Flatness Issue

[BrianP.]

Having some issues trying to keep decent flatness on 42 inch long plates 3.75 to 6.25 wide. Start at 7/8 thick and finish at .770 for grind. Have tried a variety of different feeds and speeds and cut depths. Using a 2" Shear hog from AB Tools 5000 rpm's @ 50 . ipm w/1.6 wide cut as starting point. These cutters I have found are great for aluminum. This is the second cutter we tried the last one was a Mitsubishi and it was worse.

 

The 3.75 wide plates came out pretty good but the next set at 5.75 bowed about .01 to .020. I am standing the plates up skimming one edge. Down into milled aluminum jaws skim face about .020 deep walk around leaving +.100 on outside. Flip mill off about .060. Parts then go back in skim to clean, finish outside contour, drill some .25 and .406 holes. Flip and mill in to finish thickness. Would like to try and be at least around .005. This is the second go around with these parts. The last time I flipped multiple times and eventually got to .005 to .007. We have probably have about 10 more assemblies to do at 4 to 6 plates per. I would like to not be milling these forever. Any input would be appreciated.

 

Thanks

Brian

[chris m]

Whenever I have stress-relief problems with aluminum I either: 1)take some stock off both sides and then let them "rest" for [24] hours or so to stress relieve at room temperature (this sounds dumb but was a suggestion of our metallurgist and works mint) or 2) cook them at 275F for [6] hours and then let sit overnight. We have experienced success with both of these methods but usually just rip some stock off and let them sit.

 

C

[Guest CNC Apps Guy 1]

I like skim, flip, skim, release, skim, flip, and go to town. I've held crazy flatness doing that on some hand forged 7050.

[Bruce Caulley]

The key is to NOT tap the part down while taking semi finish skims after leaving the part "rest" as Chris described.

 

Bruce

[Guest CNC Apps Guy 1]

NEVER tap down as Bruce just said. That DEFINITELY bears repeating.

[BrianP.]

Thanks guys. Chris I will try the let them rest. Can't send them out for stress as this adds an operation and would need to go through the customer for added process. I never tap down till the final op to hold thickness dimension. I am doing the multiple flips. Had some success going to one way and smaller steps. Last set had 4 under .005 1 at .008 and 2 at .015.

[chris m]

We can heat treat up to 48" in house, so my life is a lot easier. Good luck.

 

C

[bob flat]

can you slow down and use hss? carbide face mill can add a lot of stress. The boss is steaming if the machine aint screaming. Tell him to go sit on the fire hydrant.

[jeff]

You may not be beating the part down as you flip, but are you using your hand to push the part down as you tighten the vises?

The key is that you want ZERO down pressure as you are skimming and flipping.

Tooling plate may be another option if it's in the budget.

[MACHINEMASTERG]

some times i have better luck..i mean skill using an endmill verses an insert just better geometry on the bottom and we have been using peel milltool pathes to machine down ss with great flatness results ..just a thought

[Tim Johnson]

some times i have better luck..i mean skill using an endmill verses an insert just better geometry on the bottom and we have been using peel milltool pathes to machine down ss with great flatness results ..just a thought

 

+1Greg. I am almost to the point of dynamic milling all parts that need to be flat with an end mill.

[Matthew Hajicek - Singularity]

If you use inserts specifically designed for aluminum they shouldn't impart much stress at all. Some of them are wickedly sharp, whereas inserts for steel have a somewhat rounded edge for durability.

[MACHINEMASTERG]

^^^^^ yes the Iscar Heli-alu are great at ripping Aluminum

[Jayson Kramer]

I do as CNC appsguy except i do not use a vise but double sided tape to a table always get flat with in .001

[spade117]

I do as CNC appsguy except i do not use a vise but double sided tape to a table always get flat with in .001

I've done that as well. You just have to be careful on how you get the part off the tape/table.