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END USER: Bolton Aerospace Inc., (860) 649-2727. CHALLENGE: Reduce rough machining time. SOLUTION: A combination of high-performance, solid-carbide endmills. SOLUTION PROVIDERS: JJ Industries of Connecticut Inc., (800) 382-0012, www.jjind.com
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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.
Related Glossary Terms
- chatter
chatter
Condition of vibration involving the machine, workpiece and cutting tool. Once this condition arises, it is often self-sustaining until the problem is corrected. Chatter can be identified when lines or grooves appear at regular intervals in the workpiece. These lines or grooves are caused by the teeth of the cutter as they vibrate in and out of the workpiece and their spacing depends on the frequency of vibration.
- depth of cut
depth of cut
Distance between the bottom of the cut and the uncut surface of the workpiece, measured in a direction at right angles to the machined surface of the workpiece.
- endmill
endmill
Milling cutter held by its shank that cuts on its periphery and, if so configured, on its free end. Takes a variety of shapes (single- and double-end, roughing, ballnose and cup-end) and sizes (stub, medium, long and extra-long). Also comes with differing numbers of flutes.
- feed
feed
Rate of change of position of the tool as a whole, relative to the workpiece while cutting.
- flutes
flutes
Grooves and spaces in the body of a tool that permit chip removal from, and cutting-fluid application to, the point of cut.
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
- hardness
hardness
Hardness is a measure of the resistance of a material to surface indentation or abrasion. There is no absolute scale for hardness. In order to express hardness quantitatively, each type of test has its own scale, which defines hardness. Indentation hardness obtained through static methods is measured by Brinell, Rockwell, Vickers and Knoop tests. Hardness without indentation is measured by a dynamic method, known as the Scleroscope test.
- inches per minute ( ipm)
inches per minute ( ipm)
Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.
- machining center
machining center
CNC machine tool capable of drilling, reaming, tapping, milling and boring. Normally comes with an automatic toolchanger. See automatic toolchanger.
- metalworking
metalworking
Any manufacturing process in which metal is processed or machined such that the workpiece is given a new shape. Broadly defined, the term includes processes such as design and layout, heat-treating, material handling and inspection.
- milling
milling
Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.
- milling machine ( mill)
milling machine ( mill)
Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.
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