Rapid prototyping technology in the field of ceramics (3)

2.2 FDC

Mukesh K. Agarwala et al. ^{[11] of the} American Ceramic Research Center used the FDC process to prepare Si ₃ N ₄ parts, which works in the same way as FDM. FDM can use a polymer or wax wire as a feed material to form a prototype layer by layer from a CAD file. The wire radius is usually 1.8 mm, which is softened and melted after being sent to the liquefier, and then ejected from the nozzle. The nozzle can be moved horizontally in the xy direction under computer control, and the non-fixed platform can move up and down. The nozzle pressure is 1.7 MPa, and the principle of operation is equivalent to a conventional plunger extrusion device. The nozzle diameter is generally 0.2-1.3mm. The extruded material is called “road” after solidification. The “road” width is 1.2-1.5 times of the nozzle diameter. The road width can be controlled by adjusting the screw flow speed in the liquefier. Adjustment. The FDM process is shown in Figure 2.

Figure 2 Schematic diagram of FDM process

Fig.2 Schematic representation of LOM process

The conversion of wire to ceramic material is the FDC (Fused Depositon of Ceramics) process, the key to the process is to prepare wire with suitable thermal and mechanical properties. The wire produced has been GS-44 with 55 vol% Si ₃ N ₄ and the binder is a four-component RU series with a diameter of 1.8 mm.

They use a nozzle diameter of 0.25 to 0.64 mm, a road width of 0.25 to 0.75 mm, a layer thickness of 0.25 mm, a GS-44 wire, a RU series binder, and a melting temperature of 100 to 150 °C. After forming, the mixture was heated to 450 ° C to remove 90% by weight to 95% by weight of the binder, and then placed in an Al ₂ O ₃ crucible and heated to 500 ° C to remove the remaining binder, and then sintered at a high temperature. GS-44 is mainly Si ₃ N ₄ and about 10 vol% oxide sintering aid. At high temperature, the oxide melts to provide a liquid phase to achieve densification, while α-Si ₃ N _{4 is} converted into β-Si ₃ N ₄ .

The FDC process was compared with the isostatic pressing process and the extrusion molding process, and the results are shown in the following table. Due to the different forming pressures, the FDC body density is slightly lower than the extrusion molding process, and the sintered body density is also slightly lower. FDC shrinkage has anisotropy, and the strength is slightly higher than the extrusion molding process, lower than the isostatic pressing process. The three fractures have similar morphology, and the FDC process defects have little effect on the strength. At present, the FDC process is mainly used for rapid forming and investment casting.

Table isostatic pressing process, extrusion molding process, FDC process GS-44 parts physical and mechanical properties

Table Physical and mechanical properties of GS-44 parts processed via isopressing,extrusion and FDC

2.3 SLS

Due to the low original density of the SLS process powder, the product density is also low, and it is currently used in the production of cast shells. Feng Tao et al. ^{[12] of} Beijing Longyuan Automatic Forming System Co., Ltd. used SLS process to manufacture cast shells. The ceramic powder coated with the reactive resin is used as a raw material. During the SLS sintering process, the shell portion becomes a sintered body, and the part portion is still an unsintered powder. After the sintering is completed, the powder inside the casing is cleaned, and the resin which has not been cured in the sintering process is sufficiently solidified at a certain temperature to obtain a shell. The results show that the shell strength, gas permeability and gas generation can meet the requirements, but the surface finish still needs to be improved.

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