Formulation of alumina suspensions focused on defect-free debinding for stereolithography-based additive manufacturing
BARCELONA P. 1, PADILLA SÁNCHEZ J. 1,2, MARTÍNEZ LÓPEZ M. 1, SEGARRA M. 1, XURIGUERA E. 1
1 Universitat de Barcelona, Barcelona, Spain; 2 Universitat Politècnica de Catalunya, Barcelona, Spain
Stereolithography is an additive manufacturing technology for obtaining ceramics based on curing a photosensitive resin, containing ceramic particles, with a light source. The wide availability of the technology has led to many advances in obtaining materials that can be printed by stereolithography. Despite this, ceramic material processing by stereolithography requires large amounts of a binder for the manufacture of the parts, associated with some problems. Since the objective is to obtain ceramic pieces, subsequent thermal processing is necessary to eliminate the polymeric part and to be able to sinter the ceramic. The burnout of this organic part is a key step to avoid the formation of cracks due to the formation of combustion gases, requiring very slow and long debinding.
In this work, a suspension of alumina at 50 vol% has been formulated with great stability. To obtain ceramic pieces without burning defects, it is necessary to process these pieces in a nitrogen atmosphere and heating rates below 1 ?C/min. To reduce the treatment time, the use of polyethylene glycol (PEG), with a molecular weight of 200, as a diluent for a controlled stepwise debinding is also studied. The use of PEG allows a debinding of the different components at different temperatures, facilitating the outflow of gases, and avoiding the formation of defects. The PEG-resin compatibility has been verified and the amount to be incorporated has been optimized to 20 %. Through thermogravimetric tests, a specific thermal treatment has been designed with different steps for the debinding at different temperatures. The use of the PEG as a diluent increases the maximum heating rate, reducing the processing time by less than half compared to a formulation without PEG. In addition, the use of PEG allows debinding in air atmosphere, instead of nitrogen. Rheology-UV tests have been used to corroborate the processability of the formulations obtained, as well as the effect of PEG on the reactivity and properties of the resulting mixture.