August 2011 / Volume 63 / Issue 8|
Drilling without catastrophe
By CTE Staff
Three Sigma Manufacturing Inc. is a Tier 2 supplier that has been in the aerospace supply chain since the 1980s and has 21 employees. Commercial airplane parts is its primary line of work, but the Kent, Wash.-based company also makes parts for the firearms industry and marine industry, including hydraulic actuators and propellers for race boats.
One aerospace part Three Sigma was looking to produce more efficiently was a guide fitting made of 15-5 PH solution annealed-condition stainless steel. Three Sigma has been making the part since 1997. “It is a reasonably complex part that goes in the overhead exit wing door of an airplane,” said Ken Frankel, company president. “It is a guide fitting with deep counterbores.” Three Sigma makes about 2,500 of these parts per year.
Courtesy of Three Sigma Manufacturing
Courtesy of Allied Machine
The part starts as a 15-lb. workpiece and weighs 2 lbs. when finished. The largest diameter on the 9.5"-long part is 2.5".
One operation requires the part to be drilled and turned at the same time to produce more than one feature. In addition, the part requires four different turning operations, a milling operation and a few manual processes. The turning and drilling is performed on an Okuma LU300 lathe, with 80-psi through-coolant capability.
The part requires a 0.9843"-dia., 5.0"-deep blind-hole. Previously, the company applied a spade drill with a TiAlN-coated HSS bit at 329 rpm and 0.005 ipr, which calculates to 1.645 ipm.
Drilling, including spot drilling, took more than 4 minutes. Tool life was 30 parts.
Looking for performance improvement, Dave Fitzpatrick, vice president of Three Sigma, asked Allied Machine & Engineering Corp., Dover, Ohio, about the GEN3SYS replaceable-tip drill he saw at IMTS.
Three Sigma was able to run the drill at 679 rpm and 0.008 ipr, which calculates to 5.43 ipm. It finished a hole in 55 seconds, tool life increased to more than 90 parts, and spot drilling was eliminated.
While Three Sigma appreciated the reduced cycle time and increased tool life, the company also required a tool that progressively wears rather than suddenly fails. According to Frankel, GEN3SYS predictably wears. “The nature of the failure is a key criterion that determines to what extent you can use the tool,” he said. “Can you use it to 90 percent of its life, or do you get scared at 50 percent and change it out?”
Frankel explained that Three Sigma tried various drills over the years and found one that produced a hole as needed, but when it failed, it was catastrophic. That failure not only damaged the tool body and insert beyond repair but also affected the machine, “forcing us to do a 5-hour realignment,” he said.
Predictable tool behavior provides the machinist with wear indicators. These include sounds, chip size and machining load, which Three Sigma’s machines monitor.
“Another indicator is visual,” Fitzpatrick said. “We see deterioration of the point and where it chips on the outer margins.”
In addition, GEN3SYS effectively evacuates chips. “Sometimes with the old drill we would have some chip wrap,” Fitzpatrick said. “This one tends to do less of that.”
According to Greg Torres, AMEC’s sales manager, 15-5 stainless steel is difficult to machine. “Sometimes it’s hard to break the chip, or the chips are stringy,” he said. “The GEN3SYS has the right kind of geometry to make it work.”
To reduce downtime, a machinist can change the drill’s replaceable tip without removing the holder from the machine. To extend tool life, the AM200 multilayer coating provides lubricity. “The resulting finish was also a success,” Torres said. “The drill produces a very good finish and keeps the hole concentric. It doesn’t require lot of thrust like a spade drill does.”
Overall, the GEN3SYS met Three Sigma’s requirements for performance and productivity improvement.
“More than cycle times, we want to know what we yield per shift or per day,” Frankel said. “If the machine is running and the machinist can be doing something else 10' or 20' away, then yield for the shop goes up dramatically. Our question isn’t how much is it costing to make this hole, but how much more is our shop producing a day by using this drill.”
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