A solid model-based off-line adaptive controller for feed rate scheduling for milling process

Most CAM packages available today provide NC simulation systems that generally use inexact solid representation as they are computationally intensive. Popular inexact volumetric NC simulation packages use either a voxel based 2.5D approach (particularly Image-space modeling) or Polyhedral approximations of 3D objects. The former does not degenerate with time but has limited resolution whereas the latter has a selectable resolution but degenerates rapidly with time. As against these, the authors’ use octree solid representation in their volumetric NC simulation system. This hierarchical space decomposition (HSD) technique combines the benefits of both the earlier approaches, i.e., it has a selectable resolution and does not degenerate with time. The basic input to the octree-based NC simulation system is the NC cutter path either in cutter location (CL) format or G/M-code format. After the CL data are interpreted, the swept volume of the cutter is intersected with the blank at every small sampling interval along the tool path and the intersection is considered as the undeformed chip. The chip parameters necessary for predicting the milling force are extracted and using the material removal rate (MRR) model and cutting force is predicted. According to the simulation result the feed rate is adjusted based on force calculation to generate optimized CL File. The improvement can be seen from the experimental results presented. Such a simulation system will be useful, in addition to the visual check, for automatic verification of safety of machining and conformance of the produced part to design specifications as well as for the optimization of the feed rate and spindle speed.