extruding brackets

[heloman29]

My boss suggested today that we have a company extrude a bracket that typically is bent out of sheet metal, it’s a typical "u" bracket 4- 90 deg angles made of 2014 aluminum (unknown temper). Then with a long extrusion we could simply cut the brackets to length. Also, this bracket typically cracks in one of the bend radii, so he wants to thicken the area of the radii slightly for strength, I suggested that since the problem is cracking in the radii maybe the part should be stress relieved after bending the part as it is now fabricated. Please any thoughts are appreciated.

 

[TVP]

I like your boss's suggestion to use an extrusion, and to increase the radius/section through the fillet area. I'm not sure that stress relieving a sheetmetal fabrication will be sufficient to overcome what sounds like an overstress issue.

 

[desertfox]

Hi heloman29

What bending radius are you currently using? and what thickness is the material your bending?
It may just be that your using to small a bend radius and an increase may stop the cracking.
whether to extrude or not depends on cost do you use a lot of these brackets per year?
Certainly using an extrusion will reduce manual effort in bending at least but presumably there will be holes to drill
in the extruded bracket that would or could have been punched in the fabricated bracket prior to bending?

regards
desertfox

desertfox

 

[KENAT]

To follow on from desertfox, if the radius is too tight for the sheet metal but is required by function then the extrusion may be an advantage.

KENAT, probably the least qualified checker you'll ever meet...

 

[MintJulep]

It sounds as if you are speculating as to the cause of the failures in the original. It therefore follows that the proposed "improvement" is also speculation.

Understand the problem, then design the solution.

The other way around tends to get expensive.

Also, extrusion dies can be expensive. Does your volume justify the cost?

 

[MikeHalloran]

Sawcutting and deburring an extrusion is fairly slow and expensive, especially if the extrusion is delicate.

I'd be inclined to control/ increase the bend radius on the formed part, and maybe control the grain direction in the blank.

Last time I looked at extrusion, the dies were surprisingly inexpensive, but the minimum lot size was 5000 lb, which is just enough to warm up a big extrusion press, but may be more than you want to buy at one time and store.





Mike Halloran
Pembroke Pines, FL, USA

 

[40818]

I would have to say that you should probably go for the extrusion which seems to be the simplest and probably cheapest option. Am i reading your post incorrectly, as i take it that your going to get a company to produce a speciality piece?
have a look in places such as the Tierney catalogue, i'm sure they will be able to show you part numbers that companies will have on the shelf.

 

[RPstress]

Agree with Halloran.

2014 is nice and formable in the right temper; even in T3 and T4 you can form it if it's got a big enough radius. It's usual to do heavy forming in condition O or W (W is just after quenching during solution treatment; you can prolong the period of good formability by refrigeration, as used to be common with rivets. It'll harden to T4 in 3 or 4 days if not refrigerated).

Outside the US it's quite likely you're getting material in T4, after it's hardened by natural aging. This will need more generous bend radii than condition W or annealed (annealed is condition O). In T4 you should probably get away with an IBR of 4t, and just maybe 3t.

If you're in the US then it's likely to be T6 and you need a big rad; 5 or even 6t might be sensible, although most people don't form T6. (US specs don't like 2014 in T4 or T3. It tends to be provided annealed or in T6. If it's annealed then it would need solution treating after forming unless it was used as annealed, and using 2014 annealed is unlikely.)

Post-forming heat treat is unlikely to help unless cracks are happening because of SCC. (I assume that the cracking is caught in production, not found in service.)

NB: extrusion will almost certainly be HEAVIER.

 

[rb1957]

i'd've thought you'd be able to dig out a standard extrusion from Tierney without the cost of specialised dies and without too much added weight

 

[heloman29]

Thanks for insight, thank you to all who responded. We do regularly find the crack in service not after forming, the part is from an engine mount/nacelle structure.

 

[KENAT]

Has the fact that fatigue may be causing the problem been considered then?

KENAT, probably the least qualified checker you'll ever meet...

 

[RPstress]

Cracks in engine mounts are usually taken rather seriously.

Is the bracket used only for supporting a system such as a firewire or similar?

If it's "only" a systems support bracket, then it's probably a vibration fatigue problem, though SCC remains a possibility.

If it's SCC then a post forming stress relief op might do the trick.

If it's fatigue then tweaking the vibration frequency or making it stronger might work.

The nature of the crack should reveal whether it's fatigue or SCC. You might need someone with experience of failure investigation to determine that.