Understanding Lost Wax Metal Casting: Techniques & History

What Is Lost Wax Metal Casting?

The lost wax metal casting, also known as the lost wax process, is a method of metal casting in which the molten metal is poured into a mold or a die that is made by a wax model. The process is called lost-wax metal casting because once the mold or the die is formed, the wax will be melted and got rid of. The performance of the lost wax metal casting can be traced back thousands of years ago in ancient Egypt, Levant, and China.

Though the lost wax process has sustained for thousands of years in human history and not many changes have been made through this period of time, the lost wax metal casting method is considered a type of precision making in the modern manufacturing industry. This is due to several advantages that come along with the process. The lost-wax process is often called investment casting or precision casting these days.

How Does Lost Wax Casting Work?

Lost wax casting is used to produce detailed and intricate metal components that will then be applied to a series of industrial operations. There are several steps included in the lost wax metal casting process. Some steps may be carried out differently for particular purposes, but others can be generally seen in other casting processes.

● Create a Model

The first step in lost wax casting is model making. Model making refers to the process that a mold or die is formed with wax. This original model of the die will then be used to make a metal die. In addition to waxes, the mold can also be made of other materials such as clay.

● Form the Mold

The next step is mold making. In this stage, the wax model or the clay model will be covered by materials such as latex, rubber, silicone, or fiberglass. When the mold is finished, molten wax will be poured into the mold until an even wax coating is formed on the inner surface of the mold. The excess molten wax will be poured out, and this step is finished until the wax coating is thoroughly cooled down and hardened.

● Remove Wax from the Mold

The hollow wax copy of the original model will be removed from the mold. This is the lost wax step in the lost wax casting. At this stage, the mold will be heated until the wax is melted and evacuated. For now, the mold is ready to be reused to reproduce the parts. Generally speaking, the mold or die can be reused as many times as possible until it wears out.

● Refine the Finishes

Several finishes may be needed after the mold is formed and wax lost. For instance, there may be parting lines or flashing where the pieces of mold come together. The mold is used to make the shells to later cast the molten metal. To cast the metal with the shell, the molten metal will be poured into the shell. The shell is heated as the molten metal is poured into it.

● Release the Shell

Once the molten metal is cooled down and hardened into a metal piece in the shell, it will be released from the shell by breaking the shell apart. The casting products that are released from the shell may also need some finishing process to get rid of the signs of the casting process so that the products look exactly the same as the original clay model.

What Elements Are Required in Lost Wax Casting?

There are several main types of wax that are used for lost wax investment casting: natural wax, synthetic wax, and specialty wax. Each of these waxes is used to achieve certain goals and they all have their pros and cons.

● natural wax

Natural wax normally refers to beeswax. The basic properties of beeswax are fragrant, soft, flexible, and sticky. The melting point and hardness may vary because it is a natural wax. The melting point of the beeswax is affected by factors such as the pollen and the types of flowers the wax is created. The melting point of beeswax ranges from 142 degrees Fahrenheit to 150 degrees Fahrenheit.

The beeswax is preferred in certain processes because it helps reduce shrinkage and shortness. It can also be used as a finish for ironwork, steel, and bronze to hide the imperfections after the metal piece is cast. The beeswax can prevent rust and provide sheens. It can also be mixed with other oils or minerals to achieve some particular finishes.

● synthetic wax

The synthetic wax can either be microcrystalline wax or paraffin wax. The microcrystalline wax is pliable and mildly sticky. It is soft and has a smaller crystal structure than beeswax and paraffin wax. It is a petroleum-based wax with a melting point of around 160 degrees Fahrenheit. Microcrystalline wax is used mostly in casting jewelry sculptors.

The paraffin wax is a white, slick, hard wax with a larger crystalline structure. It is also a petroleum-based wax. The paraffin wax can be used alone in limited casting processes or it can be mixed with other types of wax to give them a harder property. The melting point of paraffin wax is around 135 and 140 degrees Fahrenheit.

● specialty wax

The specialty wax refers to the waxes that have specialized features for specific lost wax casting processes. The carving wax is very hard and the melting point of it is over 220 degrees Fahrenheit. The modeling wax is easily softened when exposed to the body temperature. It is used for modeling sculptures. The patch wax is very rarely used since it is applied only for finishes to fill in small imperfections on a model. There are still more subtypes of wax that are used in lost wax metal casting that is not covered in this article.