Sudden edge failure may be the bane of machining processes, but it can also be an indicator of undiscovered problems — and a sign that will point you toward a better way to make that cut.

“Unless you are seeing gradual, predictable edge wear, you are looking at an opportunity for improvement,” explained Ingersoll Cutting Tools North American milling product manager Konrad Forman. “This holds true even when you are dealing with a loose machine, a high-strength alloy, a severe interrupted cut, or an extreme form cut: a long-reach operation, high-aspect holemaking, or an ID operation with limited clearance. With the newer insert and cutter geometries, and more accessible modified standard tools available today, there will always be a workaround.”

The examples demonstrating these conditions are widespread. Consider:

•  With a simple retooling to bore a 0.25-inch diameter in a tiny medical part, MedFab Manufacturing Inc. in Lakeville, Minn., stabilized a slow, unstable operation so that it now runs unattended. After replacing a standard round-shank boring bar with a breakthrough microboring bar that features a husky, elliptical shank, though-the-tip-coolant delivery and free-cutting tip geometry, tool life increased from an unpredictable 5-20 pc to a reliable 250 pc — even at 15% higher metal removal rates (MRRs). The MedFab job is notable as the first commercial application for the Ingersoll T-Micro 250 boring bar.  

•  On a heavy, interrupted-cut rough milling operation, R.H. Sheppard in Hanover, Penn., eliminated tool wrecks resulting from spontaneous insert rupture by switching from radial to tangential milling cutters. Edge life rose from an unpredictable 60 pc to a reliable 152 pc, even at 30% to 40% higher MRRs.

•  Just about every time on a long-reach finish-slotting job in hardened S-7 tool steel, River City Manufacturing and Machine Co. in Winona, Minn., encountered edge rupture less than 5 inches into the pass. The remedy: change to high-feed milling with a cutter that reduces the contact area and resulting lateral cutting forces. The Ingersoll Form-MasterV, specially designed for high-feed machining, improved edge life a reliable 4-to-1, and it reduced cycle time from 20 hours to four.  

•  In Ciudad Acuna, Mexico, off-road equipment OEM Terex ran into sudden, random edge failures and tool wrecks while rough milling big, boxlike weldments in hardened alloy steel. The existing radial cutter generated so much heat that the inserts glowed orange and ruptured catastrophically, and projecting chunks of carbide around the workplace. No inserts ever lasted through even one piece! Again, tangential milling, with its intrinsically stronger cutting geometry, brought everything under control, even on heavy interrupted cuts with a middle-aged “loose” machine. Now, the edges last through five complete parts, reliably, throughput has doubled, and all the hazards of shattered inserts and an overheated operation are a thing of the past.

 “More often than not, insert rupture begins with the edge going dull, which raises cutting forces to the point of sudden breakdown — triggering a chain reaction,” according to Forman. “The other root-cause may be chatter, which ‘hammers’ the edge. The chain reaction happens so quickly, the sequence is easy to miss,” he emphasized.

Among the remedies he suggested are changing the presentation geometry to have the necessary cutting edge design, or substituting a different insert substrate to achieve either increased ductility or increased hardness. A third remedy is to shift machining parameters completely, toward higher feed rates and lighter cuts, and changing inserts accordingly.  “Sometimes it is necessary to change all three,” Forman said. “The key is to keep experimenting until you achieve predictable edge wear.”