Chip Breaker for Aluminum

[tpsimer]

Good Afternoon,
I have a part that has a bore that is deep. It is 2.5 diameter and drops down to .875 at the bottom 4.5 inches deep. I am having trouble with chatter and chipbreaking. This is 6061 and it is running out strings rather than breaking. Any suggestions for a cnmg insert chipbreaker and grade? Also any pointers on getting rid of chatter? I am running way to slow for any production but speeding up produces chatter.
Thanks,
Tony

[packrat]

I know this is BLASPHEMY on this site, but, insert tooling is not the best thing for aluminum cutting, Especially boring in the lathe. There is no way that you can get a insert that is as sharp as a correctly ground HHS tool. The metallurgy of the material makes it impossible.

I would switch to a HHS boring tool for this. and make sure the cutting edge is on center.

cary

[plasmator]

Originally Posted by packrat I know this is BLASPHEMY on this site, but, insert tooling is not the best thing for aluminum cutting, Especially boring in the lathe. There is no way that you can get a insert that is as sharp as a correctly ground HHS tool. The metallurgy of the material makes it impossible. I would switch to a HHS boring tool for this. and make sure the cutting edge is on center. cary

[citation required]

[roninB4]

Well I may get flamed for this too but I'll be in good company. I also don't care much for any type of machining (especially in the lathe) of aluminum with anything but HSS. With HSS you can adjust the nose radius, rake, and chip breaker fairly quick and easy with HSS. Carbide is great stuff, don't get me wrong. But it works best in a continuous cut with a rigid machine on ferrous material (mostly). Aluminum is so soft and gummy it sometimes takes some experimenting to get a good breaker to work per your speed/feed. A good finish seems easier to obtain with HSS also. I'm sure there's something out there with insert geometry that works well but if I can adjust/grind the right geometry mix myself I find it easier and less time consuming. Chatter will often come from too small a boring bar diameter. Use the largest one possible or make one for the job. JMO.

[PixMan]

Some shops just don't have the holders (boring bars i this case) for using HSS tools.

There are MANY good inserts out there for boring, turning, milling of aluminum that will break a chip.

What holder do you have and/or what is the insert size & shape?

[ImanCarrot]

Bore from the bottom out- that way the tool will drag the chips out of the bore instead of pushing them in the hole.

Drill a hole just inside the O/D required- the chips will break and no stringy things can form.

[Shane123]

i usually use kenametal black inserts for boring aluminum on the lathe, and run high rpm and high feed with light passes. if possible, coolant thru the bar. also, a .005 radius insert works well. haven't used much of the hss bore bars.

[rowbare]

An old timer machinist told me the same thing packrat said about being able to get a sharper edge on HSS.

The Arthur Warner company makes HSS Inserts in standard sizes. You might find an appropriate insert there.

High Speed Steel (HSS) tool bits and blanks - Arthur R. Warner Co

bob

[mc_n_g]

If you are stuck using CNMx inserts you should try using a CNMP or CNMG.
You shoudll get a polished or ground insert designed for aluminum. The CNMP is a positive cut to sit in negative toolholder. An insert designed for aluminum will not work9 or have extremely short life) for other materials.

[packrat]

Originally Posted by plasmator [citation required]

I can't point you to a specific website or book, BUT, stop and think about it for a minute;

HSS is an alloy, chemically combined at the molecular level. It can be ground/sharpened down to a single molecule width.


Carbide is a sintered mix of many larger compounds. There a carbides, binders and fillers in the mix. While the carbides are hard they are also larger than a single molecule, when sharpened/ground a inserts edge is comprised of much large particles than a tool steel.

That and 48 years of experience as a die maker/ machinist is what I based my answer on.

cary

[roninB4]

Originally Posted by PixMan Some shops just don't have the holders (boring bars i this case) for using HSS tools. There are MANY good inserts out there for boring, turning, milling of aluminum that will break a chip.

-I'm not going to knock using inserts I haven't tried but making a boring bar isn't that difficult. Take the largest piece of round stock that will fit (your stock rack may vary....). Drill a hole (on an angle if you need a blind hole bored) through to accept whatever HSS blank you have, drill and tap the end ( in line with the boring bar axis)for a set screw to hold the blank in place. Now grind your geometry on the HSS blank. Takes about 20 minutes to make and doesn't cost much either.

I've been a die maker & machinist for 25 years. Use HSS or carbide according to the application, don't reach blindly for one or the other.

[iknowyoudo]

When I bore I use a G74 (drill chip break routine) I set my retract (K) at .01" and hog out .08" per pass 5" deep 1" ID. I use carbide Circle brand boring bars. The one I use to hog has a hole in the center for through coolant. I soldered one end closed then filled 3/4 full with sand then soldered that end closed. The sand absorbs the vibration leaving a silky smooth finish when I do a clean up pass of .007" to .01". I hope this helps