What is Painting ?
In CNC machining, surface painting refers to the process of applying a protective or decorative coating to the surface of a machined part after its production. This is a post-machining surface finishing technology that alters the appearance and performance of objects, aiming to improve appearance, durability and resistance to environmental factors such as corrosion, wear and chemical exposure. The surface coating can also provide color coding or branding elements to the parts for beautification. Different coating materials and processes can achieve different results. It is widely used in industries such as automotive, aerospace, electronics and consumer goods.
Importance of Painting
- Beautify the appearance: Paining can give products specific visual effects, such as gloss, matte, texture, etc., and some will even use painting to strengthen the brand impression, such as spraying logo on the product, thereby enhancing the attractiveness and influence of the product.
- Protection function: One of the biggest functions of painting is to provide a protective layer for the workpiece, which can resist oxidation, corrosion, chemical substances and weather factors. High-quality painting can significantly extend the service life of the product.
- Meet customer customization needs: The variety of painting processes makes it an important tool to meet the various needs of customers. painting can be adjusted according to requirements, so as to achieve a variety of different effects, such as specific colors, gloss, and special functions, like heat, chemical resistance coating…
- Add value: A high quality paint process can add value to a part, making it not only functional, but also reflects the brand value through appearance.
Application
Paint spraying process has a wide range of applications in the automotive industry, aerospace and aviation industry, construction industry, home appliance manufacturing and high-tech fields.
- Automobile Manufacturing: In the automobile manufacturing industry, painting can achieve different colors and textures through multi-layer painting, which can be used for decorative painting of the car body, and can also play a protective role to prevent rust and scratches on the car body.
- Construction
painting is widely used in the field of construction of steel structures, bridges and other protective coating, used to prevent corrosion or aging of building materials in harsh weather conditions. - Furniture and home appliances
Furniture and home appliances are mainly painted to enhance the appearance of the surface, so that it has a smooth, shiny texture. At the same time, painting also provides a certain degree of protection for materials such as wood, plastic and metal, extending the service life of the product. - Aerospace
In aerospace and military equipment, paintings are used to protect parts against corrosion and wear. These painting coatings require extremely high weather and chemical resistance to ensure performance in complex environments. At the same time, special processes such as stealth coatings can be used to meet the special functional requirements of military equipment.
Three Typical Painting Process
Air spraying, high pressure spraying and electrostatic spraying are three typical modern coating processes.
- Air spraying
Using compressed air to atomize the paint spraying method, is a convenient operation, easy to change the color, atomization effect is good, you can get detailed modification of high-quality surface coating method. Spray gun structure is simple, inexpensive, according to the shape and size of the workpiece to adjust the spray shape and spray width, so far, this spraying method is still popular. However, the coating transfer efficiency of this spraying method is only 25%-40%. - High-pressure airless spraying
It is a more advanced spraying method, the use of pressurized pumps to increase the paint to high pressure, through the very fine spray holes to spray the paint to form a fan-shaped mist. This spraying method makes the paint not mixed with air, which is conducive to the improvement of surface quality. Airless spraying is significantly better than air spraying in these aspects due to the lower rate of advancement of the spray width and the higher efficiency of paint transfer and productivity. - Electrostatic spraying
Electrostatic spraying involves creating an electrostatic field between a grounded workpiece and a spray gun with DC high voltage. Charged paint particles are sprayed and deposited uniformly on the workpiece surface, with scattered particles still affected by the electrostatic field, ensuring even coverage on complex geometries. This method is ideal for fences, pipes, steel structures, and diesel engines, with a coating transfer efficiency of 60-85% and uniform film thickness. However, not all coatings are suitable, and equipment investment is significant.
Advantages
- Improve the wear resistance: High quality painting can improve the wear resistance of the parts and prolong their service life.
- Anti-corrosion: painting layer can effectively isolate air and moisture, prevent metal materials from rusting, especially for steel, iron and other metals.
- Beautify the appearance: painting can increase the color and luster of the surface and make the parts more attractive.
- Versatility: The painting process is applicable to different materials such as metal, plastic and wood. By adjusting the paint formulation, various functional requirements can be met, such as heat resistance, UV or chemical resistance.
- Ease of application: Paint spraying can be carried out manually or with automated equipment, and is suitable for different production scales, from small to large batches.
- Variety of processes: Paint spraying has many different processes, such as air spraying, airless spraying, electrostatic spraying, etc., which can enrich the customer’s choice.
How to Assess the Quality of the Painting Process
- Appearance Inspection: Check the uniformity of the surface coating, whether there are obvious brush marks, bubbles, particles, pinholes and other defects. Observe whether the coating is too thick, cloudy, not bright enough or the paint color is dark.
- Use a gloss meter to check the surface gloss after painting to ensure that it meets the requirements of the customer or design, and to check the drying quality of the paint film, etc.
- Thickness test: Use coating thickness gauge to measure the thickness of the coating to ensure that it is within the specified range.
- Adhesion Test: Cross-Cut Test or Pull-Off Test, mark out the grid on the surface of the workpiece with a special tool, then pull the coating with a tape to check whether there is any peeling phenomenon. The coating bonding strength is tested by a mechanical tensile instrument.
- Abrasion Resistance Test: Abrasion test on painted surfaces using a friction meter.
- Corrosion resistance test: Salt spray test or chemical immersion test are two ways to check the anti-corrosion effect and chemical resistance of the coating.
