In order to turn an ordinary workpiece into a suitable part for the mechanism, use turning, milling, grinding and other machines. If milling is necessary for the manufacture of more complex parts, for example, gears, cutting splines, then turning are used to create simpler parts and give them the necessary shape (cone, cylinder, sphere). The cutting conditions during turning are very important, because, for example, for brittle metal it is necessary to use a lower spindle speed than for a strong one.
Features of turning
In order to grind a specific part on a lathe, as a rule, use cutters. They come in a wide variety of modifications and are classified by type of processing, direction of feed and shape of the head. In addition, the cutters are made of various materials: alloy steel, carbon, tool, high-speed, tungsten, hard alloy.
The choice of one or another depends on the material of the workpiece, its shape and the method of turning. The cutting modes during turning necessarily take into account all these nuances. When turning, the workpiece is fixed in the spindle; it performs the main rotational movements. A tool for processing is installed in the support, and feed movements are made directly by him. Depending on the machine used, both very small and large parts can be machined.
Essential elements
What elements of cutting conditions during turning can be used? Despite the fact that turning is not always a very easy operation, its main elements are speed, feed, depth, width and thickness. All these indicators depend primarily on the material of the workpiece and size. For very small parts, for example, the cutting speed is chosen the lowest, since even 0.05 millimeters, which were accidentally cut, can lead to the marriage of the entire part.
In addition, very important indicators on which the choice of cutting conditions during turning depends on the stages at which it is performed. Consider the basic elements and stages of metal cutting in more detail.
Roughing, semi-finishing and finishing
Turning a workpiece into a necessary part is a complex and time-consuming process. It is divided into certain stages: roughing, semi-finishing and finishing. If the part is simple, then the intermediate (semi-final) stage, as a rule, is not taken into account. At the first stage (draft), the details are given the necessary shape and approximate dimensions. At the same time, allowances are left for the subsequent stages. For example, a blank is given: D = 70 mm and L = 115 mm. It is necessary to carve out a part from it, the first dimension of which will be D 1 = 65 mm, L 1 = 80 mm, and the second - D 2 = 40 mm, L 2 = 20 mm.
Roughing will be as follows:
- Trim the end by 14 mm.
- Cut the diameter along the entire length of 66 mm
- Cut the second diameter D 2 = 41 mm for a length of 20 mm.
At this stage, we see that the part was not completely processed, but as close as possible to its shape and size. And the allowance for the total length and for each of the diameters was 1 mm.
Finishing this part will be as follows:
- Finish trimming the end with the necessary roughness.
- Cut along a length of 80 mm to a diameter of 65 mm.
- Finish turning along a length of 20 mm to a diameter of 40 mm.
As we can see, finishing requires maximum accuracy, for this reason the cutting speed in it will be less.
Where to start the calculation
In order to calculate the cutting mode, first of all, it is necessary to choose the material of the cutter. It will depend on the material of the workpiece, the type and stage of processing. In addition, cutters in which the cutting part is removable are considered more practical. In other words, it is only necessary to select the material of the cutting edge and fix it into the cutting tool. The most profitable mode is the one in which the cost of the manufactured part will be the smallest. Accordingly, if you select the wrong cutting tool, it is likely to break, and this will cause losses. So how do you determine the necessary tool and cutting conditions during turning? The table below will help you choose the best cutter.
The thickness of the cut layer
As mentioned earlier, each of the processing steps requires a particular accuracy. These indicators are very important precisely when calculating the thickness of the cut layer. The cutting modes during turning guarantee the selection of the most optimal values ββfor turning parts. If they are neglected and the calculation is not performed, then both the cutting tool and the part itself can be broken.
So, first of all, you need to choose the thickness of the cut layer. When the cutter passes through the metal, it cuts off a certain part of it. Thickness or depth of cut (t) is the distance that the cutter will take in one pass. It is important to consider that for each subsequent processing it is necessary to calculate the cutting mode. For example, you should perform external turning of part D = 33.5 mm for the diameter D 1 = 30.2 mm and the internal boring of the hole d = 3.2 mm for d 2 = 2 mm.
For each of the operations, the calculation of cutting conditions during turning will be individual. In order to calculate the cutting depth, it is necessary to subtract the diameter of the workpiece from the diameter after processing and divide it into two. In our example, we get:
t = (33.5 - 30.2) / 2 = 1.65 mm
If the diameters have too much difference, for example 40 mm, then, as a rule, it must be divided by 2, and the resulting number will be the number of passes, and the depth will correspond to two millimeters. For rough turning, you can select a cutting depth of 1 to 3 mm, and for fine turning, from 0.5 to 1 mm. If the cutting of the end surface is performed, then the thickness of the material to be removed will be the depth of cut.
Feed rate assignment
It is impossible to imagine the calculation of cutting conditions during turning without the amount of movement of the cutting tool in one revolution of the part β the feed (S). Her choice depends on the required roughness and the degree of accuracy of the workpiece, if it is finishing. When roughing, it is permissible to use the maximum feed, based on the strength of the material and the rigidity of its installation. You can select the required feed using the table below.
After S has been selected, it must be specified in the machine passport.
Cutting speed
Very important values ββthat affect the cutting conditions during turning are the cutting speed (v) and spindle speed (n). In order to calculate the first value, use the formula:
V = (Ο x D x n) / 1000,
where Ο is the Pi number equal to 3.12;
D is the maximum diameter of the part;
n is the spindle speed.
If the last value remains unchanged, then the rotation speed will be greater, the larger the diameter of the workpiece. This formula is suitable if the spindle speed is known , otherwise you must use the formula:
v = (C v x K v ) / (T m x t x S),
where t and S are the calculated cutting depth and feed, and C v , K v , T are coefficients depending on the mechanical properties and structure of the material. Their values ββcan be taken in the tables of cutting conditions.
Cutting mode calculator
Who can help to calculate the cutting conditions during turning? Online programs on many Internet resources cope with this task no worse than a person.
It is possible to use the utility on both a desktop computer and a telephone. They are very comfortable and do not require special skills. It is necessary to enter the required values ββin the fields: feed, cutting depth, material of the workpiece and cutting tool, as well as all necessary dimensions. This will allow you to get a comprehensive and quick calculation of all the necessary data.