What problems should we pay attention to in the processing of optical glass lenses?
In the process of optical glass lens processing, we need to pay attention to the following problems:
A, raw material inspection and preparation stage
Quality inspection
The quality of optical glass directly affects the performance of lens. Carefully check whether the optical parameters such as refractive index and dispersion coefficient of glass meet the design requirements. For example, for the optical glass lens used for photographic lens, the deviation of its refractive index may lead to color difference of imaging and affect the quality of photos.
Check the uniformity of glass, including internal stress distribution and impurities. Uneven internal stress may lead to lens breakage during processing, while impurities will affect the transparency and optical properties of the lens. You can use a polarizer to check the stress and a microscope to observe the impurities.
Blank cutting
According to the size and shape requirements of the lens, choose the appropriate cutting method. When cutting, ensure the cutting accuracy, because the accuracy of blank size will affect the subsequent grinding and polishing processes. For example, for high-precision microscope lenses, the error of blank size should be controlled within a very small range.
Attention should be paid to avoid excessive edge collapse and cracks during cutting, because these defects will be further expanded in subsequent processing. Appropriate cutting speed and coolant can be used to reduce these problems.
Second, the grinding stage
Selection and debugging of grinding equipment
Select a suitable grinding machine, and determine the material and rotational speed of the grinding disc according to the size, shape and accuracy requirements of the lens. For example, for the large-size astronomical telescope lens, it is necessary to use large-scale grinding equipment, and the rotating speed of the grinding disk should be moderate to ensure the grinding uniformity.
Debug the grinding equipment to ensure the flatness and concentricity of the grinding disc. Poor flatness of the grinding disk will lead to uneven surface of the lens after grinding, and poor concentricity will affect the curvature accuracy of the lens.
Control of grinding process parameters
The choice of abrasives is very important. The particle size, hardness and chemical properties of abrasive should match the material of optical glass. For example, for optical glass with higher hardness, abrasive with finer particles and slightly higher hardness should be used to ensure the grinding effect.
Control grinding pressure and grinding time. Excessive pressure may lead to scratches, depressions and other defects on the lens surface, and too long time will also affect the accuracy of the lens. According to the material of the lens and the required grinding amount, the appropriate pressure and time parameters should be determined through experiments.
Third, the polishing stage
Polishing materials and tools
The material and shape of the polishing mold should be selected according to the requirements of the lens. Commonly used polishing die materials include polyurethane, asphalt, etc. For example, for high-precision optical lenses, asphalt polishing molds can provide better surface flatness and smoothness.
The composition and concentration of polishing solution should be appropriate. Generally, polishing solution contains polishing powder and chemical additives, whose function is to chemically react with the glass surface, soften the glass surface, and facilitate the removal of tiny scratches and defects. The polishing solution should be prepared according to the glass material and polishing requirements.
Polishing process control
Control the polishing speed and pressure. Similar to the grinding stage, too fast polishing speed or too high pressure will cause damage to the lens surface. The polishing speed and pressure should be adjusted according to the size, shape and material of the lens.
Attention should be paid to temperature control during polishing. Because the temperature is too high, the polishing solution may dry up, affecting the polishing effect, and may also cause thermal deformation of the lens. Appropriate cooling measures can be adopted, such as using a coolant circulation system.
Four, cleaning and inspection stage
Cleaning process
The lens will be contaminated with abrasives, polishing solution and other impurities during processing, and it needs to be thoroughly cleaned. Select appropriate cleaning solvents, such as organic solvents and deionized water, and determine the cleaning method according to the nature of impurities. For example, for organic impurities, organic solvents can be used for dissolving and cleaning, and then deionized water can be used for washing.
During the cleaning process, attention should be paid to prevent the lens surface from being polluted again. For example, the cleaning equipment and tools should be kept clean, and the cleaned lens should be placed in a clean environment to dry or dried with clean nitrogen.
Inspection items and standards
Check the optical performance of the lens, including focal length, aberration, chromatic aberration, etc. Professional equipment such as optical interferometer and focal length instrument can be used for measurement. For example, for the lens used in projector, the chromatic aberration and aberration should be controlled within a certain range to ensure the clarity and color reproduction of the projected image.
Check the surface quality of the lens, such as surface roughness, scratches, pits, etc. Surface roughness can be measured by surface profilometer, and scratches and pits can be observed by microscope. For high-precision optical lenses, the size and number of surface scratches and pits are strictly limited.