An overview of typical dimensional tolerances, flatness, and geometric tolerances by most Chinese suppliers.

In China's rapid prototyping industry, suppliers generally offer competitive manufacturing capabilities across various processes, with achievable tolerances aligning with international standards for prototype and low-volume production. Below is an overview of typical dimensional tolerances, flatness, and geometric tolerances for key processes provided by most Chinese suppliers.

1. CNC Machining

• Dimensional Tolerance:

• Metals (Aluminum, Steel, etc.): ±0.05 mm to ±0.1 mm for standard parts; high-precision machining can achieve ±0.02 mm or tighter.

• Plastics (ABS, PC, Nylon, etc.): ±0.1 mm to ±0.2 mm, influenced by material stability and part size.

• Flatness: Typically 0.05 mm to 0.1 mm per 100 mm span for standard machining; can be improved to 0.02 mm with precision milling or grinding.

• Geometric Tolerances (Parallelism, Perpendicularity, Circularity):

• Parallelism/Perpendicularity: 0.05 mm to 0.1 mm per 100 mm.

• Circularity (Roundness): 0.02 mm to 0.05 mm for holes or shafts.

• Positional Tolerance: ±0.05 mm to ±0.1 mm for features like holes or pins.

2. 3D Printing

FDM (Fused Deposition Modeling)

• Dimensional Tolerance: ±0.2 mm to ±0.5 mm, depending on part orientation, layer height, and calibration.

• Flatness: Limited by layer adhesion and warping; typically 0.3 mm to 0.5 mm per 100 mm.

• Geometric Tolerances: Generally lower due to layer stacking; parallelism/perpendicularity around 0.3 mm to 0.5 mm.

SLA/DLP (Stereolithography/Digital Light Processing)

• Dimensional Tolerance: ±0.1 mm to ±0.2 mm, with high-resolution printers achieving ±0.05 mm.

• Flatness: 0.1 mm to 0.2 mm per 100 mm, influenced by resin shrinkage and support structures.

• Geometric Tolerances: Parallelism/perpendicularity within 0.1 mm to 0.2 mm.

SLS/MJF (Selective Laser Sintering/Multi Jet Fusion)

• Dimensional Tolerance: ±0.2 mm to ±0.3 mm for nylon-based materials; shrinkage is a key factor.

• Flatness: 0.2 mm to 0.4 mm per 100 mm.

• Geometric Tolerances: Similar to dimensional tolerances, with positional accuracy around ±0.2 mm.

3. Vacuum Casting (Urethane Casting)

• Dimensional Tolerance: ±0.2 mm per 100 mm, or ±0.1 mm for smaller parts (<100 mm). Total tolerance can reach ±0.3 mm to ±0.5 mm for larger parts (>500 mm).

• Flatness: 0.2 mm to 0.3 mm per 100 mm, influenced by mold quality and casting process.

• Geometric Tolerances:

• Parallelism/Perpendicularity: 0.2 mm to 0.3 mm per 100 mm.

• Positional Tolerance: ±0.2 mm to ±0.4 mm.

• Note: Tolerances depend heavily on the master pattern (often CNC-machined or 3D-printed) and silicone mold stability.

4. Sheet Metal Bending

• Bend Angle Tolerance: ±1° to ±2° for standard bends; precision tooling can achieve ±0.5°.

• Linear Dimension Tolerance: ±0.2 mm to ±0.5 mm for cut/flange dimensions.

• Flatness (After Bending): 0.2 mm to 0.5 mm per 100 mm, depending on material thickness and tooling accuracy.

• Geometric Tolerances:

• Parallelism between bends: 0.3 mm to 0.5 mm per 100 mm.

• Hole-to-bend position: ±0.2 mm to ±0.4 mm.

General Notes for Chinese Suppliers

1. Standard vs. Precision Tolerances: Most suppliers quote "standard" tolerances (as above). Tighter tolerances are often achievable but may incur higher costs and longer lead times.

2. Material Influence: Plastics and resins generally have wider tolerances than metals due to thermal expansion, shrinkage, or flexibility.

3. Part Size Consideration: Tolerances are often scaled with part dimensions (e.g., ±0.1 mm per 100 mm).

4. Design for Manufacturing (DFM): Suppliers usually provide DFM feedback to optimize tolerances based on the selected process.

5. Quality Control: Leading suppliers use CMM (Coordinate Measuring Machine), laser scanners, and other inspection tools to verify critical tolerances.

Comparison Summary

For precise requirements, it is recommended to:

• Specify critical tolerances on drawings and discuss them with the supplier early.

• Request inspection reports for critical dimensions.

• Consider prototyping before full production to validate tolerances.

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