Modern Machine Shop

JAN 2018

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Modern Machine Shop 83 Five-Axis Turning Adding Tilt to Trunnion-Table Turning Turning large parts on a milling machine consolidates setups. Leveraging two rotary axes at once puts the spindle closer to the work. Multi-process equipment is not always based on a turning platform. By locking the spindle in place and spinning the trunnion table, a properly con- figured five-axis machining center can consolidate setups by turning symmetrically round parts, particularly large aerospace and energy industry components. Some machines can even leverage two rotary axes at once, adding tilt to spin in order to get even closer to the workpiece surface. As is the case with moving from three- to five-axis milling, adding rotary motion can enable turning with shorter, more rigid cutters at more aggres- sive parameters to improve cycle times, surface finishes and tool life. Granted, not just any five-axis machine can turn, let alone securely angle a large, heavy part that spins at hundreds of rpm. Gunther Schnitzer, vice president of sales and engineering for Hermle North America (Franklin, Wisconsin), says his company laid the groundwork for the latter capa- bility long ago with a design that's standard to all its machine tools. The fact that this design was con- ceived with milling in mind evidences the extent to which modern machining equip- ment can defy traditional operational categorization, not to mention the potential viabiltiy of a machining-cen- ter-based approach for reduc- ing setups on larger parts. MATT DANFORD | SENIOR EDITOR Turbine parts like this and the one on the next page are prime candidates for tilted-trunnion- table turning. All photos courtesy of Hermle. A Rigid Platform If turning the trunnion table into what is essen- tially an adjustable lathe spindle wasn't the top priority for Hermle engineers when they designed this machine configuration, it's cer- tainly a significant side benefit. Mr. Schnitzer says the key enabler is a factor underlying the performance of virtually any variety of machin- ing equipment: rigidity. At first glance, the only differentiating fea- ture from other gantry designs is that the gantry structure rides on top of the machine's sidewalls. However, the two sidewall-mounted guideways are not the only support for the Y-axis gantry and the X-axis slide mounted on top of it. Locating the guide system above and outside the workzone enables adding another guideway (or two in the case of larger machines) underneath the center of the gantry structure without interfering with the machine's operation. Located farther toward the back of the machine than the sidewall-mounted guideways, this third point of support completes a rigid, triangular foundation for the gantry structure, one that remains intact regardless of X-Y location. This configuration helps combat what Mr. Schnitzer calls the "horsehead" effect: that is, the tendency for the front of the gantry structure to sag as it moves farther along the Y axis and out over the workzone. Rather, rigidity is maintained even at the fullest extent of Y-axis travel. Meanwhile,

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