January 2010 / Volume 62 / Issue 1|
By CTE Staff
Sun Manufacturing Co. is well established at making parts for the oilfield and subsea industries—companies that drill holes for a living. However, when the Houston job shop was drilling holes through the 8 "-thick flanges in a 4130 medium- to high-alloy steel part called a spool, it seemed like drilling holes to China. Each 2.375 "-dia. hole took about 30 minutes and the part has 44 such holes—24 on one side and the remainder on the other. In addition, drilling the holes made Sun’s 30-hp Kuraki KBT11Z CNC horizontal boring mill a bottleneck to accomplishing other work.
Courtesy of Kennametal
According to Steve Eldridge, shop superintendent for Sun, the workpiece material isn’t particularly challenging to machine, having a hardness of about 212 to 235 HB and a tensile strength of about 75 ksi.
The holes were mounting holes without threads or a fine surface finish requirement, so Sun initially used a conventional holemaking method and applied a titanium-nitride-coated, 2.375 "-dia. spade drill. Because the spade drill had a single cutting edge, Sun had to run it in pecking cycles, which are usually performed to break chips so they are small enough to flow through the tool’s flutes without damaging the hole surface or drill.
For example, a variable-peck cycle could start with a 1 " peck, the tool would be retracted slightly to break the chips, and the next peck would go 0.50 " deeper, followed by one 0.25 " deeper, with the last peck going 0.05 " deeper than the previous peck. “It keeps continuously going back and forth until you finally complete the drill depth you need,” Eldridge said. “That adds to the drilling time because you’re cutting a lot of air instead of the material.”
The deeper the drill goes, the more difficult it is for coolant to reach the tool/workpiece interface, so pecking is also done to provide more coolant to the tool tip.
“We were certainly feeling pressure to decrease cycle time,” Eldridge said. “This part required both lathe work and mill work, so a complete job was taking in the area of 185 to 200 hours.”
Sun searched for a solution and solicited quotes from toolmakers. After producing four spools with the spade drill applied for drilling the flange hole, Sun switched to the KSEM Plus modular drill from Kennametal Inc., Latrobe, Pa., based on the recommendation of David Hray, applications engineer at Kennametal. In addition, Kennametal’s tool cost less than the other drills that Sun Manufacturing quoted. The KSEM Plus modular drill consists of a steel body coupled to an indexable-insert, high-strength steel head, and a single tool body accepts a range of drill-head sizes.
Like the spade drill, the modular drill has through-coolant capability but that’s where the similarities end. Instead of consuming about half an hour to drill one hole, the KSEM Plus drill was able to produce a hole in 1.6 minutes. Plus, the spade drill caused chips to coil up after 1 " to 3 " of depth, whereas the KSEM Plus geometry generated small C-shaped chips that were easily evacuated. The drill’s differential-helix flutes enhance chip evacuation, according to Kennametal.
Sun was feeding the spade drill at about 1 ipm and was able to increase that tenfold with the modular drill. And feeding faster is possible with the appropriate machine tool. “We could have run at 12 ipm, but it turns out we didn’t have the horsepower,” Eldridge said, noting that a call to the toolmaker’s customer application support line yielded new machining parameters. “I plugged in the new numbers and we were running again in 15 minutes.”
Although the shop only had three more of those spools to produce, Sun found the modular drill is suitable for other applications and continues to apply the tool whenever possible. “It was phenomenal,” Eldridge said. “We hadn’t seen anything that could provide this kind of drilling performance at the hole depths we needed. The KSEM Plus paid for itself on the first part.”
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