Conventional optimized roughing strategies call for shallow radial stepovers and high depths of cut with multi-flute cutting tools. Now, imagine how much more productive the strategy would be if it were possible to up those stepovers to as much as 70 percent of the cutting tool’s diameter. With today’s innovative continuously variable geometry end mills, such stepovers are possible and standard operating procedure for a new version of the strategy referred to as high-performance optimized roughing (HPOR) that also requires high-performance machine tools and toolholders as well as specialized CAM software.
Much like high-feed tools, continuously variable geometry end mills perform best when they are fully loaded in the cut as opposed to lightly loaded. Therefore, the radial stepovers of 12 percent or less of a tool’s diameter typically used in optimized roughing prove much too shallow to work well for optimized roughing with these advanced end mills – such as the Niagara Cutter Stabilizer 2.0 – that operate best with stepovers of at least 20 percent or more of the tool’s diameter.
To handle such high stepovers, these new age end mills sport robust core designs and a high heat and abrasion resistant AlTiN coating. At such aggressive stepovers, chip evacuation is key and having the right combination of core diameter and flute spacing is crucial to a tools optimal performance.
But what really makes Stabilizer 2.0 so strong is its patented continuously variable geometry that eliminates detrimental harmonics and chatter vibrations. Other conventional end mills are unable to withstand such depths of cut and metal removal rates and will most likely fail if a shop tries to use them for HPOR.
With the Stabilizer 2.0 geometry, each of the tool’s cutting edges varies from front to back and differs from the one next to it. Additionally, each of the tool’s four flutes are spaced at different degrees from one another instead of evenly at 90 degrees apart. The helix, radial relief, radial clearance and indexing are all varied. And, any given point along the cutting edge of each flute is different from another point on that same flute as well as varies from any points on the other three flutes.
In addition to the cutting tools themselves, machine tools must have heavy-duty high-torque and high-horsepower spindles such as CAT 50, HSK100A and HSK125A. HPOR can be performed on lighter duty machine tools with CAT 40 and HSK63A spindles, but caution must be used not to overload or max out the machine’s horsepower capabilities. With such strong forces in play from the machine tool spindle, toolholding must be equally rigid to minimize runout, and standard side-lock holders with set screws or heavy-duty mill chucks are the best choices. Most shrinkfit holders and collets lack the ability to hold variable geometry tools in place under such high-powered cutting conditions.
Currently, HPOR is mainly used in European markets, but shops in North America are realizing the benefits of this new strategy. In fact, several CAD/CAM software developers have already created the necessary CAM software needed for HPOR.
Because continuously variable geometry end mills, like Stabilizer 2.0, are stronger and better at eliminating harmonics than any of their predecessors, shops can adapt cutting strategies to optimize the new tools’ capabilities. These cutting tools, along with the right machine tools, toolholders and software, can significantly boost a shop’s metal removal rates.