In Part II of our overview of common 3D printing processes, we’re going to take a look at binder jetting and multijet/polyjet printing. If you’re just joining us, I highly recommend checking out Part I to learn about sintering and extrusion.
We left off having covered two of our four orchids- both in plastic. Because printing in plastics can be done at home and is quite affordable for hobbyists, that’s what most people imagine when they think of 3D printing. But today, we’re going to move onto two common ways to 3D print in metal- and this is where things get VERY interesting.
One of my favorite things is when someone compliments a piece of my metal jewelry. I love watching their face when I say, “Thanks, it’s 3D printed.” Then they say, “You can 3D PRINT METAL?” and I nod like a smug a-hole as I say, “Let me tell you how.”
TYPE 3: BINDER JETTING/DROP-ON-POWDER/POWDER BED AND INKJET 3D PRINTING
And in the category of least-catchy technical name, the award goes to….
You know all those 3D printed selfie pop-ups you see up these days? Where you go and have your body scanned and then they print out a little tiny colorful statue of you (or in some cases, Sad Keanu)? Those are typically made with this type of 3D printing. It’s similar to the powder-bed sintering from part one, but instead of shooting a laser at the material, an inkjet print head deposits “a liquid binding material” (aka “GLUE”) onto the powder.
In the case of the full-color prints you see, colored ink is also laid down along with the binding material. The resulting print can look cool, but it’s also pretty brittle, so the items fall more into the “novelty shelf candy” category, rather than being truly functional products.
However, this same technique can be used for stainless steel powder- in fact, that’s how Orchid #3 was made. The biggest difference here is that after the glue is laid down, the model goes through an infusion step, where the glue is replace with bronze, resulting in a solid, durable metal piece. The finished result is a pebbled, textured piece that can then be lightly polished and plated in a number of different materials, from nickel to gold.
To sum up:
Binder Jet= (Bed of powder + glue/ink) x plastic/sandstone/metal/colorful stuff
TYPE 4: MULTIJET/POLYJET MODELING
Multijet and polyjet modeling is, in a lot of ways, the closest thing we have to the fantasy of being able to print anything. Working much like your home inkjet printer, with cartridges of various polymers and materials, a multijet printer works by spraying layers of a given material/materials down on a plate, then UV-curing those materials, all in one fell swoop. This YouTube video can show it better than I can explain it (skip ahead to about 0:57 for the sexy stuff).
I include this category because in a roundabout way, this is how Orchid #4 was made. One of the great applications of multijet modeling specifically is creating casting waxes for jewelry. The way they do it kind of blows my mind, because it’s so obvious, but so ingenious, too.
They fill up the printer with two types of wax, with two different melting temperatures. The waxes are laid down simultaneously, one building the main object, the other building the support material (because as we established earlier, you can’t really print into thin air). Then, after the model is finished, they’re placed in a warm bath, at just the right temperature, and the support material (which has a lower melting point) melts away, leaving a squeaky clean model ready to be treed and cast in any number of metals.
After that point, it’s cast and finished just like any other traditionally manufactured jewelry.
Like…. Orchid #4, cast in bronze.
Multijet= (Your home printer + steroids + uv light) x multiple materials
So I’ve got some news for you- good or bad, depending on whether you’re a “printer half-full” or not type of gal. This is by no means an exhaustive list of the processes, materials, results, etc. of 3D printing. If you want to feel a little overwhelmed, go ahead and clear your schedule, then go check out the Wikipedia page for 3D printing.
But here’s the good part: you don’t have to memorize this information in order to really start to delve deep into 3D printing. But, like any other craft or practice, it’s good to have a basic understanding of how things work. Once you understand the mechanics behind a given process, it makes designing and modeling for that process about 1000 times easier.
Plus, you want to have a good answer to accompany that smug smile when you start showing off your sick custom stuff to your friends, and they say, “So… how exactly does 3D printing work…?”