Binder Jetting for Investment Casting: AM Is Transforming an Age-Old Industrial Process

Investment casting has come a long way from its origins, with AM now playing a lead role.

Investment casting is one of humanity’s oldest manufacturing technologies. In fact, investment casting, which was first done with beeswax, has been creating like-items for more than 5,000 years. Over the course of the millennia, the evolution of casting has seen a number of marked improvements. New investment materials have been developed and more effective production methods have been introduced, giving the manufacturing method reach into a number of high-tech markets.

Though investment casting has been around a long time, it’s still developing. One of the most promising recent developments in casting has been the introduction of additive manufacturing (AM), which can build high-precision sand cores of complex geometries. This new method, known as binder jetting (which can be used to build with metal, carbon fiber and other materials), leverages highly granular material and a binding agent to create models.

How Binder Jetting Works

Binder jetting technology builds models by depositing a binding agent into a layer of powdered material. To construct artifacts, binder jetting systems lay down a layer of powder material (for castings this is typically a sand-based material) that is selectively impregnated with a binding agent adhering the granular substrate into a cohesive whole. After that step is complete, the process begins anew until the model is finished.

Additive Abilities in Investment Casting

Because binder jetting technology functions similar to a 2D ink-jetting process that employs extremely accurate deposition technology, features can be built with high resolution. When combined with finely granulated material, binder jetting can produce high-definition 3D models.

One of the attributes that make binder jetting attractive is its scalability. Because the system relies on binder deposition which can move quickly and work rapidly, the system can be used to build objects of large size rapidly.

The Downside of Binder Jetting for Investment Casting

NASA engineers show off a cast part that began as a binder jet print.

NASA engineers show off a cast part that began as a binder jet print.

Like all technologies, binder jetting has its shortcomings. Most notably, binder jetting builds parts with limited mechanical abilities. Because parts are comprised of glued-together powders, reliable stress analysis is impossible and a consistent material is unlikely unless secondary processes like casting are employed. In addition, most binder jet parts are fragile and cannot be articulated to test a part’s function in any meaningful way. For both of those reasons, it’s not recommended that binder jetting with sand be used for anything but mold production.

Major Players in the Sand Casting, Binder Jetting Field

As of now, the two biggest players in sand cast binder jetting are Germany’s voxeljet and U.S.-based ExOne. Though both of these companies have been able to become brand names in the world of additive sand casting, the entrance of Hewlett-Packard into the AM sphere could alter the playing field in coming years. HP’s 3D printing technology uses a method that is similar to binder jetting and the company says it may have the potential to build models of different materials and properties all from the same substrate. That, by itself, should put ExOne and voxeljet — and the rest of the 3D printing community — on high alert.

Binder jetting systems range in price from the low $200,000s for an entry-level system to $1,400,000 for the largest machines.

In the end, binder jetting technology dramatically increases the design freedom available to engineers working with cast products. In other words, binder jetting is an excellent resource for creating complex, one-off, or short-run designs that can’t be produced economically by other means. Still, binder jetting is hindered by the fact that, in the case of sand casting, it’s only a preliminary manufacturing process from which a finished product still needs to be made. Sprues, material validation and casting methodology must be taken into account when producing a part using binder jet technology.