A tangential milling cutter takes a roughing cut at the Akebono automotive braking plant in Elizabethtown, Ky. Retooling boosted edge life by 18 to 1, and eliminated a vibration problem on the machine that formerly caused four to five unpredicted line stops per shift.

Eliminate Sudden Tool Failures

May 15, 2013
Net surfing to longer life One tool for roughing and finishing Minimizing edge breakdown No vibration alarm

Of course, cutting-edge security matters a lot in every machining operation, but never more than in synchronous machining cells or carousel arrangements. Sudden tool rupture or edge breakdown at one operation can affect the entire process. Moreover, the risk of failures is often the main cause of extra operator attendance.

“Especially in cells and carousels, the number-one priority in tool selection should be zero tool rupture or edge breakdown,” said Konrad Forman, North America milling tool manager for Ingersoll Cutting Tools. “Unless you are replacing an edge due to gradual wear only, you are missing an opportunity to improve cell-wide efficiency -- and even to run unattended.”

Forman cited three recent cases to illustrate what can be done.

Net Surfing to Longer Edge Life — At Busche-CNC in Albion, Ind., a simple retooling de-bottlenecked the rough turning operation for difficult-to-machine wrought 5130 and hardened 4140. Previously, cutting edges cratered after an average 20 pc on the 5130; toolbars snapped every other day. The Ingersoll Hex-Turn inserts improved edge life nearly 10 to 1, and eliminated completely the unpredictable, cutting-edge rupture and all the hazards and disruptions that followed.

Now, a single tool completes both roughing and finishing. Moreover, the machining operation has been able to raise its feed rates and throughput by 50% on the wrought stock, and 50% on the hardened material — with no trade-off in edge life.

Busche-CNC in Albion, Ind., operates seven machining cells, like this on, to produce 2.75 million automotive ring gears per year, in 5130 forgings and hardened 4140 bar stock. Ingersoll Hex-Turn inserts, with a stronger cross section, improved edge life by 8 to 1 and completely eliminated sudden insert failures.

Running 24/5, Busche uses seven two-lathe turning cells to produce 2.75 million/year automotive ring gears in a 400-person shop. Operations there include OD turning, ID turning and facing. As any Tier 2 automotive supplier knows, this is a very competitive business, turning on pennies per part and rock-solid delivery.

The switch was from 80-deg rhombic inserts to Ingersoll Hex-Turn inserts. “I found them the day they hit the market because I regularly surf the ‘net for new solutions we can use,” said Jerry Busche, vice president.

This retooling was essentially a drop-in replacement. The only processing changes were to modify the program to increase feed rates, decrease the scheduled stops for indexing, and write out all the steps associated with a separate finishing operation that is no longer needed. Standard parameters for roughing the 5130 are now 900 sfm, 0.0250 IPR, 0.150 DOC.

For the hardened 4140 stock, the feed is cut back only slightly. In each case, the DOC is backed off for the finishing passes.

The primary reason for the big improvement in cutting-edge security is the Hex-Turn insert’s stronger geometry, according to Ingersoll turning product manager Ed Woksa. “On the one hand, the insert has a 45-degree lead angle that thins the chip and reduces notch wear,” he explained. “On the other, the hex shape is closer to a true round, intrinsically the strongest shape due to the absence of stress-raisers.”

Secure Processing on Loose Machines

Old, ‘loose’ machines are torture for cutting tools. They create an ideal setting for chatter to start, which can create excessive impact forces on the tools leading to sudden tool rupture.

Many managers in manufacturing operations regard these types of failures as unavoidable on tired equipment, or they keep cutting back on parameters and stepovers, hoping to find some stability.

That was the case in the machining-assembly cells at a high volume universal joint manufacturer that turns out 60,000 units a year. Each cell contains a vertical CNC mill and a lathe, plus assembly and inspection jigs. All the chipmaking machines are showing their age.

The most challenging operation is milling out the main yoke slot. Previously, this had been done by roughing in a multi-pass cycle with a conventional zero rake cutter using eight square inserts, and finishing with a separate tool. Sudden edge breakdown during roughing was an accepted part of the production process, even after radically reducing stepovers to avoid pounding. Ironically, the lighter stepovers required more passes, causing work hardening that punished the tool even more.

Figure 2 — This sketch shows how a single Ingersoll Hex-Turn tool handles both OD turning and facing at Busche CNC.

Now, the shop gets the job done with a modified, standard Ingersoll S-Max tangential milling cutter that has increased edge life by a predictable 10 to 1 and eliminated all the pounding, even at the original higher material removal rates (MRRs). Since the tool is size-matched to slot width and has corner radii, it takes fewer passes to complete the slot and the singular tool does both the roughing and finishing.

The improvement stems mainly from the tangential orientation of the inserts in the cutter, Ingersoll’s Konrad Forman explained (see Fig. 2). “Unlike conventional radial cutters, the inserts in a tangential tool lie flat in the pitch circle, presenting the insert’s strongest cross section to the main cutting vector and converting shear stresses to more manageable compressive forces.”

Positive rakes and helical cutting edges on the inserts combine to create a smooth cleaving action, all leading to a much more secure process even on a loose machine.

Even without raising throughput rates in the cells, the shop reported it achieved savings of $80,000/year in tooling and tool-servicing costs. The only edge failure mechanism now is predictable flank wear, with zero rupture in more than a year.

“The application also illustrates the benefits of modified standard tools,” Forman said. “This is basically a standard tangential mill made in a special size and with special radii, not a complete ‘special,’” he added. “It brings the production benefits of a ‘special’ in a high-volume operation with the supply-chain security of a ‘standard.’”

Small Tangential Mills Make a Big Difference

At its automotive brake plant in Elizabethtown, Ky., Akebono became one of the first companies to apply tangential milling (TM) to production of smaller parts. Originally, Ingersoll developed the TM design mainly to improve hogging wide flats on large automotive castings and steel parts, and offered cutters no smaller than 4 inches. Recently, it introduced TM cutters in 1- and 2-in. diameters.

Figure 3 — This diagram shows how the insert’s strongest cross-section aligns with main cutting force vector and converts shear forces into compressive forces. (Left: tangential milling cutter. Right: conventional cutter). Inserts lie flat, rather than upright, in the pitch circle. Combined with a positive rake and helical geometry at the cutting edge, the tangential cutter is fundamentally stronger and more secure in heavy roughing operations, even on older, worn, loose machines prone to vibration and pounding.

Akebono produces the brake calipers in an auxiliary machining cell that feeds a traditional transfer line (see Fig. 3). Because the whole operation is synchronous, there’s no way to speed up a single operation without unbalancing the whole line.

One troublesome operation in the cell is rough milling a 1.1-in. hose mounting area on the caliper. It’s an interrupted cut that cratered cutting edges and often set off the machine’s vibration alarm. “We were getting 7,100 parts per edge with a conventional 4-pitch cutter, and we were satisfied,” said Terry Alvey, Akebono central purchasing manager of indirect materials. During a plant visit, however, Ingersoll field engineer Paul Nugent spotted the operation and the opportunity to do better. He explained the TM concept and suggested a trial run for the new 2 inch S-MAX tangential cutter.

To make a short story long, the tangential inserts ran through 127,000 parts – four months – before requiring a change due to edge wear and deterioration of surface finish. That amounted to an 18-to-1 gain in edge life.

There’s more: It wasn’t until two days into the test that an operator realized that the vibration alarm hadn’t gone off even once. The new, smaller TM tools smoothed out the cutting action just as the larger ones have for decades.

When inserts are oriented tangentially, more inserts can fit on a cutter size for size, thereby distributing cutting forces more widely for smoother cut. Also, insert pockets don’t cut as deeply into the cutter body, which leaves more metal intact for a sturdier cutting platform. New Ingersoll 2 inch S-MAX Micro tangential milling (TM) cutter (l) fits seven effective inserts in the same circle as a conventional cutter (r), which can fit only four. Note how little of the TM cutter body needs to be machined away to provide insert pockets on new cutter.

Also aiding smoother cutting was the higher insert count in the cutter, made possible by the tangential design. The new 2-inch tangential S-MAX has seven inserts, versus four in the previous 2-inch cutter. “Under the same parameters, more inserts means lower cutting forces on each one,” Forman explained.

Soon after the test, Akebono transferred the idea to four more, “small” roughing jobs at the Kentucky plant, and it alerted the other plants worldwide as well. “For a global company in such a competitive business, the faster the good news spreads, the better,” Alvey said.

“Operations in cells must run in lockstep,” said Ingersoll’s Konrad Forman, “so it’s doubly important there to achieve longer, more predictable edge life on the tooling. “Take any failure root-cause other than gradual wear as a wake-up call to find a better tooling solution, even on a loose machine or any other in unfavorable condition.”

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