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MILLING TOOLS


is a key factor, according to Alyssa Walther, applications engineer, OSG USA Inc. (Glendale Heights, IL). “High-feed milling is also excellent at minimizing radial defl ection, which will positively impact parts that require long reach from the tools,” she said.


Another important factor in HFM is that the orientation of the inserts in the tool direct most of the cutting forces back towards the spindle (parallel to the tool axis), with only a small portion acting perpendicular to the spindle (tool axis), accord- ing to Luke Pollock product manager, Walter USA LLC (West Waukesha, WI). This makes for a stable operation since the cutting forces push directly against the machine in the direction that provides the greatest stability. “That’s why this technique is very useful when trying to machine deep pockets where long extensions—which are inherently unstable—must be used.” HFM uses light DOCs, but because of the insert orienta- tion, it also employs high advances per tooth (APT). “If the workpiece is large enough, and the machine has the capabil- ity to move at high advancement rates, the metal-removal rate [MRR] can actually be higher compared to traditional face or pocket milling,” said Pollock.


Different Tools Cutting tools required for high-feed milling differ from standard milling tools in several ways. Typically, a high-feed


tool has a lead angle of 10–20° from the surface being machined, according to Martin. This lead angle helps thin-out the chip and allows for much higher feed rates than conventional-style cutters. Walther added that HFM tools have either a very large


corner radius or a specifi c “cutting angle” ground into the end face of the tool or insert. “At small DOCs, either confi gu- ration allows for smaller true chip loads, which in turn allows higher feed rates,” she said. High-feed mills are differentiated by the design of the insert and the way the insert is oriented in the cutting tool, added Pollock. “The large lead angles generate a high chip thinning factor, where chip thickness is something less than the APT. In these cases, a feed rate multiplier—calculated by dividing the recommended APT by the cosine of the lead angle—should be used to achieve the desired chip thickness. This adjusted value should be used to program the feed rate.”


Within the past year Iscar introduced the FFQ4, a high-feed type milling cutter incorporating single-sided inserts, for diffi cult-to-machine materials. It generates less heat than cutters using double-sided inserts, according to Iscar.


50 AdvancedManufacturing.org | August 2017


Holding True Toolholding and workholding requirements for HFM are also somewhat different than standard milling operations. In high-feed operations, the tool should be held tightly and true due to the forces put on the part, according to Sumitomo’s Schultz. “Traditional collets and end mill holders, with two set screws to clamp the tool, will typically push the tool off center, producing runout and hindering tool life and tool performance. With 1" [25.4-mm] indexables, it’s better to use a milling chuck, hydraulic chuck, or Rego-Fix type holder—not ER 32 collets or expandable collets. The latter are generally weak, and there is a lot of Z axial force being pushed down onto the part, and because of the high lead angle, forces are pushed back up into the spindle. You need a tool that is stable, rigid, and doesn’t move or push up into the toolholding system.” Martin pointed out that a fi xturing system is only as good as its weakest link. “In high-feed milling, since much of the cutting force is directed into the spindle, tools can perform at longer gage lengths than can a conventional cutter. This can also be easier on the spindle because less lateral force is being put on the connection interface. HFM can prove diffi cult on parts with poor fi xturing or unsupported areas because of the force direction as well.”


Photo courtesy Iscar Metals


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