On Mon, 13 Feb 2012 20:41:18 -0600 Jon Elson <el...@pico-systems.com> wrote:
> gene heskett wrote: > > > > > > Guy's, maybe I don't understand cutting alu as well as I thought. > > > > All along, I have believed that it was more important to keep the > > oxygen in the air away from the cutting surface in order to slow > > the formation of alu oxide on the surface, which in normal air, not > > blown, can get a good start in 0.001 seconds > I have some doubts about this. The oxide will form unless you run > under Argon shielding, > which may not be real practical. > > This oxide is also the 2nd > > hardest substance known to man and can take the edge off a carbide > > tool that has to cut thru it in seconds under the right set of > > wrong cutting params, which my slow feed made worse. > Any slow cutting so that the tool is barely getting below the surface > increases wear. > Taking the biggest cuts the tool can survive reduces tool wear by > removing more > workpiece material with each cut. > > Sealing the cut surface against the air and its oxygen, blown or > > otherwise, that causes this instant alu oxide film with its > > subsequent wear on the cutting tool has always been the reason for > > my use of a cutting oil, deep enough to flood and seal the surface, > > or misted, particularly when I don't have the spindle rpms to throw > > it away from the cut. > Our shop at work does ALL aluminum dry, and usually use HSS cutters > (although possibly > they may be M42 or such cobalt cutters.) So, I think you are going > WAY overboard > with this oxide thing. > > The majority of the heat you are referring to is not the heat of > > the tools cutting action, but is the result of the chemical > > reaction that forms this alu oxide film so rapidly. > OH, COME ON! Where do you GET this stuff? Yes, oxidation is > exothermic, but really. > Shave some aluminum with an X-acto knife and see if you can detect > this heating! > I seriously doubt you can detect it. Rubbing of the tool when it is > having trouble > digging below the material is the largest source of heat, next is the > heating of the > chips as they are curled up. That heat should not get to the > remaining workpiece > material when things are done at the right speed, but we both have > that problem > of limited spindle RPM. > > That is my take on it. How right or wrong am I? > > > Sorry, I think your theory is full of holes. Many shops cut aluminum > dry, some at > insane rates. I read a book on high-speed machining, they were > cutting aluminum > at 640 cubic inches a minute removal rate, putting 80 HP into a 1/2" > end mill at 75,000 RPM. This was done dry, as no coolant could reach > the cutting are due to the bullet-like spray of chips coming out. > Also, the thermal > shock was harder on the carbide than running dry. > > I cut a fair amount of it dry, and get excellent tool life either > with M42 Cobalt > cutters in the larger sizes, and solid carbide in the 1/8" size. I > do use water-based > coolant when I am doing a lot of cutting in a small area to prevent > heating of > the workpiece, or when there is a lot of material to remove. I can > often run > for days on one tool. > > And, don't ignore climb milling, it makes a HUGE improvement in tool > life. > > Jon Aluminum to the oxide yields about 60 Kcal/g but calculate the weight of a small area of Al 0.001 thick and I don't think you are going to see the heat. I suspect the only reason to use carbide is that small HSS mills are really flexible. Even though my mill has serious backlash I can climb mill with small mills, eg. <= .25". I have had occasional trouble with a .5 rougher but I had really buried it. I can climb mill with .5 carbide roughers on steel if I take a light cuts like 50 to 100 thou. Dave > ------------------------------------------------------------------------------ > Keep Your Developer Skills Current with LearnDevNow! > The most comprehensive online learning library for Microsoft > developers is just $99.99! Visual Studio, SharePoint, SQL - plus > HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when > you subscribe now! http://p.sf.net/sfu/learndevnow-d2d > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
