How to optimize cutting paths and extend tool life

Speaking of the cutting path, let us first analyze the cutting process of the milling cutter cutting edge in detail: Milling is a cyclic process in which the cutting edge continuously cuts in and out of the workpiece. With universal (radial) infeed, the resulting chip thickness is constantly changing (plunging/axial infeed creates a constant chip thickness). No matter how the position of the milling cutter and the workpiece and the feed direction (climb milling/up milling) change, the cutting action of the cutting edge can be divided into three cutting areas, namely "cut into the workpiece", "circular cutting" and "cut out" artifact".

For milling, these three cutting areas exist at the same time, but their impact on the cutting action is very different, which is directly related to the life of the insert:

1) Cut into the workpiece

This is the area where the cutting action is least affected among the three cutting areas. Carbide inserts handle the effects of the accompanying compressive stress well when plunging into the workpiece, be it thick or thin chips.

2) Arc cutting

For full slot milling, the maximum arc of the contact arc is 180°. For finish copy milling, the arc of contact can be very short. The longer the arc of contact, the more heat is transferred to the cutting edge. Therefore, depending on the cutting width, the requirements for the blade grade will be completely different.

Long Contact Arc - CVD coated grades provide the best thermal barrier.

Short arc of contact - Chips are generally thin, and sharper cutting edges on PVD-coated grades generate less heat and cutting pressure.

3) Cut out the workpiece

With carbide inserts, if the insert cuts out of the workpiece with thicker chips, this can lead to a dramatic reduction in tool life. The resulting chip lacks adequate support at the final point of the cut, which will bend the chip rather than continue to be cut. Because of the change of direction, the cutting force (compressive stress becomes tensile stress) acting on the carbide cutting edge is easy to break the cutting edge.

The cutting area that has the greatest impact on tool life is cutting out the workpiece. In order to improve tool life and optimize the machining process, the chip state when cutting out the workpiece is the focus of our attention.

Through the study of the chip thickness of the cut workpiece, we have concluded a golden rule in milling:

The machining process must ensure that the insert cuts out the workpiece with the thinnest chips.

With this golden rule in hand, we can do a lot of optimization work in terms of cutting paths. Climb and up-cut milling is one example. Climb milling results in better tool life when the workpiece is cut with zero chip thickness, which fully complies with the golden rule.

Let's take a look at the influence of linear and arc cutting on tool life when the milling cutter cuts into the workpiece.

If we program so that the tool cuts straight into the workpiece, thick chips will continue to be generated when the blade cuts away from the workpiece until the tool completely cuts into the workpiece. reduce the feed.

We now recommend an optimized machining method that guarantees the best possible feed rate during tool entry:

Arc cut in clockwise.

We can see that the circular plunge of the milling cutter makes the chip thickness always zero when the insert cuts out of the workpiece, so that higher feed and longer tool life can be obtained.

At the same time, it should be noted that counterclockwise cutting will not only solve the problem of excessively thick chips, but will make the situation worse.

Four experiments compared the effects of straight and circular incisions on tool life when cutting heat-resistant alloys and stainless steels.

In addition to arc cutting into the workpiece, there is another milling method that is also recommended, that is, oblique cutting. This method can not only ensure that the blade obtains thin chips when cutting out the workpiece, but also meet the small cutting width when cutting into the workpiece, so as to reduce the tendency of vibration and improve the tool life.

Optimizing the cutting process and prolonging the tool life is a major topic in the machining industry. Making some small changes in the cutting path can also give us unexpected results.