Improving the Sand Casting Process with 3D Printing
Sand casting is the process of using a mold made of sand to create metal casted parts. It is one of the oldest processes used to create metal parts, dating back thousands of years. The basic process of sand casting involves several steps: First, a part shape, runner layouts, and gates are placed into special sand to create a mold. Next, a molten metal material is poured into the mold and cooled to solidify it. Last, the sand mold is broken away leaving a metal part that is ready for clean up and production.
Sand casting is used for a wide range of industry applications with the primary manufacturers being foundries and pattern shops. If this process seems so simple and has been around this long, how can 3D printing improve the sand casting process?
One of the really nice things about 3D printing is the ability to bring projects that would initially be outsourced in-house. For example, bottle necking can occur when a foundry sends out a part design to a pattern maker, then has to wait to get the mold made in order to begin creation of the metal cast part. By using a 3D printer, the foundry could cut out the pattern maker and quickly create the part design for the mold in house.
3D printers, in particular the Fusion Deposition Modeling (FDM) printers, can use strong materials like plastic filaments such as acrylonitrile butadiene styrene (ABS) to substitute for CNC machined molds. This process can generally save around 60% of the cost to create a mold and speeds up the manufacturing process of the part significantly. This type of 3D printer utilization also allows for quick design changes in the event that the metal cast isn’t up to standards. FDM printed parts are extremely accurate to the designs of the mold.
Stratasys, the largest producer of 3D printers in the world, provides a step by step process for using 3D printing to improve the sand casting process:
- 3D print the master: In CAD, design a master that will maximize the capabilities of inkjet or FDM. Print the master, which will become the pattern, with the best build parameters for the desired surface finish and strength.
- Accommodate parting: Mount the pattern on parting-line elements (which can be FDM or inkjet 3D-printed fixtures). The parting line helps avoid issues with undercuts.
- Mount the casting pattern and parting line elements on a wooden plate. The parting line elements will be fixed in place to the plate.
- Apply a surface release agent on the 3D-printed master pattern.
- Create the mold: Pour sand around the pattern and parting line element and remove the pattern. A cavity appears in the shape of the pattern, the upper half forming the cope and the lower half forming the drag.
- Use the mold: Pour the molten metal in the cavity. Once it cools, it can be removed and finished.
Using an FDM 3D printing machine can be beneficial. However, it has to be under the right circumstances. FDM 3D printed parts can significantly reduce costs for medium to complex designs where you let the printer do the work that a pattern maker would otherwise have trouble with. Also, these molds are good for low- to mid-volume production, if you have under 5000 parts that need to be casted for example. Last, try to make sure your part fits the envelope of the 3D printer you are working with. If you are creating a mold that is larger than your printer there is a possibility that you could run into trouble if having to do two or more separate parts and then have to fuse them together.
3D printing can be a great technology for those who are looking to figure out how to effectively reduce costs and save time. In the case of sand casting for the right application, 3D printing can be an invaluable option for producing quality parts at a much smaller price.