There are many different approaches to direct metal additive manufacturing—from laser powder bed fusion to binder jetting. However, there are also non-direct options that can already offer some very real solutions for metal part production applications. One of the most influential proponents for non-direct metal AM is the German company voxeljet, a specialist in industrial sand and polymer binder jet 3D printing.
Today, voxeljet’s binder jetting technology plays an integral role in the production of metal parts by creating molds or patterns which can then be used in metal casting. This process, called Additive Casting, is a dual approach that combines the benefits of 3D printing with the time-tested reliability and quality of casting. 3D printing for metal casting today is a fairly well-established and certified process, which has been in use for over two decades in the automotive, aerospace, engineering, heavy industry and art sectors, among others. Compared to other metal AM processes, additive casting also offers certain advantages, including fewer size limitations, broader material diversity and lower costs. In regards to the latter, compared to Direct Metal Laser Sintering (DMLS), where powder costs range from about €300 to €400 per kilogram, a 3D printed sand mold costs approximately €5 per box liter and casting steel costs between €6.50 to €32 per kg.
In terms of size, voxeljet’s binder jetting systems can build molds and patterns up to 4,000 x 2,000 x 1,000 mm, enabling the production of large components—or several smaller components. For even larger metal parts, molds can also be printed in several pieces and assembled before casting. To date, the size of direct metal 3D printed parts has been more limited in scope.
Looking at materials, additive casting gives customers the freedom to choose between hundreds of metal alloys. Alloys can also be tailored to meet specific part properties in special cases. Notably, materials that are notoriously challenging to 3D print directly, such as Magnesium, can be used, especially for applications that require lightweighting, like in aerospace.
Proof of concept
To illustrate how additive casting is not only viable but also advantageous, voxeljet highlights a case study undertaken by software specialist Autodesk and Aristo-Cast Inc, an investment casting foundry based in Almont, Michigan. The goal of the proof of concept was to manufacture an aircraft seat frame using the additive casting process. The overwhelming success of the project—which we’ll look at in more detail below—showcases the hybrid process’ unique manufacturing capabilities and power.
In developing the aircraft seat frame, Autodesk and Aristo-Cast set out to significantly reduce the part’s weight, to improve fuel consumption, carbon emissions and, consequently, cost savings per aircraft. Because of the part’s size (432 x 442 x 20 mm) and the need to produce it in a single piece, DMLS was not a viable option. The cost of DMLS for the part would have been prohibitive (three times higher).
By opting to use additive casting—and specifically by using voxeljet’s binder jetting technology—the partners successfully produced an aircraft seat frame with 56% less mass. 30% of this reduction was due to the optimized lattice structure design integrated into the part, and the other 26% was the result of switching from an aluminum (Al) alloy to magnesium (Mg). The final cast part weighed less than 800 grams.
In addition to improving the part’s design and meeting the project’s weight goals, Autodesk and Aristo-Cast were also able to improve production efficiency. Thanks to voxeljet’s large build envelopes and the ability to strategically nest parts in the build space, it was actually possible to produce 80 seat frames in a single build.
On-demand, right on time
In the aforementioned proof of concept, voxeljet’s binder jetting technology was employed by its customer Artisto-Cast, which has a voxeljet VX1000 at its Michigan facility. However, voxeljet also offers worldwide, on-demand services for casting molds and patterns. With production facilities in Germany, the U.S. and China, voxeljet can produce parts with dimensions of up to 4,000 x 2,000 x 1,000 mm for sand molds and 1,000 x 600 x 500 mm for plastic patterns. This service offers customers a cost-efficient and low-risk entry into additive casting.
voxeljet also has an extensive, globally operating network of resale and foundry specialists, providing access to virtually every casting process and metal material, whether its magnesium, aluminum, gray iron and iron castings, steel castings or gunmetal. Through its optimized supply chains, voxeljet’s trusted and specialized partner foundries are able to deliver casted parts within days, resulting in reduced product development cycles, practically limitless part size and broad material options.
This article first appeared on 3dpbm’s AM Focus 2020 Metal eBook