4 Tips That Will Extend End Mill Life
End mill breakage and premature wear are not only costly, but they also put a crimp in productivity. Time spent locating, installing, and calibrating new tools takes time away from processing metal. Fortunately, the best practices for increasing productivity and work quality also extend tool life. Regal offers some considerations for making your end mills last as long as possible:
Feeds and Speeds
Any discussion of proper milling operation has to start with cutting speed and feed rate. These two variables dictate much of what follows. Proper speed and feed, to a large extent, will determine chip load. For every work material and end mill design there is a narrow niche for running at optimal speed to maximize efficiency. Even if you run at the ideal spindle speed, feeding too fast will break the mill. The correct feed rate is no good, either, if the spindle speed is not dialed in. Too fast will generate enough heat to soften the tool, causing it to become dull and wear at a much greater rate.
Coatings
Coatings give mills a hard shell that protects cutting edges, and in many cases, allows them to withstand the high temperatures produced when processing hard materials. Made from Titanium nitride (TiN), coatings offer general-purpose protection against wear of high-speed steel (HSS) and carbide end mills. Coatings that also contain carbon (TiCN) allow carbide end mills to be run nearly twice as fast as their uncoated counterparts without undue wear from the extra heat generated. Even on HSS mills, the coating retards wear as long as the feeds and speeds do not create extreme heat. Coatings with aluminum (TiAlN) can take the heat generated by the blazing speeds and feed rates required for milling high temperature alloys, cast iron, steel alloys, and heat-treated materials.
Deflection
Trying to cut too much material at too high a speed or feed rate can result in tool deflection, which is doubly taxing on end mills. First, deflection causes the mill to bend. Constant flexing and relaxing along the mill flutes weakens them, like worrying a paperclip. Second, when the mill bows while it is inside the cut, the flutes can dig too deeply into the workpiece, in effect biting off more than it can chew. The resulting chip load can break the mill outright or cause build up and/or recutting of chips too big to evacuate effectively that leads to premature wear. Combat deflection by operating at proper speed and feed rates and by using the most rigid mill – the shortest and widest mill that will get the job done. You can shorten the tool’s effective length by “choking up” on the shank to just below where the flutes begin, while still maintaining clearance.
Chip Handling
As mentioned above, evacuating chips from the cutting area is a primary concern for productivity, surface finish, and especially reducing tool wear and tear. Chips absorb a lot of heat during the cutting process, and we know heat is an end mill’s worst enemy. Heat also helps bind and adhere some materials – aluminum in particular – to the end mill. As aluminum chips “weld” themselves to tool edges, a broken end mill is only a matter of time. Most aluminum mills feature only two or three flutes. Fewer flutes mean wider flutes, and more material that is expelled from the pocket, groove, or slot you’re working on with each mill revolution. Another way to prevent costly chip buildup is through liberal use of coolant. Flood coolant not only reduces the chips’ temperature below the critical point, it also helps flush them away. When using coated tools, mist coolant and air blasts is generally enough to clear the chips.
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