Machineability of 6061 vs 7075

Post by Shirley Luton
Hi,
Hoping someone out there can help.
We've been machining flat parts out of 1 1/2" aluminum plate. The pieces
are then annodized. We've done similar parts in 6061 aluminum and 7075.
We're now getting reports that there's "warping" in the 7075 pieces. I
understand that 7075 can have problems with regard to "fracture toughness
applications", but is that relevant to the warping problem? Is one type of
the aluminum more of a problem when annodizing? Or is it that 7075 doesn't
lend itself to machining without stresses leading to warping?
Any and all comments would be appreciated.
Les

Was there a change in thickness between the two alloys, which required
facing of the material? Or, was it faced at all when cutting?

--
Later,

Charlie

fix the e-mail address and it will get to me

Shirley Luton

2003-11-19 02:23:39 UTC

Hi Charlie,

In both cases (6061 and 7075) we started out with 2" plate. There was
extensive machining with .020 left for finishing.

Les

Post by Shirley Luton
the aluminum more of a problem when annodizing? Or is it that 7075

doesn't

Post by Shirley Luton
lend itself to machining without stresses leading to warping?
Any and all comments would be appreciated.
Les

Was there a change in thickness between the two alloys, which required
facing of the material? Or, was it faced at all when cutting?
--
Later,
Charlie
fix the e-mail address and it will get to me

hamei

2003-11-19 02:46:21 UTC

Post by Shirley Luton
the aluminum more of a problem when annodizing? Or is it that 7075

doesn't

Post by Shirley Luton
lend itself to machining without stresses leading to warping?
Any and all comments would be appreciated.
Les

Was there a change in thickness between the two alloys, which required
facing of the material? Or, was it faced at all when cutting?

Do you face one side but not the other side ? 6061 is gooey, 7075
is not. 7075 rolled plate will have stress on both sides - if you
relax the stress on the one side but not the other, over time it
will relax itself ... by warping.

"PrecisionMachinisT"

2003-11-19 02:49:04 UTC

Post by hamei
Do you face one side but not the other side ? 6061 is gooey, 7075
is not. 7075 rolled plate will have stress on both sides - if you
relax the stress on the one side but not the other, over time it
will relax itself ... by warping.

Yup, rolled is a different aminal from extruded.

BTW : on the 777 we went from 7075 to an different alloy 7050 on many
parts.........hepled some with the warpage problem.

--

SVL

--

SVL

Shirley Luton

2003-11-19 02:52:30 UTC

So, is there potentially more warpage with 7075 than with other alloys, like
6061?

Yup, rolled is a different aminal from extruded.
BTW : on the 777 we went from 7075 to an different alloy 7050 on many
parts.........hepled some with the warpage problem.
--
SVL
--
SVL

"PrecisionMachinisT"

2003-11-19 03:02:19 UTC

Post by Shirley Luton
So, is there potentially more warpage with 7075 than with other alloys, like
6061?

Yeah, especially where there is pocketing on one side and only a faced off
surface on the other.

Common procedure is to rough the pockets and then re machine the back side
before finishing pockets........Also, straightening operations are typical
in airframe structural applications of 7075.

Shirley, if you attach your reply to the bottom of a previous post, it is
usually easier for a responder to keep discussion in context.......most of
usenet seems to dislike top posted messages for this reason.

--

SVL

Shirley Luton

2003-11-19 03:09:18 UTC

Post by Shirley Luton
So, is there potentially more warpage with 7075 than with other alloys,

Post by Shirley Luton
6061?

Yeah, especially where there is pocketing on one side and only a faced off
surface on the other.
Common procedure is to rough the pockets and then re machine the back side
before finishing pockets........Also, straightening operations are typical
in airframe structural applications of 7075.
Shirley, if you attach your reply to the bottom of a previous post, it is
usually easier for a responder to keep discussion in context.......most of
usenet seems to dislike top posted messages for this reason.
--
SVL

Thanks for the tip - hope this works!

Les

"PrecisionMachinisT"

2003-11-19 03:21:44 UTC

Post by Shirley Luton
So, is there potentially more warpage with 7075 than with other alloys,

Post by Shirley Luton
6061?

Yeah, especially where there is pocketing on one side and only a faced off
surface on the other.
Common procedure is to rough the pockets and then re machine the back side
before finishing pockets........Also, straightening operations are typical
in airframe structural applications of 7075.
Shirley, if you attach your reply to the bottom of a previous post, it is
usually easier for a responder to keep discussion in context.......most of
usenet seems to dislike top posted messages for this reason.

Thanks for the tip - hope this works!

Yeah, thats much better.....somebody else gets to nail you on snipping
previous sigs and cutlines. ( or did I just do that ??? )

Notice the headers at the top and how they line up, showing who wrote
what---all (fairly) neat and orderly.

Below is a cutlined sig---two dashes and a space, everything below the
cutline is considered a signature.

Cheers, and good luck with the 7075.

--

SVL

Joe Osborn

2003-11-19 07:03:32 UTC

Post by "PrecisionMachinisT"
Yeah, especially where there is pocketing on one side and only a faced off
surface on the other.
Common procedure is to rough the pockets and then re machine the back side
before finishing pockets......

Good advice. Note that you can get plenty of warpage in large flat parts with
6061 as well. It is also helpful to roughly balance the *volume* of material
taken off of both sides. E.g, if one side has shallower pockets than the other,
take additional material off that side. We often do quick volumetric
calculations to figure out how much volume of AL is coming off both sides. You
don't need a perfect answer, but getting in the ballpark helps tremendously in
reducing warpage.

Best Regards,

Joe

Joe Osborn

OMW Metalcrafts
"Custom Precision Machining
in all Metals and Plastics"
23 Pamaron Way, Ste. E.
Novato, CA 94949
WWW.OMWMETAL.COM
EMail: ***@AOL.COM

Shirley Luton

2003-11-19 02:53:38 UTC

Both sides were machined in an equivalent manner.

Post by Shirley Luton
the aluminum more of a problem when annodizing? Or is it that 7075

doesn't

Post by Shirley Luton
lend itself to machining without stresses leading to warping?
Any and all comments would be appreciated.
Les

Was there a change in thickness between the two alloys, which required
facing of the material? Or, was it faced at all when cutting?

Kathy

2003-11-19 03:18:53 UTC

Are you saying that the parts were not warped prior to anodize?
I would think that 7075 would be more stable than 6061.

Shirley Luton

2003-11-19 05:50:07 UTC

Post by Kathy
Are you saying that the parts were not warped prior to anodize?
I would think that 7075 would be more stable than 6061.

Unfortunatey, there is no confirmation either way on the warping, i.e.,
whether it was there before anodizing or not.

Les

Charlie Gary

2003-11-19 15:12:35 UTC

Post by Kathy
Are you saying that the parts were not warped prior to anodize?
I would think that 7075 would be more stable than 6061.

Unfortunatey, there is no confirmation either way on the warping, i.e.,
whether it was there before anodizing or not.
Les

The warpage could have been caused by the parts being left in direct
sunlight. Or a dark closet, for that matter. Time and temperature
fluctuations will do it for you. One post mentioned removing material from
both sides, and that is what we always strive for in our parts. We cut lots
of 6061 and 7075, and once I get the part straight in my CAD system, I draw
the material with the part as close to the center as I can. If it's a big
flat plate we'll face an equal amount from both sides. Other parts get
roughed and finished on one side, and then we prep them for turning over to
rough and finish the second side complete. As soon as we started following
this procedure, warped parts went away. I can't remember how many years
it's been since we had to straighten anything, but it's been several.

--
Later,

Charlie

fix the e-mail address and it will get to me©®

Cliff Huprich

2003-11-19 15:31:36 UTC

Post by Shirley Luton
"warping" in the 7075 pieces.

What temper? Is it possible to stress relieve this material in
some way before machining (IF that's the problem)? Ask the
vendor ...?

If it's machining-induced stress sharper tools & high-positive
rakes may help. But first identify the actual problem. A few test
parts (well qualified) run thru the anodizing may help. IIRC Anodized
surfaces expand slightly .... but that may well be immaterial. Or not.

--
Cliff

Cliff Huprich

2003-11-19 21:00:44 UTC

BTW, IF your stock is warped to begin with and you restrain it
for machining it will be warped when you are done and release
the clamps/constraints.

So it might be bent/warped raw stock to begin with ....

--
Cliff

PrecisionMachinisT

2003-11-19 22:41:38 UTC

Post by Cliff Huprich
BTW, IF your stock is warped to begin with and you restrain it
for machining it will be warped when you are done and release
the clamps/constraints.
So it might be bent/warped raw stock to begin with ....

Good point, Cliff......

And....

Care must be also be taken to not warp it from clamping forces, on release
it will tend to return towards it's unrestrained position, your freshly
cut surface no longer being a flat surface.

Kind of difficult to put into words, but we often referred to the ideal
machining situation as one in which the part is clamped in a "free
state".......

I suppose on reflection, this condition would be best described as being
met when clamping pressures exert only equalized compressive forces---no
sections under forces causing tension, torsion or otherwise.

Fixturing and processing can sometimes be a real bugger, esp. when you are
working with a die castings having tooling point datums, rather than
starting out with solid billet raw stock........

For this reason, the trend in machining complex aerospace structural
components of aluminum has moved away from cast or forged raw material over
the last decade or so towards solid billet--the savings in process time and
enhanced process reliability attainable using high speed machining
techniques far outweighs any possible material savings in using near-net raw
materials excepting perhaps extruded shapes in the majority of situations.

--
SVL

Cliff Huprich

2003-11-20 01:00:32 UTC

Post by PrecisionMachinisT
Kind of difficult to put into words, but we often referred to the ideal
machining situation as one in which the part is clamped in a "free
state".......

Yep. Sometimes though the part only matters in the constrained
state. It's rare though.

Post by PrecisionMachinisT
Fixturing and processing can sometimes be a real bugger, esp. when you are
working with a die castings having tooling point datums, rather than
starting out with solid billet raw stock........

Then's when you start adding tighter manufacturing tolerances, doing
tolerance stack-up analysis, create temp machining datums ..... sometimes
redimension & re-tolerance the whole thing & processes ...

Just hope nobody insists on incremental dimensions & tolerances <G>.

Don't forget the tolerance stack-up and min/max material conditions
on the raw casting either. Pray nobody else already made some handy
assumptions & semi-finished the casting or forging. Then you can be
in real trouble. And bless the designers & engineers that got the
castings/forgings right in the first place so that the thing can be made.

--
Cliff

PrecisionMachinisT

2003-11-20 01:07:04 UTC

Post by Cliff Huprich
in real trouble. And bless the designers & engineers that got the
castings/forgings right in the first place so that the thing can be made.

Dont push your luck, bubba.

--
SVL

Anthony

2003-11-20 02:31:01 UTC

Post by Cliff Huprich

Post by Shirley Luton
"warping" in the 7075 pieces.

What temper? Is it possible to stress relieve this material in
some way before machining (IF that's the problem)? Ask the
vendor ...?
If it's machining-induced stress sharper tools & high-positive
rakes may help. But first identify the actual problem. A few test
parts (well qualified) run thru the anodizing may help. IIRC Anodized
surfaces expand slightly .... but that may well be immaterial. Or not.

Anodizing, by nature, also induces some amount heat into the parts. There
are quite a few variables that control the anodizing layer thickness.
Remember that the anodizing layer thickness will be half in the part,
material, and half external, so this needs to be figured in to the
tolerances when machining.

(In a 20 micron anodized layer thickness, 10 microns of the layer will be
within the material, 10 microns will be external. So in the case of a
tight tolerance hole, you will need to bore it 20 microns oversize (10
microns per side) prior to anodize, provide the print gives an after
anodize 'finished' dimension.)

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

hamei

2003-11-20 04:59:15 UTC

Post by Anthony
(In a 20 micron anodized layer thickness, 10 microns of the layer will be
within the material, 10 microns will be external. So in the case of a
tight tolerance hole, you will need to bore it 20 microns oversize (10
microns per side) prior to anodize, provide the print gives an after
anodize 'finished' dimension.)

I usually hone afterwards :-)

even the regular stuff is HARD, by the way.

"PrecisionMachinisT"

2003-11-20 06:42:54 UTC

I usually hone afterwards :-)
even the regular stuff is HARD, by the way.

Dont the alkali etch take some amount off prior to the actual anodize
process too ???

--

SVL

Anthony

2003-11-20 12:37:38 UTC

Post by Anthony
(In a 20 micron anodized layer thickness, 10 microns of the layer

will

Post by "PrecisionMachinisT"
be

Post by Anthony
within the material, 10 microns will be external. So in the case of a
tight tolerance hole, you will need to bore it 20 microns oversize (10
microns per side) prior to anodize, provide the print gives an after
anodize 'finished' dimension.)

I usually hone afterwards :-)
even the regular stuff is HARD, by the way.

Dont the alkali etch take some amount off prior to the actual anodize
process too ???
--
SVL

Actually, I don't believe it's and 'etch', the alkali is used to
clean/degrease. (In our process anyway)

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

Kathy

2003-11-20 13:00:39 UTC

Post by Anthony
(In a 20 micron anodized layer thickness, 10 microns of the layer

will

Post by "PrecisionMachinisT"
be

Post by Anthony
within the material, 10 microns will be external. So in the case of

Post by Anthony
tight tolerance hole, you will need to bore it 20 microns oversize

(10

Post by Anthony
microns per side) prior to anodize, provide the print gives an after
anodize 'finished' dimension.)

I usually hone afterwards :-)
even the regular stuff is HARD, by the way.

Dont the alkali etch take some amount off prior to the actual anodize
process too ???
--
SVL

Actually, I don't believe it's and 'etch', the alkali is used to
clean/degrease. (In our process anyway)

I think it may be an acid etch. I've had parts that came back with holes
oversize with the plater apologizing for leaving them in the acid etch too
long.

Cliff Huprich

2003-11-20 14:57:21 UTC

Post by Kathy

Post by "PrecisionMachinisT"
Dont the alkali etch take some amount off prior to the actual anodize
process too ???

Actually, I don't believe it's and 'etch', the alkali is used to
clean/degrease. (In our process anyway)

I think it may be an acid etch. I've had parts that came back with holes
oversize with the plater apologizing for leaving them in the acid etch too
long.

Aluminum OXIDE is somewhat soluable in strong alkalis.
Bare, unoxidized, Aluminum (anyone ever see such? <G>)
oxidizes at a very rapid rate ....

Think Draino ....

--
Cliff

hamei

2003-11-20 13:53:41 UTC

Post by Anthony
(In a 20 micron anodized layer thickness, 10 microns of the layer

will

Post by "PrecisionMachinisT"
be

Post by Anthony
within the material, 10 microns will be external. So in the case of

Post by Anthony
tight tolerance hole, you will need to bore it 20 microns oversize

(10

Post by Anthony
microns per side) prior to anodize, provide the print gives an after
anodize 'finished' dimension.)

I usually hone afterwards :-)
even the regular stuff is HARD, by the way.

Dont the alkali etch take some amount off prior to the actual anodize
process too ???

Actually, I don't believe it's and 'etch', the alkali is used to
clean/degrease. (In our process anyway)

either way, I've never been lucky enough like Garlicdood to find
an anodizer who could second-guess how the etch/clean and anodize
swell proportions would equal out - so I hone after. All it takes
is one batch of screwed-up parts to negate any savings you could
earn from not-honing over several years.

Garlicdude

2003-11-20 13:27:41 UTC