Precision Investment Casting, also known as lost wax casting, is a process in which metals are cast into different shapes using wax and ceramics to serve as the mould for the casting. This is one of the oldest known techniques for metal casting and has endured through centuries.

It is utilised in various industries such as firearms, energy, gas and oil, and even the food industry. While many debate the strength and durability of this casting method, doubting that it might produce weaker metal shapes compared to forging or metal fabrication, these doubts have been dispelled since aerospace, defence, and medical fields trust equipment made from Precision Investment Casting.

What is the process of Precision Investment Casting?

As mentioned earlier, the process of Precision Investment Casting involves using wax and ceramics as the mould for the main metal. This is carried out in a very simple yet precise manner (hence the name), and the steps are:

• Pattern Formation – The manufacturing of the wax pattern is the very first step in investment casting. It should be noted that wax is preferred over plastic because wax melts easily and can be reused for another casting, which is also cost-effective. Special aluminium moulds are created to cast the pattern, requiring some trial and error to account for factors like wax shrinkage, ceramic expansion, or metal contraction.

• Assembly – For Precision Investment Casting, there are two methods of assembly: single moulds and tree formation. One of the main advantages of this method is that since there is no need to open the master mould, it allows for creating many intricate shapes for moulds. After the design is set, the wax is poured in to fill the shape.

• Shell Building – For the tree formation, a ceramic pouring cup is attached to the end of the main bar, which acts as the roots. This is then dipped in refractory slurry made of fine silica, sand, and water. Once the initial ceramic layer is formed, the set is covered with sand and left to harden.

• Dewaxing – This crucial step in Precision Investment Casting requires patience and precision. The hardened mould is turned upside down and heated to a temperature of 200°F to 375°F, causing the shell to further harden and the wax to melt and drain completely. This creates the cavity used for casting the metals.

• Pouring and Solidification – After all the wax has been removed, the ceramic cavity is heated further to a temperature of 1000°F to 2000°F, and the molten metal is poured into this hot, hardened cavity. This facilitates the smooth flow of metal into even the smallest detailed sections of the cast. The metal is then left to solidify.

• Cutting – Once the metal has solidified and the shape is formed, the outer ceramic shell is cut away or broken off. Any residual sand is brushed away.

• Customisation – The final step involves customising the design unless it was already created in a mould designed for that purpose.

Advantages and Disadvantages

Like all manufacturing processes, Precision Investment Casting has its advantages and disadvantages, but the benefits generally outweigh the drawbacks. While some may argue that this method is more time-consuming and requires high skill and precision to achieve the desired outcome, the effort invested in manufacturing ensures that the final product is not damaged during shaping.

Intricate designs can be cast as a single piece with this method. It is renowned for its excellent dimensional accuracy and detailed finish, and a wide range of alloys can be used. Although it costs more in production, customers are willing to pay for high-quality products.

As one of the oldest methods, Precision Investment Casting has stood the test of time, continuously evolving and attracting more manufacturers to adopt this technique for producing premium-grade metal designs.