Lesson 8.5ShapeChapter 8 · Additive manufacturing

Binder jetting

Inkjet heads glue powder, then the part is cured or sintered (binder jetting)

Binder jetting builds a part by spreading thin layers of powder and printing a liquid glue, called binder, onto each one with an inkjet head. It works much like an office printer, but with powder instead of paper. It matters because it is one of the fastest ways to print metal parts in batches, and foundries use it to print sand molds for casting.

Photo: Oak Ridge National Laboratory, CC BY 2.0, via Wikimedia Commons

Binder jetting build box in cross-section, with depowdering and furnace sinteringCircled numbers match the steps below; steps 2 to 4 repeat for every layer.

How it works

Slice the model. Software cuts the 3D model into thin layers. Parts can be packed tightly and stacked, because the powder holds them up.
Spread a layer. The supply piston rises and a recoater (a roller or blade) spreads a thin, even layer of powder, typically 0.05–0.1 mm for metal.
Jet the binder. An inkjet print head sweeps across and drops tiny droplets of binder only where the part's slice should be. The glued grains stick together; the rest stay loose.
Lower and repeat. The build box drops by one layer and the cycle repeats until the box is full. No laser or heat is needed during printing.
Cure and depowder. The box is warmed to harden the binder, then the loose powder is brushed and blown away and reused. The glued "green" parts are fragile, like chalk.
Sinter in a furnace. Metal parts go into a furnace near their melting point, where the binder burns off and the grains fuse together. The part shrinks by roughly 15–20% in each direction as it densifies.

Key facts

Materials: Stainless steels, tool steels, copper and other metals; foundry sand; ceramics; gypsum for full-color models
Typical parts: Small metal parts in batches, sand molds and cores for casting, ceramic parts, color figurines
Part size: Metal parts usually fist-sized or smaller; sand printers build boxes up to several meters long
Precision: Metal: about ±1–2% after sintering because of shrinkage; sand molds: about ±0.3 mm
Surface finish: Matte and slightly grainy, like a fine casting; often blasted or polished
Batch size it suits: Hundreds to tens of thousands of small metal parts; one-off to small runs of sand molds
Tooling and machine cost: No tooling; machines plus furnaces cost a few hundred thousand to over a million dollars
Speed: Printing is fast, often hours per full box, but curing and sintering add a day or more

Strengths and limits

Strengths

Fast printing of a whole box of parts, with no supports
No heat while printing, so no warping or locked-in stresses
Prints sand molds and cores with no pattern, straight from a file
Lower cost per metal part than laser powder bed fusion at volume

Limits

Parts shrink during sintering, which makes tight tolerances hard
Green parts are fragile and need careful handling
Some porosity can remain, so strength can trail fully melted metal
Thin walls and large flat parts can sag or distort in the furnace

Where it's used

FoundriesSand molds and cores for engine blocks, pump housings, prototypes
AutomotiveSmall metal brackets and fittings; molds for cast parts
Consumer goodsSteel parts for locks, tools and eyewear in batches
IndustrialPump impellers, nozzles, ceramic parts
Art and designFull-color figurines and architectural models in gypsum

How to recognize it

A matte, slightly grainy surface, a little like a fine casting or sintered metal.
No support marks, and parts that look slightly soft-edged.
On sand molds, a sandy, crumbly texture with faint stair-steps on curves.
Very small metal parts made in large, identical batches.

Compare with

Laser powder bed fusion8.4melts metal powder with a laser instead of gluing it; denser parts with no shrinkage, but slower and costlier.Metal injection molding (MIM)9.2also produces green parts that are sintered; needs a mold, but is cheaper at very high volumes.Sand casting1.1binder jetting can print its molds directly, with no wooden or metal pattern.

Watch it

Mars Gadgets · Powder layer, inkjet binder and sintering, for beginners

AM Media | The Cool Parts Show · Industry journalists on binder jetting and its sintering step

CATI: Computer Aided Technology is now GoEngineer · A printer demo, with green parts being depowdered

voxeljet · Printed sand molds and cores, then poured metal

See real photos

Wikipedia: Binder jetting — process steps, materials and history; text-led
Wikipedia: 3D printing processes — binder jetting compared with other additive processes
Wikimedia Commons photo search

Remember

Binder jetting glues powder with inkjet droplets, layer by layer, with no heat during printing.
Metal parts come out fragile and must be sintered in a furnace, where they shrink.
It suits batches of small metal parts and printed sand molds for casting.