Silica sol process, commonly known as investment precision casting, as a kind of casting process with less cutting or no cutting that was developed on the basis of ancient lost wax casting. As an excellent technology in the casting industry, it has been extensively applied.

China, as an ancient civilization, applied this technology earlier. The ancient Chinese working people created this kind of lost wax casting technology several centuries BC, and they used it for casting products such as tripod and household utensils with a variety of fine decorative pattern and text, such as the Tomb off Marquis Yi of Zeng during the Spring and Autumn Period.
Modern investment casting methods was practically applied in the industry production in the 1940s when the development of aviation jet engine required to produce complicated shapes, such as blade, impeller and nozzle, size precision and smooth heat resistant alloy parts. It is difficult to process heat resistant alloy materials, and the parts have complex shape, so that it can’t or difficult to be made through other methods. Therefore, it is necessary to find a new precision forming technology. By referring to ancient stream lost wax casting, and through the improvement of materials and technology, modern investment casting method has achieved important development on the basis of ancient technology. The development of aviation industry promotes the application of investment casting; the continuous improvement and perfection of investment casting also creates favorable conditions for the further performance improvement of aviation industry.
Simply speaking, investment casting process steps are as follows: Make into melt-able model (referred to as “investment pattern or model”) with fusible materials (such as wax material or plastic), apply several layers of tailor-made refractory coating; wait it to form a whole shell through drying and hardening, melt the model with steam or hot water from the in model shell, and then put model shell s in the sand box, fill in dry sand moulding all round, place the casting model into the furnace through the high-temperature roasting (for high strength shell, directly conduct roasting demoulding shell without modelling), pour molten metal after cast type or shell is roast.
Investment castings have high dimensional accuracy and surface finish, so they can reduce machining work, and it is ok to leave a little machining allowance on the parts with a little higher requirements and even some casting parts can leave only grinding, polishing allowance, and be directly used without needing machining. Therefore, investment casting method can considerably save machine tool equipment and processing time, and greatly save metal materials.
In addition, investment casting method can be used to cast complicated casting of all kinds of alloy, especially high temperature alloy castings. For example, it is almost impossible to form streamlined profile and cooling inner chamber of jet engine blades by machining work art. Investment casting process can not only achieve batch production, and ensure the consistency of castings, but also avoid the stress concentration of residual knife lines after machining.