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Theses

Ceramic powder-based hybrid binder jetting system

Abstract : Binder jetting (BJ) is an additive manufacturing process in which powders are selectively joined by a binder to reproduce an object layer by layer. Despite numerous advantages, BJ is still plagued by two main limitations. Ceramics printed with BJ remain very porous after sintering and exhibit poor finish surfaces. The present thesis is an attempt to circumvent these limitations. A first part or our work was devoted to the study and development of an alumina powder compatible with a custom BJ equipment as well as to the optimization of the printing and densification conditions. The aim of this preliminary work was two-fold: firstly, to reproduce the state of the art of alumina manufacturing by binder jetting and secondly to develop a comprehensive methodology for the preparation of suitable ceramic powders for our machine (but in fact for all the machines technologically similar). This was also the technological baseline from which all further developments have been evaluated. The influence of the powder characteristics (particle size distribution, morphology, flowability, packing density and roughness of powder beds) and printing parameters (recoating speed, layer thickness and binder saturation) were carefully assessed. The mechanical performances of sintered bodies were also evaluated and compared with the literature. Densities up to 64% of the theoretical density and average compressive strengths up to 102 MPa were obtained, similar to previously reported results. To improve further the sintered density, we then developed a processing route involving a post-infiltration of pre-sintered bodies with a ceramic suspension. Different factors suspected to influence the process have been carefully studied such as the number of successive infiltrations, the influence of the pre-sintering temperature (rarely reported), solid loading, the infiltration duration, etc. The density and porosity distributions inside of the samples were also analysed using different tools combining SEM, X-ray Microtomography and porosity measurements. Using this approach, the densities of our sintered parts reached almost 90% of the theoretical density representing an increase of 33%. Finally, the last part of our work was focused on the development of a hybrid process to improve the surface roughness and dimensional accuracy of fabricated parts. The idea was to use a laser directly mounted in the machine with the objective to refine the outline of each printed layers and produce sharper edges. A parametric study was carried out to assess the effects of different laser parameters like laser power, repetition frequency and scanning speed. The influence of the laser refining on the sharpness and roughness of simple bodies has been studied by comparing them with their “only printed” counterparts. It is shown that the laser refined samples exhibit better roughness (divided by 3) and sharpness thus demonstrating the benefit of the hybridization.
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Submitted on : Tuesday, May 10, 2022 - 10:39:47 AM
Last modification on : Wednesday, May 11, 2022 - 9:00:18 AM

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  • HAL Id : tel-03663418, version 1

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Qirong Chen. Ceramic powder-based hybrid binder jetting system. Material chemistry. Université Polytechnique Hauts-de-France; Institut national des sciences appliquées Hauts-de-France, 2022. English. ⟨NNT : 2022UPHF0006⟩. ⟨tel-03663418⟩

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