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 ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
