Lost Wax Casting

The earliest use of the lost-wax casting process dates back to around 3000 BC, initially applied in bronze artifact production. By the Spring and Autumn and Warring States periods, the technique had reached a high degree of maturity. In the modern industrial era, the same process is also known as investment casting.

Lost-wax casting, now known as investment casting, is a low-machining or no-machining casting process. It stands as an outstanding technological achievement in the foundry industry and enjoys extensive application. It is suitable for casting various types and alloys, producing castings with superior dimensional accuracy and surface quality compared to other casting methods. Even complex, high-temperature-resistant, and difficult-to-machine castings that are challenging for other methods can be successfully produced using investment casting.
Modern investment casting methods were first applied in industrial production during the 1940s. The development of aviation jet engines at that time demanded the manufacture of heat-resistant alloy components with complex shapes, precise dimensions, and smooth surfaces, such as blades, impellers, and nozzles. Given the difficulty in machining heat-resistant alloys and the complexity of part geometries, alternative manufacturing methods proved impractical or infeasible. This necessitated the development of a new precision forming process. Drawing inspiration from the ancient lost-wax casting technique, modern investment casting evolved through material and process innovations, achieving significant advancements over its historical predecessor. Thus, the advancement of the aviation industry has driven the application of investment casting, while the continuous refinement and improvement of investment casting have also created favorable conditions for enhancing the performance of the aviation industry.
The investment casting process, simply put, involves creating a meltable model (referred to as a melt model or simply a model) from a low-melting-point material (such as wax or plastic). This model is then coated with several layers of specially formulated refractory clay (high-temperature resistant sand powder). After drying and hardening, this forms an integral mold shell. The wax is then melted out of the shell using steam or hot water, leaving the sand mold shell. Finally, the sand mold shell is placed in a baking furnace for high-temperature baking. Molten metal is poured into the sand mold shell to produce the casting.
Investment castings exhibit high dimensional accuracy, typically achieving CT4-6 (compared to CT10-13 for sand casting). However, due to the complexity of the investment casting process, numerous factors influence dimensional accuracy. These include wax pattern shrinkage, mold deformation, thermal expansion/contraction of the mold shell during heating/cooling, alloy shrinkage rates, and casting deformation during solidification. While standard investment castings exhibit high dimensional accuracy, consistency remains an area for improvement (castings using medium-to-high-temperature wax materials demonstrate significantly enhanced dimensional consistency).
The surface finish of investment castings generally exceeds that of conventional castings, typically achieving Ra 1.6–3.2 μm. The foremost advantage of investment casting lies in its exceptional dimensional accuracy and surface finish, which substantially reduces machining requirements. Only minimal machining allowances are needed on critical component areas, and certain castings may even be used directly after grinding or polishing without further machining. Thus, investment casting significantly reduces the need for machine tools and machining hours while substantially conserving metal raw materials.
Another advantage of investment casting is its ability to produce complex castings from various alloys, particularly high-temperature alloys. For instance, jet engine blades with their streamlined exteriors and cooling cavities are nearly impossible to achieve through conventional machining. Investing casting enables not only batch production with consistent part quality but also eliminates stress concentrations caused by residual machining marks.
Alloy types produced via investing casting include carbon steel, alloy steel, heat-resistant alloys, stainless steel, precision alloys, permanent magnet alloys, bearing alloys, copper alloys, aluminum alloys, and titanium alloys.