t is a new technology developed in 60s by using the sharp natural diamond knife to turn the soft metals such as aluminum alloy and copper alloy to get the optical mirror. It has been a new technology in 60s, and has been in history for nearly thirty years.
At the beginning, it was mainly used in advanced technology such as aerospace electronics. The mid 70s has become one of the main means of processing optical parts. High reflectivity can be obtained by cutting optical metal mirrors with diamond knives. With the advent of computer numerical control (CNC) ultra precision lathe in recent years, the contour processing of aspheric surfaces is better solved.
Then, what are the factors that affect the roundness and surface accuracy of optical lens in turning?
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1. Factors affecting the roundness of the lens
There are two main factors that affect the roundness of the lens, one is the rotary error of the spindle, and the other is the deformation of the clamping part of the. The rotation error of the spindle will be directly transmitted to the lens. Only by improving the rotation accuracy of the spindle can the roundness error of the lens be reduced. Improving the roundness of the spindle of the original machine tool and the verticality of the journal and the shoulder of the thrust table is an effective way to improve the rotation accuracy of the spindle. The accuracy of the measurement is the key to the perpendicularity of the journal and the thrust shoulder. In the actual work, the axis and the axis of the shaft are used as the measuring datum, which not only has enough precision but also the detection state is the same as the use state. The unity of the three benchmarks.
The error of the clamping of the workpiece is the error source of the processing lens. There are two requirements for the installation of high-precision optical lens. The first is that the clamping fixture can not cause or cause deformation of the workpiece. Second, it is easy to disassemble the card. The use of any card loading method will cause local stress on the lens, but it should be reduced as far as possible.
2. Factors affecting the accuracy of lens surface shape
In some countries, some countries use a closed loop numerical control system with the ability of micro time resolution to control the trajectory of the tool, and the surface shape accuracy can reach 2~0.5 microns.
According to the previous processing experience, it is necessary to improve the precision of measuring the taper of the lens first, and then improve the precision of the copying plate, and then improve the precision and stiffness of the hydrostatic guide.
3. Influence of hot deformation of machine tool and workpiece on machining precision
The thermal deformation is mainly caused by thermal expansion and thermal stress, and it occupies a large proportion in the machining error. Even for a small part, the temperature variation of one degree centigrade can cause unacceptable error.
In order to control the temperature rise of the machine tool, the two oil tanks of the machine tool are separated from the machine tool bed, and the machine tool is turned into a stable state for more than two hours before machining. In the process of processing, the local heat source is eliminated, the machine tool light is closed at any time, and the operator pays attention away from the machine tool after the knife, and the internal oil of the part is taken. The bath method reduces the thermal distortion of the lens. The machine tool works in the constant temperature room.
The aspheric mirror that is superfined and turned off by a diamond knife needs polishing and polishing the surface of the parts to further improve the accuracy and smoothness of the surface.
epilogue
It is necessary to use advanced diamond tools to turn over optical parts. The spindle bearing of machine tool usually adopts hydrostatic bearing with liquid or gas, the rotary precision is 0.05~0.025 micron, and all of them have enough stiffness and good repeatability. Besides, machine tools require higher level in vibration control, temperature control, servo performance and positioning accuracy. The preparation of diamond tools, the selection of process parameters, the stress free loading of workpiece and the selection of tools should be carefully prepared and implemented.
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