Page 13 - Curriculum Visions Dynamic Book

Metalworking techniques
Metals can be used hot or cold, pure or mixed together (as an alloy). Many processes involve heating, because when metals are heated, they are much easier to work with.
There are seven kinds of metal- working: casting, rolling, extrusion, drawing, forging, sheet-metal forming, and powder forming. They can be done either hot or cold.
Hotworking
Metals are made of crystals, usually in the form of tiny particles called grains. This is not easily seen in most metals, although it sometimes shows
up in special cases, such as when zinc is plated on steel. The pattern you see is crystals of the metal element zinc (see page 7).
It is important to know about crystals because when a metal is worked with a hammer or a roller,
the force involved strains the crystals. Strains can lead to weakness. But if
the metal is first heated sufficiently and then worked, the metal will grow a new set of strain-free crystals as it changes shape. That is why many processes
are done with hot metal. This is called hotworking. Hotworking does not add strength to the metal.
13