BJT

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Binder
Jetting

Inkjet printheads selectively deposit liquid binder into powder beds at high speed — sand casting tooling, full-colour models, and high-volume metal parts via furnace sintering.

Speed at scale

Binder Jetting deposits binder across the full layer width simultaneously — delivering build rates far exceeding laser-based processes. Parts are "green" and fragile until cured and sintered, but the separation of build and sinter steps enables enormous throughput.

Desktop Metal and ExOne systems produce metal parts up to 100× faster than LPBF — enabling competitive economics for medium-volume metal production previously requiring expensive die casting tooling.

Applications

Sand casting moulds and cores for foundry production
Full-colour architectural, design, and presentation models
Stainless steel, bronze, and copper metal parts
Ceramic components for electronics and industrial filtration
High-volume automotive metal bracket and fastener production

Metal Binder Jetting process steps

1. Print — binder deposited into metal powder bed layer by layer
2. Cure — part dried in low-temperature oven to harden binder
3. Depowder — fragile "green" part removed from powder cake
4. Sinter — furnace burns out binder, sinters metal (~15–20% shrinkage)
5. Infiltrate (optional) — bronze fills residual porosity for density

Binder Jetting Specifications

Layer Height50–400µm

Build VolumeUp to 800×500×400mm

Tolerances±0.3–0.5mm (post-sinter)

MaterialsSS, sand, ceramics, full-color

Sintered Density~97% (metal)

Build SpeedVery High vs. LPBF

Sinter Shrinkage~15–20%

Best ForCasting, high-vol. metal AM

Fundamentals

BJT Basics

How inkjet printheads deposit liquid binder into powder beds at high speed — the fastest AM process for sand, ceramics, and high-volume metal production.

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Binder Deposition

Industrial inkjet heads jet liquid binder selectively into powder beds. Unlike MJF, no energy source cures the layer during printing — binder simply adheres particles together. The result is a fragile "green" part embedded in the powder cake.

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Why It's Fast

Binder Jetting has no thermal energy input during printing — no waiting for powder to cool between layers. Multi-pass printhead arrays cover enormous areas in seconds. Desktop Metal claims 100× faster throughput vs LPBF for metal parts.

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Green Part & Curing

After printing, the "green" part is extremely fragile — held together only by dried binder. It must be carefully unpacked and cured in a low-temperature oven (60–90°C) to harden the binder before depowdering.

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Sintering & Shrinkage

Metal binder-jetted parts undergo furnace sintering (1200–1380°C) which burns out the binder and fuses metal particles. This causes ~15–20% linear shrinkage — predictable and compensated for in the CAD model. The sintered part reaches ~97% theoretical density.

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Sand Casting Application

Sand binder jetting produces casting moulds and cores directly from CAD — no pattern making required. Foundries can produce first-off castings in days vs weeks. ExOne and voxeljet systems produce automotive engine blocks and aerospace casting moulds at commercial volumes worldwide.

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Full-Colour & Ceramics

Silica-based gypsum powder combined with CMYK binding agents produces full-colour architectural models and art objects. Ceramic binder jetting produces high-purity alumina, zirconia, and silicon carbide parts for filtration, electronics, and industrial applications.

Step 01

Print

Binder jetted into powder bed layer by layer. No energy input — extremely fast build rate.

Step 02

Cure

Oven cure at 60–200°C hardens binder. Part still fragile — "brown" state for metals.

Step 03

Depowder

Carefully excavate and brush clean. Compressed air clears cavities. Powder recycled.

Step 04

Sinter

High-temperature furnace burns out binder and sinters metal. 15–20% shrinkage occurs.

Step 05

Finish

Optional bronze infiltration for full density. CNC, polish, heat treat as required.

Deep Engineering

BJT Engineering

Metal Binder Jetting vs LPBF economics: At 500+ identical parts per month, metal Binder Jetting achieves cost parity with — or beats — LPBF due to dramatically higher throughput and lower machine cost per part. The tradeoff: maximum achievable density is ~97% (vs >99.5% LPBF) and tolerances are ±0.3–0.5mm vs ±0.1mm. For non-critical structural applications, the economics are compelling.

100×

Faster than LPBF
(Desktop Metal claim)

Sintering Science & Shrinkage Control

Linear Shrinkage ≈ 15–20% (isotropic for round parts)
Scale factor in X,Y,Z: typically 1.18–1.22×
Density after sinter: ~95–97% theoretical

Shrinkage is not perfectly isotropic — Z-axis may shrink 1–3% differently than XY
Part geometry affects local shrinkage — thin walls sinter faster than thick sections
Setter plates and support media in furnace control part droop during high-temp sintering
Shrinkage simulation (Desktop Metal Live Sinter, Simufact AM) predicts and pre-compensates distortion
316L SS shrinks ~16–17%; 17-4 PH shrinks ~15–16%; Inconel 625 shrinks ~18–20%

Metal BJ vs MIM vs LPBF

Factor	Metal BJ	MIM	LPBF
Relative Density	~97%	~99%	>99.5%
Tolerances	±0.3–0.5mm	±0.3–0.5%	±0.1mm
Tooling Cost	None	High (moulds)	None
Min Volume	1 part	10,000+ parts	1 part
Unit Cost (high vol.)	Low	Lowest	High

Binder Systems Engineering

Organic binder (standard): polyvinyl alcohol or acrylic in water — low residue, suitable for most alloys
Furan binder (sand): furfuryl alcohol with acid catalyst — fast set, high green strength for large sand cores
Binder burnout profile: critical for metal AM — incomplete burnout leaves carbon contamination affecting final alloy properties
Multi-step debind: catalytic debind (acid vapour attacks backbone) + thermal debind gives cleanest burnout
Desktop Metal uses a proprietary aqueous binder (Separable Supports System) — no solvent required

Sand Casting Integration Engineering

Furan-bonded silica sand: permeability 150–200 AFS for good gas escape during pouring — avoids casting porosity
Binder content: 1.8–2.5% by weight — higher binder improves strength but reduces gas permeability
Hollow cores achievable at 3mm wall — eliminates material in large cores, improves gas permeability
voxeljet VX4000 (4×2×1m build volume) produces full car body casting moulds in a single print
Dimensional accuracy: ±0.5mm on printed dimensions — comparable to traditional sand casting patterns

DfAM for Binder Jetting

Minimum wall: 1.5mm for metal BJ (green strength constraint); 3mm recommended for depowdering robustness
Avoid sharp internal corners — stress concentration during sintering causes cracking; fillet ≥0.5mm
No supports needed during printing — design with sintering setter support in mind instead
Exit holes for powder: ≥5mm diameter — more critical for BJ than SLS due to binder residue
Sinter distortion is geometry-dependent — simulate with Live Sinter before committing to first print

Quality Control for Metal Binder Jetting

Archimedes density measurement (ASTM B962) per lot — verifies sintered density against specification
Dimensional mapping: CMM on sintered parts accounts for actual vs predicted shrinkage
Tensile specimens sintered alongside production parts — per-furnace-run mechanical traceability
CT scanning recommended for internal geometries — sintering densification voids are not always visible externally
Surface roughness (Ra): as-sintered ~4–8µm — CNC or glass bead blasting achieves Ra <1.6µm