I recently completed a project for a client involving 3D printing models for both Sand Casting and Investment Casting.

For Investment Casting, I selected two materials: Imagin Plastics' PLA CAST GREY and Polymaker's PolyCast. Imagin PLA performed well, producing fine surfaces that could be smoothed easily. PolyCast, on the other hand, had some printing issues, especially with nozzle clogs due to its high hygroscopic nature. Despite these challenges, both materials provided fine surface finishes for casting.

In Sand Casting, the model is retained for reuse, so material durability in high-temperature environments and strength for frequent handling are critical. I chose PC Blend CF, a strong, high-temperature material with excellent dimensional accuracy. This material addresses shrinkage during cooling and compensates for metal expansion and contraction during casting.

To achieve dimensional accuracy, I considered both the plastic material's shrinkage and the metal's expansion and contraction during casting. I conducted research to determine the linear coefficient of expansion for the plastic material and metal (Phosphor Bronze) and applied these factors to upscale the model accordingly.

In summary, for successful casting, 3D printing requires two scales for expansion/contraction to ensure the final model matches the original in all dimensions. Fortunately, the necessary data and calculation tools for this process are readily available online. The choice between the materials for Investment Casting will ultimately depend on the client's utility for the task at hand.