What are the types of surface finishes for CNC machining?
Not all parts are utilized immediately after CNC machining. Most of them require post-processing, such as surface polishing. After generating the desired form, surface finishing must improve surface quality. Surface finishing is vital in CNC machining for aesthetic reasons and to improve the product’s overall functioning and longevity.
Tool markings are visible on the surface after CNC machining. Surface finishing approaches erase the markings and make the surface corrosion-resistant. ProleanHub offers over 20 surface finishing methods for CNC machined items. Let us now go through some crucial techniques.
| Type | Suitable materials | Effect on Tolerance | Advantages |
| As-machined | All types | No effects | It is cost-effective and suitable for prototype development.
|
| Anodizing | Aluminum, titanium | Type I & II: negligible
Type III: 0.001″ to 0.004 | Various color options, durable, and excellent corrosion, wear, & abrasion resistance. |
Black-oxide coating
| Steel & stainless steel | Negligible (0.00006” to 0.0001”) | Aesthetically appealing, Excellent corrosion resistance facilitates the lubrication process. |
Bead-Blasting
| All type | Slightly influence the tolerance | Matte or stain finish |
Powder coating
| Steel, stainless steel, and aluminum | Slightly (0.002 to 0.005”) | Cost-effective, excellent corrosion resistance |
As- Machined
As machined finish does not involve any post-processing. It refers to maintaining the surface in the machined state; the machined finish is the best way to keep the tight tolerance. The roughness of parts will be approx. 3.2 μm, while tool marks will still be visible. If the roughness is not fallen in the required range, additional polishing and smoothing can be done.
Since as machined finish does not require additional processing, it is cost-effective and suitable for prototype development projects.
Anodizing
Anodizing is the process of applying a thin coating of aluminum oxide to CNC machined parts using electrolysis, which makes the parts highly resistant to corrosion, wear, and scratching. It is best suited for aluminum components. Anodizing adds several metallic colors, the most prevalent being black, red, or gold.
- Type I: chromic acid is used, and the layer will be the thickest and gray.
- Type II: boric-sulfuric acid is used for anodizing and provides a range of colors, blue, red, gold, and more.
- Type III: sulfuric acid is used for anodizing, Thicker than Type I & II (0.001″ to 0.004″), the widest range of colors.
Black-oxide coating
The black oxide coating is suitable for steel and stainless steel. It is a chemical coating applied to the surface of CNC machined parts that provides outstanding corrosion & abrasion resistance and aesthetic appeal without distorting dimensions. The black-oxide layer also facilitates the lubricating process.
Bead-Blasting
Bead blasting removes the incremental material from the surface, leaving it smooth with a matte or satin finish and outstanding aesthetic quality. Bead blasting is the application of high-speed compressed air combined with an abrasive material such as steel grit or glass beads to a surface.
It may influence the dimensional consistency of CNC machined parts, although the effect is usually negligible with good jet handling.
Powder coating
Powder coating provides excellent corrosion resistance to the CNC machined parts made with steel, stainless steel, and aluminum. Next, the deburred parts are dipped into the polyester powder of the desired color. After dipping, the parts are cured in a heated oven (320-4500 C).
The powder coating does not affect the dimensional stability but might influence the tolerance of parts. In addition, the shiny surface with different dyes makes the parts aesthetically appealing.
Factors to be considered
Several factors must be considered when selecting a surface finishing process for CNC machined components. Some of the factors are as follows:
- Type of materials
- End-application of machined parts
- Required dimensional stability
- Cost
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