Part quality and shrinkage
For metal parts, CMF offers cost and convenience considerations to consider that can make a significant difference depending on the application.
First: parts quality. According to Akbas, CMF parts are equivalent to or better than all other metal powder part processes. Cold metal fusion parts are characterized by a dimensional accuracy of approximately ±100 micrometers and even more by optimizing 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 than can be achieved using billet machining with the same material,” says Calhoun. “For advanced, high-end applications like aerospace, electric vehicles, medical devices and things where weight is critical, manufacturers can produce parts with titanium that is better than the titanium we can machine Safety factor and lower overall mass. Weight, which will be a big step forward.”
Akbas points out that the CMF 316L stainless steel parts have an elongation of 60%, demonstrated last year by the French CETIM Institute, while the MIM industry standard is 50%.
Calhoun says that because of the quality of the metal parts, Nexa3D is expected to attract customers who are initially looking for a metal 3D printer and have no intention of ever printing polymers.
The next obvious advantage is that you no longer need two separate machines for polymer and metal 3D printing.
“We have customers who might only want to make a metal part once a month, or they might want to make a small production run of 200 metal parts and then switch back to polymer,” Calhoun says. “We also already have an installed base of MIM houses that use our machine to produce complete production parts.”
Metal injection molding company MIMplus uses its Nexa3D QLS230 to produce tens of thousands of parts, Calhoun says. (MIMplus also offers CMF as a service if you would like to test the products yourself.)
The appeal of SLS and CMF is that they can print polymers one day and metals the next. However, according to Akbas, it actually takes at least half a day to thoroughly clean the machine of one type of material before printing with the next. Because CMF materials are processed at much lower temperatures than polymers, they carbonize at higher temperatures and contaminate the structure if not thoroughly cleaned.
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 claims to have achieved the holy grail of consistent part shrinkage that remains the same regardless of part size, shape or complexity.
“The shrinkage is 15% for steel and 12% for titanium,” says Calhoun. “There is no special software or calculations. Simply enlarge your steel part by 15% in your CAD program and the final part will meet exact specifications.”
According to Akbas, additive manufacturing users have struggled with uneven part shrinkage for years. “[Metal binder jetting users] Tell us that my part shrinks more in the Z direction than in the XY direction, or if it’s up here in the printer, I’ll have a different shrinkage than down there,” he says. “We don’t have that problem.”
