Cold forming the chosen material into a given part shape is governed by that material's structural properties. These properties help make up the "rules" of how to form parts, all based on the combination of 3 basic forming methods.
Method to reduce diameter, where, depending on % of reduction, the material flows open or trapped on the cavity of lesser diameter.
Method to make hollow shaped holes, where material flows backward around a penetrating punch.
Method to form heads on fasteners, where material is upset at the face of dies and can be open or trapped to upset a particular shape.