ROUGH TRANSMISSION

Ask Jim Rice how that big roughing job is running after retooling, and he'll gladly talk about plant debottlenecking, doubled throughput, 90 percent lower tooling costs, cleaner plant air and averting a huge capital investment. He's the operations manager at Terex's big off-road equipment plant down in Ciudad Acuna, Mexico, just over the border from Del Rio, TX.

Big roughing job indeed. The parts are transmission boxes, essentially huge tubes big enough to stand in ? 9 ft or 12 ft diameter, 8 ft to 10 ft long with walls 4½ in to 8 in thick. The bottleneck operation is to rough-mill about 0.700 in of Rc32 alloy steel off both ends.

Previously it limped along, taking 3½ hours per part, wrecking inserts midway through the cut, and occasionally fogging the work area with fugitive mist from the oil-based cutting fluid. Now the massive trannie parts are done in half the time and inserts last five times longer per edge – with the cutting fluid spigot shut off for good. On a 144 pc/yr production schedule, machining savings from all sources easily exceed $50,000 a year. 

The gains on this first job stemmed from retooling the plant's 40 hp G&L horizontal mill with an Ingersoll S-MAX tangential milling cutter in place of a conventional radial-type milling cutter. With the intrinsically stronger inserts and cutters characteristic of tangential milling, Terex runs the operation at double the feed rate as before ? 30 ipm vs. 15 ipm at the same 0.100 DOC ? with absolutely no risk of insert failure.

"The inserts never suddenly rupture or crack anymore, they just wear out gradually now," says Roberto Magallanes, a Terex lead man. Based on this success, Terex is switching over to tangential milling for all heavy roughing jobs.

Terex's main driver for retooling was to speed up the operation ? reliably ? in order to free up machine time for additional work. "Free up time on the machine in hand, and do it reliably, and we can postpone a big-ticket capital investment," reasoned Mr. Rice. The changeover began in July 2007 with help from Terex's primary tool distributor, Tool Tech Industrial of San Antonio, and was fully implemented the next month. Terex and Tool Tech invited several tooling suppliers to evaluate the operation and suggest a remedy. 

This was the situation they all saw: using the existing 6 in face mill with conventional radial-oriented inserts running under an oil-mist coolant that messed up the work area, the best Terex could muster was a 15 ipm feed rate. At that rate it took 3.15 hours and two insert changes to complete one part.

Even then, the as-machined finish was a barely acceptable 125 RMS. Despite the oil mist coolant, the cutter ran so hot that the operator had to wait for it to cool before he could safely replace broken inserts. To feed at 15 ipm,  the cutter ran at 600 rpm, 0.100 in DOC.

Two leading suppliers proposed essentially the same type of tooling remedy, all of which promised only marginal improvements. The third (Ingersoll) came in with a generically different approach: the S-MAX tangential milling cutter. This means the inserts are oriented tangentially in the cutter pitch line, basically at right angles to what you see in conventional roughing face mills (see Figure 1).

The main benefit of this tangential orientation is that it presents the insert's strongest cross section to the main cutting force and makes for a stronger cutter body as well (see Figure 2). Ingersoll led development of tangential milling about 30 years ago, precisely for the Terex-type of rugged rough milling, and has continued to expand the technology.  

Mr. Rice and plant manager Jorge Robles agreed on a trial for the tangential cutter, overseen by Ingersoll's Anthony Myers, who is bilingual, and Randy Holt, field project engineer. They started the trial at the end of the second shift, fiddling with machining parameters to optimize the operation with a four-inch cutter, the same diameter as before.

Because the G&L machine had the horses, Myers and Holt suggested increasing the cutter diameter to eight inches. At one point, they ran at 25 ipm feed and 0.200 in DOC. The spindle nearly stalled at this rate, but the tangential cutter was unscathed. 

By the end of the third shift, the team settled on the eight-inch cutter with settings at 25 ipm feed rate/0.100 in DOC/600 rpm and no cutting fluid. Under those conditions, throughput was improved about 75 percent and the insert edges were lasting through 1.5 parts ? about five times longer than before.

"Most important, the operation ran reliably faster with edges lasting reliably longer," said Mr. Rice. "It was the kind of improvement we could count on at production-and budget-planning time." Subsequent tweaking brought the feed rate up to 30 ipm, which more than doubled throughput over the old method. "Still, the insert edges last through more than one part with not a single catastrophic failure," added Mr. Rice.

Each tangential insert has four edges, the same as before. "Over that same period using the previous cutter, we'd typically have broken 35 to 40 inserts," remarks Mr. Rice. "Even though the old inserts had four edges, the other three were rendered useless when the insert broke." As a result of this retooling and Myers' bilingual rapport with the Terex crew, the plant is converting all milling and drilling operations over to Ingersoll tooling.

Myers isn't surprised at all about the consistently longer edge life at the higher cutting rates. "The basic tangential cutting geometry is sturdier. Beyond that, new inserts are freer cutting and the PVD-applied TiAlN coating has more lubricity than CVD coatings and can be applied over a sharper edge. The CVD coating on the previous inserts had to be applied over a honed edge, which can never be as sharp as a pressed edge. On the one hand, the insert geometry is stronger. On the other, the cutting edge is sharper and the cutting action is gentler.  No wonder the edges last longer."

Ron Schneider, product manager for these cutters, is not surprised with the increase in productivity either. "I tell many people, putting a tangential cutter on a spindle is like bolting a turbocharger onto a race car. You don't replace the machine (engine), but you get more power and performance from it. More efficient performance wins on the factory floor just as it does on the race track."

As further proof of more efficient cutting action, the chips are hotter than before, yet the cutter and inserts are just warm to the touch even after a full roughing pass. "The heat of cutting is generated in the workpiece metal, to soften it at the cutting point, then leaves with the chips," Mr. Myers explains. "They say heat is the enemy at the cutting edge, but here it's an ally. It's all in where you put the heat." 

"The other lesson here is that, when the guys on the floor are in at the outset, you get a better solution and more ready acceptance of new ideas," Mr. Rice emphasized. "Jorge and Roberto worked right alongside Anthony and Randy to make it happen.  A bond was formed ? at the shop-floor level where it counts ? that I'm sure will make future milling and drilling retoolings go more smoothly and pay off sooner."

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Ingersoll Cutting Tools, 845 S. Lyford Road, Rockford, IL 61108-2749, 815-387-6600, Fax: 815-387-6337, www.ingersoll-imc.com.