CNC (Computer Numerical Control) machining has become an indispensable technology in modern manufacturing. Whether it’s aerospace, automotive or medical devices, surface preparation plays an important role in ensuring the quality and performance of parts.

What is CNC machining surface treatment?

CNC machining surface treatments are processes that improve and optimize the surface of a part after computer numerical control CNC machining has been completed, using a variety of techniques. These treatments can enhance the surface smoothness, durability and functionality of a part.

Common CNC Surface Finishing Techniques

Polishing:

Improves the smoothness and gloss of a part by removing minor surface imperfections and irregularities. This process usually involves the use of abrasives or chemicals to make the surface smoother and shinier.

Common types of polishing

• Mechanical Polishing: Physical grinding using a polishing machine and abrasives, commonly used on metal and plastic surfaces.
• Chemical Polishing: Removes surface irregularities using a chemical solution and is used for complex shaped parts.
• Electrolytic Polishing: Removes surface layers through an electrochemical reaction, often used for metals such as stainless steel.

Polishing reduces the surface roughness of the part, improving the feel and appearance. The smoothness of the polished surface helps prevent dirt and corrosion from adhering. The most important factor is to improve the appearance of the part, as a glossy surface enhances the overall aesthetics of the product, making it more competitive in the marketplace.

Abrasive blasting:

Processing that improves surface smoothness and adhesion by blasting particles (usually grit, metal particles, or other abrasives) at high speeds onto the surface of a part to remove dirt, surface oxides, or other surface irregularities from the processed part.

Types of sandblasting

• Dry blasting: A dry abrasive is used to remove surface impurities using a sandblasting machine.
• Wet blasting: Water or other liquid is mixed with the abrasive, which reduces dust generation and reduces the aggressiveness of the abrasive compared to dry blasting.
• Carbonate blasting: Usually uses carbonate particles and is suitable for finer product surfaces, with the advantage that it does not damage the surface of the product.

The advantage of sandblasting lies in the treatment of complex parts, which can ensure that all corners of the parts can be fully processed, and the surface of the sandblasted parts becomes rough, so that the subsequent enhancement of the coating, bonding and other subsequent processes to improve the adhesion of the surface.

Anodizing:

Anodizing is an electrochemical process that uses an electric current to form an oxide film on the surface of a metal part (usually aluminum and its alloys) as an anode in an electrolyte. The film has excellent corrosion resistance and wear resistance, and can also improve the appearance.

Advantages of anodizing

1. The oxide film can effectively prevent the metal surface from contacting with air or other corrosive environments, causing oxidation and corrosion of the product.
2. In general, the hardness of the oxide film is usually higher than that of the metal body, which improves the wear resistance of the product and improves the surface hardness.
3. Through dyeing treatment, the oxide film can be given a variety of colors to improve the aesthetics.
4. The chemicals used in the anodizing process are relatively environmentally friendly and do not produce harmful waste.

Electroplating:

Electroplating is an electrochemical surface treatment technology. By immersing metal parts in an electrolyte containing a metal salt solution, the metal ions are deposited on the surface of the parts through an electric current to form a metal coating. Electroplating can be used to improve the corrosion resistance, wear resistance and appearance of parts.

Advantages of electroplating

1. Like anodizing, it can effectively prevent oxidation and corrosion, thereby extending the service life of parts.
2. Electroplating can also make the product surface smooth and shiny, improving the aesthetics of the product.
3. Secondly, electroplating can give parts special functionality: such as conductivity, insulation or antibacterial properties.

Chemical nickel plating – What is chemical nickel plating?

It is a non-powered electroplating technology that deposits a layer of nickel coating on the metal surface through a chemical reaction. This method does not require current and is suitable for parts with complex shapes and internal structures.

Advantages of chemical nickel plating: It has the same functional advantages as electroplating and is suitable for application scenarios that cannot be achieved by electroplating, with higher flexibility.

Powder coating

Powder coating is a dry coating form, which is a mixture of resin, curing agent, pigment and additives. The flowing coating is applied or sprayed on the surface of parts or substrates by electrostatic adsorption, and a tough and uniform coating is formed on the surface by heating or UV curing. It is widely used for the protection and decoration of metal surfaces.

Heat Treatments and Surface Finishes

Heat treatment is a process that changes the physical and chemical properties of metal materials by heating and cooling them. This process can improve the hardness, strength, toughness and wear resistance of metals and is widely used in the treatment of parts after CNC machining.

Importance of surface treatment

• Improve durability: Through effective surface treatment, the service life of parts can be greatly extended.
• Improve appearance: High-quality surface treatment can enhance the aesthetics of products and thus improve the market competitiveness of products.
• Enhance functionality: Certain surface treatment technologies such as electroplating and blackening can improve the functionality of parts, such as wear resistance and corrosion resistance.

Surface Treatment FAQ:

1. How to Measure Surface Roughness

Surface roughness can be measured using several methods:

• Contact Profilers: These devices, such as a stylus profilometer, measure surface roughness by dragging a fine stylus across the surface. The vertical movement of the stylus generates a trace that is converted into a roughness profile.
• Optical Profilers: These non-contact systems use light to measure surface features. Techniques include white light interferometry and laser scanning, providing high-resolution images of the surface.
• Surface Roughness Testers: Portable devices can provide quick measurements of roughness parameters (e.g., Ra, Rz) in various applications.

2. What is an Ra Unit?

Ra (Roughness Average) is a commonly used parameter in surface finish measurement, representing the average roughness of the surface. It is calculated as the arithmetic average of the absolute values of the surface height deviations from the mean line over a specified sampling length. The unit for Ra is typically measured in micrometers (µm) or microinches (µin):

• 1 Ra = 1 µm = 39.37 µin

3. How Does Surface Finish Affect Fatigue Life?

Surface finish significantly impacts fatigue life in materials due to the following reasons:

• Stress Concentration: Rough surfaces tend to have higher stress concentration points, which can act as initiation sites for fatigue cracks.
• Surface Defects: Surface irregularities can create micro-cracks and flaws that reduce the material’s ability to withstand cyclic loading.
• Surface Hardness: A smoother surface often has higher hardness, which can enhance fatigue resistance.
• Lubrication: Better surface finishes improve lubrication, reducing wear and tear under cyclic loads.

4. How is Surface Finish Indicated on Engineering Drawings?

Surface finish is typically indicated on engineering drawings using:

• Symbolic Notation: A surface finish symbol (usually a triangle) with a roughness value (e.g., Ra) and often a finish type (e.g., “machined”, “ground”).
• Notes: General notes specifying the surface finish requirements can also be included on the drawing.

For example, a notation like Ra 0.8 µm would specify that the surface finish should have an average roughness of 0.8 micrometers.

5. How to Achieve 0.8 Ra Surface Finish

To achieve a surface finish of 0.8 Ra, consider the following machining practices:

• Tool Selection: Use high-quality cutting tools with appropriate coatings to reduce friction.
• Cutting Parameters: Optimize cutting speed, feed rate, and depth of cut. A slower feed rate generally yields a finer finish.
• Cooling/Lubrication: Use cutting fluids to minimize tool wear and enhance surface finish.
• Finishing Operations: Use finishing processes like grinding or polishing after machining to achieve the desired roughness.

6. How to Achieve a 32 Surface Finish

To achieve a 32 µin (0.8 Ra) surface finish, which is a common standard in machining, you can:

• Select the Right Cutting Tools: Use tools designed for fine finishes.
• Adjust Cutting Speeds: Increase the spindle speed to reduce the chip load and improve surface finish.
• Optimize Feed Rate: Keep the feed rate low to minimize tool marks.
• Use Appropriate Machining Techniques: Techniques such as fine boring, honing, or using a lathe with finer tooling can help achieve this finish.

7. How to Calculate Surface Finish

Surface finish can be calculated using several parameters. The most common are:

• Ra (Roughness Average):Ra=1N∑i=1N∣yi∣Ra = \frac{1}{N} \sum_{i=1}^{N} |y_i|Ra=N1​i=1∑N​∣yi​∣Where yiy_iyi​ are the deviations of the surface profile from the mean line, and $N$ is the number of measurements.
• Rz (Average Maximum Height): Measures the average height of the five highest peaks and the five lowest valleys within a sampling length.

8. How to Get Good Surface Finish on a Lathe

To achieve a good surface finish on a lathe, consider the following tips:

• Proper Tool Setup: Ensure the cutting tool is sharp and properly aligned.
• Optimal Cutting Parameters: Adjust the feed rate, cutting speed, and depth of cut to minimize tool marks.
• Use of Tool Inserts: Utilize high-quality inserts with coatings that reduce friction and wear.
• Maintain Machine Condition: Regular maintenance of the lathe (including bearings, belts, and alignment) ensures smooth operation.
• Finishing Passes: Make a final finishing pass with minimal depth of cut and appropriate speed to refine the surface finish.

Future Trends in CNC Surface Treatment

The future CNC surface treatment technology will develop in the direction of intelligence, environmental protection and personalization. Intelligent manufacturing and automation will optimize the processing process, improve efficiency and reduce human errors. At the same time, environmental regulations promote the application of low environmental impact treatment processes and sustainable materials. The rise of functional coatings and nanotechnology will make surface treatment not only limited to anti-corrosion and aesthetics, but also respond to environmental changes and achieve multifunctionality. In addition, the combination of data-driven and virtual simulation technology will optimize the production process and meet the needs of personalization and small batch production.

 

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