Key Steps in the Aluminum Extrusion Process

Aluminum extrusion creates complex shapes with high precision. Understanding the key steps in the aluminum extrusion process helps you design better, more cost-effective parts.

This guide details the process from start to finish. We cover die design, extrusion, cooling, and post-finishing options like CNC machining.

What is Aluminum Extrusion?

Aluminum extrusion is a manufacturing process. It forces a heated aluminum alloy "billet" through a "die." The die is a tool with a specific cross-sectional opening.

Think of squeezing toothpaste from a tube. The tube's opening shapes the toothpaste. In extrusion, the die shapes the aluminum.

This method creates profiles with a constant cross-section. It is perfect for complex parts like heat sinks, T-slots, or window frames. The process is efficient and creates lightweight, strong parts.

The Extrusion Process Step-by-Step

The extrusion process is highly precise. It involves seven key stages to turn a raw billet into a finished, usable profile.

Step 1: Die Design and Creation

The process begins with the die. This tool is the steel "blueprint" for your profile.

It is machined from high-grade tool steel, like H13. The steel must withstand extreme heat and pressure. Simple, solid profiles use a single-piece die. Hollow profiles require complex, multi-part dies.

A well-designed die is critical. It ensures your final part has the correct dimensions and a smooth surface.

Step 2: Preparing the Aluminum Billet

The raw material is a solid log of aluminum alloy. This is called a billet.

Billets are cut to a length based on the press and final part weight. They are then loaded into an induction furnace. The billet is heated to a precise temperature. This is typically 800°F to 925°F (425°C to 500°C).

The billet is softened, not melted. This makes it malleable for the press.

Step 3: The Extrusion Press

The hot billet is transferred to the extrusion press. A release agent (lubricant) is applied to the billet and the ram.

A powerful hydraulic ram pushes the billet. It applies immense pressure, from 100 to 15,000 tons. This pressure forces the soft aluminum through the die's opening.

The shaped aluminum profile emerges on the other side. It is now the exact shape of the die.

Step 4: Cooling and Quenching

The new aluminum profile is extremely hot. It moves onto a "runout table" as a long piece.

It must be cooled rapidly. This process is called "quenching." Profiles are cooled using high-speed fans or water baths.

Quenching is vital. It "freezes" the aluminum's grain structure. This step gives the metal its strength and hardness.

Step 5: Stretching and Straightening

The quenching process can cause the long profile to twist or warp.

To fix this, the profile is moved to a "stretcher." This machine grips both ends of the cooled profile. It pulls the extrusion until it is perfectly straight.

Stretching also aligns the material's internal structure. This relieves internal stresses built up during cooling.

Step 6: Cutting to Final Length

The straightened profile is now very long. It can be over 100 feet.

It is transferred to a finish saw table. Here, a high-speed saw cuts the long extrusion into standard, manageable lengths. These are often 8 to 24 feet, depending on the customer's needs.

Step 7: Aging (Heat Treatment)

This is the final step for strengthening. Profiles are loaded into an aging oven.

This is a precipitation hardening process. For alloys like 6061, this is what creates the "T6" temper. The parts are "baked" at a low temperature (around 350°F / 177°C) for several hours.

This process maximizes the aluminum's strength, hardness, and durability.

Common Aluminum Extrusion Alloys

Your choice of alloy impacts strength, finish, and cost.

• 6063 Aluminum: Very popular. It has an excellent surface finish. It is ideal for complex shapes and architectural uses.
• 6061 Aluminum: A versatile structural alloy. It has a high strength-to-weight ratio. It also has very good machinability.
• 6005 Aluminum: Offers good strength, similar to 6061. It is often easier to extrude into complex, thin-walled shapes.

Direct vs. Indirect Extrusion

There are two primary methods for extrusion.

• Direct Extrusion: This is the most common method. The ram pushes the billet, which moves along the container wall. This creates friction, which requires more pressure.
• Indirect Extrusion: The die is on the ram. The ram pushes into the stationary billet. This creates less friction. It allows for more consistent grain structure and better dimensional control.

Post-Extrusion Finishing Options

A raw, mill-finish extrusion is rarely the final product. Most parts require finishing for function or appearance.

CNC Machining Services

Extrusion creates the 2D profile. CNC machining adds the 3D features.

You need machining to add precise features. This includes holes, threads, pockets, and complex contours. Precision milling and turning convert a simple extrusion into a finished, functional component. This is essential for parts in automotive, aerospace, and electronics.

Anodizing and Powder Coating

These are common surface treatments.

• Anodizing: An electrochemical process. It creates a hard, durable, corrosion-resistant oxide layer. It can also be dyed in various colors.
• Powder Coating: A dry, powdered paint is applied. It is then cured with heat. This creates a very tough, uniform, and decorative finish.

Industries Using Aluminum Extrusions

Because it is versatile, aluminum extrusion is used everywhere.

• Automotive: Frames, battery enclosures, trim.
• Aerospace: Seat tracks, structural brackets.
• Electronics: Custom heat sinks, device enclosures.
• Construction: Window frames, curtain wall systems, railings.
• Medical: Diagnostic equipment frames, mobility aids.

Your Partner for Machined Extrusions

Creating a great part starts with a good extrusion. It ends with precision machining.

We specialize in machining raw aluminum extrusions. We transform your profiles into finished components that meet your exact specifications.

Trust us for your high-tolerance CNC machining needs. We deliver quality, precision, and fast lead times.

Conclusion

The aluminum extrusion process is a multi-step method. It turns a raw billet into a complex, finished profile. It offers incredible design flexibility, strength, and value.

Need to turn your aluminum extrusions into finished parts? Contact Standard Machining. We provide expert CNC machining for high-quality, fast-turnaround components.

FAQs: Aluminum Extrusion Process

1. What is the difference between aluminum extrusion and drawing?

Extrusion pushes material through a die to create a shape. This process is done at high temperatures. Drawing pulls material through a die to reduce its size. Drawing is often done cold to improve surface finish and dimensional tolerance, such as for tubes or wire.

2. How strong is extruded aluminum?

The strength depends entirely on the alloy and the temper. Alloys like 6061, when heat-treated to a T6 temper, offer excellent strength. They are strong enough for structural applications in buildings and vehicles. As engineering professionals, we always recommend verifying the material specs (like tensile and yield strength) for your specific alloy.

3. What tolerances can aluminum extrusion hold?

Standard dimensional tolerances for extrusion are good, but not as tight as CNC machining. Typical tolerances might be $\pm 0.008$ inches per inch of width. For critical features, post-extrusion CNC machining is required. Machining can hold tolerances as tight as $\pm 0.001$ inches or better.