Sand casting is one of the most used production type of heavy metal parts. These heavy metal parts can be very complex in shape, and other production types may not be suitable for commercial production of them. To produce these complex geometries in sand casting from metals, a proper mold cavity must be opened inside cast sand. These cavities are obtained with patterns.
In here, we explain the patterns that are used in casting operations and types of these patterns.
How To Design A Pattern In Sand Casting Operations?
To obtain an internal void inside sand to fill it with cast metal, pattern of a produced part must be designed and produced. These patterns must have same shapes with original part. But some parameters must be considered in the phase of pattern design;
- A thickness of after-machining operations: After the cast part is obtained from its mold, surface characteristics may not be good as well that is desired from customer. So, additional machining operations can be applied to obtain required surface characteristics. A bit of thickness ratio must be left in the phase of pattern design.
- Ration for shrinkage: Shrinkage is an another parameters. All the materials shrink after solidification generally. So, pattern must design a bit over-sized according to original shape of part to compensate this shrinking.
Which Materials Are Used For Patterns?
In general, three types of materials are used in the design of patterns; Wood, metal and plastics. Metals are very costly to produce. Various machining operations must be applied. But for high quantity of productions, metal are better.
Wood patterns are also used, and they are very cheap and shepable. But, during the packing of sand upon wood patterns, they can abrade and deform. So, they are suitable for low-quantity of productions.
In terms of both cost and production quantity, plastics take place between woods and metals. They can preferred for middle-quantity production of cast parts.
What Are The Types Of Sand Casting Patters?
For san casting operations, casting patterns are produced according to complexity of produced part and the quantity.
- Solid patterns: Solid patterns are one-piece pattern that has completely the same shape with original part. They are suitable for low-quantity productions with complex parts. Specifiying of parting line for these patterns can be a problem. This is the type that has easiest production.
- Split patterns: This is the type of pattern that has two halves of solid patterns. The difference is, there is no requirement of judgement of parting line. Sliced geometry gives the parting line.
- Plate patterns: This is an also type of pattern that two halves of part divided by a plane, and these two halves are not detachable. Cope and drag sections can be determined easily and building the sand casting system with these patterns is much more easy. So, it is suitable for higher production rates. Production of these plate patterns are quite hard compared with others.
- Cope-Drag patterns: Cope-drag patterns sliced type of plate patterns. Gating systems, risers are also added into this type of pattern. Production of sand casting system is easier than other with cope-drag patterns, but production of these patterns is quite hard.
These are the general expressions of patterns that are used in general sand casting operations. Do not forget to leave your comments and questions about patterns that are used in sand casting operations below. Your precious feedbacks are very important for us.