Pattern is the solid form that is used to make the mould. Even though a pattern generally resembles the casting being produced, it differs from the casting in terms of certain allowances that are required for producing the correct shape and dimensions and in eliminating some minor details which are too complicated or small to be produced by casting and are left to be produced later by machining.
A pattern has to be designed to facilitate moulding and ensure good quality castings. The quality of the castings produced depends on the design of the pattern, its material and construction. A poor casting may result from a good pattern due to various other factors but a poor pattern would never make a good casting.
The design of the pattern depends upon the shape and complexity of the casting, the material of the costing and of the pattern, the type of moulding adopted and the number of castings to be produced.
Pattern properties are:
1. Easy to work, shape and join
2. Strong, hard and durable so as to be resistant to wear
3. Light in weight
4. Dimensionally stable
5. Cheap and easily available
6. Resistant to corrosion and chemical action
7. Able to take good finish
Pattern Materials are:
Metals and Alloys
Epoxy casting and molding
Selection of pattern material are:
1. Number of castings to be produced
2. Shape, complexity and size of the casting
3. Degree of accuracy and surface finish required
4. Design of casting
5. Casting method to be used.