Warped 6061 Aluminum Jig Plate

[donovaf]

As everyone knows jig plate is supposed to be stress relieved.
I have an 80"x60"x1" plate that we machined a pocket 19.75 x 7.25X.5 deep. It has warped about .068 at the ends. Apparently and surprisingly this pocket is the cause. I am thinking if I machine a small grove on the opposite side of the plate the flatness will come back.

Anyone please comment.
Thanx

 

[tbuelna]

donovaf-

You have no reliable way to predict what result machining that groove will have on the accumulated mechanical strain in your jig plate. Yes it's true that 6061 tooling plate is normally supplied stress-relieved, and it's likely that machining the pockets caused the plate to warp. But the typical approach to machine a part like this is to rough machine leaving sufficient stock on critical surfaces, stress relieve, and then finish machine the critical surfaces.

The problem with aluminum parts that have not been fully stress relieved is that over time (during service) they will naturally stress relieve, and their free-state shape/flatness will change from the as-manufactured condition. If you do not want to risk a thermal stress relief, then you can look into mechanical stress relief (stretching) or vibratory stress relief.

Good luck to you.
Terry

 

[Compositepro]

The heat treatment of 6061 also involves "aging" where the grain structure of the aluminum is established. If the aging is not completed at elevated temperature (about 375F) it will occur slowly at room temperature, and result in some dimensional changes. This is different from stresses that may be stored in the plate from the forming process. Follow Tbuelna's advice.