What is lost wax casting?

1. Creating a model

To create the lost wax mold, a model of the required part is fabricated either manually or by machining from wax, or via computer aided design (CAD) and then reproduced to scale. Sprues, providing paths for the molten wax to flow out and to fill the cavity, are then added to the wax model. This wax model can only be used once. Thermal contraction or shrinkage is already considered in this process step.

2. Mold-Making

Afterwards, the wax pattern is repeatedly covered with refractory ceramic material and a ceramic slurry, also known as ceramic shell mold material, to create a shell around the investment casting pattern. This shell is then allowed to dry and harden. Afterwards, the wax is melted out of the shell in a kiln, leaving behind a negative cavity in the shape of the original model. As the wax is burned and cannot be totally reused, the process is called “lost wax casting”.

3. Pouring and revealing the final part

Before casting, the lost wax mold is heated again in a kiln to reduce the temperature difference with the molten metal. Finally, molten metal is poured into the cavity and compressed with gravity or vacuum pressure. After the metal has solidified and cooled, it has taken on the shape of the original wax pattern. The final cast part is revealed by breaking away the ceramic shell and cutting off the sprues.

4. Finishing operations

After the metal part has been revealed, several post-processing operations, for example sandblasting or grinding, are implemented. To reach their desired properties, lost wax casting parts are often exposed to additional machining. 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.

Lost wax casting is a highly versatile process that can accommodate a wide range of materials, offering flexibility for various applications across industries. It allows for processing alloys like steel and bronze, as well as pure metals such as iron, aluminum, magnesium and copper. The versatility of the lost wax method extends beyond these materials, with the process capable of accommodating other alloys and metals based on specific application requirements.

It’s because of the high degree of flexibility that industries such as automotive, aerospace or fine arts rely on the lost wax casting process to create, precise, complex and high performing cast parts. From intricate sculptures to complex engine components, lost wax casting offers a reliable and cost-effective method for producing 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 requiring precision and flexibility in their production processes.

• Complex Geometries and high tolerances

Lost wax casting is a metal manufacturing process that can produce intricate shapes and designs with high precision and accuracy. It is ideal for applications where dimensional accuracy is critical, as it can achieve internal features and high tolerances.

• Material efficiency, cost effectiveness and sustainability

In the lost wax casting process, the wax used to create the mold isn’t really lost. It can be reused for patternmaking. Silicone molds, created from wood patterns and used for wax injection molding can also be reused, reducing the costs per part, while also making the process stand out as a sustainable solution. The precision of lost wax casting also reduces finishing and machining times and costs.

• Consistency and reproducibility

Whether it’s small and filigree parts or larger castings. Lost wax casting enables the production of consistent, high quality parts with minimal variation between production runs. This benefits industries where uniformity is critical, such as aerospace, automotive or fine arts.

Although the industry has made continuous advancements, the lost wax process remains predominantly manual, with only a few steps being automated and streamlined. As a result, many industry professionals now rely on PMMA 3D printed investment casting patterns instead of the traditional lost wax process. Polymethyl methacrylate (PMMA) is an acrylic plastic with excellent burnout behavior, a negative coefficient of thermal expansion, which reduces the risk of shell cracking, and contains very low residual ash content. Most importantly however, 3D printed PMMA patterns can be handled exactly the same as conventional wax patterns. For industries that rely on lost wax casting, it opens up a brand-new scope for new applications, better performing products and rapid product development as well as additive serial production opportunities.

Integrating 3D printing into the lost wax casting process eliminates the need for a tool for wax model in or pattern-making via injection molding. Instead, computer-aided design (CAD) is used to design parts, which are then directly printed in PMMA using the Binder Jetting process, a support structure-free 3D printing process. The patterns are printed within a powder bed, which acts as a support and keeps the patterns in place during manufacturing. After printing, the patterns are removed from the jobbox and clean of any residual powder. Then, the patterns can be integrated into the ceramic shell building and lost wax casting process.