Cutting Tool Engineering
March 2010 / Volume 62 / Issue 3

Easier roughing

By CTE Staff

Courtesy of Bolton Aerospace

Bolton Aerospace reduced roughing time on this steel helicopter tail rotor hub by more than 85 percent by applying a combination of solid-carbide endmills from YG-1 Tool.

Bolton Aerospace Inc., Manchester, Conn., is completing the transition from tool and die shop to aerospace manufacturer. Owner Brian Martin bought the operation 2½ years ago, moved it to a new facility last year and added new equipment. A large portion of the shop’s work is for suppliers to Sikorsky Aircraft Corp. That role in the supply chain has unique challenges. “Being a sub tier supplier, we have to perform quickly,” Martin said. “Our backlog and our lead times have to be very short. That’s a way of life.”

One example of Bolton’s ongoing effort to accelerate its performance involves the rough machining of a five-spoke helicopter tail rotor hub about 1 ' in diameter and 3 " thick. The shop machines the part from a 15 "×15 "×3 " slab of 4140 steel. First, the block is roughed to an oversize condition and then sent out to be heat treated to a hardness of 32 to 35 HRC. When the part returns from heat treatment, it is roughed on a Kia vertical machining center. The operations form the external contours of its central hub and five 2½ "-dia., 3 "-long cylindrical features spaced at 72° intervals around the hub periphery.

“We take quite a bit of material off,” said Dave Chapdelaine, manufacturing engineer. “Axial depths of cut are as deep as 1 "; on the edge of the cylinder, we take a big depth of cut that gets progressively lighter as the cutter works its way up to the cylinder top.”

Bolton had been roughing the part with ¾ "-dia. and ½ "-dia., 4-flute, fine-pitch cobalt endmills, run at 500 rpm and single-digit-ipm feed rates. The slow cutting parameters meant roughing one side of the part took up to 8 hours. “We basically set it up and walked away,” Chapdelaine said. In addition, tool life was poor. The two tools could barely rough one part before wearing out.

Because Chapdelaine “dreaded” working with a part that took so long to produce and consumed so many tools, he sought application assistance from Bill Juskhas, representative for YG-1 Tool Co., Vernon Hills, Ill. After analyzing the job, Juskhas suggested applying two YG-1 ½ "-dia. endmills, which, like much of its tooling, Bolton purchased from distributor JJ Industries of (Plainville) Connecticut Inc.

For heavy roughing, Juskhas recommended the HOSS 3-flute, 35° helix, 0.035 " corner radius, TiAlN-coated, solid-carbide endmill, which has deep flutes to facilitate chip evacuation and speed roughing cuts. For semiroughing after the HOSS mill, Juskhas selected the V7 5-flute, 0.030 " corner radius, AlTiN-coated, solid-carbide endmill, which features a variable-helix design to break up the harmonic vibrations that can cause chatter.

Milling the tail rotor hub, the HOSS tool ran at 2,300 rpm and 20 ipm, followed by the V7 tool at 2,600 rpm and 40 ipm. Together, the two tools roughed the part in 22 minutes. “The first cutter, especially, just rips material right off the part. It’s amazing to watch,” Chapdelaine said. “For the first couple of cuts, which are real heavy, it looks like it’s never going to make it, but it does.”

In addition, tool life nearly doubled. After initial tests, Chapdelaine ordered six of each of the two YG-1 mills, “and I did a dozen parts. Not only did the tools rough the parts a lot faster, but I am getting more than one part per tool.”

Martin said while the time savings afforded by the new cutters is significant, their ease of use “is phenomenal,” noting that the process went from being a “white-knuckle operation” to a routine job. Applications of new metalworking technologies like this “have changed the shop’s thought patterns,” he said, and are enabling it to continue its positive evolution.

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