The part in this example was originally a copper sand casting in the late 1960s. After that, the foundry created the part by machining and welding it out of solid billet. Now, it has made a comeback as a casting for the first time in 50 years. 

3D printed sand (3DPS) for molds is an additive manufacturing process (binder jetting) that is a toolingless sand casting option for use in replacement parts, functional prototyping for new product development, and low- as well as high-volume production. 
In this process, all the tooling-related design constraints, such as drafts, are eliminated, giving the design engineer much more freedom with feature placements and much higher complexity than the conventional sand-casting process. 

The process provides the opportunity for part consolidation, optimization for lighter weight, increased value with reduced costs (no tooling design, fabrication, storage, or handling), as well as reduced lead time and tighter dimensional tolerances than conventional sand castings!

The hollow structure design with relatively thin walls and overall size made it an ideal choice for 3D printing sand technology and offered tremendous cost savings from reduced raw material used and from less finish machining.

Thin walls and hollow structure (1)

•    Conventional sand casting would require a corebox to make the body core that creates the hollow interior feature of the casting, and the core print clearances with drafts will impact the wall thickness variations. 3D printed molds offer much higher precision and requires little or no core print clearances. Additionally, 3D printing also can enable self-coring for the interior, which eliminates the placement of the body core completely and the cored feature will be integral to the mold.

•    3D printed sand molds allow complex cored features without needing draft or limiting their orientation with respect to the parting plane since there is no parting plane, loose piece, corebox, or tooling with 3DPS. 

•    The conventional sand-casting process using physical tooling (a pattern and core boxes) introduce variability caused by tool wear and tear, binder build-up in the coreboxes, spring-back during demolding, and print clearances. Overall, tighter tolerances  with no draft will result in lower unit component weights with reproducible wall thickness in critical areas.

Rigging freedom with 3DPS

•    The 3DP process also offers flexibility with the rigging element, both in design and placement. This process also allowed for: classic bottom gated or innovative step gating, riser placement inside the core or at an oblique angle, external chills, as well as filters and feeding systems.

•    Because of greater complexity and stringent requirements, simulation modeling of mold flow, solidification, residual stress, and porosity predictions are valuable. This is especially true with the toolingless approach as traditional pour and validation may not be time and cost effective.

•    Collaborative engineering between the 3DP provider, the OEM, the foundry and the engineering house is a key to the success of a project like this.

Generous fillet, radii and transitions for better cast component identical to the conventional sand-casting design rules (2)

•    With 3DPS, melting, pouring, solidification, choice of alloys, and subsequent sand-casting metal additive processes must be approached differently from the conventional sand-casting process. Due to very high solidification rates, conventional alloy grades have to be adjusted and slowed.

• Smooth transitions and generous fillet and radii offer better flow of liquid metal into the mold cavity with the least turbulence and dross, resulting in a higher-quality casting without sand inclusions. 

•    Complexity of the design makes rigging design––and desired quality––challenging in the production of 3DPS molded sand castings. Again, employing casting process modeling is very valuable for validating the rigging scenarios and process conditions. Engineers can predict the casting quality with a higher degree of confidence, which is very crucial for the toolingless process.