Hot Extrusion Lecture Notes

Overview of Hot Extrusion

• Primary Type: Direct or Forward Extrusion
• Process: Hot billet is loaded into a thick-walled container and extruded through a die.
• **Components:
  • Billet: The raw material used.
  • Container: Thick-walled structure that holds the billet.
  • Die: Opening through which the material is forced.
  • Ram: Applies force to extrude the material.
  • Dummy Block: Intermediate reusable component that aids in the process.**

Mechanics of Direct Extrusion

• Direction of Flow: Metal flow aligns with the ram's forward motion.
• Friction:
  • The extrusion force is influenced by friction between the billet and container walls.
  • Reducing friction with lubrication can decrease the force needed.
• Force Dynamics:
  • Force increases as the billet is upset to fill the container.
  • Breakthrough force occurs just before extrusion starts.
  • After breakthrough, force decreases until reaching a minimum, then rises again as the billet thins.
  • Resistance to deformation increases as the unused portion of the billet decreases.

Equipment and Presses

• Type of Presses Used: Horizontal hydraulic presses.
• Rating: Hot extrusion presses rated by force capacity.
• Factors Influencing Pressure:
  • Billet material and temper.
  • Cross-section and complexity of the billet.
  • Length and temperature of the billet.
  • Speed of extrusion and reduction ratio.

Extrusion Ratio

• Definition: The extrusion ratio is the ratio of the cross-sectional area of the container liner to the cross-sectional area of the die openings.

Key Takeaways

• Understanding the relationship between friction, force, and the parameters influencing hot extrusion is critical for efficient manufacturing.
• The dynamics of force during the extrusion process highlight the importance of controlling conditions to optimize performance.