Copper Experience

[rustyh]

Good Day All,

I wonder if I can get some help.

Currently running as copper job using 3/8" thick, 1 1/2" wide and 75mm long C101 copper. Having to mill the part down (pretty simple features) with a thickness tolerence of +/- 0.05mm.

I run op 1 doing a face op with a 6mm 3 flute cutter (face off 0.5mm followed by a 0.1mm finsish pass), followed by milling the outside rectange profile with the same tool, and then a small shallow pocket in the middle of the part (around 1mm deep) with a 2mm end mill (it has internal rads that need the 2mm cutter size). Also a couple of tapped holed.

I then flip the part over to simply face off the opposite side to achieve the thickness. Im facing off about 3.5mm, hitting it in one roughing pass of 3.4mm then a finish pass of 0.1mm.

Im finding that when I take the parts off to inspect, I see them bowing. This in turn throws the part out of tolerence.

Can anyone help with the reasons to why it is doing this, and any ways to prevent it or improve it to hit the tolerences required?


I am using Aluminum 3 flute, uncoated cutters by the way.

Thanks

Rusty

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[hfjbuis]

May be you stressed the copper to much. Looking at the data, you are cutting 3.4 mm on a total thickness of 9.5 mm.
Try another part at 0.5 mm cutting depths just to see if the problem has gone. If not, the copper isn't stress relieved. Glow the copper and let it cool down slowly. You will probably see the copper gets very soft!

[rustyh]

Thank you

We have not done any stress relief of the copper, only used it straight from stock.

What temperature does it need to be heated to to relieve the stresses?

[hfjbuis]

You have to glow it to red, just for a few seconds to minutes. It will oxidize (above 400 °C) so the surface will not be pretty.

Take a copper washer, hit it hard with a hammer, feel how it bends, heat to red, led it cool down in the air, bend it again, feel the difference!

[awerby]

Copper and other non-ferrous metals don't anneal the same way as steel. While heating steel up to red heat and letting it cool slowly will relieve stresses and soften the metal, with copper you need to quench it in the red-hot state to achieve full annealing. This hardens carbon steel, but softens copper. If the black copper oxide bothers you, there are surface treatments like Cupronil you can use to stop it from forming: https://www.riogrande.com/product/Cu...E&gclsrc=aw.ds

[AeroTool]

You are using plenty of coolant, correct ???