What is sand casting?

Despite its long history, sand casting is still one of the most important manufacturing processes today. Its main advantage is the high versatility with which metal parts can be produced. Complex shapes and geometries can be manufactured without constraints encountered by other casting methods due to their strict tooling requirements. The sand casting method can therefore be used to produce different sizes with high surface quality, dimensional accuracy and heat resistance.

1. Creating a model

To create the sand mold, a model of the required part is fabricated either manually or by machining from wood or metal, or via computer aided design (CAD) and then reproduced to scale. It can also be used to reproduce or copy an already existing part. Thermal contraction or shrinkage is already considered at the beginning of this process step. To ensure a regulated metal flow, gating and risers must also be included in the sand casting model.

2. Mold-Making

Next, the model is pressed into molding material that is stable at high temperature. In the context of sand casting, it is typically sand mixed with a binding agent which retains its shape even after the finished pattern has been removed. Sand as a refractory material is adequate as it is stable at high temperature. The sand casting “flask” usually consists of two parts, the upper “drag” and the lower “cope”. After the materials have bonded, the pattern is removed, leaving behind a cavity in the shape of the desired part.

3. Pouring and revealing the metal part

The resulting cavity in the sand casting mold is then filled with molten metal. After the metal has cooled and solidified, the sand mold is broken open to remove the finished sand casting part. This process is known as “lost mold” casting because the mold is destroyed in a shakeout process and cannot be reused. However, a large portion of the sand is captured and can be reused again after it has been purified.

4. Finishing operations

The parts that are still split after they have been taken out of the sand mold are then assembled. Any residue particles are removed through several post-processing steps, for example via sandblasting or grinding operations. To reach their desired properties, sand casting parts are often exposed to additional machining.

The sand casting process is a versatile method to produce castings of various sizes and complexities using an extensive range of materials. Molding sand for casting can be used for the majority of metals, as well as metal alloys including those with high melting temperatures such as steels, nickel, and titanium. Furthermore, different types of sands can be processed to create the mold, such as dry sand, resin sand or green sand, to name a few.

The advantages of sand casting extend beyond material flexibility alone – it stands as one of the most universal solutions for manufacturing metal parts and structures. The versatility of the sand molding process makes it suitable for diverse applications in various industries, such as automotive, aerospace, art and construction. Despite its century-long existence, sand mold casting has not been resilient towards continuous innovation and development. Especially in recent years it has gained new momentum through additive manufacturing and is destined to pave a future oriented way for foundries.

• Cost-optimization
  The main advantage of sand mold casting is the low cost of mold creation once a model is ready. Creating tools is a significant expense in permanent mold casting methods such as die casting. Since sand and models can be reused, the costs per part are reduced further. Automated equipment makes sand casting an economical solution for creating small, detailed, and intricate shapes, as well as larger and simpler designs.

• Design freedom and quality
  Sand casting is an ideal choice for core-intensive, multi-part molds and complex cast parts. Depending on the choice of sand it is possible to realize complex geometries or thin-walled structures, while ensuring high surface quality, dimensional stability and heat resistance. The sand casting process also has virtually no restrictions in terms of size and weight and is easily scalable. It offers high flexibility, as virtually any material or alloy can be casted making, sand mold casting suitable for various applications.

• Accelerated time to market and high flexibility
  Sand casting is commonly used for prototyping, due to its lower initial tooling costs compared to other casting methods such as die casting or investment casting. It also offers reduced set-up and lead times, enabling rapid iteration and design validations, resulting in faster product development cycles and product launches. The flexibility of the sand casting process also allows for quick adjustments and modifications, ensuring agile responses to design changes and scalability without compromising quality. Sand mold making is a fast process that allows for quick turnarounds in production.

However, there are some disadvantages to sand casting. The surface finish cannot be particularly fine, why extensive post-processing operations have to be implemented. Furthermore, the finished parts have low material strength due to excessive porosity. As the sand casting process is mostly non-automated, skilled labor is required to manufacture complex sand molds and sophisticated cast parts. These aspects often prove to be costly and time-consuming. Frequently, the process offers low sand reusability, highlighting it as an unsustainable choice while also introducing disposal issues. In recent years in particular, there have been calls for a supplementary solution that could advance the traditional sand casting process.

Since its beginnings, the sand casting process has evolved and improved considerably to become one of the most important industries of our modern world. Especially in recent years, through the integration of 3D printing sand molds and cores, sand casting has gained new momentum. From prototype and spare parts production to industrial series production, combining classic foundry technologies with flexible additive manufacturing processes stands out as a substantial advantage in terms of cost-effectiveness, geometric freedom and flexibility in production.

The technology of choice for the application is Binder Jetting. Our binder jetting 3D sand printers use foundry know materials such as sand and furanic, phenolic or inorganic binders. To print a sand mold or core a CAD file is needed. The file is digitally sliced into thousands of cross-sections which are then printed by applying thin layers of sand onto a building platform that will be selectively bonded by the print head. Each layer represents a cross-section of the part needed. These process steps are repeated until the sand mold or core is finished. The integration of 3D printed molds and cores into established workflows is seamless, as they behave no differently during casting.