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Machining 44 MoldMaking Technology May 2015 M oldmakers know that a three-axis approach to deep and tall features requires the use of long, skinny tools, but this approach doesn't work very well. Speeds and feeds suffer because the entire process must be slowed down to accommodate the longer, weaker tooling. This means overall mold-production time suffers as well. Five-axis machining, however, enables the tool body to be tilted away from the contact point, ensur- ing that the tool does not extend too far from the holder, and permitting the use of shorter, more stable tools when cutting deep cavities or tall-core molds (see Figure 1). It's no secret that five-axis technology offers other huge ben- efits to mold manufacturers. More efficient mold production, improved surface finishes and decreased polishing require- ments, to name a few. But what is it specifically about five-axis technology that yields the biggest benefit to mold shops work- ing with deep and tall features? What actually provides the ability to keep the tool tilted in all the varying directions with total control and without the worry of part interference or col- lision? The answer is tool center point management. Visualize exactly what is happening as a tool moves around a part in five-axis simultaneous machining, and then try to imagine the types of calculations that are necessary to main- tain control during this fluid dance of the tooltip. It doesn't take long to realize that there is much more going on behind the scenes than what meets the eye. Tool center point management, or rotary tool center point, is a feature within advanced machine tool controls that signifi- cantly simplifies five-axis programming and setup complexity. It makes the program and the part setup independent from machine setup and configuration. Without tool center point management, the programmer has to account for the distance from the center lines of rotation for the rotary and tilting axes, either in the program or in the postprocessor. With tool center point management, the setup is as simple as it is on a three- By Michael Cope Tool center point management streamlines five-axis programming and setup. Making the Complex Simple Figures courtesy of Hurco Companies Inc. FIGURE 1 axis machine, and the control tracks the relationships among the tooltip, axis center lines and part setup. The Path to Programming Efficiency All five-axis machines, regardless of the actual axis configura- tion, have a fixed mechanical center line for the machine's rotary or tilting axes, around which each axis rotates (see Figure 2). The machine table surface, workpiece position, spindle gage line and cutting tooltips are all located at some measurable distances away from the center line (see Figure 3). When the programmer performs the machine's part and tool setup, something needs to account for and track the varying distances as the part is machined, and as the tool and workpiece move throughout the machine's space (see Figure 4). Before tool center point management was an option, this tracking was accomplished within the CAM program itself. This proved problematic and time-consuming. The machine tool control isn't smart enough, or advanced enough, to account for the relationship between the machine tool's kine- matics and their relationship to the workpiece and program, so the responsibility falls on the CAM program or postprocessor. Without tool center point management, the programmer must program all settings from the center line of rotation instead of the traditional workpiece zero point. This means that the solid model must be moved away from the zero refer- ence point in the CAM system the exact same distance as it is Five-axis technology can be very benefcial for deep core or cavity features, and will allow for the use of shorter and more rigid tooling. Because the tool body can be tilted away from the surface of the workpiece, long tooling that can accommodate the full-depth of the feature is not necessary.