machining 7075 in the as quenched condition

[brin]

We have a drawing for an aircraft part that uses a 7075 hand forging. The drawing requires it to be rough machined, solution heat treated, quenched, held in the refrigerated state before final machining, and aged to the T6 condtion. This is different from most drawings which require final machining in the T6 condition.

Can anyone shed some insight into why a part would be final machined in the as quenched condition rather than -T6 condition? I understand that the T6 condition is easier to machine.

 

[mfgenggear]

brin

contact your customer & ask them why it drawn this way.
it is easier to machine in the T6 condition.
what is the nature of the part. is it a very thin wall or
a large & very thick, are tolerance very liberal or very precise.
what specification is it being heat treated to?

there will be movement after aging.


Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[brin]

thanks mfgengear-

This is a dwg that we have inherited, but the original designers are no longer available. It is our responsibility now. The part is relatively small (approx 10 inches long) with 1.0 inch thick main section and thinner flanges and a lug. Tolerances are fairly tight (+.002/-.000) at the lug. Heat treat is to AMS2770.

I have found one reference (eg: NASA 7075 handbook) that mentions machining in the W condition to achieve a better surface finish, but this has not been a problem on other parts.

Would final machining in the quenched condition tend to reduce residual stress (due to machining)? How about distortion during machining?

 

[mfgenggear]

brin

machining aluminum even 7075 will machine easily. no worries.
Yes I seem to believe the intent of the designer was to alleviate stress.
I Google the Data Sheet & it said it machines great in the annealed condition.
but I do not like machining any metal in the annealed condition, it tears, gets a bad finish & the machinist don't generally like it.
Machining In the final temper should be fine if the machine feeds & speeds are the recommended for 7075.

I like to heat treat any time I can before final machining.when it is possible.
To to be safe just machine some sample parts then evaluate after machining.
but I predict there will be no issues.

sometime if there to much hogging out, I like to rough machine rough with stock then heat treat & final machine.
this is generally more expensive but less stress build up.
so there's more than one way to attack this.

HTH


Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.