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Sand Casting

3D print durable, accurate patterns.

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Overview

Sand casting patterns can be 3D printed with PolyJet or FDM Technology for substantial savings in cost, labor and time, ultimately speeding new product development.

Sand Casting with PolyJet and FDM Patterns

The green sand casting process uses a mold made by pressing a pattern into a sand mixture. The pattern leaves a cavity into which molten metal is poured. This process works well for low–volume production. With automated equipment, it can be efficient for high–volume production. Three common types of sand casting patterns are:

  • Loose patterns, replicate the cast piece; patterns are not connected to other patterns or mounted on a plate.
  • Cope and drag patterns, or split patterns, are like loose patterns with a gating system added and a split along the parting line.
  • Match plates are similar to cope and drag patterns except for the cope and drag sides are combined into a single piece.

Producing sand molds and cast metal parts is relatively straightforward and suitable for automated methods that can reduce cycle time and labor. However, fabricating the patterns is often difficult, time-consuming, and expensive. The most common approach is to produce aluminum patterns using CNC machining. The biggest problems with this approach are the high cost and lengthy lead time.The potential for problems, such as incorrect shrink compensation and design flaws, means the initial pattern often must be redone, which adds to the expense and lead time. It is not usually practical to machine the intricate gate and runner systems on CNC machines because testing is required to finalize the design. Instead, the gate and runner system is cut from Ren board or similar material and then hand-carved and sanded to the finished shape. Constructing the gating system adds expense and lead time.

Because of the problems associated with traditional pattern production, foundries have long been interested in 3D printing (also called additive manufacturing). With 3D printing systems available from Stratasys, foundries can fabricate patterns with either inkjet-based technology or FDM Technology. This results in substantial cost savings, labor, and time, ultimately speeding up new product development.

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Application Checklist

PolyJet or FDM patterns are the best fit for sand casting when:
  • Molds are intended for prototype or production use
  • Casting designs need verification
  • Gate and runner refinements are likely
  • Castings will be complex or large
Benefits of PolyJet and FDM patterns for sand casting include:
  • Pattern cost reduction of 50 to 70 percent
  • Lead-time reduction of 30 to 70 percent
  • Faster design revisions
  • Interchangeable gate and runner system
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FDM Sand Casting Both Parts 800x600 1

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.
Sand Casting Core Box scaled

Mount the Casting Pattern

Mount the casting pattern and parting line elements on a wooden plate. The parting–line elements will be fixed in place to the plate.
Sand Casting Core Set Fixture With Hand scaled

Apply a Surface Release Agent

Apply a surface release agent on the 3D-printed master pattern.
Sand Casting 800x600 1

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.

Method Cost Time
CNC Matchplates $5,000 3-4 weeks
FDM Tooling Matchplates $2,000 1.5 weeks
SAVINGS $3,000 (60%) 1.5-2.5 weeks (37%-62%)
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