bending / shaping 7075-T73 extusion 2

[zuluyankee]

This question is primarily for aerospace metal material and process engineers

I have a 7075-T73 extrusion. L angle, .2 thick, 1.5" flange, 5ft length.
1) The last 24" I need to arc/bend the extrusion to approx 2.5" up from center line.
2) The last 24" I also need to bend out the lower flange 20deg to open up
3) AT the 24" location and the end I need a hot joggle.

I am interested in getting the proper process and sequencing of events

1) It was recommended that I obtain the arc by using a shrinker on the vertical flange.
2) Bend out lower flange
3) Hot joggle

I am concerned that the arc/bend/shrinking in the T73 condition could crack the extrusion, what is the correct process?
1) work in the O condition?
2) heat and work in the T73 condition?
3) refrigerate after T73 heat treat, then bend.....

Any references to process documentation would be helpful.
Cheers

 

[rb1957]

if you work in O condition you can pretty much form it however you want ... but the part will distort in the heat treat which might be the logic of heat treating to T73 rather than T6

Quando Omni Flunkus Moritati

 

[berkshire]

You do not say what heat treatment facilities you have if any.
Preferred would be to form in O condition, Heat treat, hand straighten in the AQ condition then age to final temper.
Next best Heat treat, quench, do forming ops, then age.
The hot joggle can be a mixed blessing,especially if you are off setting more than the thickness of the metal. Sometimes the things will crack , just when you think you have it made. Do trial setups on scrap metal before putting your part in there.
B.E.

You are judged not by what you know, but by what you can do.

 

[WKTaylor]

zuluyankee... berkshire hit the nail on the head.

Heat treat, tooling and forming facilities are critical to this operation. Without knowing these details, whatever we suggest could be for-naught.

ZY. The material C/O on the drawing [if signed by an M&P engineer who actually put thought into it] will generally indicate HOW the part was intended to be made. If the material was specified as 7075–T73, then someone thought out how to make it in that temper [probably with special production tooling and hot-forming]; otherwise if material was specified as ‘7075-O’ [and a HT process was referenced] then it needed to be formed in-line with the heat treat process… which changes the fab concept quite a bit.

ZY. It sounds to me that what makes Your part particularly difficult to form is not the end curvature or the joggles: it is the need to open the flange angle 20-deg [90-to-110-deg, progressively?] with the joggle.

NOTE.
Generally speaking, forming while in the “W” [‘as quenched’, unstable] temper integrates the best elements of all aspects of HT and subsequent forming. The critical solution heat treat operation initiates the heat treat process… yet produces the greatest potential for warpage. This warpage is controlled/eliminated when the part is subsequently formed in the as-quenched ‘W’ temper. At this point, the straining is relatively beneficial/benign since it is in-sequence with the HT operation. What makes this sequence work, is control of the rate of aging by freezing the part [between forming operations]; then quickly and accurately forming [straining] the wrought material; then resuming the heat treat process by age-hardening [low temperature long-bake] to the desired final temper [in this case –T73]. The low temperature bake, combined with light support to prevent sagging, minimizes and usually eliminates any possibility for subsequent warpage/distortion.

NOTE.
Forming in the ‘O’ [NOT 0-zero] temper allows the greatest possible strain with minimum forces. However, the material then has to undergo full heat treatment with induces potential for warpage that would have to be controlled, post solution HT in the ‘W’ temper [Hmmm…imagine that]; and then there is a possibility that undesirable uncontrolled grain-growth [permanent enlarged/irregular metallurgical grain formation relative to straining severity] could occur in areas that were highly strained in the ‘O’ temper… which generally doesn’t occur in the ‘W’ temper. This is fair warning: significant reduction in strength, strain to failure and toughness can occur in these areas of grain growth [MMPDS has subtle warnings to this effect in the user-HT allowables tables].

NOTE.
Most aerospace companies have exceptional manuals, processes, data, people and tech resources for this very subject; with relatively little explanation as to the phenomena that occurs during these processes. However, for a Q/D education, The Aluminum Association [AA] has a fairly good/generic document titled “Forming and Machining Aluminum”. When combined with the AA “Aluminum Design manual” and the current AA “Aluminum Standards and Data” book, provides a fairly complete picture of wrought aluminum basics. BTW, the AA also has great manuals for castings, forging, extrusions, welding, temper discussions, etc.


Regards, Wil Taylor

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