Printed Sand Molds and Cores for Large and Complex Castings

Additive manufacturing, or 3D printing, is the process of making usable objects from digital models.  By building-up successive layers of material, additive manufacturing provides access to capabilities not available with traditional manufacturing processes.  Not only can additive manufacturing technology build objects using materials such as plastics and metals but recent advances have proved successful in printing sand molds and cores on large scales.

In February 2015, the C.A. Lawton company partnered with the Wisconsin Manufacturing Extension Partnership (WMEP) and the Milwaukee School of Engineering (MSOE) Rapid Prototype Center to preforms trials on printed sand molds and cores for large and complex castings.  Because the C.A. Lawton Company specializes in large, complex and low-volume castings, the ability to skip the expensive, and sometimes limiting, pattern step and go straight to printing of the molds and cores is compelling.

The objective of this project was to validate this new technology on practical applications.

Some of the advantages of Sand Printing are:

• Fast:Printed cores and molds are turned in days.  Traditional core boxes can take many weeks to build.
• Accurate: Feedback from the initial part can be easily incorporated into the digital model resulting in dimensionally accurate parts.  This is not always practical or even possible for traditional patterns due to scope of the adjustments (< .020”) and the high expense of altering existing wood or urethane tooling.
• Near-Net: Because 3D printed sand molds do not require draft for pattern extraction as well as special accommodations for under-cuts, molds can be built to exact profiles resulting in weight savings as well as less machining.
• Surface quality and contour consistency:Printed sand molds produce surfaces many degrees higher vs foam tooling.
• Complexity:No need to watch out for undercuts and allows for internal features not possible with traditional cores.
• Integrated: Complete molds can be printed inclusive of internal features.  Cores integrated into mold.
• Cost-effective: Quick and efficient production of models and prototypes without expensive patterns. Ideal for large, low-lot size / single run parts and complex cores.
• Combination:3D printed complex cores can be combined with the traditional in-house sand mold.
• Easy de-coringafter casting: Due to low binder content of cores and hence easier outgassing of components.

This project successfully produced a series of parts using sand molds and cores.   The applications were unique due to the size (1,000+ pounds) and complexity of the parts.   3D scanning of the final parts proved the accuracy of the process and the viability of this process was confirmed.