Cutting modes for turning: description, selection and technology

In order to turn 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, slitting, the lathes are used to create simpler parts and give them the necessary shape (cone, cylinder, sphere). The cutting modes for turning are very important, because, for example, for a brittle metal, it is necessary to use a lower spindle speed than for a durable one.

Features of turning

In order to carve a particular part on a lathe, as a rule, cutters are used. They come in a variety of modifications and are classified according to the type of processing, the direction of feed and the shape of the head. In addition, the tools are made of various materials: alloy steel, carbon, tool, high-speed, tungsten, hard alloy.

The choice of one or the other depends on the material of the workpiece, its shape and grinding method. The cutting modes for turning require these nuances. When turning the workpiece is fixed in the spindle, it performs the main rotational movements. The tool is installed in the support, and the feed movements are made directly to them. Depending on the machine used, it is possible to process both very small parts and large ones.

Essential elements

What elements of cutting modes can be used during turning ? Despite the fact that turning is not always a very easy operation, its main elements are speed, pitch, depth, width and thickness. All these indicators depend primarily on the material of the workpiece and the size. For very small parts, for example, the cutting speed is chosen the smallest, because even 0.05 millimeters, which accidentally cut off, can lead to the marriage of the entire part.

In addition, very important indicators on which the choice of cutting modes depends on the turning process are the stages on which it is produced. Let's consider the basic elements and stages of metal cutting in more details.

Roughing, semi-finishing and finishing

Turning the workpiece into the necessary detail 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, they leave the allowances for subsequent stages. For example, the workpiece is given: D = 70 mm and L = 115 mm. From it, you need to cut out the part whose first dimension is D ₁ = 65 mm, L ₁ = 80 mm, and the second - D ₂ = 40 mm, L ₂ = 20 mm.

Roughing will be as follows:

1. Cut the butt to 14 mm.
2. Protrude the diameter over the entire length by 66 mm
3. Protect 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.

The finishing of this part will be as follows:

1. Finish the butt end with the required roughness.
2. Protect along the length of 80 mm in diameter 65 mm.
3. Perform finishing turning along a length of 20 mm in diameter of 40 mm.

As we see, finishing requires maximum accuracy, for this reason, and the cutting speed in it will be less.

How to start the calculation

In order to calculate the cutting mode, the cutting tool material must first be selected. It will depend on the material of the workpiece, the type and the processing step. In addition, more practical are cutters, in which the cutting part is removable. In other words, it is necessary to select only the material of the cutting edge and fix it in the cutting tool. The most profitable mode is the one at which the cost of the manufactured part will be the least. Accordingly, if you choose the wrong cutting tool, it is likely to break, and this will bring losses. So how do you determine the necessary tools and cutting modes for turning? The table below will help you select the optimal cutter.

Thickness of cut layer

As already mentioned earlier, each of the processing stages requires one or another accuracy. These indicators are very important when calculating the thickness of the cut layer. The cutting modes during turning enable the selection of the most optimal values for the grinding of parts. If they are neglected and do not perform the calculation, then you can break both the cutting tool and the part itself.

So, first of all, you need to choose the thickness of the cut layer. When the cutter passes through the metal, it cuts a certain part of it. Thickness or depth of cutting (t) is the distance that the cutter will take in one pass. It is important to take into account that for each subsequent processing it is necessary to perform the calculation of the cutting regime. For example, an external turning of the workpiece D = 33.5 mm per diameter D ₁ = 30.2 mm and internal boring of the hole d = 3.2 mm at d ₂ = 2 mm.

For each of the operations, the calculation of cutting modes for turning is individual. In order to calculate the depth of cut, it is necessary to subtract the diameter of the workpiece from the diameter after processing and divide by two. On our example it turns out:

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. When roughing, you can choose the depth of cut from 1 to 3 mm, and for finishing - from 0,5 to 1 mm. If the end face is trimmed, the thickness of the material to be removed will be the depth of cut.

Assignment of feed amount

Calculation of cutting modes during turning is impossible to imagine without the amount of displacement of the cutting tool for one revolution of the detail-feed (S). Its choice depends on the required roughness and the degree of accuracy of the workpiece, if this is a finishing treatment. With roughing, it is permissible to use the maximum feed rate, based on the strength of the material and the rigidity of its installation. You can select the required feedrate using the table below.

After S was chosen, it must be specified in the machine's passport.

Cutting speed

Very important values affecting the cutting modes during turning are the cutting speed (v) and the spindle speed (n). In order to calculate the first value, use the formula:

V = (π × D × n) / 1000,

Where π is the Pi number equal to 3,12;

D is the maximum diameter of the part;

N is the speed of the spindle.

If the last value remains unchanged, then the rotation speed will be the greater, the larger the diameter of the workpiece. This formula is suitable if the rotational speed of the spindle is known, otherwise it is necessary to use the formula:

V = (C _v x K _v ) / (T _m x t x S),

Where t and S are the calculated depth of cut and feedrate, and C _v , K _v , T are coefficients that depend on the mechanical properties and structure of the material. Their values can be taken in the tables of cutting modes.

Calculator of cutting modes

Who can help to calculate the cutting modes for turning? Online programs on many Internet resources cope with this task is not worse than a person.

It is possible to use utilities on both the desktop computer and the phone. They are very comfortable and do not require special skills. In the fields you need to enter the required values: feed, depth of cut, material of the workpiece and cutting tool, as well as all necessary dimensions. This will provide a comprehensive and quick calculation of all the necessary data.