Infiltration Adds Strength, Eliminates porosity without shrinkage

This is a big topic that I’ll get in to more detail on as we go along. It’s a very important concept. Nearly all of our users are harnessing Shrinkage to increase part density. This is pretty normal in Powder Metallurgy. But there’s another option that needs more exploration.

Infiltration, also called Liquid Phase Sintering, LPS, Metal Matrix Composites. Plus a few other terms that I can’t think of right now. They’re all basically the same thing. Picture you FFFMetal Print as a sponge, and the infiltration metal as water. When you place your print in contact with a metal with a lower melting point during sintering, your part will soak up the lower melting metal.

What’s even more interesting is that this property of Capillary action is powerful enough to lift the melted metal several feet. (sidebar: It’s the same force< capillary action> that lifts water to the top of a tree. So it will likely lift the metal at least several feet.)

What’s more interesting is that you can use this technique to create pure metal parts with very little shrinkage. In fact, we’ve gotten to 97+% solid with little shrinkage and only minor distortion.

Here’s an email blast from one of our metal suppliers on this topic. It provides some baseline info that’s helpful.

Here’s a photo of an engine block model I printed with 316l and infiltrated with Bronze. I’ve attempted this probably a dozen times. The successes are spectacular, but my failure rate is about 80%.

I’m really hoping that some more people start working on perfecting this process for our open architecture strategy here. It’s done every day in industrial settings. I’ll be doing a sort of brain-dump in the forum here. I’ll be going back and sharing all of my notes and photo’s. This engine block is from about 2.5 years ago. I haven’t had much time to work on this process since then.

-Brad

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Here’s a How It’s Made showing Infiltration/LPS/Metal Matrix Composite, etc. They don’t say this in the video, but this footage is taken from a Binder Jetting Operation. The Printer is an ExOne. https://youtu.be/aSjjrEni_sY?t=193

I made the engine block essentially the same way. I used scraps of 316l filament to make a sort of “straw” so the bronze could soak up into the part. I put the bottom part of the straw in a pool of bronze powder that would become molten during the sintering process. Here you can see where I cut the straw off of the part after processing.

We just recorded a podcast on this topic. Check it out here: https://youtu.be/C6YpsCra0wE

@WayneWayneHello You’ll appreciate the ending.

This will be amazing if we can do it consistently, will be keen to give it a go soon.

This is cool and I haven’t heard of it before. Will most certainly try it down the road!

So I just watched the video and in order, here are my comments:

1: So I know of 1 hobbytype person/company doing this method of of metal printing, and which relies on it exclusively: The iro3d printer. It doesn’t do any kind of debinding/filament at all, but instead builds the shape directly by pouring loose powder powder in layers with the rest of the crucible filled in the exact inverse with sand or aluminum oxide. And then also different from this method, they put filler metal on top and in the form of a lump (not powder).

However, both your methods still have more in common than what you’ll usually find if you search for liquid phase sintering, where both metals start mixed together, and shrinkage is still expected to occur. So definitely might be worth reaching out to him for a chat.

2: absolutely love the idea of using a 3D printer pen for metal printing, not just for the straw, but in general. For touch ups and individual adornments, especially for more precious metals.

3: Have you consider to try 3D printing the “straw” directly as part of the model? You’re going to have to snip it off afterwards anyway, right?

4: Do you have a picture of the crumbling dark powder you get when it fails? Anything like this? Metal printing my head attempt #2 - YouTube

I would really like to see some more pictures of the results and failures and in-betweens of this method, if you have them. I don’t have 316 steel at the moment (or bronze powder), so right now I will have to read and speculate. Hope I can try soon though — the idea of being able to make really precise small parts that are strong is too good to pass up!

Just ordered some zinc powder to give this a shot with copper, will post results when I have em’

It’s been 22 days, has anyone tried anything new? I had the plan to debind and try to just pour liquid metal in so I can see what happens or if it “soaks”.

Hi I did a very small print in 316 but used bronze filament as support material on one layer with the thinking it would melt and infiltrate the stainless steel. The result was encouraging - I didn’t get a failed part as described by Brad but the part was too small and it’s hard to tell if it infiltrated well or not, I am going to retry but with a larger part and will update. I also have some other cunning plans but will wait and see if they work before sharing.

I got my powdered metal in and will be doing some tests hopefully in a few days

Hi All,
Ever since hearing about infiltration I have been wanting to try it out.
My approach is similar to how Brad described it but I used the steel ends of hypodermic needles instead of scrap filament as I thought the needle would act as a capillary tube and less likely to break away and make for an easier flow path to the part.
So I bought some needles, hacked off the plastic end. I also bought some bronze powder and I wrapped up the bronze in some tool steel wrap, I was concerned the refactory would block the end of the needle sitting in the bronze. I also wanted to limit the options for the molten bronze to go any way other than up through the needle.
I had some issues getting a successful stainless print but my fist attempt with this method was a thin gear, it showed promise as you could tell the bronze had made it’s way up the needle and some bronze colouration on the part.
Just finished sintering my latest attempt, a 20mm cube. The std non infiltrated cube shrunk by appox 1.3mm and the infiltrated one by about 0.3mm

Needles I used. before cutting off the ends

My little packet of bronze with the needles sticking out.

On my first attemp I just sat the part on top of the needle but this time it was a challenge to sit it on top of two needles inside the refactory so I drilled a couple of small holes into the part to a shallow depth for the needle to sit into.
image
You can no longer tell on the infiltrated part where those holes are

The inflitrated one was actually a failed print (my SS challenges continued) that is shorter in the Z direction than the completed cube. The infiltrated one was also in a crucible with refactroy that has a lot of carbon fines through it which gives a rough surface compared to the one in nice new refactory like the non-infiltrated one.
Infiltrated one is the one on the right - has a definite bronze tint to it. I have done no clean up other than a minute in a rock tumbler to get rid of the refactory.

image

More tests to do but thought I would share my limited success so far.

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Nice! I forgot to link mine back here, also did 20mm cubes but with zinc and copper

I’ll be posting some different tests hopefully within a week or so at a slightly different formulation

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