3D printing in Ceramics is unique, powerful and sometimes a challenge. In an effort to help you as you design for Ceramics, we are sharing more insight into the manufacturing process and potential pitfalls through a series of short tutorials.
One of the more challenging factors when designing for ceramics is the use of ‘Spans’ in its geometry.
A Span is any feature in a model that is not supported by its own geometry or the model’s geometry, and thus has to fight the force of gravity (such as a long handle on a mug, an arm or a tree branch).
Spans can cause issues that are relatively unique to 3D printed ceramic art and objects due to the process required to create it. After the model is 3D printed, it is in a fragile “green state,” before it is fired in a kiln. Spans are more likely to warp due to their unsupported nature during the firing process, as it undergoes a chemical reaction and becomes softer due to the heat.
Spans are generally an issue when they protrude greater than 20mm perpendicular to the base of the kiln if they are not supported (too thin or lack of support structures), so design unsupported spans at under 20mm long.
These three images show warping on both supported Spans (within the triangle) and unsupported Spans (perpendicular to the base and cantilevered outward). Each Span is 5mm thick, and progressively 5mm longer both inside and outside of the triangle box.
The complete model. Notice that longer Spans are completely bent due to gravity.
Supported Spans, seen within the triangle, begin to bend at 20mm width and seriously warp by 25mm.
Unsupported Spans, cantilevered out to the left, are straight until they are 15mm long, but seriously warp starting by 25mm.
These Spans exhibit the impact of thickness (diameter of the Span) on warping - each Span is 20mm wide, and start at 3mm thick in diameter, growing thicker by 1mm.
Notice that at 3mm, there’s substantial warping but at 10mm there is none.
Thinner free wire Spans warp more, whereas thicker Spans are more resistant to the forces of gravity, even when they protrude the same amount of distance.
A span that is supported by the geometry of the 3D model, can withstand the heat of the kiln. For instance, the ceramic vase Phamora by Vitrox has spans longer than 20mm, but its geometry and shape counterbalances the forces of gravity - the spans never have to fight to stay the same shape.
3D printing gives ceramic artists endless possibilities in your art, enabling designs with complexities otherwise impossible to create. It is a powerful and unique ceramic tool, but is still fired in a kiln, so remember to consider how your model will sit in the kiln and to support your longer spans with fillets and more geometry.