Minimum bend radius 1

[verymadmac]

I am trying to work out how a manufacturer put a ninety degree bend in a component 0.125” thick 2024-T42 with a bend radius of about 0.094”. The minimum bend radius charts give 0.250” when folded prior to heat treatment. This part is a flap bracket for a light aircraft and has not shown any cracking in service.

Also does any one know what are the minimum bend radius's for 6013-T4

Duncan

 

[berkshire]

It was probably bent in the "O" condition and heat treated.
B.E.

 

[debodine]

As I understand it, the T42 temper versus a T4 temper means it was heat treated after delivery in the O condition. I believe that the the TX tempers are manufactured and delivered as TX, but the TX2 tempers (I am most familiar with T42 and T62) are delivered in the O condition and heat treated in the field to the TX2 temper. I found that in an industry standard some months ago, but I don't recall which standard.

In other words, tempers without the "2" suffix were delivered from the manufacturer at that temper (e.g. 2024-T4, 7075-T6). Heat treating in the field after delivery at condition O can only result in suffix "2" temper (e.g. 2024-T42, 7075-T62).

debodine

 

[WKTaylor]

verymadmac...

None of the charts I have allow any 0.125" thick aluminum alloy to be bent on a 0.094" Radius, regardless of heat-treatment. At best, 0.25"R is shown for heat-treatable aluminum alloys. Sometimes a smaller BR is possible if 100% inspected for cracks... say 0.22"R or MAYBE 0.19"R is possible... but I seriously doubt that 0.094"R is attainable without 100% cracking.

I suspect that You may be dealing with an extrusion, where the edge was radiused to match the fillet-radius between the flanges (to appear like a constant thickness around a bent radius).

Regards, Wil Taylor

 

[verymadmac]

The part has two flanges on it and as such can't be made from an extrusion. The only suggestion we can come up with is that they preheated it before bending, maybe in a hot water bath.

Duncan

 

[whalesA3D]

Is it possible that your part may have been machined from aluminum bar or plate? That is the only other explanation I can think of. I am involved with machined parts in the aircraft industry, after milling and a good polishing it is often hard to tell a machined part from a brake formed part.

 

[rb1957]

we're just speculating, on possible ways to manufacture this detail ...
is it possible to talk to the people who made it ?

 

[WhiteRabbit]

My one cent:
But the temper does not match that of plate or extrusion. Also, that is an extremely tight bend radius for .125 sheet.

Here's a question that may warrant a new thread. I have heard countless conflicting opinions on this matter. Should a part be bent parallel or perpendicular to the grain direction?

 

[diamondjim]

Is grain directional?
Can aluminum be coined?

 

[verymadmac]

The part is folded, the edge of the part shows the usual slight deformation you get with folding. As for the grain direction its probably the easiest ( which is parallel to the grain, I think) as only one of the flanges is that tight, the other is a more normal bend radius of 0.250”.

Asking the original manufacture, well the only person who would respond to questions has left there.

Duncan

 

[aeroz]

I think berkshire and debodine hit the nail on the head. T42 indicates that is heat treated and naturally aged by the end user. We heat treat some floor ribs during manufacture. We start with 2024-T3 (not condition 'O' as it is much easier to get T3) and carry out the heat treat process for T4 (i.e. heat and quench), we then form the part straight away (it is still fairly soft before it has naturally aged). This allows us to form over a fairly tight radius. I guess technically this adds cold working to the T4 process also. As for the bend radius, AC43.13-1A (don't have the latest -1B to hand at the moment) figure 2.17 gives recommended bend radii for 90 degree bends. The recommended bend radius for 0.125 thick annealed 2024 is 0 to 1 times the thickness, so the bend radius of 0.094" mentioned would be OK if formed with 2024-O (i.e. annealed) and then heat treated to T4 (T42).

Regards,

Matt

 

[kontiki99]

In A&P school decades ago I was taught you try to orient the metal so you never bend parallel to the grain.

Cracks start in grain lines.

Ideally a bend is perpendicular to the grain.

In a case where you have two bends 90 degrees to each other (like a box corner) orient the grain so it’s 45 deg to both bends.

I worked a few years as a full time sheet metal mechanic in an overhaul hangar and proved to myself, that was sound advice.

 

[Kwan]

The mimimum bend radii for .125 2024-o is .25. it's always best to bend 90 degree (to minimize the cracks). If you heat and quench you do not have "o" you have "W" condition. min bend for .125 2024-W is .50. as stated previously you can bend tighter than the above recommendation but you should be checking for cracks using pen inspect.

I'd guess that if it is indeed formed then the manufacture used hot forming or the part is not that critical (for cracks in the radii).

are you trying to repair this part?

 

[berkshire]

verymadmac (Mechanical)
I think Kwan has it right, your part was most likely bent in the "W" condition not "O".
With 2024 you have a very short window to do this, about 10 to 15 mins after it comes out of the quench tank.
If you have solution heat treat facilities you can duplicate this part, if you do not I would not even try.
B.E.

 

[Sparweb]

Questioning all facts and assumptions: Are you sure it's 2024? I can bend 6061 with that radius. Not that 6061-T6 should be bent at that radius either, but it is possible.


Steven Fahey, CET

 

[berkshire]

SparWeb (Aerospace)
Steve, you are right, bending 6061 in the "W" temper would be a simple job, it might show a bit of orange peel on the back of the bend but that's about all.
verymadmac (Mechanical)
The other question here is how do you know it is T42 in 2024 and not 6061 T6. Is the part marked with a serial number and a part number?
B.E.

 

[verymadmac]

We have the original manufacturer's drawing, It calls out AU4G1-T42 which is the old French designation for 2024-T42. The drawing does not call out such a tight radius, although I suspect the the radius is that tight to allow for their assembly tolerances. We can make the part to the drawing . My interest is more for future reference how they made it (also in case we find a reason why it needs to be that tight).

Duncan

 

[aerodog]

1. Matched steel dies heated to 350 to 400 degrees F and mounted in a brake press might form .125 2024-O and a .094 radius with no cracking or other deformation. Then heat treat to T42. This is not a routine operation and may not be addressed in any of the design process manuals but rather, a successful technique developed thru experimentation.

2. On grain direction. For sheet metal parts, grain direction is usually not specified. When direction is specified, it usually relates to parts that will only form accurately when the grain is oriented in a particular manner. And typically, parts will conform to the forming tool with less springback when the bend is perpendicular to the grain direction.

3. On 6013-T4. From the Alcoa Green Letter dated 12-87.

.022 sheet zero T bend radius 4-6 degrees spring back
.038 sheet zero T bend radius 4 degrees spring back
.065 sheet one T bend radius 4.5 degrees spring back
.105 sheet one T bend radius 5 degrees spring back

The bend radii noted are minimum values.

Several years ago I spoke to a Cessna design engineer regarding 6013 material. When 6013 came out, Cessna had high hopes for the material since it could be easily formed in the T condition, then aged, eliminating the heat treat cycle.

But Cessna discovered 6013 was prone to cracking when compressed like when a joggle is formed on a rib flange. 6013 can be stretched but does not like to be pushed around.

Cessna uses quite a bit of 6013, but only in certain applications.

 

[verymadmac]

Thank for the illuminating post aerodog. The cracking of joggles in 6013 ribs is interesting given at work we have just changed all the rib material (& a couple of frames) from 5086 to 6013 although I can't think of any joggles in the ribs. Will have to look tomorrow.

Duncan