Mirror polishing is a core precision process of injection molds, which directly determines the surface gloss, flatness and appearance quality of plastic products. It is widely used in high-gloss home appliances, transparent parts and precision electronic products. Standardized mirror polishing can eliminate surface defects, optimize demolding performance and improve mold durability, which is an important symbol of mold manufacturing precision.
I. Quantitative Polishing Grade StandardsMirror polishing is graded by surface roughness Ra value and SPI international standards. General industrial mirror (SPI A3) is suitable for ordinary high-gloss products with stable surface brightness and no processing lines. High-precision mirror (SPI A2) applies to transparent and food-grade products with clear imaging and no fog shadow. Optical super mirror (SPI A1) is used for high-end optical parts with ultra-smooth microscopic surface and no light distortion. Unified quantitative standards ensure consistent polishing quality.
II. Visual Appearance Acceptance Standards
Qualified mirror cavity surface has no scratches, pitting, orange peel, ripple and material lines under strong light inspection. The light reflection is uniform without distortion. The edges and corners are smooth without collapse and chamfer deformation. Key positions such as gates, welding lines and rib roots are polished evenly without insufficient or excessive polishing. Functional surfaces such as parting surfaces maintain sealing precision while ensuring smoothness. Trial products have uniform gloss and no bad appearance defects.
III. Mold Substrate and Hardness RequirementsHigh-quality mirror molds must use qualified steel materials with uniform metallographic structure and few impurities. S136 and 420SS stainless steel with HRC48-52 hardness are the best choices for high-precision mirror molds, featuring corrosion resistance and stable polishing effect. Pre-hardened steel such as 718H and P20 is only suitable for ordinary mirror polishing. Complete heat treatment ensures uniform hardness and avoids polishing deformation and residual lines.
IV. Standard Polishing Process Specifications
Mirror polishing must follow gradual refinement rules without jumping steps. Coarse oil stone and sandpaper remove CNC and EDM lines to ensure flat substrate surface. Medium and high-mesh sandpaper refine surface texture step by step. Ultra-fine diamond paste is used for fine mirror finishing to achieve smooth and bright surface. High-precision polishing must be completed in a dust-free environment to avoid particle scratch and fog surface.
V. ConclusionMirror polishing quality is determined by quantitative roughness standard, visual inspection standard, steel substrate performance and standardized process. Strict implementation of polishing specifications can effectively eliminate product appearance defects, improve mold demolding performance and prolong service life. Standardized mirror polishing management is essential for manufacturing high-precision and high-quality injection molds.
