Many times, manufactured parts require additional processing such as surface finishing treatments to get the desired result. Some surface finishing treatments will add a kind of coating to cover the visible lines resulting from cutting the material with a machine tool. Others will remove a very thin layer of material from the surface to make the surface look better. For example, painting is a type of surface finish where a layer of coating is added to the surface, while polishing is a good one of those where material is removed. However, not all the parts require these types of treatments. Sometimes the surface roughness is more important, and the one obtained from machining can be exactly what is needed.
As machined parts surface roughness
Surface roughness is a feature associated with quality, and it is usually measured as the average surface roughness (Ra).
The average surface roughness or Ra represents the average the profile of the machined part has deviated from the ideal surface.
For parts with “as machined” surface finishes, the standard deviation or standard average surface roughness (Ra) is measured at 3.2 μm (125 μin). However, this could be high for some applications.
Fortunately, the average surface roughness of as machined parts can be reduced to 1.6, 0.8 or 0.4 μm (63, 32 or 16 μin) depending on the requirements of the application. The drawback from doing this is the fact that postprocessing is required to achieve the required reduction, meaning that extra costs and increase lead time will be added to the manufacturing of the part.
As machined parts tolerance
A very relevant aspect of the as machined surface finish is the fact that current machine tools technologies, namely CNC machine tools, provide highly accurate machining results.
Therefore, as machine parts can cope with the most demanding tolerance requirements. Applications where tight tolerances are required can benefit from this aspect. However, it is important to highlight that, when improving the aesthetics is required and processes such as polishing are applied, the dimensional tolerances of the part are affected.
Nevertheless, this is not an issue when the parts are used as machined. If your application requires that postprocessing to improve the surface appearance, make sure the extra material removal is considered when calculating the dimensional tolerance.
Advantages and disadvantages of as machined surface finish
Each surface finish comes with its own advantages and disadvantages. This is the main reason why some surface finishes work for some applications while others are more suitable for different ones.
In the case of as machined surface finish, the main advantages and disadvantages can be summarized as follows.
Advantages of as machined surface finish
- Highly accurate to meet tight tolerances.
- No extra costs for standard average surface roughness.
- Short lead times since postprocessing is not required.
Disadvantages of as machined surface finish
- Machine tool cutting marks are visible.
- No protection for materials with a low corrosion resistance.
Finish ★ ★ ☆ ☆ ☆
Tolerances ★ ★ ★ ★ ★
Protection ★ ☆ ☆ ☆ ☆
Suitable for Any material
As you can see, as machined surface finish can be a good cost-effective alternative in some cases. If your application only needs to meet tight dimensional tolerances and will not expose the material to harsh conditions, then as machined might be your go-to surface finish solution.