Oberflächenrauheit, measured by the Ra (Arithmetic Average Deviation) Wert, is a critical indicator of CNC -Bearbeitung quality—it directly impacts part functionality, Resistenz tragen, und fit. Whether you’re making consumer goods, industrielle Komponenten, or medical implants, knowing the achievable Ra range of CNC processing and how to control it is essential. Dieser Artikel schlüsselt die auf RA values that CNC processing can reach across common methods, explains key influencing factors, and shares practical selection strategies.
1. RA Value Ranges by Common CNC Machining Methods
Different CNC machining techniques—from rough turning to ultra-precision grinding—deliver vastly different Ra values. Below is a detailed table of achievable ranges, tailored to help you match methods to your roughness needs.
| CNC Machining Method | Sub-Method | Achievable RA Value Range (μm) | Typische Anwendungsszenarien |
| CNC drehen sich | Rough Turning | 20 – 10 | Initial shaping of metal blanks; parts with no surface finish requirements (Z.B., temporary structural supports) |
| Semi-Finishing/Finishing Turning | 1.6 – 0.8 | Allgemeine Teile (Z.B., langsamlaufende Wellen, unkritische Gehäuse) | |
| Mirror Turning (Diamond Tools for Non-Ferrous Metals) | 0.04 – 0.01 | High-Gloss, Präzisionsteile (Z.B., aluminum decorative components, optical instrument parts) | |
| CNC -Fräsen | Grobfräsen | 6.3 – 2.5 | Große Strukturteile (Z.B., Maschinenrahmen, Halterungsrohlinge) |
| Finish Milling | 1.6 – 0.63 | Fitted parts (Z.B., sliding guides, Ausrüstungsgehäuse) | |
| Super Fine Milling (High-Speed, Small Feed) | 0.4 | Präzisionsmechanische Komponenten (Z.B., high-speed bearing seats) | |
| CNC langweilig | Ordinary Boring | 2.5 – 0.63 | Hole machining for general parts (Z.B., hydraulic cylinder bores) |
| Fein langweilig | 0.32 – 0.08 | High-precision holes (Z.B., engine cylinder bores, precision valve holes) | |
| Schleifen | Präzisionsschleife | 0.16 – 0.04 | Teile mit hoher Verschlüsselung (Z.B., Tragrennen, Werkzeugbits) |
| Ultrapräzises Schleifen | < 0.01 | Ultra-high-precision components (Z.B., medical implant surfaces, Halbleiterteile) |
2. Practical RA Value Selection: Balancing Function, Kosten, and Scenarios
Not all parts need ultra-low Ra values—over-processing wastes time and money. Below is a guide to standard RA options and their cost implications, aligned with real-world use cases.
2.1 Standard RA Grades for CNC Processing
| RA Value (μm) | Grade Type | Wichtige Anwendungsszenarien | Kostenauswirkungen (vs. Ra 3.2 μm) |
| 3.2 | Economy Grade | General consumer parts (Z.B., Plastikspielzeugkomponenten, Einfache Klammern); light-load, low-speed moving parts. Surface has slight knife marks but no functional impact. | Grundkosten (0% Zunahme) |
| 1.6 | Functional Grade | Tightly fitting or stressed parts (Z.B., sliding guides, low-speed rotary shafts); requires high-speed cutting and fine feed. | ~3% cost increase |
| 0.8 | High-Grade | Lager, high-stress concentration areas (Z.B., gear teeth roots); improves wear resistance and fatigue life. | ~5% cost increase |
| 0.4 | Ultra-Fine Grade | Hochvorbereitete Lager, Medizinische Implantate (Z.B., künstliche Gelenke); demands strict surface smoothness to avoid tissue irritation or friction damage. | 11–15% cost increase |
| < 0.01 | Ultra-Precision Grade | Halbleiterteile, optische Komponenten; only achievable via ultra-precision grinding. | 50–100% cost increase |
2.2 Beispiel: How to Choose RA for an Automotive Shaft
- If the shaft is a non-critical auxiliary component (Z.B., a cover support shaft): Wählen Ra 3.2 μm (economy, no unnecessary cost).
- If the shaft is a rotating part with a sliding fit (Z.B., a transmission auxiliary shaft): Wählen Ra 1.6 μm (balances function and cost).
- If the shaft is a high-speed bearing journal (Z.B., an engine crankshaft): Wählen Ra 0.8 μm (ensures wear resistance and long life).
3. 3 Key Factors That Affect CNC Processing Surface Roughness
To achieve your target RA value consistently, you need to control these three critical variables:
3.1 Werkzeugauswahl & Schneidenparameter
- Tool Edge Accuracy: Dull or low-precision tools leave deeper tool marks, increasing Ra values. Verwenden Sie scharf, Hochhärtungswerkzeuge (Z.B., carbide tools for steel, diamond tools for non-ferrous metals).
- Schnittgeschwindigkeit: Higher speed (within material limits) reduces friction between tool and workpiece, creating a smoother surface. Zum Beispiel, increasing turning speed from 100 m/min bis 300 m/min can lower Ra from 1.6 μm zu 0.8 μm.
- Futterrate: Kleinere Vorschubgeschwindigkeiten (Z.B., 0.1 mm/U vs. 0.3 mm/U) reduce the distance between tool paths, minimizing surface irregularities.
3.2 Workpiece Material Properties
- Nichteisenmetalle (Z.B., Aluminiumlegierungen, Kupfer): Weich und einfach zu maschinell, making it simple to achieve low Ra values (Z.B., Ra 0.04 μm via mirror turning).
- Ferrous Metals (Z.B., Kohlenstoffstahl, Edelstahl): Harder and more prone to tool wear, requiring stricter process control (Z.B., higher tool hardness, optimized cooling) to reach Ra < 0.8 μm.
3.3 Nachbearbeitungstechniken
Post-processing can further improve surface roughness, but note its impact on dimensional tolerances:
- Polieren: Reduces Ra by 50–70% (Z.B., aus 1.6 μm zu 0.4 μm) but may slightly reduce part size.
- Schleifen: Suitable for removing minor tool marks (Z.B., Ra absenken 3.2 μm zu 1.6 μm) but is labor-intensive.
- Elektroplierend: Creates a smooth coating (Z.B., Chrombeschichtung) to lower Ra, but adds cost and requires strict environmental controls.
4. Yigu Technology’s Perspective on CNC Processing Surface Roughness
Bei Yigu Technology, we often see clients overspecify RA values—for example, choosing Ra 0.4 μm for a non-critical bracket that only needs Ra 3.2 μm, Erhöhung der Kosten durch 15% unnecessarily. Unser Rat: Start with the functional requirement, not the lowest possible Ra. Für die meisten industriellen Teile, Ra 1.6–0.8 μm balances performance and cost. We also help clients optimize processes: For a recent automotive client, adjusting their milling feed rate from 0.2 mm/rev to 0.1 mm/U (while keeping speed constant) lowered Ra from 1.6 μm zu 0.8 μm without extra cost. For ultra-precision needs (Z.B., Medizinische Implantate), we combine fine boring with polishing to hit Ra 0.4 μm consistently, ensuring both quality and cost efficiency.
FAQ: Common Questions About CNC Processing Surface Roughness RA
- Q: Can CNC turning achieve Ra < 0.01 μm wie Ultrapräzisionsschleifen?
A: NEIN. Auch mit Diamantwerkzeugen, Spiegeldrehung (das präziseste CNC-Drehverfahren) erreicht nur Ra 0,01–0,04 μm. Ra < 0.01 μm erfordert ein hochpräzises Schleifen, Dabei werden abrasive Partikel verwendet, um Material im Mikrometerbereich abzutragen.
- Q: Wird eine zunehmende Schnittgeschwindigkeit den RA-Wert immer senken??
A: NEIN. Über eine bestimmte Grenze hinaus, Eine zu hohe Drehzahl führt zu Überhitzung und Verschleiß des Werkzeugs, was Ra erhöht. Zum Beispiel, Drehen von Aluminium bei > 500 m/min kann die Materialoberfläche zum Schmelzen bringen, Unregelmäßigkeiten entstehen. Befolgen Sie stets materialspezifische Geschwindigkeitsrichtlinien.
- Q: How do I verify if a CNC shop can actually achieve the RA value I need?
A: Ask for a sample part machined with the same material and process as your project. Use a surface roughness tester (Z.B., a portable Ra meter) to measure the sample’s Ra value—don’t rely solely on the shop’s claims. Für kritische Teile (Z.B., Medizinische Implantate), request a third-party inspection report.