Hot Forging Vs.Cold Forming

Hot forging and cold forging are two different processes for forming metal that deliver similar

Cold Forming Versus Hot Forging

results. The manufacturer will look at a number of criteria before choosing which type of forging is best for a particular application.

The Hot Forging Process (Also called Hot Forming)
Hot forging is the process in which the material must be heated  significantly to be formed, thus the name. The average temperatures necessary for hot forging are:

• Up to 1150 degrees Celsius for Steel
• 360 to 520 degrees Celsius for Al-Alloys
• 700 to 800 degrees Celsius for Cu-Alloys

Heating the material during hot forging raises the temperature above the recrystallization point of the metal. The extreme heat is necessary to avoid strain hardening of the metal during deformation. A type of hot forging called isothermal forging is useful in order to prevent the oxidation of certain metals, like super alloys. In isothermal forging, the process occurs in a highly controlled atmosphere, similar to that of a vacuum.

Hot Forging Considerations
Manufacturers commonly choose hot forging for the production of parts that have a greater influence in the technical arena. Hot forging is also recommended for the deformation of metal that features a high formability ratio. Other considerations for hot forging include:

  1. Production of discrete parts
  2. Low to medium accuracy
  3. Scale Formation
  4. Low stresses or low work hardening
  5. Homogenized grain structure
  6. Increased ductility
  7. Elimination of chemical incongruities

Possible disadvantages of hot forging include:

• Less precise tolerances
• Possible warping of the material during the cooling process
• Varying metal grain structure
• Possible reactions between the surrounding atmosphere and the meta

Cold Forging (Also called cold forming or cold heading)
Cold forging deforms metal while it is below its recrystallization point. Cold forging is simplest when dealing with soft metals, such as aluminum but can be achieved with hard metals like steel too. This process is usually more cost effective than hot forging and the final product requires little, to no, finishing work. Often times, when aluminum has been cold forged into a desired shape, it is then heat treated to strengthen the piece, called "tempering."

The Cold Forging Process
Although the process uses the term cold, cold forging actually occurs at or near room temperature. The most common metals used for cold forging are usually standard or carbon alloy steels. A very common type of cold forging is called impression-die forging. During this impression-die process, the metal is placed into a die, typically a carbide die, that is attached to an anvil.

The metal is then struck by a hammer and forced into the die, forming the desired part. The hammer may strike the part multiple times rapidly to form the product.

Cold Forging Considerations
Manufacturers may choose cold forging over hot forging for a number of reasons. One reason being that cold forged parts require very little or no finishing work. Removing this step from fabrication process can save the manufacturer money. Cold forging also creates less contamination problems, and the final product features a better overall surface finish.

Other benefits of cold forging include:

• Easier to impart directional properties
• Improved interchangeability 
• Improved reproducibility
• Increased dimensional control
• Handles high stress and high die loads
• Produces net shape or near-net shape parts

Some possible disadvantages include:

• Easier to impart directional properties
• Improved interchangeability
• Increased dimensional control
• Handles high stress and high die loads
• Produces net shape or near-net shape parts
• The metal surfaces must be clean and free of scale before forging occurs
• The metal is less ductile
• Residual stress may occur
• Heavier and more powerful equipment is needed
• Stronger tooling is required