{"id":13727,"date":"2026-07-23T05:52:10","date_gmt":"2026-07-23T05:52:10","guid":{"rendered":"https:\/\/hlh-js.com\/?p=13727"},"modified":"2026-07-23T05:52:10","modified_gmt":"2026-07-23T05:52:10","slug":"improving-ra-and-rz-on-3d-printed-parts-how-abrasive-blasting-reduces-surface-roughness","status":"publish","type":"post","link":"https:\/\/hlh-js.com\/de\/resource\/blog\/improving-ra-and-rz-on-3d-printed-parts-how-abrasive-blasting-reduces-surface-roughness\/","title":{"rendered":"Improving Ra and Rz on 3D Printed Parts: How Abrasive Blasting Reduces Surface Roughness"},"content":{"rendered":"<div class=\"hlh-3dp-c08\">\n<style>\n.hlh-3dp-c08{font-family:'Inter',-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif;color:#374151;line-height:1.78;max-width:860px;margin:0 auto;padding:0;font-size:16px}\n.hlh-3dp-c08 *,.hlh-3dp-c08 *::before,.hlh-3dp-c08 *::after{box-sizing:border-box}\n.hlh-3dp-c08 h1{font-size:2rem;font-weight:800;color:#1a3456;line-height:1.22;margin:0 0 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\"Organization\",\n        \"name\": \"Jiangsu Henglihong Technology Co., Ltd.\",\n        \"url\": \"https:\\\/\\\/hlh-js.com\"\n    },\n    \"publisher\": {\n        \"@type\": \"Organization\",\n        \"name\": \"Jiangsu Henglihong Technology Co., Ltd.\",\n        \"url\": \"https:\\\/\\\/hlh-js.com\"\n    },\n    \"mainEntityOfPage\": {\n        \"@type\": \"WebPage\",\n        \"@id\": \"https:\\\/\\\/hlh-js.com\\\/resource\\\/blog\\\/improving-ra-and-rz-on-3d-printed-parts-how-abrasive-blasting-reduces-surface-roughness\\\/\"\n    },\n    \"keywords\": \"3d printed parts surface roughness Ra, surface finish improvement additive manufacturing, abrasive blasting Ra reduction, 3d printing Ra Rz improvement\"\n}<\/script><script type=\"application\/ld+json\">{\n    \"@context\": \"https:\\\/\\\/schema.org\",\n    \"@type\": \"FAQPage\",\n    \"mainEntity\": [\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What is the difference between Ra and Rz, and which matters more for AM parts?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Ra (arithmetic mean roughness) is the average absolute deviation of the surface profile from the mean line over the measurement length. Rz (mean roughness depth) is the average of the five largest peak-to-valley heights within the measurement length. For AM parts, both are important. Ra gives the average surface texture severity \\u2014 useful for corrosion resistance, friction, and general surface quality assessment. Rz reflects the deepest features (peaks and valleys) \\u2014 more directly relevant to fatigue crack initiation (cracks start at the deepest valleys) and coating adhesion anchor profile. For blasted AM surfaces, the relationship Rz \\u2248 4\\u20137 \\u00d7 Ra is typical. Specifying both Ra and Rz for AM parts provides a more complete surface quality description than Ra alone.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"How many blast passes does it take to achieve Ra below 3 \\u00b5m on SLM parts?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"For typical SLM steel or titanium parts (starting Ra 10\\u201320 \\u00b5m), one to two passes of glass bead blasting (100\\u2013200 mesh, 55\\u201375 psi) are sufficient to achieve Ra 2\\u20134 \\u00b5m. EBM parts with higher starting Ra (25\\u201340 \\u00b5m) require two to three passes or a cascade sequence (coarser first pass, finer second pass). The diminishing-returns principle applies to blasting: each additional pass after the first produces progressively smaller Ra improvement. Beyond three passes, additional blasting rarely produces meaningful Ra reduction and may start slightly increasing Ra by creating a deeper, more irregular micro-texture. If Ra below 2 \\u00b5m is required after three blast passes, switch to a secondary process (vibratory, electropolishing, or mechanical finishing).\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Can Ra be measured accurately on complex 3D printed geometry?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Yes, with appropriate measurement strategy. Contact profilometry (stylus) is the standard method per ISO 4287, but the stylus tip radius (typically 2\\u20135 \\u00b5m) limits measurement resolution on very fine features. For complex curved surfaces, portable hand-held profilometers with flexible probe holders are most practical. Areal surface texture measurement per ISO 25178 using confocal, focus variation, or white-light interferometry microscopy provides three-dimensional Sa and Sz values that better characterise the isotropic blasted AM surface than single-profile Ra measurements. For production quality control of blasted AM parts, a well-calibrated portable contact profilometer at consistent measurement locations is sufficient for most applications.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What Ra does abrasive blasting achieve on down-skin AM surfaces?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Down-skin surfaces (overhanging surfaces facing downward during the build) have the highest as-built Ra of any AM surface orientation \\u2014 typically 18\\u201335 \\u00b5m for SLM and 30\\u201350 \\u00b5m for EBM. After glass bead blasting, down-skin surfaces achieve Ra 2\\u20136 \\u00b5m for SLM alloys and 4\\u201310 \\u00b5m for EBM \\u2014 somewhat higher than the Ra achieved on up-skin or side-wall surfaces of the same part under the same blast parameters. This is because the deeper sub-surface features on down-skin surfaces cannot be fully removed by blasting without excessive material removal. For parts where down-skin Ra must match up-skin Ra closely, a cascade blast approach (coarse first pass, fine second pass) on down-skin surfaces specifically, combined with optimised support strategy to minimise the extent of down-skin surface area, produces the best results.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"At what Ra value should blasting be replaced by a secondary finishing process?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"For most AM applications, blasting achieves Ra in the range of 1\\u20135 \\u00b5m, which covers the majority of functional, coating-prep, and aesthetic specifications. When your target Ra is below 0.8 \\u00b5m, plan for a secondary finishing process after blasting. Options and their achievable Ra from a blasted (Ra ~2 \\u00b5m) starting surface: vibratory superfinishing (Ra 0.1\\u20130.4 \\u00b5m), electropolishing on metals (Ra 0.1\\u20130.5 \\u00b5m from blasted Ra ~2 \\u00b5m), barrel tumbling with fine media (Ra 0.3\\u20130.8 \\u00b5m), laser polishing (Ra 0.1\\u20130.3 \\u00b5m on metals), and manual polishing (Ra 0.05\\u20130.4 \\u00b5m). Blasting always serves as the essential first stage for these secondary processes \\u2014 it normalises the AM surface to a consistent Ra starting point from which the secondary process can work efficiently.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Is there a risk of increasing Ra if a part is blasted too long?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Yes \\u2014 over-blasting can increase Ra rather than reduce it. This occurs when the blast parameters create a more aggressive surface texture than the as-built surface being treated, or when cumulative material removal is sufficient to expose deeper sub-surface porosity or microstructural features. This is most commonly observed when angular Al\\u2082O\\u2083 grit is used at high pressure on soft or thin-walled AM structures: the aggressive cutting action eventually creates a rougher, deeper texture than the finer glass bead finishing pass would leave. The practical rule: use the finest media and lowest pressure that achieves the required Ra within a reasonable cycle time. More is not always better in blasting \\u2014 define the minimum effective blast duration and pressure for each part type and stick to it.\"\n            }\n        }\n    ]\n}<\/script>\n<span class=\"hlh-3dp-c08-badge\">Technical Guide<\/span>\n<h1>Improving Ra and Rz on 3D Printed Parts: How Abrasive Blasting Reduces Surface Roughness<\/h1>\n<div class=\"hlh-3dp-c08-meta\">\n  <span>Updated July 2026<\/span>\n  <span>By Jiangsu Henglihong Technology Co., Ltd.<\/span>\n  <span>~5,000 words \u00b7 11 min read<\/span>\n<\/div>\n<p class=\"hlh-3dp-c08-intro\">Surface roughness \u2014 quantified as Ra (arithmetic mean roughness) or Rz (mean peak-to-valley height) \u2014 is the primary measurable output of abrasive blasting in AM post-processing. Every production metal AM facility and most advanced polymer AM operations specify and measure surface roughness on finished parts. Abrasive blasting is the most effective single-step method for reducing as-built AM surface roughness by 60\u201380%, creating a uniform, controlled surface texture that meets functional specifications for fatigue resistance, corrosion protection, coating adhesion, and dimensional compliance. This guide explains how blasting reduces Ra and Rz, what values are achievable for each AM process and alloy, how to use cascade blasting for finer results, and when to add secondary finishing processes for specifications below Ra 0.8 \u00b5m.<\/p>\n<div class=\"hlh-3dp-c08-back\">&#8617; Part of our complete resource: <a href=\"https:\/\/hlh-js.com\/resource\/blog\/abrasive-blasting-3d-printed-parts-surface-finishing-guide\/\" target=\"_blank\" rel=\"noopener noreferrer\">Abrasive Blasting for 3D Printed Parts: The Complete Post-Processing and Surface Finishing Guide<\/a><\/div>\n<nav class=\"hlh-3dp-c08-toc\"><p class=\"hlh-3dp-c08-toc-title\">Table of Contents<\/p>\n<ol>\n<li><a href=\"#c08-s1\">Understanding Ra and Rz in Additive Manufacturing<\/a><\/li>\n<li><a href=\"#c08-s2\">As-Built Ra\/Rz Values by AM Process and Orientation<\/a><\/li>\n<li><a href=\"#c08-s3\">How Abrasive Blasting Reduces Surface Roughness<\/a><\/li>\n<li><a href=\"#c08-s4\">Ra Achievable by Media Type and AM Material<\/a><\/li>\n<li><a href=\"#c08-s5\">The Cascade Blasting Technique<\/a><\/li>\n<li><a href=\"#c08-s6\">Media Sequence and Diminishing Returns<\/a><\/li>\n<li><a href=\"#c08-s7\">When Blasting Is Not Enough: Ra Below 0.8 \u00b5m<\/a><\/li>\n<li><a href=\"#c08-s8\">Surface Roughness Measurement Standards for AM Parts<\/a><\/li>\n<li><a href=\"#c08-s9\">Ra Acceptance Criteria by Application<\/a><\/li>\n<li><a href=\"#c08-faq\">H\u00e4ufig gestellte Fragen<\/a><\/li>\n<\/ol><\/nav>\n\n<a id=\"c08-s1\"><\/a>\n<h2>1. Understanding Ra and Rz in Additive Manufacturing<\/h2>\n<p>Surface roughness is a statistical description of the micro-geometry of a surface. For AM parts, two parameters dominate engineering specifications:<\/p>\n<h3>Ra \u2014 Arithmetic Mean Roughness<\/h3>\n<p>Ra is calculated as the arithmetic mean of the absolute deviation of the surface profile from its mean line over the evaluation length (typically 5 \u00d7 \u03bbc, where \u03bbc is the cutoff wavelength). It is the most widely used single parameter for surface quality specification. Ra captures the average surface texture intensity but does not distinguish between peaked surfaces (many small sharp peaks) and pitted surfaces (few deep valleys) \u2014 two surfaces with the same Ra can have very different functional properties.<\/p>\n<h3>Rz \u2014 Mean Roughness Depth<\/h3>\n<p>Rz is the average height of the five deepest profile peaks and valleys within the evaluation length. For the same surface, Rz is always greater than Ra. For blasted AM surfaces, the typical relationship is Rz \u2248 4\u20137 \u00d7 Ra. Rz is more sensitive to extreme features (deep valleys, high peaks) and is therefore more relevant to fatigue crack initiation (cracks start at valleys) and coating thickness adequacy (the coating must fill valleys without bridging gaps).<\/p>\n<h3>Sa and Sz \u2014 Areal Parameters<\/h3>\n<p>Sa (areal arithmetic mean height) and Sz (maximum height of the evaluation area) are the three-dimensional equivalents of Ra and Rz, measured per ISO 25178 using optical or confocal profilometry. Because AM surfaces are anisotropic \u2014 Ra measured parallel to layer lines differs from Ra measured perpendicular to them \u2014 areal parameters provide a more complete and representative characterisation of blasted AM surfaces. For high-accuracy surface specification on AM parts, Sa and Sz are preferred over Ra and Rz alone.<\/p>\n<p>For all AM post-processing reporting in this guide, Ra is used as the primary metric (the most common specification parameter in industry), with Rz noted where it provides additional insight.<\/p>\n\n<a id=\"c08-s2\"><\/a>\n<h2>2. As-Built Ra\/Rz Values by AM Process and Orientation<\/h2>\n<p>As-built surface roughness in AM is not uniform \u2014 it varies significantly with build orientation, process parameters, and alloy. Understanding the starting Ra is essential for selecting the correct blast parameters and setting realistic expectations for post-blast Ra.<\/p>\n\n<div class=\"hlh-3dp-c08-tw\">\n<table>\n<thead><tr><th>AM Process<\/th><th>Material<\/th><th>Up-skin Ra (\u00b5m)<\/th><th>Side-wall Ra (\u00b5m)<\/th><th>Down-skin Ra (\u00b5m)<\/th><th>Rz (approx.)<\/th><\/tr><\/thead>\n<tbody>\n<tr><td>FDM (0.2mm layers)<\/td><td>ABS, Nylon<\/td><td>5\u201312<\/td><td>15\u201325<\/td><td>18\u201330<\/td><td>5\u20138 \u00d7 Ra<\/td><\/tr>\n<tr><td>SLS<\/td><td>PA12 nylon<\/td><td>10\u201316<\/td><td>12\u201320<\/td><td>14\u201322<\/td><td>4\u20137 \u00d7 Ra<\/td><\/tr>\n<tr><td>MJF<\/td><td>PA12 nylon<\/td><td>8\u201312<\/td><td>8\u201315<\/td><td>10\u201318<\/td><td>4\u20136 \u00d7 Ra<\/td><\/tr>\n<tr><td>SLM\/DMLS<\/td><td>Ti-6Al-4V<\/td><td>8\u201314<\/td><td>10\u201318<\/td><td>18\u201330<\/td><td>4\u20137 \u00d7 Ra<\/td><\/tr>\n<tr><td>SLM\/DMLS<\/td><td>316L SS<\/td><td>8\u201314<\/td><td>10\u201318<\/td><td>18\u201330<\/td><td>4\u20137 \u00d7 Ra<\/td><\/tr>\n<tr><td>SLM\/DMLS<\/td><td>AlSi10Mg<\/td><td>8\u201316<\/td><td>10\u201320<\/td><td>18\u201335<\/td><td>4\u20137 \u00d7 Ra<\/td><\/tr>\n<tr><td>SLM\/DMLS<\/td><td>Inconel 718<\/td><td>8\u201315<\/td><td>12\u201320<\/td><td>20\u201335<\/td><td>5\u20137 \u00d7 Ra<\/td><\/tr>\n<tr><td>EBM<\/td><td>Ti-6Al-4V<\/td><td>20\u201330<\/td><td>25\u201335<\/td><td>30\u201340<\/td><td>5\u20138 \u00d7 Ra<\/td><\/tr>\n<\/tbody><\/table><\/div>\n\n<p>The data above illustrates two critical points: (1) down-skin surfaces are substantially rougher than up-skin surfaces for the same part; (2) EBM titanium starts roughly twice as rough as SLM titanium. Blast protocols must account for these starting Ra differences \u2014 a single parameter set will not achieve uniform final Ra across all orientations of a complex part without targeted attention to down-skin surfaces.<\/p>\n\n<a id=\"c08-s3\"><\/a>\n<h2>3. How Abrasive Blasting Reduces Surface Roughness<\/h2>\n<p>The Ra reduction mechanism of abrasive blasting depends on the media morphology:<\/p>\n<h3>Spherical Media (Glass Beads, Steel Shot, Zirconia): Peening Mode<\/h3>\n<p>Spherical particles impact the surface and plastically deform the material at the contact point. The high local contact stress flattens the surface peaks \u2014 the highest points on the Ra profile \u2014 by cold-working them. The peak material flows laterally into adjacent valleys, partially filling them. The net effect is a reduction in both peak height and valley depth, lowering Ra. This peening mechanism does not remove material in the traditional sense; it redistributes it. After multiple passes, diminishing returns set in as the remaining peaks are progressively smaller and require more energy per unit Ra reduction.<\/p>\n<h3>Angular Media (Al\u2082O\u2083, Steel Grit): Cutting Mode<\/h3>\n<p>Angular particles with sharp edges remove material by micro-cutting. Each impact of a sharp particle removes a tiny chip of surface material from the peak it strikes, leaving a sharp-edged micro-pit. The Ra reduction comes from peak removal, but the remaining micro-pits left by angular impacts create a characteristic surface texture that is rougher on a micro-scale than a peened surface. This is why angular media (Al\u2082O\u2083) at equivalent grit size produces a slightly higher Ra than spherical media (glass beads) at equivalent mesh size, despite both reducing Ra from the as-built condition.<\/p>\n<h3>Impact of Media Size on Ra<\/h3>\n<p>Media size directly determines the scale of surface modification. Coarse media (large particles, low mesh number) creates larger impact zones and removes larger peaks more rapidly, but leaves a coarser surface texture at the micro-scale. Fine media (small particles, high mesh number) creates smaller impact zones, producing a finer micro-texture but requiring longer cycle times. For the lowest achievable Ra in a single-stage blast, use the finest media that achieves adequate coverage in a reasonable cycle time.<\/p>\n\n<a id=\"c08-s4\"><\/a>\n<h2>4. Ra Achievable by Media Type and AM Material<\/h2>\n<div class=\"hlh-3dp-c08-tw\">\n<table>\n<thead><tr><th>AM Material\/Process<\/th><th>As-Built Ra (\u00b5m)<\/th><th>After Glass Beads 100\u2013150M<\/th><th>After Glass Beads 150\u2013200M<\/th><th>After Al\u2082O\u2083 80\u2013120<\/th><th>After Al\u2082O\u2083 150\u2013220<\/th><\/tr><\/thead>\n<tbody>\n<tr><td>FDM ABS (vertical)<\/td><td>15\u201325<\/td><td>4\u20138<\/td><td>3\u20136<\/td><td>N\/A<\/td><td>N\/A<\/td><\/tr>\n<tr><td>SLS PA12 nylon<\/td><td>12\u201320<\/td><td>3\u20136<\/td><td>2\u20134<\/td><td>N\/A<\/td><td>N\/A<\/td><\/tr>\n<tr><td>MJF PA12 nylon<\/td><td>8\u201315<\/td><td>2\u20134<\/td><td>1.5\u20133<\/td><td>N\/A<\/td><td>N\/A<\/td><\/tr>\n<tr><td>SLM Ti-6Al-4V (side)<\/td><td>10\u201318<\/td><td>1.5\u20134<\/td><td>1\u20133<\/td><td>\u2014<\/td><td>\u2014<\/td><\/tr>\n<tr><td>SLM 316L SS (side)<\/td><td>10\u201318<\/td><td>1.5\u20134<\/td><td>1\u20133.5<\/td><td>2\u20135<\/td><td>1.5\u20134<\/td><\/tr>\n<tr><td>SLM AlSi10Mg (side)<\/td><td>10\u201320<\/td><td>1.5\u20134<\/td><td>1\u20133.5<\/td><td>2\u20135<\/td><td>1.5\u20134<\/td><\/tr>\n<tr><td>SLM Inconel 718 (side)<\/td><td>12\u201320<\/td><td>1.5\u20134<\/td><td>1\u20133.5<\/td><td>2\u20135<\/td><td>1.5\u20134<\/td><\/tr>\n<tr><td>EBM Ti-6Al-4V (side)<\/td><td>25\u201335<\/td><td>3\u20137<\/td><td>2\u20135<\/td><td>\u2014<\/td><td>\u2014<\/td><\/tr>\n<tr><td>SLM Ti-6Al-4V (down-skin)<\/td><td>18\u201330<\/td><td>3\u20137<\/td><td>2\u20135<\/td><td>\u2014<\/td><td>\u2014<\/td><\/tr>\n<\/tbody><\/table><\/div>\n<p><em>Note: Al\u2082O\u2083 is not used on titanium or stainless steel due to iron-free media requirements. All values are approximate ranges under optimised parameters; actual results depend on specific machine, powder, parameters, and part geometry.<\/em><\/p>\n\n<a id=\"c08-s5\"><\/a>\n<h2>5. The Cascade Blasting Technique<\/h2>\n<p>Cascade blasting is the sequential use of two or more blast stages with progressively finer media \u2014 starting with a coarser media to rapidly reduce as-built Ra, then following with a finer media to refine the surface to the target Ra. It is the most efficient approach when the as-built Ra is very high (EBM parts, FDM vertical surfaces, SLM down-skin surfaces) and the target Ra is low.<\/p>\n<p>Example cascade for EBM Ti-6Al-4V (as-built Ra 25\u201335 \u00b5m, target Ra \u2264 3 \u00b5m):<\/p>\n<ol>\n<li><strong>Stage 1:<\/strong> Glass beads 80\u2013100 mesh at 70\u201380 psi \u2014 rapid peak removal; reduces Ra from 25\u201335 \u00b5m to 5\u201310 \u00b5m in 3\u20135 minutes<\/li>\n<li><strong>Stage 2:<\/strong> Glass beads 150\u2013200 mesh at 60\u201370 psi \u2014 surface refinement; reduces Ra from 5\u201310 \u00b5m to 1.5\u20134 \u00b5m in 3\u20135 minutes<\/li>\n<\/ol>\n<p>Total cascade time: 6\u201310 minutes per part, achieving Ra below 4 \u00b5m. Compare to using only 150\u2013200 mesh glass beads from the start on the same part: 10\u201315 minutes to achieve Ra 4\u20136 \u00b5m, without reliably reaching below 4 \u00b5m within reasonable cycle time.<\/p>\n<p>The cascade principle also applies to Al\u2082O\u2083 blasting for pre-coating preparation:<\/p>\n<ol>\n<li><strong>Stage 1:<\/strong> Al\u2082O\u2083 80 mesh at 65\u201380 psi \u2014 aggressive peak removal, cleaning, and oxide removal<\/li>\n<li><strong>Stage 2:<\/strong> Al\u2082O\u2083 150\u2013180 mesh at 55\u201365 psi \u2014 refine anchor profile to target Ra 2\u20134 \u00b5m for paint\/powder coat<\/li>\n<\/ol>\n\n<a id=\"c08-s6\"><\/a>\n<h2>6. Media Sequence and Diminishing Returns<\/h2>\n<p>Understanding the diminishing returns of repeated blasting at the same parameters prevents over-processing and media waste:<\/p>\n<ul>\n<li><strong>First pass:<\/strong> Largest Ra reduction \u2014 50\u201370% of the total achievable reduction from blasting occurs in the first pass. The as-built peaks (tallest features) are addressed most rapidly.<\/li>\n<li><strong>Second pass:<\/strong> An additional 15\u201325% Ra reduction is typical. Remaining smaller peaks are flattened.<\/li>\n<li><strong>Third pass:<\/strong> 5\u201310% additional Ra reduction. Diminishing returns are pronounced.<\/li>\n<li><strong>Fourth pass and beyond:<\/strong> Less than 5% additional Ra reduction; risk of increasing Ra by creating a more irregular micro-texture; unnecessary media and equipment wear.<\/li>\n<\/ul>\n<p>Practical rule: define blast cycle time and number of passes by Ra measurement on first-article coupons, not by guesswork. Once the first-article Ra target is confirmed at a specific number of passes and parameters, use that as the production specification.<\/p>\n\n<a id=\"c08-s7\"><\/a>\n<h2>7. When Blasting Is Not Enough: Ra Below 0.8 \u00b5m<\/h2>\n<p>For applications requiring Ra below 0.8 \u00b5m \u2014 precision sealing surfaces, optical components, PVD coating substrates, certain medical devices \u2014 abrasive blasting must be followed by a secondary finishing process. The blasted surface at Ra 1\u20133 \u00b5m serves as the starting point for these secondary processes:<\/p>\n\n<div class=\"hlh-3dp-c08-tw\">\n<table>\n<thead><tr><th>Secondary Process<\/th><th>Starting Ra (after blast)<\/th><th>Achievable Ra<\/th><th>Compatible Materials<\/th><th>Notes<\/th><\/tr><\/thead>\n<tbody>\n<tr><td>Electropolishing<\/td><td>1\u20134 \u00b5m<\/td><td>0.1\u20130.5 \u00b5m<\/td><td>Stainless steel, titanium, Al<\/td><td>Also passivates; changes dimensions<\/td><\/tr>\n<tr><td>Vibratory superfinishing<\/td><td>1\u20134 \u00b5m<\/td><td>0.1\u20130.4 \u00b5m<\/td><td>Metals<\/td><td>Isotropic; no complex geometry<\/td><\/tr>\n<tr><td>Manual polishing<\/td><td>1\u20134 \u00b5m<\/td><td>0.05\u20130.4 \u00b5m<\/td><td>All<\/td><td>Labour-intensive; directional<\/td><\/tr>\n<tr><td>Laser polishing<\/td><td>1\u20134 \u00b5m<\/td><td>0.1\u20130.3 \u00b5m<\/td><td>Metals<\/td><td>High capital; line-of-sight only<\/td><\/tr>\n<tr><td>Chemical smoothing<\/td><td>1\u20134 \u00b5m<\/td><td>0.1\u20130.4 \u00b5m<\/td><td>Some polymers<\/td><td>Hazardous chemicals; limited materials<\/td><\/tr>\n<\/tbody><\/table><\/div>\n\n<p>The blasted surface at Ra 1\u20133 \u00b5m requires significantly less secondary processing than the as-built AM surface (Ra 8\u201335 \u00b5m) to reach the same final Ra. Using blasting as a mandatory pre-step before secondary finishing is the most efficient workflow for tight Ra specifications.<\/p>\n\n<a id=\"c08-s8\"><\/a>\n<h2>8. Surface Roughness Measurement Standards for AM Parts<\/h2>\n<p>Accurate Ra measurement requires correct selection of measurement parameters, particularly the cutoff wavelength (\u03bbc) and the evaluation length. For blasted AM surfaces:<\/p>\n<ul>\n<li><strong>ISO 4287 (profile) \/ ISO 4288 (measurement conditions):<\/strong> The primary standards for Ra and Rz measurement using contact profilometry. For blasted AM surfaces with Ra 1\u201310 \u00b5m, \u03bbc = 0.8 mm is the standard cutoff wavelength.<\/li>\n<li><strong>Evaluation length:<\/strong> 5 \u00d7 \u03bbc = 4.0 mm (five sampling lengths). For small AM part features where 4 mm measurement length is not available, document the reduced evaluation length and note this on the inspection record.<\/li>\n<li><strong>Measurement direction:<\/strong> AM surfaces are anisotropic \u2014 Ra measured parallel to build layers differs from Ra measured perpendicular to build layers. Measure in the most critical direction for your application, or measure in both directions and report both values for a complete characterisation.<\/li>\n<li><strong>ISO 25178 (areal):<\/strong> For R&#038;D and critical applications, areal measurement using focus variation, confocal, or white light interferometry provides Sa, Sz, Sku, and Ssk \u2014 a complete three-dimensional surface characterisation that is more appropriate for the complex, isotropic blasted AM surface than a single-profile Ra measurement.<\/li>\n<li><strong>Instrument calibration:<\/strong> Stylus profilometers must be calibrated with traceable reference specimens per ISO 12179. For aerospace and medical QC, calibration records must be maintained and available for audit.<\/li>\n<\/ul>\n\n<a id=\"c08-s9\"><\/a>\n<h2>9. Ra Acceptance Criteria by Application<\/h2>\n<div class=\"hlh-3dp-c08-tw\">\n<table>\n<thead><tr><th>Anmeldung<\/th><th>Ra Target (\u00b5m)<\/th><th>Can Blasting Achieve Directly?<\/th><th>Measurement Standard<\/th><\/tr><\/thead>\n<tbody>\n<tr><td>General structural AM parts<\/td><td>3.2\u20136.3<\/td><td>Yes<\/td><td>ISO 4287 \/ ASME B46.1<\/td><\/tr>\n<tr><td>Pre-coating (paint\/primer)<\/td><td>3\u20135<\/td><td>Yes<\/td><td>ISO 8503 \/ ASTM D4417<\/td><\/tr>\n<tr><td>Medical implant (osseointegration)<\/td><td>1.5\u20134.0<\/td><td>Yes<\/td><td>ISO 25178 (Sa)<\/td><\/tr>\n<tr><td>Automotive functional parts<\/td><td>1.6\u20133.2<\/td><td>Yes<\/td><td>ISO 4287<\/td><\/tr>\n<tr><td>Aerospace structural (non-sealing)<\/td><td>\u22643.2<\/td><td>Yes<\/td><td>ASME B46.1<\/td><\/tr>\n<tr><td>Aerospace fatigue-critical (pre-peen)<\/td><td>\u22643.2<\/td><td>Yes<\/td><td>ASME B46.1<\/td><\/tr>\n<tr><td>Consumer product aesthetics<\/td><td>0.8\u20133.2<\/td><td>Partially (lower end needs fine blast)<\/td><td>Visual + profilometer<\/td><\/tr>\n<tr><td>Aerospace sealing surfaces<\/td><td>\u22641.6<\/td><td>Partially (needs secondary)<\/td><td>ASME B46.1<\/td><\/tr>\n<tr><td>Food-contact (3-A standard)<\/td><td>\u22640.8<\/td><td>No \u2014 secondary required<\/td><td>3-A Standard No. 74<\/td><\/tr>\n<tr><td>Pharma (EHEDG)<\/td><td>\u22640.8<\/td><td>No \u2014 secondary required<\/td><td>EHEDG Document 8<\/td><\/tr>\n<tr><td>PVD coating substrate<\/td><td>0.3\u20131.0<\/td><td>No \u2014 secondary required<\/td><td>Supplier specification<\/td><\/tr>\n<\/tbody><\/table><\/div>\n\n<p>For more on pre-coating specific Ra requirements, see: <a href=\"https:\/\/hlh-js.com\/resource\/blog\/pre-coating-surface-preparation-for-3d-printed-parts-blasting-before-paint-powder-coat-and-pvd\/\" target=\"_blank\" rel=\"noopener noreferrer\">Pre-Coating Surface Preparation for 3D Printed Parts: Blasting Before Paint, Powder Coat, and PVD<\/a>. For shot peening and fatigue life, where Ra of the pre-peen surface is a key input parameter, see: <a href=\"https:\/\/hlh-js.com\/resource\/blog\/shot-peening-3d-printed-metal-parts-improving-fatigue-life-with-compressive-residual-stress\/\" target=\"_blank\" rel=\"noopener noreferrer\">Shot Peening 3D Printed Metal Parts: Improving Fatigue Life with Compressive Residual Stress<\/a>.<\/p>\n\n<a id=\"c08-faq\"><\/a>\n<h2>H\u00e4ufig gestellte Fragen<\/h2>\n<div class=\"hlh-3dp-c08-faq\"><details class=\"hlh-3dp-c08-fi\"><summary>What is the difference between Ra and Rz, and which matters more for AM parts?<\/summary><div class=\"hlh-3dp-c08-fa\"><p>Ra (arithmetic mean roughness) is the average absolute deviation of the surface profile from the mean line over the measurement length. Rz (mean roughness depth) is the average of the five largest peak-to-valley heights within the measurement length. For AM parts, both are important. Ra gives the average surface texture severity \u2014 useful for corrosion resistance, friction, and general surface quality assessment. Rz reflects the deepest features (peaks and valleys) \u2014 more directly relevant to fatigue crack initiation (cracks start at the deepest valleys) and coating adhesion anchor profile. For blasted AM surfaces, the relationship Rz \u2248 4\u20137 \u00d7 Ra is typical. Specifying both Ra and Rz for AM parts provides a more complete surface quality description than Ra alone.<\/p><\/div><\/details>\n<details class=\"hlh-3dp-c08-fi\"><summary>How many blast passes does it take to achieve Ra below 3 \u00b5m on SLM parts?<\/summary><div class=\"hlh-3dp-c08-fa\"><p>For typical SLM steel or titanium parts (starting Ra 10\u201320 \u00b5m), one to two passes of glass bead blasting (100\u2013200 mesh, 55\u201375 psi) are sufficient to achieve Ra 2\u20134 \u00b5m. EBM parts with higher starting Ra (25\u201340 \u00b5m) require two to three passes or a cascade sequence (coarser first pass, finer second pass). The diminishing-returns principle applies to blasting: each additional pass after the first produces progressively smaller Ra improvement. Beyond three passes, additional blasting rarely produces meaningful Ra reduction and may start slightly increasing Ra by creating a deeper, more irregular micro-texture. If Ra below 2 \u00b5m is required after three blast passes, switch to a secondary process (vibratory, electropolishing, or mechanical finishing).<\/p><\/div><\/details>\n<details class=\"hlh-3dp-c08-fi\"><summary>Can Ra be measured accurately on complex 3D printed geometry?<\/summary><div class=\"hlh-3dp-c08-fa\"><p>Yes, with appropriate measurement strategy. Contact profilometry (stylus) is the standard method per ISO 4287, but the stylus tip radius (typically 2\u20135 \u00b5m) limits measurement resolution on very fine features. For complex curved surfaces, portable hand-held profilometers with flexible probe holders are most practical. Areal surface texture measurement per ISO 25178 using confocal, focus variation, or white-light interferometry microscopy provides three-dimensional Sa and Sz values that better characterise the isotropic blasted AM surface than single-profile Ra measurements. For production quality control of blasted AM parts, a well-calibrated portable contact profilometer at consistent measurement locations is sufficient for most applications.<\/p><\/div><\/details>\n<details class=\"hlh-3dp-c08-fi\"><summary>What Ra does abrasive blasting achieve on down-skin AM surfaces?<\/summary><div class=\"hlh-3dp-c08-fa\"><p>Down-skin surfaces (overhanging surfaces facing downward during the build) have the highest as-built Ra of any AM surface orientation \u2014 typically 18\u201335 \u00b5m for SLM and 30\u201350 \u00b5m for EBM. After glass bead blasting, down-skin surfaces achieve Ra 2\u20136 \u00b5m for SLM alloys and 4\u201310 \u00b5m for EBM \u2014 somewhat higher than the Ra achieved on up-skin or side-wall surfaces of the same part under the same blast parameters. This is because the deeper sub-surface features on down-skin surfaces cannot be fully removed by blasting without excessive material removal. For parts where down-skin Ra must match up-skin Ra closely, a cascade blast approach (coarse first pass, fine second pass) on down-skin surfaces specifically, combined with optimised support strategy to minimise the extent of down-skin surface area, produces the best results.<\/p><\/div><\/details>\n<details class=\"hlh-3dp-c08-fi\"><summary>At what Ra value should blasting be replaced by a secondary finishing process?<\/summary><div class=\"hlh-3dp-c08-fa\"><p>For most AM applications, blasting achieves Ra in the range of 1\u20135 \u00b5m, which covers the majority of functional, coating-prep, and aesthetic specifications. When your target Ra is below 0.8 \u00b5m, plan for a secondary finishing process after blasting. Options and their achievable Ra from a blasted (Ra ~2 \u00b5m) starting surface: vibratory superfinishing (Ra 0.1\u20130.4 \u00b5m), electropolishing on metals (Ra 0.1\u20130.5 \u00b5m from blasted Ra ~2 \u00b5m), barrel tumbling with fine media (Ra 0.3\u20130.8 \u00b5m), laser polishing (Ra 0.1\u20130.3 \u00b5m on metals), and manual polishing (Ra 0.05\u20130.4 \u00b5m). Blasting always serves as the essential first stage for these secondary processes \u2014 it normalises the AM surface to a consistent Ra starting point from which the secondary process can work efficiently.<\/p><\/div><\/details>\n<details class=\"hlh-3dp-c08-fi\"><summary>Is there a risk of increasing Ra if a part is blasted too long?<\/summary><div class=\"hlh-3dp-c08-fa\"><p>Yes \u2014 over-blasting can increase Ra rather than reduce it. This occurs when the blast parameters create a more aggressive surface texture than the as-built surface being treated, or when cumulative material removal is sufficient to expose deeper sub-surface porosity or microstructural features. This is most commonly observed when angular Al\u2082O\u2083 grit is used at high pressure on soft or thin-walled AM structures: the aggressive cutting action eventually creates a rougher, deeper texture than the finer glass bead finishing pass would leave. The practical rule: use the finest media and lowest pressure that achieves the required Ra within a reasonable cycle time. More is not always better in blasting \u2014 define the minimum effective blast duration and pressure for each part type and stick to it.<\/p><\/div><\/details>\n<\/div>\n<div class=\"hlh-3dp-c08-cta\">\n  <h2>Source Blasting Media for Ra Improvement in AM Post-Processing<\/h2>\n  <p>Jiangsu Henglihong Technology Co., Ltd. manufactures glass beads and aluminum oxide in a complete range of mesh sizes for Ra reduction in AM post-processing \u2014 from coarse 80 mesh for rapid peak removal to fine 325 mesh for precision surface conditioning. Contact our team for media selection guidance and cascade blasting protocol support.<\/p>\n  <a class=\"hlh-3dp-c08-btn\" href=\"https:\/\/hlh-js.com\/contact\/\" target=\"_blank\" rel=\"noopener noreferrer\">Contact Our Technical Team<\/a>\n<\/div>\n<hr class=\"hlh-3dp-c08-div\">\n<p style=\"font-size:.8rem;color:#9ca3af;margin:0;\">Published July 2026 by Jiangsu Henglihong Technology Co., Ltd. \u2014 Specialists in industrial abrasive blasting media for additive manufacturing post-processing.<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Technical Guide Improving Ra and Rz on 3D Printed Parts:  [&#8230;]<\/p>","protected":false},"author":1,"featured_media":13750,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[62,175,138],"tags":[],"class_list":["post-13727","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog","category-industry","category-resource"],"_links":{"self":[{"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/posts\/13727","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/comments?post=13727"}],"version-history":[{"count":2,"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/posts\/13727\/revisions"}],"predecessor-version":[{"id":13729,"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/posts\/13727\/revisions\/13729"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/media\/13750"}],"wp:attachment":[{"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/media?parent=13727"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/categories?post=13727"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/hlh-js.com\/de\/wp-json\/wp\/v2\/tags?post=13727"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}