Calculation of cutting conditions is the most important stage in the manufacture of any part. It is very important that it be rational. This is due to the fact that for various mechanical operations it is necessary to individually select the cutting speed, spindle speed, feed rate, as well as the thickness of the layer to be removed. A rational regime is one during which production costs will be minimal and the quality of the resulting product as accurate as possible.
Basic principles of calculations
In order to manufacture a part with the required dimensions and accuracy class, first of all, carry out its drawing and paint the route technology. In addition, it is very important to choose the right workpiece (forging, stamping, rolling) and the necessary material from which the product will be made. Choosing a cutting tool is also quite an important task. For each individual operation, the necessary tool is selected (cutter, mill, drill, countersink).
In addition, for each item written in the route technology, a separate process is performed, even if it is applied to the same work surface. For example, you need to make a hole D = 80 mm and cut the internal metric thread with a pitch of P = 2 mm. For each of the operations, it is necessary to separately select values such as cutting depth, cutting speed, speed, and in addition, select a cutting tool.
Required Surface Quality
It is also important to take into account the type of processing (finishing, roughing and semi-finishing), because the choice of coefficients in the calculations depends on these parameters. As a rule, during roughing, the cutting speed is much higher than during finishing. This is explained as follows: the better the quality of the processed surface, the lower should be its speed. It is interesting that when turning titanium alloys, the roughness increases at high rates, since strong fluctuations occur in the processing zone, but it does not affect the parameters Ra and Rz at all.
Factors affecting the cutting speed during milling and other operations
A huge number of factors affect the choice of calculations. All of them differ from each other depending on the type of processing of the part. For example, for drilling holes, you can select a feed twice as large as for drilling. In addition, this indicator during processing without limiting factors is chosen as the maximum allowable, according to the strength of the tool used. When planing and cutting grooves in the main formula of the cutting mode, add a coefficient that takes into account the impact load - K v .
When threading, it is very important to pay attention to the choice of the cutting tool, since when using the cutter at point-blank manual retraction is required, which means that the speed should be minimal.
The cutting speed during milling depends on the diameter of the working tool (D) and the width of the surface (B). Moreover, when machining steel surfaces with face mills, it is imperative to position the workpiece asymmetrically with respect to the cutting tool. If this rule is neglected, then its durability can significantly decrease.
This is a very important indicator that affects the calculation of cutting speed. It indicates the period of operation of the cutting tool until it is dull. The durability period is increased with multi-tool processing.
Basic formulas
The cutting speed during any operation primarily depends on the selected cutting tool, on the material of the workpiece, on the depth and amount of feed. Its formula is also affected by the method of machining. You can determine the cutting speed both by tabular method and by calculation. So, with boring, as well as external, transverse and longitudinal turning, use the formula below.
How does this calculation differ from the rest? With shaped turning, cutting and cutting, the cutting depth is not taken into account. But in some cases, a value such as the width of the slot can also be taken. For example, when machining a shaft with a width, its diameter will be considered, and when turning a groove, its depth. Due to the fact that when cutting, it is quite difficult to retract the cutter, the feed is selected no more than 0.2 mm / rev, and the cutting speed is 10–30 mm / min. You can also perform a calculation using a different formula.
When drilling, coredrilling, reaming and reaming, it is very important to correctly determine the cutting speed and feed. If the values are too high, the cutting tool may “burn out” or break. For calculations during drilling, use the formula below.
The cutting speed during milling depends on the diameter of the cutter, the number of teeth and the width of the machined surface. The selected depth is determined by the rigidity and power of the machine, as well as side allowances. The resistance value of the cutter depends on its diameter. So, if D = 40-50 mm, then T = 120 min. And when D is in the range of 55–125 mm, the value of T is 180 minutes. The cutting speed during milling has the formula shown in the photo.
Designations:
C v - coefficient, which depends on the mechanical properties of the treated surface.
T is the resistance of the cutting tool.
S is the feed rate.
t is the depth of cut.
B - milling width
z is the number of teeth of the cutter.
D is the diameter of the hole being machined (in some cases, a cutting tool, for example, a drill)
m, x, y - exponents (selected from tables), which are determined for specific cutting conditions and, as a rule, have values m = 0.2; x = 0.1; y = 0.4.
K v - correction factor. It is necessary, since the calculations are carried out using coefficients taken from the tables. Its use allows you to get the actual value of the cutting speed, taking into account certain values of the above factors.
Tabular and software way
Since performing calculations is a rather time-consuming process, in the specialized literature and on various Internet resources there are special tables in which the necessary parameters are already indicated. In addition, there are programs that themselves perform the calculation of cutting conditions. For this, the necessary type of machining is selected and indicators such as the material of the workpiece and cutting tool, the required dimensions, depth, and accuracy qualifications are introduced. The program itself calculates the cutting speed during turning, feed and speed.