Minimum Bend Radius - Sheet Metal 3

[Joselito]

I'm interested in bending a piece of sheet metal to a specific radius. In one case the sheet will be formed from 6092 aluminum. In another case the sheet will be formed from 304 stainless steel.

I need to be able to bend these sheets without cracking the outer surface of the bend. However, I need to form these sheets to a radius ~ sheet thickness. I have a general manufacturing text which says I will have problems doing this at room temperature.

Any advice or references are much appreciated. Happy New Years.

 

[sancat]

I will expect that the outside of the sheet will elongate, and the interior will remain roughly constant in lenght.
If you are trying to bend to an inner radius approximatelly to the plate thickness, the inside radius surface lenght will be th x pi, and on the outside lenght will be th x 2 x pi, therefore, you will need a method to elongate your materials a 100% without breaking them. The actual lenght will be slightly shorter due to the fact that the plate thickness will shrink a little to bring the extra material you need in lenght.
Try to look on the tensile test for those materials and find if there is a way to elongate them so much without breaking them.
Factors that would help you are a very smouth exterior surface (to avoid crack starting points) and some temperature.
Aluminum should soften by sudden cooling (tempering).
sancat

 

[diamondjim]

It would help if you mentioned the plate
thickness and the max allowable radius that
you can use or are you saying that the maximum
inside radius is equal to the plate thickness?
Also do you have a width of plate that you are
using?

 

[houndog1]

Joselito
It has been my experience with aluminum to anneal it, with an oxydizing flame before working it. The 6094 aluminum may not bend without cracking at all. I don't have any experience with this particular grade, but as a rule of thumb anything higher than 5054 is not intended to bend.
Aluminum anneals very easily with a oxy/acetylene torch.
Just light the torch with a neutral flame and sweep it across the surface until a black film occurs. Sweep it in the same manner you would if you were spray painting it. It should only take a few sweeps (depending on the thickness) be careful not to get it too hot. The black film will just wipe away.
If the plate is heavy, say 1/4" or so, cracking can be detered by grinding a small grove at each end of the piece only about a half inch or so. It should give the heel of the piece some relief when it is broke.

 

[Tunalover]

Joselito-
Don't forget that the grain should be parallel to the bend line.

I use Machinery's Handbook and Aluminum Association guides often, but usually contact a sheetmetal fabricator who sometimes has more information than any reference books on minimum bend radii of all kinds of metals.

 

[gascupwalker1]

Joselito ,I`ve been in the industry for 20 years and to this day we`ve had no need for 6092(composite),sorry I can`t help you there,but obviously your desired degree of bend in conjunction with material thickness will ultimately be the deciding factors.You may drop a line to

http://www.engineersedge.com.

I find their site helpful often ,in a pinch. PS Let us know what you come up with. gscpwlkr1

 

[Joselito]

Thanks everyone. Very useful info.

FYI: The sheet thickness will be in a range of 0.06" to 0.09". The inner radius can be as large as 0.25". The reason for the cap on bend radius is that clearance is very limited where the sheet will be used. This particular aluminum alloy is 6092/B4C/25p-T6. It is about a time and a half stiffer than Aluminum. Mark's Mechanical defines the range for the minimum bend radius of Aluminum from r = 0 (right angle bend), for very soft alloys, to r = 6*thickness, for very hard alloys, at room temperature.

Thanks again. I am going to contact the manufacturer and see what forming options we have. Otherwise I will look into alternative materials (e.g. 304 stainless, Al alloys < 5054, etc.)

Take Care,

Jose

 

[drawoh]

Jose,

I am not familiar with 6092 aluminium either. I have seen things bent out of 6061-T6 and 2024-T4, but this requires a lot of skill by the fabricator. These materials are brittle, and they develop cracks easily. I have seen stuff crack.

Most of my sheet metal winds up inside aircraft. I specify 5052-H32. It is fairly strong. The sheet metal shops like it and stock it. You don't have workmanship problems. The bend radii are specificed in the aluminium catalogues.

High strength material is a waste of time if it cracks at the bend.

JHG

 

[boo1]

Having never seen Aluminium 6092/B4C/25p I looked it up. The matrix alloy and reinforcement material of a given type and volume loading. Material systems are expressed using the American National Standard Institute (ANSI H35.5) nomenclature.

6092 is the matrix material
B4C is the reiforcement material
25 is the volume percent of reinforcement
p is reinforcement form (p=particulate)

see other info:

http://www.semiconductorfabtech.com/datatech/journals/edition3/download/dt3-4_3.pdf

 

[TVP]

6092 reinforced with 25% B₄C cannot be bent to a 1T bend. I doubt very much that it can be bent at all-- strain to failure is likely to be < 5% at room T.

304 stainless steel on the other hand, is quite ductile, so forming this into a bend is much easier. You did not indicate in what condition the stainless steel would be? Annealed? Strain hardened (1/4 hard, 1/2 hard, etc.)? If it is in the fully annealed condition, then 1T bends can be done. The following are typical bending limits for Types 301, 302, & 304 stainless steel:

minimum bend radius
annealed to 4.75 mm 0.5T for 180 degree bend

cold-rolled, quarter hard 0.5T for 180 degree bend
to 1.27 mm

cold-rolled, quarter hard 1T for 90 degree bend
1.3-4.75 mm

 

[smcadman]

I am unfamiliar with 6092 aluminum, but when we use 6061 T6, we have it annealed first, form it, then have it sent out to be tempered. An INSIDE radius of the material thickness is typical forming practice.
The max-minimum inside radius sheet metal (unhardened) can be formed on the brake press is .63 x material thickness. It cannot be formed tighter without creasing and forming a &quot;v&quot; shape along the bend.

Flores

 

[sancat]

smcadman,

Even though this is not the case of the composite that originated this thread; I tought that Aluminum actually softened by sudden cooling, and hardened by aging. Am I wrong? Please un-dunce me.

sancat

 

[smcadman]

Sancat, with aluminum, the faster the quenching (cooling) process the stronger the material, but the internal stresses are greater. Aging reduces residual stress. T6 is heated to 500 degrees, quenched, then artificially aged. Age hardening occurs after the quench.

Flores