The ceramic injection molding process mainly includes four processes: feeding, injection molding, degreasing and sintering.
(1) Selection and optimization of powder
The study found that different Al2O3 powder mixing ratios caused great differences in the injection molding binder ratio, feed fluidity, product shrinkage and grain boundary diffusion. Alumina is a composite material prepared by doping other ceramics or metal materials. The composite ceramic material doped with Cr3C2, SiC, Ti, WC, ZrO2, Al, MgO in alumina can enhance dislocations and inhibit grain growth. Conducive to grain refinement and improve the mechanical properties of the product.
Another research field of powder selection is the influence of powder average particle size, bulk density, powder shape, specific surface area, and particle gap on the flow performance of the feed and product quality. As the main material of injection molding, powder is the most important requirement is fine particle size and regular shape. The powder with small particle size has good fluidity during injection molding, large filling amount and low sintering shrinkage.
The selection of the binder system is the core link in alumina ceramic injection molding. It not only directly affects the injection performance of the feed, but also determines the degreasing method and affects the final performance of the product. The binder system has two basic functions in the injection molding process: firstly, to ensure that the feed has good fluidity; secondly, to ensure the strength of the green body.
At present, the most commonly used binder in alumina ceramic injection molding is composed of paraffin wax (PW), polypropylene (PP) and stearic acid (SA).
The influence of surfactants
According to rheological theory, surfactants largely control the properties of the ceramic feed, and the stability of the feed will increase as the absorption layer on the surface of the ceramic particles increases. In the injection molding process of alumina ceramics, the amount of surfactant will vary with the other components of the binder, and its content is mostly between 1% and 5%.
The degreasing process is the longest time-consuming process in the injection molding process, and it is also the most critical process for quality control. Improper degreasing can cause many product defects. A lot of research work has shown that the degreasing process and the addition of the binder are inseparable, and the degreasing method used is also different for different binders.
The degreased ceramic green body is a porous formed body with a low density. It needs to be densified and sintered at a high temperature to obtain a dense ceramic part with the required dimensional accuracy and fiber structure.