Machining 2mm alu plate

[Lugy]

Hi folks, today I'm attempting to machine up a lid as part of a job we're trying really hard to get.
The lid is made from 2mm (.080") 6082 - this is the finished size, and has pockets 1mm (.040") deep, see the attached screen shot showing completed part.

The first method I tried was to just carpet tape the part to a fixture, then machine the part complete, the profile worked easy enough, though it went wrong on the pocket.

Next, I carpet taped the blank to the fixture again, drilled the holes and screwed it down all round the profile before trying the pockets, this was better, but the finish on the pocket was terrible and the part began to vibrate.

The material would also appear to be quite chewy, almost like 5251 (IIRC) which doesn't seem to help much. Especially as I'm not using coolant (when I tried using it, the tape lost it's stickiness!).

The I'm using a 6mm 2FA type slot drill at 10krpm and between 200-300mm/min.

Any suggestions to help me would be greatly appreciated (except a vac table, we can't afford one of them ).

Lucas

[nickswimsfast]

I'm by no means an expert, but will throw a few ideas for you to try.

If the part is vibrating than you are near a natural frequency for your setup. If you can afford to decrease or increase the RPMs of the spindle, you might be able to get out of that response frequency.

You've probably already considered this - but are there any features that go through the whole part which you could use to clamp? Could you ask your customer for a concession of a new feature for clamping in the middle? Sometimes engineers are focused more on the design and can overlook some of the requirements of manufacturing a part. Good design/manufacturing communication really helps.

Another option would be to simply clamp a bar across the lid with a bar as shown in the picture. Make sure your CNC program clears the fixture bar. Obviously you could get more complicated with a clamp like this.

[chuck5121]

A vacum table would be good if you don't have to machine through the work piece. A second option would be to machine a thicker piece with your profiles machined through then clamp it on top of your work piece. Good luck

[Ed from NY]

you could try clamping 5-6 blanks at a time, doing a few pockets, clamping the set again thru the pockets and machining the profile and whatever is left. If it still vibrates you could try machining the same piece in steel plate, but with a slightly smaller diameter and larger pockets so to use that on top of the pile to help clamp everything down -- kinf of a sandwich. if you have a lot of these to do you could add some aligning blocks to that plate that partially fill the pockets to save you some time in aligning the features done in the two passes. Good luck!

[underthetire]

Really looks like a perfect vacuum table part. Don't know about Scotland, but here we can get little vacuum pumps at places like harbor freight pretty cheap. The fixture woul be simple enough.