What Is Air Bending for Bending Aluminum?

What is air bending on a press brake? Air bending is a process that uses a press brake to create an angle in a flat sheet of metal, particularly for bending aluminum, utilizing air pressure instead of dies or tooling. It’s only the punch tip and the die edges touching the metal for less contact with the material being bent. The angle of the bend depends on how deeply the punch pushes the workpiece into the die. The air bends have the benefits of allowing for greater flexibility and the possibility to create unique, customized bends.

 

 

Air Bending VS Bottoming for Aluminum

Press brake Air bending and bottom bending are common in all bending styles during sheet metal fabrication.

Air Bending 

What is air bending for bending aluminum on press brake machines? In the air bending process, a punch applies pressure to the sheet metal part in the die cavity. The metal part doesn’t touch the die bottom of a press brake.

Air bending is preferred for aluminum because it reduces the contact area (preventing scratches) and requires less tonnage.

• Reduced Surface Damage: Air bending only touches the material at three points (the punch tip and the two die shoulders). This is important for aluminum because its soft surface is easily gouged or scratched by the heavy friction of bottoming.
• Lower Tonnage: Air bending requires significantly less force.

 

Bottom Bending

Bottom bending is a press brake operation to create precise angles in sheet metal by enclosing the sheet between the punch and the die. The material is forced almost to the bottom of the die, with the metal touching the sides of the die down.

• The Cracking Risk: Bottoming aluminum is dangerous. It forces the metal’s grain structure to compress and stretch at the same time in a confined space. This often results in “orange peeling” or deep cracks along the bend line.
• Bottoming or coining forces the material into the bottom of the die, which requires 3x to 5x more tonnage.

What is the difference between air bending and bottoming on a metal brake press? Air bending sheet metal is a less accurate technique that is easy to springback.

COMPARISON	AIR BENDS	BOTTOM BENDS
Accuracy & Precision	1. A greater level of inaccuracy and variation between pieces.	1. Ensures reliable, accurate bends in sheet metal.
	2. Springback is more prevalent, requiring overbending.	2. Ideal for precise parts and consistent bend angles.
	3. Not well suited for parts requiring highly accurate bend angles.	3.  Less spring back. More accurate angles than air bending.
Working Speed	1. Faster than bottom bending.	1. Slower due to full pressing into the die.
	2. Airbending abilities for most material types and thicknesses.	2. The process is slower
	3. Less pressure is required for the bend.
Flexibility & Cost	1. No retooling changing is needed for different bend angles.	1. A unique tool is required for different bend angles
	2. Less contact with tooling results in less surface damage.	2. Requires more pressure on the press brake than air bending.
	3. Using older press brake equipment often results in inaccurate bends.	3. Contact with punch and die can leave tooling marks on the part.
	4. More control over bend angle during bending.	4. Older, inaccurate presses can be used.

 

How Accurate are sheet metal air Bends?
Quality Air bend or air bender can achieve an accuracy of +0.75°. However, if a more accurate process is required, bottom bending may be required with a firm angle and bend radius.  bottoming bends can achieve + 0.25 – 0.5°.

 

Material

What material of air bending is suitable for low-strength metals, such as bending aluminum sheet metal or stainless steel? Aluminum bending is ideal for air bending due to its light and plasticity. Although stainless steel is harder than bending aluminum sheets, it can still be effectively processed.  Both carbon steel and mild steel are suitable for air bending sheet metal with appropriate thickness and solidity.

 

The “Alloy Factor”: 5052 vs. 6061

The specific alloy you choose is the biggest predictor of whether your part will succeed or snap.

5052-H32 Aluminum (The “Gold Standard”)

• Characteristics: Highly ductile and specifically designed for sheet metal work.
• Bending: It is very forgiving and can handle tight radii without cracking. It is the best choice for air bending intricate parts.

6061-T6 Aluminum (The “Brittle Beauty”)

• Characteristics: This is a structural alloy. While strong, it is very brittle in its T6 (tempered) state.
• The Problem: If you try to bend 6061 like mild steel, it will snap like a cracker.
• The Solution: You must use a larger bend radius—typically 3x to 4x the material thickness. If a sharp bend is required, you must anneal the bend line with a torch first to soften the grain.

Minimum Bend Radius” Chart

Material Thickness	Alloy	Min. Inside Radius (Air Bend)
1.0 mm	5052-H32	1.0 mm (1xT)
1.0 mm	6061-T6	3.0 mm (3xT)
3.0 mm	5052-H32	3.0 mm (1xT)
3.0 mm	6061-T6	8-10 mm (3-4xT)

 

Calculating Springback in Aluminum Air Bending

When air bending aluminum, you typically need to over-bend by 1 to 3 degrees to compensate for springback.It means if you require a 90° finished angle, you should bend the part to 88° or 87° inside the machine. Once the tooling releases the pressure, the material will spring back to the desired 90°.

• Factors Affecting Aluminum Springback

Not all aluminum behaves the same. The amount of over-bending required depends heavily on the alloy and temper:

Example: For a perfect 90° finished bend, set your press brake to 88°.

Material Typical	Springback
5052-H32(softer)	1.0° to 1.5° over bending
6061-T6 (Harder/Brittle)	2° to 4° over bending

• How to achieve a 90° bend in aluminum?

To achieve a perfect 90° bend in aluminum, do not use standard 90° punches and dies.
Since you must over-bend to ~88°, using 90° tooling will cause you to bottom out against the die faces before reaching the required angle. At JSTMT, we recommend our Acute 85° or 88° punches to provide the necessary clearance for air bending.

 

Avoiding Die Marks (Protecting Your Work)

Because aluminum is soft, standard steel dies act like “knives,” leaving ugly pressure marks on the bottom of the part. This is a major issue for architectural or painted parts.

To achieve a “Mark-Free” bend, use these professional tactics:

1. Polished Chrome Dies: High-polish finishes reduce the friction that causes gouging.
2. Urethane Film: Place a thin strip of urethane tape or film over the die. This acts as a cushion between the steel and the aluminum.
3. Nylon or Urethane Tooling: Instead of steel dies, use inserts made of high-density nylon.

These are available in our catalog and are specifically designed for aluminum and stainless steel applications.

 

Tips for bending aluminum sheets:

1. Bend radius
The bend radius should be 3–5 times the thickness of the aluminum sheet. A smaller bend radius increases the chance of cracking.
2. Bend line
The bend line should run diagonally or across the material’s grain for fewer cracks.
3. Aluminum grade
Some aluminum grades bend more easily than others. For example, 3003 and 5052 aluminum alloys bend well, but 6061 aluminum is more difficult to bend.
4. Annealing
Softening aluminum with heat annealing can make bending aluminum easier. You can use a blowtorch or an annealing oven.
4. Heating
To avoid overheating, you can use black carbon soot to make the aluminum malleable enough to bend.