Aspherical surfaces are more and more used in some high precision optical systems of Thales Angenieux. They must conform to the same quality criteria of form and roughness as the other surfaces. However, their manufacturing is complex and cannot use the conventional methods of spherical or plano surfaces manufacturing. It is particularly difficult to meet simultaneously the form and roughness requirements even with the latest production techniques.
Among the different possible aspherical surfaces manufacturing methods, Thales Angenieux chose to develop an industrial manufacturing process which combines two manufacturing methods: a microgrinding and a magnetorheological finishing. It was at first considered a manufacturing process with two stages of microgrinding and one stage of magnetorheological finishing. However, it was not possible to produce surfaces which meet the required criteria with
these three stages despite an optimisation of microgrinding parameters. It proved to be necessary to insert a stage to insure the transition between a microgrinding stage and a magnetorheological finishing stage. This manufacturing process allows on the one hand to produce an aspherical surface with a form PV around 150 nm and a roughness Rms between 1 to 2 nm and, on the other hand, proves to be compatible with industrial manufacturing requirements.