Table of Contents:
Surface Roughness: Understanding Surface Finish in Manufacturing
- November 28, 2024
- Tony
1. overview
1. What is surface roughness?
Surface roughness refers to the surface of the part machining has a smaller pitch and tiny peaks and valleys of the unevenness of the tiny irregularities, which mainly reflects the surface morphology of the details of the characteristics.
2. Surface roughness VS surface finish
Surface roughness is a measurable physical parameter, while surface finish is a quality standard that is observed and described.
While both describe surface quality, roughness provides more precise, objective data, while finish relies more on subjective perception. In practice, roughness values are often used to indirectly assess finish.
3. Surface Roughness vs. Finish Grade Comparison
Roughness Parameter (Ra) | Surface Finish Grade | Surface Features | Processing Methods |
Ra 0.012 - 0.025 | 14 | Mirror-like Gloss | Superfine grinding, polishing, super finishing, mirror finish |
Ra 0.025 - 0.05 | 13 | High Gloss | Fine grinding, polishing, super finishing |
Ra 0.05 - 0.1 | 12 | Glossy Surface | Precision turning, precision grinding, fine surface grinding |
Ra 0.1 - 0.2 | 11 | Matte Mirror | Grinding, precision turning with diamond tools, precision grinding |
Ra 0.2 - 0.4 | 10 | Slightly Visible Marks | Grinding, polishing, cold drawing |
Ra 0.4 - 0.8 | 9 | Visible Marks | Grinding, polishing, cold drawing |
Ra 0.8 - 1.6 | 8 | Noticeable Tool Marks | Rough grinding, rough turning, rough milling, rough planing |
Ra 1.6 - 3.2 | 7 | Visible Machining Marks | Rough turning, rough milling, rough planing, drilling |
Ra 3.2 - 6.3 | 6 | Slightly Visible Machining Marks | Rough turning, rough milling, rough planing |
Ra 6.3 - 12.5 | 5 | Distinct Machining Marks | Rough turning, rough milling, rough planing |
Ra 12.5 - 25 | 4 | Noticeable Tool Marks | Turning, boring, planing |
Ra 25 - 50 | 3 | Distinct Machining Marks | Turning, boring, planing |
Ra 50 - 100 | 2 | Rough Surface | Rough turning, rough milling, rough planing |
Ra > 100 | 1 | Extremely Rough Surface | Rough machining, casting, forging |
- Ra Value (Average Surface Roughness): It measures the average height variation of the surface; a lower Ra value indicates a smoother surface and a higher finish quality.
- Finish Grade: Ranges from 1 to 14, indicating surface smoothness. Grade 1 is very rough, and grade 14 is a mirror-like finish.
- Processing Methods: Different techniques are used based on the Ra value to achieve the desired surface finish.
2. Surface roughness measurement methods
Principle: Probe scans the surface.
Use: General roughness measurements.
Pros: Simple, direct.
Cons: May damage surface, slower.
Principle: Laser or optical scanning.
Use: High-precision, non-destructive.
Pros: Fast, precise, no damage.
Cons: Expensive, surface restrictions.
3. Factors affecting surface roughness
Main influencing factors: type of material to be machined, machining process, tool condition and machining speed.
For example, high hardness materials usually require the use of higher precision CNC machining tools to obtain lower roughness values. Also, machining speeds that are too fast may result in uneven surfaces, which can affect part performance.
4. Surface roughness requirements in manufacturing
1. Automotive Industry
In automotive manufacturing, surface smoothness is crucial for performance and safety. Engine parts, transmission systems, and brakes require smooth surfaces to reduce friction and wear, ensuring long-term reliability. Excessive roughness can lead to faster wear and decreased fuel efficiency.
2. Aerospace Industry
The aerospace industry demands tighter surface roughness standards, especially for aircraft parts and engine components. Smooth, high-precision surfaces reduce drag, improve fuel efficiency, and enhance safety and durability. Even minor surface defects can lead to material fatigue and jeopardize flight safety.
3. Mechanical Parts
For mechanical equipment like gears and bearings, smoother surfaces reduce friction and wear, extending component lifespan and improving efficiency. Precision parts often require highly smooth surfaces to minimize energy loss and heat buildup.
4. Precision Instruments
Parts for precision instruments and electronics, such as optics, sensors, and microprocessors, require extremely smooth surfaces for accurate measurements and stable performance. Even small surface irregularities can cause performance issues and affect measurement accuracy.
5. Surface roughness symbols and abbreviations
Standard surface finish symbol, applicable to surfaces produced by any method.
The horizontal bar shows machining is needed, with extra material added.
Indicates the surface must be formed by processes like casting or forging, with no material removal.
a – average roughness value (Ra);
b – production method, coating, note, or other additional information;
c – roughness sampling length in millimeters or inches;
d – direction of the surface lay;
e – minimum material removal requirement in millimeters;
f – alternate surface finish parameter.
Common Codes：
- Ra = average roughness
- Rz = ten-point height roughness
- Ry = maximum height roughness
- RMS = Root Mean Square
- CLA = Centerline Average Roughness
- Rt = Total height roughness
- N = Grade value
6. Summary
Texture and quality of the product surface are vital for both aesthetics and product performance, affecting factors like corrosion resistance, adhesion, conductivity, and abrasion resistance. Understanding these aspects leads to better design and improved functionality.
