AM 101: Binder Jetting
Binder jetting requires no support structures, is accurate and repeatable, and is said to eliminate dimensional distortion problems common in some high-heat 3D technologies. Here is a look at how binder jetting works and its benefits for additive manufacturing.
What Is Binder Jetting?
Binder jetting is a 3D printing process that uses a liquid binding agent (think: glue) deposited onto a build platform to bond layers of powder material and form a part. Binder jetting can be used to print a variety of materials including metals, sands and ceramics. Markets for this process include industrial applications, dental and medical devices, aerospace components, part casting, luxury applications, and more.
Binder jetting 3D printing systems include machines from Desktop Metal, Digital Metal, ExOne, GE Additive, HP (known as Metal Jet Fusion), Viridis3D, and Voxeljet. Binder jetting services are also available from 3DEO, creator of a proprietary binder jetting technology (known as Intelligent Layering), as well as many of the suppliers mentioned.
How Does Binder Jetting Work?
First, a recoating blade spreads a thin layer of powder over the machine’s build platform. Next, the printhead (a carriage with inkjet nozzles, similar to those used in desktop 2D printers) precisely jets the binding agent into the powder according to the part’s geometry.
When the binder layer is complete, the build platform lowers, and the recoating blade spreads a fresh layer of powder across the platform and top of the part being printed. The printhead binds another layer and this process repeats until the part is complete. Finally, the part is cured while still encased in powder. The entire build box is then removed from the machine and loose powder is blown away with compressed air in a controlled environment. These green parts may be processed further to impart desired porosity and mechanical properties.
Because binder jetting is performed at room temperature, the process avoids dimensional distortions common to high-heat 3D printing processes, such as warping or curling. If sintering is required, only the bonded powder that forms the parts is subjected to the heat of the furnace, so leftover loose powder can be recycled without fear of degradation.
What Postprocessing Is Required?
Because the loose sand itself is the only support necessary for parts as they are being printed, support removal is not a typical postprocessing step for binder jetting. Many parts made via binder jetting, including sand casting cores and molds, typically require no additional processing and are ready to use in the green state after binder jetting.
Green parts are sometimes infiltrated with another material to strengthen them without sintering. However, most binder jetted parts are cured and placed in a sintering furnace to bond the powder metal and burn away the binder. This burn-off method causes shrinkage that must be accounted for in part design and limits the recommended part size. The sintering process results in an average surface roughness fine enough for many end-use parts and features without further processing. Sandblasting and polishing can enhance the surface finish when necessary. Hot isostatic pressing (HIPing) may be employed to achieve high densities and reduce porosity in solid metals and some ceramics.
Why Use Binder Jetting?
Binder jetting machines offer larger build volumes than many powder-bed 3D printing technologies and make it possible to stack multiple layers of parts on top of each other in the build box. Parts made this way can be nested within all three dimensions of the printer’s build volume, enabling parallel manufacturing of multiple parts at the same time. Materials used in binder jetting tend to be more affordable and more easily recycled than those used in other powder-based AM processes, which translates to cost savings and competitive part pricing. The technology is also accurate and repeatable, making it suitable for serial production of small, precise parts.