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6 Solutions to Long Reach Machining Problems

Ingersoll Cutting Tools has found that high-feed insert geometries and extra-rigid shanks and extensions are the keys to handling long reach challenges. The company applied those principles to 6 different applications and the results included reduced chatter, reduced cycle time, tripled removal rate, and improved tool life 20 to 1.

For longer than most of us remember, long-reach machining has given many a manufacturing manager many a headache. That's the bad news. The good news is that recent tooling innovations have eased the pain over a very diverse range of applications.

Long reach milling on steel.

 

 

Today you can have a stable contour milling operation 22 inches deep inside a hardened steel mold cavity or stainless steel turbine bucket. Today you can open large holes deep down between the webs in steel castings and face-mill deeply recessed flats in iron castings -- 3 to 5 times faster than before, with none of the usual chatter much less risk of sudden tool rupture. Today, medical device manufacturers have a stable process for boring 4:1 aspect holes in thin walled titanium, an application that has stymied conventional boring tools for more than a decade.

Tool Commonalities

"No single tool meets all such diverse long-reach challenges, but those that do usually share two common features: high-feed insert geometries and extra-rigid shanks and extensions," says Konrad Forman, North American milling product manager for Ingersoll Cutting Tools. "That said, the right choice for a particular long-reach application will hinge mainly on geometry of the cut to be made."

Although it's a gear in the spindle, Allied Specialty Precision Inc. treats this part as something else to achieve "done-in-one" production from 17 4PH cut-off bar stock, to deliver sooner and to cut machining costs.

 

 

 

 

By and large, high-feed insert geometries cut faster while reducing lateral cutting forces that can trigger chatter leading to sudden tool failure. More rigid shanks reduce both chatter and runout all the way to the bottom of the cut.

Improved Mold Cavity Hogging

Some of the greatest successes come out of the die and mold industry, with its familiar diet of contour milling deep in the cavities within hardened steel mold blocks. Recent market trends that drive demand for larger, deeper molds simply intensify the problem. "Mold cavities typically are 5-8 inches deeper than just five years ago," says Jay Noble, lead machinist at Redoe Mold, Ltd., Windsor, ONT.

These days, Redoe finish-mills 15-22 inch deep pockets in half the time as before, with no sudden edge breakdown. The new tooling package is an Ingersoll Form MasterV high-feed cutter mounted on an advanced Ingersoll Inno-Fit shank extension.

In high-feed milling, the tool feeds faster while taking lighter cuts. The metal comes off faster, but at lower cutting forces, especially the lateral forces that complicate long-reach work. High-feed inserts are typically triangular with low lead angles (10-20 degrees) relative to conventional inserts.

Redoe operator assembles Ingersoll Inno-Fit long-reach tool to mill bottom of deep mold cavity. For extra rigidity, coupling features three point contact, self-centering design and large contact area at mating surfaces.

 

 

Key to the Inno-Fit shank's extra rigidity is a self-centering 3-point coupling design, enlarged contact area between the mating surfaces and an extremely wear-resistant material of construction. By contrast, most conventional shank extensions use a slide coupling system.

Another moldmaker, Chicago Mold Engineering, St. Charles, IL, approaches many small deep cavities a different way, using an Ingersoll Hi Feed Mini Cutter, one of the smallest milling tools available with the high-feed geometry. As a result, they complete a semi-roughing operation in less than half the time. The new tool has more flutes than the previous one, reducing the cutting force per flute without slowing down the operation. With the lower lateral cutting forces, they get good results with a less expensive standard extension.

Twenty Inches Deep in Stainless Steel

Machining the buckets in big hydropower turbines is almost 100 percent long-reach, always posing the risk of chatter that specs would not allow. Accordingly, Canyon Hydro, Sumas, WA did everything possible to eliminate "chatter triggers" from the get-go in their new lights-out, six-axis machining facility.

Termed "runners" in the power-gen industry, the turbines may measure up to 11 feet long and lose a ton and a half of metal in a three-month 24/7 long-reach milling process. Almost all machining is done with 19-inch extensions, yet all as-machined surfaces must be smoother than 32µ and geometrically correct within 0.010 inches.

It takes about 500 hours of long-reach contour milling for Canyon Hydro to complete these 11 foot "runners" in its state of the art lights-out CNC machining center. (Note long-reach milling head lower left.)

 

 

 

 

Canyon and Ingersoll worked together on the total tooling package, emphasizing accuracy and finish above throughput. For smaller turbines, the tool of choice is an Ingersoll FormMaster Pro, specially designed for stable long-reach roughing and finishing. Besides using a free-cutting, high-feed geometry, the three-flute tool features serrated inserts in a timed array that nibbles the metal away progressively. Each insert is located "five minutes" behind the other in the pitch circle, so each edge engages a different part of the toolpath. The operation runs twice as fast as before, holding all tolerances -- lights out.

Larger runners involve some undercuts along with 20.5 inch extensions. Accordingly, the undercuts are done with a modified standard FormMaster Pro button cutter with additional cutting surfaces on the top. It works like a high-feed button cutter for most of the cut, then as a T-slotter to complete the undercuts as it is withdrawn. The improvement on the big runners is about the same as with the smaller ones, again holding all specs.

Big Holes, Deep Down

Large long-reach holemaking has also been improved with high-feed tooling. Recently, Baldor Electric Company, Gainesville, GA, used it so successfully that they've applied it to ten different jobs and are considering it at several other plants.

The first application was on a large cast steel housing with holes to be opened more than ten inches down between the webs. Previously, Baldor did it with a solid carbide endmill in an orbital toolpath. Now they do it with a high-feed Ingersoll Deka mill in a corkscrew orbit. The process and tooling switch tripled the material removal rate and improved tool life 20 to 1.

Schematic shows how inserts in tangential milling cutter (left) lie flat in the pitch circle, aligning insert's strongest cross section with main cutting force vector. This configuration enables faster long-reach facemilling, withstands higher cutting forces, extends edge life and makes for a more secure process.

 

 

 

 

The gain stems from the Deka's high-feed geometry plus the orbital toolpath, which advances through the work -- from the solid, (no pilot holes needed) -- without the stop-and-plunge delays inherent in orbital milling. Moreover, the indexable tool reduces the engagement area with the work, and the resultant lateral forces.

Advanced Boring Bar Improves Deep-Hole Microboring

If experience at Medfab Manufacturing, Lakeville, MN, is any indicator, long-reach boring in tiny parts needn't be the problem it once was.

Medfab described their challenge as a machining "perfect storm:" ID machining, thin walls in titanium, 4:1 aspect ratios and a 16µ surface finish spec. The workpiece is a 1 inch long x ¼ inch diameter piece of titanium tubing with walls thinner than your fingernail.

The remedy is a very advanced boring bar with a novel elliptical cross section, through-the-insert coolant delivery and high-feed tip geometry. It is called the Ingersoll T-Micro boring bar. The long axis, aligned with the cutting tip, provides additional rigidity and vibration control. The short axis expands the channels for chip disposal.

Medfab Manufacturing dramatically improved boring of small diameter medical parts with a new Ingersoll T-Micro micro-boring tool. Operation shown is a ¾ inch hole in tantalum. Even on bores down to 0.243 inches in thin-wall titanium tubing, the tool produces as-machined surfaces of 8-10µ, lasts up to 10 times longer than previous tooling at 16 percent faster machining rates.

 

 

 

 

Cycle time with all previous boring bars was 3½ minutes -- followed by 15 minutes of hand polishing on every single piece to reach the 20µ ID finish spec. With the T-Micro boring bar, cycle time was reduced to 3 minutes, as-machined surface came in at 8-10µ (even on the 250th piece), and all hand finishing was eliminated. Based on that success, Medfab now uses the T-Micro cutter on tantalum, MM35P (machinability like Waspalloy) and other high nickel alloys.

Deep Between the Webs

Long-reach work on flats benefits from the same high-feed, free-cutting insert, but in a different presentation, according to Forman. Case in point: skinning and plunge-milling the bosses 15 inches down between the webs on big iron castings at Hol-Mac Inc., Bay Spring, MS.

Typical skin milling operation on big steel castings at Hol-Mac Corp, Bay Springs, MS involves 15-inch reaches down between the webs. The company has standardized on tangential milling with Ingersoll S-Max face mills for initial operations on most big castings. Throughput doubled as a result, with edge life rising by 4 to 1 and cutter wrecks a thing of the past.

 

 

 

 

During such an operation a couple of years ago, one insert ruptured, triggering a tool wreck that blew out the spindle before the operator had a chance to shut down. John Scarbrough, manufacturing engineer, looked for alternatives and settled on a facemill that orients the inserts tangentially, an Ingersoll S-Max. The switch not only wiped out all catastrophic tool failures but also doubled throughput on more than 20 different long-reach jobs.

In tangential milling (TM), the inserts lie flat in the pitch circle, not upright. This presents the insert's strongest cross section to the main cutting force vector, leading to a more durable cutting system even in long-reach conditions. Today's TM mills can handle limited ramping as well as flat work, says Forman.

According to Forman, the gain in efficiency stems from a combination of factors: carbide's far superior strength and wear resistance over HSS, the high-feed geometries possible in pressed carbide inserts that cannot be cut into solid carbide endmills, and the larger cutter diameters possible with indexable inserts in steel cutter bodies. The larger pitch circles take advantage of chip thinning to enable faster feeds and create a gentler entry angle into the cut, he explains.

"Requirements for long-reach machining will never go away, but with updated tooling solutions and practices, the headaches can," concludes Forman.

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