If you decide that CNC machining operation is the method you need to get your piece done, then you need to know that Depth of Cut (DOC) is one of the top 3 most important parameters affecting the quality of the machining product.
This article will help you understand what is meant by Depth of Cut in machining, why you need to control it, what the difference between chip thickness and depth of cut, and how to calculate it.
What Is Depth Of Cut In Machining?
In the machining process, depth of cut is simply how deep the cutting tool gets into a workpiece and cuts through it to create a chip. In an ideal cutting process, when the CNC cutting tool moves to the left with a certain depth inside the workpiece’s surface, it creates a chip. This depth is named Depth of Cut or DOC. If you need a similar and simple application you can see how chocolate curls or chocolate shavings are cut.
turning process showing feed and depth of cut
The depth of cut values is measured either in inches or millimeters and usually varies between 0.1 to 1 mm.
Why Do You Need To Control Depth Of Cut In Machining?
Depth of cut has a direct effect on the machining process, such as:
The heat rises at the tool tip;
Tool wear rate;
Strength of the processed product;
The quality of the machined surface.
For example, there is a tendency for the Built-up Edge (BUE) formation with annealed metals than cold-worked ones in the cutting process. BUE chip type consists of layers of chips accumulating at the tool tip. Therefore, if the depth of cut is too deep, uncontrolled BUE also adversely affects the surface finish.
depth of cut in machining
How Does Depth Of Cut Interact With Other Machining Factors?
Depth of cut is one of the independent factors affecting the machining process, which means it is controlled by the operator. However, the depth of the cut interacts with other factors and affects the resultant surface of the workpiece and its properties.
Depth of Cut and Cooling Fluid
With decreasing the depth of cut the chip curvature decreases and the chip becomes curly. In this case and when heat rises at the tool tip, you might think that adding cooling fluid will cool up the process.
However, adding CNC coolant fluid makes the chip even more curlier, decreases the contact between the tool and the chip, and concentrates the heat at the tool which significantly increases the tool wear. In this case, a chip breaker might be handy.
Depth of Cut, Rake Angle, and Cutting Speed
Another example can be found in machining thermoplastics. Thermoplastics generally have low thermal conductivity and low elastic modulus. This means that they are greatly affected by heat fluctuations at the tool tip in machining. Depth of cut, rake angle, and cutting speed all have to be adjusted relative to each other to avoid temperature rise and the formation of gummy and sticky chips at the tool tip.
It is also worth to be known that depth of cut is one of the top three parameters affecting tool life along with cutting speed and feed.
How To Calculate The Depth Of Cut?
The significance of having quantitative relationships among different variables is obvious when you need depth of cut calculation, why the tool’s temperature is getting high? why is the surface finish poor? Why does the cutting tool wear rapidly? And many more.
In order to calculate the depth of cut, you need to specify the following parameters:
What is the machining process (Milling, Turning, etc.)
Workpiece material
Tool tip properties
Machine capabilities
Required surface finish and tolerance
Depth of Cut in Turning Process
In CNC turning, the workpiece rotates while the tool removes a layer of material as it moves along the length of the workpiece. The depth of cut can be the same as the feed or feed rate which is simply the distance the tool travels along the workpiece at each revolution over time, and it has the unit of mm/min.
Therefore, depth of cut can be simply defined by the thickness of the material removed and can be calculated from:
turning depth of cut calculation formula
depth of cut schematic of the turning process
Depth of Cut in Milling Process
In the CNC milling process, the tool rotates while the workpiece is steady. The depth of cut is simply how deep the tool cuts in the workpiece in one turn. Commonly, the cutting depth is 4 times the diameter of the cutting tool for large diameters above 20mm and 10 times the diameter size for smaller tool diameters.
depth of cut in milling process
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