Binder Injection Additive Manufacturing is a flexible new method for 3D printing with coarse, inexpensive, or recycled powders. It combines elements of material extrusion and binder jetting, but instead of spreading thin layers of powder, it injects liquid binder directly into a loosely packed powder bed. This simplifies the hardware, reduces the need for fine powders, and enables faster deposition.

A key feature of binder injection is its versatility across materials. Different types of binder–powder interactions allow the process to be tailored to specific applications. These include:

• Adhesive binders, such as PVA glue in sand, which harden as the liquid evaporates.
• Reactive binders, like sodium silicate in cement, which chemically react to form a solid.
• Dissolving binders, such as acetone dissolving ABS powder, which then resolidify.
• Thermal binders, like hot wax, which cool and solidify—or even melt the surrounding powder.
• Displacing binders, such as epoxy displacing loose fibres, forming a composite on curing.

This range of mechanisms makes binder injection compatible with a wide array of low-cost materials, including glass, sawdust, sugar, cement, plastic, and fibres.

The process works by immersing a nozzle into the powder and injecting binder along a toolpath. Maintaining a stable interaction with the powder requires the nozzle to be immersed at a controlled depth. A simple predictive model relates the injection rate, powder packing, and nozzle speed to the width of the printed track. This enables reliable tuning of process parameters for different materials and geometries.

Print speeds of over 80 mm³/s have been achieved, exceeding typical desktop extrusion rates and approaching those of commercial binder jet systems. Demonstrations include printing complex shapes such as vases, Benchy models, and calibration cubes, with no issues at self-intersecting paths thanks to the natural collapse and refilling behaviour of the powder bed.

Post-processing varies with the material: cement parts are cured with water; glass parts sintered to remove binder; sugar parts freeze-dried; and organic or composite prints can be strengthened with wax or resin infusion. One sintered glass sample showed a 1,345% increase in strength after heat treatment, reaching 12 MPa.

Binder injection is not tied to any specific machine type and can be implemented on Cartesian printers, robotic arms, or gantry systems. With its material flexibility, low equipment cost, and high deposition rate, it opens new possibilities for sustainable, scalable additive manufacturing—from large architectural components to biodegradable tools and artistic forms.