Worry free: Medical Manufacturing

Courtesy of Haimer USA

Hogging 6061-T6 aluminum on a horizontal machining center using a Haimer Safe-Lock-equipped HSK collet chuck.

Antipullout toolholders reduce scrap, increase tool life and eliminate anxiety while milling.

In the winter of 1918, Carl A. Bergstrom opened the Weldon Tool Co. in Cleveland. Working from his shop atop the Blackstone Building, he developed a new kind of endmill, one with a 30° helical flute. The thing cut like crazy. Yet Bergstrom quickly realized that his toolholder lacked the gripping power to hang onto his cutting-edge endmill, as the darned thing kept spinning right out of the holder. In a fury, he grabbed that newfangled tool and ground a flat spot on its side, giving the toolholder’s clamping screw a place to bite into. Bergstrom had invented the Weldon shank.

The old toolmaker has long since turned to dust, but his invention lives on. For decades, the Weldon shank has taken first place in the contest for raw gripping force. Until now, that is. Brendt Holden, president of tooling provider Haimer USA LLC, Villa Park, Ill., aims to retire Bergstrom’s brainchild to a well-deserved place in the milling hall of fame with the development of Safe-Lock, a system that utilizes a no-fail clamping technique.

“Weldon-style endmill holders by their very nature push the cutter off center,” Holden said. This creates runout and drastically reduces tool life. Worse, even the rugged Weldon flat is prone to failure under modern cutting conditions—people weren’t hogging huge blocks of titanium in Bergstrom’s day or machining aluminum at 600 ipm and 20,000 rpm.

But hold on. The Weldon flat may not be history. Other toolholder manufacturers, including Iscar Metals and Rego-Fix Tool, have developed hydraulic and press-fit toolholders that use new technology, in conjunction with the Weldon flat, to provide antipullout characteristics. While suppliers may debate the benefits of each system, machine shops have a growing list of choices for securing their endmills when performing extreme milling.

An Expensive Problem

For Haimer, the road to pullout prevention began in 2006. “A big aerospace company came to us for help,” Holden explained. “They were machining aluminum wing spars worth $40,000 apiece and had problems with their high-helix endmills pulling out of the holder when going around the corners.” The company tried everything: shrink-fit and hydraulic holders, high-end collet chucks, and even press-fit systems. Nothing worked.

“They had these holders with tremendous gripping force, but still the tools were pulling out,” Holden said. “They settled for a side-lock holder with a Weldon-style endmill, but tool life decreased dramatically compared to the shrink-fit or hydraulic systems. And even then the screw on one of their Weldon holders backed out while roughing a $100,000 block of titanium and scrapped the workpiece. They challenged us to come up with a toolholder that ensured the tool would stay put.”

The aerospace company had other requirements as well. Minimal runout was an obvious one, but they also needed to adjust the tool’s gage length. “They have these big 3-spindle gantry mills, and each spindle has to be at the same Z-axis height,” Holden said.

Courtesy of Haimer USA

Cutaway view of Haimer’s Safe-Lock clamping system.

Since Haimer was already producing shrink-fit toolholders, it started by modifying one of its standard shrink-fit chucks, adding a pair of angular rods immediately behind the clamping area. These rods engage a pair of precision-ground helical grooves on the endmill shank to securely hold the tool during high-feed milling. Because the helical locating grooves on a Safe-Lock endmill run in the same direction as the cutter’s helix angle, rotational forces can only drive the endmill into the holder, not force it out.

To satisfy the requirement for Z-axis length adjustment, Haimer designed the system to allow about 12mm of length adjustment, and then placed an adjusting screw in the bottom of the holder. This butts up against the endmill, preventing axial movement. The Safe-Lock system was born.

“We brought it to back to that aerospace company and it solved their problem,” Holden said. “Runout was less than 0.0001 ” at a distance 3 times diameter from the chuck face. Tool life increased five to seven times compared to Weldon shank holders. They were very happy.”

Haimer then brought its invention to other aerospace shops, which experienced similar results. The company expanded its product line to include mechanical toolholders, accommodating those shops that do not have shrink-fit machines.

Partner Up

There was a problem, however—Haimer doesn’t make cutting tools. Its new system was unlikely to take off if Haimer couldn’t provide the modified endmills needed to use it. As a result, Haimer licensed the system to several toolmakers, including Kennametal Inc., Latrobe, Pa. Global Product Manager Ron West said Safe-Lock is one of the most innovative locking systems he’s seen in a long time. “It seems like the more torque you apply to the tool, the tighter it holds.”

West agreed the Safe-Lock system solves the laundry list of problems cited by Holden, but went one step further. Because Safe-Lock tends to send cutting forces toward the spindle, rigidity is improved compared to conventional toolholders. “Anytime you have a high radial load,” West said, “you’re pushing perpendicular to the spindle. It’s hard on the spindle bearings and can lead to wear and tear on the machine. Because tools in a Safe-Lock holder push straight upward in the Z-axis, the machine should be able to better absorb that energy into the spindle.”

Courtesy of Haimer USA

Cutting forces are directed into the Safe-Lock chuck.

In addition to Safe-Lock-compliant endmills, Kennametal also makes a line of shrink-fit toolholders outfitted with Haimer’s patented antipullout technology. West said, “This system basically eliminates pullout. I’m a firm believer.”

Don’t Cheap Out

The up-front investment needed for any shrink-fit system can be a hurdle, and the Safe-Lock is no different. Dropping $20,000 for a machine to heat and cool toolholders makes most shop owners think twice. West offered the following argument: “An antipullout toolholding system offers many benefits. Productivity is improved because the feed rate and depth of cut are no longer limited by potential tool creep. This means less scrap and lost production due to unexpected pullout. The cutter will literally break before it comes out of the holder. Improved concentricity means better tool life and higher speed, again increasing throughput. And because shrink-fit endmills don’t have a flat on the side as with a Weldon shank, tool balance is better, reducing vibration.”

Courtesy of Kennametal

Cutaway view of a Kennametal shrink-fit HSK Safe-Lock toolholder.

Critics of shrink-fit technology point to the potential for metal fatigue. After all, repeated heating and cooling can turn even the toughest of metals into Silly Putty. To silence these naysayers, Haimer tested the typical shrink/heat thermal cycle more than 2,000 times against four sizes of toolholders, quickly bringing them up to 426° C, then chilling them down again to room temperature in less than 2 minutes. The results showed no loss of accuracy, gripping torque or metallurgical properties.

Another toolmaker embracing Safe-Lock technology is Seco Tools Inc. Bob Winegard, application support analyst for the Troy, Mich.-based company, said Seco is planning to roll out its own version of antipullout toolholders this fall. “Customers making aerospace, energy and medical parts cut a lot of Inconel, titanium, cobalt chrome, nitronic and high-strength duplex and super-duplex stainless steels, such as Ferralium and Zeron 100.” These alloys give toolholders a run for their money. “With precision components, even a few thousandths pullout will scrap the part. That’s why it’s critical to entirely eliminate all movement,” Winegard said.

Images courtesy of Iscar Metals

An Iscar HYDRO-SURE sidelock hydraulic toolholder.

That assurance comes at a cost. While Winegard wouldn’t speculate on the price of Seco’s new system, both Winegard and Holden indicated Safe-Lock holders cost 10 to 15 percent more than standard shrink-fit tooling. They also require high-quality, modified endmills. “You’re doing yourself a disservice in terms of productivity and tool life if you buy on price alone,” he said.