Surface treatment of CNC machined parts: an in-depth analysis of when and why

CNC (computer numerical control) machining technology occupies an important position in the manufacturing industry with its high precision and high efficiency. However, even CNC-machined parts may still have certain defects on their surfaces, such as roughness, residual stress, etc., which may affect the performance and service life of the parts. Therefore, it is particularly important to perform surface treatment on CNC-machined parts. This article will discuss when and why to perform surface treatment on CNC-machined parts in chapters.

Surface condition of CNC machined parts

After CNC machining is completed, the surface condition of the parts may vary depending on the processing method, material and other factors. Some parts may have large roughness and residual stress on the surface, which not only affects the appearance of the parts, but also may reduce their accuracy and fit. In addition, for certain specific application scenarios, such as highly corrosive environments, the surface corrosion resistance of parts is also a key factor.

When to perform surface treatment

Determine the timing of surface treatment based on part functional requirements

Parts subject to high stress and friction

• For CNC machined parts working in high stress and high friction environments, such as pistons of automobile engines and screws of machine tools, surface hardening treatment should be given priority after rough machining. For example, quenching, carburizing and other processes can effectively improve the surface hardness of parts and enhance wear resistance and fatigue resistance. This is because in the subsequent finishing process, the hardened surface can better maintain shape accuracy and avoid premature wear caused by machining stress and friction during use.

Parts with high corrosion resistance requirements

• When parts are used in corrosive environments such as moisture, acid and alkali, such as pipe connectors of chemical equipment and parts of marine equipment, anti-corrosion surface treatment is required immediately after CNC machining to near finished product size. Processes such as galvanizing, chrome plating or spraying anti-corrosion coatings can form a dense protective film on the surface of parts to prevent the intrusion of corrosive media. If the treatment is too late, the parts may have been slightly corroded during the processing process, affecting their ultimate corrosion resistance and service life.

Parts that require conductivity or insulation

• In the electronics industry, some CNC-processed metal parts may require good conductivity, such as metal inserts for printed circuit boards; while others require insulation properties. For such parts, after the shape processing is completed, the corresponding surface treatment should be carried out in a timely manner. For example, for parts that need to be conductive, the contact resistance can be reduced and the conductivity can be improved through processes such as silver plating and copper plating; for parts that need to be insulated, methods such as coating with insulating paint can be used. This can ensure that in the subsequent electronic assembly process, the parts can accurately perform their electrical functions and avoid electrical failures caused by improper surface treatment.

Choose the timing of surface treatment according to the appearance quality requirements

Consumer electronic product parts that pursue the ultimate appearance

• In the field of consumer electronics, parts such as mobile phone shells and tablet computer frames have extremely high requirements for appearance. After CNC precision machining is completed, surface treatment such as anodizing and polishing is required immediately. Anodizing can give parts rich colors while improving surface hardness and wear resistance; polishing can make the surface of parts smooth as a mirror, improving the texture and aesthetics of the product. Timely treatment can prevent the surface of parts from being scratched or contaminated during subsequent circulation, ensuring that the final product has a perfect appearance.

Parts with decorative needs

• For some parts with decorative functions, such as metal handles of high-end furniture and metal shells of lamps, surface treatment should be carried out as soon as possible after CNC machining has shaped the basic shape. Electroplating, wire drawing and other processes can be used to achieve mirror effects such as chrome plating and unique wire drawing textures to meet the decorative needs of the product. Early surface treatment can better match the subsequent assembly and coating processes to ensure the overall decorative effect.

Consider the timing of surface treatment in combination with production process and cost

Timing of surface treatment in mass production

• In mass production of CNC machined parts, in order to improve production efficiency and reduce costs, surface treatment is usually carried out after most of the machining processes are completed and the quality inspection is qualified. This can avoid the scrapping of processed parts due to defects in the previous processing and reduce unnecessary cost waste. At the same time, centralized surface treatment is also convenient for large-scale operation and improves production efficiency. For example, in the large-scale production of automotive parts, batches of parts are uniformly galvanized after turning, milling and other processing are completed and inspected.

Connection with subsequent processes

• The timing of surface treatment also needs to consider the connection with subsequent processes. If the parts need to be welded, heat treated or other processes that may affect the surface treatment effect, then the surface treatment should be arranged after these processes. On the contrary, if the surface treatment may affect the subsequent assembly or other processing, such as certain coatings may affect the assembly accuracy of the parts, then appropriate surface pretreatment should be carried out before the assembly or key processing steps to ensure the smoothness of the entire production process and the stability of product quality.

Reasons for surface treatment

Improving Part Performance

• One of the main reasons for surface treatment is to improve the performance of parts. Through various surface treatment processes, such as quenching to improve hardness, nickel plating to enhance corrosion resistance, and nitriding to improve wear resistance, parts can operate more reliably in specific working environments, extend service life, and reduce maintenance and replacement costs. For example, after the blades of aircraft engines are treated with complex surface coatings, they can maintain good performance in harsh environments with high temperature, high pressure and high-speed airflow, ensuring the efficient operation of the engine.

Meeting appearance requirements

• In today's market, the appearance of a product is an important factor in attracting consumers. Surface treatment can achieve a variety of appearance effects, such as different colors, gloss, textures, etc., to meet the aesthetic needs of different industries and consumers for product appearance. From the fashionable appearance of electronic products to the exquisite texture of household items, surface treatment plays a key role in improving the market competitiveness of products.

Complying with specific industry standards

• Different industries have strict standards and specifications for the performance and quality of parts. For example, the medical industry requires parts to have good biocompatibility and corrosion resistance; the food industry has hygienic and non-toxic requirements for the surface of parts that come into contact with food. Appropriate surface treatment, such as passivation for medical device parts and special coatings for food machinery parts, can ensure that parts meet these industry standards, safeguarding product safety and compliance.

How and why to treat the surface

Anodizing

• Anodizing is an electrolytic passivation process commonly used for surface treatment of aluminum alloy parts. By forming a dense and hard oxide film on the surface of aluminum parts, the corrosion resistance, wear resistance and aesthetics of the parts can be improved. In addition, anodizing can also achieve a variety of color options to meet different application requirements.

Metal plating

• Metal plating is a technology that coats or changes the surface of a substrate with a thin layer of metal. The plating layer can improve the durability, corrosion resistance, surface friction and appearance of the parts. For example, PTFE or nickel plating can effectively prevent corrosion of parts in highly corrosive environments.

Chemical treatment

• Chemical treatment includes pickling, chemical plating, etc. Pickling can remove the oxide layer, rust and contaminants on the surface of the parts to achieve surface cleaning. Chemical plating can form a uniform metal layer on the surface of the parts to improve corrosion resistance, oxidation resistance and wear resistance.

Shot peening

• Shot peening is a technology that uses high-pressure airflow to spray fine particles at high speed onto the surface of the parts to improve surface quality and performance. Shot peening can remove surface deposits, oxide layers and old coatings, smooth surface roughness, and improve the corrosion resistance, fatigue strength and coating adhesion of parts.

Powder coating

• Powder coating is a process of melting dry plastic powder onto metal to form a textured, matte or glossy coating. Powder coating can improve the wear resistance, corrosion resistance and decorativeness of parts and is suitable for a variety of application scenarios.

Conclusion

The timing of surface treatment of CNC machined parts needs to comprehensively consider the functional requirements of the parts, appearance quality requirements, production process and cost. The reasons for surface treatment include important aspects such as performance improvement, appearance optimization and compliance with industry standards. Only by accurately grasping these key points can manufacturing companies give full play to the advantages of surface treatment in the production process, produce high-quality, high-performance products that meet market demand, and stand out in the fierce market competition.

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