Methods for polishing and grinding:

Grinding involves embedding or coating the surface of a grinding tool (hereafter referred to as the "tool") with abrasive particles, along with the addition of a lubricant. Under a specific pressure, the tool and the workpiece come into contact and undergo relative motion. Through the action of the abrasives, an extremely thin layer of material—known as swarf—is removed from the workpiece surface, resulting in precise dimensions, accurate geometric shapes, and exceptionally high surface finish quality. At its core, grinding is a process where free abrasive grains, guided by the tool, perform a subtle cutting action on the workpiece surface, involving both physical and chemical interactions.
Features: (1) In mechanical grinding, the machine-tool–tool–workpiece system operates in an elastically floating state.
(2) The workpiece being ground is not subjected to any external force and thus remains in a free state.
(3) The speed of the grinding motion typically remains below 30 m/min, a figure that is approximately one percent of the cutting speed.
(4) During grinding, only an extremely thin layer of material can be removed, resulting in minimal heat generation, reduced machining deformation, and a correspondingly thin surface-mechanically altered layer.
(5) Residual compressive stress exists in the ground surface, which helps enhance the fatigue strength of the workpiece's surface.
(6) Operation is simple and generally doesn’t require complex or expensive equipment.
(7) Good adaptability.
(8) Grinding can achieve very low surface roughness.

1. Fluid Polishing

Fluid polishing relies on the high-speed flow of liquid and the abrasive particles it carries to scour the surface of the workpiece, achieving the desired polishing effect.

Common methods include abrasive jet machining, liquid jet machining, and hydrodynamic polishing. Hydrodynamic polishing is driven by hydraulics,

Pass the liquid medium carrying abrasive particles rapidly back and forth across the workpiece surface. The medium primarily consists of a special compound that flows well under lower pressure.

(Made from a polymer-like substance mixed with an abrasive, which can be silicon carbide powder.)

2. Mechanical Polishing

Mechanical polishing is a method of achieving a smooth surface by removing the raised areas after polishing through cutting and plastic deformation of the material's surface.

Generally, tools such as oil stones, wool wheels, and sandpaper are used, with manual operation being the primary method. For special parts, such as surfaces of rotating bodies,

Auxiliary tools such as rotary tables can be used, and for surfaces with high-quality requirements, ultra-precision lapping and polishing is recommended. Ultra-precision lapping and polishing employs specially designed abrasive tools,

In an abrasive polishing fluid, it is tightly pressed against the workpiece's surface being processed and subjected to high-speed rotational motion.

Using this technology, surface roughness as low as Ra0.008 μm can be achieved—highest among various polishing methods.

Optical lens molds often use this method.

3. Ultrasonic Polishing

Place the workpiece into the abrasive suspension and immerse it together in an ultrasonic field; relying on the oscillating action of the ultrasound,

Use abrasive materials to grind and polish the surface of the workpiece. Ultrasonic machining generates minimal macroscopic forces, preventing deformation of the workpiece; however, the fabrication and installation of tooling are relatively challenging.

Ultrasonic machining can be combined with chemical or electrochemical methods. By applying ultrasonic vibration to stir the solution on top of processes like solution etching or electrolysis,

Ensure that dissolution products on the workpiece surface are removed, while maintaining uniform corrosion or electrolyte distribution near the surface.

Ultrasound-induced cavitation in liquids can also inhibit the corrosion process, promoting surface brightening.

4. Electrolytic Polishing
The basic principle of electrolytic polishing is the same as that of chemical polishing—specifically, it relies on the selective dissolution of the tiny protruding areas on the material's surface.

Make the surface smooth. Compared to chemical polishing, it effectively eliminates the influence of cathodic reactions, delivering superior results. The electrochemical polishing process consists of two steps:

(1) Macro-level leveling: Dissolved products diffuse into the electrolyte, reducing the geometric roughness of the material surface, with Ra > 1 μm.

(2) Micro-illumination smoothing with anodic polarization enhances surface brightness, achieving Ra < 1 μm.

5. Fluid Polishing

Fluid polishing relies on the high-speed flow of liquid and the abrasive particles it carries to scour the surface of the workpiece, achieving the desired polishing effect.

Common methods include abrasive jet machining, liquid jet machining, and hydrodynamic polishing. Hydrodynamic polishing is driven by hydraulics,

Allow the liquid medium carrying abrasive particles to flow reciprocally at high speed across the workpiece surface.

The medium is primarily made by combining a special compound (a polymer-like substance) that flows well under lower pressure with abrasive materials.

Abrasive materials can be made from silicon carbide powder.

6. Chemical Polishing

Chemical polishing allows the microscopic protruding parts of a material's surface to dissolve preferentially over the recessed areas when immersed in a chemical medium.

Thus, a smooth surface is achieved. The main advantage of this method is that it doesn’t require complex equipment, allowing for the polishing of workpieces with intricate shapes.

It can polish multiple workpieces simultaneously, making it highly efficient. The core issue in chemical polishing is the formulation of the polishing solution. The surface roughness achieved through chemical polishing

Typically around 10 μm in size.

7. Magnetic Abrasive Polishing

Magnetic abrasive polishing uses magnetic abrasives to form an abrasive brush under the influence of a magnetic field, enabling grinding and finishing of workpieces. This method boasts high processing efficiency,

High quality, easy-to-control processing conditions, and excellent working environment. With the appropriate abrasive material, the surface roughness can reach Ra0.1 μm.

Polishing in plastic mold manufacturing differs significantly from surface polishing required in other industries.

Strictly speaking, polishing a mold should be referred to as mirror finishing. It not only demands extremely high standards for the polishing process itself but also places stringent requirements on surface flatness and…

Smoothness and geometric accuracy also meet high standards. Surface polishing typically only requires achieving a glossy finish.

The standards for mirror finishing are divided into four levels: AO = Ra 0.008 μm, A1 = Ra 0.016 μm, A3 = Ra 0.032 μm,

A4 = Ra0.063 μm. Since methods like electrolytic polishing and fluid polishing are difficult to use for precisely controlling the geometric accuracy of parts,

However, the surface quality achieved by methods such as chemical polishing, ultrasonic polishing, and magnetic abrasive polishing fails to meet the required standards. Therefore, mirror finishing for precision molds remains a challenge.

Mechanical polishing still remains the primary method.