Aluminium Machining and Properties 1

[Payyan1234]

Our team is thinking of machining a 0.063" thick casing/fairing from an aluminium bar ( 6.5" thick bar) due to complex shape.
Similar location mod on Aircraft all used 0.063 2024-T3 sheet metal.

* Is it possible to Machining this to such a small thickness ?
* Which Aluminium grade and what treatment are suggested?
* Which billet mechanical properties need to use? ( For aluminium it make no difference, but my question is generic??)

Thanks

 

[Sparweb]

Before we proceed... WHY do you not have access to sheet-metal forming tools if you are in a position to duplicate a part that was made from 2024 sheet? Even if you don't have the tools in-house, there are many facilities that do.
Is this a repair?
Whether in sheet or bar, your selection of the grade and heat treatment will be strongly determined by the resulting deformation of the part.
I just don't have enough information to guess whether working in the "O" condition and heat-treating afterward will be better or worse.

STF

 

[Payyan1234]

Sorry , It is not duplicating a part . It is an avionics modification , where the casing is little complicated to form in sheet metal, so decided to do CNC machining.

 

[MikeHalloran]

Well, next you face a conundrum.

2024-T3 machines like butter. Just set your mill to the highest surface speed it can manage and go.
But you can expect to hear odd noises as the machining progresses, and locked-in stresses are released.
... and the partially completed part distorts as a result. It may distort A LOT.

It happens with all cold-worked alloys of course. So you should anticipate it, and remove stock in several stages.



Mike Halloran
Pembroke Pines, FL, USA

 

[rb1957]

how about fiberglass ?

it is difficult to machine, but it'll be done in several steps with intermediate stress relief.

Does remind me of the cartoon ... getting a single toothpick from a tree.

another day in paradise, or is paradise one day closer ?

 

[MikeHalloran]

OR, consider dip-brazing, especially if modest production numbers are anticipated.
At its best, you can blank or laser cut sheet metal flats or simply bent parts to self-fixture and interlock into the 3D box you want. Yes, it's easier said than done, but you can use different thicknesses in different parts to allocate weight where strength is required.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

Payyan1234,

When you remove that much material stock and are left with a flexible thin-section part, it will be extremely difficult to keep the part from distorting excessively. As MikeHalloran noted, one way to minimize distortion is a planned process of rough machining/stress relieve/finish machining.

Another thing that would help finish machining the thin flexible areas is to use some type of conformal backup support. If you are making several pieces, one common method is to make a vacuum fixture that matches the casing OML. For a single piece, there are temporary casting materials (like Cerrobend or DynaPlast) you can make a conformal fixture from at little cost.

One approach used in aerospace that you might consider is machining the part thicker all over, leaving an extra material (.020" or so) on all surfaces. Then chem mill the part to its final size. Machining an aluminum part to an overall thickness of .100" versus .063" would reduce its tendency to distort from cutter forces.

 

[IRstuff]

Wow, that seems a bit brutal to remove 99% of the stock material.

Have you considered dip brazing separate components that could be individually formed?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Payyan1234]

Thanks all..It sounds like a wrong decision to machine it..

 

[MikeHalloran]

No, machining is not 'wrong'.
Machining from billet became more practical when CNC removed much of the labor cost.

In order to make an informed decision, you need to estimate the costs associated with every possible process, and strike a balance that makes sense to you.

Our answers might be different if we saw the actual part or drawing, but we understand why you might not wish to share it here in public.



Mike Halloran
Pembroke Pines, FL, USA

 

[rb1957]

why is fiberglass unacceptable ?

another day in paradise, or is paradise one day closer ?

 

[blakmax]

I'd be very careful estimating design properties. Sheet material is usually under plane stress from the rolling process and thick materials are usually under plane strain and as such the properties may be different, especially fracture toughness. Consult MMPDS and look into properties for thick material.

Regards

Blakmax

 

[berkshire]

Whilst not a part as small as what you are describing, I had the task of hand straightening some aircraft fuel tanks made from 3/16" thick rolled aluminum material, they were Chem etched to a final wall thickness of .o62" between a quilted diamond pattern laid out on the original material thickness. Even though the original tanks were under rolled to anticipate their movement after Chem etch , as soon as that outer layer of material was removed the tanks curled to an over rolled condition.
So beware of material movement as the material stress relieves when material is removed.
B.E.

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

 

[rb1957]

that's why the plate would be machined in several steps and stress relived. But hogging a fairing out of plate would be my last resort. 3rd time ... why not fiberglass ? How about sheet metal (5082 maybe) ... something weldable?

another day in paradise, or is paradise one day closer ?

 

[MikeHalloran]

I don't know why not fiberglass.
I don't know why not hydroformed sheet.
Only the OP knows what the damned part looks like, so we are shooting in the dark.


Mike Halloran
Pembroke Pines, FL, USA

 

[rb1957]

would hydro-forming have an expensive set-up ?

another day in paradise, or is paradise one day closer ?

 

[berkshire]

Hydro forming is about as cheap a setup as you can get, but the machine is expensive.
However, the buck you are forming on, needs to be able to withstand 5000 to 6000 psi of pressure.
B.E.

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

 

[Payyan1234]

Sorry about the late reply, Fiberglass/hydro-forming option is on my back pocket. Still waiting from the CNC machining supplier about the possibility and cost. The case is protruding out from the fuselage skin and has good amount of contours to make it aerodynamic . It is a restricted part , so not sharing

 

[Sparweb]

...The case is protruding out from the fuselage skin and has good amount of contours to make it aerodynamic . It is a restricted part , so not sharing

Your other thread tells us exactly what this enclosure is for. Your other thread also tells me that if you don't take your project more seriously, you will be out of a job in a few months.

Fiberglass and hydroforming should be your first choices for this part. Machining should be in your back pocket. Back pocket of pants in your closet.

STF

 

[tbuelna]

If machining ends up being your only option, there are aluminum tooling plate materials designed to be more stable with a large amount of stock removal.

http://www.howardprecision.com/aluminum/aluminum-cast-tool-jig-plate-stock-list/mic-6-aluminum