Sand casting Flashcards
Sand casting Stage 1 - Mold-making
The first step in the sand casting process is to create the mold for the casting. A sand mold is formed by packing sand into each half of the mold. Any internal features of the casting are formed in separate parts which are made of sand prior to the formation of the mold. The amount of time to make the mold is affected by the size of the part, the number of parts, and the type of sand mold.
Sand casting stage 2 - clamping
Preparing the molten metal to be poured, The surface of the mold cavity is lubricated Then, the parts are positioned and the mold halves are closed and securely clamped together.
Sand casting stage 3 - pouring
After the mold has been clamped, the molten metal can be ladled and poured into the mold. It must have filled the entire cavity. The filling time is very short
Sand casting stage 4 - cooling
The mold cannot be opened until the cooling time has elapsed. The desired cooling time can be estimated based upon the wall thickness of the casting and the temperature of the metal. Most of the possible defects that can occur are a result of the solidification process. If some of the molten metal cools too quickly, the part may exhibit shrinkage, cracks, or incomplete sections.
Sand casting stage 5 - removal
After the sand mold can be broken, and the casting removed. This is typically performed by a vibrating machine that shakes the sand and casting out of the flask. Once removed, the casting will likely have some sand and oxide layers adhered to the surface. Shot blasting is sometimes used to remove any remaining sand, especially from internal surfaces, and reduce the surface roughness.
Sand casting stage 6 - trimming
The excess material must be trimmed from the casting either manually via cutting or sawing, or using a trimming press. The time required to trim the excess material can be estimated from the size of the casting’s envelope. A larger casting will require a longer trimming time.
Sand casting advantages (3)
Scrap can be reused in the process
Cheap
Many material options
Sand casting disadvantages (3)
Low production rate
Poor surface finishes
Poor material strength
