Cutting Tool Engineering
December 2011 / Volume 63 / Issue 12

No more blowups

By CTE Staff

New and improved is in the eye of the beholder. After using a style of indexable-insert drill for nearly 20 years, Marquardt Engineering Inc. experienced problems when the toolmaker replaced it, according to Brian Mueller, president of the Huntley, Ill., machine shop.

“The new drill chattered and would blow up inserts,” Mueller said. “The new design wasn’t better—it failed miserably.”

The toolmaker indicated that the vast majority of its customers found the new drill boosted productivity, but that was little consolation for Marquardt Engineering and other shops that didn’t experience those results, Mueller noted. “They indicated, ‘you’re the unfortunate 10 percent and there’s nothing we can do for you,’” he said.

Mueller added that when chatter destroyed an insert, primarily the one in the tool’s center pocket, the destruction usually caused catastrophic tool failure. That required replacing the drill body, which can cost up to several hundred dollars.

The problems were pronounced when drilling 4150 prehardened steel, which varies in hardness from about 30 to 35 HRC, according to Mueller. Marquardt Engineering also machines a variety of other workpiece materials, including mild, tool and stainless steels. Jobs range from screw machine parts to ones 26 " in diameter and volumes range from one a year to 10,000 monthly.

TDX_large2_c copy.psd
Courtesy of Tungaloy America

The TDX-type Tungdrill Twisted drill from Tungaloy America provides stable machining in a range of materials, including 4150 prehardened steel.

The parts manufacturer initially tried to make the new drill work by reducing machining parameters and changing chipbreaker geometries, but soon realized it needed to switch tools. After testing a variety of inserts and drill bodies from different manufacturers and still having the center-pocket insert blowup when drilling the difficult-to-cut 4150, the shop found success with TDX-type Tungdrill Twisted drills from Tungaloy America Inc., Arlington Heights, Ill. The 0.500 "- to 2.00 "-dia. drills accept parallelogram-shaped inserts and are available to produce holes 2, 3, 4 and 5 diameters deep. In addition, the drill body’s balanced shape reportedly minimizes chatter.

Not only did the inserts remain intact, but Marquardt Engineering was able to increase the cutting speeds and feed rates 30 percent compared to the previously applied drill, Mueller noted. That enables the shop to drill 4150 at around 500 sfm and a chip load of 0.006 " to 0.008 " per flute. “We’ve got the machines maxed out,” he said.

In addition to increasing productivity when drilling 4150, Mueller pointed out that the Tungaloy drills are effective when machining less challenging materials, such as 8620 alloy steel. “I drill a 5 "-long hole in under 32 seconds,” he said, noting that the 2 "-dia. drill runs at 700 sfm and a chip load of 0.010 " per flute.

According to Mueller, the Tungaloy inserts cost about the same as ones from other manufacturers, but the lack of catastrophic damage means that tool life is significantly extended. “The cutting edges are lasting an unbelievable amount of time,” he said.

The timing of the shop’s switch to the new drills was fortunate, enabling Marquardt Engineering to replace all of its indexable-insert drills from about ¾ " to 2 " in diameter with ones from Tungaloy. “They came out with a second-generation body that uses the same insert,” he said, “so they gave me a heck of a deal on pricing to get rid of the old inventory. I went out and bought about 30 or 40 bodies.”

Mueller noted that Marquardt Engineering generally applies tools up to 3¼ " to drill up to 5 diameters deep, and expects Tungaloy in the near future to expand its line and offer indexable-insert drills up to 3 1⁄8 " in diameter.

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