An Introduction to Metal FFF 3D printing

Print farm

For over twenty years, 3D printing has shown exciting potential as a manufacturing process. In some industries, it has already started a revolution. But there has always been a material limitation. 

You see, most 3D printers print plastic. You can engineer plastics like PLA, PET, and ABS to demonstrate desirable mechanical characteristics, but they are still plastics – and plastics cannot replace metals in every application, especially in industry.

A solution for tooling and manufacturing high-strength parts to replace metal parts is 3D printing nylon with composite reinforcement. Markforged introduced this gamechanger with the Mark One (since superseded by the Mark Two), which can 3D print parts as strong as metal.

But the demand for metal parts remains and will endure for the rest of time. After all, metal is easy to work, cheap, and durable. It’s proven and irreplaceable. And if it fails or loses its shape with use, it can be melted down and reformed, or recycled and transformed and repurposed into something new.

So, what if you could 3D print metal? Wouldn’t that be something?

Enter metal 3D printing from Markforged.

The Metal FFF process

Metal FFF is a proprietary 3D printing process developed by Markforged. It is a metal 3D printing process built on the foundation of metal injection moulding, a metalworking process that uses a mould, powdered metal, and binding agents to create three-dimensional models.

However, in the case of Metal FFF, no moulds are involved. Instead, a 3D printer (the Metal X) creates the 3D model from scratch itself by building up layers.

The metal itself is no ordinary metal. It is a speciality filament, composed of metal powder and two binding agents. The metal powder is bound in plastic to give it solid form, with some of that plastic dissolved in a solvent wash. The part is then placed in a furnace, with this stage called the ‘sintering’ stage. This is the point where the metal powder fuses into solid metal.

Here’s the process broken down in simple steps:

Design: Parts are designed in CAD, perhaps from a 3D scan of a legacy part or from scratch. Eiger (Markforged’s software) then slices the file for you. During slicing, Eiger will scale your parts to accommodate for shrinkage in the furnace.


Print: The Metal X gets to work printing, using metal powder and two binding agents. 


Sinter. Printed parts go through a washing stage to remove some of the plastic material. They are then transferred to a furnace to fuse into solid metal.

Metal FFF produces parts that are 99.7% dense. They are pure, solid metal, with no binding agent content once sintered. Parts are as strong as cast and forged parts.

On close inspection, the Metal FFF process results in crystal growth throughout all axes, to give parts the strength and mechanical properties of solid metal in all directions. This means parts printed on the Metal X can replace cast parts. Some materials, such as H13 Tool Steel, are also suitable for tempering and double tempering.

The metals (materials)

Speaking of materials, the Metal X prints quite a few.

Available right now are 17-4 PH Stainless Steel and H13 Tool Steel.

17-4 PH Stainless Steel is for end-use applications, where high strength and corrosion resistance are necessary. It’s a highly versatile steel widely used in manufacturing and engineering. It’s ideally suited to mechanical applications. When heat-treated, it reaches a tensile strength of 1,250 MPa.

H13 Tool Steel is for high temp, high wear applications. It is ideally suited to tooling, forming, dies and punches. When heat-treated, it reaches a tensile strength of 1,500 MPa. This material is widely used to make moulds and wear-resistant parts that have a finite useful life.

In time, the Metal X  will also print A2 Tool Steel, 316L Stainless Steel, Inconel 625, and Titanium 6-4. These upcoming materials are in the beta (testing) stage right now and listed as coming soon.

The applications

Metal 3D printing has a use case wherever metal parts are cast and forged. Best part is, the Metal X manufactures these parts without human input. All a human has to do is wash the parts and stick them in a furnace. The production process is otherwise automated, meaning you can go from CAD to part in a fraction of the time versus traditional tooling processes.


One of the standout benefits of metal 3D printing in the case of Metal FFF is you can print closed parts with complex internal geometries. For example, you can print a hexagon infill, to reduce material use and significantly reduce weight without compromising integrity.

Another benefit is replacing the mould making process entirely. As you may or may not be aware, metal injection moulding is a time-intensive process and much of that time is spent creating the mould. With the Metal X, you don’t need a mould at all. Or, if you do, you can 3D print a mould out of metal in around a day and a half, versus the weeks it takes to make with machining.

Metal X parts

Not all parts are great candidates for metal 3D printing, though. With 3D printing, there are build size restrictions and there’s an obvious geometry restriction because of the extruder system. In an ideal world, there would be no real geometry restrictions but we’re a long way off this yet.

The printer (Metal X)

The Metal X has a build volume of 250 mm x 220 mm x 200 mm (9.8 in x 8.7 in x 7.9 in) and a 575 mm x 467 mm x 1120 mm footprint, which makes it desktop-sized. It has an on-board camera for remote monitoring, and it runs cloud-based Eiger software developed by Markforged.

Metal X

Quality matters greatly to Markforged, so the Metal X utilises the same thorough quality inspection process as the Mark Two. Tolerances are logged, and the printer reacts in real-time to ensure parts come out true-to-design. In other words, absolutely perfect.

The Metal X doesn’t wash or sinter parts itself, so Markforged also offer a medium-sized furnace called the SINTER-1, a large furnace called the SINTER-2, and a washing station called the WASH-1. These are complementary machines designed to the same standards as the printer itself.


In terms of ease of use, the Metal X is excellent. Cloud-connected software and a 4.3” touchscreen comes standard with every printer. There are also over-the-air updates, and when you first plug the Metal X in, you are guided through the setup process on the touchscreen. There’s also material usage tracking and waste management so you can make the most of material.

Eiger is also excellent. It’s easy to use and makes collaboration simple. You can queue print jobs and view progress in real-time. There’s also real-time fleet management, which allows you to control several Metal X printers at the same time, or independently, on a single network. It makes manufacturing easier and managing your print farm a doddle.