All Glossary

3D Printing Clay

Clay for 3D printing. People are getting carried away with the technology and forgetting the common sense things relating to the clay.

Key phrases linking here: 3d 3d-printed clay, 3d printing clay - Learn more

Details

3D printers that can extrude a clay paste are available now, the industry is surprisingly mature and making great strides into large-scale manufacture. While other technologies do exist (e.g. glue-bonding powder particles layer by layer), paste extrusion is pervasive. Objects are most commonly printed by extruding layers from a nozzle. These are additive processes (as opposed to subtractive where material is cut away from a block).

At first, it appears that a clay-paste 3D printer is basically a tiny pugmill moving around squirting out jello-consistency goop, hoping that it will stand up! But people are just getting this to work anyway (e.g. by sticking to vertical shapes, printing slowly, and having a fan blow on pieces as they are being printed). That being said, limiting factors to the process are steadily being overcome. Companies are developing the process so well that almost any powder can be made into a paste (with appropriate additives like deflocculants, binders, polymers) and printed, even in extreme shapes. There are already things that cannot be done any other way (e.g. pieces that have complex interior channels, infills). Even metal powders can be printed and fired - with enough precision that tiny turbines can spin at 500k RPM!

The RepRap international movement to develop open-source hardware and software platforms for 3D printing helped push 3D printing in hobby ceramics starting around 2005. Anyone can now buy and assemble a standard filament printer to learn many details of their mechanics and operation. Once understood, a printer of any size could theoretically be constructed. In clay printing the focus is on the print head and how to deliver a thick paste to it and extrude it at a constant rate without air bubbles (flow cannot easily be turned on and off, it has to flow constantly, placing limits on what can be printed). One type of extruder print head has a barrel and auger driven by a stepper motor, basically a small pugmill, its extrusion nose is the printhead nozzle. Another uses a stepper motor and worm gear to drive a piston to pressure clay into a flexible tube that feeds the printhead.

There is an inertia problem with scaling to a bigger sizes using paste extrusion: The printhead and/or platform must be able to move quickly. Of course, mass must be kept to a minimum to achieve precise and quick movement. But clay is heavy and if the printhead is full it cannot be responsive (e.g. Delta printer designs). These printers must deal with this by pumping the clay from a syringe-like cylinder through a flexible tube that runs to the head. On other printers where the bed must move the problem is even more acute - the quickness of the movement is obviously limited by how heavy and fragile the soft clay on it is (rather like a big cube of jello on a plate being jerked around).

A major challenge is making the clay set fast enough so that the next layer applied over it will have a firm base. When plastic filaments are extruded in typical home 3D printers they simply cool and firm up immediately. But clay pastes are soft and fragile. Theoretically, multiple things could be done to accelerate the stiffening of the already extruded clay. For example, additions of light or laser senstive polymers. Or, augmenting the water with alcohol (e.g. ethanol is preferred over isopropyl alcohol because it carries off more water as it evaporates). Pure ethanol is flammable and clay plasticity and dry strength are poor (but a 50:50 water:ethanol is not flammable and workability is sufficient). However, even though the clay feels cold evaporation does not proceed that quickly, it still needs a fan to stiffen up fast enough. Fortunately, newer printers are able to operate under greater pressure, thus stiffer pastes of lower water content can be delivered. With fans and enough extra time between layer delivery structural integrity is possible. In some types of 3D printing, support structures of a different material are printed with the item and these are later removed, this would be practical for ceramics also.

Printers designed for clay are appearing with increasing frequency. A potter could easily spend $10k but use caution, the laws of physics and common sense apply. Machines have differing priorities. Lutum and WASP machines push clay through a flexible tube to a tiny pugmill in the printhead. The PotterBot is moving the entire piece being printed (on the x-y axes). The only solution is often to simply print really slowly. Many are shocked when they realize that even normal printing time for a large piece could be days!

Don’t be stuck with a fancy machine and no clay that works with it. Manufacturers are making cartridges to work in their machines, claiming the clay to be soft, bubble-free (avoiding the mini-explosions that happen when air bubbles find their way to the nozzle!). The advantage will be more stable & repeatable performance and a ready-to-use product with good strand adhesion and plastic strength. Of course, these cartridges are expensive! Individuals will always have the flexibility to make their own clay bodies. 3D printable clay has no secret recipe, its utility lies in consistent stiffness and no particulates or bubbles. A good cone 6 porcelain starting recipe is L3778D. Zero4 fritware porcelain is another option, this enables much lower firing temperature without loss in strength. Both of these bodies are plasticized using Veegum, so just experiment with its percentages to optimate the paste ("optimize" might not be the right word, perhaps the best you can hope for is a clay that can be tolerated). More Veegum imparts plasticity and stickiness but dries slower and is more difficult to slurry and dewater. Use the slurry-up method to make the paste. A hand extruder can also be used to create the diameter needed to feed the machine. The character and suitability of the body will be a big part of success, understanding the recipe and being able to control it will give you the edge (especially if incorporating alcohol).

Traditional clay suppliers are also producing clays for this. But be skeptical. One of the bodies claims to have 40% 80 mesh grog, however, our testing found no grog! Besides, grog is undesirable since it would wear out the print head quickly or clog it. Another porcelain has 25% water yet claims to have drying shrinkage of 6.5% (this is highly improbable and even if true would make it too non-plastic and fast-drying). Some have shipped in, at considerable cost, non-plastic 3D printing clays and found that the plastic bodies they have used for years work better! When printing takes a long time the bottom and top of a piece are soft and the center gets stiffer, a plastic clay that dries slower is better. In addition, printing overhangs is a big issue - again, plastic clays hold up better.

Related Information

Polar Ice Porcelain for 3D printing

The stickiness and extreme plasticity of Polar Ice porcelain has enabled many people to use it for 3D Printing. This is a piece being done by Bryan Cera. Polar Ice in plastic form is better than Polar Ice for casting because the former contains much more Veegum. Layers adhere well and pieces can hold up even though the clay may be very soft. We manufacture it in soft form, although it may feel very stiff in the box, open wedging the clay softens markedly and might be suitable if you have a 3D printer that can handle stiffer paste (of course, if the clay is getting old it will be stiffer). The Veegum in Polar Ice slows drying and increases drying shrinkage - be judicious about how fans are set (they should expose all sides to draft). Printing on a piece of plaster is also advisable (it will draw water from the base). If the plastic version of Polar Ice is just too stiff then you might consider mixing the printing paste from the casting version. It will not be as plastic but will dry faster. Adding Veegum will improve its plasticity (but beware of how difficult it can be to slurry up a body containing a lot of it). If you cannot get this body then just make your own using the L3778D recipe.

Here is what happens when an overnight 3D print goes wrong

From Brooks Talley. At some point during the night the base could not support the layers being added and it collapsed. The printer happily just kept printing in mid air for the rest of the night!

G-Code 3D Printer instructions

Simplify3D knows how to convert the 3D geometry generated by Fusion 360 into G-Code (shown in the black text window lower right). I have just told Fusion 360 to print this and it automatically launched this and passed the 3D geometry to it. Simplify3D is a "slicer" because it knows how to convert a 3D object into slices that a 3D printer can lay down (one on top of the other). Simplify3D is fairly expensive and competes with a number of free products (like Slic3r, Cura). It gives me a 3D view of the object and enables positioning and rotating it on the bed and configuring dozens of parameters. It is about to deliver the G-Code (via a USB connection) to my RepRap 3D printer (although it is often preferable to use the "Save Toothpaths to Disk" button to generate G-Code and write it to an SDCard which the printer can accept). The black text-edit window shows what the G-Code looks like. It is just text. With hundreds of thousands of commands that mostly move the head to successive X-Y positions and a defined filament feed-rate.

CERA-1 Open Source Clay 3D Printer Extruder

Bryan Cera designed this in partnership with Amaco/Brent and Duet3D. It is documented and published as open source. And amazing project from an amazing technician and artist.

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