What is investment casting?

1. Creating a model

To create a mold of the required component, a model is fabricated either manually or by machining from wax, or via computer aided design (CAD) and then reproduced to scale. Clay, wood, plastic or other materials could also be used to produce the model. Thermal contraction or shrinkage is already considered in this process step. Sprues, which serve as pathways for molten wax and metal during casting, are then attached to the wax model. This wax model can only be used once in the investment casting process.

2. Mold-Making

Afterwards, the wax pattern undergoes repeated coatings of refractory ceramic material, also known as ceramic shell mold material. Then, it is dipped into a ceramic slurry to create a shell around the investment casting pattern. This shell is then allowed to dry and harden. Subsequently, the wax is melted out of the shell in a kiln at high temperature and pressure using an autoclave. This process step leaves behind a negative cavity in the shape of the desired component. It is also crucial for removing any residual wax, therefore preparing the mold for investment casting.

3. Pouring and revealing the final part

Once the finished mold has fully cured, it is heated again in a kiln to minimize temperature differences with the molten metal. Finally, molten metal is poured into the cavity and compressed with gravity or vacuum pressure. Once the metal has solidified and cooled, it has taken on the shape of the original wax pattern. The ceramic shell is eventually broken away to reveal the investment cast part, followed by the removal of the sprues.

4. Finishing operations

After the metal part has been revealed, several post-processing operations, for example sandblasting or grinding, are incorporated into the investment casting process. Finally, the metal part undergoes post processing operations to refine its surface quality. If the final product consists of several components or requires additional features, welding or assembly processes can be carried out to join the parts together.

Investment casting is renowned for its ability to process a wide range of materials. It can be used for almost all pure metals such as iron, aluminum or copper. Alloys can also be processed, making it the ideal solution for applications such as bronze or steel investment casting. There are very few limitations on the types materials that can be cast, which in turn facilitates the creation of intricate parts that are characterized by superior mechanical properties and surface quality.

But there are more advantages to investment castings beyond the high versatility of processable materials. The investment casting process offers numerous advantages over other casting methods, making it suitable for a wide range of applications in industries such as automotive, aerospace or art. From intricate sculptures to complex engine components, investment casting offers a reliable and cost-effective method for crafting high-quality parts with intricate details and tight tolerances. Its ability to capture fine details and produce near-net-shape components makes it a preferred choice for manufacturers seeking precision and flexibility in their production processes.

Freedom of design
Investment casting offers unparalleled design capabilities. The process often provides the realization of difficult details such as undercuts, which could not be manufactured with other processes. Parts can be designed with great freedom because the investment casting process makes it possible to overcome the limits generally set by conventional manufacturing means. Its ability to manufacture highly-detailed components makes investment casting stand out as the ideal solution for crafting small, complex geometric shapes that have intricate features.

High-quality properties

The investment casting process is ideal for creating precise components with unique shapes while maintaining tighter tolerances and excellent surface finishing. Both of these aspects reduce the amount of machining required, but post-processing can always be used to achieve even more refined properties. The investment casting process enables the creation of components which are characterized by features that might be challenging to achieve with other manufacturing methods.

 Substantial cost- and time-savings
The investment casting process requires less expensive equipment and cuts down labour time, which allows for costs to remain relatively low. After casting, the melted wax can often be reused for another pattern. Furthermore, the flexibility to cast almost any metals and alloys of varying melting points also contributes to the efficiency of the investment casting process. Lead times can be accelerated with investment casting because the process greatly reduces the amount of machining usually required after casting.

Investment casting, while versatile and precise, faces several drawbacks. The process can be time-consuming and labor-intensive, especially for intricate designs. The need for extensive pattern-making and mold preparation further adds to production costs and lead times. Additionally, investment casting is limited in terms of the size and weight of the castings it can effectively produce. Once finished, parts often require extensive post-processing to achieve desired surface finishes and dimensional accuracy. Despite continuous advancements in the industry, the investment casting process remains mainly manual, with only few steps being automated and streamlined.

That`s why many industry professionals today rely on 3D printed PMMA patterns instead of traditional investment castings. Polymethyl methacrylate (PMMA) is an acrylic plastic with excellent burnout behaviour, providing strength, durability, and impact-resistance. It therefore opens up a brand-new scope for industries that have a long history of implementing precision investment casting, such as aviation and automotive.

Integrating 3D printing into the investment casting method does not require making a wax model or pattern. Instead, parts are designed by using computer-aided design (CAD) and directly printed in PMMA afterwards. The rest of the investment casting process remains practically the same. The integration of 3D printed molds and cores into established workflows is seamless, as they behave no differently during casting.

Wherever conventional investment casting reaches its economic limits due to cost-intensive mold and tool making, 3D printing of PMMA offers essential economic and design advantages. Therefore, the technology is destined to enable the foundry of the future to supply different market segments both sustainably and economically.