CNC machining is a highly accurate and precision manufacturing process that can produce parts with tolerances as small as 0.025 mm. Because it is a subtraction-based manufacturing method, it is inevitable that subtle cuts will be left on the surface of the finished product during the processing of the parts, which leads to the surface roughness to a certain extent.
What is surface roughness?
Surface roughness is the measurement of the average texture of the surface of the part, which refers to the surface roughness after CNC machining. There are different parameters used to define surface roughness, of which Ra (average roughness) is the more common. Ra is derived by calculating the difference between surface height and depth. When measured under a microscope, Ra is usually quantified in micrometers (x 10~⁶ m). It should be made clear that surface roughness and surface finish are two different concepts. Although the surface finish of machined parts can be improved by finishing techniques such as anodizing, sandblasting and electroplating, surface roughness refers specifically to the surface texture of the part directly after processing.
How to achieve different surface roughness?
Usually, the surface roughness of the machined parts is not generated randomly, but is carefully planned and controlled to meet specific standards. This means that the surface roughness value is pre-set. However, this does not mean that you can specify any value at will. In the manufacturing industry, there are a range of widely accepted Ra value standards, such as those specified in ISO 4287, which can be clearly specified during CNC machining. These standard values range widely from 25 microns to 0.025 microns to meet the needs of different manufacturing and post-processing operations.
We offer four surface roughness grades that are also typically specified values for CNC machining applications:
3.2 μm Ra
1.6 μm Ra
0.8 μm Ra
0.4 μm Ra
Different applications have different requirements for surface roughness. Lower surface roughness is specified only for specific needs. This is because a lower Ra value means that more processing operations and stricter quality control are required, which will inevitably increase processing costs and time. Therefore, post-treatment operations are not usually preferred in cases where specific surface roughness is required, as these operations are difficult to control precisely and may adversely affect the dimensional tolerances of the part.
Comparison of surface roughness between CNC milling and turning
In some applications, surface roughness has a significant impact on the function, performance and durability of a part. It is directly related to the friction coefficient, noise level, wear degree, heat condition and adhesion of parts during use. The importance of these factors varies depending on the specific application scenario. So while the surface roughness of a part may not seem so critical in some cases, it plays a crucial role in many other applications. These applications include, but are not limited to, high tension, high stress and high vibration environments, components that require precise fit and smooth movement, rapidly rotating parts, and medical implants. As mentioned earlier, different applications have different stringent requirements for surface roughness.
The roughness grades provided by junjie mold parts are described below, along with everything you need to know to choose the right Ra value for your application
3.2 μm Ra
This is a standard commercial machine finish. It is suitable for most consumer parts and is smooth enough, but contains obvious cut marks. This surface roughness is adopted by default unless otherwise specified.
Machining cut of 3.2 μm Ra
3.2 μm Ra is the maximum surface roughness recommended for parts subjected to stress, load and vibration. When the load is light and the movement is slow, it can also be used to match the moving surface. Processing to high speed, fine feed, light cutting.
1.6 μm Ra
Normally, there will only be slightly visible cut marks with this option. This Ra value is recommended for tight fitting and stressed parts, and is sufficient for slow moving and lightly loaded surfaces. However, it is not suitable for rapidly rotating parts and violently vibrating parts. This surface roughness is machined by high speed, fine feed and light cutting under controlled conditions.
Price: For standard aluminum alloys (e.g. 3.1645), this option adds about 2.5% to the production price. As the complexity of the parts increases, so does the price.
0.8 μm Ra
This surface finish is considered high-grade and requires very tight control during production, so costs are high. Parts needed for stress concentration. When movement occurs occasionally and the load is light, it can be used for bearings.
Price: For standard aluminum alloys (e.g. 3.1645), this option adds about 5% to the production price. As the complexity of the parts increases, so does the price.
0.4 μm Ra
This surface roughness reaches a finer level (the technical term is “less rough”) and represents a very high quality surface finish. It is particularly suitable for those parts that are subjected to high tension or stress, and rapidly rotating parts such as bearings and shafts also require this surface roughness. Because the process required to create this surface roughness is more cumbersome, it is only chosen when smoothness is critical.
Price: For standard aluminum alloys (e.g. 3.1645), this option adds about 11-15% to the production price. As the complexity of the parts increases, so does the price.
We have the capacity to produce CNC-machined parts that offer you the surface roughness options you need. Simply upload your model to our real-time quotation platform and choose your preferred surface roughness to get a real-time quote.
