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Design of a 3D print head for mixing additives into cement mixtures
Vícha, Daniel ; Dočkal, Aleš (referee) ; Škaroupka, David (advisor)
The subject of the thesis is the design of a 3D printing head for cement-composite mixtures (concretes). The device enables the addition of the basic component of the mixture by using a liquid solidification accelerator, followed by active homogenization of the mixture and dosing at the printing site. 3D printing of cementitious mixtures often leads to a loss of buckling stability of the printout. Therefore, it is necessary for the printed material to contain additives that accelerate the solidification of the mixture. However, these additives can cause clogging of the hoses when the mixture is pumped into the print head due to premature solidification. Hence, a more suitable solution is to mix these additives in the print head itself. The objective was to develop a 3D print head that allows for homogeneous mixing of the additives in the mixture, thereby eliminating complications associated with pumping. A working prototype of the print head was designed, which consists of a mixing and extrusion chamber. The mixing efficiency of this prototype was verified through numerical simulations using Particleworks. Subsequently, the prototype underwent a mixture experiment without a solidification accelerator to investigate pumpability through the printhead. Based on the numerical simulations, it was determined that the proposed prototype provides sufficient homogeneity of the solidification accelerator with the cement mixture, which should resolve the issues associated with pumping the accelerated mixture. By having a separate mixing chamber, the mixing efficiency can be controlled by adjusting the speed of the motor that drives the mixing shaft. The print head was designed to allow extrusion to be interrupted during print head passes. This was achieved by extruding the mixture into the open space of the chamber using a screw feeder. Therefore, based on the conducted experiments and numerical simulations, it can be concluded that the developed print head has the potential to enhance the quality of 3D printing of cement mixtures and eliminate the problems associated with pumping.
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