Obtaining a spiral path for machining STL surfaces using non-deterministic techniques and spherical tool

•Machining STL surfaces, without a volume inside, is useful and it can be optimized.•To optimize this process we use the piece contour, defining 2D spiral paths.•With non-deterministic techniques, the third coordinate of the tool-path is obtained.•This method was simulated and applied to a workpiece, with positive results.•Its precision was tested using confocal microscopy and coordinate-measuring machine.

For milling an arbitrary surface, several models exist in which the tool must be moved close and away from the workpiece with its consequential problems caused by the contact between the tool and the mechanized material. One of these problems is the undesirable mechanizing marks on the surface, which can be avoided with the use of tangential tool-paths, causing another disadvantage: the additional time-consumption. Spiral tool-paths eliminate these problems and allow for continuous machining of the part without approach or withdrawal.Deterministic models for obtaining the tool positions referred to the part need to apply complex mathematical operations. For this reason, the idea of using non-deterministic techniques, with a controlled tolerance margin, allows to avoid those mathematical and geometrical operations. It also makes possible to reduce the processing times with no loss of dimensional quality and a good superficial finishing, which was confirmed with a coordinate measuring machine and with confocal microscopy, respectively.Finally, the effectiveness of the described method was assessed comparing its results with the performance of three of the most relevant CAM software commercially available. The obtained results are shown at the end of this paper.

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