{"id":51630,"date":"2026-01-21T12:45:51","date_gmt":"2026-01-21T04:45:51","guid":{"rendered":"https:\/\/zetarmold.com\/?p=51630"},"modified":"2026-05-04T11:30:07","modified_gmt":"2026-05-04T03:30:07","slug":"normes-de-finition-de-surface-spi","status":"publish","type":"post","link":"https:\/\/zetarmold.com\/fr\/normes-de-finition-de-surface-spi\/","title":{"rendered":"What Are SPI Surface Finish Standards and How Do You Choose the Right One?"},"content":{"rendered":"<h2>What Is the SPI Surface Finish Standard?<\/h2>\n<p>Le <a href=\"https:\/\/zetarmold.com\/fr\/injection-molding-complete-guide\/\">SPI<\/a><sup id=\"fnref1:1\"><a href=\"#fn:1\" class=\"footnote-ref\">1<\/a><\/sup> Surface Finish Standard is a four-grade system (A through D) that defines mold cavity surface quality.<\/p>\n<p>See our supplier sourcing guide for RFQ prep and vendor qualification.<\/p>\n<p>For a broader look at <a href=\"https:\/\/zetarmold.com\/fr\/injection-mold-complete-guide\/\">conception de moules d'injection<\/a>, our pillar guide covers tooling structure, thermal control, and manufacturability tradeoffs.<\/p>\n<p>The SPI Surface Finish Standard is a classification system used across <a href=\"https:\/\/zetarmold.com\/fr\/injection-molding-complete-guide\/\">moulage par injection<\/a> projects to define cosmetic and tactile finish requirements on molded plastic parts. For buyers, it gives a shared language for quotation, <a href=\"https:\/\/zetarmold.com\/fr\/injection-mold-complete-guide\/\">mold polishing<\/a><sup id=\"fnref1:2\"><a href=\"#fn:2\" class=\"footnote-ref\">2<\/a><\/sup>, inspection samples, and final part approval.<\/p>\n<div class=\"callout-key\" style=\"background:#f0f7ff; border-left:4px solid #2563eb; padding:1em 1.2em; border-radius:6px; margin:1.5em 0;\">\n<strong>Principaux enseignements<\/strong><\/p>\n<ul>\n<li>SPI surface finish is both a cosmetic requirement and a tooling-cost decision, not just a drawing note.<\/li>\n<li>Choose the finish together with resin, draft angle, steel grade, ejection layout, paint or texture needs, and inspection method.<\/li>\n<li>Lock the target finish during DFM so polishing, sampling, and final approval do not become late-stage cost or lead-time surprises.<\/li>\n<\/ul>\n<\/div>\n<p>These standards provide a common language between industrial designers, engineers, mold makers, project managers, and quality teams. When everyone references the same SPI grade, it eliminates ambiguity about what a surface should look like, how much polishing effort is required, and what cost and lead time to expect. The SPI system also helps bridge communication gaps between OEMs and overseas mold shops, where different terminology or regional standards like VDI 3400 might otherwise create confusion.<\/p>\n<p>The standards are categorized into four primary grades, and each grade should be tied to a clear cosmetic target, inspection method, resin choice, and tooling budget before the mold quote is finalized:<\/p>\n<p><strong>Grade A (Gloss\/Diamond Polish):<\/strong> Mirror-like finish for optical, transparent, or premium cosmetic parts where scratches and sink marks are highly visible.<\/p>\n<p><strong>Grade B (Semi-Gloss\/Paper):<\/strong> Smooth finish without high reflection.<\/p>\n<p><strong>Grade C (Matte\/Stone):<\/strong> Non-reflective, standard industrial finish.<\/p>\n<p><strong>Grade D (Textured\/Blast):<\/strong> Rough finish created via dry blasting or Electrical Discharge Machining (EDM).<\/p>\n<h2>What Are the Technical Parameters of SPI Finishes?<\/h2>\n<p>The technical parameters for SPI finishes are surface roughness (Ra), polishing method, and minimum draft angle per grade.<\/p>\n<p>To ensure manufacturability, engineers must adhere to specific roughness averages (Ra) and draft angle requirements. The following table details the twelve primary SPI designations.<\/p>\n<table style=\"width:100%;border-collapse:collapse;margin:1.5em 0;\">\n<thead>\n<tr>\n<th style=\"border:1px solid #ddd;padding:8px;background:#f5f5f5;\">SPI Grade<\/th>\n<th style=\"border:1px solid #ddd;padding:8px;background:#f5f5f5;\">Finish Description<\/th>\n<th style=\"border:1px solid #ddd;padding:8px;background:#f5f5f5;\">Method of Application<\/th>\n<th style=\"border:1px solid #ddd;padding:8px;background:#f5f5f5;\">Typical Ra (\u00b5m)<\/th>\n<th style=\"border:1px solid #ddd;padding:8px;background:#f5f5f5;\">Typical Ra (\u00b5in)<\/th>\n<th style=\"border:1px solid #ddd;padding:8px;background:#f5f5f5;\">Min. Draft Angle<\/th>\n<th style=\"border:1px solid #ddd;padding:8px;background:#f5f5f5;\">Primary Use Case<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">A-1<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Super High Gloss<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Grade #3 Diamond Buff<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">0.012 \u2013 0.025<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">0 \u2013 1<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">1\u00b0<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Lenses, mirrors, visors<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">A-2<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">High Gloss<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Grade #6 Diamond Buff<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">0.025 \u2013 0.05<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">1 \u2013 2<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">1\u00b0<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Cosmetic cases, electronics<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">A-3<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Normal Gloss<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Grade #15 Diamond Buff<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">0.05 \u2013 0.10<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">2 \u2013 4<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">2\u00b0<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Household goods, opaque parts<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">B-1<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Smooth \/ Semi-Gloss<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">600 Grit Paper<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">0.05 \u2013 0.10<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">2 \u2013 3<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">1\u00b0<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Medium polish parts<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">B-2<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Smooth \/ Medium<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">400 Grit Paper<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">0.10 \u2013 0.15<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">4 \u2013 5<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">1\u00b0<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Quels sont les avantages et les inconv\u00e9nients de chaque cat\u00e9gorie de grade ?<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">B-3<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Smooth \/ Low Gloss<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">320 Grit Paper<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">0.28 \u2013 0.32<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">9 \u2013 10<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">2\u00b0<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Economy molding<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">C-1<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Matte \/ Fine<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">600 Grit Stone<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">0.35 \u2013 0.40<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">10 \u2013 12<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">1.5\u00b0<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Die cast look, internal parts<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">C-2<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Matte \/ Medium<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">400 Grit Stone<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">0.80 \u2013 0.95<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">25 \u2013 28<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">1.5\u00b0<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Structural parts, easy release<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">C-3<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Matte \/ Rough<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">320 Grit Stone<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">0.95 \u2013 1.10<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">38 \u2013 42<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">2\u00b0<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Heavy utility parts<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">D-1<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Textured \/ Satin<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Dry Blast (Glass Bead)<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Varies<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Varies<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">2.5\u00b0+<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Satin finish handles<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">D-2<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Textured \/ Dull<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Dry Blast (Alum. Oxide)<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Varies<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Varies<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">3\u00b0+<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Industrial housing, grip<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">D-3<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Textured \/ Rough<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Dry Blast (#24 Oxide)<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Varies<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Varies<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">3\u00b0+<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Heavy texture, defect hiding<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><em>Remarque : <a href=\"https:\/\/en.wikipedia.org\/wiki\/Surface_roughness\">Ra (Roughness Average)<\/a><sup id=\"fnref1:3\"><a href=\"#fn:3\" class=\"footnote-ref\">3<\/a><\/sup> values are approximate and depend on the steel type and measuring equipment.<\/em><\/p>\n<h2>How Is the Polishing Process Executed Step-by-Step?<\/h2>\n<p>Achieving a specific SPI finish is a subtractive manufacturing process applied to the mold cavity steel.<\/p>\n<p><strong>Rough Machining:<\/strong> The mold core and cavity are CNC machined to the approximate shape. The surface is rough, often showing tool marks.<\/p>\n<p><strong>Stoning (Leveling):<\/strong> Toolmakers use abrasive stones to remove CNC tool marks and level the surface. This is the baseline for <strong>C-Grades<\/strong>.<\/p>\n<p><strong>Paper Polishing:<\/strong> If a smoother finish is required, the surface is sanded with progressively finer grit sandpaper (from 320 to 600 grit). This achieves <strong>B-Grades<\/strong>.<\/p>\n<div class=\"factory-insight\" style=\"background:#f0f7ff;border-left:4px solid #0066cc;padding:12px 16px;margin:1.5em 0;\"><strong>\ud83c\udfed ZetarMold Factory Insight<\/strong><br \/>Factory Insight: In our Shanghai mold shop, our team checks SPI finish together with resin choice, draft angle, ejector layout, and inspection lighting. Our engineers compare finish targets against 400+ plastic material options and 47 injection molding machines before quoting. We also ask whether the surface will be painted, laser marked, touched by users, cleaned with chemicals, or approved under strong light, because those details decide whether mirror polishing adds value or just cost.<\/div>\n<p><strong>Diamond Buffing (Optional):<\/strong> Pour <strong>A-Grades<\/strong>, a diamond paste is applied to a rotary buffing tool. The steel is polished until it reaches optical reflectivity.<\/p>\n<figure style=\"text-align:center;margin:2em 0;\">\n<img fetchpriority=\"high\" decoding=\"async\" width=\"800\" height=\"457\" src=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-1.jpg\" alt=\"Polissage du moule pour la finition SPI\" class=\"wp-image-53270 size-full\" style=\"max-width:100%;height:auto;\" srcset=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-1.jpg 800w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-1-300x171.jpg 300w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-1-768x439.jpg 768w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-1-18x10.jpg 18w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-1-600x343.jpg 600w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><figcaption style=\"font-size:0.78em; color:#888; font-style:italic; margin-top:4px; text-align:center;\">SPI mold polishing process<\/figcaption><\/figure>\n<h2>What Are the Pros and Cons of Each Grade Category?<\/h2>\n<p>The pros and cons of SPI grades are defined by the tradeoff between surface polish level, tooling cost, and defect visibility.<\/p>\n<table style=\"width:100%;border-collapse:collapse;margin:1.5em 0;\">\n<thead>\n<tr>\n<th style=\"border:1px solid #ddd;padding:8px;background:#f5f5f5;\">Consultez le Mouleur :<\/th>\n<th style=\"border:1px solid #ddd;padding:8px;background:#f5f5f5;\">Avantages<\/th>\n<th style=\"border:1px solid #ddd;padding:8px;background:#f5f5f5;\">Inconv\u00e9nients<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">Grade A (Gloss)<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Highest aesthetic appeal; optical clarity for transparent parts; perceived high value.<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Highest tooling cost; prone to &#8220;vacuum seal&#8221; sticking; highlights surface defects (scratches, fingerprints, sink marks.<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">Grade B (Semi-Gloss)<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Good balance of cost and aesthetics; suitable for painting or plating; removes machining marks.<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Can still show some molding defects; requires manual polishing labor.<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">Grade C (Matte)<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Low tooling cost (fastest to machine); excellent for part release; hides minor tool marks.<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Can look &#8220;unfinished&#8221; or industrial; not suitable for high-end consumer facing surfaces.<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #ddd;padding:8px;\">Grade D (Textured)<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Excellent for hiding sink marks and flow lines; improves grip; durable surface appearance.<\/td>\n<td style=\"border:1px solid #ddd;padding:8px;\">Hardest to clean (fingerprint traps); requires significant draft angles for textured surfaces; difficult to repair if the mold is damaged.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div class=\"claim claim-true\" style=\"background-color: #eff7ef; border-color: #eff7ef; color: #5a8a5a;\">\n<p><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"20\" height=\"20\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"#16a34a\" stroke-width=\"2\"><path d=\"M9 16.17L4.83 12l-1.42 1.41L9 19 21 7l-1.41-1.41z\"\/><\/svg><b>&#8220;Textured finishes (SPI D-series) generally require larger taper per unit of texture depth than polished finishes to prevent part sticking.&#8221;<\/b><span class=\"claim-true-or-false\">Vrai<\/span><\/p>\n<p class=\"claim-explanation\">Textures create undercuts at a microscopic level; a general rule is 1.5 degrees of taper for every 0.001 inch of texture depth to prevent drag marks.<\/p>\n<\/div>\n<div class=\"claim claim-false\" style=\"background-color: #f7e8e8; border-color: #f7e8e8; color: #8a4a4a;\">\n<p><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"20\" height=\"20\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"#dc2626\" stroke-width=\"2\"><line x1=\"18\" y1=\"6\" x2=\"6\" y2=\"18\"\/><line x1=\"6\" y1=\"6\" x2=\"18\" y2=\"18\"\/><\/svg><b>&#8220;A higher SPI finish grade (like A-1) always improves part ejection.&#8221;<\/b><span class=\"claim-true-or-false\">Faux<\/span><\/p>\n<p class=\"claim-explanation\">Mirror finishes can actually create a vacuum seal effect between the part and the mold steel, causing parts to stick. This often requires air poppets or vacuum breakers to eject the part without deformation.<\/p>\n<\/div>\n<h2>What Practical Tips Help Optimize Surface Finish Selection?<\/h2>\n<p><strong>Compatibilit\u00e9 des mat\u00e9riaux :<\/strong> Not every resin can reproduce every SPI grade. PC, PMMA, and ABS usually hold high-gloss A-grade finishes well, while PP, POM, and nylon can show different texture across flow direction. Glass-filled grades are hardest because fiber read-through appears above C-1. If you specify a Class A surface on 30% glass-filled nylon, budget for S136 or H13 steel, extra polishing, and realistic sample approval.<\/p>\n<p><strong>The Sink Mark Strategy:<\/strong> Sink marks are most visible on glossy A-grade surfaces, where even a 0.05 mm depression can stand out under inspection lighting. On matte C-grade or textured D-grade surfaces, the same sink is far less obvious. Use A-grade only on buyer-facing surfaces, then use C or D on hidden sides with ribs, bosses, or wall variation. This split-grade approach can reduce polishing cost by 30% to 50% while preserving perceived quality.<\/p>\n<p><strong>Gestion des co\u00fbts :<\/strong> Polishing labor is a major variable cost in mold manufacturing. Moving from C-1 to A-1 can add 15% to 30% to mold cost because diamond buffing is slow skilled work. Deep ribs, undercuts, and complex parting lines increase that multiplier. Grade-map the part: A-grade on the primary cosmetic face, B-grade on secondary surfaces, and C or D on hidden faces. This keeps the mold competitive and reduces maintenance risk during production.<\/p>\n<figure style=\"text-align:center;margin:2em 0;\">\n<img decoding=\"async\" width=\"800\" height=\"457\" src=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/plastic-part-surface-finish-guide.webp\" alt=\"Guide de finition de surface des pi\u00e8ces plastiques\" class=\"wp-image-51634 size-full\" style=\"max-width:100%;height:auto;\" srcset=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/plastic-part-surface-finish-guide.webp 800w, https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/plastic-part-surface-finish-guide-300x171.webp 300w, https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/plastic-part-surface-finish-guide-768x439.webp 768w, https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/plastic-part-surface-finish-guide-18x10.webp 18w, https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/plastic-part-surface-finish-guide-600x343.webp 600w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><figcaption style=\"font-size:0.78em; color:#888; font-style:italic; margin-top:4px; text-align:center;\">SPI finish grade comparison<\/figcaption><\/figure>\n<h2>What Are Common Application Scenarios?<\/h2>\n<p>Common SPI application scenarios are matched to the product type: optical lenses use A-1, consumer housings use B-1, and tool grips use D-2.<\/p>\n<p><strong>SPI A-1 (Diamond #1):<\/strong> Automotive headlight lenses, optical prisms, medical pipettes, and premium cosmetic packaging where flawless clarity is the primary selling point. Any surface defect, micro-scratch, or flow line becomes immediately visible under direct light, so only the highest-grade steel polishing and meticulous process control can achieve this finish consistently. A-1 is also specified for medical device windows and fluid-path components where surface roughness could trap contaminants or affect fluid dynamics.<\/p>\n<p><strong>SPI A-2 (Diamond #2):<\/strong> Smartphone screens, high-end cosmetic compacts, automotive interior trim, and premium consumer product enclosures where visual appeal directly influences perceived product quality. A-2 delivers near-mirror reflectivity with slightly more tolerance for tool marks than A-1, making it a practical choice for visible surfaces that still demand a polished, professional appearance in competitive retail environments. Consumer electronics manufacturers frequently choose A-2 for display bezels and control panels that must look premium without incurring A-1 tooling costs.<\/p>\n<h3>When to Use Textured and Industrial Finishes<\/h3>\n<p><strong>SPI B-1 (Paper #1):<\/strong> Keyboard keys, housings intended for painting, consumer electronics casings, and appliance covers. B-grade finishes provide enough smoothness for post-molding operations like painting, printing, or applying texture coatings without requiring the expense of diamond polishing. In our experience, B-1 is the most cost-effective grade when the part will receive secondary surface treatment after molding. This grade is also widely used for internal structural brackets and hidden components that still require a clean, consistent surface for assembly fit.<\/p>\n<p><strong>SPI C-3 and D Grades:<\/strong> Power tool handles, steering column covers, ruggedized laptop cases, outdoor equipment enclosures, and any application where a combination of grip, durability, and visual concealment of processing artifacts is more important than gloss. Textured D-grade finishes are particularly effective at hiding sink marks, weld lines, and flow marks that would be glaring on a polished surface, which is why they are the default choice for structural and industrial components.<\/p>\n<h2>How Do You Choose the Right SPI Finish Step by Step?<\/h2>\n<p>Choosing the right SPI finish is a five-step process: define function, check the polymer, review taper, set budget, then consult your molder.<\/p>\n<figure style=\"text-align:center;margin:2em 0;\">\n<img decoding=\"async\" width=\"800\" height=\"457\" src=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/spi-mold-finish-guide.webp\" alt=\"SPI finish selection guide\" class=\"wp-image-51633 size-full\" style=\"max-width:100%;height:auto;\" srcset=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/spi-mold-finish-guide.webp 800w, https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/spi-mold-finish-guide-300x171.webp 300w, https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/spi-mold-finish-guide-768x439.webp 768w, https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/spi-mold-finish-guide-18x10.webp 18w, https:\/\/zetarmold.com\/wp-content\/uploads\/2025\/12\/spi-mold-finish-guide-600x343.webp 600w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><figcaption style=\"font-size:0.78em; color:#888; font-style:italic; margin-top:4px; text-align:center;\">SPI finish selection guide<\/figcaption><\/figure>\n<p><strong>Define Functionality:<\/strong> Does the part need to be transparent? (Choose A). Does it need grip or a tactile surface? (Choose D). Does it need to release easily from the mold with minimal draft? (Choose C). Start every SPI selection by writing down the functional requirement \u2014 not the appearance preference. In many cases, the cosmetic target conflicts with the functional need, and the earlier you surface that tension, the faster you resolve it with your tooling partner.<\/p>\n<p><strong>Check the Polymer:<\/strong> Is the material unfilled or glass-filled? If glass-filled, cap your expectations at B-3 or C-1 because the fiber orientation at the surface creates visible streaks that no amount of polishing can eliminate. Record resin grade, filler percentage, color, gloss target, and sample swatches in your SPI specification document so there is no ambiguity between buyer and molder.<\/p>\n<p><strong>Review Taper Requirements:<\/strong> Check your CAD model. If you have 0 degrees or 0.5 degrees taper on vertical walls, you cannot use a texture (D-grade) because the rough surface increases friction during ejection and will cause the part to stick or warp. You must add at least 1 to 3 degrees of draft for textured finishes, or switch to a polished finish that allows lower draft angles.<\/p>\n<p><strong>Determine Budget:<\/strong> If cost is the primary driver, specify SPI C-1. It is the standard machined finish that requires minimal post-processing and is achievable on standard P20 tool steel. Upgrading from C-1 to A-2 can add 20% to 40% to the mold cost because of the additional polishing hours. Always get a tooling quote with the exact SPI grade specified, not just a default finish level.<\/p>\n<p><strong>Consult the Molder:<\/strong> Before finalizing, ask the injection molder if the chosen finish requires specific mold steels such as H13 versus P20, which could impact lead time and cost. An experienced molder can also advise on whether the finish will interact well with the chosen resin, whether ejector pin marks will be visible at the target finish level, and whether any secondary operations like painting or texturing overlays are compatible with the base SPI grade.<\/p>\n<figure style=\"text-align:center;margin:2em 0;\">\n<img loading=\"lazy\" decoding=\"async\" width=\"800\" height=\"457\" src=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-2.jpg\" alt=\"polissage de moule de finition SPI\" class=\"wp-image-53271 size-full\" style=\"max-width:100%;height:auto;\" srcset=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-2.jpg 800w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-2-300x171.jpg 300w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-2-768x439.jpg 768w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-2-18x10.jpg 18w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-mold-polishing-800x457-2-600x343.jpg 600w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><figcaption style=\"font-size:0.78em; color:#888; font-style:italic; margin-top:4px; text-align:center;\">SPI mold polishing work<\/figcaption><\/figure>\n<div class=\"claim claim-true\" style=\"background-color: #eff7ef; border-color: #eff7ef; color: #5a8a5a;\">\n<p><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"20\" height=\"20\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"#16a34a\" stroke-width=\"2\"><path d=\"M9 16.17L4.83 12l-1.42 1.41L9 19 21 7l-1.41-1.41z\"\/><\/svg><b>\u00ab La s\u00e9lection de la finition SPI doit \u00eatre confirm\u00e9e avant le polissage final de l'acier du moule. \u00bb<\/b><span class=\"claim-true-or-false\">Vrai<\/span><\/p>\n<p class=\"claim-explanation\">Les changements tardifs de finition peuvent n\u00e9cessiter un repolissage, une retexturation, une revue suppl\u00e9mentaire du d\u00e9gagement et un temps d'\u00e9chantillonnage suppl\u00e9mentaire, surtout lors du passage de surfaces mates \u00e0 des surfaces tr\u00e8s brillantes.<\/p>\n<\/div>\n<div class=\"claim claim-false\" style=\"background-color: #f7e8e8; border-color: #f7e8e8; color: #8a4a4a;\">\n<p><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"20\" height=\"20\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"#dc2626\" stroke-width=\"2\"><line x1=\"18\" y1=\"6\" x2=\"6\" y2=\"18\"\/><line x1=\"6\" y1=\"6\" x2=\"18\" y2=\"18\"\/><\/svg><b>\u00ab Toutes les finitions de surface SPI n\u00e9cessitent le m\u00eame d\u00e9gagement de d\u00e9moulage et les m\u00eames param\u00e8tres d'\u00e9jection. \u00bb<\/b><span class=\"claim-true-or-false\">Faux<\/span><\/p>\n<p class=\"claim-explanation\">Les finitions brillantes, mates et textur\u00e9es se comportent diff\u00e9remment lors du d\u00e9moulage, donc le c\u00f4ne, la direction de polissage, le retrait de la r\u00e9sine et la force d'\u00e9jection doivent \u00eatre examin\u00e9s ensemble.<\/p>\n<\/div>\n<h2>Quelles FAQ sur la finition SPI les acheteurs posent-ils ?<\/h2>\n<h3>Quelle est la diff\u00e9rence entre les normes SPI et VDI 3400 ?<\/h3>\n<p>SPI est couramment utilis\u00e9 dans les projets de moulage par injection nord-am\u00e9ricains, tandis que VDI 3400 est largement utilis\u00e9 dans la communication d'outillage europ\u00e9enne. Les deux d\u00e9crivent la texture de surface, mais ils ne correspondent pas parfaitement car les m\u00e9thodes de mesure et les familles de textures diff\u00e8rent. Si un dessin liste une norme et que le fournisseur en utilise une autre, demandez un tableau de conversion, une plaque de texture ou un \u00e9chantillon approuv\u00e9. Cela \u00e9vite une situation o\u00f9 la m\u00eame surface est interpr\u00e9t\u00e9e diff\u00e9remment par le concepteur, le fabricant de moule, l'inspecteur final et l'acheteur lors de l'approbation de production.<\/p>\n<h3>Peut-on changer la finition de surface apr\u00e8s la fabrication du moule ?<\/h3>\n<p>Parfois, mais la direction du changement importe consid\u00e9rablement. Passer d'une surface polie \u00e0 une texture plus rugueuse est souvent possible car l'outil peut \u00eatre sabl\u00e9, grav\u00e9 ou textur\u00e9 apr\u00e8s polissage. Passer d'une surface rugueuse ou d'\u00e9lectro\u00e9rosion \u00e0 une finition haute brillance est beaucoup plus difficile car l'acier doit \u00eatre enlev\u00e9 et repoli, ce qui peut alt\u00e9rer les dimensions critiques. Les nervures profondes, les fermetures et les parois verticales textur\u00e9es peuvent \u00e9galement n\u00e9cessiter une v\u00e9rification suppl\u00e9mentaire du d\u00e9pouille et un \u00e9chantillonnage. C'est pourquoi l'intention de finition finale doit \u00eatre fig\u00e9e lors de la DFM, et non apr\u00e8s le premier \u00e9chantillonnage, pour \u00e9viter des retouches co\u00fbteuses et des retards.<\/p>\n<h3>La finition de surface affecte-t-elle le temps de cycle ?<\/h3>\n<p>Oui. Une finition haute brillance peut n\u00e9cessiter un refroidissement plus soigneux, une \u00e9jection plus lente et une meilleure ventilation pour \u00e9viter les marques de tra\u00een\u00e9e ou les contraintes esth\u00e9tiques. Une finition textur\u00e9e peut augmenter l'adh\u00e9rence de la pi\u00e8ce si le d\u00e9pouille est trop faible, ce qui peut ralentir l'\u00e9jection ou causer des \u00e9raflures. La finition de surface influence \u00e9galement les normes d'inspection car les d\u00e9fauts esth\u00e9tiques sont plus visibles sur les pi\u00e8ces brillantes. Pour la planification de production, les ing\u00e9nieurs doivent examiner ensemble la finition, la r\u00e9sine, l'angle de d\u00e9pouille, la disposition d'\u00e9jection, les crit\u00e8res de d\u00e9fauts acceptables, les marques de manipulation attendues et les objectifs de temps de cycle avant l'\u00e9chantillonnage.<\/p>\n<h3>Quelle finition SPI est la meilleure pour les pi\u00e8ces plastiques peintes ?<\/h3>\n<p>SPI B-1 ou B-2 est souvent un point de d\u00e9part pratique pour les pi\u00e8ces plastiques peintes, car la surface est suffisamment lisse pour l'adh\u00e9rence du rev\u00eatement mais pas aussi co\u00fbteuse qu'une finition miroir grade A. Le choix exact d\u00e9pend du syst\u00e8me de peinture, du type de r\u00e9sine, de la compatibilit\u00e9 de la primaire, du niveau de brillance attendu et si la pi\u00e8ce sera ponc\u00e9e avant peinture. Une surface tr\u00e8s rugueuse peut transmettre la texture sous la peinture, tandis qu'une surface trop brillante peut r\u00e9duire l'adh\u00e9rence de la primaire. Confirmez toujours le processus de rev\u00eatement avec des pi\u00e8ces d'\u00e9chantillon avant de s'engager dans la production en masse, surtout pour les finitions multicouches ou m\u00e9tallis\u00e9es.<\/p>\n<h3>L'acier du moule affecte-t-il la finition SPI finale ?<\/h3>\n<p>Absolument. Vous ne pouvez obtenir toutes les finitions sur toutes les grades d'acier. Les finitions miroir n\u00e9cessitent g\u00e9n\u00e9ralement des aciers de qualit\u00e9 sup\u00e9rieure comme le H13 ou le S136 avec un polissage minutieux, tandis que les mat\u00e9riaux plus tendres ou les outils en aluminium peuvent limiter la qualit\u00e9 de surface atteignable. La duret\u00e9 de l'acier, sa puret\u00e9, l'uniformit\u00e9 du traitement thermique, les r\u00e9parations par soudure et les couches de recast EDM peuvent tous affecter l'apparence finale. Pour les pi\u00e8ces cosm\u00e9tiques critiques, le devis du moule doit sp\u00e9cifier le type d'acier, l'objectif de finition, la m\u00e9thode d'inspection et tout \u00e9chantillon de texture ou de brillance n\u00e9cessaire pour approbation avant que l'outil soit lib\u00e9r\u00e9 pour la production.<\/p>\n<h3>Comment le grade de finition SPI affecte le co\u00fbt du moulage par injection ?<\/h3>\n<p>Le grade de finition SPI a un impact direct et significatif sur le co\u00fbt du moule. Passer d'une finition pierre grade C \u00e0 un polissage diamant grade A peut augmenter le temps de fabrication du moule de 15 \u00e0 30 %, car chaque \u00e9tape sup\u00e9rieure n\u00e9cessite progressivement plus de travail de polissage manuel. Les finitions grade A peuvent \u00e9galement n\u00e9cessiter un acier de meilleure qualit\u00e9, des cycles d'\u00e9chantillonnage suppl\u00e9mentaires et des crit\u00e8res d'inspection cosm\u00e9tique plus strictes pendant la production. Pour les projets sensibles au budget, les ing\u00e9nieurs sp\u00e9cifient souvent les finitions grade A uniquement sur les surfaces visibles, tandis qu'ils utilisent les grades C ou D sur les surfaces non visibles ou internes pour \u00e9quilibrer l'apparence avec l'investissement total en outillage.<\/p>\n<h2>Quel est l'essentiel des normes de finition de surface SPI ?<\/h2>\n<p>L'essentiel des normes de finition de surface SPI est d\u00e9fini par la fonction, les contraintes et les compromis expliqu\u00e9s dans cette section. S\u00e9lectionner la <strong>SPI Surface Finish<\/strong> n'est pas seulement un choix esth\u00e9tique ; elle dicte l'acier du moule, le d\u00e9gagement n\u00e9cessaire pour un d\u00e9moulage net et le co\u00fbt final de l'outil. Alors que <strong>SPI A-Grades<\/strong> offer premium, optical-quality looks, they come with higher maintenance and manufacturing costs. <strong>SPI C and D Grades<\/strong> offrent des surfaces pratiques et robustes qui masquent les d\u00e9fauts de moulage et r\u00e9duisent les co\u00fbts d'outillage. Les ing\u00e9nieurs doivent \u00e9quilibrer les exigences visuelles avec les r\u00e9alit\u00e9s physiques du polym\u00e8re choisi et de la g\u00e9om\u00e9trie de la pi\u00e8ce. Consultez notre <a href=\"https:\/\/zetarmold.com\/fr\/injection-mold-complete-guide\/\">Injection Mold Complete Guide<\/a> for a comprehensive overview.<\/p>\n<p>Need a Quote for Your Injection Molding Project?<\/p>\n<p>Obtenez des tarifs comp\u00e9titifs, des retours DFM et un calendrier de production aupr\u00e8s de l'\u00e9quipe d'ing\u00e9nierie de ZetarMold. Pour le contexte de sourcing, consultez notre guide de sourcing de fournisseurs de moulage par injection.<\/p>\n<p>Request a Free Quote \u2192<\/p>\n<hr style=\"margin:2em 0;border:none;border-top:1px solid #e0e0e0;\" \/>\n<ol class=\"footnotes\">\n<li id=\"fn:1\">\n<p><strong>SPI :<\/strong> SPI est une classification de finition de surface utilis\u00e9e pour communiquer les exigences esth\u00e9tiques et d'outillage pour les pi\u00e8ces plastiques moul\u00e9es. <a href=\"#fnref1:1\" class=\"footnote-backref\">\u21a9<\/a><\/p>\n<\/li>\n<li id=\"fn:2\">\n<p><strong>polissage de moule :<\/strong> Le polissage d\u00e9signe le processus d'abrasion contr\u00f4l\u00e9 appliqu\u00e9 aux surfaces d'acier de la cavit\u00e9 du moule pour atteindre une rugosit\u00e9 de surface et un grade cosm\u00e9tique sp\u00e9cifi\u00e9. <a href=\"#fnref1:2\" class=\"footnote-backref\">\u21a9<\/a><\/p>\n<\/li>\n<li id=\"fn:3\">\n<p><strong>Ra (Rugosit\u00e9 Moyenne) :<\/strong> Ra (Rugosit\u00e9 Moyenne) est une mesure quantitative de la texture de surface, calcul\u00e9e comme la moyenne arithm\u00e9tique des valeurs absolues des \u00e9carts de hauteur de surface par rapport \u00e0 la ligne moyenne. <a href=\"#fnref1:3\" class=\"footnote-backref\">\u21a9<\/a><\/p>\n<\/li>\n<\/ol>","protected":false},"excerpt":{"rendered":"<p>Qu'est-ce que la norme de finition de surface SPI ? La norme de finition de surface SPI1 est un syst\u00e8me \u00e0 quatre grades (A \u00e0 D) qui d\u00e9finit la qualit\u00e9 de surface de la cavit\u00e9 du moule. Consultez notre guide d'approvisionnement des fournisseurs pour la pr\u00e9paration des demandes de devis et la qualification des vendeurs. Pour une vue plus large de la conception des moules d'injection, notre guide pilier couvre la structure de l'outillage, le contr\u00f4le thermique et les compromis de fabricabilit\u00e9. [\u2026]<\/p>","protected":false},"author":1,"featured_media":51633,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_robots_primary_cat":"none","_seopress_titles_title":"SPI Finish Standards Guide for Injection Molded Parts","_seopress_titles_desc":"Explore SPI surface finish standards: A to D grades for mold surface cosmetics. Learn how polishing and textures affect tooling cost, quality, production.","_seopress_robots_index":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[43],"tags":[48,384,385],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/zetarmold.com\/fr\/wp-json\/wp\/v2\/posts\/51630"}],"collection":[{"href":"https:\/\/zetarmold.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zetarmold.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zetarmold.com\/fr\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zetarmold.com\/fr\/wp-json\/wp\/v2\/comments?post=51630"}],"version-history":[{"count":0,"href":"https:\/\/zetarmold.com\/fr\/wp-json\/wp\/v2\/posts\/51630\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/zetarmold.com\/fr\/wp-json\/wp\/v2\/media\/51633"}],"wp:attachment":[{"href":"https:\/\/zetarmold.com\/fr\/wp-json\/wp\/v2\/media?parent=51630"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zetarmold.com\/fr\/wp-json\/wp\/v2\/categories?post=51630"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zetarmold.com\/fr\/wp-json\/wp\/v2\/tags?post=51630"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}