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From physics class we learned that the linear velocity at the center of a spinning disc is zero, while maximum speed occurs at points around the disc’s perimeter. What that means for a drilling operation is the drill’s point remains stationary while its outer cutting edges rotate at high speed. The resulting pressure on the point can cause it to chip if the drill’s substrate doesn’t have sufficient toughness. However, the substrate must also provide adequate hardness to prevent premature wearing of the fast-moving cutting edges. Therefore, drills made from a single carbide grade must find a happy medium between toughness and hardness.
ATI Stellram (LaVergne, Tennessee) has developed a dual-carbide-grade drill technology called HardCore that is said to possess both of these attributes. These drills have a core made of a micro-grain carbide grade blended to provide toughness and shock resistance at low rotational speeds. This hinders chipping at the drill’s point. Surrounding the core is a second carbide grade that provides sufficient hardness for wear resistance at the outer edges. According to the company, this dual-carbide technology can provide four times the life of other drill designs and cut drilling operation times in half.
The drills feature a 140-degree point geometry, TiAlN coating and open flute profile to assist in chip evacuation. They are available in diameters ranging from 3 to 16 mm (0.118 to 0.63 inch) and maximum length-to-diameter (L:D) ratio of 5:1 for cutting steel and cast iron. Coolant-through versions with L:D ratios as high as 8:1 will soon be available. The drills are suitable for use with minimum quantity lubrication (MQL), although, the company recommends using coolant-through models for stainless and heat-treated steels.
HardCore technology is currently available in drill versions for iron, steel and titanium with hardness as high as 50 HRc. The models for drilling titanium have a more positive geometry with smaller defined edge preparation. The company says it is developing drills using dual-carbide, replaceable tips in addition to other types of cutting tools.