Precision casting, also known as investment casting or lost wax casting, is a manufacturing process that involves creating a disposable ceramic mold with a wax pattern shaped precisely to the item to be cast. This pattern is coated with refractory ceramic materials. After the ceramic material hardens, it is inverted and heated until the wax melts and flows out. The hardened ceramic shell becomes a disposable investment mold. Molten metal is poured into the mold and allowed to cool. The metal castings are then removed from the used molds.
This casting technique's design flexibility allows for the production of products of various sizes and shapes. Furthermore, this technique is more critical today as a large number of products require high dimensional tolerances and repeatability with complex shapes. Most importantly, the smooth surface finish of the cast product is an added value of precision casting or lost wax casting.
Overview of Precision Casting
casting allows you to manufacture complex parts that may be challenging to
produce using CNC machines. For instance, if you need to create intricate
internal channels in metal components, curved blades for impellers, or cooling
passages in complex equipment with excellent surface smoothness, precision
investment casting should be considered. Precision casting provides greater
design freedom, enabling the production of larger and more complex geometries compared
to other manufacturing techniques.
A wide range of metals can be used, including aluminum, bronze, magnesium, carbon steel, and stainless steel. Parts manufactured using investment casting include various components in industries such as aerospace, automotive, and medical equipment.Gun components, gears, jewelry, golf club heads, and many other machine parts with complex geometric shapes are produced using precision casting.
Precision Casting Process
Mold Engineering and Production
Precision investment casting begins with the design and production of casting molds, also known as wax patterns. These molds are developed in-house and serve as the "negatives" for the final castings. The molds allow for the precise spraying of wax patterns with highly accurate dimensions and excellent contours. These wax patterns are then attached together onto a so-called wax "tree" with a casting funnel mounted on top. In the later stages of this process, steel is poured into the funnel. Depending on the size of the series, the molds are mounted on manual or automatic pressure machines.
After the wax patterns are attached together, they are given a refractory ceramic shell. This shell is made by repeatedly dipping the assembly into a slurry (up to 7 or 9 times) and sprinkling it with ceramic sand. The ceramic layers then harden in a drying chamber exposed to the air.
Once each layer has formed and dried, the wax is melted out from the ceramic tree using steam (at 120°C). This is why it is called "lost wax casting." The melted wax can be recycled and reused. Next, the ceramic tree is baked at high temperatures (1100°C) and reaches its final strength through a sintering process. During this process, the remaining wax is burned away.
The required steel alloy is melted in a large furnace and brought to the casting temperature. Simultaneously, the ceramics are heated in an oven to prevent thermal shock during the casting process. After being heated, they are removed from the oven using a mechanical arm and the steel is poured in via gravity. Cooling takes place on a cooling conveyor (using nitrogen). The ceramic shell is then broken using an automatic hammer to remove the tree from the ceramic shell, which removes most of the ceramic.
Precision Finishing and Machining
The remaining ceramic is removed in the precision finishing department through grinding, sandblasting, and/or water blasting. The remaining steel is sorted by alloy and may be melted down again for future casting. Finally, gating systems are ground off, and if necessary, machining, calibration, or heat treatment is performed. After a final inspection, the process is complete.