End mill

Abstract

An end mill has an outer peripheral cutting edge and a bottom edge along a helical groove. The helical groove has a first groove (21) and a second groove (22). The bottom of the first groove (21) has a linear portion (41), a circular-arc-shaped portion (42), and a gradient portion (43). The linear portion (41) is parallel to the axis O and extends linearly from the front end of the tool toward the rear end side to a position separated from the front end of the tool by an amount corresponding to the length of the outer diameter of the tool. The gradient portion (43) is provided at a position on the rear end side of the linear portion (41) and is inclined linearly toward the radial outside as it goes from the linear portion (41) side toward the rear end side. The circular-arc-shaped portion (42) connects the rear end of the linear portion (41) and the front end of the gradient portion (43) and is curved in a circular arc shape toward the radial outside as it goes from the linear portion (41) side toward the gradient portion (43) side. The rake angle of the outer peripheral cutting edge and the bottom edge is constant over the entire circumference.

Description

Technical Field

[0001] This invention relates to an end mill. Background Technology

[0002] Roughing end mills used for heavy and rough cutting require the collection and removal of large amounts of chips generated. Therefore, it is important to ensure sufficient chip flutes. Increasing the chip flutes reduces the tool cross-sectional area. A smaller tool cross-sectional area means the tool cannot withstand the bending stresses during cutting, potentially leading to breakage.

[0003] Patent Document 1 discloses a tapered end mill in which the flute bottom radius decreases from the shank side towards the tool tip side. The flute bottom radius is the distance between the flute bottom and the axis. The flute bottom radius changes linearly in the axial direction with a predetermined gradient angle. The gradient angle changes at predetermined points such that the gradient angle on the tool tip side is smaller than that on the shank side. On the tool tip side with a smaller gradient angle, the core thickness is smaller. Therefore, chip evacuation can be ensured on the tool tip side where cutting is mainly performed. On the shank side with a larger gradient angle, the core thickness increases at a larger rate of change towards the shank side. Therefore, the tapered end mill can ensure strength or rigidity.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2019 / 244361 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] When the tapered end mill described in Patent Document 1 is used for heavy cutting and rough cutting, the generated chips are relatively large. As a result, the gradient of the groove bottom on the tool tip side cannot form a chip evacuation groove capable of collecting and discharging large chips. Furthermore, the rake angle of the cutting edge gradually decreases with the gradient of the groove bottom. In this case, there is also the problem of reduced sharpness relative to the workpiece and increased cutting resistance. The reduction in rake angle becomes a major cause of chip clogging due to unstable chip shape.

[0009] The purpose of this invention is to provide an end mill that can improve machining efficiency.

[0010] Solution for solving the problem

[0011] A cutting edge is provided in an end mill of the present invention along a plurality of spiral grooves twisted around an axis. The spiral groove bottom comprises: a straight portion extending linearly from the tool tip toward the rear end, parallel to the axis, to a position corresponding to a length from the tool tip that is separated from the tool tip by an amount corresponding to the tool's outer diameter; a gradient portion located closer to the rear end than the straight portion, inclined linearly outwards radially from the straight portion toward the rear end; and an arcuate portion connecting the rear end of the straight portion and the front end of the gradient portion, curving arcuately outwards radially from the straight portion toward the gradient portion. The rake angle of the cutting edge is constant throughout the entire circumference of the cutting edge.

[0012] The spiral groove of this embodiment has a straight section at its bottom, thus ensuring sufficient chip containment. Furthermore, the bottom of the spiral groove has a gradient section at its rear end. The gradient section slopes radially outward in a straight line from the straight section towards the rear end. Therefore, the groove bottom radius increases towards the rear end, thereby improving the rigidity of the rear end. Moreover, an arc-shaped section is provided between the straight section and the gradient section. The arc-shaped section curves radially outward in an arc shape from the straight section towards the gradient section. Therefore, during workpiece cutting, the stress applied between the straight section and the gradient section can be absorbed by the entire arc-shaped section. This improves the rigidity of the tool body. In addition, even with the arc-shaped section and gradient section at the bottom of the groove, since the rake angle is constant throughout the entire circumference of the cutting edge, the cutting performance relative to the workpiece can be ensured. Therefore, the end mill can perform high-penetration and high-feed machining relative to the workpiece, thus improving machining efficiency.

[0013] In this embodiment, the end mill can be configured such that the plurality of helical grooves are unequally divided, with each of two adjacent helical grooves having a different groove division angle when viewed from the front of the tool tip, and the plurality of helical grooves are unequally guided, with each of two adjacent helical grooves having a different torsion angle. Therefore, the end mill can suppress self-excited oscillations generated during workpiece cutting.

[0014] The end mill in this embodiment may have a plurality of helical grooves alternately having a first groove and a second groove with different groove division angles in the circumferential direction. The first groove division angle of the first groove is smaller than the second groove division angle of the second groove. The groove width of the first groove at the tool tip side is narrower than the groove width of the second groove at the tool tip side. The groove width of the first groove gradually widens from the tool tip side to the rear end side, and the groove width of the second groove gradually narrows from the tool tip side to the rear end side. Therefore, the end mill can accommodate an equal amount of chips in the first and second grooves and discharge them towards the rear end side. Thus, the end mill can ensure chip discharge performance. Furthermore, even if the end mill has unequal division and unequal guidance, the spacing between the first and second grooves can be maintained in the circumferential direction.

[0015] In this embodiment, the end mill may have a first gradient angle of the gradient portion of the first groove and a second gradient angle of the gradient portion of the second groove that are different from each other. Therefore, the end mill can achieve a balance between improved chip removal performance and increased rigidity.

[0016] In this embodiment, the end mill may have a hemispherical tip and a groove in the cutting edge at least near the tip. This improves chip removal performance and reduces contact friction with the workpiece.

[0017] In this embodiment, the end mill can have a radius R of 50 to 90 mm for the arc-shaped portion. This allows for the formation of a well-defined curved shape for the arc-shaped portion, thus improving rigidity. Furthermore, while grinding the arc-shaped portion, it can be formed by moving the grinding stone along an arc-shaped track. However, the diameter of the grinding stone used for grinding the arc-shaped portion can also be set to 100 mm to 180 mm, and the arc-shaped portion can be formed using a transfer-type machining method. Attached Figure Description

[0018] Figure 1 This is a 3D view of end mill 1.

[0019] Figure 2 This is a side view of end mill 1.

[0020] Figure 3 yes Figure 2 Sectional view along line II.

[0021] Figure 4 This is the unfolded diagram of spiral grooves 5 to 8.

[0022] Figure 5 This is a cross-sectional view of the end mill 1 along axis O.

[0023] Figure 6This is a diagram comparing the shapes of the first groove 21 of five different end mills.

[0024] Figure 7 This is a table showing the groove bottom radius and rake angle of five types of end mills.

[0025] Figure 8 This is a graph representing the results of Experiment 1.

[0026] Figure 9 This is a table showing the results of experiment 2.

[0027] Figure 10 This is a graph representing the results of experiment 3-1.

[0028] Figure 11 This is a graph representing the results of experiment 3-2.

[0029] Figure 12 This is a table showing the length of the straight section, the radius R of the arc section, θ5, and θ6 of seven types of end mills.

[0030] Figure 13 This is a table showing the results of experiment 4.

[0031] Figure 14 This is a graph representing the results of Experiment 4. Detailed Implementation

[0032] Embodiments of the present invention will be described. The present invention is not limited to the embodiments described below, and design changes can be made as appropriate. For clarity, portions shown in the drawings may be represented with different scales and angles than actual dimensions.

[0033] Reference Figures 1-3 This describes the structure of the roughing ball end mill 1 (hereinafter referred to as end mill 1). End mill 1 is mainly used for heavy cutting and rough cutting. Figure 1 , Figure 2 As shown, the end mill 1 integrally comprises a shank 2 and a cutting edge 3 along axis O. The shank 2 is located on the rear end side of the end mill 1, and the cutting edge 3 is located on the front end side of the end mill 1. The shank 2 is a round bar and is mounted on the spindle of a machine tool (not shown). The machine tool drives the end mill 1 to the right (refer to axis O) when viewed from the shank 2 side. Figure 1 , Figure 2 The end mill 1 rotates (arrow T) while moving relative to the workpiece in a direction orthogonal to axis O. This causes the end mill 1 to perform groove cutting on the workpiece. The base material of the end mill 1 is HSS, but it is not limited to this; for example, it can be made of supercarbide with a hard coating. As an example, the end mill 1 has a tool length of 80 mm, a tool diameter of 10 mm, a shank length of 57.6 mm, and a cutting edge length of 22.4 mm.

[0034] The cutting edge 3 is a rod-shaped part connected to the shank 2 along the axis O, and has a hemispherical ball 30 at its front end. Four helical grooves 5-8 are provided on the outer circumferential surface of the cutting edge 3 around the axis O. The helical grooves 5-8, when viewed from the shank 2 side, twist to the right, and as described later, are unequally divided and unequally guided. An outer peripheral cutting edge 11 is provided along the opening edge of each of the helical grooves 5-8. Thus, four outer peripheral cutting edges 11 are provided on the outer circumferential surface of the cutting edge 3. The rake angle of the outer peripheral cutting edges 11 is constant over the entire circumference, for example, 6°. Multiple grooves 15 are provided on the outer peripheral cutting edges 11. The grooves 15 extend parallel to the direction intersecting the axis O.

[0035] The ball portion 30 has four bottom cutting edges 12. Each of the four bottom cutting edges 12 is connected to a corresponding four outer peripheral cutting edges 11. The rake angle of each bottom cutting edge 12 is also constant throughout its circumference, similar to that of the outer peripheral cutting edges 11, for example, 6°. Each of the four bottom cutting edges 12 has two grooves 16. The grooves 16 also extend parallel to the direction intersecting the axis O. The chips cut by the outer peripheral cutting edges 11 and the bottom cutting edges 12 are cut by the grooves 15 and 16 and discharged towards the shank 2 side along with the cooling medium via the spiral grooves 5 to 8. This improves chip removal performance, thus enabling the end mill 1 to perform cutting operations with high efficiency.

[0036] Reference Figure 2 , Figure 3 This illustrates unequal partitioning and unequal orientation. For example... Figure 3 As shown, when viewing the cross-section of the cutting edge 3 of the end mill 1 from the tool tip side, the helical grooves 5 and 7 are opposite each other across axis O, and the helical grooves 6 and 8 are opposite each other across axis O. For ease of explanation, helical grooves 5 and 7 are defined as groove 21 (first groove), and helical grooves 6 and 8 are defined as groove 22 (second groove). The groove division angle θ1 of groove 21 and the groove division angle θ2 of groove 22 are different from each other; therefore, helical grooves 5 to 8 are unequally divided. As an example, the groove division angle θ1 is 81°, and the groove division angle θ2 is 99°. Because the helical grooves 5 to 8 are unequally divided, the four peripheral cutting edges 11 are unevenly arranged in the circumferential direction. As an example, the four peripheral cutting edges 11 are arranged at positions of 0°, 81°, 180°, and 261°. Therefore, during cutting, periodic self-excited oscillations will not occur, and chatter is less likely to occur even under high cutting loads. Furthermore, due to its characteristic of discharging chips in a dispersed manner, it can prevent chips from clogging in the spiral grooves 5 to 8 during cutting.

[0037] like Figure 2As shown, the torsion angle θ3 of the first groove 21 and the torsion angle θ4 of the second groove 22 are different from each other; therefore, the spiral grooves 5 to 8 are unequal guides. The torsion angles θ3 and θ4 refer to the torsion angles relative to the axis O. As an example, the torsion angle θ3 is 40° and the torsion angle θ4 is 42°. In this embodiment, the torsion angle θ4 of the second groove 22 is greater than the torsion angle θ3 of the first groove 21. Utilizing this unequal guide, while the direction of the cutting force varies according to the outer peripheral cutting edge 11 and the bottom cutting edge 12, similarly to unequal division, the periodic variation in the contact between the outer peripheral cutting edge 11 and the bottom cutting edge 12 and the machined surface can be prevented, thus avoiding self-excited oscillation.

[0038] Reference Figure 4 This describes the widths of the first groove 21 and the second groove 22. The width of a groove refers to its length in a direction orthogonal to the length direction of the groove. The two first grooves 21 and the two second grooves 22 are alternately arranged circumferentially on the outer circumferential surface of the cutting edge 3. As mentioned above, the groove division angle θ1 of the first groove 21 is smaller than the groove division angle θ2 of the second groove 22 (refer to...). Figure 3 Therefore, on the front end side of the blade 3 ( Figure 4 On the left side of the blade 3, the width of the first groove 21 is narrower than the width of the second groove 22, and the width of the second groove 22 is wider than the width of the first groove 21. The width of the first groove 21 gradually widens towards the handle 2, while the width of the second groove 22 gradually narrows towards the handle 2, unlike the first groove 21. Therefore, on the side of the blade 3 closest to the handle 2, the width of the first groove 21 is wider than the width of the second groove 22, and the width of the second groove 22 is narrower than the width of the first groove 21.

[0039] Reference Figure 5 This describes the bottom shape of each of the first groove 21 and the second groove 22. Figure 5 This is a cross-sectional view of the end mill 1 along axis O. To facilitate understanding of the bottom shapes of the first groove 21 and the second groove 22, the diagram shows the first groove 21 and the second groove 22 extended parallel to axis O.

[0040] The bottom of the first groove 21, from the tool tip side towards the shank 2 side, sequentially comprises a straight section 41, an arc-shaped section 42, a gradient section 43, and a cutting section 44. The straight section 41, located at the tip of the cutting edge 3, is a portion that extends from the tool tip side to the outer diameter Dc parallel to the axis O. The outer diameter Dc is the tool diameter of the end mill, and for example, is 10 mm. Furthermore, an expanding section 40 is provided at the tool tip side. The expanding section 40 expands in a conical shape or a curved shape based on this conical shape from the tool tip towards the shank 2 side and connects to the tip of the straight section 41. The length of the expanding section 40 can be designed according to the tool diameter. For example, the groove bottom diameter ratio of the straight section 41 is 53%. The groove bottom diameter ratio refers to the ratio of the groove bottom diameter to the tool diameter. A large chip removal groove 61 is formed in the portion of the first groove 21 corresponding to the straight section 41.

[0041] The gradient portion 43 is located at the middle of the length of the cutting edge portion 3, near the shank 2, and is a gradient portion that slopes in a straight line towards the shank 2, with the groove bottom diameter increasing. An example of the gradient angle θ5 of the gradient portion 43 relative to the axis O is 5°. The arc-shaped portion 42 is the portion that smoothly connects the rear end of the straight portion 41 and the front end of the gradient portion 43 in an arc shape. The arc-shaped portion 42 is curved into an arc shape, with the groove bottom diameter gradually increasing from the rear end of the straight portion 41 towards the front end of the gradient portion 43. As an example, the groove bottom diameter ratio of the rear end of the arc-shaped portion 42 is 55%. Furthermore, the grinding of the arc-shaped portion 42 can be performed using, for example, a well-known disc-shaped grinding stone. By abutting the grinding stone against the base material of a high-speed rotating tool or moving the grinding stone on an arc track, a gently arc-shaped arc portion 42 can be formed. The cutting portion 44 is the portion that is cut in an arc shape from the rear end of the gradient portion 43 towards the tool surface.

[0042] Furthermore, although not described in detail, the bottom of the second groove 22, like the bottom of the first groove 21, sequentially comprises an enlarged diameter portion 50, a straight section 51, an arc-shaped section 52, a gradient section 53, and a cutting section 54 from the tool tip side toward the handle 2 side. A larger chip removal groove 62 is formed in the portion of the second groove 22 corresponding to the straight section 51. As an example, the gradient angle θ6 of the gradient section 53 relative to the axis O is 3°. In this embodiment, the gradient angles θ5 and θ6 are different from each other, but they can also be the same.

[0043] Reference Figure 5This section explains the chip removal performance and rigidity when using the end mill 1 for workpiece cutting. For example, in the case of heavy cutting such as grooving, the typical depth of cut is less than or equal to the outer diameter Dc. Therefore, the tip side of the end mill 1 is required to have a large chip-collecting capacity. As described above, large chip removal grooves 61 and 62 are provided in the portions of the first groove 21 and the second groove 22 corresponding to the straight portions 41 and 51. The chip removal grooves 61 and 62 can collect large chips generated on the tip side of the tool, and therefore can be well discharged towards the shank 2. Thus, the end mill 1 can prevent chips from clogging in the first groove 21 and the second groove 22.

[0044] Furthermore, the bottom radii of the straight sections 41 of the first groove 21 and 51 of the second groove 22 are relatively small, but the bottom radii of the gradient sections 43 and 53 gradually increase towards the shank 2 side. Therefore, compared to end mills that extend the straight sections 41 of the first groove 21 and 51 of the second groove 22 to the shank 2 side, the rigidity of the shank 2 side of the end mill 1 can be improved. Consequently, for the end mill 1, the chip removal performance of the first groove 21 and the second groove 22 can be improved, and the rigidity of the shank 2 side of the cutting edge 3 can be increased.

[0045] Furthermore, in the end mill 1, the straight sections 41 and 51 and the gradient sections 43 and 53 are not directly connected, but indirectly connected via the arc-shaped sections 42 and 52. If the straight sections 41 and 51 and the gradient sections 43 and 53 were directly connected, the groove bottom radius would change abruptly at the connection point between the straight sections 41 and 51 and the gradient sections 43 and 53. In this case, during workpiece cutting, a large load would be applied to the connection point where the groove bottom radius changes abruptly, potentially leading to breakage at this connection point. The end mill 1 smoothly connects the straight sections 41 and 51 and the gradient sections 43 and 53 using the arc-shaped sections 42 and 52, thus the groove bottom radius gradually increases from the straight sections 41 and 51 to the gradient sections 43 and 53. Therefore, during workpiece cutting, the load is distributed evenly across the arc-shaped sections 42 and 52, effectively preventing breakage.

[0046] Furthermore, the machining of the arc-shaped portions 42 and 52 is performed by bringing a circular grinding stone into contact with the high-speed rotating base material, which will be described later. To machine the curved shape of the arc-shaped portions 42 and 52, the radius R (R dimension) is preferably 50 (mm) to 90 (mm). For example, if R is greater than 90 (mm), the arc-shaped portions 42 and 52 extend towards the shank 2 side, thus causing the leading edges of the gradient portions 43 and 53 to move towards the shank 2 side, resulting in a decrease in stiffness. Conversely, if R is less than 50 (mm), the arc-shaped portions 42 and 52 bend to a lesser extent, thus easily causing stress concentration and hindering the smooth discharge of chips along the first groove 21 and the second groove 22 towards the shank 2 side. Therefore, it is preferable to use a grinding stone that can process within the range of R of 50 (mm) to 90 (mm) (in the case of processing arc shapes by means of the transfer of the grinding stone radius, the grinding stone diameter is 100 mm to 180 mm) to grind the arc-shaped parts 42 and 52.

[0047] Furthermore, in the end mill 1, even though gradient portions 43 and 53 are provided in the first groove 21 and the second groove 22, the rake angle of the outer peripheral cutting edge 11 is constant at any position (for example, 6°). This improves the sharpness relative to the workpiece, thereby reducing cutting resistance. Additionally, by stabilizing the chip shape, chip clogging in the first groove 21 and the second groove 22 can be prevented.

[0048] Furthermore, the gradient angle θ5 of the gradient portion 43 of the first groove 21, which has a larger width on the shank 2 side, is greater than the gradient angle θ6 of the gradient portion 53 of the second groove 22, which has a narrower width on the shank 2 side. By making the gradient angles θ5 and θ6 different from each other, as shown in the results of Experiment 4 described later, the stiffness of the cutting edge 3 can be further improved compared to the case where the gradient angles θ5 and θ6 are the same.

[0049] Next, to verify the effect of the bottom shapes of the first groove 21 and the second groove 22, experiment 1 was conducted. For example... Figure 6 As shown, in Experiment 1, the tool life of the end mill 1 (the product of this invention) and the end mills 101-104 (comparative products) when cutting a workpiece was checked. Tool life was determined based on the cutting durability length (m). The cutting durability length was set to the length at which Vb (outer peripheral flank wear width) was 0.5 mm or the length at which the end mill broke. The end mills 101-104 changed the groove bottom shape of the first groove 21 and the second groove 22, respectively. Furthermore, in Figure 6 For ease of understanding, only the bottom shape of the first groove 21 will be used for explanation.

[0050] In end mill 101, the straight section 41 of end mill 1 extends to the shank 2 side and is cut at the cutting section 44. In end mill 102, the groove bottom of the straight section 41 of end mill 101 is shallower. In end mill 103, the groove bottom of the straight section 41 of end mill 102 is even shallower. In end mill 104, the groove bottom is deformed in a zigzag manner. The tool diameter of each end mill 1, 101-104 is 10mm, and the number of cutting edges is 4.

[0051] Specify the groove bottom diameter ratio at each position of the end mill 1, 101~104. For example... Figure 7 As shown, for end mills 1, 101-104, the groove bottom diameter ratio was measured at four points 7mm, 10mm, 15mm, and 20mm from the tool tip. The groove bottom diameter ratio represents the ratio (%) of the groove bottom diameter to the tool diameter. In end mill 1, the groove bottom diameter ratio at 7mm is 53%, at 10mm it is 53%, at 15mm it is 55%, and at 20mm it is 58%. Furthermore, the 7mm point corresponds to the front end of the straight section 41, the 10mm point corresponds to the rear end of the straight section 41, the 15mm point corresponds to the beginning of the gradient section 43, and the 20mm point corresponds to the rear end of the middle section of the gradient section 43 along its length.

[0052] In end mill 101, the ratio of the bottom diameter of the groove at the 7mm, 10mm, 15mm, and 20mm points is 53%. In end mill 102, the ratio of the bottom diameter of the groove at the 7mm, 10mm, 15mm, and 20mm points is 57%. In end mill 103, the ratio of the bottom diameter of the groove at the 7mm, 10mm, 15mm, and 20mm points is 58%. In end mill 104, the ratio of the bottom diameter of the groove at the 7mm point is 53%, the ratio at the 10mm point is 44.67%, the ratio at the 15mm point is 56.33%, and the ratio at the 20mm point is 58%. Furthermore, the rake angle of the outer peripheral cutting edge 11 of all end mills 1, 101 to 104 is set to 6°.

[0053] Description of cutting conditions. The workpiece is made of stainless steel (SUS304). Groove cutting is performed, with a cutting speed set to 80 m / min and a rotational speed set to 2547 min / min. -1 The feed rate is set to 1019 mm / min, the axial depth of cut is set to 10 mm, and the width is 10 mm. Furthermore, the feed rate refers to the speed at which the worktable with the workpiece is moved relative to the tool mounted on the spindle of a machine tool (not shown).

[0054] Reference Figure 8The results of Experiment 1 are explained. The cutting durability length of the end mill 1 of the present invention is 120.8 m. The cutting durability length of the end mill 101 is 0.1 m, and it breaks during workpiece cutting. The cutting durability length of the end mill 102 is 34 m, and it breaks during workpiece cutting. The cutting durability length of the end mill 103 is 0.1 m, and it breaks during workpiece cutting. The cutting durability length of the end mill 104 is 58 m, and it breaks during workpiece cutting. When examining these results, it is considered that in the end mill 101, the straight portion 41 extends to the shank 2 side, thus reducing the stiffness of the shank 2 side and causing it to break. In the end mill 102, compared with the end mill 101, the flute bottom diameter ratio is larger, thus slightly improving the stiffness, but the stiffness is lower than that of the end mill 1, therefore the cutting durability length (m) is shorter. It is believed that in end mill 103, the bottom diameter ratio of the flute becomes larger, and the chip evacuation flute becomes narrower. Therefore, chips become clogged in the first flute 21, leading to breakage. In end mill 104, the cutting endurance length (m) is longer than that of end mills 101-103, but significantly shorter than that of end mill 1. It is believed that this is due to the tortuous bottom of the flute, causing chips to hook onto the bottom of the flute and become clogged, leading to breakage.

[0055] Based on the above results, since the end mill 1 of the present invention has the longest cutting durability length (m), it can be concluded that the present invention can improve the chip removal performance of the first groove 21 and ensure rigidity.

[0056] Next, to verify the effects of unequal segmentation and unequal guidance, Experiment 2 was conducted. In Experiment 2, the maximum depth of cut relative to the workpiece was checked for both the end mill 1 of the present invention and the end mill of the comparative product with equal segmentation and equal guidance. Furthermore, both the present invention and the comparative product had a tool diameter of 10 mm and four cutting edges.

[0057] Description of cutting conditions. The workpiece is made of stainless steel (SUS304). Groove cutting is performed, with a cutting speed set to 80 m / min and a rotational speed set to 2547 min / min. -1 The feed rate was set to 1019 mm / min, and the width was 10 mm. Cutting was performed in nine modes with axial depths of cut: 0.5 mm, 1 mm, 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, 11 mm, and 12 mm, and the maximum depth of cut was checked. Furthermore, the tool condition was evaluated using three levels: 0, △, and ×, for each axial depth of cut.

[0058] Reference Figure 9The results of Experiment 2 are explained below. Among the comparative products, machining was possible with minimal vibration when the axial penetration depth was 0.5–6 mm, therefore a score of 0 is given. On the other hand, machining was possible with an axial penetration depth of 8 mm, but vibration occurred, therefore a score of △ is given. Furthermore, the end mill broke during cutting when the axial penetration depth was 10 mm or more, therefore a score of × is given. Since the comparative products are equally segmented and equally guided, chatter occurred during machining, and the greater the axial penetration depth, the greater the chatter. Therefore, the maximum penetration depth of the comparative products is 6 mm.

[0059] In contrast, in the product of this invention, machining can be performed without significant vibration when the axial penetration depth is 0.5–11 mm, therefore it is determined to be 0. On the other hand, machining can be performed when the axial penetration depth is 12 mm, but vibration occurs, therefore it is determined to be △. It can be seen that because the product of this invention has unequal segmentation and unequal guidance, it can effectively suppress the chatter generated during cutting. However, it is believed that when the axial penetration depth exceeds 11 mm, the chip size further increases, placing a greater load on the end mill 1, thus causing vibration. Therefore, it can be concluded that the maximum penetration depth of the product of this invention is 11 mm.

[0060] Based on the above results, it can be seen that since the maximum cut-in amount of the product of the present invention is greater than that of the comparative product, the product of the present invention with unequal segmentation and unequal guidance can effectively suppress jitter.

[0061] Next, to verify the effect of keeping the rake angle constant, Experiment 3 was conducted. In Experiment 3, an end mill 1 of the present invention and an end mill with a rake angle varying according to the gradient of the groove bottom were prepared as a comparison product, and the maximum and average values ​​of the cutting resistance (N) when the depth of cut was changed were examined. Furthermore, in the comparison product, the structure was completely identical to that of the present invention, except that the rake angle varied according to the gradient of the groove bottom.

[0062] Description of cutting conditions. The tool diameters of both the product of this invention and the comparative product are... (R10)mm. The workpiece is made of pre-hardened steel (40HRC). Groove cutting is performed at a cutting speed of 100m / min and a rotational speed of 1590min. -1 The feed rate was set to 450 mm / min, and the width was 10 mm. The cutting resistance (N) was measured when the axial depth of cut (AP) was varied within the range of 0.3D to 1.0D, and the maximum and average values ​​were checked. Additionally, D is the tool diameter.

[0063] Reference Figure 10 , Figure 11The results of Experiment 3 will be explained. First, the change in the maximum value of the cutting resistance will be explained. For example... Figure 10 As shown, among the comparative products, the maximum value for AP=0.3D is 1230, the maximum value for AP=0.4D is 1590, the maximum value for AP=0.5D is 2011, the maximum value for AP=0.6D is 2580, the maximum value for AP=0.7D is 2971, the maximum value for AP=0.8D is 3615, the maximum value for AP=0.9D is 4201, and the maximum value for AP=1D is 4952. Thus, the maximum value of the cutting resistance of the comparative products tends to increase with the increase of the depth of cut.

[0064] In contrast, in the product of this invention, the maximum value for AP=0.3D is 1225, the maximum value for AP=0.4D is 1565, the maximum value for AP=0.5D is 1951, the maximum value for AP=0.6D is 2182, the maximum value for AP=0.7D is 2476, the maximum value for AP=0.8D is 2783, the maximum value for AP=0.9D is 3065, and the maximum value for AP=1D is 3298. Thus, the maximum value of the cutting resistance of the product of this invention, like the maximum value of the comparative product, tends to increase with increasing depth of cut. However, compared to the change in the maximum value of the comparative product, especially after the depth of cut reaches 0.5D, the tendency to increase is significantly reduced, and the difference between the product and the comparative product increases with increasing depth of cut.

[0065] Explain the change in the average value of the cutting resistance. For example... Figure 11 As shown, among the comparative products, the average value of AP=0.3D is 1129, the average value of AP=0.4D is 1494, the average value of AP=0.5D is 1912, the average value of AP=0.6D is 2448, the average value of AP=0.7D is 2826, the average value of AP=0.8D is 3454, the average value of AP=0.9D is 4024, and the average value of AP=1D is 4766. Thus, the average value of the cutting resistance of the comparative products also shows a tendency to increase with the increase of the depth of cut.

[0066] In contrast, in the product of this invention, the average value of AP=0.3D is 1122, the average value of AP=0.4D is 1472, the average value of AP=0.5D is 1846, the average value of AP=0.6D is 2062, the average value of AP=0.7D is 2350, the average value of AP=0.8D is 2646, the average value of AP=0.9D is 2923, and the average value of AP=1D is 3149. Thus, the average value of the cutting resistance of the product of this invention, like the average value of the comparative product, shows a tendency to increase with increasing depth of cut. Furthermore, the tendency of the average value of the cutting resistance of the product of this invention to increase compared to the average value of the comparative product decreases significantly after a depth of cut of 0.5D, and the difference between it and the comparative product increases with increasing depth of cut.

[0067] Based on the above results, it can be seen that the maximum and average cutting resistance of the product of the present invention increases with the increase of the depth of cut, but decreases compared with the tendency of the maximum and average cutting resistance of the comparative product to increase. Therefore, by keeping the rake angle of the outer peripheral cutting edge 11 constant, the cutting resistance relative to the workpiece is reduced.

[0068] Next, to verify the gradient angles θ5 of the first groove 21 and θ6 of the second groove 22, as well as the bending shapes of the arc-shaped portions 42 and 52, experiment 4 was conducted. In experiment 4, seven end mills A to G were prepared, and their tool life was checked by cutting workpieces. End mills A and B are products of this invention, while end mills C to G are comparative products. In experiment 4, for end mills A to G, the lengths (mm) of the straight portions 41 of the first groove 21 and 51 of the second groove 22, the radius (R) of the arc-shaped portions 42 and 52, the gradient angles θ5 and θ6 of the gradient portion 43 and 53, respectively, were specified. Furthermore, the lengths (mm) of the straight portions 41 and 51 refer to the lengths from the tool tip to the respective rear ends of the straight portions 41 and 51 (hereinafter collectively referred to as the straight portions). The lengths of the straight portions 41 and 51 are the same.

[0069] like Figure 12As shown, in end mill A, the length of the straight section is 10mm, the radius (R) of the arc-shaped section is 75mm, the gradient angle θ5 is 3°, and the gradient angle θ6 is 3°. In end mill B, the length of the straight section is 10mm, the radius (R) of the arc-shaped section is 75mm, the gradient angle θ5 is 5°, and the gradient angle θ6 is 3°. The only difference between end mills A and B is the gradient angle θ5. In end mill C, the length of the straight section is 10mm, the radius (R) of the arc-shaped section is 10mm, the gradient angle θ5 is 3°, and the gradient angle θ6 is 3°. In end mill D, the length of the straight section is 10mm, the radius (R) of the arc-shaped section is 30mm, the gradient angle θ5 is 3°, and the gradient angle θ6 is 3°. In end mill E, the length of the straight section is 10mm, the radius (R) of the arc-shaped section is 50mm, and the gradient angle θ5 is 3°, and the gradient angle θ6 is 3°. In end mill F, the length of the straight section is 10mm, the radius (R) of the arc section is 90mm, the gradient angle θ5 is 3°, and the gradient angle θ6 is 3°. In end mill G, the length of the straight section is 10mm, the radius (R) of the arc section is 100mm, the gradient angle θ5 is 3°, and the gradient angle θ6 is 3°. Furthermore, the tool diameter of end mills A through G is 10mm, and they have 4 cutting edges.

[0070] Description of cutting conditions. The workpiece is made of stainless steel (SUS304). The cutting speed is set to 80 m / min, and the rotational speed is set to 2547 min / min. -1 The feed rate was set to 1019 mm / min, the groove width to 10 mm, and the axial depth of cut to 10 mm. Tool life was checked when the workpiece was grooved under these cutting conditions. Furthermore, tool life was determined by the cutting durability length (m), similar to Experiment 1. The cutting durability length was set to the length at which Vb (outer peripheral flank wear width) was 0.5 mm or the length at which the tool broke. Moreover, with the cutting durability length of the end mill with the longest cutting durability length set to 100%, the conversion values ​​for the other end mills were calculated separately under this condition. These conversion values, along with the tool condition at the time of determining the cutting durability length, were evaluated using three levels: 0, △, and ×. As an evaluation method, end mills with a conversion value of 70–100% were evaluated as 0, those with a conversion value of 40–70% as △, and those with a conversion value of 0–39% as ×.

[0071] Reference Figure 13 , Figure 14The results of Experiment 4 are explained below. The cutting durability length of end mill A is 120.8, end mill B is 131.5, end mill C is 2.4, end mill D is 13.3, end mill E is 95.2, end mill F is 102.3, and end mill G is 37.6. Based on these results, end mill B has the longest cutting durability length. Therefore, when the cutting durability length of end mill B is set to 100.0%, the equivalent value for end mill A is 91.9%, for end mill C it is 1.8%, for end mill D it is 10.1%, for end mill E it is 72.4%, for end mill F it is 77.8%, and for end mill G it is 28.6%. The reasons for determining the cutting durability length are as follows: end mills A, B, E, and F are worn, while end mills C, D, and G are broken.

[0072] Examining the above results, it can be seen that the evaluation of end mills A and B is 0. Utilizing the bottom shapes of the first groove 21 and the second groove 22, chip removal performance can be improved while ensuring rigidity. Furthermore, it can be seen that since end mill B has a longer tool life, compared to the case where gradient angles θ5 and θ6 are the same, making gradient angles θ5 and θ6 different results in an extended tool life.

[0073] The curvature of the arc-shaped portion was examined. End mills A, C through G each altered the value of R in the arc-shaped portion. A larger R value results in a smoother and more pronounced curvature of the arc (R-shape), while a smaller R value results in a sharper and less pronounced curvature. End mills A, E, and F were rated 0, while the other end mills C, D, and G were rated ×. In other words, end mills E (R value 50 mm), A (R value 75 mm), and F (R value 90 mm) did not break down; they reached the end of their tool life due to wear.

[0074] When the radius (R) of the arc-shaped portion is small, the curvature of the arc-shaped portion is more abrupt, thus the load tends to concentrate. Therefore, in end mills C and D with small R values, it is considered that the arc-shaped portion is prone to breakage. Conversely, when the R value is large, the arc-shaped portion is close to a straight line. Therefore, the groove bottom diameter remains almost unchanged from the straight portion, making it impossible to improve rigidity. Thus, in this case, it is also considered that the arc-shaped portion is prone to breakage.

[0075] Based on the above results, it can be seen that within the range of R value of the arc-shaped part being 50 (mm) to 90 (mm), the arc-shaped part can be used as a whole to accept the load applied between the straight part and the gradient part, thereby improving durability.

[0076] In the above description, the outer peripheral cutting edge 11 and the bottom cutting edge 12 are examples of the "cutting edge" of the present invention. The groove dividing angle θ1 is an example of the "first groove dividing angle" of the present invention, and the groove dividing angle θ2 is an example of the "second groove dividing angle" of the present invention. The gradient angle θ5 is an example of the "first gradient angle" of the present invention, and the gradient angle θ6 is an example of the "second gradient angle" of the present invention.

[0077] As explained above, the end mill 1 of this embodiment is a roughing end mill for heavy and rough cutting, provided with an outer peripheral cutting edge 11 and a bottom cutting edge 12 along spiral grooves 5-8 twisted around axis O. Each of the spiral grooves 5-8 has a straight section 41 (51), an arc-shaped section 42 (52), and a gradient section 43 (53) at its bottom. The straight section 41 extends parallel to axis O and in a straight line from the tool tip toward the rear end to a position corresponding to the length of the tool's outer diameter, separated from the tool tip. The gradient section 43 is located further back than the straight section 41 and slopes radially outward in a straight line as it moves from the straight section 41 toward the rear end. The arc-shaped section 42 connects the rear end of the straight section 41 and the front end of the gradient section 43, and curves radially outward in an arc as it moves from the straight section 41 toward the gradient section 43. Furthermore, the rake angles of the outer peripheral cutting edge 11 and the bottom cutting edge 12 are constant over the entire circumference.

[0078] Thus, the bottom of the spiral grooves 5-8 has a straight section 41, which ensures sufficient chip containment. Furthermore, a gradient section 43 is provided at the rear end, so the radius of the groove bottom increases towards the rear end, thereby improving the rigidity of the rear end. Moreover, an arc-shaped section 42 is provided between the straight section and the gradient section, so that during workpiece cutting, the stress applied between the straight section 41 and the gradient section 43 can be distributed throughout the entire arc-shaped section 42. This improves the rigidity of the end mill 1. In addition, even with the arc-shaped section 42 and the gradient section 43 at the bottom of the groove, the rake angle remains constant throughout the entire circumference of the outer cutting edge 11 and the bottom cutting edge 12, ensuring good workpiece penetration performance. Therefore, the end mill 1 can perform high penetration and high feed machining relative to the workpiece, thus improving the efficiency of heavy cutting and rough cutting.

[0079] Furthermore, the present invention is not limited to the above-described embodiments, and various modifications are possible. The end mill 1 is for heavy cutting and rough cutting, but can also be used for general cutting or finishing. The end mill 1 has four helical grooves 5 to 8, but the number of helical grooves can be multiple, for example, two or more. The end mill 1 has unequal division and unequal guidance, but can also be equal division and equal guidance, unequal division and equal guidance, or equal division and unequal guidance. The helical grooves 5 to 8 are right-handed, but can also be left-handed. The rake angle of the outer peripheral cutting edge 11 and the bottom cutting edge 12 is fixed, but can also be variable; for example, it can vary in conjunction with the gradient of the bottom of the helical grooves 5 to 8. The number of grooves 16 provided on the bottom cutting edge 12 is at least one, but can also be two or more. The number of grooves 15 provided on the outer peripheral cutting edge 11 is also not limited.

Claims

1. An end mill (1) having a cutting edge (11) provided along a plurality of helical grooves (5-8) twisted about an axis (O), characterized in that, The bottom of the spiral grooves (5~8) has: The straight section (41) extends in a straight line from the front end of the tool toward the rear end, parallel to the axis (O), to a position that is separated from the front end of the tool by a length corresponding to the outer diameter (Dc) of the tool; The gradient portion (43), located closer to the rear end than the straight portion (41), is inclined linearly outward in a radially outward direction as it moves from the straight portion side toward the rear end side; and The arc-shaped portion (42), which connects the rear end of the straight portion (41) and the front end of the gradient portion (43), bends in an arc shape toward the radially outward side as it moves from the straight portion side toward the gradient portion side. The rake angle of the cutting edge (11) is constant over its entire circumference. The plurality of spiral grooves (5~8) are unequal divisions in which the groove division angles (θ1, θ2) of two adjacent spiral grooves (5~6, 6~7, 7~8, 8~5) in the circumferential direction are different when the front end of the tool is viewed from the front. The plurality of spiral grooves provide unequal guidance, with each pair of adjacent spiral grooves (5~6, 6~7, 7~8, 8~5) having different torsion angles (θ3, θ4). The plurality of spiral grooves (5~8) alternately have a first groove (21) and a second groove (22) with different groove division angles in the circumferential direction. The first slot division angle (θ1) of the first slot (21) is smaller than the second slot division angle (θ2) of the second slot (22). The width of the tool tip side of the first groove (21) is narrower than the width of the tool tip side of the second groove (22). The width of the first groove (21) gradually increases from the front end of the tool to the rear end. The width of the second groove (22) gradually narrows from the front end of the tool to the rear end. The first gradient angle (θ5) of the gradient portion (43) of the first groove (21) is different from the second gradient angle (θ6) of the gradient portion (43) of the second groove (22).

2. The end mill (1) according to claim 1, characterized in that, The tool has a hemispherical tip. A groove (16) is provided in the cutting edge (11) at least at the position near the front end of the tool.

3. The end mill (1) according to claim 1 or 2, characterized in that, The radius R of the arc-shaped portion (42) is in the range of 50 to 90 mm.

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