CNC Pipe Bending Machine Die Size Chart
author: Huashun
2025-06-06
1.Die Types and Standard Sizes
| Mold Type | Key Dimensions | Applicable Tube OD (mm) | Material | Notes |
| Bend Die | Radius (R), Groove Diameter (D), Width (W) | 10-200 | Cr12MoV / 42CrMo | Must match tube bend radius |
| Clamp Die | Groove Diameter (D), Length (L) | 10-200 | Alloy Steel / Hardened | Ensures even clamping force |
| Pressure Die | Groove Diameter (D), Length (L) | 10-200 | Wear-Resistant Alloy Steel | Prevents tube deformation |
| Wiper Die | Groove Diameter (D), Angle (θ) | 10-150 | Carbide | Prevents wrinkles (for thin-wall tubes) |
| Mandrel | Diameter (D), Length (L), Number of Balls | 20-150 | Spring Steel / Stainless Steel | Prevents tube collapse |
2.Standard Die Dimension Reference Table
2.1 Bend Die
| Tube OD (mm) | Bend Radius (R, mm) | Groove Diameter (D, mm) | Mold Width (W, mm) |
| 10 | 15 / 20 / 30 | 10.2 | 25 |
| 20 | 30 / 40 / 60 | 20.2 | 35 |
| 25 | 38 / 50 / 75 | 25.2 | 40 |
| 38 | 57 / 76 / 114 | 38.2 | 50 |
| 50 | 75 / 100 / 150 | 50.2 | 60 |
| 76 | 114 / 152 / 228 | 76.2 | 80 |
| 100 | 150 / 200 / 300 | 100.2 | 100 |
Note: The bending radius is typically 1.5D, 2D, or 3D (where D is the outer diameter of the tube). The groove diameter is generally 0.1–0.3 mm larger than the tube’s OD to prevent jamming.
2.2 Clamp Die
| Tube OD (mm) | Groove Diameter (D, mm) | Mold Length (L, mm) |
| 10 | 10.2 | 50 |
| 20 | 20.2 | 70 |
| 25 | 25.2 | 80 |
| 38 | 38.2 | 100 |
| 50 | 50.2 | 120 |
| 76 | 76.2 | 150 |
| 100 | 100.2 | 200 |
Note: The clamping die length is typically 5D–8D and must match the bending die to ensure stable grip.
2.3 Pressure Die
| Tube OD (mm) | Groove Diameter (D, mm) | Mold Length (L, mm) |
| 10 | 10.2 | 60 |
| 20 | 20.2 | 80 |
| 25 | 25.2 | 100 |
| 38 | 38.2 | 120 |
| 50 | 50.2 | 150 |
| 76 | 76.2 | 200 |
| 100 | 100.2 | 250 |
Note: The pressure die length is usually 6D–10D to prevent tube deformation.
2.4 Mandrel
| Tube OD (mm) | Mandrel Diameter (D, mm) | Number of Balls | Suitable Bend Radius (R) |
| 20 | 18.5 | 3 | R30-R60 |
| 25 | 23.5 | 3/5 | R38-R100 |
| 38 | 36.5 | 5 | R57-R150 |
| 50 | 48.5 | 5/7 | R75-R200 |
| 76 | 74.5 | 7/9 | R114-R300 |
Note: The mandrel diameter is usually 1–2 mm smaller than the inner diameter of the tube. Multi-ball mandrels are recommended for small bending radii or thin-walled tubes.
3. Die Selection Recommendations
- Tube material affects die selection – different materials (e.g., stainless steel, carbon steel, aluminum) require dies of varying hardness.
- Bending radius influences die lifespan – smaller radii cause faster die wear.
- For mass production, wear-resistant coated dies are recommended (e.g., TD coating, chrome plating).
- Thin-walled tubes (t/D < 0.05) require a mandrel and wiper die to prevent wrinkling.
4. Maintenance and Replacement Standards
- Die wear limit: Replace the die if the groove diameter increases by 0.5 mm or if visible scratches appear.
- Lubrication: Use polymer-based lubricants during bending to reduce friction.
- Storage: Store dies vertically and avoid impact to prevent deformation.
Common Tube End Forming Defects and Prevention
Environmental Impact on CNC Benders and Fixes
