Speed is essential when developing new products. The faster you get your parts into the customers’ hands the better your chances of winning their business. This puts the project focus on tooling lead time. Sand casting patterns and core boxes don’t take as long to produce as metal casting dies, but they can still add weeks to the project timeline. That’s where 3D printing comes in.

While 3D printing is possible in metal, parts made this way can rarely substitute for those that are sand cast. The metals aren’t the same and the printed part won’t have the look, feel or functionality of one that’s been cast. However, as a method of producing molds and cores, 3D printing offers advantages in some applications.

Conventional Sand Casting

Conventionally, molds for sand casting are made by packing sand around a pattern that replicates the part being made. The sand is held together in one of two ways. Either it contains a clay binder, in which case it’s called “green sand” because it has some moisture, or it’s coated with a resin binder.

Sand density is a key variable in the sand casting process. It should be packed tightly enough that it can’t be infiltrated by the metal, but not so tightly that it’s impermeable to air in the cavity.

The pattern is then removed, leaving a cavity for metal to fill.

When the cast part needs hollow regions, as would be the case with valve bodies, manifolds and housings, this is achieved by using cores. These are essentially compacted sand shapes that reproduce the hollow volume needed in the part. The core is then placed in the sand mold cavity where it occupies space otherwise taken up by the liquid metal.

After metal pouring and solidification, the sand mold and core are broken away to release the metal part.

Using 3D Printing

Impro uses 3D printing as an alternative way of producing both sand molds and cores. This is done through a process called “binder jetting.”

Mold and core production starts with CAD models of both. These files are then prepared for 3D printing by defining a series of very thin slices through the mold and core.

The printer works by depositing thin layers of sand corresponding to these CAD slices. After each layer is put down, in a process similar to screen printing tee-shirts, a binder liquid is applied to those areas that need to be solid. This is done by a device similar to and scaled up from an inkjet printer head.

After depositing and binding all the layers, the loose sand is shaken off to reveal the print sand mold. Cores are produced in much the same way.

Benefits of 3D Printing in Sand Casting

The main reason for using 3D printing is to avoid the lead time needed to make and prove-out patterns and core boxes. This saves a lot of time from order placement to delivery of first parts, making the process ideal for pilot production quantities.

The more complex the part being cast, the greater the time savings from printing the sand mold. However, as quantities grow the economics shift and the conventional mold-making process, with patterns and core boxes, becomes the more cost-effective choice.

3D printing for Sand Casting at Impro

Impro is able to print sand molds measuring up to 78” x 39” x 39” (2m x 1m x 1m). This makes it suitable for complex parts like engine blocks and cylinder heads as well as housings and large brackets. If you’d like to get parts sand cast in the metal specified in your design, and want to minimize the lead time involved, ask us about 3D printing.