Knowledge

Precision ceramic polishing with a high-precision requirement of Ra 0.025 μm is a complex and highly delicate processing technology that requires the integration of mechanical, chemical, and precise control techniques.

 

1. The core steps of the polishing process are as follows:

 

(1) Pre-treatment

Coarse grinding and fine grinding

Gradual grinding is carried out using diamond or silicon carbide grinding wheels (e.g., from #800 to #3000 grit), reducing the surface roughness to Ra 0.1 - 0.2 μm to lay the foundation for polishing.

Ultrasonic cleaning

Residual grinding particles are removed using isopropyl alcohol or deionized water to prevent scratches during subsequent polishing.

 

(2) Polishing stage

Mechanical polishing (coarse polishing)

Equipment: Variable-speed polishing machine (100 - 500 rpm)

Polishing agent: Diamond suspension (1 - 3 μm particle size) or alumina polishing liquid

Parameters: Pressure 20 - 50 kPa, time 30 - 60 minutes, target roughness Ra 0.05 - 0.1 μm

Chemical mechanical polishing (CMP, fine polishing)

Polishing liquid: Nano-silica (SiO₂) or cerium oxide (CeO₂) colloid solution (pH 10 - 12, promoting surface hydrolysis)

Polishing pad: Polyurethane porous pad (Shore D hardness 50 - 60)

Parameters: Speed 50 - 150 rpm, pressure 5 - 15 kPa, time 1 - 2 hours, achieving sub-nanometer flatness through the combined action of chemical etching and mechanical grinding.

 

(3) Post-treatment

Ultra-precision cleaning

Megasonic cleaning (950 kHz) is combined with plasma cleaning to remove adsorbed organic matter and nanoparticles from the surface.

Surface passivation

Oxygen plasma treatment (300 W, 10 minutes) is applied to active ceramics such as silicon nitride to form a dense oxide layer and prevent contamination.

 

2. Key technical parameter control

Temperature control

The polishing fluid temperature must be stabilized at 25 ± 0.5℃. Excessive temperature difference can cause thermal expansion and lead to surface shape accuracy deviation.

Vibration suppression

The equipment should be installed on an active vibration isolation platform (vibration frequency < 2Hz, amplitude < 50nm) to avoid the influence of environmental vibration.

Pressure uniformity

A pneumatic feedback control system is adopted to ensure pressure fluctuation < ±1%. For irregular-shaped parts, a conformal fixture needs to be designed.

 

3. Inspection and Quality Control

Roughness Inspection

Five-point measurement is conducted using a white light interferometer (vertical resolution 0.1nm) or an atomic force microscope (AFM), with a sampling area of 50×50 μm².

Subsurface Damage Inspection

Chemical etching (HF solution for 5 minutes) combined with SEM observation is used to ensure that the subsurface crack depth is less than 50nm.

Surface Flatness Inspection

A laser interferometer (λ/100 accuracy) is used to inspect the flatness, with a requirement that the PV value is less than 0.1 μm.

 

4. Common Problem Solutions

Problem Phenomenon Cause Analysis Solution

Polishing Stripes Clogging of polishing pad grooves Use a diamond dresser to dress the polishing pad every 30 minutes

Edge Collapse Concentration of edge stress Use edge compensation polishing (reduce pressure in the edge area by 20%)

Surface Fogging Accumulation of nano-scratches Add 0.1% sodium dodecylbenzene sulfonate (SDBS) to the polishing liquid to enhance lubrication

 

5. Advanced Technology Development

Magnetic Fluid Finishing (MRF)

It utilizes magnetic fluid (carbonyl iron powder + nano-diamond) to form a flexible "polishing mold" in a magnetic field, suitable for complex surface processing, and can achieve a surface roughness of Ra 0.01 μm.

Ion Beam Polishing

It achieves atomic-level removal through Ar+ ion sputtering (energy 500 eV, beam current density 1 mA/cm²), and is used for processing ceramic mirrors in laser gyroscopes.

 

6. Economic Considerations

The traditional CMP cost is approximately 150 yuan per square meter, while the cost of ion beam polishing can be as high as 5,000 yuan per square meter. The choice of process should be based on the application of the parts (such as semiconductors vs. optical components).

The adoption of a diamond polishing fluid recovery system can reduce the cost of consumables by 30%.

Through the above-mentioned precise control and technological innovation, modern precision ceramic polishing can stably achieve a super-smooth surface with a Ra of 0.025 μm, meeting the demands of cutting-edge fields such as inertial navigation and photolithography machine lenses. In actual production, it is recommended to establish a DOE (Design of Experiments) model to optimize the combination of various parameters and implement SPC (Statistical Process Control) to ensure a yield of over 95%.

 

Vigor has more than 18 years experience on castings, we know how to avoid defects when production. If you have any questions and demand of products development or improve your supply chain, please feel free to contact us at info@castings-forging.com