Types of Patterns Used for Casting -->

Types of Patterns Used for Casting


There are different kinds of patterns depending on the complexity and procedure of casting and molding. Some of them are briefly explained below.

Single piece pattern

These are the simplest and least expensive types of pattern. The pattern is made of a single piece and expected to lie entirely either in the drag or cope.

Application: These are used where the casting is simple and does not create any withdrawal problem. It is good to use single piece pattern in small scale production and Prototype development.

Split pattern or two piece pattern

Many patterns cannot be made in one piece. For example, a sphere pattern cannot remove from mold cavity if it is a single piece pattern. The split pattern has two halves aligned properly by using dowel pins. Dowel pins which are fitted to the cope half precisely match the hole dug in the drag half. In this case, the split surface is same as the parting plane of mold.

Application: These are the widely used types of a pattern where it is hard to withdraw casting from the mold. Split patterns used for large casting and when the depth of casting is high.

Cope and drag pattern

These are similar to the split piece pattern. In addition to split pattern, it has a gating and riser system attached separately to the face plates. By using Cope and drag pattern, two parts of mold can be produced separately, and later it can assemble into one.

Application: used in high scale production, for casting which is heavy and inconvenient to handle.

Match plate pattern

This is similar to cope and drag pattern.  In match plate pattern the gating and riser systems are mounted on a single matching plate. It is used to simultaneous production of both drag and cope molds. The cope and drag flask is prepared on two sides of this match plate. The match plate is removed after molding, the complete mold obtained by joining two pieces of mold.

Usually, aluminium and its alloys are used to make match plate patterns due to its light weight and machinability. However, when dimensional accuracy is critical, steel alloys are used to make match plate. In flat parting plane, the gating system and the patterns are screwed to the match plate. In the case of the irregular parting plane, gating system and the patterns are made integral with the matching plate.

- Types of pattern material - Application, advantages and limitation
- Types of pattern allowance and its reason
- Properties of Moulding Materials/Sand

Loose piece/ multi-piece pattern

Loose piece pattern is expensive, and molding with these patterns requires highly skilled workers. As the name suggest, loose piece pattern has more than two pieces of the pattern. Small pieces (sibling pieces) of the pattern is attached to the main piece of pattern using wire. When molding is over, the main piece of pattern (large pieces) is removed from the mold, then loose and withdraw the small pieces through the gap generated by the main piece.

Application: loose piece pattern is used when the removal of other types of pattern from the mold is impossible. The mold of too complicated shapes requires a pattern that can split into small pieces.

Skeleton pattern

These skeleton patterns are made of stripes of woods then the final pattern is made by packing sand around this framework. The skeleton to made depends on the geometry of the casting.
Application: small scale production. Skeleton pattern is used were large, and expense patterns are not justified such as in the prototyping.

Follow board pattern

The structurally weak portions of the pattern may break under the force of ramming. Such cases Follow board pattern are adopted to protect structurally weak portions. Modified bottom board (follow board) is used to support theses fragile sections during ramming. Follow board is not necessary for drag because sand packed in drag already supports the weak portions of the pattern.

Sweep pattern

Sweep pattern is suitable when the casting is large and symmetrical about the axis (e.g., bells). A 2D pattern is used to produce a 3D mold cavity (so it is a pseudo pattern). In this type, the mold cavity is created by the complete sweep of the pattern. The advantage of Sweep pattern is that it reduces both expense and weight of pattern for the 3D object.

🔗Applications, Advantages and Disadvantages of Sweep pattern

Gated pattern

The gated pattern is used for mass production of small objects (investment casting). This pattern has a gating system itself. The single pattern used to create a mold having some cavity. A single gate and runner system used to feed metal to all of these cavities. It saves considerable molding time.
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