Recently I had the incredible opportunity to be one of the first Americans to see the 3D printed Fibonacci house under construction by Twente Additive Manufacturing. Maybe you saw it in the video I posted last week.
I also got to explore their facility and watch a few prints. I took the opportunity to ask pointed questions about the process so that I could compile the golden nuggets of knowledge directly from the experts during a print to share with you. For this weeks video, I have made an instructional introduction to operating a concrete 3D printer. There is a lot going on and so this short video barely scratches the surface of the various challenges one can face with different prints. Like Jim Ziemlanski says every print is different and with those differences come different challenges. At this point Jim has racked up many hours on the machine and is highly knowledgeable.
To understand what is involved on a basic level, here are the steps I’ve contrived from my observations during my time in the Twente Additive Manufacturing facility.
- Test Run of first layer
- Choosing 1K vs 2K material
- Filling the mixer
- Dialing in the details
- Material consistency testing
- Water Content Testing
- Watch for problems
- Analyze water content
- Insert rebar & lifting hold
- End the print gracefully
Designing the file is usually done in Rhino with the Grasshopper plugin. This is the industry standard software for parametric design in 3D printed construction. The file is then converted into a print path for the specific printer and its parameters can be updated in real time during a print if any changes need to be made thus eliminating the need to start over.
Next you test the first layer path of the printer to ensure that you are printing on a uniform high from the print surface. If you print surface is uneven it may be possible to compensate for that with your printer assuming it is a correctable margin (< 2cm). It is best to start on a perfectly flat surface because that will ultimately be the plane of your objects first layer.
Twente prints in two different material types, 1K and 2K. 1K is a simpler concrete mix developed by Laticrete. I’ve had Matthew Carli, the Director of Innovation at Laticrete on my podcast (Episode 3) to talk about the 3D printed construction space. The 2K material is developed by Baumit and requires a unique Baumit extruder along with an accelerant additive that is plugged into the nozzle and extruded with the proprietary material that it reacts with to allow the concrete to be printed on steeper angles, even permitting bridging and overhangs that would not be possible with regular concrete. As one may expect this more complicated material is much more expensive.
Loading the concrete mixer is the next step. The mixer used at TAM is loaded by hand but long term as the demand increases for 3D printed concrete parts it is likely they will use larger hoppers so they need to fill them less often.
Before printing, the concrete mix has to be dialed in properly. The settings need adjusting based off environmental factors like humidity and temperature. The hose from the mixer is nearly 20 ft long so it takes a while for the changes made to show in the end of the extruder. As the concrete drips from the extruder it is collected in 5G buckets and used for something that doesn’t need as particular parameters that way it doesn’t go to waste.
To verify the water content wt% a 50 gram sample of the wet extruded concrete is taken and microwaved to remove the water. It is then weighed again to determine how many grams of water were in it. This difference in weight allows you to find the wt%.
Before you start printing, back pressure must be applied to the extruder that way the concrete hose from the mixer stays full and doesn’t get any air pockets. This is done by hand with a spatula until the printer hits the print bed and starts on the first layer. This is similar to my Prusa MK3 desktop 3D printer that will extrude excess plastic which needs to be removed immediately before the print starts.
Printing is actually the easy part. If everything is going smoothly all you have to do is watch but at this scale, issues can be costly and time consuming to clean up so its best to keep an eye on it. Concrete has a tendency to clog so if the print shows signs of looking sloppy it may be best to pause the print, clear the clog, and resume from where you left off. Other issues can arise if the design doesn’t allow the concrete enough strength to support itself. Making a 3D model is easy but without an understanding for the limitations of a printer/material a novice could easily design something impossible to print. While printing, it would be wise to do more water wt% calculations as you go.
During the print it can be opportune to add supports in the form of rebar or supports for a hold that the piece can be lifted from in the future. This can be done by hand as long as it is placed evenly to allow the next concrete layer to print over top of it.
Ending the print is similar to starting it because once again you must apply back-pressure to the printer that way it doesn’t drip all over the freshly done print. This is once again done with a spatula by hand.
Just because the object is done, doesn’t mean you are. Next every part of the system that touched wet concrete has to be cleaned rigorously otherwise it could easily ruin the equipment. This paragraph is short but that process is long.
Next week we will take a look at the things TAM has printed around the grounds of their facility. There are all kinds of prints they have achieved that range from practical to creative. We will also take a look at how the offsite prints are transported to their final locations.