The Process Cycle of Sand Casting Process
Ⅰ. Learn about sand mold casting
Sand mold casting, the most widely used casting process, uses consumable sand molds to form composite metal parts that can be made from almost any alloy. Since the sand mold must be destroyed in order to call the part a sand casting part, therefore, sand mold casting usually has a lower productivity. The sand casting process involves the use of furnaces, metals, patterns and sand molds. The metal is melted in the furnace and then poured into the cavity of the mold formed by the mold.
Sand mold casting is used to produce various metal parts with complex geometries. The size and weight of these components vary greatly, ranging from tens of grams to several tons. Some smaller sand casting parts include components as gears, pulleys, crankshafts, connecting rods and propellers. Larger applications include enclosures for large equipment and heavy machine bases. Sand casting is also common in the production of automotive parts such as engine blocks, engine manifolds, cylinder heads and gearboxes.
Ⅱ. Process cycle of sand casting process
1. Mold making: The first step in the mold sand casting process is to create molds for casting. In the consumable mold process, this step must be performed for each sand casting part. The sand mold is formed by packing sand in each half of the mold. Sand is wrapped around the pattern, which is a replica of the shape of the casting. When the pattern is removed, a cavity of the casting will be formed. Any internal features of the casting that cannot be patterned are formed by a separate core made of sand before forming the mold.
2. Clamping: Once the mold is completed, the second step of the sand casting process must be prepared to pour molten metal. First lubricate the surface of the mold cavity to facilitate removal of the casting. Then, the core is positioned and the mold halves are closed and clamped firmly together. After the mold is clamped, the molten metal can be charged from its holding container in the furnace and poured into the mold.
3. Cooling: The third step of the sand casting process is cooling. The molten metal injected into the mold begins to cool and solidify as soon as it enters the cavity. When the entire cavity is filled and the molten metal solidifies, the final shape of the sand casting parts is formed. The mold cannot be opened before the cooling time has passed. The required cooling time can be estimated based on the wall thickness of the casting and the temperature of the metal.
4. Removal: After a predetermined solidification time, the sand mold can be simply broken and the casting is removed. This step, sometimes called rocking, is usually performed by a vibrating machine that vibrates the sand and flows out of the flask. Once removed, sand casting parts may have some sand and oxide layers sticking to the surface.
5. Trimming: During the cooling process, the material of the channel in the mold solidifies and adheres to the part. This excess material must be trimmed from sand casting parts by cutting or sawing, manually or using a trimming machine. The time required to trim excess material can be estimated based on the shell size of the casting. Larger castings will require longer dressing times. The waste from this trimming is discarded or reused in the sand-blasting process.