Cutting Tools for CAM – Part 5
Mastercam’s Dynamic Motion Technology reduces tool wear by taking deeper cuts with much smaller stepovers than those used in conventional milling. When stepovers of less than 50% are used, it is essential to run at higher feed rates to compensate for and take advantage of a phenomenon known as RCT (Radial Chip Thinning).
Here is the basic idea:
– When the stepover is 50% of the tool’s width or greater, the thickness of chips being removed at any speed remains constant.
– When the stepover is less than 50%, the chip thickness becomes progressively smaller as the stepover decreases.
This is important knowledge, because most of the heat generated in the tool and the steel part is removed, not by coolant, but by the chips. If you decide (for good reasons) to use stepovers smaller than 50%, you will need to run at a faster feed rate to get the chip thickness back up to target so the chips will have sufficient mass to retain the heat, pull it away from the tool and the part and into the chip bin. This strategy for cutting steel not only reduces tool wear but it improves cutting efficiency.
The factor for taking best advantage at a given conventional feed rate and stepover is found in tables readily available on the Internet. Multiply this times the conventional feed rate to get the optimized feed rate for when the stepover is more than 50%:
(Conventional feed rate) / (RCT factor) = (RCT optimized feed rate)
Tool vendors are also beginning to work with CAM suppliers to incorporate these factors into the software’s tool library.
Here’s an example of how well this works: A cutting tool vendor and a CAM software developer visited a tool & die shop’s mold plate manufacturing cell. It took 70 minutes to cut single pockets on A and B mold plates using a conventional insert cutter, aggressive but shallow cuts with a conventional insert tool. There were six plates per job and the plates were stacked up all around the machine waiting to be cut. During a single shift they could complete one job.
Next, the visitors used the same cutting parameters but exchanged the conventional insert for a good quality carbide tool. Now they were cutting a plate in 45 minutes — a 36% machine cycle improvement.
Once more the visitors exchanged tools — this time using a variable pitch carbide cutter in conjunction with toolpaths incorporating Dynamic Motion Technology with feed rates calculated to take advantage of radial chip thinning. This made it possible to cut one plate every 12 minutes. Production in the cell went from 0.86 plates an hour to 5 plates an hour — a 580% improvement! The only downside many shops find with these high productivity rates is that conveyors can no longer remove chips fast enough to keep pace with their accumulation.
Users of this approach have seen productivity improvements (depending on the job) ranging between 30% to 500% with far less wear and tear on tools, parts and equipment. RCT is easily compensated for and implemented. A discussion with your tool vendor and CAM reseller can resolve issues regarding appropriate tool selections and cutting strategies and RCT parameters for particular applications.