The influence of the helix angle of the end mill on the cutting performance

1. Basic characteristics and problems of spiral edge end mills The basic edge shapes (spiral groove shapes) of end mills are straight and spiral. Compared with the straight edge, the spiral edge end mill has the advantages of light cutting, smooth cutting, high efficiency and wide application range, so it has been widely used in milling. According to the different requirements of processing equipment and processing objects, spiral edge end mills have 4 different combinations of left edge, right edge and left helix and right helix;

1. The axial cutting resistance of the left helix of the left blade and the right helix of the right blade during processing has a tendency to pull out the end mill from the tool holder, and it is necessary to use a tension bolt to overcome the axial cutting resistance. The axial cutting resistance of the left helix and the left helix of the right blade just press the end mill to the side of the chuck, so taper shank and flat tail are mostly used to adapt to high-power cutting. Because the right-edge right-spiral end mill can discharge the chips to the shank along the chip flute, it is easy to ensure the smooth progress of cutting, which conforms to the standard of the spindle rotation of the machine tool. The most widely used and the largest. The helix angle of helical edge end mills in practical applications is usually 30° to 45°. In the field of tool principle, design and application technology, according to the difference of workpiece material, tool material and cutting parameters, the design of cutting force, torque, cutting power, rake angle, relief angle and other main tool angles of helical edge end mills There are many materials such as calculation formulas, experimental data and experience, but there are few discussions and materials about the size of the helix angle and the machining performance of end mills. It is generally believed that the helix angle β of the helical edge end mill is the edge inclination angle λs, but the introduction and discussion of the edge inclination angle are mainly based on turning processing. After all, there are many differences between milling and turning, so it is impossible to fully apply.

2. For milling, it is generally believed that a larger helix angle can increase the number of teeth working at the same time, reduce the impact during the milling process, increase its stability, and make the end mill sharper and the actual rake angle increases. In addition, what effect will the size of the helix angle have on the performance of the end mill? The tool angles are interrelated and influenced. May wish to first through experiments and actual processing examples, to obtain preliminary understanding and relevant knowledge, to prepare for further in-depth discussion.

2. The helix angle and 2-blade end mill milling experiments were carried out on a vertical machining center. A 2-flute end mill with different helix angles with a diameter of  12mm is used to mill a slot with a width x height of 12mm x 12mm, and the bottom surface of the slot after machining is used as the benchmark to measure the verticality error of the two sides of the slot (the maximum deformation of the side surface). ΔX), by comparing the size of the error value to evaluate the influence of the helix angle on the machining accuracy of the end mill when milling grooves. The material to be cut is carbon steel with a hardness of 28HRC. The cutting parameters of each tool in the experiment are unified as follows: the feed rate is 50mm/min, the cutting speed is 29m/min, and the cutting depth is 12mm. The coolant in cutting is oily. The experimental results are shown in Figure 1. Fig. 1 Helix angle and machining accuracy when milling grooves Fig. 2 Helix angle and machining accuracy when milling side faces It can be seen from the experimental results:

1. There is always overcut on the up milling side, and on the contrary, the down milling side always has missed cuts, and the maximum point of the overcut and missed cuts is the farthest extension of the end mill. This is in line with the deformation law of the tool during up milling and down milling and the deformation law of the extension length of the tool.

2. Before the helix angle of the end mill is less than 30°, the verticality error value increases with the increase of the helix angle, whether it is the down milling side or the up milling side. After the helix angle is greater than 40°, it becomes smaller as the helix angle increases. Therefore, it can be considered that when the end mill has a small helix angle or a large helix angle, the shape accuracy of the milling groove is high.

3. In terms of machining accuracy, when the helix angle is 0, that is, when the cutting edge is a straight edge, the accuracy is the highest. However, from the basic characteristics of the helix angle of the end mill, it can be seen that the cutting is completely interrupted at this time, the cutting impact force is large, the production accuracy of the tool itself is high, and the machining accuracy is strongly dependent on the accuracy of the tool itself, and the service life of the tool is high. short. Therefore, in practical application, it should be considered dialectically according to the specific situation.

3. Side milling experiment of helix angle and 4-flute end mill On a vertical machining center, the 4-blade end mill with helix angle of 30° and 55° was used to mill the side, and the two end mills were compared with the cutting width ( The influence of the change of radial cutting amount) on the machining accuracy. The diameter of the end mill is 25mm, and the material to be cut is No. 45 steel with a hardness of 94HRB. All cutting adopts down milling and dry cutting. The cutting parameters are unified as follows: the feed rate is 100mm/min, the cutting speed is 26mm/min, and the cutting depth is 38mm. The squareness error, flatness error and surface roughness values measured after machining are shown in Fig. 2. It can be seen that when the cutting width is not particularly large, the machining accuracy of the 55° helix angle end mill is higher than that of the 30° helix angle end mill. This is consistent with the experimental results of slot milling in Figure 1. Analyzing the reasons, it can be considered that when the cutting width is small, the end mill with a large helix angle has a large actual rake angle, a sharp edge, and good penetration; the tangential cutting resistance is small, which reduces energy consumption and tool deformation. The cutting is light and fast; there are many contact points between the cutting edge and the surface to be cut, so that the end mill is relatively stable when cutting in and out, and the fluctuation of cutting resistance is small, which weakens the comprehensive effect of the vibration excitation of the end mill during processing.

4. Induction of helix angle characteristics

1. Helix angle and cutting resistance: The tangential cutting resistance decreases with the increase of the helix angle, and the axial cutting resistance increases with the increase of the helix angle.

2. Helix angle and rake angle: The increase of the helix angle increases the actual rake angle of the end mill, and the cutting edge is sharper.

3. Helix angle and machined surface accuracy: Generally, the verticality and flatness tolerances of the machined surface increase with the increase of the helix angle, but when the helix angle is greater than 40°, it decreases with the increase of the helix angle. trend.

4. Helix angle and tool life: The wear rate of the circumferential land is basically proportional to the size of the helix angle; on the other hand, when the helix angle is very small, slight tool wear will also significantly reduce the cutting performance of the tool, causing vibration and causing The tool can no longer be used. When the helix angle is too large, the rigidity of the tool deteriorates and the life is reduced.

5. Helix angle and material to be cut: When machining soft materials with low hardness, use a large helix angle to increase the rake angle and improve the sharpness of the cutting edge; when machining hard materials with high hardness, use a small helix angle, To reduce the rake angle and improve the rigidity of the cutting edge.

Finally, the helix angle is one of the main parameters of the helical edge end mill, and the change of the helix angle has a great influence on the cutting performance of the tool. With the development of CNC machining technology and flexible manufacturing technology, it has become possible and very simple to change the size of the helix angle in the tool manufacturing process. If the various influences of the helix angle on the cutting performance of the helical edge end mill are further studied, when manufacturing and selecting the helical edge end mill, the performance of the machine tool and the fixture should be combined with the performance of the material to be processed and the machining accuracy, Taking into account factors such as machining efficiency, tool material and tool life, optimizing the size of the helix angle will undoubtedly play an important role in promoting efficient and high-precision milling.