Polishing Methods for Optical Injection Molds

Polishing of optical injection molds is critical, directly determining the micro-topography of mold cavities and thus the light transmittance, imaging accuracy and surface quality of optical parts. Optical products (lenses, light guides, etc.) demand ultra-high cavity surface roughness and flatness. Scientific polishing processes are required for ultra-precision machining while avoiding scratches and pits. Combined with practical production, this paper elaborates on the basic requirements, core methods and quality control points of optical injection mold polishing, integrating industry-recognized key data for production guidance.

I. Basic Requirements for Optical Injection Mold Polishing

Surface Precision Standards

Industry-recognized optical-grade surface roughness is Ra ≤ 0.01 μm (Ra ≤ 0.005 μm for high-end molds). Surface flatness error must be ≤ 0.003 mm/m to ensure optical part performance.

Material Adaptation Principles

Mainstream materials include S136 (HRC 58-62), H13 and titanium alloy. Material hardness (HRC 55-65) must match polishing processes; heat treatment optimizes hardness uniformity in advance.

Pre-treatment Requirements

Remove machining tool marks and oxide layers, ensuring cavity roughness Ra ≤ 0.8 μm. Maintain consistent grinding direction with subsequent polishing; clean oil stains and impurities to avoid secondary pollution.

II. Core Polishing Methods for Optical Injection Molds

Mechanical Polishing

Adopt stepped process: rough polishing (diamond abrasives W40-W10, Ra ≤ 0.1 μm), medium polishing (alumina W5-W2.5, Ra ≤ 0.02 μm), fine polishing (diamond micropowder W1-W0.5 or chromium oxide paste, optical-grade finish). Control pressure (0.1-0.3 MPa) and speed (1500-3000 r/min) to avoid surface burning; suitable for complex cavities.

Chemical Polishing

Ideal for hard-to-reach cavity areas, using mixed acid solutions (phosphoric, sulfuric, nitric acid) for selective corrosion. Control temperature (50-80 °C) and time (10-30 minutes) to achieve Ra ≤ 0.01 μm; rinse and dry thoroughly to prevent deformation from excessive corrosion.

Modern Precision Polishing Technology

Plasma polishing achieves Ra ≤ 0.005 μm with 40% shorter processing time, enabling uniform polishing of complex cavities. Magnetorheological polishing uses magnetic fluid for flexible finishing, avoiding mechanical damage; both technologies feature high automation, ideal for mass production.

III. Polishing Quality Control and Precautions

Process Monitoring Key Points

Use white light interferometers or atomic force microscopes for regular testing—every 2 hours for rough polishing, 30 minutes for fine polishing. Maintain Class 100 cleanliness to prevent dust contamination.

Operation Specification Requirements

Use dedicated, regularly cleaned tools; avoid mixing abrasives of different grain sizes. Adopt light-pressure slow polishing to prevent scratches; calibrate equipment to ensure parameter error ≤ ±5%.

Integration of Technical Trends

Automation and intelligence are the development direction. AI visual inspection systems adjust parameters in real time; laser-assisted polishing improves efficiency and surface integrity. The integrated process of mechanical polishing, modern precision polishing and intelligent detection will meet high-end optical product demands.