Need Help with Aluminum Finish!!

[audiiuda]

I am having difficulty machining the finish on these aluminum wheels. I cannot get a clean surface on the face of the wheel where there are no inserts or lug holes. I have tried using all types of coolant, at different pressures, but cannot get the face to have a nice fine finish. Does anyone have any idea what is going on?!? I don't think chips are building up on the tool.

Anyone have any recommendations?! A few people claim that this finish is from the metal itself, but that I do not believe so because the transition occurs at one exact spot.

[Stevo]

What type of aluminum are you running? Do you have the proper inserts. IIRC aluminum in the O condition is very hard to get a good finish on.

Stevo

[audiiuda]

It's an OEM audi wheel, so I believe it is a 6061 alloy. The interesting part is, I machined the faces of these wheels about 1 year ago and they came out perfect, taking about .03 inches off. Now going back with the same exact program, I am getting these defects. It is much easier to understand if you see the pictures, unfortunately I cannot post them yet as I am new to the forum.

Again thank you for the help. Perhaps I can email the pictures to you for a better understanding.

[dtc2002]

If those are literally the same wheels, then the aluminum has aged, both through fatigue from being worked (work hardening) as well as deterioration from time itself. We had a bunch of 6061 T6 round bar come into our shop that we were putting a 1/4x20 hole 1" deep, skim cutting to put a nice finish on it, cutting off at 6" then bending 90 deg in the middle. worked GREAT for the first batch. We let that same stock sit for about a year or so and they all machined horribly and snapped when bent. We called a metallurgist about it and he said that the aluminum will naturally become brittle over time, whether or not it is being used for anything.

We did find though that turning the surface speed up as much as possible and using a very light flood coolant (~5% concentration) with super sharp, polished inserts helped considerably.

Hope that helps.