5
How MJF Works & Key Advantages
Multi Jet Fusion (MJF) builds parts by spreading a thin layer of nylon powder across a build bed, then using inkjet printheads to apply fusing and detailing agents. Infrared lamps fuse only the treated areas, layer by layer. This process delivers:
Speed & Throughput: Multiple parts in a single run for quick prototyping or production.
Isotropic Properties: Uniform strength in the XY plane for functional, load‑bearing components.
Fine Detail: Feature resolution down to ~0.3 mm for intricate geometries.
Minimal Supports: Self‑supporting powder bed eliminates dedicated support structures, reducing cleanup time.
These strengths make MJF ideal for complex assemblies, consumer goods, and end‑use parts that require consistent quality and repeatability.
Choosing the Right Material
MJF 3D printed nylon:
PA12 (General Purpose): Excellent toughness, chemical resistance, and affordability—ideal for enclosures, fixtures, and functional prototypes.
PA11 (High‑Ductility): Greater elongation and bio‑compatibility for wearable devices or parts requiring flexibility.
Filled Grades: Glass‑bead and carbon‑fiber fillers boost stiffness and dimensional stability; heat‑stabilized powders resist deformation in elevated‑temperature environments.
3D printing rule of thumb: prioritize PA12 for most applications and step up to specialty powders only when performance requirements demand it.
Wall Thickness & Feature Size Guidelines
Correct wall thickness and feature dimensions ensure reliable fusion and part strength:
Minimum Wall Thickness:
Unfilled PA12/PA11: ≥ 1.0 mm for non‑load areas; ≥ 1.5 mm for load‑bearing walls.
Filled Nylon: ≥ 1.5 mm non‑load; ≥ 2.0 mm for structural sections.
Small Features: Ribs, bosses, and channels should maintain at least 0.5 mm width; holes ≥ 1.0 mm diameter (1.5 mm for tight tolerances).
Hollow Sections: Incorporate drainage holes (Ø 2–4 mm) spaced no more than 50 mm apart to remove unfused powder.
By following these MJF 3D printing design guidelines, you’ll avoid weak zones, incomplete fusion, and part failures.
Detail Resolution & Orientation Strategies
Achieving crisp details and optimal strength involves both design and part orientation:
Fine Text & Logos:
Engraving: Depth ≥ 0.5 mm, stroke width ≥ 1.0 mm.
Embossing: Height ≥ 0.75 mm for reliable reproduction.
Feature Orientation: Align critical features parallel to the XY plane to leverage MJF’s superior XY resolution. Vertical features may exhibit slightly rougher surfaces.
Overhangs & Bridges: Angles up to 45° print smoothly; for steeper overhangs, add gentle chamfers or sacrificial ribs to maintain geometry. Span bridges ≤ 10 mm or include temporary supports for longer gaps.
Strategic orientation reduces post‑processing, enhances mechanical performance, and sharpens fine details.
Dimensional Tolerances & Fit Considerations
Quality assemblies depend on predictable dimensions and clearances:
Standard Tolerances:
Flat surfaces: ± 0.2 mm
Features < 50 mm: ± 0.3 mm
Large features > 100 mm: ± 0.4–0.5 mm
Fit Types:
Press Fit: Shaft +0.2–0.3 mm oversize.
Slip Fit: Clearance of 0.3–0.5 mm.
Post‑Print Machining: For critical holes or shafts, plan for +/-0.05 mm machining to achieve exact fits.
Use these guidelines to design assemblies that snap together easily or maintain tight alignment—key components in functional prototypes and end‑use parts.
Support Free Design & Overhang Management
One of the biggest advantages of Multi Jet Fusion is its support‑free nature. However, smart design further minimizes risk:
Overhang Angles: Keep primary overhangs ≤ 45°. For steeper angles, add fillets or breakaway supports that are easy to remove.
Deep Cavities: Include escape channels or perforations so powder evacuates effectively.
Long Bridges: For spans > 10 mm, add sacrificial ribs that can be sanded or broken off during post‑processing.
By embracing support‑free principles, you’ll reduce material waste, cut down on manual cleanup, and speed up your MJF 3D printing workflow.
Surface Finish & Post Processing Options
As‑built MJF 3D printed nylon parts have a matte, slightly granular finish (Ra ~ 10–15 µm). Enhance aesthetics and performance with these post‑processing methods:
1. Vibratory Tumbling: Mechanical abrasion for a uniformly smooth surface and de‑powdering.
2. Vapor Smoothing: Chemical smoothing (e.g., cyclohexane vapor) yields glossy finishes; test on samples to account for slight dimensional shifts.
3. Dyeing & Coatings: Nylon readily absorbs dyes; hydrophobic coatings improve fluid handling and weather resistance.
4. Painting & Dyeing: Use a primer to promote paint adhesion; dye the parts to get vibrant colors.
Assembly Features & Snap Fit Design
Designing for assembly streamlines production and user experience:
Snap‑Fits:
Cantilever snaps require wall thickness ≥ 1.5 mm, 20–30% taper, and relief notches to reduce stress.
Annular snaps benefit from uniform radial geometry and controlled clearance.
Alignment Aids: Bosses and pins (Ø 2–3 mm) with 0.3–0.5 mm clearance help self‑locate mating parts.
Sacrificial Tabs: Hold nested or interlocking parts in place during the build and break off cleanly afterward.
Thoughtful assembly features to cut down on manual fixturing and ensure reliable end‑use performance.
Pro Tips & Design Checklist
|
Design Tip |
Recommendation |
|
Orient for Strength |
Align key load-bearing features in the XY plane for optimal isotropic strength. |
|
Balance Material Distribution |
Avoid large solid masses or unbraced flat areas to prevent warping or curl. |
|
Validate Critical Features |
Print test coupons to confirm tolerances and feature accuracy before scaling up. |
|
Optimize Nesting |
Arrange parts tightly within the build volume to reduce cost per part. |
|
Account for Post-Processing Changes |
Allow for dimensional changes when planning dyeing, smoothing, or plating. |
|
Use Reliefs for Snap-Fits |
Add notches or fillets at stress points to prevent part cracking or failure. |
|
Design for Powder Removal |
Include escape holes (Ø 2–4 mm) in hollow sections for thorough powder cleaning. |
|
Label Your Parts |
Emboss part numbers or version codes with at least 0.75 mm height. |
|
Document Orientation & Specs |
FAQs
Q: What materials are available for MJF?
A: MJF primarily uses PA12 and PA11 nylon powders, with optional fillers like glass bead, carbon fiber, or heat stabilizers to tailor stiffness, thermal resistance, and surface finish.
Q: How precise are MJF parts?
A: Expect standard tolerances of ± 0.2–0.5 mm depending on part size. For tight fits, plan secondary machining to achieve ± 0.05 mm accuracy.
Q: Do MJF parts need support structures?
A: No dedicated supports are required—the powder bed acts as natural support. For extreme overhangs or bridges longer than 10 mm, consider sacrificial ribs or breakaway features.
Q: Can I dye or paint MJF prints?
A: Yes! 3D printed nylon readily accepts dye, paint, and coatings. Use a primer for paint and test on samples for color consistency.
Q: What is the typical surface finish?
A: As‑built Ra is ~ 10–15 µm with a matte look. Media tumbling or vapor smoothing can further refine the appearance.
Q: How do I get started with Hi3DP?
A: Simply upload your CAD file to the Hi3DP platform, choose your material and finish options, and receive instant quotes. Our experts are ready to advise on MJF 3D printing design guidelines and bring your parts to life. Check out our user guide here >>
