Exploring the Multifaceted Approaches to CNC Mirror Machining

How many types of mirror machining are there in CNC machining and in the field of practical application?

Turning: This process involves rotating a workpiece on a lathe while a cutting tool removes material to create a cylindrical shape. It is commonly used for creating cylindrical components such as shafts, pins, and bushings.

Milling: Milling is a process in which a rotating cutting tool removes material from a stationary workpiece to create various shapes, such as flat surfaces, slots, and intricate 3D contours. This technique is extensively employed in the manufacturing of components for industries like aerospace, automotive, and medical devices.

Grinding: Grinding involves the use of an abrasive wheel to eliminate material from a workpiece. This process results in a smooth surface finish and ensures precise dimensional accuracy. It is commonly employed in the production of high-precision components such as bearings, gears, and tooling.

Drilling: Drilling is the process of creating holes in a workpiece by using a rotating cutting tool. It is utilized in various applications, including the production of engine blocks, aerospace components, and electronic enclosures.

Electrical Discharge Machining (EDM): EDM utilizes electrical discharges to eliminate material from a workpiece, enabling the production of intricate shapes and features with high precision. It is commonly employed in the manufacturing of injection molds, die-casting dies, and aerospace components.

 

The practical applications of mirror machining in CNC machining are diverse. It includes the production of components for various industries such as aerospace, automotive, medical devices, electronics, and consumer goods. These processes are used to create a wide range of components, from simple shafts and brackets to complex aerospace components and medical implants.

Mirror processing refers to the fact that the processed surface can reflect the image like a mirror. This level has achieved a very good surface quality for the machining parts. Mirror processing can not only create a high-quality appearance for the product but also reduce the notch effect and prolong the fatigue life of the workpiece. It is of great significance in many assembly and sealing structures. The polishing mirror processing technology is mainly used to reduce the surface roughness of the workpiece. When the polishing process method is selected for the metal workpiece, different methods can be chosen according to different needs. The following are several common methods of polishing mirror processing technology.

 

1. Mechanical polishing is a method of polishing that involves cutting and deforming the surface of a material to remove imperfections and obtain a smooth surface. This method typically involves using tools such as oil stone strips, wool wheels, and sandpaper for manual operation. For special parts like the surface of rotary bodies, auxiliary tools like turntables can be used. When high surface quality is required, ultra-fine grinding and polishing methods can be utilized. Superfinishing grinding and polishing involves using special abrasives in a liquid containing abrasives, pressed on the workpiece for high-speed rotary motion. Using this technique, a surface roughness of Ra0.008μm can be achieved, making it the highest among various polishing methods. This method is often used in optical lens molds.

2. Chemical polishing is a process used to dissolve the microscopic convex parts of a material’s surface in a chemical medium, leaving the concave parts untouched and resulting in a smooth surface. This method doesn’t require complex equipment and is capable of polishing workpieces with complex shapes while being efficient for polishing many workpieces simultaneously. The key challenge in chemical polishing is preparing the polishing slurry. Typically, the surface roughness achieved by chemical polishing is around ten micrometers.

3. The basic principle of electrolytic polishing is similar to that of chemical polishing. It involves selectively dissolving the tiny protruding parts of the material’s surface to make it smooth. Unlike chemical polishing, electrolytic polishing can eliminate the effect of cathodic reaction and provides a better outcome. The electrochemical polishing process consists of two steps: (1) macroscopic leveling, where the dissolved product diffuses into the electrolyte, decreasing the geometric roughness of the material surface, and Ra becomes greater than 1μm; and (2) micropolishing, wherein the surface is flattened, the anode is polarized, and the surface brightness is increased, with Ra being less than 1μm.

 

4. Ultrasonic polishing involves placing the workpiece in an abrasive suspension and subjecting it to ultrasonic waves. The waves cause the abrasive to grind and polish the surface of the custom cnc parts. Ultrasonic machining exerts a small macroscopic force, which prevents workpiece deformation, but it can be challenging to create and install the necessary tooling. Ultrasonic machining can be combined with chemical or electrochemical methods. Applying ultrasonic vibration to stir the solution aids in detaching dissolved products from the workpiece’s surface. The cavitation effect of ultrasonic waves in liquids also helps inhibit the corrosion process and facilitates surface brightening.

 

5. Fluid polishing uses high-speed flowing liquid and abrasive particles to wash the surface of a workpiece for polishing. Common methods include abrasive jetting, liquid jetting, and hydrodynamic grinding. Hydrodynamic grinding is hydraulically driven, causing the liquid medium carrying abrasive particles to move back and forth across the workpiece surface at high speed. The medium is mainly composed of special compounds (polymer-like substances) with good flow at lower pressures, mixed with abrasives such as silicon carbide powders.

 

6. Mirror polishing, also known as mirroring, magnetic grinding, and polishing, involves the use of magnetic abrasives to create abrasive brushes with the help of magnetic fields for grinding and processing workpieces. This method offers high processing efficiency, good quality, easy control of processing conditions, and favorable working conditions.

When suitable abrasives are applied, the surface roughness can reach Ra 0.1μm. It’s important to note that in plastic mold processing, the concept of polishing is quite distinct from surface polishing requirements in other industries. Specifically, mold polishing should be referred to as mirror finishing, which places high demands not only on the polishing process itself but also on surface flatness, smoothness, and geometric accuracy.

In contrast, surface polishing generally only requires a shiny surface. The standard of mirror processing is divided into four levels: AO=Ra 0.008μm, A1=Ra 0.016μm, A3=Ra 0.032μm, A4=Ra 0.063μm. Since methods like electrolytic polishing, fluid polishing, and others struggle to accurately control the geometric accuracy of CNC milling parts, and the surface quality of chemical polishing, ultrasonic polishing, magnetic grinding and polishing, and similar methods might not meet the requirements, the mirror processing of precision molds mainly relies on mechanical polishing.

 

 

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