Japanese scholar Omori and others have researched superabrasive grinding wheels since 1987, developed a grinding method using electrolytic In Process Dressing (ELID), and realized high-grade mirror grinding and ductile grinding of hard and brittle materials. , and now the method has been successfully applied to the ultra-precision machining of spherical, aspherical lenses and molds.
① ELID mirror grinding principle
ELID grinding system includes: metal bond ultra-fine grained super-hard abrasive grinding wheel, electrolytic dressing power source, electrolytic dressing electrode, electrolyte (also used as grinding liquid), electric brush and machine tool equipment. In the grinding process, the grinding wheel is connected to the positive pole of the power supply through the electric brush, the dressing electrode installed on the machine tool is connected to the negative pole of the power supply, and the electrolyte is poured between the grinding wheel and the electrode, so that the power supply, grinding wheel, electrode, grinding wheel and the electrolyte between the electrodes to form a complete electrochemical system.
When using ELID grinding, there are some special requirements for the grinding wheel, power supply and electrolyte used.
The bonding agent of the grinding wheel is required to have good electrical conductivity and electrolysis, and the hydroxide or oxide of the bonding agent element is non-conductive and insoluble in water. The power source used for ELID grinding can use the DC power source of electrolytic machining or various Waveform pulse power supply or DC base pulse power supply. In the ELID grinding process, the electrolyte not only acts as a grinding fluid, but also plays a role in reducing the temperature of the grinding zone and reducing friction. ELID grinding generally uses a water-soluble grinding fluid, which is a machine tool that uses a bond-based grinding wheel. The strength is high, and the grinding wheel wear is small by setting the appropriate amount of electrolysis. At the same time, high shape accuracy can be obtained. Applying this principle, ultra-precision mirror grinding of optical components of various shapes from flat to aspherical surfaces can be realized.
②ELID mirror grinding experimental system
On the ASG-2500T machine tool of Rank Pneumo Company, the Omori ELID system composed of grinding wheel, power source, electrode, grinding fluid, etc. is installed to use 400# for rough forming and 1000# or 2000# for semi-finishing. When mirror grinding, use 4000# (average particle size is about 4μm) or 8000# (average particle size is about 2μm) cast iron bond diamond grinding wheel, electrolytic sharpening power supply (ELID power supply), using DC high frequency pulse voltage Type special power supply, the working voltage is 60V, the current is lOA. When using the grinding fluid, it is required to dilute the water-soluble grinding fluid AFH-M and CEM by 50 times with pure water.
③ ELID mirror grinding experimental method and experimental results
For aspherical surface machining, the flat grinding wheel is only formed and integrated by the bowl-shaped grinding wheel (325# cast iron bond diamond grinding wheel is φ30×W2mm) installed on the workpiece shaft. Rough grinding and 1000# semi-finishing, and finally use 4000# for ELID mirror grinding. On the ultra-precision aspheric processing machine, with the help of ELID grinding technology, the optical glass BK-7 aspheric lens was successfully processed. . The surface accuracy is better than o. 2μm, the surface roughness reaches Ra20nm, and for the aspheric surface processing of slightly soft materials such as LASFN30 and Ge, the surface accuracy can also be better than O. 2-O. 3μm, surface roughness up to Ra30nm.