What is the Bearing in a Metal Extrusion Die?

The bearing is the last point of contact in the extrusion die where the workpiece takes the final desired shape. The bearing region is a critical part of the extrusion die, as it controls the metal flow through the die.

The objective is to have all parts of the profile emerge from the die at the same speed. The longer the bearing length, the greater the resistance to the flow of aluminum and the shorter the bearing length, the less resistance to flow. Through effective design, the thick parts of a profile can be slowed through the use of longer bearings to match the speed of the thinner parts with short bearings.

Typical problem with incorrect bearing in die

  • Large profile deflection
  • Imbalanced flow
  • Surface cracks
  • Variation in grain structure (peripheral coarse grain)
  • Die drag due to adhesion of aluminum on the die bearing

Typical Die Assembly containing - Die and Mandrel:

Bearing on Die and Mandrel:

  • The bearing on the die makes the outer shape of the part, hence they are also called outer bearings.
  • The bearing on the mandrel makes the inner shape of the part, hence they are also called inner bearings.