Шероховатость поверхности, measured by the Раствор (Arithmetic Average Deviation) ценить, is a critical indicator of Обработка с ЧПУ quality—it directly impacts part functionality, износостойкость, и подходит. Whether you’re making consumer goods, Промышленные компоненты, or medical implants, knowing the achievable Ra range of CNC processing and how to control it is essential. В этой статье разбивается 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 (мкм) | Typical Application Scenarios |
| КПН -поворот | Rough Turning | 20 – 10 | Initial shaping of metal blanks; parts with no surface finish requirements (НАПРИМЕР., temporary structural supports) |
| Semi-Finishing/Finishing Turning | 1.6 – 0.8 | Общие части (НАПРИМЕР., low-speed shafts, non-critical housings) | |
| Mirror Turning (Diamond Tools for Non-Ferrous Metals) | 0.04 – 0.01 | Высокий Гласс, точные детали (НАПРИМЕР., aluminum decorative components, optical instrument parts) | |
| Сторонний фрезерование | Rough Milling | 6.3 – 2.5 | Large structural parts (НАПРИМЕР., машинные рамки, bracket blanks) |
| Finish Milling | 1.6 – 0.63 | Fitted parts (НАПРИМЕР., sliding guides, корпусы передачи) | |
| Super Fine Milling (High-Speed, Small Feed) | 0.4 | Точные механические компоненты (НАПРИМЕР., high-speed bearing seats) | |
| Расточка с ЧПУ | Ordinary Boring | 2.5 – 0.63 | Hole machining for general parts (НАПРИМЕР., hydraulic cylinder bores) |
| Fine Boring | 0.32 – 0.08 | High-precision holes (НАПРИМЕР., engine cylinder bores, precision valve holes) | |
| Шлифование | Точное шлифование | 0.16 – 0.04 | Высокие части (НАПРИМЕР., Гонки, tool bits) |
| Ultra-Precision Grinding | < 0.01 | Ultra-high-precision components (НАПРИМЕР., medical implant surfaces, полупроводниковые детали) |
2. Practical RA Value Selection: Balancing Function, Расходы, 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 (мкм) | Grade Type | Ключевые сценарии применения | Влияние стоимости (против. Раствор 3.2 мкм) |
| 3.2 | Economy Grade | General consumer parts (НАПРИМЕР., Пластиковые компоненты игрушек, Простые скобки); light-load, low-speed moving parts. Surface has slight knife marks but no functional impact. | Базовая стоимость (0% увеличивать) |
| 1.6 | Functional Grade | Tightly fitting or stressed parts (НАПРИМЕР., sliding guides, low-speed rotary shafts); requires high-speed cutting and fine feed. | ~3% cost increase |
| 0.8 | High-Grade | Подшипники, high-stress concentration areas (НАПРИМЕР., gear teeth roots); improves wear resistance and fatigue life. | ~5% cost increase |
| 0.4 | Ultra-Fine Grade | Высокие подшипники, Медицинские имплантаты (НАПРИМЕР., Искусственные суставы); demands strict surface smoothness to avoid tissue irritation or friction damage. | 11–15% cost increase |
| < 0.01 | Ultra-Precision Grade | Полупроводниковые детали, Оптические компоненты; only achievable via ultra-precision grinding. | 50–100% cost increase |
2.2 Пример: How to Choose RA for an Automotive Shaft
- If the shaft is a non-critical auxiliary component (НАПРИМЕР., a cover support shaft): Выбирать Раствор 3.2 мкм (economy, no unnecessary cost).
- If the shaft is a rotating part with a sliding fit (НАПРИМЕР., a transmission auxiliary shaft): Выбирать Раствор 1.6 мкм (balances function and cost).
- If the shaft is a high-speed bearing journal (НАПРИМЕР., an engine crankshaft): Выбирать Раствор 0.8 мкм (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 Выбор инструмента & Параметры резки
- Tool Edge Accuracy: Dull or low-precision tools leave deeper tool marks, increasing Ra values. Используйте Sharp, Инструменты высокой жесткости (НАПРИМЕР., carbide tools for steel, diamond tools for non-ferrous metals).
- Скорость резки: Higher speed (within material limits) reduces friction between tool and workpiece, creating a smoother surface. Например, increasing turning speed from 100 м/мин до 300 m/min can lower Ra from 1.6 мкм до 0.8 мкм.
- Скорость корма: Меньшие скорости подачи (НАПРИМЕР., 0.1 мм/об против. 0.3 мм/rev) reduce the distance between tool paths, minimizing surface irregularities.
3.2 Workpiece Material Properties
- Нерухозные металлы (НАПРИМЕР., алюминиевые сплавы, медь): Мягкий и простой в машине, making it simple to achieve low Ra values (НАПРИМЕР., Раствор 0.04 μm via mirror turning).
- Ferrous Metals (НАПРИМЕР., углеродистая сталь, нержавеющая сталь): Harder and more prone to tool wear, requiring stricter process control (НАПРИМЕР., higher tool hardness, optimized cooling) to reach Ra < 0.8 мкм.
3.3 Методы постобработки
Post-processing can further improve surface roughness, but note its impact on dimensional tolerances:
- Полировка: Reduces Ra by 50–70% (НАПРИМЕР., от 1.6 мкм до 0.4 мкм) but may slightly reduce part size.
- Шлифование: Suitable for removing minor tool marks (НАПРИМЕР., снижение Ра от 3.2 мкм до 1.6 мкм) but is labor-intensive.
- Гальванизация: Creates a smooth coating (НАПРИМЕР., хромирование) to lower Ra, but adds cost and requires strict environmental controls.
4. Yigu Technology’s Perspective on CNC Processing Surface Roughness
В 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 мкм, Увеличение затрат 15% unnecessarily. Наш совет: Start with the functional requirement, not the lowest possible Ra. Для большинства промышленных частей, 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 мм/rev (while keeping speed constant) lowered Ra from 1.6 мкм до 0.8 μm without extra cost. For ultra-precision needs (НАПРИМЕР., Медицинские имплантаты), we combine fine boring with polishing to hit Ra 0.4 μm consistently, ensuring both quality and cost efficiency.
Часто задаваемые вопросы: Common Questions About CNC Processing Surface Roughness RA
- Q.: Can CNC turning achieve Ra < 0.01 μm like ultra-precision grinding?
А: Нет. Even with diamond tools, mirror turning (the most precise CNC turning method) only reaches Ra 0.01–0.04 μm. Раствор < 0.01 μm requires ultra-precision grinding, which uses abrasive particles to remove material at the micron level.
- Q.: Will increasing cutting speed always lower the RA value?
А: Нет. Beyond a certain limit, excessively high speed causes tool overheating and wear, which increases Ra. Например, turning aluminum at > 500 m/min may melt the material surface, creating irregularities. Always follow material-specific speed guidelines.
- Q.: How do I verify if a CNC shop can actually achieve the RA value I need?
А: Ask for a sample part machined with the same material and process as your project. Use a surface roughness tester (НАПРИМЕР., a portable Ra meter) to measure the sample’s Ra value—don’t rely solely on the shop’s claims. Для критических частей (НАПРИМЕР., Медицинские имплантаты), request a third-party inspection report.