{"id":755,"date":"2025-12-04T08:49:23","date_gmt":"2025-12-04T08:49:23","guid":{"rendered":"https:\/\/preciseworksplus.com\/?p=755"},"modified":"2025-12-04T09:16:38","modified_gmt":"2025-12-04T09:16:38","slug":"surface-roughness-blueprint-for-precision-injection-molds","status":"publish","type":"post","link":"https:\/\/preciseworksplus.com\/es\/surface-roughness-blueprint-for-precision-injection-molds\/","title":{"rendered":"Plan de rugosidad superficial para moldes de inyecci\u00f3n de precisi\u00f3n"},"content":{"rendered":"
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\u2014\u2014From optical mirror to leather grain, one chart tells you exactly how shiny to polish<\/p>\n<\/blockquote>\n\n\n\n

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1. Why “roughness” decides both LOOKS & YIELD<\/h2>\n\n\n\n

In the molding world, every 0.01 \u00b5m drop in cavity Ra lifts yield by 2\u20134 %<\/strong>.
If a glossy-transparent part sees Ra > 0.05 \u00b5m, “cloudy spots” appear;
if a textured surface falls below 1.0 \u00b5m it feels sticky.
Polishing is therefore a numbers game\u2014never a matter of gut feeling.<\/p>\n\n\n\n

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2. The universal language: SPI grade \u00d7 Ra look-up table<\/h2>\n\n\n\n

Tabla<\/p>\n\n\n\n

SPI Grade<\/th>How we get it<\/th>Typical Ra \/ \u00b5m<\/th>Visual result<\/th>Typical application<\/th><\/tr><\/thead>
A-1<\/strong><\/td>6000# diamond paste<\/td>0.012 \u2013 0.025<\/td>Mirror \/ optical clear<\/td>Lenses, light-guides, clear packaging<\/td><\/tr>
A-2<\/strong><\/td>3000# diamond paste<\/td>0.025 \u2013 0.05<\/td>High gloss \/ sharp reflection<\/td>Automotive lamps, phone housings<\/td><\/tr>
A-3<\/strong><\/td>1200# diamond paste<\/td>0.05 \u2013 0.10<\/td>Bright \/ slight reflection<\/td>Cosmetic caps, appliance skins<\/td><\/tr>
B-1<\/strong><\/td>600# sand paper<\/td>0.05 \u2013 0.10<\/td>Semi-bright \/ fine satin<\/td>Key tops, inner frames<\/td><\/tr>
B-2<\/strong><\/td>400# sand paper<\/td>0.10 \u2013 0.15<\/td>Matte \/ visible scratches<\/td>Hidden brackets, ribs<\/td><\/tr>
B-3<\/strong><\/td>320# sand paper<\/td>0.28 \u2013 0.32<\/td>Dull \/ brushed look<\/td>Tool shells, bases<\/td><\/tr>
C-1<\/strong><\/td>600# stone<\/td>0.35 \u2013 0.40<\/td>Flat matte<\/td>Car interior, handles<\/td><\/tr>
C-2<\/strong><\/td>400# stone<\/td>0.45 \u2013 0.55<\/td>Light orange-peel<\/td>Small household devices<\/td><\/tr>
C-3<\/strong><\/td>320# stone<\/td>0.63 \u2013 0.70<\/td>Heavy orange-peel<\/td>Industrial bins<\/td><\/tr>
D-1<\/strong><\/td>Glass bead #11<\/td>0.80 \u2013 1.00<\/td>Velvet<\/td>Buttons, remote controls<\/td><\/tr>
D-2<\/strong><\/td>Al\u2082O\u2083 #240<\/td>1.00 \u2013 2.80<\/td>Fine texture<\/td>Housings, grips<\/td><\/tr>
D-3<\/strong><\/td>Al\u2082O\u2083 #24<\/td>3.20 \u2013 18.0<\/td>Coarse leather<\/td>Tool boxes, door panels<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
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Figures are from the July-2025 revision of the SPI standard, rounded to two decimals.<\/p>\n<\/blockquote>\n\n\n\n

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3. Un-written rules for precision molds<\/h2>\n\n\n\n
    \n
  1. Cavity surface \u2264 0.2 \u00b5m<\/strong>
    Even if the final part will be textured, polish first to Ra 0.1-0.2 \u00b5m to guarantee dimensional fidelity and draft consistency.<\/li>\n\n\n\n
  2. Parting line \u2264 0.8 \u00b5m<\/strong>
    Rougher faces collect plastic dust and peen over time, causing flash; below 0.4 \u00b5m you pay for shine you don’t need.<\/li>\n<\/ol>\n\n\n\n
      \n
    1. Ejector area 0.4 \u2013 0.8 \u00b5m<\/strong>
      Too glossy \u2192 vacuum drag & stress-whitening; too rough \u2192 ejector pin galling. Tests on ABS show minimum ejection force at Ra 0.6 \u00b5m.<\/li>\n\n\n\n
    2. Cooling channel walls \u2264 1.6 \u00b5m<\/strong>
      Guarantees turbulent flow, improves cooling by 8-12 % and retards fouling.<\/li>\n<\/ol>\n\n\n\n
      \n\n\n\n

      4. Plastic-specific mirror requirements<\/h2>\n\n\n\n

      Tabla<\/p>\n\n\n\n

      Resin<\/th>Recommended SPI<\/th>Reason<\/th><\/tr><\/thead>
      PC, PMMA<\/td>A-1<\/td>Any scratch > 0.05 \u00b5m scatters light into “fog lanes”<\/td><\/tr>
      ABS, PC\/ABS<\/td>A-2<\/td>High-gloss paint substrate; Ra 0.03 \u00b5m is enough<\/td><\/tr>
      POM, PA66<\/td>B-1<\/td>Crystalline shrinkage high; too shiny reveals sink<\/td><\/tr>
      TPE\/TPU<\/td>C-2<\/td>Orange-peel hides knit line, improves grip<\/td><\/tr>
      PP house-ware<\/td>C-3<\/td>Cost-driven; allows heavy peel, conceals weld<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
      \n\n\n\n

      5. Four steps to reach 0.01 \u00b5m class<\/h2>\n\n\n\n
        \n
      1. Start with clean steel: H13 ESR, FS136, M333 \u2014 inclusion rating \u2264 1.0, no “fish-eyes” after polish.<\/li>\n\n\n\n
      2. Stress-free heat treat: Deep-cryo \u2013196 \u00b0C plus double temper \u2192 retained austenite < 2 %.<\/li>\n\n\n\n
      3. Diamond paste ladder: 1200# \u2192 3000# \u2192 6000# \u2192 8000#, cross-hatch 45\u00b0, spindle \u2264 1500 rpm.<\/li>\n\n\n\n
      4. Class 1000 clean-room: 1 \u00b5m dust landing on cavity = permanent pit; apply anti-rust coating within 30 min.<\/li>\n\n\n\n
      5. <\/li>\n<\/ol>\n\n\n\n
        \n\n\n\n

        6. Take-away<\/h2>\n\n\n\n

        Surface roughness in precision injection molds is not “the shinier the better”<\/strong> but “just right”<\/strong>\u2014balancing resin replication, appearance, ejection, cost and cycle time.
        Print the SPI vs Ra chart, pin it above your polishing station, and let every stroke be data-driven.
        That’s how you mass-produce “micron-level beauty” shot after shot.<\/p>\n<\/blockquote>\n\n\n\n

        We are a Chinese leading company in the manufacture of tooling, stamping, injection molding, CNC machined parts. If you wish to learn more about this subject, please do not hesitate to contact us.<\/p>\n\n\n\n

        Cont\u00e1ctenos \u2013 preciseworksplus.com<\/a><\/p>\n\n\n\n

        <\/p>","protected":false},"excerpt":{"rendered":"

        From optical mirror to leather grain, one chart tells you exactly how shiny to polish<\/p>","protected":false},"author":1,"featured_media":531,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[15],"tags":[],"class_list":["post-755","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-technology"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/posts\/755","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/comments?post=755"}],"version-history":[{"count":3,"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/posts\/755\/revisions"}],"predecessor-version":[{"id":762,"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/posts\/755\/revisions\/762"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/media\/531"}],"wp:attachment":[{"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/media?parent=755"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/categories?post=755"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/preciseworksplus.com\/es\/wp-json\/wp\/v2\/tags?post=755"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}