Re: 316 stainless
- From: Kirk Gordon <kg1@xxxxxxxxxxxxxxx>
- Date: Tue, 06 Sep 2005 23:02:26 -0400
Steve Walker wrote:
Need some advice on feeds & speeds. Using Sandvik CNMG-432 MM, grade 2025. Using their feeds & speeds, I only got 10 minutes of (repeatable) tool life ( 18 pieces, then failure, edge worn away). It's a solid part, no overhang, short tools etc. Using water soluble at 8 percent. The problem is I need to get through a pallet of 128 pieces. Anybody have any better luck with a different grade, or style Sandvik insert? I dropped the speed to 275 SFM, and I'm getting 18 minutes, then same failure. the D.O.C. is .100" , Feed .013 IPR.
I'm no expert on Sandvik grades; and I certainly don't want to contradict what Tom Liption wrote, since he sounds like he knows what he's doing; but...
As a GENERAL rule, when an insert (or any other cutting edge) fails by wearing down, that's a signal that you need more feedrate. That'll mean higher cutting forces, and more heat, but it often solves wear problems pretty dramatically.
Think about this: At .013 IPR, you'd need 77 revs to cut one inch of length. That means the cutting edge sees 77 times the workpiece circumference for every Z axis inch that you program. If the part is just 1" diameter, that means 242 inches of wear on the insert edge for every inch of length you turn. If you went to, say, .015 IPR, the same inch of cutting would only need about 209 inches of edge wear - a reduction of almost 14%. If you get 10 minutes out of an insert now, then you could expect to get almost 11.6 minutes, just by adding two thousandths to the feedrate. If you increase chip loads even more, the increased life can be even better.
The reason, of course, is that you're now using only 013" of the insert's face to make chips. You could be using a wider piece of it, and getting more and more carbide into the act. That would spread the abuse around a bit, instead of letting just one little stripe, right at the cutting edge, do all the work.
Obviously, increased cutting forces have limits. If you increase the feedrate enough, then the whole insert will just break and die. In some cases, inserts will wear and crater BEHIND the cutting edge, on their top faces, because that's where all the work is being done to curl and break the chips. But somewhere between the extremes of chip load, there's normally a lot of room to manuever. Premature breakage typically means chips that are too fat. But premature wear means too many chips that aren't fat enough.
Increased heat can become a problem; but it doesn't have to. Thicker chips will generally carry more heat away from the work and the tool, if they're curling and breaking properly. The total heat that remains in the work and on the tool can actually get smaller as chip thickness grows.
Hope this helps!
- 316 stainless
- From: Steve Walker
- 316 stainless
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