Types and applications of post-processing of CNC machined parts

What is surface finishing of CNC machined parts? CNC machining post-processing and surface finishing usually refer to a series of processing steps performed on the workpiece after the CNC machine tool completes the machining of the workpiece to improve the quality and performance of the product. Because, usually after the metal or plastic parts are precisely machined by CNC, they may need to undergo a series of surface treatments to improve the appearance, enhance the strength, adjust the conductivity, etc. according to the requirements of the part design. The more common treatment methods include anodizing, powder coating and pearl blasting. But if no special surface treatment is required, retaining the original state after processing is also an option. In this article, we will talk about the relevant knowledge about the types and applications of surface treatment of CNC machined parts.

Importance of CNC machining surface

CNC machining is an important part of modern manufacturing technology and is widely used in industrial fields such as automotive parts, aerospace equipment, shipbuilding and machinery manufacturing. The quality of part surface treatment is an important factor in ensuring part quality.
Because a good surface treatment process can improve the durability and life of parts. If the surface of the part is not treated, the burrs, oil stains, unevenness and unevenness on the surface of the part during the processing may have a serious impact on the strength, toughness and fatigue life of the part, and the surface finishing technology can effectively repair these defects, thereby improving the overall quality of the part.
In addition, good surface finishing technology can improve the appearance of the part. The roughness and glossiness of the surface of the part directly affect the beauty of the part. Therefore, the surface treatment process can directly affect the appearance of the part.
The surface treatment process can also improve the function and service life of the part. The level of surface quality will affect the friction coefficient, wear performance and other factors of the part, and the surface treatment technology can effectively improve the overall performance of the part, thereby extending its service life. Therefore, most machined parts will be surface finished according to the design requirements after the processing is completed.

Classification of surface treatment methods for CNC machining parts

Surface treatment of CNC machining is an important part of improving product quality. Reasonable selection of surface treatment methods can improve product performance and appearance. Through the combined application of different methods such as mechanical processing, chemical treatment and heat treatment, more efficient and fine surface treatment effects can be achieved, providing more possibilities for the development of the CNC machining industry.

Surface treatment methods for mechanical processing

Mechanical processing is one of the commonly used surface treatment methods for CNC machining, which mainly includes grinding, polishing, sandblasting and grinding. Grinding is to reduce the surface roughness, while polishing is to improve the surface finish by using abrasives and polishing agents. Sandblasting can change the shape and roughness of the surface by spraying sand particles at high speed, while grinding is to remove the uneven parts of the surface by friction to improve the surface flatness.

Surface treatment methods for chemical treatment

Chemical treatment is a surface treatment method that uses acid, alkali or other chemical agents to change the chemical properties of the surface, which mainly includes pickling, electroplating, anodizing and chemical deposition. Pickling is to remove the surface oxide, electroplating is to deposit a layer of metal on the surface to improve corrosion resistance and aesthetics, anodizing is to thicken the surface oxide film through an oxidant, and chemical deposition can change the surface properties by depositing a layer of chemical substances.

Heat treatment surface treatment method

Heat treatment is a surface treatment method that heats the material to a certain temperature and then cools or keeps it warm to change its structure and properties. It mainly includes quenching, tempering and annealing. Quenching is to cool the material quickly to increase its hardness and strength, tempering is to heat the quenched material to a certain temperature and then cool it to improve its toughness and plasticity, and annealing is to heat the material to a certain temperature and then slowly cool it to eliminate internal stress and improve the toughness of the material.

Factors to consider when choosing the right surface treatment for machined parts

The choice of material and post-processing for a part depends on the environment and manner in which the part will be used. Key factors to consider when choosing 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 material and treatment. Temperature, exposure to flame, UV light, chemicals, or the need for autoclaving all need to be considered to ensure the usefulness of the part.
• Electrical properties: Whether the part needs to be conductive or insulated is a key consideration when choosing a material. If you need the part to be conductive, you might 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, you must choose a material that can withstand these forces. Identifying the optimal or necessary properties 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.

Detailed introduction to post-processing and finishing processes of CNC machined parts

Surface treatment of CNC machining is an essential part of the CNC machining process. Good surface treatment can not only improve the quality and life of parts, but also improve the requirements of parts in appearance and function. Through the methods and techniques introduced below, you can quickly master the key points and precautions of various surface treatment processes for CNC machined parts, and improve your skills in selecting CNC machining surface treatment for the designed parts.

• Standard surface treatment: Standard surface treatment aims to completely remove impurities such as oil, rust, dust, and cutting fluid residue on the surface of parts during the cleaning process, which not only helps to improve the adhesion and effect of subsequent treatment, but also ensures the hygiene standards and stable performance of parts during use. Deburring focuses on eliminating the sharp edges and tiny protrusions generated by parts during the machining process. These burrs not only affect the appearance quality of the parts, but may also cause wear, scratches, and even safety hazards during use. Through fine deburring processes such as mechanical grinding, electrochemical deburring or ultrasonic cleaning, the surface of the parts can be made smoother, the overall processing accuracy and service life can be improved, and a solid foundation can be laid for subsequent surface treatments such as painting and electroplating.
• Oxidation: It is an electrolytic oxidation process that converts the surface of the material into a protective film, making it less prone to oxidation and corrosion, which can extend the life and achieve the appearance of various colors. Common oxidation treatments are divided into: ordinary anodizing, wire drawing oxidation, hard oxidation, thick film oxidation, micro-arc oxidation, etc. The materials that can be oxidized are: aluminum alloy, magnesium alloy, titanium alloy, etc.
• Electroplating: The basic process of electroplating is to immerse the parts in a solution of metal salt as the cathode, the metal plate as the anode, and pass the current to deposit the required coating on the parts. The appropriate electroplating effect will make your product more high-end and fashionable and bring it a better market. Common electroplating includes: copper plating, nickel plating, silver plating, gold plating, chrome plating, zinc plating, tin plating, vacuum plating, etc.
• Electrophoresis: With the continuous improvement of industrial demand, electrophoresis technology can be customized in various colors to maintain the metallic luster while enhancing the surface corrosion resistance. It has little effect on the precision of the product. The thickness of one side is about 10-25um, and thicker ones can also be customized.
• Passivation: Passivation, also known as chromate treatment, is a pickling process. It can remove surface oil, rust, and oxides by immersion or ultrasonic cleaning. Through the chemical reaction of the passivation liquid, it can prevent corrosion and prolong rust. The color of the passivation film will change with different materials. Passivation will not increase the thickness of the product, so there is no need to worry that it will affect the precision of the product.
• Blackening: Blackening is also called bluing. Its principle is to immerse the product in a strong oxidizing chemical solution to produce an oxide film on the metal surface to isolate the air and achieve the purpose of rust prevention. This process is applicable to both steel materials.
• QPQ: QPQ is the abbreviation of Quench-Polish-Quench, which means that ferrous metal parts are placed in two salt baths of different properties, and multiple elements are infiltrated into the metal surface to form a composite infiltration layer, thereby achieving the purpose of modifying the surface of the parts. It has good wear resistance, fatigue resistance, corrosion resistance, and small deformation. This process is applicable to both steel and iron materials.(Note: Stainless steel products cannot be blackened, and can only be blackened by QPQ)
• Laser engraving: Laser engraving, also known as laser engraving or laser marking, is a surface treatment process based on optical principles to form a LOGO or pattern on the product. The laser engraving effect is permanent, with high surface quality, and is suitable for all kinds of hardware and plastic products.
• Silk screen printing: Silk screen printing refers to the transfer of ink patterns to products through screens. The color of the ink can be customized according to customer needs. Zhuanxin Precision has made 6 colors on the same product, including black, red, blue, yellow, white, and green. If you want the silk screen effect to be more durable, you can also add a layer of UV after silk screen printing to extend its life. Silk screen printing is suitable for all kinds of hardware and plastic materials, and can also be combined with oxidation, painting, powder coating, electroplating, electrophoresis and other surface treatments.
• Polishing: Polishing is to make the product beautiful, transparent and protect the surface. Polishing is a good choice for you. The polishing of hardware products is divided into manual polishing, mechanical polishing and electrolytic polishing. Electrolytic polishing can be used to replace heavy mechanical polishing, especially for parts with complex shapes and parts that are difficult to process by manual polishing and mechanical methods. Electrolytic polishing is often used for steel, aluminum, copper and other parts.
• Wire drawing: Wire drawing is a surface treatment method that forms lines on the surface of the workpiece through a flat-pressed sand belt and a non-woven roller brush to achieve a decorative effect. Surface wire drawing can reflect the texture of metal materials and is becoming more and more popular in modern life. It is widely used in the shells of mobile phones, computers, monitors, furniture, electrical appliances, etc.
• Powder spraying and painting: Spraying and powder spraying are two common surface treatments in the spraying of hardware parts. They are the most commonly used surface treatments for precision parts and small batch customization. They can protect the surface from corrosion and rust, and can also achieve a beautiful effect. Both powder spraying and painting can be customized with different textures (fine lines, coarse lines, leather lines, etc.), different colors, and different glossiness (matte, flat, high gloss).
• Sandblasting: Sandblasting is one of the commonly used surface treatments for hardware products. It can improve cleanliness and roughness, increase the adhesion and durability between the product and the coating. Therefore, many surface treatments choose sandblasting as their pre-treatment, such as: sandblasting + oxidation, sandblasting + electroplating, sandblasting + electrophoresis, sandblasting + powder spraying, sandblasting + baking paint, sandblasting + passivation, etc.
• Teflon spraying: also known as Teflon spraying, is a very personalized surface treatment. It has excellent anti-stickiness, non-stickiness, high temperature resistance, low friction, high hardness, non-wetting, high chemical resistance and other characteristics. Therefore, it is widely used in food industry, tableware, kitchenware, papermaking industry, medical equipment, electronic products and automotive products, chemical equipment, etc. At the same time, it can protect the material from chemical corrosion and extend the service life of the product.
• Powder coating: Powder coating is an advanced surface treatment method that uses electrostatic principles to attract evenly distributed dry powdered paint (i.e. powder coating) to the surface of the part to be coated. The coating is then melted and tightly adhered to the substrate through a heat curing process, forming a continuous, protective and colored surface layer.
• Deburring: Deburring is the process of removing sharp edges, burrs and other imperfections from parts after machining. Deburring can improve the safety and functionality of the parts and make them easier to handle.
• Tumbling: Tumbling is a process in which the part is placed in a rotating barrel with abrasives to produce a smooth polished surface finish. Tumbling can improve the look and feel of the part and remove any remaining burrs or imperfections.
• Heat treatment: It can improve the mechanical properties of the part, such as hardness, strength and toughness. Heat treatment involves heating the material to a specific temperature, holding it at that temperature for a period of time, and then cooling it to room temperature at a controlled rate.
• Annealing: This involves heating the material to a high temperature and then slowly cooling it. This process helps reduce internal stress, improve ductility and soften the material.
• Tempering: This involves heating the material to a moderate temperature and then cooling it slowly. The process helps reduce the brittleness of the material due to hardening and improves its toughness and ductility.
• Hardening: This involves heating the material to a high temperature and then cooling it rapidly, usually by quenching in water or oil. The process produces a hard, brittle material that is wear-resistant and resistant to deformation.
• High-frequency heating: This involves heating the surface of the material to a high temperature while keeping the core cool. The process forms a hard, wear-resistant surface layer while the core remains relatively soft and ductile.
• Stress relief: It is usually used to eliminate residual stresses accumulated from previous manufacturing processes. There are many ways to eliminate tensile residual stresses on the surface. For example, mechanical treatment includes mechanical vibration, shot peening, etc., diffusion treatment includes carburizing, nitriding, and heat treatment includes annealing, tempering, and other heat treatment processes. The desired reduction in residual stress is usually achieved by heating to a low temperature and holding at that temperature for a desired time.
• Heli-Coil Inserts: Mainly used to provide stronger threads in materials that are prone to stripping or cross-threading. Inserts are designed to be installed into existing holes, creating new threads that are stronger than the original. Improving the strength and durability of threaded connections. It can also be used to repair damaged threads in soft alloy components. Its benefits make it a popular choice, extending service life by providing a more durable, less prone to wear and tear.
• Assembly: Assembly is the process of putting multiple CNC machined parts together to create a complete product. Assembly may involve the use of adhesives, fasteners, or other methods to securely connect parts together.

Case description of surface treatment of common CNC machined parts

Different CNC machined parts have specific surface treatment requirements due to their different functions and application environments to ensure optimal performance, service life and cost-effectiveness. The following are some case descriptions of surface finishing treatment of common CNC machined parts.

Gears

Gears require appropriate surface treatment processes to improve performance, reduce wear and reduce noise. Precision grinding or honing is usually used to provide smooth and accurate profiles to ensure consistent meshing; for gears that need to be used in corrosive environments, electrolytic polishing is used to remove surface defects and improve wear resistance; in addition, nickel plating can improve hardness and corrosion resistance.

Bushings

Generally speaking, the environment in which bushing parts are used determines that it has a high degree of wear, and surface treatment must be performed to minimize friction and ensure that bushing parts have a long service life. Electrolytic polishing can provide a smooth surface, which helps reduce friction and prevent contaminants from adhering to the surface; or anodizing surface treatment can provide additional hardness and wear resistance for aluminum bushings; bushings usually have strict tolerances and require surface treatment with minimal thickness variation, such as anodizing or electroplating.

Shafts

Shaft parts generally require a balance between wear resistance and friction reduction. Fine grinding and electropolishing can minimize friction and extend service life; where corrosion resistance is critical, anodizing or passivation may help; shaft parts with tight tolerances require surface treatments with minimal thickness variation, such as anodizing or plating; surface treatments that are prone to wear, such as powder coating, should not be used.

Fasteners and Screws

Most engineers who design fasteners and screws choose to electroplate with zinc, nickel or other metals to protect the fastener or screw parts from corrosion while improving their appearance; for fasteners or screws exposed to corrosive environments, electropolishing or passivation ensures the best durability; and anti-corrosion coatings can be used to provide the most comprehensive corrosion protection for fasteners.

Valves

Valve parts generally require tight tolerances and smooth surfaces to prevent leakage and ensure efficient operation. Precision grinding or honing can minimize surfaces that cause friction and contamination; tight tolerances require surface treatments with minimal thickness variation, such as plating or anodizing; surface treatments that are prone to wear, such as powder coating, should not be used.

Housing

Regardless of the type of product, housing parts are commonly sandblasted and powder sprayed to provide a consistent, aesthetically pleasing, corrosion-resistant finish; in addition, anodized surface treatment can provide a high-quality, durable coating for aluminum housings.

Summary

Post-processing or surface finishing services help improve the function, appearance and quality of CNC machined parts. The specific post-processing services required will depend on the material of the part, its intended use, and the desired properties and appearance. Each method has its own characteristics and applicable occasions. When choosing a surface treatment method, it is necessary to make comprehensive considerations based on the specific requirements of the product and the use environment to achieve the best surface treatment effect. Working with an experienced CNC machining service provider can help ensure that your parts receive the necessary post-processing services to meet your specific requirements. If you have a need for customized parts, no matter what kind of process, material, or precision requirements, Elimold can serve you.