Aluminum Casting acting gooey

[ulysses]

Aluminum casting made of 356-T51 (V process) is kind of acting "gooey". We get lot of cases of threads stripping. Granted aluminum casting is not the best material for internal threads, but we never had such stripping problems in the past made from the same aluminum alloy from the same casting house. Is there any testing that I can do to find a difference between past (good) castings from the present (perceived as gooey) material

[PinkertonD]

Google these for "About 4,260,000 results"
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I fear for the future of Engineering!

[Kelly_Bramble]

Is there a porosity specification for the casting? Is it being verified?
Is there any post-cast material verification required? Hardness or other?

T51 temper is simply an aging process that improves the dimensional stability and quality of the material.

Is your foundary simply casting and delivering the part?

[ulysses]

There is no porosity specification. We have never done any post-cast material verification in the past; only dimensions were checked as QC criteria. But now I am thinking of checking the hardness. I found from Search that the hardness for A356-T51 should be 71 on Rockwell E scale 1/16 ball. Do you know what should be the hardness number with a 1/8 dia ball (our QC test machine has 1/8 ball)?

[RWOLFEJR]

I'm assuming you're cutting these threads? Not rolling them? If rolling them I'd look at material condition prior to rolling. I've found it best to let any fresh cut aluminum get its haze back before any forming.

Could the issue be on your end? Same cutters? Same feeds and speeds? Same coolant? Be a good idea to take a closer look there while having some samples looked at. What I've found here at our shop a lot of times... conversations like this... (Not saying that this is your situation... just amusing myself )

...These inserts are junk.

What's wrong with them?

...They aren't lasting for more than ten or fifteen parts.

What did you change?

...Nothing.

Didn't change anything at all?

... Nope... All I did was bump the speed up a few hundred rpm but they're holding size fine and the finish is great.

Oh... I see... And how much time per pass are we saving now?

...About 5 seconds

How many parts did we get before this rpm change?

...About 100

So let me see if I understand you... The inserts are now junk because you're running them too fast?

That was somewhat of an exaggeration but stuff like that used to happen around here a lot.

Good luck...!
Bob