The table has a pod layout, so downward spiral should work, but earlier posts have disagreed upon the type of the helix (angle). Some say straight flute, some say use the normal helical angle and others say a high angle will work best. All quoting chip breakage as their reasoning. Somewhere between .005" and .02" seems to be the range for chip breakage.
How many flutes? I've heard 13,000 rpm and 150 ipm and 15,000 rpm and 250 ipm. With only 2 flutes that's only a .005-.008 chip. That seems low and the speeds seem high (like it might push my part on the pods). More flutes should keep my tool cooler but my chip breakage goes down drastically, which would cause me to feed faster. I think feeding anything over 150 ipm is going to give me problems.
The machine has a spindle speed of 18,000 rpm and a feed rate of 600 ipm. I do not have a cooling system in place at this time. This is a prototype and I am working on getting air or a mist blower. In regards to my approach, can I just feed in an end mill since the aluminum is so thin? What feed would you suggest? I will be machining the outside perimeter and two inside pockets.
1200 (SPM) div .250 = 4800
Feed speeds are governed by the size of the tool. The harder the material, the slower the feed speeds. Softer material will be on the higher end of feed speeds.
Above is based on a 45^ helix tool, which allows for fast removal of material. (#CU-250-AL)
I've had the same problem and I had the best result with air cooling and a special silicon-spray. You must first spray your material and your tool.
The biggest problem you are going to have is chip welding, because you are machining a very soft aluminum. Any type of coolant will be a help and you may find it impossible to machine without it.
I have some concerns about increasing the number of flutes due to the fact that you are machining a very soft aluminum. Is the core material the same grade as the skins? How are the skins and core bonded? Are they chemically bonded with an adhesive? If so, you will have some real issues with aluminum buildup on the tools.
The other area which concerns me is the pocket area of honeycomb. Is part finish a concern? Do you need to cut the honeycomb clean without any flagging? What diameter tool are you looking at? Do you have radius constraints?
There is an article in the February 2001 Modern Machine Shop about machining aluminum. They were talking about three flute bits and about speeds and cutting speeds.
We have both 5x and 3x cnc in our shop. We cut this type everyday and have found this bit to work the best, 300,000 lin. feet per bit. Lach Diamond, Inc. p.n.LI-1211/2. Try a feed rate of 100 and speed of 18,000. You might want to run a mister on the cutter--that will help cut a clean edge.
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