The fastest way to mill away a lot of material may be to attack it head on with a move in the Z direction. Compared to conventional milling tool paths in the X-Y plane, the increased rigidity of a move in Z can let the tool cut through a larger cross section of material for the same feed rate, resulting in faster metal removal. Many shops now rough out large volumes of material though overlapping plunges with a milling tool that cuts on its face.
One reason many shops have adopted this approach only recently is that there are now many more tools available for this sort of cutting. Three such tools are described here. All have very different designs. One significant way they differ is in the percentage of the face diameter capable of engaging the material at once. This characteristic alone says nothing about the productivity of the tool, because lighter cuts might be mated with higher feed rates to keep metal removal rate high. Instead, the following examples of Z-axis milling cutters represent a range of designs suited to a range of plunge milling applications.
The Axial Feed Milling System from Walter-Valenite consists of shell mills and end mills ranging from 1.5 to 6 inches in diameter, all of which cut on the outer 0.40 inch of their face. The tools are not designed to plunge into a wide cross-section of material, but they are well-suited to machining along an edge, or along the walls of a pre-existing pocket or cavity. Different tools in this line employ 2 to 8 identical inserts around the periphery.
The Rainbow Cutter design from Tungaloy (Itasca, Illinois) is capable of cutting on nearly 40 percent of its face diameter. The cutter features the equivalent of exhaust ports in the face of the tool that carry chips away by channeling them through the cutter body. The name of the design comes from an arc-shaped configuration of three different cutting inserts along the tool’s face. The tool also has side-cutting inserts around its periphery that allow it to cut in X-Y. Tool diameters available include 100, 125 and 135 mm.
The Plunger line of milling tools from Iscar (Arlington, Texas) includes Z-axis milling tools that do plunge fully into solid material, cutting along 100 percent of their diameter. This tool design represents a cross between a milling cutter and a drill.
Other tools in the Plunger line feature a central hole that improves performance, the company says. When using one of these tools, the pattern of step-over moves between plunges is set to ensure that the remaining center material from the previous cut is machined away with each new plunge.