Cutting mode for milling: calculation, definition, specifications

Milling is far from the simplest operation of processing metals and other materials, which is not always known in detail to the average person. The matter is that for this process a special device is needed, which is called a milling cutter - it can be found at many enterprises, factories, factories. How does this process happen? In this case, a cutting tool and a workpiece are involved. The cutting tool is the milling cutter itself - it performs rotational movements, unlike the workpiece itself, which with the machine performs translational movements towards the milling cutter. The result is a type of processing that would be difficult to repeat with the help of any other tool. However, this article will not cover surface information - this material is intended for those who are already more or less familiar with the milling process. The main and the main theme here is the cutting mode, that is, the calculation and determination of how the milling cutter should function and which nozzle for it should be used for specific types of metal of different hardness will be made here. To make it easier for you to understand the data that will be provided later, you should immediately know what concepts will be used here.

All you need to know

So, in each paragraph it will be indicated which material is considered, as well as its hardness according to the Brinnel method - the most well known and widespread of all methods for determining the hardness of bodies. They are measured in HB, that is, units of hardness of Brinnel. Next, the cutting speed will be determined , which is indicated in meters per minute (m / min). Here you should pay special attention to the fact that it is not the cutter's turns, but it is an absolutely different parameter. This parameter will be considered in several examples - if the material that is machined by the cutter has no additional coating, and if the cutter has different types of TI-NAMITE coating. And, of course, another very important parameter of milling will be described - a feed to the tooth. For people far from this sphere, this parameter may seem quite unusual, but if you carefully study its details, everything will become quite simple. So, this parameter is measured in millimeters per tooth and determines how many millimeters the workpiece moves while the milling cutter rotates by one tooth. From this feed, you can calculate and others - for example, turnaround and minute, but it is the feed to the tooth is the key factor. And it will also depend on the diameter of the tool used. Well, all the basic data you got - now it's time to find out which cutting mode to use for milling in a particular case.

Steel of general application

So, the first material that is discussed in this article is a general application. What cutting mode to use for such material? First of all, you need to determine the hardness of the material. If the hardness of steel is less than 150 Brinnel units, then it is necessary to set the speed from 150 to 210 meters per minute, depending on the coating. 150, respectively, in the total absence of coating, and 210 - in the presence of the most effective coating TI-NAMITE-A. As for the feed to the tooth, everything here depends, as already said, on the diameter of the tool. If its diameter is less than three millimeters, the feed per tooth will be from 0.012 to 0.018 millimeters, with an increase in diameter to 5 mm, the feedrate will increase to 0.024 mm, if the diameter increases to 9 mm, then the feed increases to 0.050 mm, with a diameter of up to 14 Mm feed can rise to 0.080 mm, well, and with a maximum diameter of 25 millimeters, the feed per tooth will be 0.18 mm. This data also allows you to choose the correct cutting mode. But do not forget that there are also more solid types of steel for general use. With a hardness of less than 190 Brinnel units, the speed should be from 120 to 165 meters per minute, and with a hardness of less than 240 Brinnel units, from 90 to 125 meters per minute. Naturally, the supply to the tooth changes. It becomes smaller and in the first case can be from 0.01 to 0.1 millimeter per tooth, while in the second case it is from 0.008 to 0.08 millimeter per tooth. Naturally, this is not the only material used for milling, so it's worth paying attention to other metals.

Cemented steels

The cutting conditions for the treatment of cemented steels will depend on the hardness of the material. If it is less than 235 Brinnel units, then the cutting speed will be corresponding - from 100 to 140 meters per minute. With a hardness of less than 285НВ the indicator falls - from 80 to 110 meters per minute. But do not forget about feeding on the tooth. In principle, you can not say much about it, because it does not differ from what you already saw in the previous paragraph. In the first case, it will have the same intervals as when processing a steel of general application with hardness less than 190NV, and in the second - the same as for processing steels of general use with hardness less than 240NV. But it can not be said that the feed to the tooth will be identical, because to the maximum diameter of the tool in the first case the feedrate is not 0.1, as in the previous example, but 0.15. That is why the calculation of cutting modes is such a difficult task that it is best to comply with all norms and in accordance with strict regulations.

Nitrided steels

Calculation of cutting modes for the processing of nitrided steels is no different from previous cases - only in this case the materials are slightly harder than the previous ones, so you should not be surprised that the cutting speed here will be from 90 to 125 meters per minute with less hard steel And from 70 to 95 meters per minute with a harder material. As for filing on the tooth, in the first case here is quite a standard take-off step - from 0.008 to 0.08 millimeters, but if the metal will have a large number of Brinnel hardness units, this will mean that its feed will decrease, and noticeably. With a minimum tool diameter, it will be 0.006 millimeters, and at the maximum - 0.06 millimeters. At the moment, this is the lowest feed per tooth considered in this article. Calculation of cutting modes for this information is usually done using the standard formula, which will be discussed at the end of the article.

Mild steel

Mild steel is very common, and most importantly - there are several different levels of their hardness. And, naturally, each of them will have its own cutting speed. For example, the first two types of steel have the same index, if the cutter does not have a coating - 80 meters per minute. But with the maximum coverage of the first type, the speed increases to 110 meters per second, and in the second - only up to 85 meters per second. But there are two more types, the first with a hardness of less than 340NV, and the second - less than 385NV. Accordingly, the first parameter of cutting will be from 50 to 70 m / min, and the second - from 35 to 50 m / min. Compared to the types that you saw earlier, it's a pretty low speed. Accordingly, these types of steel and feed to the tooth is not too high - separately it is worth highlighting the last hardness steel, which with a minimum diameter of the tool has an incredibly low feed, only 0.005 millimeters. Immediately it is worth noting that here we consider milling, and not cutting modes for turning. As already mentioned above, the formula is used for calculation, with which you will be familiar with above. The cutting modes for turning are calculated slightly according to a different formula, so you do not have to try to apply one calculation to all types of work.

Tool steels

Instrumental steels are divided into even more species by hardness than medium-carbon ones, so the cutting regimes for milling tool steel can be numerous. If you briefly tell about this steel, that is, five types of hardness: less than 230NV, less than 285NV, less than 340NV, less than 395NV and more than 395NV. Each of them has its own cutting speed: from 90 to 125 m / min, from 70 to 95 m / min, from 60 to 85 m / min, from 45 to 65 m / min and from 30 to 40 m / min, respectively. Strictly speaking, the name of these data will be already halfway to replenishment of all missing gaps in the calculation of the formula by which the cutting modes for milling are determined. In order for the formula to replace all variables with numbers, you also need to know the diameter of the tool (and the data received from it for feeding to the tooth).

How to choose a mode?

The choice of cutting modes is quite simple - each cutter has a switch that allows you to control the speed of the cutting tool. With this small switch you can set an approximate value of rpm, and then your machine will work at this level. Strictly speaking, this is the cutting regime, but such a simple process has a large number of calculations, which will be discussed below. The point is that the determination of the rotational speed of the cutter's cutting tool should be as accurate as possible, and rarely when you have enough time and material to pick up the metal cutting regimes at random. That is why there is a theory that must be used before practical application.

Cutting speed formula

It is very important to comply with the standards of cutting modes, since it's not just that you will spend a lot of time, and even worse, there is a lot of material to choose the necessary mode blindly. This can also be unsafe. Therefore, it is best to be guided by theoretical knowledge in the first place. So, now you will learn the formula by which the mode for a particular metal is calculated. How it can be used in practice will be described below. The formula itself assumes that the speed expressed in meters per minute is multiplied by the conversion factor 1000, and the result is divided by the product of the "pi" number multiplied by the diameter of the mill. This is all the cutting mode elements you need to calculate the rotational speed of the cutter.

Simplified Formula

It makes no sense to carry out two multiplications when you know that the number "pi" is a digit without any variables. Initially, it is common to shorten 1000 and 3.14 to get 318. 318 is multiplied by the speed, and then the result is divided by the diameter of the cutter. That's all, this formula is already much simpler than the previous one, and it is with its help that the definition of the cutting mode is most often made.

Calculation

In such material it is impossible to do without an example. Well, for example, you can take general-purpose steel with a hardness of less than 150NV and a cutter with a TI-NAMITE coating and a diameter of 10 millimeters. So, you first need to check the data that was described in the article above - at such rates the cutting speed will be 175 m / min, so you need to multiply 318 by 175, it's 55650. Now it needs to be divided by the diameter of the cutter, that is 10 - it turns out 5565. This is what is the desired value. Now you need to put it on your machine, and if it is impossible to set such a value, then it is recommended to take a little less.

Catalog of foreign instruments

If you use a domestic cutter, then, most likely, you can easily find the necessary data for determining the cutting regime. If you have a foreign sample, you may have some problems. That's why when buying a foreign milling machine it is extremely necessary to ask for a catalog with all the necessary explanations that you can then use as a theoretical basis when working with the machine.

Special graphics

The real salvation is the graphs that are compiled for a faster and more convenient determination of the cutting regime. What is such a schedule? This is a set of straight lines of different colors that are between two axes - one of them shows the speed, that is, the amount that you know, since you know what material you are handling, and the second is the number of revolutions per minute your milling cutter , That is, in simple terms, the mode of its operation. Why lines of different colors? If you have not forgotten, then the number of turns of the cutter per minute can not be calculated only by the cutting speed - you also need the diameter of the tool, and each color is responsible for its diameter.

How to use the schedule?

All that is required of you is to find the diameter of your instrument in the table and select the straight line of the desired color on the chart. Then you need to determine the speed and draw a straight line from the y axis, that is, the axis on which the values of this parameter are indicated. From the point of intersection of your line with the straight line of your chosen color, you must draw a straight line to the x-axis in order to know the exact number of revolutions per minute.