Select Page

Deep Dive:

BOUND METAL DEPOSITION

Leveraging the most widely-used plastic
3D printing method (fused filament fabrication or FFF)
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.

CONTACT AN EXPERT

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 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

EXTRUDER

(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.

RAFT

(2/5) The raft is printed first, and then the part with its supports. The interface layer printed between the part and its supports is engineered to ensure controlled shrinkage throughout the part, while advanced support structures are designed to fully support the part geometry throughout the print, debind, and sinter processes.

DEBINDER

(3/5) In the second step of the process, the part is placed in the debinder where a significant portion (30 to 70%) of primary binder is removed by chemical dissolution while the remaining binder helps the part to retain its shape. An open-pore structure is created throughout the part in preparation for sintering.

FURNACE

(4/5) In the furnace, part is heated to temperatures near melting. Remaining binder is released and metal particles fuse together, causing the part to densify up to 96 to 99.8%. Depending on the material, the part shrinks about 17 to 22% during densification. Understanding and controlling shrinkage due to sintering it critical to achieve dimensional accuracy. Optimised through dilatometry, the sintering cucle is tuned to each build and material to ensure repeatable shrinkage and densification.

SEPARABLE SUPPORTS

(5/5) To enable Separable Supports™, the interface layer printed between the part and its supports doesn’t bond to the metal and prevents the part from sintering with its supports. The ceramic media disintegrates in the furnace, making it easy to remove parts from their supports.

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.

Materials

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.

Large parts

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.

Print-in-place assemblies

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.

Customisation

In addition to print-in-place assemblies, BMD enables part light-weighting and quick fabrication of custom metal parts.

Complex geometries

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.

Application #1: Functional prototyping

Whereas plastic 3D printed parts often allow us to test form and fit, metal 3D printing allows you to produce functional prototypes quickly and iterate quickly on the part design. Functional prototyping applications call for parts that adhere to specific thermal and chemical requirements. Some examples of these applications are worm gears, connecting rods, brake calipers and manifolds. And by eliminating lead times, costly complex machining operations, and the need for tooling, product development and time-to-market is accelerated significantly. Expedited fabrication with in-house metal 3D printing allows engineers to explore an iterative design process that includes functional testing—something that is not possible with plastic prototypes.

Application #2: Jigs & fixtures

On a production line, jigs and fixtures have complex geometries and are produced in low volume. Typically, these parts must be made in metal to meet stiffness and strength requirements. Frequent use results in wear, so the ability to produce replacement parts quickly is critical to operational efficiency. These parts must allow for repeatability and meet high tolerances. Metal parts printed with the Studio System meet strength and durability requirements and can be post-processed after sintering to achieve critical dimensions And the nature of the layered BMD printing process is the ability to print assemblies together which is not possible with traditional manufacturing methods.

Application #3: Tooling

Typically, custom tooling applications have parts with complex geometries that are difficult—if not impossible—to achieve with traditional manufacturing methods. An example of this is mold cavity inserts with conformal cooling channels that are designed to improve injection mold cycle times and quality of the molded part. In these applications, initial tooling expenses represent a major factor of overall part cost. Often, these high costs make it impossible to use processes such as casting, injection molding, and extrusion for smaller, customized parts. The Studio System builds reliable, highly accurate, durable tools that outperform a plastic equivalent.

Application #4: Low volume production

The Studio System brings the benefits of additive manufacturing into the office, enabling quick, customized parts for low volume production. Traditionally, the cost for producing metal parts in low volume is high—particularly if its geometry requires manufacturing by casting or injection molding. The Studio System results in reduced lead time, and the part costs do not increase based on part complexity, allowing designers to focus on the function of the part rather than limitations of traditional manufacturability.

Case Studies

Built-Rite Tool & Die

Injection moulding firm investigates quick-turn mould application, identifies 90% cost savings. Download Now

Lumenium

Desktop Metal Studio System™ for rapid prototyping: Virginia-based startup to reduce product development timeline by 25%. Download Now