Machining 2024-T3 1

[rwild]

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I am having warping issues while machining .125" thick 2024-T3 alluminum. It is potato chipping as bad as 7075. I am removing .05". I started off with HSM contouring with a 3/8 dia. ball nose. 10000 RPM at 150 IPM and .01" step over with bad results. I then tried face milling with an indexable to remove .04" before contouring, and the face mill also warped the material. Any one have a solution to the warping, and is T3 that much different than T6? T6 does not seem to warp at all.

 

[MikeHalloran]

The problem is in the heat treat:

-T3 Solution heat treated, then cold worked.
-T351 Solution heat treated, stress-relieved stretched, then cold worked.
-T36 Solution heat treated, then cold worked (controlled).
-T4 Solution heat treated, then naturally aged.
-T451 Solution heat treated, then stress relieved stretched.
-T5 Artificially aged only.
-T6 Solution heat treated, then artificially aged.

The 2024-T3 gets its great strength from the cold working, which leave high stresses locked in. Machine it, and you remove some of the stressed material, which is no longer in balance with the material that remains. ... which then moves around so as to rebalance the stresses.
Machine it asymmetrically, and you get distortion.

If your finished workpiece is not symmetrical, e.g. not machined on both major faces (and/or doesn't remain clamped throughout the process), you may need a different material.



Mike Halloran
Pembroke Pines, FL, USA

 

[twinny]

Try using chemi-mill quality sheet material. This material is designed for aircraft skins which have pockets chemically eroded into it and it resists warping much better.
I always used to machine just enough to break the skin on the first side holding the skins on a vacuum chuck, flip it and break the skin on the 2nd side, flip it and machine pockets etc to size. Time consuming but better.
Any good aerospace material stockholder should have cmq material.

 

[dicer]

If you have to use that material. Use a vaccum fixture to hold parts down, depending on the size of the part of course. Machine it then straighten it. Pretty much that simple. If the customer doesn't like it, tell em to use some different material.