The near net shaped investment casting process offers tighter dimensional and profile tolerances with minimal or no draft and excellent as-cast surface finish. This process uses a disposable wax pattern, which is typically assembled using multiple pieces, allowing design engineers the freedom of consolidating complex features and sub-assemblies into a one-piece casting configuration. 
This part—a one-piece engine cooling system component for a heavy truck OEM—was converted from a weldment that required machining and welding. The customer achieved 11% lighter weight thanks to reduced wall thickness; they also enjoyed a 3.5% cost reduction by eliminating the need for machining that was previously required on the welded surface. 
According to the foundry, the optimized product structure reduced the wall thickness while simplifying the pouring system and improved production efficiency; it ensures the castings have no defects such as shrinkage and shrinkage holes after pouring and meets the requirement for no leakage during the 30S test under 51 PSI pressure.
With investment casting, the ceramic shell mold is preheated, thus making thinner wall sections with greater details possible, compared to a sand casting. However, design engineers must consider the minimum wall thickness required from castability, fluidity, and solidification of the liquid metal during the casting process, and they should validate all with simulation—incorporating the process parameters and rigging to validate design and ensure desired soundness and strength.

Thin-wall near net shaped feature with as-cast weld surface finish (1)

•    A key driver for the design was to have thin wall thickness of 0.04 in. cast successfully without any misfill or warpage.  
•    Myth: Casting has limited features/complexity because it can have only one parting plane––or the position of parting planes is constrained by the parting plane orientation.
•    Fact: Investment casting 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––so 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. 
Feeding pad for shrinkage-free casting (2)
•    A feeding pad feature assists with directional solidification of the molten metal toward the riser connection to produce a sound casting that is free from shrinkage in high-stress critical areas.
•    Simulation is a powerful tool to validate rigging and process parameters to achieve directional solidification. Generous fillets and radii (3)
•    It is important to have generous fillets and radii to reduce stress concentration, improve fatigue life, and create smoother flow of liquid metal into the cavity.
•    Lower thermal gradients due to the preheated ceramic shell in the investment casting process favor thinner walled casting configurations with intricate shapes. The surface finish achieved with investment casting process is the best among all other casting processes due to the smooth finish of the wax pattern––made possible by the initial layer of ceramic slurry containing fine stucco powder. CS