The processing technology of quartz optical glass lens is introduced in detail.

The processing technology of quartz optical glass (usually referred to as Shi Ying glass, which has the characteristics of high transmittance, high temperature resistance and low expansion coefficient) is a high-precision and multi-link process, which needs to be combined with mechanical processing, optical grinding, coating and other technologies to meet the strict requirements of optical system for flatness, smoothness and accuracy. The following is its detailed processing flow:

First, preparation before processing

Selection and pretreatment of raw materials

Material selection: Shi Ying glass blank (transparent Shi Ying glass, fused Shi Ying glass, etc.) with appropriate purity should be selected according to the purpose of the lens (such as laser lens and high-temperature resistant window), and the internal stress, bubbles, impurities and other indicators of the blank should be detected to avoid affecting the subsequent optical performance.

Size cutting: Cut the Shi Ying glass blank into coarse materials close to the finished product size with a diamond saw blade or laser cutting equipment (with a machining allowance of 1-3mm), and cool it (such as water cooling) during cutting to avoid glass cracking caused by high temperature.

Second, the rough machining stage: forming and trimming.

Milling (rough grinding)

Objective: To remove the cutting marks on the surface of the blank, and process the lens to be close to the designed curvature (spherical mirror) or flatness (flat mirror), while controlling the thickness tolerance within 0.1 mm..

Process: The glass surface is ground by a diamond grinding wheel (particle size 80-200 mesh) with resin binder. Plane lens adopts single-sided or double-sided grinding machine, while spherical lens needs to match the mold with corresponding curvature (the curvature of grinding wheel is consistent with the design curvature of lens).

Note: Shi Ying glass has high hardness (Mohs hardness 7) and high brittleness, so it is necessary to control the grinding pressure (usually 0.1-0.3MPa) and feed speed to avoid cracks.

fine/precision grinding

Objective: To further reduce the surface roughness (from Ra 1-5μm after rough grinding to Ra 0.1-0.5μm), correct the dimensional accuracy and prepare for polishing.

Process: Replace a finer diamond grinding wheel (200-800 mesh) or silicon carbide abrasive, and adopt a lower grinding pressure and speed. For high-precision lenses, on-line thickness measuring instrument should be used to monitor the dimensions in real time at this stage to ensure that the tolerance is controlled within 0.01 mm.

Third, the precision machining stage: polishing and correction

polish

Objective: To eliminate the surface damage layer left by fine grinding, obtain the optical smoothness (Ra≤0.01μm), and ensure the surface accuracy (flatness ≤λ/10, λ is the wavelength, usually based on 632.8nm He-Ne laser).

Technology:

Tools: Use asphalt, polyurethane or wool felt polishing mold, and cooperate with polishing liquid (the main components are cerium oxide, silicon dioxide and other micro-powders, the particle size is 0.5-5μm).

Principle: Ultra-precision machining is realized through the mechanical friction and chemical action between the polishing die and the lens surface (micro-powder reacts with the glass surface to generate an easy-to-remove softening layer).

Equipment: High-precision polishers (such as double-sided polishers and special polishers for spherical surfaces). Some high-end equipment is equipped with real-time surface detection system (such as laser interferometer) to dynamically adjust polishing pressure and time.

Key parameters: polishing pressure (0.05-0.2MPa), rotating speed (50-200r/min) and polishing solution concentration should be optimized according to lens size and material to avoid scratches or surface deviation.

Centering edging

Objective: To align the optical center (curvature center) with the geometric center (excircle center) of the lens to ensure the coaxiality during assembly. At the same time, grind the excircle to the design size (tolerance ±0.02mm).

Technology: The centering edger is used to fix the lens by vacuum adsorption or mechanical clamping, and the excircle is ground by diamond grinding wheel. For double-sided aspheric or special-shaped lenses, it is necessary to cooperate with the fixture for positioning.

Fourth, surface treatment and strengthening

wash

Objective: To remove the residual polishing solution, micropowder and oil stain after polishing to avoid affecting the coating quality.

Process:

Ultrasonic cleaning (using neutral cleaning agent, frequency 28-130kHz)→ pure water washing → hot air drying (temperature 50-80℃, to avoid lens deformation caused by high temperature).

Requirements: After cleaning, the granularity of lens surface (particles ≥0.5μm) should be ≤10/cm, which meets the optical cleanliness standard.

coating film

Objective: To optimize optical properties by plating different film systems (such as antireflection film, reflective film, filter film and wear-resistant film) according to the application.

Common technologies:

Vacuum evaporation coating: In high vacuum (10⁻⁴-10⁻⁶Pa) environment, film materials (such as MgF₂, TiO₂, SiO₂) are heated and evaporated and deposited on the lens surface, which is suitable for simple film systems such as antireflection films.

Magnetron sputtering coating: using plasma to bombard the target, atoms escape and deposit on the lens surface, and the film has stronger adhesion, which is suitable for high hardness wear-resistant film or multilayer composite film.

Control: During the coating process, it is necessary to accurately control the film thickness (error ≤1nm), and ensure that the optical parameters (such as transmittance and reflectivity) reach the standard through real-time monitoring of the crystal oscillator.

Edge enhancement (optional)

For lenses that are vulnerable to impact (such as window pieces), the edges can be chamfered (R-angle treatment) by sandblasting or chemical etching to reduce stress concentration and improve impact resistance.

V. Testing and Quality Control

Geometric parameter detection

Size: use micrometer and thickness gauge to detect thickness and cylindrical diameter;

Surface type: laser interferometer (to detect flatness and spherical curvature radius) and profilometer (to detect aspheric surface type);

Parallelism/verticality: use autocollimator or goniometer, and the accuracy shall be ≤ 10 "(arc seconds).

Optical performance detection

Transmittance: The transmittance of designated wavelength (such as ultraviolet, visible light and infrared) is detected by spectrophotometer, and the transmittance of Shi Ying glass in ultraviolet band (200-400nm) is usually ≥ 85%;

Surface quality: visual inspection under strong light (or automatic surface defect detector) is used to determine the grade of scratches and pits (in line with MIL-PRF-13830B and other standards);

Film properties: Wear resistance was tested by friction tester, corrosion resistance was tested by salt spray test, and spectral characteristics of the film system were verified by spectrometer.

Environmental adaptability test (for special purposes)

High and low temperature cycle test (-55℃ to+125℃): detect whether the lens cracks or the film falls off due to temperature change;

Vibration impact test: simulate transportation or use environment to ensure structural stability.

VI. Packaging and Storage

Packaging: use anti-static tray, dust-free paper or special packaging box to avoid scratches or pollution on the lens surface;

Storage: The environment should be clean (clean room above class 1000), at constant temperature (20 2℃) and constant humidity (40%-60%), away from acid, alkali and organic solvents to prevent film corrosion or glass mildew.

summary

The processing core of quartz optical glass lens is * * "gradually reducing the surface roughness, accurately controlling the size and profile, and optimizing the optical performance" * *, which needs to go through many links such as rough grinding → fine grinding → polishing → edging → cleaning → coating → testing, and each step depends on high-precision equipment and strict process control. The difficulty lies in balancing the processing efficiency and accuracy (such as the polishing stage takes several hours to dozens of hours), and dealing with the loss of processing tools caused by the high hardness of Shi Ying glass. The final product needs to meet the strict requirements of optical system for light transmittance, surface accuracy and stability, and is widely used in laser equipment, astronomical telescopes, semiconductor testing instruments and other fields.