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How to bending aluminum without cracking it

The aluminum sheet is easy to break after bending, or it will crack after anodizing bending. Many aluminum alloy processing companies are confused about this. So, how to bend aluminum without breaking it?8 main reasons and preventive measures for aluminum to break after bending.

Three Factors Affecting The Bending Of Aluminum Alloy

Normally, higher strength means the aluminium alloy will be more difficult to bend, due to the tradeoff between strength and elongation – ductility. As one increases, the other decreases.
So what points factors affecting can help you identify the right alloy for bending? And what alloys are best for bending?
Then we can know the answer from three aspects: Formability, thickness, bend radius, and the percentage of elongation of aluminum profiles.

Formability

One of the most useful characteristics of aluminum is its formability, and one way to form the metal into the shape you want is through bending. Some aluminum alloys and tempers are better suited for bending than others. This is what you need to know to choose the one that’s right for you.

Formability is the ability of a given material to experience permanent deformation without the forming process cracking or tearing it. Permanent deformation is also known as plastic deformation in the materials science world.

Generally speaking, formability is a relative term and not a specific value. For example, the applied force necessary to shape a product depends on more than just the strength and ductility of a material. It also depends on factors such as the shape of the part and the thickness of the starting material.
In other words, we can measure the forming force to produce a specific part from a particular starting material. However, changing the shape of the part or the physical properties of the starting material will change the amount of force that needs to be applied.
That said, there are standardized tests, such as the ASTM E2218: Standard Test Method for Determining Forming Limit Curves. We can use these tests to establish a formability “ranking” for different sheets of alloy. We can use them to learn which alloys have better baseline formability.

Click for the chart of tensile strengths for aluminum and stainless steel to compare with mild steel

Thickness and bend radius

Aluminium alloys harden and become stronger during the bending process. As a result, thickness and bend radius are factors you need to consider.

  • If you’ve handled regular aluminum foil, you’ll know that it is effortless to bend. However, if you had to bend a sheet of aluminum that was one-thousand times thicker than aluminum foil, it would be much harder! That is because the thicker a material is, the more difficult it is to bend.
  • You can also bend an aluminum gutter with your bare hands. But if you try to bend it to a tight angle without breaking it, you will have a hard time! Bending metal to a small bend radius has the potential to cause tearing or cracking.

Minimum bending radius table

The Fabricator’s website offers certain key tables and general rules which are helpful for understanding the limits to bendability for specific aluminum alloys. You can use these to determine the minimum allowable bend radius for particular thicknesses of aluminum sheets.
The following is their specific content:

Aluminum alloy minimum bending radius table

The Fabricator offers certain key tables and general rules which are helpful for understanding the limits to bendability for specific aluminum alloys. You can use these to determine the minimum allowable bend radius for particular thicknesses of aluminum sheets.

Aluminum alloy minimum bending radius
Aluminum alloy minimum bending radius. This recommended minimum bend radius chart is for illustrative purposes only. For minimum bend radii information about the material in your shop, consult your material supplier.
Chart source: Fabricator

In the chart diagram above with numbers that reflect the minimum inside bend radius for different alloys and tempers of aluminum. This chart shows a minimum bend radius of 0 to 1 times the material thickness for 0.125-in.-thick 5052-H32. This is slightly different from the recommendation you have from your aluminum supplier, but that’s no surprise. Variation is expected among different material producers. Regardless, 0 to 1 is a wide range of values, and the variation is amplified by temperature and the natural grain direction within the sheet.

A Simple Rule of Thumb

There’s a rule of thumb to determine a steel’s minimum bend radius, and this generally works for aluminum too: Divide 50 by the material’s tensile reduction percentage as specified by your supplier. This value will vary by grade.

If the steel 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.

Percentage of elongation

Investigating the percentage of elongation and the difference between yield strength and ultimate tensile strength will also help you make the right decision. When comparing alloys and tempers, lean toward those with the largest range between yield and tensile strength, because this indicates better forming ability.

Percent elongation represents the ability of the material to be plastically deformed under tension. It is also known as plastic strain or stain applied beyond the yield strength limit of a material.

The more ductile aluminum alloys can experience more significant plastic deformation with small increases in applied stress. This results in better overall aluminum bendability.

stress-strain curves
Stress-Strain Curves. Chart source: ResearchGate

Like the other properties, the percent elongation varies for each alloy. Take a look at the stress-strain curve above. You’ll see that annealed aluminum alloy 3003 (shown as AA3003-O) has a very high percent elongation (strain %) of roughly 35%. It has very high bendability relative to other alloys.

Click for the chart of tensile strengths for aluminum and stainless steel to compare with mild steel

What aluminum alloy is best for bending?

The best series for forming – and thus for bending – are the alloy series 3xxx, 5xxx and in some cases 6xxx. Aluminium alloy 6063 is a good choice, for example, while 6082 is more difficult.

Numerous metal alloying agents can be combined with aluminum to produce different aluminum alloys. The system for naming them uses four digits, with the first digit representing their chemical composition.

Generally speaking, aluminum alloys from the 1XXX, 3XXX, and 5XXX series demonstrate better bendability than other aluminum alloys. Some 6XXX series alloys are fairly bendable as well.

However, the different properties offered by each may make some more desirable than others. For example, 1XXX series aluminum generally has poor mechanical properties and is not suited to structural applications.

Four aluminum alloys recommended for bending

The best series for forming – and thus for bending – are the alloy series 3xxx, 5xxx and in some cases 6xxx. Aluminum alloy 6063 is a good choice, for example, while 6082 is more difficult. I would avoid using alloys in the 2xxx and 7xxx families because they are so strong and therefore difficult to form. However, in the right temper, the bending of those alloys is also possible.

Aluminum alloy 3003

In most cases, this is probably the best alloy for bending. You get average strength, very good cold workability, and high elongation. It also offers one of the biggest differences between yield and tensile strength.

This alloy is primarily alloyed with manganese and is one of the most commonly used aluminum alloys for bending applications. It has excellent formability properties and does not require heat to be bent or molded.

Companies often make gutters, roofing, siding, chemical equipment, and storage tanks from 3003 aluminum.

Aluminum alloy 5052

This alloy comes right behind. You get high elongation (not as high as 3003, however) and a solid difference between yield and tensile strength. You also get high strength when compared with other non-heat-treatable grades and outstanding corrosion behavior. When annealed, it beats the 3003 alloys in formability.

With magnesium as the primary alloying element, AA5052 demonstrates moderate-to-high strength characteristics. At the same time, it retains good bendability, and designers can use it for more intensive applications than AA3003. The corrosion resistance of this alloy is also excellent against seawater, meaning it is excellent for applications in marine equipment.

Manufacturers often produce hydraulic tubes, traffic and hardware signs, medical equipment, marine equipment, and electronics (chassis and enclosures).

Aluminum alloy 5083

Not far behind 5052 comes this one, its big brother, and a classic alloy for marine applications with good corrosion resistance and weldability. There is some variation with regard to temper, but if you chose H111, H112 or O temper you will be fine.

Aluminum alloys 6061 and 6082

These are versatile heat-treatable alloys that, when annealed, offer a satisfactory difference between yield and tensile strength, and good elongation. Their bending ability will decrease, however, when you move to T4 and T6 tempers. My recommendation, therefore, is to bend in T4 condition and then heat treat to T6 if this is possible.

Don’t forget that the grain structure of the material will also impact bending capabilities, although grain structure affects several processes, not only bending.

Alloy 6061 is widely referred to as “structural aluminum” because it is so commonly used in structural (construction) applications. Nevertheless, due to its outstanding properties, it is also used in food and beverage containers, ladders, aircraft and automotive parts, scuba tanks, bicycle frames, and more.

Why Are These 4 Alloys Important?

Despite their different properties, these alloys are excellent examples of bendability in aluminum alloys. They demonstrate that even though some aluminum alloys feature better formability and percent elongation for a given bend radius and thickness, they each serve a unique purpose and a wide variety of applications.

Even with slightly lower bendability, the strength of alloy 6061 makes it one of the most widely used aluminum alloys. In the same way, alloy 3003 has multiple uses in applications that require superior bendability. Meanwhile, alloy 5052 is commonly used thanks to its balance in terms of bendability and strength.

Consider tempers in alloy’s bending ability

Look at tempers when it comes to optimizing the bending ability of the aluminum alloy. Temper is as important as alloys.

  • For non-heat-treatable 3xxx and 5xxx alloys, O-temper is the easiest temper to bend in.
  • 6xxx, 7xxx and 2xxx heat-treatable alloys should if possible be bent in the T4 condition, as this has a lower yield strength. However, there is a drawback. The yield strength in the T4 condition varies over time, due to natural ageing, a slow hardening process that occurs over time.
  • Although the variation in yield strength is small over short times, this might cause spring-back variation in some bending processes. So, in some cases, bending in T6 could be a better option. There are also special heat treatments that stop natural aging and allow the material to be heat-treated to T6 after bending, which could be considered.
  • T4 temper is moderate to bend, with low yield strength, however, for some bending processes, spring-back variations might occur
  • T6 temper is the most difficult to bend, but there is no spring back variation
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The aluminum sheet is easy to break after bending, or it will crack after anodizing bending. Many aluminum alloy processing companies are confused about this. So, how to bend aluminum without breaking it?8 main reasons and preventive measures for aluminum to break after bending.

8 main reasons and preventive measures for aluminum to break after bending

  1. Thickness: Too thick aluminum plate is not easy to bend. Everyone knows they should use the thinnest possible sheet of aluminum.
  2. Hardness: The aluminum plate is too hard and easy to break. The choice of aluminum sheet mainly depends on the grade and condition of the aluminum. Usually, T1, T3, and T5 are used. T6 and T7 series are too hard and need to be annealed to 0 tempers before bending.
  3. Textured direction: The bending direction should be perpendicular to the textured direction of the aluminum plate and cannot be parallel. For aluminum sheet parts that need to be drawn, if processing allows, it is best to process them after bending, otherwise, the possibility of bending fracture will increase.
  4. Bending angle R: The larger the R angle, the higher the success rate, so try to increase the bending R angle as much as possible.
  5. Cracks after the bending of aluminum profiles are caused by high tensile force and unsatisfied laying stress. The edge of the aluminum profile is not in place, which will cause wrinkling. This can be solved by improving the cross-sectional area of the profile or adjusting the tension.
  6. The depression of the curved surface mainly occurs on the aluminum cavity profile. Before stretching and bending this material, it is necessary to fill the curved portion of the cavity with filler. Open cavities can be stacked with spring steel sheets or filled with Teflon, while closed cavities are usually filled with sand.
  7. According to the position generated by the vertical marks on the side, properly adjust the mold gap and improve the mold material, which can effectively prevent the surface of the aluminum profile from being scratched.

three Tips for aluminum bending

  • Pay attention to the grade: For aluminum, the harder the grade, the greater the amount of spring back that you will need to deal with; very soft aluminum may exhibit no spring back at all.
  • Watch out for creasing along the bend line: Aluminum generally loses its integrity if the material is creased. If you make aircraft parts with that crease along the bend line, that alone will make the parts unacceptable.
  • Inside bend radius: When bending aluminum, know that the smaller your inside bend radius, the larger the chance that cracking will occur in the part. Also know that, 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.
    Ideally, part designers should know that when it comes to aluminum grades, 3003 and 5052 will bend, and 6061 will not. This is generalizing, of course, as there are ways to form 6061. The aluminum series’ ability to bend tends to decrease as you move down the list of tempers, from annealed to T4 and T6. Bending these tempered alloys is not impossible, but it is very difficult and will most likely require large bend radii to avoid cracking on the outside of the bend. If you’re not careful, you can completely fracture the bend line.
How to bending T5 aluminum without cracking it
Aluminum Profile Bending Machine bends 3 specifications of T5 aluminum C-Channel in two ways

How To Choose The Aluminum Bending And Forming Methods?

When bent and formed aluminum extrusions, need to consider factors, such as inside and outside diameters, critical surface areas, and mechanical strength can affect a part’s final fit and finish. Different types of bending and stretch-forming methods deliver different results.

3 factors to decide which aluminum profile bending method to choose

Aluminum can be extruded and bent to specified tolerances or to standard dimensional tolerances. While a product’s dimensions and bend angles can be methodically measured and re-measured, the end product will only be as precise as the bending equipment or method used. Deformation of the inside or outside radii can be a design issue and can also determine which forming process to use in bending or forming the aluminum profile.

So several 3 factors should be considered when choosing which bending process is appropriate for a certain product.

  1. What tolerances, or deviations, are expected on the inside radius, the outside dimension radius, and the overall length of the part?
  2. What surface areas are critical for appearance?
  3. What mechanical strength is required?

5 common bending and forming methods for aluminum profiles

Each of these following 5 bending methods has various benefits. Designing for success and determining the best method ultimately comes down to an end product’s desired tolerance, appearance, and strength.

Bending and forming methods 1#: Ram or Push Bending

  1. Definition: Ram or push bending, as the name implies, uses a ram to force the extruded metal piece on a bending die.
  2. Work principle: A die pushes the extrusion onto the pressure dies, forcing the extrusion into your desired bent form.
  3. Features: With programmable bend angles, this form of bending allows close proximity to multiple planes bends, though only one radius can be bent at a time. Ram bending offers inexpensive tooling and good bend precision with low per-bend cost.
  4. Application: Ram or Push Bending is ideal for components such as boat gunnels, portable structure supports, wheelchair frames, and medical beds.

Bending and forming methods 2#: Hydraulic Rotary Draw Bending

  1. Definition and work principle: In the hydraulic rotary draw bending process, manufacturers place extruded aluminum onto a bender and hold it in place with a stationary or sliding pressure die and clamping block. The round bending die, powered by hydraulics, is rotated up to 90 degrees, bending the extrusion as it rotates.
  2. Features:
    • With Hydraulic Rotary Draw Bending method, an extrusion can only be bent one radius at a time.
    • Incorporating a mandrel or other tool component to grip the rotary die can prevent creasing or misshaping of the product, though its use isn’t required.
    • The single-axis-controlled revolution can bend within one-tenth of a degree for extremely precise bend angles.
  3. Application: Hydraulic bending is often used when forming round tubes or pipes for applications such as handrails, and is ideal for extrusions with a large diameter, such as building signage.

Bending and forming methods 3#: Electric Rotary Draw Bending

  1. Definition and work principle: Electric rotary draw bending uses the same process as the hydraulic method, but allows faster setup.
  2. Features:
    • The bends also are more accurate and easily repeated because angles and rotations can be automated in a machine’s programmable logic controller.
    • Rotations of the extruded aluminum also can be mechanized for variable plane bends.
  3. Application: The electric rotary draw method is best for applications that require multiple bends per part in close proximity to each other, or different radii bends for each part.

Bending and forming methods 4#: Three-Roll Bending

  1. Definition: Three-roll bending pushes an extrusion around three different rolls placed in a triangular shape.
  2. Work principle: The rolls are adjusted to form a precise angle, up to a 360-degree rotation, that can roll horizontally or vertically. As the extrusion is slowly moved across the power-driven rollers, it begins to curve and bend.
  3. Features:
    • Extrusions are limited to a single bend per cycle, meaning a higher angle of the bend would take longer to reach the desired angle.
    • Though it may take longer, the maximum bend radius is unlimited.
  4. Application: Symmetrical profiles are preferable for roll bending.

Read More: The Best Guide to the Stretch Forming Process

Bending and forming methods 5#: Stretch Forming

  1. Definition and work principle: During stretch forming, an extrusion is placed along a rounded, fixed bending die and clamped in place on each end. The machine begins to swing the clamped ends downward to angles up to 180 degrees, and the extrusion is bent around the die to reach the desired form.
  2. Features:
    • The bend radius is unlimited with this method.
    • A stretch forming machine can bend, twist and lift an extrusion simultaneously to create unique, specified shapes and angles for parts up to 25 feet long.
    • This method also offers the most accurate and consistent bending through elongation control.
    • Because of the way the rounded, fixed bending die pushes on the extrusion, stretch forming has the least amount of surface distortion and traffic marking on the extruded piece.
  3. Application: Stretch forming is commonly used for parts with a larger bend radius, as the minimum bend radius is generally two to three times greater than other forming/bending methods.
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