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Lost wax casting is a technique for manufacturing simple to complex objects from various metals such as gold, silver, brass or bronze by casting an original model or pattern.
It is one of the oldest known metal forming techniques, dating back 6,000 years, but is still widely used in the production of jewelry, dentistry and art. Its industrial form, investment casting, is a common method of making precision metal parts in engineering and manufacturing.
While traditionally associated with manual craftsmanship, creators can now transform the lost-wax casting process through digital design and 3D printing to streamline workflows, save time, reduce costs and reinvent craftsmanship for the 21st century.
The lost-wax casting process may vary by industry and application, but generally includes the following steps. Castings can be made from the wax pattern itself, known as the direct method, or from a replica of the original wax pattern, known as the indirect method. The direct method skips directly from the first step to the fourth step.
Model making: The artist sculpts the design in wax. The size and complexity of the wax model are limited by the skill of the wax carver and the capabilities of the casting equipment.
Create the mold: The caster then casts the model and polishes the cast to produce the "master" pattern. The master model is used to create a wax pattern out of rubber, which is heated and "vulcanized" around the master casting to make a flexible wax pattern.
Make a Wax Model: Molten wax is injected or sometimes poured into a rubber mold. This can be done over and over to make copies of the original design.
Assembling the wax pattern: Sprues are added to the wax pattern and they connect to form a tree-like structure that provides paths for the molten wax to flow out and for the molten metal to later fill the cavity.
Apply investment material: Dip the wax tree in a silica slurry, or place in a flask and surround with liquid investment plaster.
Burnout: After the investment material has dried, the flask is placed upside down in a kiln where the wax melts, leaving the cavity in the shape of the original model.
Pouring: The investment pattern is further heated in a kiln to reduce the temperature difference with the molten metal. The metal is melted and poured, using gravity or vacuum pressure to pull the metal into the cavity.
Demolding: Once the molten metal has cooled slightly, the investment pattern is quenched in water to dissolve the refractory plaster and release the rough casting. . The sprue is cut and recycled, while the casting is cleaned to remove traces of the casting process.
Finishing: Filing, grinding, machining or blasting of cast parts to achieve final geometry and surface finish. When necessary, the castings are also heat treated to enhance the mechanical properties of the material.
A Short Summary of the Long History of Lost Wax Casting
It is no exaggeration to say that lost wax casting is as old as civilization itself. Artifacts such as scepters, sculptures and furniture made by lost-wax casting have been found as far away as Israel, Vietnam, Nigeria, Nicaragua and the Indus Valley. The oldest known lost-wax cast objects are amulets created by Indus Valley societies over 6,000 years ago.
After being used for centuries in the production of sculptural ornaments and textile reliefs, lost-wax casting began to be replaced by block molding in Europe in the 18th century. Part of the process was adapted to investment casting to meet the needs of industrial development in the 19th century.
In dentistry, the lost wax method is widely used to create gold crowns, inlays and onlays. Thus, the legacy of lost-wax casting is still evident today.
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