Nowadays, with the technological innovation of CNC machining technology, more and more surface finishing technologies are also being developed and applied to various industries. This also poses a challenge for mechanical design engineers to understand and choose the right surface finishing process. Surface finishing is that after metal or plastic parts are precisely processed by CNC, they also need to go through a series of surface treatment processes to improve appearance, enhance strength, adjust conductivity, etc. Of course, if no special surface treatment is required, retaining the original state after processing is also an option.
In the manufacturing industry, the surface treatment process of parts plays a vital role in the quality, performance and durability of the product. Different surface treatment processes can provide different characteristics for parts, so when choosing, it is necessary to consider the specific use of the parts, environmental conditions and required performance. This article will explain the basic knowledge involved in surface treatment processes and guide you on how to choose the appropriate treatment method according to different usage requirements.
What is surface treatment?
Surface treatment (surface or metal) is carried out during the manufacturing process and is a mechanical process. It mainly uses the technology of modern physics, chemistry, metallurgy and heat treatment to change the condition and properties of the surface of the parts, so that it can be optimized with the internal materials to achieve the predetermined performance requirements. The process method is called surface treatment.
Surface treatment is a process method that artificially forms a surface layer on the surface of the base material that has different mechanical, physical and chemical properties from the base.
Surface treatment is to clean, sweep, deburr, degrease, and descale the surface of the workpiece. Surface treatment is not just for beauty. It can also improve wear resistance, lubricity, strength, impact resistance, electrical conductivity, thermal conductivity, corrosion resistance, chemical resistance, heat resistance and adhesion, as well as improve decorative performance. If the surface of the machined parts is properly treated, the metal surface can be well protected, which can make the service life of the parts longer.
Importance of Metal Surface Finishing
Surface finishing is an important aspect of CNC machined parts and can affect the functionality and aesthetics of the final product. It can change the appearance of a part, making it look more attractive and professional, improving the surface finish and enhancing the overall aesthetics of the part. It can also provide a protective layer to protect the part from corrosion or damage from environmental factors such as moisture or salt water, thereby extending its service life.
- Anti-corrosion
- Anti-rust treatment
- Improve hardness and strength
- Improve wear resistance
- Improve heat resistance
- Improve metal appearance
Classification of metal surface treatment processes
- Improvement treatment: change the surface state of the substrate through physical and chemical methods; the chemical composition of the substrate remains unchanged
- Through physical methods, the added material enters the matrix to form an alloying layer.
- Through chemical methods, the added material and the substrate react chemically to form a conversion film.
- Add a layer of film on the surface of the substrate, and the substrate does not participate in the formation of the film.
How to choose a surface treatment to avoid future problems?
Surface treatment is the process of modifying the surface of a material to enhance its properties. Surface treatments for parts will vary depending on the specific requirements of the part and the application. The choice of surface treatment technology will depend on factors such as the material of the part, the expected service life, the expected surface finish, and the specific requirements of the application, such as corrosion resistance, wear resistance, lubricity, adhesion, or aesthetics. There are several different surface treatment technologies that can be used for CNC machined parts.
Guide to Selecting Surface Treatments for Machined Parts
The selection of materials and post-processing methods for a part depends on the environment and manner in which the part will be used. Key factors to consider when selecting part materials and surface treatments include:
- Environmental factors: The specific conditions of the environment in which the part will be used are critical to selecting the most appropriate materials and treatments. Temperature, exposure to flames, ultraviolet light, chemicals, or the need for high-pressure steam sterilization are all factors that need to be considered to ensure the practicality of the part.
- Electrical properties: Whether the part needs to be conductive or insulated is a key consideration when selecting materials. If you need the part to be conductive, you may use a conductive material such as copper; conversely, if you are looking for a material with good insulating properties, nylon 66 may be a good choice.
- Mechanical properties: If the part needs to be subjected to heavy loads, friction, or other external forces, it is necessary to select a material that can withstand these forces. Identifying the optimal or necessary characteristics required for the part, such as flexibility, impact resistance, tensile or compressive strength, will help determine the most suitable material selection.
- Appearance: Although appearance may be a secondary factor for some parts, it is very important for many consumer products. Some parts or applications may require materials with specific requirements for color, transparency, or surface effects.
- Dimensional tolerance: Differences in dimensions between parts are expected in manufacturing, and dimensional tolerance refers to the acceptable range of part variation. More precise dimensional tolerance requirements can be repeatedly achieved, but it is more labor-intensive and costly, and this accuracy is sometimes necessary based on the application characteristics of the part.
Types of Surface Treatment Processes for Machined Parts
- Shot Peening: The shot peening process uses high-pressure air or other abrasive media to blast a surface to clean, polish or roughen it to the desired finish. It is an efficient and versatile surface treatment method for machined parts. It is often used to create a uniform surface with a dull, smooth or rough texture. It can also be used to remove any remaining burrs or blemishes and rust, mainly to improve the appearance of the part.
- Anodizing: Anodizing is an electrochemical process that forms a protective oxide layer on the surface of a part. Anodizing can improve the corrosion resistance, durability and appearance of a part. There are several types of anodizing, including clear anodizing, black anodizing and color anodizing.
Anodizing Type I, also known as chromic acid anodizing, is a surface treatment process used to form a thin layer of oxide on the surface of aluminum and aluminum alloys. The thickness of the oxide layer depends on the duration of the anodizing process.
Anodizing Type II (clear or color) adds a corrosion-resistant ceramic layer to the surface of the part. Applicable only to aluminum and titanium, anodized parts can be dyed in a variety of colors.
Anodizing Type III (hard coating) adds a wear- and corrosion-resistant ceramic layer to the surface of the part. It provides better protection than Type II and can be dyed in different colors. Applicable only to aluminum and titanium.
- Powder coating: Powder coating is a process where a dry powder is applied to the surface of the part and then baked to create a durable and decorative surface. Powder coating adds a wear- and corrosion-resistant surface to the surface of the part. It is more impact-resistant than anodizing, comes in a variety of colors, and can be applied to any metal. The coating resists peeling, fading, scratching, and abrasion. This durability makes it ideal for metal parts exposed to sunlight and other environmental factors.
- Painting: Painting is a common finishing treatment for CNC machined parts. It includes metal spray painting, plastic spray painting, rubber oil painting, UV oil painting, and imitation leather oil painting. Parts are cleaned, primed, and painted with high-quality paint to create a protective and decorative finish. Spray painting can provide a variety of colors and finishes, including metallic, glossy, and matte finishes.
- Polishing: Polishing is a mechanical process that involves removing the surface layer of a part to create a smooth, shiny surface. Polishing can improve the look and feel of a part and can also remove any flaws or imperfections from the machining process. Polishing generally includes chemical polishing and hand polishing. Chemical polishing is a quick way to brighten the surface of a metal part to make it look shiny, rather than a way to create a perfect surface. Hand polishing works well on any material, including plastics. It can achieve a mirror polish grade. However, due to the complex shape of the part, hand polishing cannot polish narrow areas such as grooves and small holes well, which is the biggest disadvantage of hand polishing.
- Electroplating: Electroplating is the process of applying a thin layer to the surface of a part. Electroplating can improve the corrosion resistance, wear resistance and appearance of a part. There are many types of electroplating, including nickel plating, chrome plating and gold plating.
Conclusion
Surface treatment is a key step in the manufacturing process and can significantly affect the function and appearance of the final product. It can improve the performance, durability and appearance of the final product. Metal surface treatment technology can protect and strengthen the surface of the workpiece without increasing or increasing too much cost, thereby improving the service life and reliability of the product, improving the performance and quality of mechanical equipment, and enhancing the competitiveness of the product. Therefore, metal surface treatment technology is of great significance for promoting the development of high-tech, saving materials, saving energy, etc.