Precision granite bases are core load-bearing components for coordinate measuring machines, semiconductor inspection equipment, and ultra-precision CNC machine tools. The flatness and surface finish of the base directly determine the accuracy of equipment testing and processing. As the final forming process, improper control of grinding and polishing will easily cause scratches, waviness, flatness errors and other defective products. This article summarizes the key quality control points throughout the whole process, including pre-processing, rough grinding, fine grinding, precision grinding, polishing and post-treatment, providing standardized production references for precision stone processing enterprises.
1. Pre-processing Control to Reduce Polishing Defects
1.1 Aging Treatment Control
Before processing, imported Indian granite blocks and domestic black granite plates must undergo secondary natural aging and constant-temperature aging to release internal stone stress and avoid deformation after finishing.
Standard: Large bases require at least 45 days of aging in a constant-temperature workshop maintained at 22±0.5℃.
1.2 Pre-inspection for Stone Defects
Ultrasonic testing is used to detect internal cracks and voids. Strong light inspection is applied to check surface lines, dark veins and pinholes. Materials with deep defects are eliminated before grinding to reduce rework rate.
1.3 Tooling and Protection
Soft dust-proof rubber pads are used on grinding platforms. Uniform clamping force prevents edge chipping. Protective tapes are pasted on workpiece edges to avoid collision damage during rough grinding.
2. Rough Grinding: Remove Tool Marks and Build Flatness Foundation
Rough grinding eliminates milling marks and corrects overall flatness through segmented diamond wheel grinding.
1. Grit grading control: Use 120# and 240# diamond discs step by step. Skipping grit grades will cause deep scratches that cannot be removed in later processes.
2. Cooling water control: Circulating water must be filtered within 5μm to avoid hard particles causing permanent pits. Filter elements are replaced regularly.
3. Real-time inspection: Flatness is checked with straight edges and dial indicators after each grinding cycle. For large bases, detection points are set every 200mm, with flatness tolerance controlled within 0.02mm/m before fine grinding.
3. Fine & Precision Grinding: Eliminate Scratches and Reduce Roughness
3.1 Fine Grinding (400#–800#)
Remove rough grinding traces and correct minor height differences. Workshop humidity is kept at 45%–60% to prevent slight water absorption deformation.
3.2 Precision Grinding (1500#–3000#)
Reduce grinding pressure by 30% and operate at low uniform speed. After precision grinding, surface roughness must reach Ra0.8 or lower.
3.3 Process Isolation
Rough grinding and precision grinding zones are separated with independent cooling water systems to prevent coarse dust contamination.
4. Polishing Process Control for Mirror Finish and Micron Precision
4.1 Progressive Polishing Materials
Use 5000#, 8000#, and 10000# resin polishing pads step by step. For Indian Black Galaxy and pure black granite bases, special microcrystalline polishing pads are applied to achieve glossiness above 100°.
4.2 Speed and Pressure Standardization
Spindle speed is controlled at 1200–1800 r/min with uniform low-pressure movement. Consistent polishing passes prevent local concave defects. Over-polishing is forbidden for air-floating equipment bases to protect surface mineral structure.
4.3 Dust and Environment Control
Dust extraction systems are installed at polishing stations. Floating dust is fully removed to avoid fine scratches that affect semiconductor-grade precision.
5. Post-polishing Cleaning and Protection
5.1 Multi-stage Dust-free Cleaning
High-pressure water rinsing and ultrasonic cleaning with neutral stone detergent remove all polishing powder residue. Hidden dust in gaps is cleaned with dust-free brushes to prevent yellowing.
5.2 Drying and Re-inspection
Workpieces are dried at constant temperature for 2 hours. After full cooling, flatness, roughness and dimensional tolerance are re-measured and recorded.
5.3 Sealing and Protection
Inorganic stone protective coating is thinly applied without affecting flatness, providing long-term anti-oil and anti-moisture performance for industrial use.
6. Full-process Quality Inspection and Traceability
1. Sampling inspection for each process: Record disc model, processing time, temperature and humidity data for each batch.
2. Defect handling mechanism: Minor defects are repaired by low-speed precision polishing; deep defects return to rough grinding process.
3. File archiving: Independent processing records are created for each granite base to meet factory inspection standards for CMM and semiconductor customers.
Conclusion
Granite precision base grinding and polishing is a refined continuous process. Any deviation in parameters, environment or consumables may cause batch quality problems. Standardized grading procedures, constant-temperature dust-free workshops and filtered water circulation systems are essential for producing high-precision granite bases for CNC and semiconductor equipment. 