Modern Machine Shop

JAN 2018

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Page 85 of 163

Features contributing to the rigidity required for turning include a rigid, triangular gantry foundation; double-sided, high-torque trunnion tables; a balancing system; and various CNC adjustments. MMS JANUARY 2018 84 MACHINING CENTERS centrally locating the drive unit in essentially the same area—at the apex of the support triangle— ensures even application of drive force across all guideways. "No matter where you are within the work area, you are always dealing with the same, rigid support structure," he says. Double-sided trunnion tables also contribute to the rigidity and flexibility required for turning, Mr. Schnitzer says. Twin points of connection with the machine, one on each side, provide a stable plat- form for heavy workpieces. Similarly to the linear axes, the motors and drives are located outside the workzone. An open workzone translates to a wide range of motion for the table: in this case, +100 to -130 degrees. The wider the range of table motion, the easier it is to manipulate the work in a way that enables more efficient turning (or milling, for that matter) of complex, contoured geometries. Turning to New Options Mr. Schnitzer emphasizes that enabling tilted trun- nion-table turning wouldn't be possible without any adjustments to the base design. Nonetheless, most of the modifications made to Hermle machin- ing centers that offer turning capability (which feature the designation "MT," for "mill-turn," in the product name) are still largely about provid- ing a stable, rigid platform. For instance, rather than the standard worm gears, trunnion tables employ 4,000-Nm torque drives that can handle high turning forces without stalling. MT machines also ship with a system of weights for precisely balancing the trunnion table. During setup, the CNC (a choice of Heidenhain or Siemens models) instructs the user in precisely how to shift the positions of these weights based on the weight of the workpiece, the C-axis rotational speed, and other part attributes and parameter settings. These adjustments take only a few minutes at most, Mr. Schnitzer says, noting that the basic concept is similar to balancing tires on a car. The addition of this balancing routine isn't the only example of the company tweaking machining center CNCs for turning capability. Mr. Schnitzer says the company also paid particular attention to functions that help track the locations of critical

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