Abstract
In 3½½-axis machining, the machined part surface is partitioned in pre-processing in order to calculate the tool position and patch boundaries and then machined in patches, thereby minimizing the intermediate manual part re-positioning and the overall machining time. Each patch requires a constant, but different, tool orientation. In previous research, local properties have been used to subdivide surfaces into patches. For an ideal tool position and orientation, however, the tool’s shape and curvature should exactly match the shape and curvature of the part surface. The rolling ball method, originally developed for 5-axis machining, considers the regional characteristics of tool positioning. This work extends the rolling ball method to 3½½-axis machining, thereby successfully delivering 5-axis quality with currently installed 3-axis computer numerical control milling machines. The pseudo-radius of curvature provides a novel geometrical subdivision criterion. Two Bézier curved surfaces are tested and compared with the 5-axis rolling ball method. Two additional surfaces are presented to further demonstrate the partitioning capability of the method. The results suggest that the rolling ball method for 3½½-axis machining is comparatively competitive in performance and quality.
Highlights
The so-called 31⁄21⁄2-axis machining combines the flexibility of positioning offered by 5-axis machines, as well as the low cost and ease of programming offered by 3-axis machines
The following section describes the extended rolling ball method (RBM) for 31⁄21⁄2-axis machining, which includes the clustering algorithm for subdividing the surface into patches, the tool path generation method, and the experimental setup designed to compare the performance of the proposed 31⁄21⁄2-axis machining method against the conventional 5-axis machining
We found that for more than eight patches, the estimated machining time continued to increase and the partitioning process was not continued
Summary
The so-called 31⁄21⁄2-axis machining combines the flexibility of positioning offered by 5-axis machines, as well as the low cost and ease of programming offered by 3-axis machines. Recent work has shown methods for 31⁄21⁄2-axis machining that resulted in time savings over 3- and 5-axis machining.[1,2] Time savings are even being considered in high-speed machining.[3] These methods are based on the partitioning of the surface into patches and determining an adequate tool orientation and tool path strategy for each patch. The parameters used for partitioning include the surface coordinates and normal vectors, which provide only local information at the sample points. Tool orientation is a regional issue, and both the tool surface and the part surface must be considered for adequate or optimal tool positioning, as demonstrated by Warkentin et al.[4]
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