Where Does the Wax Go When it Gets “Lost?”
One of the parts of the investment casting process that I initially found hard to understand was the process of removing the wax patterns and runner from the ceramic shell once it hardens. If you scour the Internet’s offerings on the lost wax casting process, if you find anything at all, it might not always be clear how the whole investment casting process works, let alone how each stage in the process is executed. This can be the case with a lot of industrial processes, and as someone who regularly writes about industry, I know that this can be frustrating.
So let this article be an opportunity to help fill in the knowledge gap about this part of the investment casting process. Just as a quick review, investment casting is the process of forming a wax pattern that exactly resembles the desired shape of the finished metal investment cast product. That wax pattern is then submerged in a slurry of ceramic materials that coat every contour of the wax pattern. This ceramic coating process usually happens more than once; this is in order to reduce the chances of wall thinness, which can cause the casting process to fail or produce defective parts.
Now the wax pattern must be removed from the ceramic shell. How does this happen? It’s important to note that while the ceramic shell around the wax is somewhat fragile, it is not particularly sensitive to the amount of heat it takes to melt wax. So the shell with the wax still inside is directed into an oven. The heat causes the wax to liquefy, and the wax is drained out (this is where the term “lost wax casting” comes from). The last phases of the process are quite intuitive: molten metal is poured into the now hollow ceramic shell. The metal fills the inside of the shell, and once it hardens the shell is removed to reveal cast products. Precision casting methods like investment casting are capable of producing highly detailed products.