3D Printed Rheometry Tooling
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See more design and implementation details below.
Example design of the cup: it is composed of two parts connected by custom acme threads for fluid-tight seals. Depending on the printer you use to fabricate it, it may require additional sealant between the threads.
Six lower arms grip onto the native Peltier plate of the DHR rheometer, centering the cup.
The vane itself is composed of a back coupling to the rheometer's M14 shaft with a light interference fit (~ 50 µm overlap), and a threaded insert, and the front fractal section with a uniform cross-section.
Printing tolerances with our Form2 are marginally able to produce the right fit on the coupling, but can be thrown off by variations as small as printing in a different orientation. As long as approaches are consistent, however, a vane can be printed, washed (but not UV cured), and immediately used on the rheometer with a new sample, producing reliable rheological flow data.
After design, vanes were printed by stereolithography using a Form2 3D printer.
After printing, tools were mounted onto the rheometer shaft and the runout was assessed using a Keyence laser profilometer (projecting a blue line here to create a surface map).
The maximum point of the projected profile was tracked while rotating the vane many times to extract the runout at that height. This test was then repeated for different heights and then coupling designs.
Following this, with multiple design iterations varying the coupling size, coupling type, material, and finishing steps, principal component analysis (PCA) was performed to extract the most significant and optimized coupling designs. The inner diameter of the printed vane and the type of threaded insert were found to be the most significant parameters to ensure low runout.
We selected an embedded nut as the best inserted coupling for this application.
As-printed threads worked well, but only for 2-3 attachments before the plastic threads began to wear.
Finally, measurements could be made using the printed tools. Here, a measurement was made on ketchup still in the bottle. This demonstration shows the main advantage of the fractal-like structure: it minimizes sample displacement, allowing measurement of the ketchup properties as they have aged on the shelf for days to months. In comparison, other measurement tools would disrupt and change this structure when loading the tool into the dispensing bottle, leading to false measurements of disturbed samples.