Sand casting steps and mould parts

Sand casting is a process in which molten metal is poured into a cavity formed in compacted sand and allowed to solidify; the sand mould is then broken to take out the casting.

Steps

1. Pattern making - a pattern slightly larger than the part (allowances added) is made of wood, metal or plastic.
2. Core making - cores of sand bonded with resin or oil are made to form internal cavities.
3. Moulding - the pattern is placed in the drag and moulding sand is rammed around it; the cope is then rammed on top, the pattern is withdrawn, and the gating system is cut.
4. Core setting and closing - cores are placed in the cavity on core prints, and the cope and drag are clamped together.
5. Melting and pouring - metal is melted (cupola, induction or arc furnace) and poured through the sprue.
6. Solidification and cooling.
7. Shakeout and fettling - the casting is removed, gates and risers are cut off, sand is cleaned off and flash is ground.
8. Heat treatment and inspection.

Mould sketch

        pouring basin                 riser
           \      /                  +----+
   +--------\    /-------------------|    |-----+
   |  COPE   |  |  sprue             |    |     |  <- cope
   |         |  |          +---------+----+--+  |
   |         |  |          |   mould cavity  |  |
   |=========|  |==runner==gate==[ core ]====|==|  <- parting line
   |         |__|          |                 |  |
   |  DRAG                 +-----------------+  |  <- drag
   +--------------------------------------------+
        (vents are pierced through the cope sand)

Parts: pouring basin, sprue, runner, gate, riser, cavity, core, cope, drag, parting line, vents.

Advantages

• Almost any metal can be cast, including high melting point alloys.
• Sizes range from grams to many tonnes, and complex shapes are possible.
• Low tooling cost; suitable for both small and large batches.

Limitations

• Poor surface finish (Ra about 12-25 micrometre) and wide tolerances (about plus or minus 1 mm).
• A machining allowance is required.
• Defects such as porosity and sand inclusions are common; the process is labour intensive and slow for high volumes.