1. Introduction
Dimensional tolerancing is a fundamental aspect of manufacturing, ensuring that individual components fit together and function as intended. HP Multi Jet Fusion (MJF) technology offers an innovative approach to additive manufacturing, allowing for high-precision parts that can be assembled with other components, including traditionally manufactured metal parts. This white paper provides an in-depth analysis of dimensional tolerancing for HP MJF, focusing on International Tolerance (IT) grades, process capability metrics, and best practices for achieving optimal results.
2. The Importance of Dimensional Tolerancing in HP MJF
In additive manufacturing, tolerances define the permissible variation in dimensions, ensuring that parts remain functional while maintaining production efficiency. MJF’s capability to produce high-resolution parts enables engineers and designers to optimize tolerances for different applications, from precision assemblies to high-tolerance mechanical fits.
Dimensional tolerancing in HP MJF is influenced by several factors:
- Material properties – The behavior of polyamide powders under thermal exposure impacts dimensional accuracy.
- Process parameters – Layer thickness, cooling rate, and post-processing affect part shrinkage and tolerances.
- Design considerations – Geometries, wall thicknesses, and support structures influence the final dimensional stability.
3. International Tolerance (IT) Grades for HP MJF
Dimensional tolerances in manufacturing are standardized under ISO 286/ANSI B4.2-1978, which defines International Tolerance (IT) Grades. These grades establish tolerance limits based on nominal size and manufacturing process capabilities.
IT Grades and Their Applications
| IT Grade | Application |
| 01 – 4 | Measuring tools, high-precision components |
| 5 – 11 | Engineering fits, bearings, machining (grinding, turning) |
| 12 – 16 | Large manufacturing processes (die casting, stamping, sand casting) |
HP MJF technology typically achieves IT10 – IT12 tolerances, making it suitable for engineering applications requiring moderate to high precision.
Standard Tolerance Values (mm) for HP MJF
| Nominal Size (mm) | IT 9 | IT 10 | IT 11 | IT 12 | IT 13 | IT 14 | IT 15 |
| 10 | 0.025 | 0.040 | 0.075 | 0.140 | 0.210 | 0.260 | 0.400 |
| 50 | 0.090 | 0.140 | 0.220 | 0.390 | 0.580 | 0.900 | 1.500 |
| 100 | 0.120 | 0.190 | 0.350 | 0.580 | 0.900 | 1.500 | 2.700 |
| 200 | 0.220 | 0.350 | 0.580 | 1.200 | 1.800 | 3.200 | 5.400 |
4. Process Capability and Statistical Tolerancing in HP MJF
4.1 Process Capability Index (CpkC_{pk})
Process capability quantifies how well a manufacturing process produces parts within tolerance. It is defined as:
Cpk=Cp×(1−2×bias)C_{pk} = C_p \times (1 – 2 \times \text{bias})
Where:
- CpC_p = Repeatability (low variability)
- Bias = Deviation from nominal
- CpkC_{pk} = Process capability considering both repeatability and accuracy
4.2 Evaluating Process Performance
| CpkC_{pk} | Sigma Level | Dimensions Within Specs (%) | Dimensions Out of Specs (Units per Million) | Part Yield (10 Dimensions) |
| 0.33 | 1 | 68.27 | 317,300 | 2.20 |
| 0.67 | 2 | 95.45 | 45,500 | 62.77 |
| 1.00 | 3 | 99.73 | 2,700 | 97.33 |
| 1.33 | 4 | 99.9937 | 63 | 99.94 (Desired) |
| 1.50 | 5 | 99.99966 | 3.4 | 100 |
| 1.67 | 6 | 99.99997 | 0.6 | 100 |
A CpkC_{pk} ≥ 1.33 (4 sigma) is the desired benchmark for statistical process control (SPC) in MJF, ensuring high part yield with minimal defects.
5. Optimizing Dimensional Tolerances in HP MJF
5.1 Best Practices for Designers
- Consider shrinkage and warping – HP MJF parts may shrink 1-2%, requiring compensation in CAD models.
- Account for powder spreading – Feature resolution is affected by powder deposition accuracy.
- Optimize support structures – Well-designed supports reduce distortion and improve tolerance consistency.
5.2 Quality Control Strategies
- In-situ monitoring – HP Jet Fusion printers use real-time thermal imaging to ensure consistent layer fusion.
- Post-processing compensation – Techniques such as machining, annealing, and controlled cooling improve final part tolerances.
- Statistical sampling – Implementing Cpk-based sampling minimizes costly 100% inspections.
6. HP Jet Fusion 3D Process Control
HP Jet Fusion technology integrates hardware and software control systems to maintain tight dimensional tolerances. The HP 5200 Series enables:
- Dimensional profiling – Automated calibration of part tolerances.
- Fleet uniformity – Ensuring consistent tolerances across multiple printers.
- Process repeatability – Achieving high yield through real-time process feedback.
7. Conclusion
Dimensional tolerancing in HP Multi Jet Fusion is critical for ensuring precision, functionality, and manufacturability. By applying statistical process control and optimizing design strategies, engineers and designers can achieve consistent, high-quality parts with minimal post-processing.
For manufacturers and designers looking to leverage HP MJF for precision engineering applications, RapidMade offers industry-leading expertise in design, prototyping, and production.
Contact RapidMade today at rapidmade.com to optimize your 3D printing workflow!