Complete Processing Workflow for # 00/000 Grade High-Precision Granite Plate

Adhering to the national standard GB/T 20428 “Granite Flat Plates”, the entire precision machining process must be completed in a dust-free, vibration-dampened workshop at a constant temperature of 20±0.5℃. The core process is divided into nine major stages: Raw Material Screening → Rough Cutting → Rough Machining → Multi-stage Stress Relief Aging → Gradient Mechanical Grinding → Manual Super-precision Matching and Grinding → Functional Hole and Slot Machining → Final Inspection and Calibration → Finished Product Stabilization Aging. Among these, manual matching and grinding, and multi-stage stress release are the core critical processes that distinguish ordinary Grade 0 from Grade 00/000.

I. Strict Raw Material Screening (The Foundation for Long-term Deformation Resistance)

Only Jinan Qinghui Longyan / Indian Black Fine-grained Granite is selected. All materials undergo full inspection to eliminate inclusions, sand holes, hidden cracks, and mica soft bands:

1. Hard Thresholds for Physical Indicators

• Compressive strength ≥245MPa, Shore hardness HS72~80, density ≥2.97g/cm³
• Water absorption ≤0.13%, linear expansion coefficient ≤4.5×10⁻⁶/℃, non-magnetic

1. Non-destructive Testing: Ultrasonic flaw detection to screen for internal hidden cracks; petrographic analysis to ensure uniform grains without stratification
2. Natural Pre-aging of Rough Blocks: Rough blocks from the mine are left to rest outdoors for 3 to 6 months to release geological native stresses; unqualified rough blocks are scrapped directly

II. Rough Cutting and Blank Shaping

1. Diamond large saws cut the material according to drawing dimensions, leaving a machining allowance of 8~12mm on each side for length, width, and thickness. Deep cutting in a single pass to cause micro-cracks at the edges and corners is strictly prohibited
2. Gantry CNC grinders rough-mill the six faces to remove saw marks and correct overall warping; after rough machining, the flatness is controlled within 0.05mm/m
3. Rough chamfering of R2 on all four sides to prevent edge chipping during transport
4. First Aging Stage after rough machining: Manual composite stress relief (24h insulation in an 80℃ drying room → 4h deep freezing at -10℃ → 72h resting at a constant 20℃) to eliminate mechanical stresses generated by sawing and milling, avoiding later creep and warping

III. Semi-precision Grinding Process (Gradient Grinding and Polishing to Gradually Compress Flatness Error)

All operations are executed in a constant temperature workshop, with the grinding wheel grit progressing from coarse to fine:

1. 200#~400# diamond wheel semi-precision grinding: Eliminates rough milling tool marks, compressing flatness to 5~10μm/m
2. 800#~1200# fine grinding: Refines surface texture, achieving flatness ≤3μm/m and surface roughness Ra ≤1.6μm
3. After each round of grinding, the plate is flipped and rested for 24h to release grinding stress; Grade 000 plates require two alternating rounds of semi-precision grinding on both sides

IV. Core Process 1: Secondary Long-term Constant Temperature Natural Aging (Mandatory for Grade 00/000)

After rough grinding, the plate must enter a constant temperature room to rest, which is the key to ensuring precision does not drift for several years:

1. Grade 00 plates: Laid flat at a constant temperature of 20±1℃ and 45% RH for 2 weeks, flipped every 7 days to allow uniform stress release
2. Grade 000 metrology reference plates: Constant temperature resting for over 4 weeks; for large plates over 1500mm, this is extended to 3 months
3. Principle: Grinding generates residual stress on the surface layer; insufficient aging will cause the finished product to slowly bend and exceed flatness standards after 1 to 3 years of use

V. Core Process 2: Manual Pairing and Ultra-Precision Grinding (Exclusive to Grade 00/000, determining micron-level accuracy)

Due to the inherent error limits of machine tool guide rails, mechanical grinders cannot achieve an ultra-high flatness of 1~2μm/m. Manual pairing and grinding correction are mandatory:

1. Grade 00 Platform Grinding Solution

• Abrasive: W7 and W10 silicon carbide micro-powder; standard cast iron reference plates are mutually ground.
• Grid multi-point cyclic grinding: Grid measurement points are checked every 30 minutes using a high-precision electronic level, and high points are manually scraped.
• All six sides are flipped and cycled for mutual grinding 3 times to ensure the parallelism and perpendicularity of the working surface, bottom surface, and four side surfaces meet standards, achieving a final flatness of ≤2μm/m.

2. Grade 000 Metrological Reference Grinding Solution (Highest Precision)

• Ultra-fine W3.5 diamond micro-powder wet grinding: Grinding time per side ≥4h, alternating mutual grinding of front and back surfaces to eliminate unidirectional stress.
• Laser reference flat block alignment: Contact spots are observed using the spot method, ensuring uniform distribution of spots across the entire plate surface without local high points.
• Final flatness tolerance ≤1μm/m, working surface roughness Ra ≤0.1μm, mirror-like finish without any scratches or pitting.

VI. Functional Feature Precision Machining (Drilling, T-slots, Thread Embedding)

Hole and slot machining is performed after precision grinding to prevent slotting from damaging the high-precision reference surface:

1. 5-axis CNC drilling and milling center processes threaded holes and T-slots, leaving a 0.5mm precision grinding allowance on one side, followed by local polishing and deburring.
2. Stainless steel wire thread inserts are embedded in threaded holes, reinforced with epoxy glue cured for 24h to prevent local collapse from clamping tools.
3. Slot walls and hole edges are finely chamfered with R3~R5 arcs to eliminate stress concentration and edge chipping.
4. Local vibration aging for 30 minutes after machining to eliminate local stresses caused by drilling and slotting.

VII. Ultimate All-Dimensional Precision Inspection (Laser Interferometry Traceable Verification)

Inspection environment maintained at a constant temperature of 20±0.5℃, using a laser plane interferometer, a 0.001mm/m high-precision electronic level, and a CMM for dimensional measurement:

1. Flatness: Data is collected from diagonals and grid multi-points; software fits and calculates the flatness error, strictly corresponding to the GB 00/000 grade tolerances.
2. Full inspection of hexahedron parallelism, adjacent surface perpendicularity, and thickness uniformity.
3. Full inspection of surface roughness and appearance: No sand holes, scratches, dents, or discolored inclusions.
4. Load deflection spot check: Centrally load the rated weight, ensuring a flatness recovery rate of ≥99.98% after unloading to confirm no permanent deformation.
5. Inspection data is archived, and a traceable verification certificate (JJG117) from the Metrology Institute is issued.

VIII. Final Stability Aging of Finished Products (Closed-loop Process Before Factory Release)

After passing inspection, an additional vibration aging constant temperature static aging step is added:

1. 30~60Hz vibration aging for 60~90min to release all residual machining stresses.
2. Constant temperature room static aging for 72h, followed by a second flatness re-test; if minor drift occurs, it must be reworked and re-ground.
3. Only after passing the re-test can it proceed to cleaning, wax sealing protection, and packaging for factory release.

IX. Comparison of Key Process Differences Between Grade 00 and Grade 000

Таблица

Process Step	Grade 00 Precision Platform (General Mold / CMM)	Grade 000 Reference Platform (Metrology Institute / Semiconductor)
Constant temperature natural aging duration	14 days	28~90 days
Manual grinding abrasive particle size	W7/W10	W3.5 ultra-fine diamond powder
Single-side hole grinding duration	≥2h	≥4h
Flatness tolerance	≤2μm/m	≤1μm/m
Шероховатость поверхности	Ra0.2~0.6μm	Ra≤0.1μm mirror finish
Factory re-inspection frequency	1 final inspection	Two laser re-tests: after grinding after aging