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Home 3D metal printing: first results

incoherency.co.uk

187 pointsjstanley31 comments

Important note here - this is not equivalent to the typical powder metal sintering printers that people are probably thinking of based on the title, which are still in the $100K+ range. This is an example of normal FDM printing with metal-infused filament and then fusing the layers in a furnace, which is quite a bit easier to accomplish, but also messier and more time consuming.

A few people are working on metal powder sintering at lower price points, but I haven't seen any massive progress in that space lately.

Something like this? Rapidia apparently uses a water-based process instead of a binder.

https://www.rapidia.com/

Yup, same idea, but the water-based setup likely has to deal with steam issues instead of fume issues. Personally I'd still go with the casting methods, but this is an interesting option.

desktop metal are another company who have a product which starts with an FDM/FFF type process: https://www.desktopmetal.com/

[a friend works there]

This is based on the metal injection molding materials already available. BASF manufactures them for MIM (Think die casting). This process is very well understood and used to make many mass produced metal parts in products we use every day. Using a 3d printer to form the green part is new, but the process and materials aren't.

The main hurdle here is the quality of the processing from the green part to the final part. BASF provides it as a service, you print the green part then ship it to them for processing in the same plant that does the processing for the metal injection molded parts. This takes a couple weeks to get your part back.

I evaluated both the BASF and virtual foundry materials and processes for use in my product design consultancy and found that neither provided a significant benefit over other 3d metal printing options (sls, investment casting of a 3d print, etc).

I have full rolls of several of the virtual foundry materials as well as the BASF SS material if anyone is interested in experimenting more.

I really wanted these materials to be more useful than they have turned out to be in relation to product design.

What they did at SpaceX, at least if I recall correctly, was use a powder metal bath and a platform, then would use a laser to melt a pattern into the top of the powder, then retract the platform a bit, shake it up to get powder evenly distributed again, then go over it again with the laser for the next layer. This design allowed for extremely precise, flight-grade hardware to be printed, and doesn't seem especially out-of-reach for a dedicated hobbyist either.

That's just garden variety selective laser melting, nothing specific to Space-X. Though I've never heard of "shaking it up", the standard way to apply powder is to use a moving arm with a powder feed.

For a hobbyist, I'd expect these could be a problem:

* Lasers that can melt metal are expensive and dangerous.

* Optics for such high powers are also expensive.

* Atmosphere control is a must, you don't want oxygen near metal powder under a laser.

I think at this point it would be better to start your own company and earn money from it, it seems a bit much for a fun garage project.

EDIT: There was a hobbyist project for an electron beam 3d printer posted to HN some time ago, maybe that would be more achievable (at least the beam shuts down itself if air enters the working area. The potential for implosion seems nasty though).

They are using EOS machines https://www.eos.info/systems_solutions/metal

This was an interesting article and the process shows some promise. I'll be interested in watching where this goes in the future. In the meantime...

...in the picture with the furnace, what role does the mayonnaise play?

https://img.jes.xxx/2336

> I don't actually understand how Markforged and BASF can print with a material that obviously becomes runny at about 250°C, and yet retains its shape while in the sintering furnace at 1300°C. It would be good to learn more about how this works.

A blind guess: the original filament has a resin to make the metal powder flow, that becomes viscous at certain temperatures. Perhaps this resin could be volatile and evaporate at temperatures below its viscous temperature.

Or maybe it could be quickly burned off by supplying extra oxygen (so that burning temperature isn't high and there's not enough time for the piece to deform).

In any case you could probably introduce some kind of automatic software correction for the deformation to the piece. As noted in the article this has some limitations/drawbacks, like limiting some geometries you can achieve (and requiring careful knowledge/control of your process).

The binder is something like PLA, and it binds powdered metal. The metal particles are quite small.

The low percentage basically puts plenty of metal into contact with other metal. This tends to hang together fairly well.

There is a process shrink, and it can be something on the order of 20 percent.

The 3D printed "Green" part is actually substantial. It can be machined, polished, drilled, etc...

One trouble area is support materials. Putting filament containing metal onto a support filament, like HIPS, can work. HIPS on top of metal generally doesn't.

One can use the same base polymer for both over and under support, but that can be difficult to remove. Often the metal filament itself is used. This is messy, can be difficult, but does generally work for most geometries.

The metal part can "wick" other metals during sintering too. Making a bronze with a copper "green" part with the other metal present in the oven works better than one might think.

I have yet to find a great use, other than art pieces and or simple metal shapes that could be machined at lower cost and difficulty.

It's kind of neat, and I've seen this done for jewelry. But the dimensional tolerances are far too loose for working parts.

Carbon fiber 3d printing, though, is starting to work as a low-end process.[1] Some filament type 3D printers can do it, if they have hardened steel parts near the nozzle. Dimensional stability is better than most 3D printed plastics.

[1] https://www.simplify3d.com/support/materials-guide/carbon-fi...

FYI it looks like the images are hosted on a .xxx domain which are commonly blocked

Blocked here, probably not the best domain to host images.

Definitely blocked in my office.

This is wonderful work!

I wonder if the porous bronze part could be solidified by wicking another (molten) metal into it, the way Bathsheba Grossman’s sculptures are first printed in stainless steel powder, sintered and burned out as in this process, and then infused with molten bronze.

Obvious metals to try to solidify bronze in this way would be tin, zinc, lead, and (if you can somehow control oxidation) aluminum. Cadmium or mercury might also work but are attended with difficulties that probably make them impractical.

Is there a big difference between 3D printing metal filament and sintering it in a crucible here and -- for instance -- 3D printing a plastic model, making a cast, filling it with metal particles and sintering that? Besides the former permitting voids, I suppose.

Considering the large empty spaces with sintered bronze shells, this is really a mix between sintering and lost-PLA casting. The requirement to add significant volume to your print object in order to have more bronze to flow into your desired shape is removing most of the advantage this has over plain lost-PLA casting. I wonder at the feasibility of producing filament that's 80% bronze by volume.

Some are higher than 90 percent!

I sampled such filament and it is just flexible enough to be useful.

IMHO, lost PLA is more efficient and less difficult. There are other materials that can be used for casting that have very low ash and print and can be smoothed with isopropyl alcohol most baths.

These are proving robust, but the material has a narrow operating band. Printing requires high degrees of process control.

https://www.thevirtualfoundry.com/

Polymaker PolyCast 3D Printer Filament, 2.85mm

https://www.amazon.com/dp/B07J4WK52F/ref=cm_sw_r_cp_apa_i_1....

For child comment as I hit the annoying post limit. :D

Could you link me to one of those? I don't seem to be able to find them.

In comment above, I hit post limit earlier

Thanks, you never can tell when you're going to be muted, can ya? It's fun to watch your point total swing wildly up and down without being able to see any changes on the individual comments. HN's system is obtuse bordering on Cthulhoid and I often get the impression there's a finger on the scales.

I totally believe that too.

And I do not care much. Their show.

Works both ways too. My investment is limited at any time too. So, take it, leave it, meh

No real worries, other than the occasional bump in the road.

I wonder if atomically pure metal powder (no oxidization) could be poured into a mold under vacuum to cold weld into shape.

Sure. Hot casting works for this use case too. You could print a pattern and use a lost-wax type process or print the mold with a refractory material.

Makes me think a better idea would be to 3d print something like a ceramic outer shell and just fill the void with casting grain. I assume there's some reason you can't print thin layers of clay and then bake them under the print head.

Hobby level clay 3d printing is still in its infancy. Current nozzles are >1.0mm, which are too big to create parts like this. Works for creating vases/decorative stuff though.

nice results for a first go. Keep at it. It's looking great!

Could the flame be acetylene gas?

You’re thinking be formed some calcium carbide, which reacted with the water? Seems plausible.

Great work!!

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