Post-Processing for CNC Machining
Evaluate standard surface finishes for CNC machined parts as well as advanced capabilities to improve durability, surface finish, and add color.
Post-Processing for CNC Machining
Evaluate standard surface finishes for CNC machined parts as well as advanced capabilities to improve durability, surface finish, and add color.
Standard Finishes
Choose from three standard surface finish options for CNC machined parts.
Edges broken (tool marks visible)
Edges deburred with visible toolmarks.
Materials: Plastic, Metals
Edges broken and light bead blast
Edges deburred with light bead blast.
Materials: Metals
Leave sharp (tool marks visible)
Edges left sharp (tool marks visible) should be handled with care.
Materials: Metals
Quick-Turn Coating Options
Anodizing and chromate coating options are available for quick-turn parts that ship within four days.
Anodizing Type II
MIL-A-8625
Colors: Black, Clear
Anodizing Type III (Hardcoat)
MIL-A-8625
Colors: Black
Chromate Type II (Non-Hexavalent)
MIL-DTL-5541
Colors: Clear
Advanced Post-Processing Options for CNC Machining Parts
Through myRapid and Protolabs Network, access a broad range of post-processing capabilities to meet your part’s exact specifications.
| Description | Materials | ||||
|---|---|---|---|---|---|
| Bead Blast | Light bead blast to provide uniform finish and light texture | Metals | |||
| Anodizing | Type I, II, and III finishes are available to improve part durability and add color | Aluminum Titanium | |||
| Chromate Coating | Improve corrosion resistance, add electrical connectivity, and the ability to better paint parts | Metals | |||
| Electroless Nickel Plating | A wear-, abrasion-, and corrosion resistant finish that is compatible with aluminum, stainless steel, and mild steel | Aluminum Steel | |||
| Part Marking | Laser engraving or pad printing to add labeling and other text to parts | Metals Plastics | |||
| Passivation | Enhance durability and corrosion resistance of metal parts | Metals | |||
| Powder Coating | Add custom color to parts while improving durability | Metals | |||
| Press Fit Hardware | Incorporate off-the-shelf hardware components to facility assembly | Metals | |||
| Silk Screening | Add design elements or labels to parts | Metals | |||
| Brushing | Achieve uniform, satin-like surface finish | Stainless Steel | |||
| Polishing | Create mirror-like finishes on metal parts | Metals | |||
| Black Oxide | Improve corrosion resistance | Metals | |||
| Brushed + Electropolishing | This combination of processing results in easy-to-clean parts that are corrosion resistant | Metals |
Common Surface Finishes
Surface treatment mainly creates a visual experience of the appearance of some products. It can make a very good surface, whether it is oxidation, dusting, or electroplating. Of course, some functional aspects, such as the plating of steel materials, can prevent rust. If it is UV-resistant and powder-sprayed, it can be used outdoors to prevent color shedding. We use different techniques to improve the appearance, corrosion resistance, hardness, conductivity, adhesion, etc.
Our company can produce high-quality surface treatments. If you have any requests in this regard, please contact our team, and we will give you a punctual and complete answer.
Anodizing
Anodizing mainly oxidizes aluminum products to give them more colors and achieve decorative purposes. It can also be hardened to make the product surface stronger and more corrosion-resistant. Anodized aluminum is UV-resistant, wear-resistant, and has strong heat dissipation. It is commonly used in outdoor products such as bicycles, motorcycles, outdoor headlights, etc.
We usually use MIL-A-8625-C-TYPE II CLASS 2 oxidation. This oxidation type is mainly used to improve the appearance and corrosion resistance of the product surface. The thickness of the coating is usually 8-12um, natural color 12-18um, black 12-18um, or color 4-8um.
MIL-A-8625-F-TYPE III anodizing also called hard anodizing, has a coating thickness of 30 to 100um. It can greatly improve the product’s chemical and physical properties.
Alodine (Aluminum Chromate Passivation MIL-DTL-5541)
Alodine is also known as a chemical film, which is a chromate conversion coating. In China, some people call it chemical oxidation, which differs from anodizing. Chromate conversion coating is a chemical conversion coating. A chemical reaction converts the existing metal surface into a protective layer, which can protect aluminum and other metals from corrosion.
The main advantage of alodine coating is that it prevents aluminum corrosion and enhances the conductivity of the aluminum surface. The base left by the chemical film or Alodine coating provides better adhesion for organic coatings and prevents the loss of conductivity.
Chromate conversion coating is mainly used for chassis interiors, radiators, car wheels, and daily hardware products.
Metal Plating
Electroplating is the process of plating a very thin layer of other metals on the metal surface through the principle of electrolysis. It can prevent corrosion (rust) and oxidation of metal parts and can also change their appearance color and increase their aesthetics. Common plating metals are zinc (black zinc, yellow zinc, white zinc, Olive Zinc), nickel, chromium (electroplating hard chromium thickness can reach 50-200um), silver, and tin.
If the product is used in a harsh environment or often outdoors, it can be electroplated and then powder coated. This can double the product’s protection and increase its service life.
Zinc flake coating – This zinc spraying method can achieve a salt spray test of 1000 hours.
Powder Coating / Painting
Powder coating is a process that uses corona discharge to make powder coating adhere to metal parts. After hot melting, curing, and other steps, a coating film is formed on the surface of the workpiece. This can also strengthen the product surface and increase wear and rust resistance. The powder coating color is usually selected according to the RAL code.
Before powder coating, polishing, degreasing, rust removal, cleaning, and other steps are generally performed. This provides adhesion to the coating and ensures its uniform and consistent thickness.
Degreasing: Remove oil stains from the surface of parts.
Rust removal: Use phosphate cleaning to remove rust from the surface of parts.
Painting usually refers to spraying, which is different from Powder Coating in that it is a liquid.
Heat Treatment
Heat treatment refers to a process in which metal materials are in a solid state and are changed by extremely high temperatures, heating, heat preservation, and cooling. It mainly changes the material’s physical properties and increases its hardness.
Heat treatment technology includes normalizing, quenching, nitriding (QPQ), tempering, precipitation hardening (17-4 PH H1025), and annealing.
In common mechanical manufacturing, bearings and gears; and in automobile manufacturing, engine parts, etc., heat treatment technology is required. Through this surface treatment process, the hardness and corrosion resistance of parts are changed, and the service life of the product is improved.
Sanding and Polishing
Polishing, in short, improves the glossiness of the product surface, even to a mirror effect. This process can produce a smooth and shiny surface by rubbing the part’s surface or using chemical reactions.
For CNC-finished products, the surface finish is usually RA1.6, which means there are a few milling lines. If the milling marks need to be removed, we need to process it through additional polishing: Ra0.8 (no milling lines), R0.1-R0.4 (mirror effect)
Sanding is also very important for 3D printing and vacuum casting. This is an essential process for making silicone molds. Sanding and Polishing
Polishing, in short, improves the glossiness of the product surface, even to a mirror effect. This process can produce a smooth and shiny surface by rubbing the part’s surface or using chemical reactions.
For CNC-finished products, the surface finish is usually RA1.6, which means there are a few milling lines. If the milling marks need to be removed, we need to process it through additional polishing: Ra0.8 (no milling lines), R0.1-R0.4 (mirror effect)
Sanding is also very important for 3D printing and vacuum casting. This is an essential process for making silicone molds.
Passivation
Passivation is a process of treating the metal surface with an acid solution. It converts the metal surface into a state that is not easily oxidized, thereby slowing down the corrosion rate of the metal.
Stainless steel (304, 316, 17-4PH) is the most common material that needs passivation. Usually, we use nitric acid or citric acid to remove the free iron on the surface, making the stainless steel more corrosion-resistant and rust-proof.
As mentioned above, anodizing is also a common passivation method, mainly used for aluminum alloy materials.
Sand Blasting
Using high pressure, we push abrasive particles of sand at high speed to the surface of the part to remove machining marks and surface contaminants on the product’s surface. Clean metal, add texture and reduce surface finish (matte effect).
Sand usually comes in two types: glass beads and emery. Glass beads are usually used in aluminum, and emery is used in steel.
The sand size is usually #80-#220. Sand diameter as below:
#80 Sand diameter (250-300um), #100 Sand diameter (180-250um), #120 Sand diameter (150-180um), #150 Sand diameter (125-150um), #180 Sand diameter, (100-125um), #220 Sand diameter (70-100um)
Black Oxide
Black Oxide is a traditional surface treatment process. The liquid chemical reacts with the material of the workpiece to form a coating, which forms a black conversion coating on the product’s surface. The black oxide coating can improve the product’s corrosion resistance and reduce light reflection. It is mainly used for stainless steel and steel alloy materials.
Commonly used alternative processing methods include electroplating black zinc, black electrophoresis, etc.
Silk Screen Printing
Silk screen printing is a common printing process. It is a printing method that uses a screen plate and printing putty to print ink onto the surface of a product.
The silk screen printing process is used to print almost all kinds of materials, including plastic, glass, metal, paper, patch materials, etc. In the CNC processing industry, silk screen printing is usually used to print the customer’s company logo or some fonts. The difference between silk screen printing and laser etching (laser etching can only be black and white; the advantage is more stable and permanent) is that it can choose different ink colors according to the RAL code to make the font or logo more vivid.
Satin Finish
Satin Finish is a surface treatment method that forms lines (satin effect) on the product’s surface by grinding it to achieve a decorative effect.
During the metal processing process, we can remove scratches on the product through brushing to make it more beautiful. Brushing is particularly widely used in the audio industry. You can usually see this brushing process on the front and back panels of the audio.
PVD Coating
PVD (Physical Vapor Deposition) coating technology is a green and clean surface treatment technology. It refers to using physical methods under vacuum conditions to vaporize the surface of the material source (solid or liquid) into gaseous atoms or molecules. Through low-pressure gas, a layer of coating from hundreds of nanometers to tens of microns is formed on the surface of the target workpiece. We can provide specific surface strengthening requirements.
PVD can deposit metal and alloy films and precipitate compounds, ceramics, semiconductors, and polymer films, among other materials.
Machined Finishing
The machined surface is often accompanied by milling lines (surface finish is R0.8-1.6um). The product’s surface is smooth when touched by hand, which is formed by the tool processing path. Most customers like this original effect because it proves the product is CNC processed, not forged, cast, or printed.
If there is no additional surface treatment, we can quickly deliver samples within 1-3 days, which can also buy more time for confirming samples.
