Ceramic materials, especially high-performance ceramics, have a series of excellent properties such as high strength, high hardness, high temperature resistance, oxidation resistance, etc. Therefore, they have great application prospects in aerospace, new materials, electronics, biotechnology, and other fields. The forming process of ceramic materials is not only prone to defects, but also difficult to compensate for through subsequent processes; Therefore, controlling the ceramic forming process is crucial for the preparation of the entire ceramic material.

1. Injection molding

    Grouting molding refers to a molding method in which mud is injected into a mold with water absorption properties to obtain a green body. Suitable for products with complex shapes, thin shapes, large volumes, and less stringent size requirements. The structure of the green body after injection molding is relatively uniform, but it has a high water content and large shrinkage during drying and firing.

The injection molding includes hollow injection, solid injection, vacuum injection, and centrifugal injection.

1.1 Hollow grouting

Hollow grouting refers to the use of gypsum molds without a core, so it is also known as single-sided grouting. Suitable for forming thin-walled small billets.

1.2 Solid grouting

Solid grouting is the process of injecting mud into a model with a core, where the mud is simultaneously dehydrated on both sides between the outer mold and the core. The slurry needs to be continuously replenished until it hardens into a billet, also known as double-sided grouting.

1.3 Vacuum grouting

Vacuum grouting is the use of extracting a vacuum outside the model or placing a fastened model into negative pressure air to reduce the pressure outside the model and increase the pressure difference inside and outside the model, thereby improving the quality and speed of grouting, increasing density, and shortening the suction time.

Vacuum grouting can significantly improve the suction speed. But during operation, attention should be paid to slowly vacuuming and intake, and the model strength should be high.

1.4 Centrifugal grouting

Centrifugal grouting refers to the process of injecting mud into a rotating model, utilizing the centrifugal force generated by the rotating model to accelerate the mud dewatering process.

Centrifugal grouting has the advantages of uniform thickness and dense billet, but the fluctuation of particle size cannot be too large, otherwise there will be uneven distribution of large particles concentrated on the surface of the mold, resulting in uneven microstructure and inconsistent shrinkage of the billet. The model speed depends on the size of the product and is generally less than 100r/min.

2. Casting forming

    Tape casting, also known as scraping or blade coating method. The preparation of ceramic materials by tape casting is usually achieved by mixing ceramic powder with organic additives in an appropriate ratio to prepare a ceramic slurry with a certain viscosity. The slurry is left in the container, scraped and coated with a certain thickness by a scraper on a dedicated substrate. After drying and curing, it is peeled off from the top to become a ceramic green body. Then, according to the size and shape requirements of the finished product, the ceramic green body is processed by punching, laminating, etc., and then sintered at high temperature, A ceramic material or product that ultimately achieves the desired shape, size, and performance (density, strength, microstructure, etc.).

Compared with traditional ceramic material preparation methods, tape casting has the following advantages:

The casting method is suitable for preparing large-area, flat ceramic material components;

The casting process can obtain ceramic materials with dense and porous microstructures;

In theory, ceramic membranes of any thickness can be obtained;

The ceramic material green body prepared by the casting process has a certain plasticity and strength, which can be easily operated and cut, and can be made into various ceramic components of different shapes. In addition, the prepared green body can be subjected to lamination operation, which is suitable for preparing layered structural ceramic materials;

The ceramic materials prepared by the casting process have a two-dimensional thin sheet structure and fewer material defects.

At present, tape casting has been widely used in the preparation of single-layer and multi-layer ceramic films.

3 Injection molding

Ceramic Injection Molding (CIM) is a branch of modern Powder Injection Molding (PIM) technology, which has many special technical and process advantages: it can quickly and automatically carry out mass production, and its process can be precisely controlled; Due to flow filling, the density of the green billet is uniform; Due to high-pressure injection, the powder content in the mixture is significantly increased, reducing the shrinkage of sintered products, making the product size precise and controllable, with a tolerance of up to 0.1% -0.2%, and superior performance; No need for mechanical processing or minimal processing, reducing the preparation of wood; Ceramic shaped parts with complex shapes, including horizontal holes, oblique holes, concave convex surfaces, threads, thin-walled parts, and difficult to cut, have a wide range of application prospects.

Ceramic injection molding, as a near net size molding technology, not only has the advantages of forming complex shaped products with high dimensional accuracy and surface smoothness, but also has the characteristics of high automation and adaptability to large-scale production. Therefore, it is still an effective method for forming complex shaped components to this day.

Injection molding has the following characteristics:

◆ It can form various complex shaped and high dimensional irregular parts in close proximity to the net size, without the need for (or very little) mechanical processing;

◆ Formed products have uniform green density, high green strength, excellent sintered body performance, and good consistency in product quality;

Formed products have extremely high dimensional accuracy and surface smoothness, with a surface roughness of up to 5 μ M;

The molding process is highly mechanized and automated, with a short molding cycle and high production efficiency.

4. Injection molding

The injection molding technology combines traditional ceramic processes with organic polymer chemistry, and flexibly introduces the method of polymer monomer polymerization into the ceramic molding process. By preparing low viscosity and high solid content ceramic slurries, it achieves net size molding of high-strength, high-density, and well homogeneous ceramic bodies. The basic principle of this process is to add organic monomers to a slurry with low viscosity and high solid content. Under the action of catalysts and initiators, the organic monomers in the slurry are crosslinked and polymerized to form a three-dimensional network structure, thereby enabling the slurry to solidify and form in situ. Then, demolding, drying, removing organic matter, and sintering can be carried out to obtain the required ceramic parts.

Gel casting is a highly practical technology, which has the following remarkable characteristics:

◆ Suitable for various ceramic materials, forming various complex shapes and sizes of ceramic parts;

◆ Since the shaping process and injection molding operation are completely separated, the shaping is achieved by in-situ polymerization of organic monomers in the slurry to form cross-linked network structure of gel. So the composition of the formed body is uniform, the density is uniform, and there are fewer defects;

The solidification time of the slurry is relatively short and controllable. Depending on the polymerization temperature and the amount of catalyst added, the solidification time is generally controllable within 5-60 minutes;

The mold used in this process is a non perforated mold with no special requirements for the mold, which can be metal, glass, or plastic.

The organic matter content in the green body is relatively small, and its mass fraction is generally 3% to 5%. But the strength is relatively high, generally above 10MPa. Machine processing (turning, grinding, planing, milling, drilling, sawing, etc.) can be performed on the billet to cancel or reduce the processing after sintering;

This is a net size forming technology. Due to the uniform composition and density of the body, it will not deform during the drying and sintering processes, and the sintered body can maintain the shape and size ratio at the time of molding;

The ceramic material used is high solid phase (volume fraction not less than 50%) and low viscosity (less than 1Pa? S). The solid content of the slurry is a factor that affects the density, strength, and uniformity of the formed billet. The viscosity is related to the shape of the billet and the exhaust effect of the slurry. This is also the difficulty of applying this technology and the key to its success.

--------Extracted from public information, content for reference only