Investment casting is a near net shape process offering tighter dimensional and profile tolerances with no or minimal draft and excellent as-cast surface finish.  

Metalcasters use a disposable wax pattern, which is typically assembled using multiple pieces––for this reason, investment casting allows design engineers the freedom to consolidate complex features and sub-assemblies into a one-piece casting configuration.
Converting from fabrication to a single investment casting, this near net shaped component resulted in a lighter weight thanks to reduced wall thickness.

For investment casting, the ceramic shell mold is preheated, making thinner wall sections with greater details possible, in contrast to sand casting. However, the design engineers must consider the minimum wall thickness required from a castability perspective, as well fluidity and solidification of the liquid metal during the casting process. These, along with process parameters and rigging design must be validated with simulation to ensure desired soundness and strength!

• The key driver for the design was to have thin wall thickness of 0.04-in. cast successfully without any mis-fill or warpage.  

• Myth: Casting has limited features and complexity because it can have only one parting plane; or position of features is constrained by the parting plane orientation. 

• Fact: Investment casing offers multiple random parting plane orientations, which allows any complex features to be cast along with the main shape. The reason: Complex shapes are broken down into individual wax shapes, which can be drawn from the wax dies with little or no draft and then assembled together. 

Result: The final assembly is an exact replica of the finished casting. At times, the loose pieces or slides are used to accommodate the stripping of the wax shapes with re-entrant angles, depending on the feature depth and thickness. 

Generous fillets and radii. 

 It is important to have generous fillets and radii for the smooth transition and flow of liquid metal into the cavity.(2)

• Compared to weldment, investment casting makes it is easier to achieve generous fillets and radii in high-stress, critical areas to reduce stress concertation and improve the fatigue life.

• The lower thermal gradients (due to this process’s pre-heated ceramic shell) favors thinner walled casting configurations with intricate shapes. The surface finish achieved with investment casting is the best among all other casting processes due to the smooth finish of the wax pattern, the initial layer of fine stucco powder, and the slurry formulated with fine mold/ceramic shell substrate material.

Cracking bracket to prevent hot-tearing, ensure sound rigging and process parameters. 

• A cracking bracket (3), also known as a cooling fin, is a casting aid feature that helps achieve smooth thermal transition when the cross section suddenly changes, avoiding warpage, hot tearing, and/or cracking during solidification and cooling.

• It is very valuable to design the key process  parameters, gating, and risering system carefully and validate them with simulation before the OEM finalizes the casting design and before the foundry begins designing or building any tooling!