Modern Machine Shop

OCT 2017

Modern Machine Shop is focused on all aspects of metalworking technology - Providing the new product technologies; process solutions; supplier listings; business management; networking; and event information that companies need to be competitive.

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24 MMS October 2017 RAPID TRAVERSE Machining Technology in Brief (from 5 min., 17 sec. to 1 min., 13 sec.). Because the radius of a barrel cutter is larger than that of a ballnose end mill, fewer passes are needed. For finishing the hub, the company uses a Starrag torus cutter with a lateral stepover to the tool diameter. A torus cutter basically looks like a regular end mill, but it has a big radius at its end. The cutting process takes place on that radius and not on the shaft/side of the cutter. A subse- quent blade root-finishing operation completes the machining process. According to Richard M. Bacon, Starrag's h e ad of e n g i n e e r i n g, th e s e c ret to re d u c e d machining time lies in the design of the barrel cutter, which was specifically intended for blisk machining. The company designed the tool to best adapt to the shape of the blades. Further- more, defined edge rounding results in lower cutting forces in all directions, and unequally spaced teeth reduce chatter. "Typically, barrel tools are critical, because they star t to excite chatter more easily due to their larger contact area," Mr. Bacon says. "This can make their application quite tricky, especially when using off-the-shelf tools." The new six-tooth design enables significantly higher axial depths of cut and high feed rates. " T h e c o nve nti o n a l p ro c e s s to o k a b o u t 10 0 passes to finish the blades," Mr. Bacon explains. "Now, the greater a xial depth of cut of 3 mm reduces the required passes to 10." In short, a barrel cutter's larger radius enables greater con- tact with the part and therefore larger stepdowns, which reduces the number of required passes and reduces cycle times. In return, the greater contact means the forces are much larger, thus they tend to excite the parts more easily and often cause chatter. "With our specific tool design, we can counter these effects," he says. The machine used in this example, a Starrag NB 251, is a five-axis machine tool that is spe- cifically made for complete machining of blisks. According to Mr. Bacon, one of the main features that ensures high dynamics for productive machin- ing is the low number of moving masses. Compared to machines with a swivel rotary table, the NB series features an angled B axis, which effectively enables the tool to rotate around the tool center point. Because the tip of the tool is located very close to the center of rotation, the compensating movements of the a xes are five times shor ter compared to machines with a swivel rotary table, leading to shorter machining times. The larger radius of barrel cutters allows for greater contact with the part and therefore larger stepdowns, which reduces the number of passes the tool needs to take compared to a ballnose end mill. Starrag USA Inc., call 859-534-5201 or visit Arcing Away From Near-Net Forging BY M AT T DA N FO R D I n the future, pounding heated metal into sub- mission will not be the only viable means of producing cer tain near-net-shape aerospace components. According to various suppliers, additive manufacturing technology continues to progress toward the same standards for material strength and reliability as forging. They also claim that these freeform deposition processes take less time than forging (a matter of hours for larger components) and bring parts even closer to final geometr y. By eliminating the need for tooling and reducing the time and cost required for

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