Ceramic Injection Molding: CIM is a new process for preparing ceramic parts developed by combining polymer injection molding methods with ceramic preparation processes. Similar to the metal injection molding (MIM) technology developed in the 1970s, they are the main branches of the powder injection molding (PIM) technology, and they are all developed on the basis of the relatively mature polymer injection molding technology. For mass production of ceramic products with high dimensional accuracy and complex shapes, the use of ceramic powder molding is the most advantageous.
Advantages:
①The molding process has the characteristics of high mechanization and automation, high production efficiency, short molding cycle, high blank strength, etc., and its process can be accurately controlled (program control), which is easy to realize large-scale and large-scale production;
②A variety of small ceramic parts with complex geometric shapes and special requirements can be formed nearly net, so that the sintered ceramic products do not need to be machined or processed less, thereby reducing expensive ceramic processing costs;
③The formed ceramic products have extremely high dimensional accuracy and surface finish.
Disadvantages: One-time equipment investment and high processing cost are only suitable for mass production.
02 CIM ceramic injection molding process
The manufacturing process of ceramic precision injection molding is shown in Figure 1, which mainly includes the following 4 links:
① Feed preparation:
The feed is a mixture of powder and binder. The injection process requires that the injection feed has good fluidity, which requires the selection of the powder and the appropriate binder system that meet the requirements, the proportion of a certain loading amount, and the appropriate method of mixing at a certain temperature into a uniform Injection molding feed, so as to ensure the smooth progress of the follow-up process, and its products from the laboratory to the high-tech market. So feed preparation is very critical in the whole process.
②Injection molding and mold design:
Improper control of the injection molding process may cause many defects in the product, such as cracks, pores, welds, delamination, separation of powder and binder, etc., and these defects can not be found until debinding and sintering. CIM often uses multi-cavity molds. The size of each cavity is different, and the wear and tear of the mold cavity will cause the size of the parts to be different. In addition, the use of injection return material will affect viscosity and rheology. Therefore, controlling and optimizing molding parameters such as injection temperature, mold temperature, injection pressure, and pressure holding time are essential to reduce green body weight fluctuations, prevent the separation and segregation of components in the injection material, and improve product yield and material utilization. .
The mold design of CIM technology mainly considers the flow control of the feeding material in the cavity during injection molding. Because most of CIM products are small-sized parts with complex shapes and high precision requirements, it is necessary to carefully design and arrange the position of the feed inlet, the length of the runner, and the position of the exhaust hole. Of course, the mold design requires a clear understanding of the rheological properties of the feed, the temperature in the mold cavity and the residual stress distribution. In addition, computer simulation technology will play an important role in the design of powder injection molding molds.
③Degreasing process:
Degreasing is a process in which organic matter in the molded body is removed by heating and other physical methods and a small amount of sintering is produced. Compared with batching, molding, sintering and post-processing of ceramic parts, degreasing is the most difficult and important factor in injection molding. Incorrect process methods and parameters of the degreasing process make the product shrink inconsistently, resulting in deformation, cracking, stress and inclusions. Debinding is also very important for its subsequent sintering. Cracks and deformations generated during debinding cannot be compensated by sintering. Binder and degreasing are related to the binder determining the way of degreasing. In addition to traditional thermal degreasing and solvent degreasing, the current degreasing process also includes catalytic degreasing and water-based extraction degreasing developed in recent years.
④Sintering:
The degreased ceramic green body is densified and sintered at a high temperature to obtain a compact ceramic part with the required appearance shape, dimensional accuracy and microstructure. Since the ceramic injection molding blank contains pores left due to degreasing, the shrinkage rate of the product during sintering is relatively large, usually reaching 13%-15%. It can be seen that the research focus of CIM technology is sintering dimensional accuracy control. In addition, sintering equipment is also the key to sintering technology.
03 Application examples of CIM ceramic injection molding
At present, injection molding technology has been applied to the preparation of various high-performance ceramic products. Such as ceramic medical devices used in the biomedical field, ceramic brackets and ceramic posts for orthodontics and restorations, etc.; zirconia ceramic ferrules and ceramic sleeves for optical communications; alumina insulating ceramic zeros used in the semiconductor and electronics industries Components, such as integrated circuit high-encapsulation shells, small vacuum switch ceramic shells and small ceramic sliding shaft cores; ceramic knives, ceramic bracelets and ceramic watch cases used in modern life and watchmaking.