Advanced CAMs Simplify Programming of Conical Barrel Cutters

Conical barrel cutters, also known as circle-segment milling tools, have consistently grown in popularity since their introduction less than 10 years ago thanks to their ability to help reduce the cycle time for finishing operations on five-axis machine tools. These cutting tools are designed for finishing in deep pockets and cavities with steep walls, as well as increasing the stepdown on tangent and planar surfaces, dramatically decreasing the cycle time for these operations. However, the more complex profiles of barrel cutters can make them more difficult to program, making it vital for users to understand how CAM features can simplify the programming process and improve the final results.

Larger Stepovers, Faster Finishing

The promise of conical barrel cutters is deceptively simple: the large radius on the profile of the cutting tool enables users to perform finishing operations on steep or contoured surfaces with significantly larger stepovers, reducing the machining time for finishing operations. But to fully achieve these benefits, the cutting tool must approach the workpiece at the correct angle to make full use of its higher cutting radius, which means using advanced CAM systems and five-axis machining centers. 

CAM systems initially struggled to accurately represent the complex shapes of barrel cutters, according to Open Mind Technologies Technical Sales Manager Alan Zielinski. “For a long time, CAM systems never really modeled the actual shape of the cutting tool,” he explains. Instead, CAM software would use a cylinder to represent end mills, adding a hemispherical tip to model ballnose end mills. These simple shapes were accurate enough to model most cutting tools, as the CAM system’s needs relied on a milling tool’s profile while spinning rather than the specific design of its flutes. Conical barrel cutters, however, have a large radius ground into an angled profile, making simple cylindrical CAM models inexact.

Early on, Open Mind’s Hypermill CAM software had an advantage over other CAM systems: the company helped develop the conical barrel cutter to meet the needs of the finishing toolpaths the company had already been developing. “We came up with the cycle before the tool even existed and helped develop the tool to fit it,” Zielinski says. “A lot of companies had been working on ways to improve roughing passes, so we worked out how to improve finishing cycles.” Other CAM providers have since developed the capacity to accurately represent cutting tools with angled profiles to meet the demand for these tools with their customers, but Open Mind’s familiarity with the needs of these cutting tools can help illustrate the benefits of using advanced CAM systems when machining with conical barrel cutters.

Hypermill released its latest update this year, improving on numerous aspects of its software. One module of particular note is its High-Performance Finishing package, designed for use with barrel cutters and advertising up to 90% time savings in finishing operations. This package is notable for numerous features that can automatically generate the complex toolpaths needed for conical barrel cutters, including strategies for reducing chatter and creating more seamless surfaces.

Generating Toolpaths for 3+2 and Simultaneous Five-Axis Finishing

The system’s tangent plane machining option — designed for machining planar surfaces including both walls and floors of deep pockets — shows how advanced CAM systems can simplify programming for conical barrel cutters. As Zielinski puts it: “In tangent plane machining you select the plane and parameters, and the system takes care of everything else for you to program the tool path.” While users may feel nervous giving the CAM system that much latitude, it accounts for many details.

For example, if the system recognizes that a path can be achieved using 3+2 machining, it uses that strategy to improve the rigidity of the machine compared to simultaneous five-axis machining. If the toolpath requires simultaneous five-axis machining, it likewise automatically recognizes this and generates code for simultaneous machining. And if the machine tool cannot handle simultaneous five-axis machining, the user can, at one click, revert to a 3+2 toolpath. Additionally, the system checks the toolpath for collisions as it generates the code. “Out of the box, at the time of calculation the toolpath is collision-checked to avoid holder and spindle collisions,” Zielinski says. “It only generates usable code if there are no collisions.”

Improving Surface Finish

As a finishing tool, the surface left by a conical barrel cutter is a vital part of its function, and CAM systems can help here as well.

One problem that barrel cutters can experience is a kind of “herringbone” pattern that results from use of its large radius. “Because the tool tilts away from adjoining surfaces, taking a large stepdown can create an edge with a zig-zag or herringbone look to it,” Zielinski says. To compensate for this, Hypermill creates a boundary path that traces along the edge to smooth it out.

Additionally, the Smooth Overlap function, originally developed for moldmaking, can disguise the edges caused by tool changes. If, for example, a user switches to a smaller cutting tool to reach corners and edges the larger tool could not reach, the tool path generated by the CAM software now overlaps between the area being finished and the area machined by the larger tool. The tool path also feathers slightly, further disguising any difference in the surface finish caused by the differences between the cutting tools.

Features like these make aggressive finishing more attainable, as the conical barrel cutter reduces finishing time while the CAM system cleans up the tool paths to ensure the proper finish. According to Open Mind, these features and others can reduce finishing time by 90% for the areas that benefit from barrel cutters. “Even though you can’t machine everything with conical barrel cutters, you’re saving 90% of your time on that 20% of your part,” Zielinski says.