---
type: process
name: "Multi Jet Fusion (MJF)"
category: "Forming"
subcategory: "Additive Manufacturing"
materials: ["Plastic"]
tolerances: "±0.008 in (±0.2 mm) or ±0.3% of nominal, whichever is greater. Tighter features are machined or reamed after the build."
volumes: "10–10,000 parts per year; unit cost is close to flat across that range when builds are nested well"
lead_time: "3–7 business days. A full build runs roughly 10–15 hours of printing plus a comparable controlled cooling cycle before depowdering."
url: https://manufacturingprocesses.org/processes/forming/multi-jet-fusion-mjf
---

# Multi Jet Fusion (MJF)

Multi Jet Fusion prints a fusing agent onto nylon powder and drives it with infrared energy, fusing whole layers at once for high throughput.

- **Category**: [Forming](https://manufacturingprocesses.org/processes/forming.md)
- **Family**: Additive Manufacturing
- **Materials**: Plastic
- **Typical tolerances**: ±0.008 in (±0.2 mm) or ±0.3% of nominal, whichever is greater. Tighter features are machined or reamed after the build.
- **Surface finish**: Ra 250–400 µin (6–10 µm) as built, a fine matte grain slightly finer than SLS. Vapor smoothing reaches roughly Ra 40–120 µin (1–3 µm) and seals the surface.
- **Typical volumes**: 10–10,000 parts per year; unit cost is close to flat across that range when builds are nested well
- **Lead time**: 3–7 business days. A full build runs roughly 10–15 hours of printing plus a comparable controlled cooling cycle before depowdering.

## Overview

Multi Jet Fusion (MJF) is a powder bed fusion process that inkjets a carbon-black fusing agent onto nylon powder and then sweeps an infrared lamp across the whole layer, fusing every printed region at once rather than tracing them with a laser. A detailing agent is jetted at the boundaries to sharpen edges and suppress thermal bleed. Standard layer height is 0.0031 in (80 µm).

Fusing whole layers is what makes MJF fast: a full 15 × 11.2 × 15 in (380 × 284 × 380 mm) build takes on the order of 10–15 hours regardless of how many parts are packed into it, so unit cost falls sharply with nesting density. Parts come out gray to near-black, dense, and closer to isotropic than [SLS](/processes/forming/selective-laser-sintering-sls) — PA12 lands near 7,000 psi (48 MPa) tensile with 15–20% elongation in XY.

Accuracy is ±0.008 in (±0.2 mm) or ±0.3% of nominal, whichever is greater. MJF is the usual choice for functional nylon parts from tens to about 10,000 pieces a year.

## How it works

1. **Preheat the powder bed.** PA12 powder is spread and the build area is held just below the melting range, so the lamps need only supply the final energy to fuse.
2. **Recoat.** A 0.0031 in (80 µm) layer is spread across the bed by a recoater moving in one axis.
3. **Jet agents.** A carriage carrying thermal inkjet arrays passes over the layer, depositing fusing agent where the cross-section is solid and detailing agent immediately around its perimeter. The fusing agent is carbon-loaded so it absorbs infrared strongly; the detailing agent cools the boundary to keep it sharp.
4. **Fuse.** Infrared lamps on the same carriage sweep the full layer. Every printed region reaches fusion temperature simultaneously — this is the throughput advantage over point-by-point laser scanning.
5. **Repeat.** The bed indexes down and steps 2–4 repeat. Build time is a function of layer count, not part count.
6. **Cool.** The build unit is moved to a processing station and cooled in a controlled cycle. Cooling typically takes as long as the print or longer, and rushing it warps flat parts.
7. **Depowder and finish.** Loose powder is vacuumed and bead-blasted away and recycled at a refresh ratio around 20–30% virgin. Parts are naturally gray with a slightly mottled surface, so most production work is dyed black; vapor smoothing and vibratory finishing are also common.

## Design guidelines

### Wall thickness
0.020 in (0.5 mm) prints, but use 0.032 in (0.8 mm) for anything structural and 0.040 in (1.0 mm) for larger panels. As with any powder bed process, distortion happens during cooling rather than printing.

### Escape holes
Enclosed cavities fill with un-fused powder. Provide two or more escape holes of at least 0.20 in (5 mm) diameter, positioned so compressed air can be blown through in a straight line. Powder that stays in an internal channel is essentially permanent.

### Bulk sections
Keep solid sections under about 0.6 in (15 mm). Heat retained in a thick region continues to fuse surrounding powder, growing the part and causing sink and warp. Shell and rib instead.

### Detail and text
The detailing agent gives MJF crisper edges than SLS. Embossed detail works from 0.020 in (0.5 mm) wide and tall; engraved text is legible from about 0.08 in (2 mm) cap height, which is finer than SLS supports.

### Clearances
Allow 0.016 in (0.4 mm) between moving surfaces on small features and 0.032 in (0.8 mm) on larger assemblies. MJF's thermal bleed is tighter than laser sintering, so gaps can be smaller, but powder still has to be blown out from between the surfaces.

### Nesting and orientation
Because you are billed on the fraction of the build unit consumed, geometry that nests densely is materially cheaper. Orientation still matters for cosmetics: down-facing surfaces and steep walls pick up slightly more texture, and long flat parts should be angled to spread thermal load.

### Threads
Use heat-set or press-in inserts below M6. Direct-tapped threads in MJF PA12 hold better than in FDM but still strip under repeated assembly; see the [tap drill chart](/charts/tap-drill-chart) for pilot diameters.

| Feature | Recommended | Limit | Why |
| --- | --- | --- | --- |
| Wall thickness | 0.032 in (0.8 mm) | 0.020 in (0.5 mm) | Thin walls distort during cooling |
| Escape hole | 0.30 in (8 mm) | 0.20 in (5 mm) | Powder must be blown clear |
| Hole diameter | 0.040 in (1.0 mm) | 0.020 in (0.5 mm) | Smaller holes retain fused powder |
| Embossed detail | 0.032 in (0.8 mm) | 0.020 in (0.5 mm) | Detailing agent limits edge sharpness |
| Clearance, moving | 0.032 in (0.8 mm) | 0.016 in (0.4 mm) | Powder must clear the gap |
| Solid section | 0.4 in (10 mm) | 0.6 in (15 mm) | Heat soak grows and warps the region |

## Cost drivers

MJF is priced on the fraction of the build unit a part occupies, and because a full build takes roughly the same time whether it holds one part or a thousand, packing density dominates everything else. Bureaus running MJF at high utilization can quote per-part prices that stay nearly flat from 10 pieces to several thousand — the reason MJF has displaced low-volume injection molding for many nylon housings and brackets.

Powder is the second cost. A refresh ratio near 20–30% virgin is typical, better than laser sintering, but you still pay for powder that leaves as waste. Dyeing, vapor smoothing, and inserts are line items on top.

Volume breakpoints: MJF competes with FDM and SLA below about 50 parts, dominates from roughly 50 to 10,000 parts a year for functional nylon, and gives way to [injection molding](/processes/forming/injection-molding) above that — though the crossover moves higher for large or geometrically complex parts where tooling would be expensive.

1. Design for nesting: compact, interlocking geometry buys real savings.
2. Hollow and rib bulk sections; you are charged on the volume you occupy.
3. Batch orders into one build rather than releasing them piecemeal.
4. Skip dyeing on internal parts — undyed gray is functionally identical.
5. Consolidate multi-part assemblies into one printed component to remove fasteners and assembly labor.

## FAQ

### What tolerance can MJF hold?

±0.008 in (±0.2 mm) or ±0.3% of the nominal dimension, whichever is larger. That is tighter than SLS, largely because the detailing agent controls thermal bleed at part boundaries. Bearing bores and dowel holes are still normally reamed.

### Why are MJF parts gray or black?

The fusing agent is carbon-loaded so it will absorb infrared energy, which leaves the finished part a mottled gray. Most production parts are dyed black to even out the appearance; the dye penetrates a few tenths of a millimeter and does not change mechanical properties.

### Is MJF stronger than SLS?

Slightly, and more consistently. MJF PA12 reaches roughly 7,000 psi (48 MPa) tensile with 15–20% elongation in XY and shows less Z-axis penalty than laser sintering because whole layers fuse at once. The practical difference matters most on thin-walled parts loaded across layers.

### What is the minimum wall thickness for MJF?

0.020 in (0.5 mm) will print, but 0.032 in (0.8 mm) is the sensible minimum for anything that carries load, and 0.040 in (1.0 mm) for larger flat panels. Distortion comes from the cooling cycle, not the print itself.

### Does MJF require support structures?

No. Un-fused powder supports every layer, so parts nest in all three axes and internal geometry prints freely. The consequence is that every enclosed cavity must have escape holes of at least 0.20 in (5 mm) to get the powder out.

### How does MJF cost scale with quantity?

Nearly flat. A build takes about the same time whether it contains one part or hundreds, so cost per part is set by how much of the build unit each one occupies. That makes MJF unusually predictable for quantities from tens to several thousand.

### When should I switch from MJF to injection molding?

Somewhere around 5,000–10,000 parts a year for small, simple geometry, where tooling amortizes quickly. For large parts or those with many undercuts and sliding actions, the tooling cost rises and MJF stays competitive well past that point.

## Alternative processes

- [Selective Laser Sintering (SLS)](https://manufacturingprocesses.org/processes/forming/selective-laser-sintering-sls.md): Selective laser sintering fuses nylon powder layer by layer with a laser, so the surrounding loose powder supports the part and no supports are needed.
- [Injection Molding](https://manufacturingprocesses.org/processes/forming/injection-molding.md): Injection molding forces molten thermoplastic into a steel mold under high pressure, producing high-volume identical plastic parts.
- [Fused Deposition Modeling (FDM)](https://manufacturingprocesses.org/processes/forming/fused-deposition-modeling-fdm.md): Fused deposition modeling extrudes molten thermoplastic filament along programmed paths so each layer welds to the one beneath it.
- [CNC Machining](https://manufacturingprocesses.org/processes/cutting/cnc-machining.md): CNC machining removes material from solid stock with a programmed cutting tool, producing accurate parts directly from a CAD model with no tooling.
- [Vacuum Casting (Urethane Casting)](https://manufacturingprocesses.org/processes/forming/vacuum-casting.md): Vacuum casting, known in the US as urethane casting, pours polyurethane resin into a silicone mold under vacuum to copy a master pattern for short runs.

## Related processes

- [Selective Laser Sintering (SLS)](https://manufacturingprocesses.org/processes/forming/selective-laser-sintering-sls.md): Selective laser sintering fuses nylon powder layer by layer with a laser, so the surrounding loose powder supports the part and no supports are needed.
- [Rapid Prototyping](https://manufacturingprocesses.org/processes/forming/rapid-prototyping.md): Rapid prototyping builds a part layer by layer directly from a CAD model, with no tooling and no minimum order quantity.
- [Fused Deposition Modeling (FDM)](https://manufacturingprocesses.org/processes/forming/fused-deposition-modeling-fdm.md): Fused deposition modeling extrudes molten thermoplastic filament along programmed paths so each layer welds to the one beneath it.
- [Binder Jetting](https://manufacturingprocesses.org/processes/forming/binder-jetting.md): Binder jetting prints liquid binder into a powder bed to hold each layer, producing green parts that are later sintered or infiltrated.
- [Stereolithography (SLA)](https://manufacturingprocesses.org/processes/forming/stereolithography-sla.md): Stereolithography cures liquid photopolymer layer by layer with a scanning UV laser, giving the smoothest surfaces in additive manufacturing.

---

*Source: [Manufacturing Processes](https://manufacturingprocesses.org/processes/forming/multi-jet-fusion-mjf)*

*Last updated: August 11, 2026*