Bart, Patterns are used as part of the foundy process used to produce cast metal parts.
Look at a car engine block or exhaust manifold. These parts were made by melting metal and pouring it into sand moulds.
Patterns are used to form the sand moulds so that each casting is the correct shape and size. How the meatal gets into the mould also needs to be considered as part of the whole process. Work is almost always to an engineers drawing of the part, suplied by the customer.
Foundries use sand with bonding properties to form the mould. When the metal has solidified and cooled the sand is washed away and recycled.
The main concern of the patternmaker are size changes due to contraction of the solid metal as it cools, how the mould will be formed, and the production of pattern equipment to produce the sand moulds.
Patternmaking also branches into other industries where a knowledge of moulding principals and model production are needed, eg fiberglass and diemaking.