Extrusion Processes

Summary

This video script explains the hot extrusion process, focusing on direct and indirect extrusion methods. It details how a hot billet is forced through a die in a thick-walled container using a ram and a reusable dummy block. The script highlights the significance of friction in determining extrusion force and discusses the breakthrough force dynamics. Additionally, it covers the use of horizontal hydraulic presses and factors affecting pressure, such as material properties, temperature, and extrusion speed. The extrusion ratio is also introduced as a crucial element in assessing the process's efficiency and capability.

Takeaways

• 😀 The primary types of hot extrusion are direct (forward) and indirect extrusion.
• 😀 In direct extrusion, the hot billet is placed in a thick-walled container and pushed through a die.
• 😀 The extrusion force is applied by a ram and aided by a reusable dummy block.
• 😀 Metal flows from the die in the same direction as the ram's motion.
• 😀 The extrusion force relies on the friction between the billet and the container, which can be reduced with lubrication.
• 😀 Initially, the force increases as the billet fills the container, reaching a peak known as breakthrough force.
• 😀 After breakthrough, the force decreases as the billet length shortens, then rises again as the billet thins.
• 😀 Resistance to deformation increases as the thickness of the unused billet portion decreases.
• 😀 Hot extrusion is commonly conducted using horizontal hydraulic presses rated by force capacity.
• 😀 The extrusion ratio is defined as the cross-sectional area of the container divided by that of the die openings.

Q & A

What is hot extrusion?

Hot extrusion is a manufacturing process where a heated billet is forced through a die to create metal shapes.

What are the primary types of hot extrusion?

The primary types of hot extrusion are direct (or forward) extrusion and indirect extrusion.

How does direct extrusion work?

In direct extrusion, the billet is pushed in the same direction as the force applied by a ram.

What role does friction play in the hot extrusion process?

Friction between the billet and the container walls affects the extrusion force; lubrication can reduce this friction.

What happens to the extrusion force as the billet is pushed through the die?

The extrusion force initially increases, peaks at breakthrough force, then decreases until the billet thins, after which it rises again as the metal flows toward the die opening.

What equipment is commonly used for hot extrusion?

Hot extrusion is typically performed on horizontal hydraulic presses.

What factors influence the pressure applied during hot extrusion?

The pressure depends on the billet material, its temperature, length, cross-section, complexity, and the extrusion speed.

What is the significance of the extrusion ratio?

The extrusion ratio, defined as the cross-sectional area of the container divided by that of the die openings, affects the efficiency and effectiveness of the extrusion process.

What occurs at the breakthrough force in the extrusion process?

At the breakthrough force, the force required for extrusion peaks before decreasing as the billet is extruded.

How does the thickness of the butt or unused portion of the billet affect the extrusion process?

As the thickness of the unused billet portion decreases, the resistance to deformation and the force requirements increase markedly.