After the CNC machining process, there are still some processes that need be applied in order to give the surface a satisfied finish. Bellows are the most commonly used for metal surface finishing.
Type 2 Anodizing
Anodizing is an electrolytic process of passivation. After the process, the parts obtain better durability and resistance.
Applicable materials—Any aluminum
Colors—The anodizing layer does not provide any particular color, many colors can be added onto the surface through the process.
Texture—Does not cover machine marks unless media blasted or polished before hand
Thickness—0.00007”
Design notes
Parts without holes will be racked with clamps, or wire wrapping, which will leave the racking area without anodize color. Consult with the anodizing shop on how to rack the parts.
Also notice that anodizing has insulative properties.
Type 3 Anodizing, also known as hard anodizing
Applicable materials—Any aluminum
Colors—Clear, darker than type 2 anodize, black
Texture—Does not cover machine marks unless media blasted or polished before hand
Thickness—0.001” or thicker. Sometimes can be up to 0.004”
Impact on Tolerances
The thickness of Type 2 anodize remains almost the same after the process. But even the thinnest Type 3 can impact a tight tolerance after the process.
Alodine
Applicable materials—Any aluminum alloys and various castings
Colors—Clear, Gold
Applicable Industries—Tools, hardware, electrical system
Passivation
Applicable materials—Steel, Stainless Steel
Colors—N/A
Applicable Industries— Food Industry, Aircraft Industry, Pharmaceutical & Medical Instrument, Automotive, Machine& Precision Engineering
Electroless Nickel Plating
Applicable materials—Aluminum, Steel, Stainless Steel
Colors—N/A
Texture—Smooth, glossy finish
Thickness—from 0.0003” to 0.002”
Black Oxide
Applicable materials—Steel, Stainless Steel
Colors—Black
Texture—Smooth, matte black
Thickness—from 0.0003” to 0.002”
Electropolishing
Applicable materials—Steel, Stainless Steel
Colors—N/A
Texture—Smooth, glossy finish
This process is very useful for polishing irregular parts. The tolerance is not affected by the process since there’s very little amount of material is removed.
Zinc Plating (galvanization)
Applicable materials—Steel, Stainless Steel
Colors—Clear (light blue), black (glossy black)
Texture—Smooth, machine marks can not be hided
This process is very useful for polishing irregular parts. The tolerance is not affected by the process since there’s very little amount of material is removed.
Tumbling
Tumbling is also applied often after the material was machined.
Applicable materials—Aluminum, Steel, Stainless Steel
Colors—N/A
Texture—Smooth edges only, does not hide all machine marks
Bead Blasting
This a process is very commonly used after the CNC machining. It removes impurities from a surface. In order to do this, fine glass beads are applied through a very high pressure. After the process, fungi or other type of components are removed from the metallic or non-metallic surfaces.