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Fig. 14. Smart cornering.
Multi-axis software is not widely used and is in the similar stage of development as 3D milling was 10 years ago. There are only a few high-priced workstation-based systems that are specialised in general multi-axis work and used mainly in aviation and turbine industry. We are expecting a further development of this section of the CAM in the future.
7. G-optim software for optimization of machining process
In order to improve a machining process at low perfor- mance machine tools, we developed an optimization soft- ware G-optim. It eliminates the bottleneck of insufficient Look-ahead function, problem of long cycle time of CNC controller and the problem of weak data connection between computer and machine tool. The program works as off-line optimizing software which adjusts the feed rate function to pre-generated standard G-code—Fig. 15.
7.1. Look-ahead function-federate adjustment
Standard NC code is combined with NC blocks. Almost every NC block represents the movement from one point to another. There are two basic elements of cutterpath: move- ment on a line and movement on a curve and two connections of those elements: smooth and sharp (corner crossing). By movement on the line there is no federate restriction, mean- while by movement on the curve the maximum federate fol-
Fig. 16. Corner crossing methods.
lows the equation:
vf,R,max = ,2GsR9.81
where R represents the curve radius and Gs represents the machine tool characteristic (cornering acceleration).
Smooth connection of elements means, that the tangen- tial movement vectors in a common point (end point of one NC block and start point of the second NC block) of two movements are the same.
To achieve accurate connection of two NC blocks by abrupt direction changes there are two alternatives—Fig. 16. Exact stop methods assures accurate cutterpath, but marks the surface when the cutting tool rotates at one stationary point. The corner crossing feed rate method is used when tool motion vectors change more then a specific angular amount It cause better surface quality but also inaccuracy by corner crossing. The cutterpath error by direction changes depends论文网
on federate value.
7.2. Optimized federate and federate smoothing
There are five crucial federate specifications used in the optimization process, the federate prescribed at NC code (vf,NC), the federate at movement on a curve (vf,R), the feder- ate by sharp direction changes (vf,α), the cycle time federate (vf,T ) and the DNC federate (vf,DNC). For these reasons the optimum value for each NC block has been satisfied all those five limitations:
vf,NC
v
vf = min vf,α
vf,T
vf,DNC
Fig. 15. Off-line optimization process chain.
Therefore, it is necessary to adjust the prescribed fee- drate value between NC blocks to machine tool accelerating and decelerating ability to enable smooth machining process. Also is necessary to pide long slow movements on slow and fast section to enable short machining time—see Fig. 17.
Fig. 17. Dividing of slow movements.
7.3. Experimental set-up
The program G-optim is designed to perform an off-line optimization of standard (G-code) NC machining program. To confirm or refuse the optimization algorithm some exper- iments by using a raw and optimized NC data were made at the MoriSeiki Frontier-M milling machine tool.