Time minimization of pocketing by zigzag passes along stability limit

Pocketing with zigzag toolpath (which maintains near to continuous tool-workpiece contact) that is continuously optimized with limiting pairs of axial and radial depths is investigated in this work. Analysis led to a set of 16 conditional expressions eligible for description of pocketing time. An eligible expression becomes effective when all associated conditions are simultaneously met while the rest of the eligible expressions remain dormant until dimensions of pocket and tool favours another. Similar analysis has been carried out in other works for one-way toolpath which permits idle return passes and thus expected to incur delay. Comparison of zigzag and one-way toolpaths shows that the former always hastens pocketing operation because it better utilizes the stability limit of the system by maintaining continuously optimized to and fro passes. Numerical studies gives that zigzag toolpath can even half pocketing time of one-way toolpath for some choice of limiting process parameters. Similar to the conclusion that has been drawn for one-way toolpath in an earlier work it is seen that utilizing the coordinate of maximum limiting material removal rate (MRRlim) for both down- and up-milling in a scheme of zigzag pocketing will not necessarily provide the minimum time because of geometrical constraints.

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