O acabamento superficial é uma métrica crítica para peças usinadas em CNC, afetando diretamente a funcionalidade, estética, e desempenho - especialmente em setores como aeroespacial, dispositivos médicos, e automotivo. This article breaks down actionable strategies to enhance CNC machining surface finish, usando comparações claras, insights baseados em dados, e soluções práticas.
1. Primeiro: Understand Surface Finish Evaluation Metrics
Before improving surface finish, you need to measure it accurately. The table below compares the most common evaluation indicators, their definitions, e casos de uso:
| Indicator | Definição | Recurso principal | Ideal Use Case |
| Valor Ra | Arithmetic average of surface microscopic undulations (in μm) | Most widely used; simple to measure | General CNC parts (girando, fresagem) |
| N-level Standard | ISO grading system (N1 to N12) | Smaller number = higher finish | International quality compliance |
| Rz Value | Ten-point height of roughness (peak-to-valley average) | Reflects extreme surface irregularities | Parts with strict wear resistance requirements |
| Grit Size | Measure of sanding/polishing particle fineness | Larger grit number = finer surface | Post-machining polishing (por exemplo, ligas de alumínio) |
2. Core Factors That Harm CNC Surface Finish: A Contrast
Poor surface finish often stems from mismanagement of key variables. Below is a contrast between detrimental practices e optimal controls for critical factors:
| Fator | Detrimental Practices (Causes Roughness) | Optimal Controls (Boosts Smoothness) |
| Tool Conditions | Dull edges, low-wear materials (por exemplo, HSS), no coating | Ultra-fine grain carbide ou PCD (polycrystalline diamond) ferramentas; TiAlN-coated edges |
| Parâmetros de corte | Low spindle speed, high feed rate, deep cutting depth | High speed (reduces tool mark spacing), low feed (0.05–0.1 mm/rev), shallow depth (0.1–0,3mm) |
| Material Prep | Unprocessed alloys (internal stress), soft metals (rebarbas) | Stress relief treatment (para peças de paredes finas); pre-machining deburring (for aluminum alloys) |
| Cooling/Lubrication | Insufficient coolant, external cooling only (para furos profundos) | Combinado high-pressure internal cooling + external cooling; coolant matched to material (por exemplo, mineral oil for steel) |
| Machine/Fixture Stability | Loose clamps, low-rigidity CNC machines | High-precision 5-axis linkage machines; rigid clamp designs (avoids vibration-induced ripples) |
3. Step-by-Step Strategies to Improve Surface Finish
Follow this linear, actionable process to achieve consistent, high-quality surface finish:
Etapa 1: Optimize Tools and Cutting Parameters
- Usar imported PCD tools for non-ferrous metals (por exemplo, alumínio) to avoid sticking and burrs.
- Apply a “de alta velocidade, low-feed” finishing strategy: For steel parts, set spindle speed to 3,000–6,000 RPM, feed rate to 0.08 mm/rev, and cutting depth to 0.2 milímetros.
- Conduct 2–3 trimming passes to eliminate residual tool marks from rough machining.
Etapa 2: Enhance Cooling and Chip Evacuation
- For deep-hole machining (por exemplo, boreholes >10x diameter), usar high-pressure internal cooling (30–50 barras) to direct coolant to the cutting zone—this reduces heat and washes away chips immediately.
- Choose water-soluble coolant for aluminum (prevents oxidation) and mineral oil for stainless steel (reduz o atrito).
Etapa 3: Upgrade Equipment and Processes
- Replace old 3-axis machines with 5-axis linkage CNC equipment for complex surfaces (por exemplo, lâminas de turbina)—it minimizes re-clamping errors and vibration.
- Adopt turn-mill composite machining for parts with multiple features (por exemplo, shafts with threads and slots)—completing all operations in one clamping avoids surface scratches from repositioning.
Etapa 4: Implement Quality Control and Post-Processing
- Establish a full-chain quality check: Por exemplo, conduct IPQC (In-Process Quality Control) inspections every 2 horas (as used by Wemet factory) detectar desvios antecipadamente.
- Add post-processing steps:
- Test oxidation before anodizing to solve “material flowering” (uneven color) in aluminum parts.
- Usar blister packaging for transportation to prevent “three injuries”: abrasions, bruises, and hanging injuries.
4. Typical CNC Machining Methods: Finish Ranges and Improvement Tips
Different CNC processes yield varying baseline surface finishes. Use this table to set targets and identify improvement opportunities:
| Machining Method | Baseline Ra Range (μm) | Improvement Tip |
| Ordinary Turning | 1.6–0.8 | Upgrade to mirror turning (use finely ground PCD tools) for Ra 0.04–0.01 μm |
| Rough Milling | 20–5 | Switch to fine milling with carbide tools for Ra 6–0.63 μm |
| Fine Boring (Aço) | 0.63–0.08 | Add a final honing pass to reach Ra <0.04 μm |
| Ultra-Precision Grinding | 0.04–0.01 | Use mirror grinding (abrasivos de diamante) for Ra <0.01 μm |
Yigu Technology’s Perspective
Na tecnologia Yigu, we believe improving CNC surface finish is not just about optimizing single factors—it’s about integrating tool selection, controle de processo, and quality management into a seamless workflow. Our clients in the medical and automotive sectors often require Ra values below 0.1 μm; to meet this, we combine 5-axis CNC machines with custom PCD tools and real-time coolant monitoring. Adicionalmente, we’ve developed a post-processing oxidation test that reduces “material flowering” rates by 90%, ensuring consistent aesthetics. Para fabricantes, investing in these integrated solutions not only boosts surface finish but also cuts rework costs by up to 30%.
Perguntas frequentes
- What is the minimum Ra value achievable with CNC machining?
With ultra-precision processes like mirror turning or mirror grinding, Ra values as low as 0.01 μm can be achieved—suitable for high-end optical or medical parts.
- Can soft materials like aluminum achieve the same surface finish as steel?
Sim, but aluminum requires extra steps: Use PCD tools to avoid burrs, apply high-pressure cooling, and conduct post-machining polishing. Aluminum can reach Ra 0.04 μm, comparable to fine-turned steel.
- How does machine rigidity affect surface finish?
Low-rigidity machines cause vibration between the tool and workpiece, leading to ripples or deep tool marks. High-rigidity 5-axis machines suppress this vibration, ensuring Ra values stay consistent across the entire part—critical for complex geometries.