Milling
Milling cutters are generally either shank-mounted or arbor-mounted tools with one or more cutting edges. In addition to indexable-insert cutter bodies, shank-mounted cutters are also available in high-speed steel and solid carbide. The use of high-speed-steel end mills has steadily declined in recent years, and they are now used mainly on manual milling machines. The performance and price of solid-carbide end mills, combined with their productivity and the machining methods enabled by modern machine tools, have established them as the most common type of shank-mounted milling cutter. A wide range of shank-mounted cutters is available for different applications, including conventional straight end mills for shoulder and slot milling, long-cutting end mills with multiple cutting edges for dynamic milling, end mills with a large radius on the face for high-feed milling, radius or segment-radius cutters (barrel cutters) for 3D surface machining, and various corner-rounding, chamfering, T-slot, and dovetail cutters. Indexable milling cutters consist of steel cutter bodies to which replaceable indexable inserts are attached with screws. Indexable cutters are cost-effective, and their replaceable inserts make tool maintenance easy. Different insert geometries, grades, and coatings can also be used in the cutter bodies for machining different materials. Indexable milling cutters are available in both shank-mounted and arbor-mounted versions, and they are generally larger than solid-carbide end mills. Indexable milling cutters include face mills, form cutters, shoulder mills, high-feed cutters, shell mills, slotting and slitting cutters, and more.
Dynamic milling is a machining method developed jointly by tool manufacturers and CAM software developers. Dynamic machining methods were originally developed for roughing difficult-to-cut materials such as hardened steels and heat-resistant superalloys, but they are also well suited to milling other materials. The method makes use of the tool’s full cutting length, allowing wear to be distributed evenly along the cutting edge and extending tool life.
The basic principle of dynamic milling is to use a large axial depth of cut (ap) and a small radial depth of cut (ae) compared with conventional machining methods. Dynamic milling avoids cutting across the full width of the tool and straight-line movements wherever possible; material is removed using smooth, flowing toolpaths.
Dynamic machining is generally always performed using climb milling. After completing a cut, the tool returns to the beginning of the next cut at a high feed rate (a so-called non-cutting feed). The approach and exit movements to and from the toolpath are always performed along a curved path (approximately 10% of Dc). In dynamic milling, the cutter diameter (Dc) should be no more than 70% of the width of the area being machined. In high-speed dynamic milling, the radial engagement ae is typically approximately 5–20% of Dc, depending on the tool and the material being machined.
Common cutting tools can be used for dynamic milling, but the greatest benefit is achieved with long-cutting solid-carbide end mills specifically designed for dynamic milling and equipped with multiple cutting edges and chipbreaker grooves. Examples include Walter Tools’ MD133 series of end mills, available with cutting lengths of 3xD, 4xD, and 5xD. In addition to the tool being used, the radial engagement in dynamic toolpaths is affected by the machining depth, the material being machined, the machine tool, the machine tool’s spindle taper, the tool holder, and the workpiece fixturing. To ensure reliable machining, always use the tool manufacturer’s cutting-data calculators, which take the above factors into account. One example of such a calculator is Walter GPS.
