Lost wax casting, also known as investment casting, is a technique used to create complex and detailed metal objects. It is one of the oldest known metal casting methods, dating back thousands of years. The process involves creating a wax pattern, encasing it in a mould, and then melting the wax to leave a cavity for the molten metal. The name "lost wax" comes from the fact that the wax is lost or burned away during the process.
Here's a step-by-step breakdown of the lost wax casting process:
Pattern Creation: The first step is to create a wax pattern of the desired object. This can be done by hand carving the wax or using moulds or 3D printing techniques. The pattern is an exact replica of the final metal object.
Wax models ready for casting
Assembly: Once the wax pattern is ready, it is attached to a central wax sprue, which acts as a channel for the molten metal to flow into the mould. Additional wax rods, called gates and runners, may be attached to allow for the flow of molten metal and the escape of air.
Wax components assembled in the casting flask ready for investment
Investment: The wax pattern, along with the attached sprue and gating system, is then coated with a ceramic shell through a process called investment. This involves dipping the pattern multiple times in a slurry of fine ceramic material, such as silica, and then coating it with a fine refractory material like zircon. This creates a hard shell around the wax pattern.
Dewaxing: The ceramic shell with the enclosed wax pattern is heated in an oven, causing the wax to melt and drain out. This leaves behind a cavity in the shape of the original pattern within the ceramic shell. The process of removing the wax is called dewaxing.
Preheating: The ceramic shell is further heated to remove any remaining moisture and ensure it is ready to withstand the high temperature of the molten metal.
Casting: The preheated ceramic shell is placed in a furnace, and the molten metal, such as gold, platinum, or silver, is poured into the cavity. The metal fills the space previously occupied by the wax pattern.
Molten metal being heated in a crucible
Cooling and Breakout: The filled mould is allowed to cool and solidify, after which it is removed from the furnace. Once the metal has cooled down, the ceramic shell is broken away or dissolved, revealing the metal object.
Finishing: The cast metal object is then cleaned and finished through various processes, including grinding, sanding, polishing, and sometimes additional metalworking techniques, to achieve the desired surface finish and details.
Cast pieces being removed from the sprue
Lost wax casting offers several advantages. It allows for the production of intricate and detailed objects with high dimensional accuracy. The process is versatile and can be used to cast various metals.. It also enables the creation of complex shapes that may be challenging to achieve with other casting methods.