Metal Stamping Guide

Metal Extrusion

Understand why Metal Extrusion is best suited for prototypes & one-off parts.

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Metal Stamping Guide

Metal Extrusion

Metal Extrusion is an alternative, low-cost metal 3D printing process that is mainly suitable for prototyping purposes or for one-off custom parts.

Here, we examine in depth the characteristics and key benefits and limitations of this additive process to help you understand how to use it most effectively.

Metal Extrusion

What is Metal Extrusion 3D Printing?

A Metal Extrusion 3D printer in action
A Metal Extrusion 3D printer in action

Metal Extrusion is a variation of the classic FDM process for plastics. The first Metal Extrusion 3D printers were released in 2018. The technology is also known under the names Bound Metal Deposition (BMD) or Atomic Diffusion Additive Manufacturing (ADAM)

Like FDM, a part is built layer-by-layer by extruding material through a nozzle. Unlike FDM, the material is not plastic, but a metal powder held together using a polymer binder. The result of the printing step is a “green” part of that needs to be-debinded and sintered to become fully metal.

How does Metal Extrusion work?

Schematic of a Metal Extrusion 3D printer
Schematic of a Metal Extrusion 3D printer

Metal Extrusion is a three-stage process. It involves a printing step, a de-binding step, and a sintering step. Here’s how the printing step works:

  • The raw material comes in a filament or rod form that typically consists of metal particles bound together by polymer and/or wax.
  • This rod or filament is extruded through a heated nozzle and deposited layer-by-layer building a part based on the CAD model.
  • At the same time, support structures are build if necessary. The interface between the support and the part is printed with a ceramic support material, which is easy to manually remove later.

When the print is complete, the resulting “green” part needs to be post-processed to become metal using similar steps as in Binder Jetting. The "green" is first washed in a solution for several hours to remove most of the binder. Then it is sintered in a furnace to bond the metal particles together and form a fully-metal part.

The three step of a Metal Extrusion process
The three step of a Metal Extrusion process

During sintering the part dimensions are reduced by about 20%. The parts are printed larger to compensate for this. Like in Binder Jetting, this shrinkage is not homogenous. This means that some trial and error is needed to produce accurate results for a particular design.

Metal Extrusion vs. FDM of plastics

The way that Metal Extrusion and plastic FDM printers work is very similar. For example, both processes print parts hollow, using a cell outline and infill.

Apart from the material, there are two other important practical differences between Metal Extrusion and FDM that you should keep in mind. Both are connected to the mechanics of the de-binding and sintering process.

  • Wall thickness: In Metal Extrusion, parts should always have a consistent wall thickness (preferably, smaller than 10 mm). If this is not the case, then the time needed to fully de-bind and sinter the parts can increase by several hours.
  • Support structures: Like FDM, in Metal Extrusion support are often required during printing. In Metal Extrusion, though, support is also needed for the sintering step. At these very high temperatures, the metal material becomes soft and pliable and may collapse under its own weight.

Benefits & Limitations of Metal Extrusion

Metal Extrusion is excellent for functional prototyping and small productions of metal parts that would otherwise require a 5-axis CNC machining to produce.

Coming at a fraction of the cost of DMLS/SLM or Binder Jetting, Metal Extrusion printers are the most economical metal system to date. This way, a wider audience can benefit from the key benefits of metal 3D printing (optimized structures, assembly consolidation, internal channels), especially for prototyping purposes and small production runs. Moreover, the ease-of-use of these systems and their low health and safety requirement make them appealing for in-house production of custom parts or tooling to support other operations.

When compared to other manufacturing technologies though (like CNC machining and sheet metal), the cost of Metal Extrusion is still considerable. For simple geometries, it is more economical (and usually faster) to choose a traditional manufacturing process, even when outsourcing production. The biggest contributor to this final cost is the time required to de-bind and sinter the as-printed “green” parts. It takes on average 24 to 72 hours to do so.

From a technical point of view, the parts produced with these systems are not suitable for demanding applications as they have lower mechanical properties than the wrought metal (~33% lower strength), due to their internal porosity (approximately 2-4%).

  Low-cost metal 3D printing
  Higher cost than CNC for simple parts
  Functional metal prototypes
  Lengthy post-processing
  Easy-to-use systems
  33% lower strength than wrought

Technical Characteristics of Metal Extrusion

The table below summarizes the basic technical capabilities of a typical Metal Extrusion 3D printer today. For additional design guidelines, jump to the design rules.

Property Metal Extrusion
Material selection Currently very limited

Stainless steel
Dimensional accuracy ± 0.5 mm with a lower limit of ± 0.5 mm (± 0.020")
Typical build size 300 x 200 x 200 mm

(-20% effective build size after sintering)
Common layer thickness 50 - 200 μmm
Support Required for printing and sintering
Internal porosity Between 2.0 - 4.0%
Cost per part $$$