By Adam Dimitroff, Applications Engineer
High efficiency milling (HEM) is an increasingly popular machining strategy that involves milling a material with a large axial and light radial depth of cut at a high speed and feed. As machine tool technology and programming software continue to advance, high efficiency milling is becoming increasingly prevalent in environments ranging from job shops to high production manufacturing facilities. HEM boasts advantages in both tool life and cycle time reduction, but it is important to understand how to fully take advantage of this strategy to maximize the performance of your milling process.
Tools designed for high efficiency milling have some common characteristics that allow for them to perform effectively at these high speed parameters. End mills for HEM typically have a long flute length, large core diameter, variable geometry, and multiple flutes. Flute length is typically chosen based on part requirements, while flute count is often overlooked, even though it can be crucial to maximizing cycle times and cost savings.
Although higher flute counts offer impressive feed rates, an increased flute count typically means the tool must be used with a lighter depth of cut. There are situations where this is highly advantageous – low rigidity setups or difficult to machine materials may favour lighter radial stepovers to maximize tool life. However, in relatively free machining materials, cutting forces and wear are typically relatively low to begin with, and a fine stepover may not be necessary. When deciding how many flutes is right for your job, the machinability of the material and rigidity of the setup should be considered. Tools should be chosen based on the material removal rate that they can achieve.
Material removal rate (MRR), often measured in cubic inches per minute, is the volumetric amount of material that a tool is removing at a time. For milling tools, this is a simple way of estimating productivity – a higher MRR typically means a reduced cycle time. When choosing tools for high efficiency milling, a larger radial stepover can often result in a higher MRR, even if the table feed is reduced. As mentioned earlier, material and setup limitations must be considered, but the ultimate goal should be to maximize MRR, rather than trying to achieve higher feed rates. It is also important to consider that in an HEM toolpath, a larger stepover will result in less air cut and rapid time, as there will be fewer number of total stepovers required. With a thorough understanding of the limitations of your setup and the material, finding the correct balance between flute count, stepover and feedrate will ultimately lead to cost savings and better performance in milling applications.