Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Sand casting is one of the oldest and most versatile metal casting processes, used to create complex shapes from molten metal like aluminum, bronze, or iron. It involves creating a mold from compacted sand, pouring in the metal, and letting it solidify. This method is accessible for DIY projects but requires caution due to high temperatures and molten metal. Always prioritize safety: wear protective gear (gloves, face shield, apron), work in a well-ventilated area, and have a fire extinguisher nearby.

Materials and Tools Needed

Pattern: A model of the part you want to cast (e.g., wood, plastic, or 3D-printed object).

Flask: A two-part metal frame (cope and drag) to hold the sand.

Molding sand: Green sand (sand + clay + water) or petrobond sand for better detail.

Molten metal source: Furnace or crucible for melting scrap metal (e.g., aluminum cans).

Gating materials: Sprue (pouring hole), runners, and risers (vents for gases and shrinkage).

Tools: Rammer (for packing sand), vent rod, parting dust (to prevent sand sticking), and a separating agent like talc.

Optional: Cores (for internal voids) made from sand or foam.

Step-by-Step Process

1.Design and Create the Pattern

Start with a pattern slightly larger than the final part to account for shrinkage (e.g., 1-2% for aluminum). It should have draft angles (2-5°) for easy removal. If making a simple part, carve it from wood or use an existing object.

2.Prepare the Sand

Mix molding sand to a damp, peanut-butter-like consistency. For green sand, combine 90% silica sand, 7% bentonite clay, 3% water, and a bit of coal dust for better casting. Sift it to remove lumps. This ensures the mold holds shape without cracking.

3.Set Up the Mold  

Place the drag (bottom flask) on a flat surface and sprinkle parting dust inside.  

Position the pattern on the drag and pack sand around it in layers, ramming firmly with a tool to compact it evenly.  

Add the cope (top flask), align with dowel pins, and pack more sand around the pattern's top half.  

Create the gating system: Cut a sprue hole (funnel for pouring) in the cope, runners (channels to the mold cavity), and a riser (reservoir for extra metal). Vent holes prevent trapped gases.

4.Remove the Pattern

Carefully separate the cope from the drag. Gently lift or pry out the pattern, leaving a cavity in the sand. If using cores for hollow parts, insert them now. Dust the cavity with a separating agent to ease metal release.

5.Close and Secure the Mold

Realign the cope and drag, clamping them together with weights or straps. Ensure no sand shifts. The mold is now ready for pouring.

6.Melt and Pour the Metal

Heat your metal in a crucible to its melting point (e.g., 1,220°F/660°C for aluminum) using a propane torch or furnace. Skim off impurities (dross). Slowly pour the molten metal into the sprue, filling the cavity completely and allowing it to rise into the riser. Pour steadily to avoid turbulence, which causes defects.

7.Cool and Break the Mold

Let the casting cool for 10-30 minutes (or longer for larger parts) until solid. Break away the sand mold by knocking off the flasks and digging out the casting. The sand can often be reused after sifting.

8.Finish the Casting

Cut off the gating system with a hacksaw or grinder. Sand, file, or polish the part to remove rough edges. Inspect for defects like porosity or cracks—if present, refine your process (e.g., better venting).