Manufacturing process of optical glass lenses


Release time:

2024-01-31

1.1 Characteristics and general processes of optical component manufacturing process There are three common types of materials used to make optical components, namely optical glass, optical crystals, and optical plastics. Among them, optical glass, especially colorless optical glass, is widely used. Although the processing of optical components is classified into the category of mechanical processing by industry, the material properties and precision requirements of the processed object are significantly different from those of metal materials, so the processing technology is completely different from metal processes and has special characteristics.

Manufacturing process of optical glass lenses

1.1 Characteristics and general processes of optical component manufacturing process
There are three common types of materials used to make optical components, namely optical glass, optical crystals, and optical plastics. Among them, optical glass, especially colorless optical glass, is widely used. Although the processing of optical components is classified into the category of mechanical processing by industry, the material properties and precision requirements of the processed object are significantly different from those of metal materials, so the processing technology is completely different from metal processes and has special characteristics.
1.1.1 Processing accuracy and representation of optical components
Optical components belong to high-precision components. The machining accuracy of flat parts mainly includes angles and flat surface shape; The machining accuracy requirements for spherical parts mainly include curvature radius and spherical surface shape. The angle error of high-precision prisms is required to reach the second level. The high-precision plane shape accuracy can reach tens to hundreds of wavelengths. The flatness of flat parts and the sphericity of spherical parts are collectively referred to as surface shape requirements. The optical workshop generally uses interferometry for measurement, and observes equal thickness interference fringes (commonly known as aperture) by overlapping a template. The symbol for aperture number representing surface shape error is N, and the symbol for irregularity (or local error) is △ N. In addition to surface accuracy, the surface of optical components also needs to have roughness requirements. The surface roughness of each process in optical processing is shown in Table 6-1. The surface roughness of optical components polished is expressed as R2=0.025um using the micro uneven ten point height, R2=0.025um using the arithmetic mean deviation of the contour, and 0.008 using the symbol. On this basis, there are also surface defect requirements, which limit the surface brightness, scratches, and pitting.
1.1.2 General process and characteristics of optical component processing
The manufacturing process of optical components varies with different processing methods. There are mainly two types of processing methods for optical components: traditional (classical) processing technology and mechanized processing technology. Here, we will only introduce traditional processing technology.
The characteristics of traditional craftsmanship mainly include:
(1) Using granular abrasives and universal machine tools, the optical glass is ground using contour forming method. During the operation, rosin tar adhesive is mainly used for bonding the upper plate. First, rough and fine grind the parts with diamond sand, and then use rosin tar polishing mold and polishing powder (mainly cerium oxide) to polish the parts. There are many and variable factors that affect the process, and the machining accuracy is also highly variable, usually in the order of several wavelengths. High precision can reach the order of hundreds of wavelengths.
(2) Manual operation requires a large amount of work, multiple processes, and high technical requirements for operators. The requirements for machine tool accuracy and fixture grinding tools are not so strict, and are suitable for processing processes with multiple varieties, small batches, and large precision changes.
The traditional manufacturing process, taking a lens as an example, goes through the following steps in sequence:
1. Rough processing. This includes selecting suitable blocks according to the optical component diagram, cutting, leveling, dividing, sealing strips, and rolling to create spherical surfaces. Opening a spherical surface is done as a single piece.
2. Rough grinding processing. Make the surface roughness and spherical radius meet the requirements of fine grinding. In traditional craftsmanship, rough grinding is carried out on a single piece. In factories that generally use traditional processing techniques, the rough grinding workshop often includes rough machining.
3. Upper plate: After rough grinding, clean and combine the lens blanks into a plate with the same radius. By relying on adhesive to fix the dispersed lens onto the spherical adhesive film, it should be noted that when forming the disc, each lens blank's machined surface should be on the same radius spherical surface.
4. Fine grinding and polishing process. When processing the first surface, it is generally not necessary to remove the disc during the polishing process, that is, one disc at a time. During the operation, first use three to four layers of gold steel sand with gradually finer particle size to grind the processed surface to the required surface roughness for polishing, then clean and polish. Polishing is carried out using a polishing die with a certain radius and polishing powder. After processing one side, apply protective film and flip it over before hanging it. Fine grinding and polishing the second surface.
5. Centering and edge grinding process. During the lens processing, there may be deviations between the optical axis and the positioning axis (known as eccentricity). The task of centering and edge grinding is to eliminate eccentricity and ensure that the radial dimensions of the side cylindrical surface meet the assembly requirements. Traditional edge grinding techniques are often performed on optical centering edge grinding machines.
6. The coating process requires adding an anti reflective film to lenses with surface transparency requirements. Spherical mirrors need to be coated with reflective film. Some also need to be coated with other properties of thin films, which are determined by the design according to the usage requirements.
7. Bonding process. Lenses that require high imaging quality are often made by bonding several lenses together. Bonding should be carried out after coating.
The above process can be briefly represented as follows:
Material selection - cutting - leveling - rubber strip - rounding - open spherical surface - rough grinding spherical surface - upper plate - fine grinding - polishing - lower plate; Second side upper plate - fine grinding - polishing - lower plate - centering and edge grinding - coating