Which rheological tests are predictive of 3D printability?

In this webinar, Ronald G. Larson, Ph.d., Department of Chemical Engineering, University of Michigan, presents his research titled "Which rheological tests are predictive of 3D printability?".

Abstract

Direct ink writing additive manufacturing with a custom-built static mixer and fine-tip nozzle is used to print polydimethylsiloxanes (PDMS) either mixed with fumed silica or as a two-part commercial liquid silicone rubber (LSR) mixed with polyethylene glycol (PEG) or as a two-part commercial room temperature vulcanizing (RTV) silicone. We assess their printability by printing a hollow slump cone, whose print quality is correlated with rheological measurements, including 1) a shear rate up-ramp followed by 2) a down-ramp in shear rate, 3) creep tests at a series of increasing stresses, and 4) large-amplitude oscillatory shear (LAOS) with increasing amplitude well into the nonlinear regime. The PDMS-fumed silica mixtures fail to print even at the highest fumed silica loading used (9 wt%), while LSR-PEG with 4 or 6 wt% PEG prints very well even with low Shore hardness LSR, and one of the two RTV silicone components is printable, as is the mixture. The large differences in printability do not correlate well with any single rheological test, but do correlate with a combination of measures of material strength and of material recoverability.  The former can be supplied by either the yield stress from creep tests or the “flow stress” at which G’ and G’’ cross-over in LAOS. The latter is given by the dynamic yield stress in test 2, measured during a down-ramp in shear rate following a previous up-ramp to the maximum shear rate of 1000 s-1, the highest shear rate in the print nozzle.

Who should attend?

  • Researchers and engineers working with 3D printing and soft materials.
  • Individuals interested in the science behind material printability.

Ronald Larson, Ph.D. (English)
Ronald Larson, Ph.D.

Ronald Larson joined the Chemical Engineering Department at the University of Michigan in 1996, after working for 17 years at Bell Laboratories in Murray Hill, New Jersey. He received a B.S in1975, an M.S. in 1977, and a Ph.D. in 1980, all in chemical engineering from the University of Minnesota. 

Larson’s research interests include the structure and flow properties of viscous or elastic fluids, sometimes called “complex fluids”, which include polymers, colloids, surfactant-containing fluids, liquid crystals, and biological macromolecules such as DNA, proteins, and lipid membranes. He is also interested in fluid mechanics, including microfluidics, and transport modeling. He has written numerous scientific papers and two books on these subjects, including a 1998 textbook, “The Structure and Rheology of Complex Fluids.” 

He was awarded the Alpha Chi Sigma and Walker Awards from the AICHE; the Bingham Medal from the Society of Rheology, and the Polymer Physics Prize of the APS, and is a member of the National Academy of Engineering. He is the GG Brown Professor of Chemical Engineering and the AH White Distinguished University Professor of the Univ. of Michigan. 

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