How Does Cold Metal Fusion Work?

Nexa3D is not the first out of the gate to offer customers this unique SLS-compatible metal power — it’s also available on Farsoon machines, the EOS Formiga P110, and more SLS makers are in the pipeline. Here’s how the technology works.

Each particle of material is sintered at a much lower temperature than SLS machines typically use to sinter polymers, about 70ºC – 80ºC, which is why the technology is called “cold.” A polymer material, such as PA12, by comparison, has a melt point of 180ºC.

To be compatible with the material, an SLS machine has to have preinstalled material profiles or open parameters, like the Nexa3D machines, so that the temperature and other settings can be tuned to the Headmade Materials feedstock. Interestingly, the print speed and print volume of SLS machines aren’t greatly effected by the metal material. Nexa3D says its high speed printing available on its QLS machines is just as high speed, or close, with metal.

Once the parts are printed, they’re in a “green” state. From here on, the processing into a full metal part is the same as metal injection molding, which involves removing the polymer binder and using a sintering furnace to produce fully metal components, up to 99.9% dense.

CMF vs. Binder Jetting, LPBF

Cold Metal Fusion’s closest cousin in additive manufacturing could be metal binder jetting because it involves metal powder and a binder, plus heat as a post-processing step.

Binder jetting metal is still a faster printing process since an entire layer can be jetted in seconds, while the laser in the SLS machine needs to trace out each part layer point-by-point. Yet, when Nexa3D and Headmade Materials compare the two technologies, they focus on overall productivity and scalability.

“For the price of one metal binder jetting solution, you could have 10 SLS machines,” says Levent Akbas, Headmade Materials’ chief commercial officer. “You do not have to invest large amounts of money to get to your first parts.” Because of the wide range of SLS printers and sintering equipment sizes available, users can customize their full process chain according to their needs from desktop-level lab work to full-series production.

The entry-level print platform from Nexa3D to process all of the Headmade materials, including titanium, is $70,000. The complete process chain including a SLS-system, a debinding and a sintering furnace is starting from around $2250,000, but enables a production output of several thousand metal parts per year, depending on the size of the part, according to Headmade Materials.

Cold Metal Fusion is also comparable to metal laser powder bed fusion (LPBF), also known as selective laser melting (SLM), direct metal laser sintering (DMLS), and just metal laser sintering.

Where CMF differentiates itself from laser powder bed fusion is, again, the scalability factor since you can leverage the full build volume of the SLS machine by closely nesting parts, according to Nexa3D.

“This process works well for small parts, but it can also do massive parts that are 25-kilos,” says Calhoun. “It’s scalable across geometries that don’t apply to MIM from a size or cost-effective production standpoint , and certainly don’t apply to binder jetting or direct metal laser sintering either.”

Part Quality & Shrinkage

For metal parts, CMF offers cost and convenience points to consider that could make a significant difference depending on your application.

First, part quality. CMF parts are on par, or better, with all other metal powder part processes, according to Akbas. Cold Metal Fusion parts boast a dimensional accuracy of around ±100 microns and even higher with optimization of design and process parameters.

“The remarkable thing about this process is that the metallurgy and science behind it allows for better mechanical properties for a fully sintered part then you can get by billet machining using the same material,” says Calhoun. “For high end advanced applications, like aerospace, electric vehicles, medical, and things where weight is crucial, having a titanium that’s better than the titanium we can machine is going to allow manufacturers to produce parts of equal safety factor with less overall mass and weight, which is going to be a big advancement.”

Akbas notes that the CMF stainless steel 316L parts have a 60% elongation proven by the French CETIM Institute last year, where as the MIM industry standard is 50%.

Calhoun says because of the quality of the metal parts, Nexa3D expects to attract customers looking for a metal 3D printer first, with no intention to ever print polymers.

The next obvious advantage is that you no longer need two separate machines for polymer and metal 3D printing.

“We have customers who maybe just want to do a metal part once a month, or they want to do a short production run of 200 metal pieces, then they switch back to polymer,” says Calhoun. “We also already have an installed base that are MIM houses doing full production parts with our machine.”

Metal injection molding company MIMplus is using its Nexa3D QLS230 to produce tens of thousands of parts, Calhoun says. (MIMplus also offers CMF as a service if you want to test the products yourself.)

The appeal of SLS and CMF is printing polymers one day and metals the next. Yet, it actually takes at least a half day to thoroughly purge the machine of one type of material before you print with the next, accordign to Akbas. CMF materials, because they’re processed at much lower temperatures than polymers, will char at higher temps and contaminate the build if not thoroughly cleaned out.

Achieving Uniform Shrinkage

All 3D printed parts made with a polymer binder and metal will shrink once the polymer is removed and the parts are sintered.

Headmade Materials says it has achieved the holy grail of uniform part shrinkage that is consistent regardless of the part size, shape, or complexity.

“Shrinkage is 15% for steel and 12% for titanium,” says Calhoun. “There’s no special software or calculations. Simply scale up your steel part 15% in your CAD program, and the final part will be exactly to spec.”

Akbas says additive manufacturing users have been struggling with inconsistent part shrinkage for years. “[Metal binder jetting users] tell us my part shrinks in the Z more than in the XY, or when it’s up here in the printer, I have different shrinkage than if it’s down there,” he says. “We don’t have that problem.”

Costs & Additional Equipment Required

Neither Headmade Materials nor Nexa3D offers powder handling machines, debinding equipment or a sintering furnace. Instead, they’ve partnered with some of the most established brands that make these pieces of equipment for the metal injection molding industry.

In fact, the array of companies joining together to create the CMF ecosystem are called the ColdMetalFusion Alliance. It includes powder removal equipment experts AM Solutions, acetone debinding solution providers Lömi, furnace maker Carbolite Gero, and others. Headmade Materials offers specific post-processing parameters for each step using these particular brands, in addition to the printing parameters on partner SLS machines.

The price of the feedstock isn’t made public, but Akbas says it’s comparable to the price of the metal powder used in binder jetting processes. In binder jetting, there’s also the proprietary binder as a consumable, but with Headmade Materials, the feedstock is an all-in-one material. “The price economics are very favorable to those who have high volume applications,” he says.

CMF at Formnext

Headmade Materials, and most of the members of the ColdMetalFusion Alliance, will exhibit at Formnext in November. “Cold Metal Fusion will be distributed all over Formnext, it’s a multi-booth experience where you can go to the different members and see their core competency and how it interacts with others,” says Akbas.

Other SLS printer makers are also collaborating with Headmade Materials. The company has not released the names of the next to joined the ColdMetalFusion Alliance created to further promote the technology, but you can expect CMF to spread rapidly.