that the form accuracy of the aluminum alloy cylindrical mirror is improved by the process chain, moreover, the process chain is the reference for the fabrication of aluminum alloy mirrors with complex surfaces.