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2 Advice on How to bend aluminum without breaking it

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Aluminum is highly malleable, which makes it easy to work. Usually, higher strength means the aluminum alloy will be more difficult to bend, due to the tradeoff between strength and elongation – ductility. As one increases, the other decreases. Thickness and bend radius. Aluminum alloys harden and become stronger during the bending process.

When it comes to very thick or high-tensile-strength aluminum, traditional rules for determining minimum bend radii, minimum punch nose radii, die openings, bending force calculations, and tooling requirements may no longer apply.

Because the aluminum workpiece can be extremely thick and strong, you need to understand the variables and learn how to work with them. First, consider the minimum material’s chemical composition, its surface, and edge condition, as well as its thickness, and determine whether the bend is with or across the aluminum’s grain direction.

All forming, regardless of scale, involves some kind of plastic deformation. Material expansion occurs on the outside surface of the bend, and compression on the inside, and you need to know how to deal with both. The limits of material ductility will be the controlling factor for the minimum bend radius.

The strains associated with the plastic deformation when cold bending can cause the aluminum to strain-harden. This can change the material’s mechanical properties in the area of the bend, where plastic deformation is occurring. At this point, ductility and resistance to fracture will need to be considered in aluminum material.

When bending aluminum, know that the smaller your inside bend radius, the larger the chance that cracking will occur in the part. For the best results and fewer cracks on the outside of the bend, the bend line should go across or diagonal to the material grain when and where possible.

Forming with the grain requires less bending force because the aluminum’s ductility is readily stretched. But this stretching causes the grains to spread, which manifests as cracking on the outside bend radius. To prevent or at least reduce this cracking when bending longitudinal to the grain direction, you may need to use a larger bend radius. When bending transverse to the grain direction, the reduced ductility will increase the required forming tonnage, but it will be capable of accepting a much tighter inside bend radius without destroying the outside surface of the bend.

Aluminum Bending Machine

For cold bending aluminum, you will find a variety of minimum bend radii-to-thickness ratios, and you will need to research these values in data provided by your material supplier.

As the thickness increases, so does the minimum radius. For 0.25-in.-thick 6061 in an “O” condition, the material supplier may specify a 1-to-1 inside radius-to-plate-thickness ratio. In 0.375-in.-thick aluminum, the minimum radius is 1.5 times the thickness; for 0.5-in.-thick, it’s 2 times the thickness.

The minimum radius also increases with harder material. For 0.25-in.-thick 6061 in a “T4” condition, the material supplier may specify the minimum radius to be 3 times the thickness; a 0.375-in.-thick plate may have a minimum radius of 3.5 times the thickness; for 0.5-in.-thick plate, it can be 4 times the thickness.

The trend is obvious: The harder and thicker the plate is, the greater the minimum bend radius. For 0.5-in.-thick 7050 aluminum, the minimum bend radius may be specified as much as 9.5 times the material thickness.

Again, the minimum inside bend radius is even larger when bending with the grain.

A SIMPLE RULE OF THUMB

There’s a rule of thumb to determine an aluminum’s minimum bend radius: Divide 50 by the material’s tensile reduction percentage as specified by your supplier. This value will vary by grade.

If the aluminum has a tensile reduction value of 10 percent, divide 50 by that value: 50/10 = 5. Next, subtract 1 from that answer: 5 – 1 = 4. Now, multiply that answer by the plate thickness. If the material is 0.5 in. thick: 4 × 0.5 = 2. So in this case, the minimum inside bend radius is 2 times the material thickness.

Note that this is just a rule of thumb. Finding the true minimum bend radius for aluminum plates requires a little research. This should include data from your material supplier, whether you are bending with or against the grain, as well as information specific to the application. Nonetheless, the answers are there, waiting for you to find them.

Aluminum Minimum Bend Radii for 90 Degree Cold Forming of Sheet and Plate

Alloy Temper RADII FOR VARIOUS THICKNESSES EXPRESSED IN TERMS OF THICKNESS “t”
1/64 in. 1/32 in. 1/16 in. 1/8 in. 3/16 in. 1/4 in. 3/8 in. 1/2 in.
3003 H12 0 0 0 1/2t 1t 1t 1.5t 2t
H14 0 0 0 1t 1t 1.5t 2t 2.5t
H16 1/2t 1t 1t 1.5t 2.5t 3t 3.5t 4t
3105 H12 0 0 0 1/2t 1t 1t 1.5t 2t
H14 0 0 0 1t 1.5t 1.5t 2t 2.5t
H16 1/2t 1t 1t 1.5t 2.5t 3t 3.5t 4t
5052 H32 0 0 1t 1.5t 1.5t 1.5t 1.5t 2t
H34 0 1t 1.5t 2t 2t 2.5t 2.5t 3t
H36 1t 1t 1.5t 2.5t 3t 3.5t 4t 4.5t
H38 1t 1.5t 2.5t 3t 4t 5t 5.5t 6.5t
5086 H32 0 1/2t 1t 1.5t 1.5t 2t 2.5t 3t
5454 O 0 1/2t 1t 1t 1t 1.5t 1.5t 2t
H32 1/2t 1/2t 1t 2t 2t 2.5t 3t 4t
H34 1/2t 1t 1.5t 2t 2.5t 3t 3.5t 4t
6061 T6 1t 1t 1.5t 2.5t 3t 3.5t 4.5t 5t

When forming aluminum, air forming any other material, you choose an appropriate die width based on the material thickness and the radius-to-thickness relationship.
Springback

Springback is the release of elastic strain and is related directly to the material yield strength. It’s the reason you need a greater bend angle to achieve the required angle, especially for most aluminum.

A certain sheet metal workpiece may have, say, 2 degrees of spring back, so you need a punch with a minimum included angle that’s at least 2 degrees less than the included die angle to provide the needed angular clearance. But as the radius increases, so will spring back, and the amount of spring back can be significant when the radius is large in relationship to the sheet or plate thickness.

The right die width and angle can help compensate for this excessive spring back. This includes relieved dies, with included angles of 78 or 73 degrees. Channel dies have included die angles that are perpendicular, straight up, and down. Both allow for the necessary penetration of the tool without interference between the die faces, punch, and material.

No matter the material, its gauge, or thickness, soft aluminum is much more ductile than high-strength materials and, therefore, can be bent to a sharper radius. When bending thick or high-tensile metals, you need to abide by a minimum inside bend radius. This will minimize the effects of strain hardening and cracking at the bend.

Generally, soft aluminum is necessary for good formability and a tight inside radius; but as the level of the hardness of the aluminum increases, its ductility and formability are limited, increasing the minimum radius that can be produced.