Deep Dive:BOUND METAL DEPOSITION
Leveraging the most widely-used plastic
3D printing method (Fused Deposition Modelling or FDM)
and the high-quality, well-studied alloys found in
metal injection molding (MIM), Desktop Metal uses
a process that enables designers and engineers to realize
the benefits of the additive manufacturing by producing
high-performance metal parts in-house.
What is Bound Metal Deposition (BMD)
Bound Metal Deposition™ (BMD) is an extrusion-based metal additive manufacturing (AM) process where metal components are constructed by extrusion of a powder-filled thermoplastic media. Bound metal rods—metal powder held together by wax and polymer binder—are heated and extruded onto the build plate, shaping a part layer-by-layer. Once printed, the binder is removed via the debind process, and then sintered—causing the metal particles to densify.
Prevalent metal AM technologies involve melting powder or wire feedstock using lasers or electron beams. While viable, these systems have substantial facilities requirements to accommodate power and safety requirements. Additionally, localized melting and rapid solidification create complex stress fields within parts, requiring rigid support structures to aid heat dissipation and resist shrinkage. As a result, support removal often requires machining.
The new Desktop Metal Studio System™ leverages BMD to deliver an office-friendly metal 3D printing solution. There are no loose powders or lasers associated with fabrication. In terms of support removal, parts are printed with their supports which are separated by ceramic interface media (or the Ceramic Release Layer™) that does not bond to the metal. This material disintegrates during sintering, making it easy to remove supports by hand.
HOW IT WORKS
(1/5) The printer has two extruders – one dedicated to printing bound metal rods and the other to the ceramic interface media rods. The rods are fed from the media cartridges into the extruders, heated to soften the binder, and then dispensed through the nozzle. Precise tool paths and extrusion rates are calculated to ensure reliable extrusion, start/stops, and feature accuracy.
The role of infill
As an extrusion-based process, BMD enables the fabrication of parts with fully-enclosed, fine voids. With the exception of extremely small geometries, all parts are printed with closed-cell infill—a fully-enclosed, internal lattice structure printed within the part. Closed-cell infill is not possible with powder-bed AM methods, such as SLM, which are restricted to open-cell lattices in order to remove unbound powder from the void spaces. Both print and debind time are directly affected by infill. The time it takes to debind a part is directly related to cross-sectional thickness which is reduced by printing with infill. Infill also reduces the weight of a part while maintaining the design-intent of the part surfaces.
BMD can be applied to virtually any sinter-able powder that can be compounded in a thermoplastic media. This includes industrially-relevant metallic alloys such as stainless steels, tool steels, and other metals that are difficult to process via other AM techniques such as refractory metals, cemented carbides, and ceramics.
Parts & capabilities
Extrusion-based additive manufacturing can build structures and geometries previously unachievable via bulk manufacturing processes—including MIM, press-and-sinter powder metallurgy, and reusable mold casting techniques. BMD results in near-net-shape parts with the strength and accuracy needed for functional prototyping, jigs & fixtures, tooling applications, and in some cases, low-volume production.
Cast vs printed
The yoke on the right was fabricated by the Studio System, demonstrating the uniform surface finish and dimensional accuracy achieved with BMD.
The Desktop Metal Studio System printer has a build volume of 30 x 20 x 20 cm and can accommodate a maximum part size of 25.5 x 17 x 17 cm (post-shrink).
A wide range of materials
For example, copper is difficult to process via powder bed fusion due to its high thermal conductivity and laser absorption characteristics. Copper media can be bound, printed, and sintered with BMD.
The non-sintering interface layer enables printing of encapsulated assemblies, such as a the hinge, shown here. Traditionally, this is made by forming, assembly, and joining of multiple parts.
In addition to print-in-place assemblies, BMD enables part light-weighting and quick fabrication of custom metal parts.
The ability to print intricate geometries is critical for topology-optimized designs, including organic designs that are difficult—if not impossible—to machine.
KEY APPLICATIONS FOR BMD TECHNOLOGY
An overview of the BMD Technology for functional prototyping,
jigs and fixtures, tooling, and low volume production.