Stereolithography Methods

Stereolithography (SLA) has been developed on the basis of photopolymerization phenomena and often includes the implementation of a light source for bonding pho- tocurable resins mixed with other materials for the manufacture of solid composite parts. Multi-material SLA processes have been carried out by successive application and washing of various types of photopolymerizable resins in single or multiple vat configurations (Figure 6.2). The versatility of these approaches has spread from the manufacture of electronic parts to biomedical implants in a variety of fields. Typically, the liquid precursor infiltration method has been used for the production of ceramics and their composites. A porous component is immersed in a liquid infiltration material in this method. As a result of the infiltration of the precursor into the pores of the ceramic component, a huge variety of microstructures such as gradient, partially or fully dense materials, and also an increase in density and mechanical properties of the compact powder can be achieved. In the SLA of ceramic materials, a ceramic suspension including photocurable liquid resin is used to produce the green part of the de-ceramic component. Drying and other debinding processes are then carried out in order to achieve a component with high density and minimal defects which has been infiltrated by an SLA process of aluminum ceramics by immersing the printed products in liquids of various altering components to create a multi-phase composite by filling the interconnected porosities witli infiltrated materials. A photo-initiator material was added to the aluminum suspension to make it UV-curable and suitable for the SLA process. Debinding and subsequent infiltration were followed by precipitation (Figure 6.2b). As a result of the infiltration process, the hardness of the part increased but the fracture strength decreased.

Binder Jetting Methods

Binder jet printing deposits binder materials on powder bed for selective bonding of powder materials layer by layer for the construction of three-dimensional parts. In binder jetting, additional extractable powder materials can be used in the binding process to achieve the desired percentage of materials in different layers of parts. Subsequently, additional materials can be extracted to achieve the desired porous or

(a) Multiple vat setup for stereolithography of multi-material parts; (b) SLA

FIGURE 6.2 (a) Multiple vat setup for stereolithography of multi-material parts; (b) SLA

followed by infiltration and precipitation process.

functionally graded material (FGM) by means of extraction techniques such as solvent materials. The application of infiltration processes to ceramic materials developed by AM was used to build multi-phase composites. As for the binder jet process, the process uses the nature of the binder jet’s porous products. While the binder material is cured to form a solid part, it burns off and leaves the porosity in the final component. The main purpose of the infiltration procedure is to fill the porosity with other functional materials in order to obtain a fully dense part. Ceramic metallic composites can be produced by bonding, curing, and sintering ceramic powder materials under special conditions in order to achieve a solid homogeneous structure and by immersing them in a molten metal bath to fill the porosities with metal. The sintering temperature of the printed ceramic component can affect the density and volume fraction of the metal phase and, as a result, the microstructure and the mechanical properties of the final part. The submerging time of the sintered ceramic component in the molten metal is another conceivable parameter that can change the properties of the products as the more sintered ceramic parts are deposited in the molten metal; apart from the phase of penetration, the more metallic material permeates the ceramic particles and the properties of the products will have a higher resemblance to the pure metallic parts made of the molten metal. This technique has also been used for the production of metallic composites. For one test, it was shown that the thickness of the printed component has a critical influence on the different properties of the final component as it alters the microstructure and chemical composition of the product.

 
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