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proactive solution is called for. Several tooling manufacturers offer dampened toolholders and boring bars, which typically utilize a heavy mass mounted on rubber elements within the tool body, and surrounded by a viscous fl uid. By utilizing the largest body possible relative to the cutting tool itself, and employing sound programming tech- niques to minimize loads—climb milling with con- sistent depths of cut, for example, and rolling into the workpiece—depth-to-diameter ratios of 8× are possible, twice that of nondampened tools. One fi nal consideration is the toolholder itself. Back in the day, Weldon shanks and ER collets were the preferred—and often only—way to hang on to cutting tools. And while those tried-and-true tool- holding strategies still have their place, they’ve largely been usurped by stronger, faster, and more accurate ways to grip cutting tools. Much of this technology has been driven by the increase in spindle speeds on machining centers today—with ranges of 20,000 rpm and higher the norm, the need for well-balanced toolholders with minimal runout is critical. Shrink fi t is one of the favored contenders in


this arena. Heat up the gripping end of a toolholder, slide in a carbide tool, and within seconds an interference fi t of 0.001–0.002" (0.025–0.050 mm) is created. Depending on the tool diameter, this can easily generate upwards of 6000 pounds in gripping force and tool runout of 0.0002" (0.005 mm) or better, making it suitable for the majority of roughing applications as well as very accurate fi nishing of almost any material imaginable. The downside to shrink-fi t toolholding is one of investment: the equipment needed to induction heat the tools starts at around $15,000, and perhaps twice that for production units. There’s also some investment in time, as it takes perhaps 6–10 seconds to heat the tool, and slightly more than that to cool it down.


Several tooling manufacturers offer dampened toolholders and boring bars.


Hydraulic toolholders are another robust way to grip tools.


Offering equivalent accuracy and gripping force as shrink fi t, hy- draulic holders are simple to use, require no special equipment, and can be purchased with internal antipullout pins for heavy


Using helical interpolation and linear ramping to create holes from a solid workpiece requires a strong insert face geometry.


roughing. This is especially important when machining titanium and other materials that tend to “grab” end mills and gradually draw them out of the holder while in the cut. Some attempt to counter this phenomenon has been made using Weldon fl at end mills, but A) Weldon holders are inherently unbalanced, making them unsuitable for high-rpm milling, and B) the holding screw in Weldon fl at holders has been known to work itself loose during heavy cuts, leading to catastrophic results. Indexable inserts are prone to movement as well. Micro- shifting is often diffi cult to detect, but it causes unpredictable process control and negative impact on tool life and part qual- ity. Here, too, cutting tool manufacturers continue developing creative ways to lock tools in one place and keep them there. Look for designs that incorporate locking rails on the sides or bottom of the insert. Shimmed toolholders—though slightly more expensive—generally offer greater insert life and lower costs in the long run. And don’t skimp on maintenance. Rou- tine cleaning of insert pockets, replacement of screws, shims, and clamps, and judicious use of lubricant on threaded parts are important ways to extend indexable cutter life and improve metal removal. And when tool pockets wear, replace the tool or send it back to the manufacturer for reconditioning. Keeping tools past their prime is a recipe for failure.


May 2016 | AdvancedManufacturing.org 95


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