Finishing tapered walls and deep walls is typically done using a bull-nose style cutting tool combined with a profile milling tool path in the X and Y axis. With this approach, the scallop height on the finished part is determined by the stepdown in the Z-axis that is used in the program combined with the size of the corner radius of the cutting tool. Because the corner radius is generally small, the stepdown in the Z-axis must also be small to achieve the targeted scallop height.
Plunge finishing provides a dramatically faster approach to this type of application by using a Z-axis cutting motion. By cutting while traveling up and down the Z-axis, the scallop height is now determined by the diameter of the cutting tool, rather than by the size of the corner radius. This allows for much larger stepovers, shortening cycle time by 30-50% while maintaining surface finish to the same specifications.
An additional benefit to plunge finishing is the creation of axial cutting forces (into the machine spindle) during semi-finishing/light-roughing vs the radial cutting forces generated when profile milling. For clearing out corners inside a workpiece, this is especially helpful in reducing chatter and vibration that is common with long length-to-diameter ratios.
While plunge finishing can be executed in both directions of travel (up and down), plunge semi-finishing/light-roughing should be done in the down direction only.
Programming plunge finishing is quite easy – it simply requires directing the CAM software to execute a vertical tool path rather than a conventional horizontal tool path along a part profile. In this training video, Mastercam is used and the tool path is called "Flowline" – a tool path generator that allows controlling which direction the tool travels along the workpiece profile. Clicking on the "geometry" link in the Mastercam menu allows choosing this aspect, as well as the starting point on the profile.
With choosing a vertical tool path, the scallop height specified will now be dictated by the diameter of the cutting tool, rather than by the size of the corner radius, creating a much larger stepover (and consequently fewer passes) to significantly shorten cycle time.