Abstract
Extrusion-based three-dimensional (3D) printing methods are preferred and emerging approaches for freely digital fabrication of ceramics due to ease of use, low investment, high utilization of materials, and good adaptability to multi-materials. However, systematic knowledge still lacks an explanation for what is their 3D printability. Moreover, some uncontrollable factors including extrudate shape retention and nonuniform drying inevitably limit their industrial applications. The purpose of this research was to present a new shaping retention method based on mathematical synthesis modeling for extrusion-based 3D-printing of ceramic pastes. Firstly, the steady-state equilibrium equation of the extrusion process was derived to provide clearer theoretical indications than purely experimental methods. Furthermore, a mathematical description framework was synthesized to better understand the extrusion-based 3D-printing of ceramic pastes from several realms: pastes rheology, extrudability, shape-holdability, and drying kinetics. Secondly, for eliminating shaping drawbacks (e.g., deformation and cracks) originating from non-digital control factors, we put forward a digital shape-retention technology inspired by the generalized drying kinetics of porous materials, which was different from existing retention solutions, e.g., freezing retention, thermally induced gelation, and using removable support structures. In addition, we developed an in situ hot air flow drying device easily attached to the nozzle of existing 3D printers. Confirmatory 3D-printing experiments of thin-walled cone-shape benchmark parts and the fire arrowhead-like object clearly demonstrated that the presented shape-retention method not only upgraded layer-by-layer forming capability but also enabled digital control of extrudate solidification. In addition, many more experimental results statistically showed that both fully solid parts and purely thin-wall parts had higher dimensional accuracy and better surface quality than the offline drying method. The 3D printed ceramic products with complex profiled surfaces conceivably demonstrated that our improved extrusion-based 3D-printing process of ceramic pastes has game-changing potentials beyond the traditional craftsmanship capacity.
Highlights
Over more than 30 years, three-dimensional (3D) printing or additive manufacturing (AM) has evolved beyond rapid prototyping and, more recently, has demonstrated great potential for mass customization production [1]
For eliminating shaping drawbacks originating from non-digital control factors, we put forward a digital shape-retention technology inspired by the generalized drying kinetics of porous materials, which was different from existing retention solutions, e.g., freezing retention, thermally induced gelation, and using removable support structures
It should be mentioned that some research suggested that fully ceramic net-shaped specimens of almost 100% densities can be produced via Selective Laser Melting (SLM) or direct energy deposition (DED) [9], but thermal shocks, melting-induced pores, and other challenges still remained due to the unstable and nonlinear laser–powder interaction [10]
Summary
Over more than 30 years, three-dimensional (3D) printing or additive manufacturing (AM) has evolved beyond rapid prototyping and, more recently, has demonstrated great potential for mass customization production [1]. With reference to the definition of AM from ISO/ASTM 17296 standard [3], AM is a variety of near net shaping processes of layer-by-layer building components driven by three-dimensional model data, absolutely different from traditionally subtractive or formative manufacturing methodologies [4]. The ME process refers to additively forming processes in which the material is layer-by-layer dispensed through a nozzle onto the platform until the 3D object is formed This standard definition of ME only highlights the feedstock dispenser and does not reflect the material solidification methodologies. The motivation of this work was to build a synthetically mathematical modeling and to present an in situ shaping retention method for the extrusion-based 3D-printing of ceramic pastes. We studied the sinterability and sintering shrinkage of 3D-printed thin-wall green bodies
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