The Geometry and Generation of NC Tool Paths

Abstract

Numerically controlled milling is the primary method for generating complex die surfaces. These complex surfaces are generated by a milling cutter which removes material as it traces out pre-specified tool paths. The accuracy of tool paths directly affects the accuracy of the manufactured surface. The geometry and spacing of the tool paths impact the scallop height and time of manufacturing respectively. In this paper we propose a new method for generating NC tool paths. This method gives the part programmer direct control over the scallop height of the manufactured surface. The method also provides options to the part programmer for generating a variety of tool paths based on practical metrics such as tool path length, tool path curvature and number of tool retractions.

Uniform Coverage of Automotive Surface Patches

“…For CNC milling applications, Suresh and Yang (1994) derive the optimal spacing between adjacent passes for a ball-end milling tool. Sarma and Dutta (1997) extend this derivation to desired distributions of scallop height, including the constant scallop height distribution. Determining the optimal inter-pass spacing for robotic spray painting is relatively more involved due to the complexity of the paint distribution flux coming out of the spray gun (Conner et al 2004).…”

5-axis Iso-scallop Tool Paths along Parallel Planes

“…In this case, the envelope surface of the tool movement may present self-intersections (figure 1b) and the resulting tool path thus contains loops. Hence, iso-scallop machining strategy loses all its interest as the tool sweeps several times the same area, decreasing accordingly machining efficiency [16,18]. A solution is to remove loops due to self-intersections.…”

“…To overcome the limits of common machining strategies (parallel planes or isoparameteric curves), which generate over-quality of surface finish, iso-scallop strategy has been developed in 3-axis milling [6], [16], [18], [19] as well as in 5-axis milling [10][11], [13], [20]. With such strategies, the respect of the dicretization parameters specified by the user is ensured in a uniform way over the whole surface.…”

An exact representation of effective cutting shapes of 5-axis CNC machining using rational Bezier and B-spline tool motions

“…The highest point, called the scallop point, traces out a curve along the tool path, called the scallop curve. The distance between two neighboring scallop curves is called step-over distance or path interval (Sarma and Dutta, 1997). When a cutter moves along a tool path without changing its orientation, the effective cutting shape is an ellipse obtained as the intersection of the cutting plane with the cylindrical cutter.…”

“…A vast amount of research has been done in the area of 5-axis tool path planning in order to achieve the competing goals of higher accuracy for manufactured surface and reduced machining time. Much of the existing work on CNC tool path generation focuses on geometric issues such as scallop heights, local and rear gouging (Vichers and Quan, 1989;Marciniak, 1991;Jensen and Anderson, 1992;Choi et al, 1993;Chen et al, 1993;Menon and Voelcker, 1993;Li and Jerard, 1994;Kim and Chu, 1994;Suresh and Yang, 1994;Lee and Chang, 1995;Lin and Koren, 1996;Sarma and Dutta, 1997;Lee, 1997 and1998;Lee and Ji, 1997;Rao et al, 1997;Lo, 1999;Rao and Sarma, 2000).…”