Sand casting is the process of metal casting using sand as the mold material. When creating a sand cast mold, sand is packed around the pattern. The resulting mold cavity is then used to create finished metal parts. If voids are required within the mold cavity, core boxes are used to create sand cores.
Sand casting is a cost-effective, efficient process for small-lot production or high-volume manufacturing when used in conjunction with automated equipment.
There are three common types of sand casting patterns:
- Loose patterns are simply replicas of the cast piece.
- Split patterns are made in two or more pieces and doweled together to permit separate removal.
- Matchplates are similar to split patterns except the cope and drag sides are combined into a single piece.
3D Printing Application
The production of sand molds and cast metal parts is relatively straightforward and suitable for automated methods. However, fabrication of the patterns used to produce the sand molds is often difficult, time-consuming and expensive.
The most common approach is to produce patterns using computer numerical control (CNC) machining, but the production costs are high and the lead time is substantial. Problems like incorrect shrink compensation and design flaws generally require that the pattern be reworked which adds to the expense and lead time.
Gate and runner systems are typically cut from Ren board or a similar material, hand-carved and then sanded to the finished shape. This also adds additional expense and lead time. Because of these problems, foundries have turned to additive manufacturing (AM).
Replacing Machined Patterns with Additive Manufacturing
To replace the machined pattern, AM patterns must withstand the ramming forces that are applied to pack the sand, be abrasion resistant, and be unaffected by the chemicals in the sand binders and mold release. Most additive manufacturing technologies have been unable to meet these challenges. However, Fused Deposition Modeling™ (FDM®) service with materials offered by Stratasys® like acrylonitrile butadiene styrene (ABS), polycarbonate (PC), PC-ABS and ULTEM™ 9085 resin thermoplastic resin meet all of these requirements. FDM is an AM process that builds plastic parts layer by layer, using data from computer-aided design (CAD) files. FDM parts have the compressive strength needed for use as a sand casting pattern.
The surface finish of FDM created parts meets all the requirements of sand casting patterns when post-processed. Post processing also seals the molding surface which prevents release agents from penetrating and sand from sticking. Finally, FDM Technology™ is also being used in both green and no-bake operations for pattern and core box production.
Sand Casting 3D printing best fit
- Low to moderate-volume (5,000+ castings)
- Prototype, pilot runs and production
- Compaction pressure < 20.7 MPa (3,000 psi)
- Moderate to high complexity
- Size (XYZ):
- < Build envelope of FDM system
- Features accessible for finishing