Multi-process equipment is not always based on a turning platform. By locking the spindle in place and spinning the trunnion table, a properly configured 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 aggressive parameters to improve cycle times, surface finishes and tool life.
That is according to Gunther Schnitzer, vice president of sales and engineering at German machine tool builder Hermle’s North American arm, which is located in Franklin, Wisconsin. He emphasizes that the key phrase here is “properly configured.” Not just any five-axis machine can turn, let alone tilt and swing what is most likely to be a large, heavy part spinning at speeds as fast as 800 rpm. For Hermle, the groundwork for achieving the latter capability was laid long ago, he says, back when the company first standardized on a modified-gantry-design scheme for all its machine tools. Although developed with milling in mind, this machine configuration is considered essential to ensuring the high levels of rigidity needed to turn the trunnion table into what is essentially an adjustable lathe spindle, one that is capable of presenting work to tool at a wide range of precisely programmable angles.
At first glance, the only differentiating feature from other gantry designs is that the gantry structure rides on top of the sidewalls of the machine. 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, 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.
Read more: Adding Tilt to Trunnion-Table Turning