New freedom of movement
How can thick sheets be laser cut even faster on a combination machine? With additional axes and a formula that takes account of contouring errors.
How about a little boost? Let’s say, thirty percent greater output for laser cutting with the TruMatic 7000? Sure enough — but it’s a tricky job. The aim is to guarantee high acceleration rates when positioning, scratch-free parts even with complex contours, and reliable machining of combination parts. Moving a large mass can become a major problem. After all, material measuring up to eight millimeters thick can quickly represent a total weight of 280 kilograms — and that has to be positioned both quickly and precisely.
Clear division of tasks
A second motion concept provides the necessary dynamics. Additional axes move simultaneous to the main axes. They move the laser cutting head in the X and Y directions — superimposed on the table’s motion axes. While the overriding NC control concept governs the main movements of the workpiece directly, the drive-based motion control shifts the laser head, as well, within a 52 millimeter radius. The superimposition of the two movements increases the absolute traversing speed and shortens machining time for ornate parts involving complex contours and many changes in direction. At the same time it smoothes out the movement sequences at the machine table, transferring abrupt movements into the tool head with its considerably smaller moving mass.
When calculating these superimposed movements, the system figures the contouring error in advance and performs higher-precision machining steps with the workpiece at rest. This means that the table no longer has to execute motions around corners, where it would have to be stopped and restarted. Instead it always takes the shortest route, while the additional parallel axes compensate for the difference and cut the filigrees. The new concept offers very high precision — despite the speed. Using appropriate automation, the intelligent combination of movements also supports cutting parts free from the sheet.
The coordinate control and additional axes work together in pre-cutting the parts, the workpiece is being moved during that step. Now the SheetMaster takes over, first using suction cups to secure the part. Following guidance along the additional axes, the laser cutting head then cuts the part free — the sheet panel remains stationary in the meantime. This means that a number of parts can be cut free, one after the other, and quickly be removed.
The right formula
The superimposed movement of the cutting head and coordinate-based control are not an easy task for the control system. It has to calculate the movement of the additional axes simultaneous to the target position of the main axes. The solution here is the appropriate formula, one that makes use of a “model contouring error.” This error is calculated in the drive, by the simulation model, and is compared with the actual contouring error in the additional axes. This real-time comparison of the target and the real values for both axes makes it possible to compensate for deviations between the calculated path and the specified contour, with no time lag.
Greater freedom of movement
Greater freedom of movement has even more advantages. The cutting head can be positioned almost at will within the laser die and the die diameter is almost twice as big as before. Significantly larger parts can be discharged directly through the die, dispensing with the path along the parts removal flap is no longer necessary. All in all, this highly dynamic solution reduces part production times by as much as thirty percent.
Contact us: MastersofSheetMetal@trumpf.com
This article was first published in summer 2011.