Abstract

A new method for 5-axis CNC tool positioning is presented in this paper that improves upon a previous tool positioning strategy named the rolling ball method (RBM), which was developed by the present authors [Gray P, Bedi F, Ismail S. Rolling ball method for 5-axis surface machining. Comput Aided Des 2003;35(4):347–57]. The special property of the RBM is that it computes tool positions by considering the area beneath the tool that the tool will be positioned to cut instead of using surface curvatures computed at a single point on the surface. This enables the RBM to generate gouge-free tool positions without secondary iterative gouge-check and correction algorithms. However, the RBM generates conservative tilt angles in order to guarantee gouge-free tool positions. The new arc-intersect method (AIM) presented in this paper improves upon the RBM by directly positioning the tool to contact the surface and thereby eliminates the conservative nature of the RBM to give optimal tool positions. Like the RBM, the AIM is an area-based method that generates gouge-free tool positions without the use of iterative gouge-check and correction algorithms. The implementation described in this paper uses triangulated surfaces and the computer's graphics hardware to assist in the tool position calculations. However, the method can be applied to any surface representation since it only uses surface coordinates and surface normals for computation. A section of a stamping die was machined to demonstrate the AIM and to show the improvement over the RBM and for comparison with 3-axis ballnose machining. The results showed that the AIM was 1.33 times faster than the RBM and that the AIM, with single direction parallel tool passes, was 1.62 times faster than a zig-zag pattern 3-axis ballnose tool path for the same feed rate, cusp height and tool diameter. The workpieces were measured with a CMM and the data were compared to the CAD model to show no gouging occurred and to check the cusp heights.

Keywords: 5-Axis machining; Triangulated surfaces; Depth buffer; Computer graphics

Article Outline

1. Introduction

1.1. 5-Axis tool positioning strategies

1.2. Multiple patch surface machining

1.3. Triangulated surface data for tool positioning

2. Rolling ball method for 5-axis surface machining

3. Graphics-assisted surface point and surface normal calculation

4. Rolling ball method issues

5. 5-Axis arc-intersect method

5.1. Arc-intersect concept

5.2. Arc-intersect algorithm

5.2.1. Case 1

5.2.2. Case 2

6. Machining test

6.1. Viewing parameters

6.1.1. RBM viewing setup

6.1.2. AIM viewing setup

6.2. RBM machining results

6.3. AIM machining results

7. Comparison

8. Conclusions and discussion

Acknowledgements

Appendix A. Pixel spacing and depth buffer resolution

Appendix B. Surface measuring with a coordinate measuring machine

References

Vitae