Optimize cutting paths and extend tool life
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Milling is a very flexible machining method that can process parts of almost any shape. However, processing flexibility also adds more variables to the cutting process, which makes optimizing the cutting process more challenging. From this issue, we will continue to share with the readers through the “Sandvik Coromant Application Center†platform to optimize the milling processing methods and processing strategies summarized by Sandvik Coromant through years of experience, in order to improve production efficiency for the majority of users. Reduce production costs and help.
Sandvik Coromant sales engineers not only provide excellent products, but also pass on the correct and optimized processing methods to the user.
To lift the cutting path, let us first analyze in detail the cutting process of the cutting edge of the milling cutter: milling is the cyclic process in which the cutting edge continuously cuts in and cuts out the workpiece. When the milling cutter uses a universal (radial) feed, the resulting chip thickness is constantly changing (prong milling / axial feed to form a constant chip thickness). Regardless of the position of the milling cutter and the workpiece and the change of the feed direction (longing/up milling), the cutting action of the cutting edge can be divided into three cutting areas, namely “cutting into the workpieceâ€, “arc cutting†and “cutting outâ€. Workpiece".
For milling, these three cutting areas are present at the same time, but their effect on the cutting effect is very different, which is directly related to the life of the blade:
1) Cutting into the workpiece This is the area where the cutting effect is the least affected in the three cutting areas. When cutting into the workpiece, whether it is thick swarf or thin swarf, the carbide insert can handle the effects of the accompanying compressive stress.
2) Arc cutting When the full-groove milling, the maximum arc of the contact arc is 180°. For finishing profiling, the contact arc is very short. The longer the contact arc, the more heat is transferred to the cutting edge. Therefore, depending on the width of the cut, the requirements for the blade grades will be completely different.
Long contact arcs – CVD coated grades provide the best thermal barrier.
Short Contact Arcs - Chips are usually very thin, and sharper cutting edges on PVD coated grades generate less heat and cutting pressure.
3) Cutting out the workpiece When using a cemented carbide insert, if the insert is cut out of the workpiece, the chip will be thicker, which will lead to a sharp decrease in tool life. The formed chips lack sufficient support at the final point of the cut, which will bend the chips rather than continue to be cut. Because of the change in direction, the cutting force acting on the edge of the cemented carbide (compressive stress becomes tensile stress) is liable to break the cutting edge.
The cutting area that has the greatest impact on tool life is the cut out of 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.
By studying the chip thickness of the cut workpiece, we have summarized a golden rule in milling:
The machining process must ensure that the blades are the thinnest when cutting the workpiece.
With this golden rule in hand, we can do a lot of optimization work on the cutting path. Climb milling and up-cut milling are examples of this. When the workpiece is cut and cut, the chip thickness is zero, which fully satisfies the golden rule, so the smoothing will bring better tool life.
Let us look at the effect of the straight cut and the arc cut on the tool life when the milling cutter cuts into the workpiece.
If we let the tool cut straight into the workpiece during programming, the thick cutting chips will continue to be generated when the cutting edge is cut off from the workpiece until the tool is completely cut into the workpiece. The thick cutting chips when the cutting blade is cut out will cause the tool life to be reduced or even completely damaged, so it has to be cut in. Reduce feeds.
Now we recommend an optimized machining method to ensure the best feed rate during tool cutting:
Cut in a clockwise direction.
We can see that the cutting edge of the milling cutter makes the chip thickness always zero when the blade is cut out of the workpiece, which results in higher feed and longer tool life.
At the same time, it should be noted that counterclockwise cutting can not only solve the problem of excessive chipping, but will make the situation more serious.
Four experiments compared the effects of linear incision and circular incision on tool life when cutting heat resistant alloys and stainless steel materials.
In addition to the circular cut into the workpiece, there is another milling method that is also recommended, that is, oblique line cut. This method not only ensures that the blade obtains thin chips when cutting out the workpiece, but also meets the small cutting width when cutting the workpiece to reduce the vibration tendency and improve the tool life.
Optimizing the cutting process and extending tool life is a major issue in the mechanical processing industry. Making small changes in the cutting path can also bring us unexpected results.