Self-aware roughing toolpaths

As you’re probably aware, the following scenario is quite common. A tooling sales rep installs the so-called “latest and greatest” cutting tool in a shop’s best vertical mill. He clamps a perfectly straight-sided block of tool steel onto the table and drives the tool to a position 1 ” deep with a 0.050 ” step-over into the block. He revs the tool to 12,000 rpm and sends it down that straight path, ripping out a large swath of material at a blinding speed. “Look how fast that tool can go,” he boasts.

Perhaps the first time you saw this demo you purchased the tool and vowed to use it to enhance the material-removal rate on your most roughing-intensive work. If so, it’s a good bet you broke the tool, damaged the part or even overloaded the machine. This happens so frequently that most machinists err on the side of being overly conservative when roughing. After all, roughing is only a small part of the total machine cycle for most parts.

The problem with the demo was not the tool—it probably was as good as the vendor claimed. However, it was demonstrated in ideal conditions where straight sides and no turns resulted in constant tool load. In a shop’s real and imperfect world, cutters are constantly changing direction and entering curves and corners where tool load can spike in the blink of an eye. In the past, CAM programmers spent a lot of time calculating and programming toolpaths to compensate for continually shifting tool loads. Shops could only afford to invest in this programming time to reduce cycle time for parts with long production runs, since shorter runs would not produce enough in savings to justify the programming expense.

Eventually, CAM vendors developed bandages that helped programmers overcome some of the most troublesome areas. For example, “trachoids,” or tiny circular loops, nibble away material on sharp curves and corners. These gizmo algorithms allowed programmers to make fine adjustments so tools ran at optimal speeds without getting buried.

A better approach, however, would be to use “self-aware” toolpaths in which an algorithm in the toolpath does everything to keep a continually sprinting and looping tool under constant load as if cutting a straight edge. A self-aware toolpath not only detects impediments to operating at optimal cutting speeds and tool loads, but also makes adjustments to correct for them. This would make it possible for every CAM program to deliver optimal cutting performance without the programmer having to make time-consuming micro-adjustments.

Courtesy of CNC Software

Mastercam X5’s OptiRough approach drives the tool to the full flute depth and uses the Dynamic Mill algorithm to machine the largest possible conical area. Once the tool roughs this area, it proceeds to step up in a series of small increments and machine the material remaining on the sides at each interval.