Research activity into 3D printing never seems to end, with an almost constant stream of new techniques and improvements upon old ones hitting the news practically daily. This time, the focus is on a technique we’ve not covered so much, namely binder jetting additive manufacturing (BJAM for short, catchy huh?) Specifically the team from Oak Ridge National Laboratory, who have been exploring the use of so-called hyperbranched Polyethyleneimine (PEI) as a binder for jetting onto plain old foundry silica sand (nature, free access.)
The PEI binder was mixed with a 75:25 mix of water and 1-propanol (not to be mixed up with 2-propanol aka isopropanol) to get the correct viscosity for jetting with a piezoelectric print head and the correct surface tension to allow adequate powder bed penetration, giving optimal binding efficiency. The team reported a two-fold increase in strength over previous jetting techniques, however, the real news is what they did next; by infusing the printed part (known as the green part) with common old ethyl cyanoacrylate (ECA, or super glue to us) the structural strength of the print increased a further eight times due to the reaction between the binder and the ECA infiltrate.
To further bestow the virtues of the PEI binder/ECA mix, it turns out to be water-soluble, at least for a couple of days, so can be used to make complex form washout tooling — internal supports that can be washed away. After a few days, the curing process is complete, resulting in a structure that is reportedly stronger than concrete. Reinforce this with carbon fiber, and boy do you have a tough building material!
Not bad for some pretty common materials and a simple printing process.
We’ve seen all sorts of 3D-printers on these pages before. From the small to the large, Cartesians and deltas, and printers that can squeeze out plastic, metal, and even concrete. But this appears to be the first time we’ve ever featured a paper-pulp extruding 3D-printer.
It’s fair to ask why the world would need such a thing, and its creator, [Beer Holthuis], has an obvious answer: the world has a lot of waste paper. Like 80 kg per person per year. Thankfully at least some of that is recycled, but that still leaves a lot of raw material that [Beer] wanted to put to work. Build details on the printer are sparse, but from the photos and the video below it seems clear how it all went together. A simple X-Y-Z gantry moves a nozzle over the build platform. The nozzle, an order of magnitude or two larger than the nozzles most of us are used to, is connected to an extruder by a plastic hose. The extruder appears to be tube with a stepper-driven screw that lowers a ram down onto the pulp, squeezing it into the hose. [Beer] notes that the pulp is mixed with a bit of “natural binder” to allow the extruded pulp to keep its shape. We found the extrusion process to be just a wee bit repulsive to watch, but fascinating nonetheless, and the items he’s creating are certainly striking in appearance.
[Nullset] uses inkjet printer technology for his 3D printing needs. We usually think of hot-plastic printing like the RepRap or Makerbot when we hear about rapid prototyping, but this setup uses a liquid bonding agent to turn powder into a solid structure. Standard inkjet cartridges can be used to precisely place the bonding agent, but it’s hard on the heads and you have to replace them often. [Nullset] is getting pretty good at it, and decided to write a tutorial on the modifications necessary to print with bonding liquid.
At its core, the method injects binder into the cartridge through one port while using a second for drainage. [Nullset] found that the needle fittings used to inflate a basketball work great for this. He drills a couple of holes that the threaded end of the needles fit into. That connection is sealed with some epoxy, and the tubing that delivers the binder is zip-tied to the needles. A bit of purging is necessary to get rid of any old ink, but after the initial flush you’ll be up and running pretty quickly. He figures the whole process can be one in around 10 minutes once you get the hang of it.