Today, as more shops are equipped with high-speed CNC machining capability and sophisticated CAM programs, high-feed milling (HFM) is becoming the methodology of choice to remove as much material as possible in the shortest time. Basically, HFM is a roughing method developed for high metal removal rates to increase productivity and save machining time.

HFM uses a smaller depth-of-cut (usually no more than 2 mm), producing a thinner chip that carries the heat away from the cutting edge. It also runs a high feed per tooth: up to five times higher feed per tooth than conventional milling is common. This approach reduces heat generation to extend tool life and provides a higher metal removal rate than normal—over 1,000 cm per minute or up to 200 to 300 percent faster than traditional milling.
The reason for this is that the HFM method takes advantage of small setting angles (45º or less).

This produces minimal radial- and maximum-axial cutting forces. Similar to plunging, the cutting forces are directed at the machine spindle in the axial direction, which reduces the risk for vibrations and stabilizes machining. This, in turn, allows for the higher cutting parameters even when machining with a large overhang. And, unlike plunge milling, in HFM the tool stays constantly engaged.

Another HFM time-saver is the number of operations. Since high-feed roughing with its small depths-of-cut generates a near-net shape close to the final requested form, semi-finishing operations can often be eliminated and NC programming is thus simplified. On top of this, the HFM process does not require increased rotational speed from the machine.

To accomplish a HFM strategy, users need to evaluate the overall machining system. Number one is the need for high-speed CNC machining control, high spindle accuracy and thermal stability against spindle growth. Secondly, is the requirement for a CAM software program that can handle toolpath smoothening strategies—such as corner rounding and helical cutting paths. Smooth toolpaths enable a gentle slicing of the workpiece through light engagement conditions while helical cutter movements reduce the cutting impact, energy consumption and cutting forces.

Additionally, the inserts used in HFM are critical. They are thick and have a big radius and strong geometry at the cutting zone. This means you can work at high speed and still have reliable and safe machining. For most HFM operations, trigon-style inserts are preferred over round. The reason is that the main cutting forces are located at the bottom of the cutting edge. Of course, there are situations when you use square inserts, but with a small setting angle.

Typically, this might be required in high-feed heavy roughing applications using powerful machines in stable conditions or in horizontal milling operations, making chip evacuation more effective. But in vertical operations or smaller machines with high rpm, trigon-style inserts are a safe choice, offering excellent chip evacuation.