Metal Shaping & Processing

Although there are a multitude of materials utilized in bicycle production, From the Workbench concentrates on alloys. We asked Rob, our materials scientist at large, to lay down some verbiage to help you understand what makes your bikes able to endure your abuses. The following are some technical concepts that deal with metallurgy (the science and technology of metals). These concepts are fundamental to understanding the mechanisms by which metals can be processed to enhance and bring out their desired properties. If you tough it out and read these definitions, you will have a new appreciation for your steed.

Crystalline - All metals have a crystalline structure where the atoms are arranged in consistent geometric patterns. Some metals have the same crystal structure as others, but, the size of the crystal unit will be different due to the difference in the size of the atoms.

Grains - Generally as a metal solidifies from the melt, it will begin to crystallize in many places at once. These ‘growing’ crystals are oriented randomly. When the metal is completely solid, each of the crystal regions is called a ‘grain’. When metals are cooled rapidly from liquid, many small grains are grown. In contrast, a few large crystals grow when metal is cooled slowly from molten state. Generally, the strength of a metal is related to its grain size. A metal that has many small grains is stronger than the same metal with a few large grains.

Recrystallization - When many dislocations are formed by plastic deformation and the metal is heated above a certain temperature, the dislocations will collect together to transform into grain boundaries for new grains. These new grains are very small and dislocation free, thus making the metal softer. This process where new crystals are formed is called recrystallization, and the minimum temperature at which it occurs is called the recrystallization temperature. The recrystallization temperature is generally 40% of the melting temperature of most metals. The new grains that are formed are small, but if the metal is held at slightly higher temperatures the grains will begin to grow larger by consuming smaller grains. This is called grain growth. This effect can be observed with soap bubbles, where many small bubbles connect to form a few large bubbles.

Forming - Forming is any process that changes the shape of a metal without removing material. Forming can be accomplished while the metal is cold or hot. Some common forming processes are forging, rolling, drawing and extruding:

Forging is where a metal is shaped by a sharp blow, or a slow pressing using a die (a hardened metal formed to an inverse of the desired shape).