The ancient art of forging falls into two distinct categories: hot forging and cold forging. Hot forging has been around for centuries, while cold forging did not begin until the Industrial Revolution of the 19th century. Although they are completely different processes, the end result is the same. Forging is a method of deforming metal into a predetermined shape using tools and equipment, where deformation is achieved by a hot, cold or warm forging process. Which process to use depends on the metal of the finished product and the desired shape.
Hot forging occurs when a piece of metal is overheated beyond its crystallization point. The average temperature at which this occurs depends on the type of metal that crystallizes between steels up to 1150°C, aluminum alloys between 360°C and 520°C, and copper alloys between 700°C and 800°C. The desired temperature must be maintained above the re-crystallization point or the point at which the metal begins to cool. Re-crystallization can form microscopic crystals that deform when the metal is reheated, causing "strain hardening," which makes it inoperable.
Environmental factors can affect the hot forging process, and exposure to the atmosphere can cause oxidation. To avoid this, it can be done in an environmentally controlled forging chamber or isothermal forging, which is similar to a vacuum.
The main advantage of hot forging is the strength gained by the metal. Hot forged metal is highly ductile and can be significantly deformed and reshaped, making it more resilient to tensile forces. Parts using hot forging are stronger because the forging process changes the internal grain of the part, changing its shape and strength properties.
Things to Consider When Choosing Hot Forging
Hot forging can be used for the production of many different parts, as the process produces parts with high precision and complex shapes. The hot forging process is ideal for metals with high formability or deformability. The metal formed in hot forging gains strength, making it more durable. This is a flexible process capable of producing custom parts. The excellent surface finish of hot forged parts allows the use of different forms of finishing and polishing processes.
Some of the unique outcomes of hot forging include the ability to easily produce discrete pieces, low to medium precision, scale formation on the metal, low metal stress levels due to lower work hardening temperatures, grain homogenization, higher ductility levels, and Eliminate chemical incongruities in metals.
Regardless of the productivity of hot forging, it does have some drawbacks to consider. During the cooling process of the metal after hot forging, there is always the possibility of metal deformation and brittleness. Some metals should not be used for hot forging because hot forging may produce less precise tolerances and differences in grain structure.
Although hot forging has its drawbacks, it is well suited for the production of aerospace products and aircraft parts. The softness created by metals allows them to be easily shaped and produce the intricate patterns required by these industries.