Special ceramic forming technology

With the expansion of application fields for special ceramics, the performance requirements for special ceramics are becoming increasingly stringent. Material forming is a crucial process in the production of special ceramics, determining the material's properties and applications. How many ceramic forming techniques are there today, and what are their characteristics?

1. Injection Molding
The thermoplastically injection molding technology for ceramics is developed from plastic molding technology. It involves heating and mixing ceramic powder with thermoplastic resin, wax, plasticizer, solvent, etc. (or extruding and pelletizing), then feeding it into an injection molding machine. After heating and melting to achieve plasticity, it is injected at high speed under pressure from the nozzle into a metal mold cavity, where it cools and solidifies within a very short time to form the shape.
Characteristics of injection molding technology: It can form parts with complex shapes, is easy to automate and mass produce, and has high dimensional accuracy and a uniform microstructure. However, injection molding has a high carrier content, and the preform must be degreased before sintering. Large preforms often lead to organic matter enrichment and particle rearrangement, resulting in poor homogeneity and a tendency to crack. This is a problem that needs to be addressed urgently when using injection molding technology.
2. Electrophoretic Deposition Molding
Electrophoretic deposition molding utilizes a direct current electric field to cause charged particles to migrate and deposit onto the electrode with the opposite polarity, thus forming the shape. During the deposition process, the distance between particles is shortened under the action of electrophoretic migration, and the Vander Waals attraction force plays a major role. The stable dispersion of the slurry begins to be lost, and the powder particles gradually deposit onto the electrode. Electrophoretic deposition molding consists of two successive processes: particle electrophoretic migration and particle discharge deposition on the electrode. To ensure that the particles can individually precipitate onto the electrode without being affected by other charged particles, the ceramic slurry needs to have good dispersibility.
Electrophoretic deposition molding has the following characteristics: simple, flexible, and highly reliable, making it suitable for forming multilayer ceramic capacitors, sensors, and gradient functional ceramics. However, it is relatively sensitive to changes in process parameters.
3. Centrifugal Slip Casting
Electrophoretic deposition molding utilizes a direct current electric field to cause charged particles to migrate and deposit onto the electrode with the opposite polarity, thus forming the shape. During the deposition process, the distance between particles is shortened under the action of electrophoretic migration, and the Vander Waals attraction force plays a major role. The stable dispersion of the slurry begins to be lost, and the powder particles gradually deposit onto the electrode. Electrophoretic deposition molding consists of two successive processes: particle electrophoretic migration and particle discharge deposition on the electrode. To ensure that the particles can individually precipitate onto the electrode without being affected by other charged particles, the ceramic slurry needs to have good dispersibility.
Electrophoretic deposition molding has the following characteristics: simple, flexible, and highly reliable, making it suitable for forming multilayer ceramic capacitors, sensors, and gradient functional ceramics. However, it is relatively sensitive to changes in process parameters.
4. Centrifugal Sedimentation Molding
Centrifugal sedimentation molding is a method for preparing plate-like and layered nano-multilayer composite materials. The principle is that different slurries are successively and uniformly deposited layer by layer into a whole under the action of centrifugal force; materials with different properties in each layer can also be deposited by utilizing the difference in particle size or mass.
Layered materials prepared using centrifugal sedimentation molding have the following characteristics:
(1) By depositing different materials, the toughness of the material can be improved;
(2) The deposited layers can be a combination of electrical, magnetic, and optical properties, exhibiting multi-functionality;
(3) Anisotropic new materials can be produced.
5. Colloidal Forming
Gel casting was developed in the 1990s by Oak Ridge National Laboratory in the United States. It combines traditional slip casting with polymer chemistry, using a polymer network to create a polymerization reaction that causes ceramic particles to aggregate and form a ceramic preform. By adding vinyl organic monomers to the suspension medium and utilizing the action of catalysts and initiators, the ceramic slurry undergoes an in-situ polymerization reaction after casting, solidifying into a ceramic preform. Gel casting is a highly practical technology. Its significant advantages include good homogeneity of the formed preform, high strength of the formed preform, direct machinability to obtain suitable dimensions, and small shrinkage after firing, making it suitable for precise dimensional forming. Ceramic colloidal injection molding solves two important key technologies: rapid in-situ solidification of concentrated ceramic suspensions and controllability of the injection process. Through in-depth research, it was found that pressure can rapidly induce in-situ solidification of concentrated ceramic suspensions, thus inventing pressure-induced ceramic forming technology.
Characteristics of colloidal injection molding technology: It can obtain high-density, high-uniformity, and high-strength ceramic preforms. This forming technology can eliminate agglomerates of ceramic powder particles, reduce deformation and cracking of complex-shaped parts during sintering, thereby reducing the amount of post-part machining and obtaining highly reliable ceramic materials and parts. This process has no limitations on the size and thickness of the formed body, avoids the difficulty of removing the binder caused by the use of a large amount of organic matter in traditional ceramic injection molding, and realizes the injection process of colloidal forming. It is suitable for large-scale production and is a core technology for the industrialization of high-tech ceramics.
Today, various ceramic forming technologies are constantly emerging, each with its own advantages and disadvantages. During production, the material's properties and application aspects should be considered to determine which forming technology to use, thereby producing high-performance ceramic products.