Cutting tool

Abstract

To provide a cutting tool capable of improving chip discharge performance especially when performing thrust machining while considering rigidity, and achieving both of chattering resistance and chip discharge performance at a higher level.SOLUTION: The cutting tool includes an end cutting edge 21 formed so as to extend in a radial direction from a center axis side, an outer peripheral cutting edge 24 forming a set of cutting edges 20 together with the end cutting edge 21, and a chip discharge groove 30 provided around the center axis. The chip discharge groove 30 is formed of two or more grooves having different helix angles and including at least a main groove 31 and a sub-groove 32, and the helix angle α of the main groove 31 forming the peripheral cutting edge 24 on the ridge line with the side 10s of the peripheral side surface is the smallest, and the helix angle β of the sub-groove 32 in contact with the main groove 31 and disposed forward of the main groove 31 in the tool-rotating direction is larger than the helix angle α of the main groove 31.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a cutting tool. [Background technology]

[0002] In rotary cutting tools (milling tools) such as end mills, which have side cutting edges (referred to herein as "peripheral cutting edges") on the side of the cutting tool and bottom cutting edges on the tip surface of the cutting tool, chatter resistance when used for groove machining and wall machining, as well as chip evacuation performance when used for drilling holes by plunge machining, are important. Therefore, achieving both chatter resistance and chip evacuation performance of the milling tool is crucial for maximizing its cutting performance. However, these two performance characteristics (chatter resistance and chip evacuation performance) are in a trade-off relationship depending on the design of the chip evacuation flutes formed around the tool rotation axis. In other words, the chatter resistance of milling tools can generally be improved by increasing the rigidity of the cutting tool. To achieve this, it is effective to design the chip evacuation flutes with a small cross-sectional area and increase the core thickness of the cutting tool. However, this sacrifices chip removal performance and results in poor chip removal, which can lead to chip clogging, particularly in groove machining and thrust machining, where sufficient space cannot be secured between the cutting tool and the workpiece (material to be cut).

[0003] Therefore, as a tool that can ensure both chatter resistance and chip evacuation performance, an end mill has been proposed in which the chip evacuation flute that is paired with the cutting edge is composed of two surfaces, a first flute surface and a second flute surface (see, for example, Patent Document 1). Here, the twist angle of the chip evacuation flute that forms the axial rake angle of the peripheral cutting edge is set to 40° to 60°, and the cutting resistance is reduced by reducing the cutting thickness of the peripheral cutting edge. In addition, the first flute surface and the second flute surface are arranged at an obtuse angle, and the cross-sectional area of ​​the cutting tool is secured to be large, thereby suppressing a decrease in the rigidity of the cutting tool. However, with the arrangement of the first and second cutting groove surfaces as proposed in Patent Document 1 (see Figure 2 of Patent Document 1, etc.), chips pass mainly through the second cutting groove surface that directly forms the peripheral cutting edge, and the first cutting groove surface, which intersects with the second cutting groove surface at an obtuse angle and is arranged so that its cross-sectional area is smaller than that of the second cutting groove surface, is not effective in terms of chip removal.

[0004] Also, by providing a recess on the end cutting edge, as disclosed in Patent Document 2, for example, it is possible to shred the chips that are generated and improve chip discharge performance. However, because the volume of chips generated per unit time remains unchanged even if the chips are shredded, chip clogging cannot be resolved unless the cross-sectional area of ​​the chip discharge groove is secured.

[0005] In this regard, for example, Patent Document 3 discloses a technology for improving chip evacuation performance at or near the bottom cutting edge by providing a sub-groove (4a) with a weaker helix angle than the main groove (4b) forming the peripheral cutting edge near the bottom cutting edge and ensuring a larger groove cross-sectional area. However, with this type of groove configuration, as the groove length increases, the sub-groove with a weaker helix angle is inevitably positioned further forward in the rotational direction than the sub-groove, digging into the circumferential flank of the peripheral cutting edge formed by the main groove (see, for example, Figure 7 of Patent Document 3). This reduces the rigidity of the peripheral cutting edge and contributes to the generation of chatter vibration during machining. For this reason, it is also impossible to provide a sub-groove with the same groove length as the main groove. In other words, with the groove configuration disclosed in Patent Document 3, improved chip evacuation performance is observed when machining to a depth equal to the sub-groove length. However, when the machining depth exceeds the groove length where only the main groove is located, the cross-sectional area of ​​the chip evacuation groove becomes significantly smaller than before, resulting in poor chip evacuation performance. In particular, in the case of plunge cutting, which requires a depth greater than the sub-groove length, chip clogging is likely to occur. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4936495 [Patent Document 2] Patent No. 5535315 [Patent Document 3] Patent No. 6693965 Summary of the Invention [Problem to be solved by the invention]

[0007] As such, it is difficult to achieve both chatter resistance and chip removal performance in cutting tools such as end mills. In particular, chip removal performance can be problematic in situations where a tool such as an end mill is used for thrust cutting, and there is thought to be room for improvement.

[0008] Therefore, an object of the present invention is to provide a cutting tool that, while taking into consideration rigidity, improves chip discharge performance, particularly when performing plunge cutting, and achieves both chatter resistance and chip discharge performance at a higher level. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the inventors have conducted various studies focusing on the structure of chip discharge grooves and their surroundings while keeping the above-mentioned problems in mind, and have come to obtain new findings. The present invention has been conceived based on such findings, and one aspect thereof is a cutting tool that rotates around a central axis, an end cutting edge formed to extend radially from a central axis side of the cutting tool in a tip end view of the cutting tool; a peripheral cutting edge extending from the tip end toward the base end of the cutting tool, the peripheral cutting edge forming a set of cutting edges together with the end cutting edge; a chip discharge groove provided around the central axis; It is equipped with The chip discharge groove is formed by two or more grooves including at least a main groove and a sub groove, which have different helix angles; This cutting tool has the smallest twist angle of the main groove that forms the peripheral cutting edge on the ridge line with the peripheral side surface of the cutting tool, and the twist angle of the sub-groove that is adjacent to the main groove and is positioned forward in phase with the main groove in the tool rotation direction is larger than the twist angle of the main groove.

[0010] With the cutting tool described above, even if the chip evacuation groove is long, the sub-groove does not interfere with the circumferential flank of the peripheral cutting edge located further forward in the tool rotation direction. The rigidity of the peripheral cutting edge is affected by the thickness of the main groove forming the peripheral cutting edge and the sub-groove located behind the main groove in the rotation direction of the peripheral cutting edge. However, with the cutting tool described above, this thickness can be maintained at a constant value or higher from the tip to the base end of the peripheral cutting edge. This makes it possible to suppress chatter vibration during machining, even when deep cutting depths are required. Furthermore, since the sub-groove can be made long, a wide cross-sectional area of ​​the chip evacuation groove can be ensured even at the base end of the peripheral cutting edge. This allows for good chip evacuation, even when deep cutting depths are required, making the maximum use of the cutting length of the peripheral cutting edge.

[0011] In the cutting tool described above, the twist angle of the (n+1)th sub-groove, which is adjacent to the nth (n is a natural number) sub-groove and is positioned further forward in phase with respect to the nth sub-groove in terms of tool rotation, may be larger than the twist angle of the nth sub-groove.

[0012] In the cutting tool as described above, the bottom cutting edge and the peripheral cutting edge may be connected by a corner cutting edge consisting of a curved cutting edge.

[0013] In the cutting tool as described above, the bottom cutting edge and the peripheral cutting edge may be connected by a corner cutting edge consisting of a chamfered cutting edge.

[0014] In the cutting tool as described above, when the cutting surface of the bottom cutting edge is positioned to face forward and viewed from the side perpendicular to the central axis, the bottom cutting edge may be configured to recede from the tip end of the tool to the base end as it moves from the outer periphery of the tool toward the center of the tool.

[0015] In the cutting tool as described above, the bottom cutting edge may be formed in a shape that does not extend beyond the central axis when viewed from the tip.

[0016] In the cutting tool as described above, the bottom cutting edge may extend linearly in the radial direction when viewed from the tip.

[0017] In the cutting tool as described above, the bottom cutting edge may extend in a concave arc shape along the radial direction when viewed from the tip.

[0018] In the cutting tool as described above, the head may be configured to be detachable from the shank. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a perspective view showing an example of an end mill in an embodiment of a cutting tool according to the present invention, viewed from the tip side. FIG. [Figure 2] FIG. 2 is a view of the end mill shown in FIG. 1 as seen from the tip side. [Figure 3] FIG. 2 is a diagram showing the cross-sectional shape of the end mill at a position that is 50% of the tool diameter along the central axis. [Figure 4] 10A and 10B are cross-sectional views comparing the shapes of the end mill before and after forming the sub-groove. [Figure 5] 1A to 1C are diagrams illustrating features of an end mill according to an embodiment of the present invention. [Figure 6] FIG. 10 is a side view showing a modified example of the end mill (an example in which the chip discharge groove is formed by one main groove and two sub-grooves). [Figure 7] FIG. 10 is a perspective view seen from the tip side, showing a modified example of the end mill (an example in which the chip discharge groove is formed by one main groove and two sub-grooves). [Figure 8] FIG. 2 is a side view of the end mill. [Figure 9] FIG. 9 is a view of the end mill shown in FIG. 8 as seen from the tip. [Figure 10] FIG. 1 is a diagram showing the shape of an example of an end mill when viewed with the rake face facing forward. [Figure 11] 1A and 1B are diagrams showing an example of a cutting tool having a tip portion formed of a carbide insert and detachable from a shank. DETAILED DESCRIPTION OF THE INVENTION

[0020] A preferred embodiment of a cutting tool according to the present invention will be described in detail below with reference to the drawings (see Fig. 1, etc.). An end mill to which the present invention is applied will be described below, but this is merely one preferred example, and as will become clear from the following description, the present invention can also be applied to tools other than end mills, which are a type of cutting tool that rotates around a central axis.

[0021] The end mill 1 is a cutting tool (milling tool) that rotates around a central axis 10A to perform cutting, and is composed of, for example, a shank 50 and an exchangeable head 10 that can be attached to and detached from the shank 50 (see Figures 1, 11, etc.). The head 10 is provided with a bottom cutting edge 21, a corner cutting edge 22, a peripheral cutting edge 24, a gash 25, and a chip discharge groove 30 (see Figures 1, 2, etc.).

[0022] The bottom cutting edge 21 is a blade formed at the tip 10t of the head 10, and is formed to extend radially from the central axis 10A of the head 10 when viewed from the tip 10t (see FIGS. 1 and 2). In other words, if the plane perpendicular to the central axis 10A that passes through the tip 10t of the head 10 is defined as the tip surface S1 (see FIG. 10), the bottom cutting edge 21 is formed to extend linearly radially from the intersection of the central axis 10A and the tip surface S1 of the head 10. Incidentally, a modified example (an example in which the bottom cutting edge 21 is not linear) is one in which the bottom cutting edge 21 extends radially in a concave arc shape (the bottom cutting edge 21 has a concave arc shape when viewed from the tip). In this case, chips generated by the bottom cutting edge 21 are curved along the concave curved surface, making them easier to discharge. Multiple bottom cutting edges 21, for example, three, are arranged at equal intervals in the circumferential direction. The specific shape of these bottom cutting edges 21 is not particularly limited. For example, in the head 10 of this embodiment, the bottom cutting edges 21 extend linearly in the radial direction and are formed so as not to extend beyond the central axis 10A when viewed from the tip (see FIG. 2). By arranging all bottom cutting edges 21 so as not to extend beyond the central axis 10A, all bottom cutting edges 21 can be used to process the area near the center of the hole, particularly during plunge cutting. This prevents damage to some cutting edges 21, even under high feed rates, ensuring stable processing. Incidentally, in a head with a structure in which one of the multiple bottom cutting edges extends beyond the central axis when viewed from the tip, only one bottom cutting edge is used to process the area around the central axis during plunge cutting. In contrast, in this embodiment, with three bottom cutting edges 21 that process the area around the central axis 10A, the load is distributed among these three cutting edges 21, leading to more stable processing.

[0023] In addition, the bottom cutting edge 21 in the head 10 of this embodiment is configured to recede from the tip 10t side to the base end 10b side as it moves from the tool outer periphery toward the tool center where the central axis 10A is located, in a side view (or a side view from a direction perpendicular to the central axis 10A) with the rake face 21r of the bottom cutting edge 21 facing forward (see FIG. 10). In other words, the bottom cutting edge 21 has an angle θ (concave angle of the bottom cutting edge 21) with respect to a line H perpendicular to the central axis 10A. 21is a positive angle, and is formed so as to retreat from the tip 10t side to the base end 10b side as it approaches the center of the tool. 21 By making the angle a positive angle, a clearance is secured between the bottom cutting edge 21 and the machined bottom surface, and good machined surface quality can be obtained.

[0024] The peripheral cutting edge 24 is a blade formed in a spiral shape on the peripheral side surface 10s of the head 10 so as to extend from the tip 10t of the head 10 toward the base end 10b of the head 10. The peripheral cutting edge 24 and the bottom cutting edge 21 are connected via corner cutting edges 22 to form a set or continuous cutting edge 20 (see Figures 1, 2, 10, etc.). Therefore, the number of cutting edges 20 is the same as the number of bottom cutting edges 21, corner cutting edges 22, and peripheral cutting edges 24. Note that while the head 10 is described here as being detachable from the shank 50, it is of course possible to apply this to a solid end mill (an end mill with a structure in which the head and shank are integrated), although this is not specifically shown.

[0025] The corner cutting edge 22 is a blade formed in the corner between the bottom cutting edge 21 and the peripheral cutting edge 24 so as to connect them (see Figures 1, 2, etc.). Although not shown in detail, the corner cutting edge 22 may be a curved cutting edge (curved cutting edge) or a straight cutting edge (chamfered cutting edge). Note that while the case where the corner cutting edge 22 is provided is described here as an example, the end mill 1 may also have no corner cutting edge and the bottom cutting edge 21 and peripheral cutting edge 24 may be directly connected (so-called pin angle specification).

[0026] The chip discharge groove 30 is a groove formed in a spiral shape around the central axis 10A of the head 10 to discharge chips generated during cutting. The chip discharge groove 30 in the end mill 1 of this embodiment is formed of two or more grooves including a main groove 31 and a sub-groove 32. There is only one main groove 31, and the sub-grooves 32 are made up of n grooves (n is a natural number). The main groove 31 is arranged so that the peripheral cutting edge 24 is formed on the ridge formed by the outline of the main groove 31 and the peripheral side surface 10s of the head 10 (see FIG. 1, etc.). The nth sub-groove 32 n are arranged so as to be located forward in the rotational direction (see FIG. 2) than the main groove 31. For example, when there are two sub-grooves 32, the first sub-groove 321 is located forward in the rotational direction than the main groove 31, and the second sub-groove 322 is located forward in the rotational direction than the first sub-groove 321 (see FIGS. 6 and 7).

[0027] The main groove 31 is formed with a helix angle α. The n-th sub-groove 32 is formed with a helix angle β n These twist angles α and β n are different in magnitude. n is α<β n For example, when there is one minor groove 32 (n=1), the twist angle β1 of the first minor groove 321 is larger than the twist angle α of the main groove. (n+1) Twist angle β (n+1) is the nth minor groove 32 n Twist angle β n (See Figs. 6 and 7, etc.) The chip discharge groove 30 is formed by a plurality of grooves (main groove 31 and sub groove 32). n ), the contact area between the chips and the chip discharge groove 30 is reduced, so that even better chip discharge can be expected.

[0028] The following describes the characteristics of an end mill 1 in which the chip discharge flute 30 is composed of the main flute 31 and the sub-floor 32 described above. To simplify the structure and make it easier to understand, we will explain the case where there is only one sub-floor 32 (n=1) (see FIG. 5). In this case, in the head 10 of the end mill 1, each of the multiple chip discharge flutes 30 is composed of two flutes (main flute 31, sub-floor 32) with different helix angles (α, β1), and the magnitude of the helix angle is α<β1. In other words, the main flute 31 has a "weak twist" and the sub-floor 32 has a "strong twist." Therefore, in a head 10 in which the chip discharge flute 30 is configured in this way, even if the chip discharge flute 30 is made longer, the sub-floor 32 will not interfere with the circumferential flank of the peripheral cutting edge 24, which is located further forward in the tool rotation (see FIG. 5).

[0029] In general, the rigidity of the peripheral cutting edge 24 is affected by the thickness T (thickness of the back metal) between the main groove 31 forming the peripheral cutting edge 24 and the sub groove 32 located behind the peripheral cutting edge 24 in the direction of rotation. In the head 10 of this embodiment described so far, the magnitude of the twist angles of the main groove 31 and the sub groove 32 is twist angle α<twist angle β1. Therefore, even in the case of a chip groove 30 with a relatively long groove length, the sub groove 32 does not interfere with the flank face 24f of the peripheral cutting edge 24 that is further forward in the direction of rotation than the sub groove 32 as it approaches the base end 10b. In fact, the thickness T of the back metal of the cutting edge 20 becomes thicker as it approaches the base end 10b (see FIG. 5). Therefore, in this head 10, the thickness T is maintained at a constant value or more from the tip (end on the tip 10t side) to the base (end on the base end 10b side of the head 10) of the peripheral cutting edge 24, and chatter vibrations can be suppressed during machining, even when a deep cutting depth is required. In addition, since the groove length of the sub-groove 32 can be increased, it is possible to ensure a wide cross-sectional area of ​​the chip discharge groove 30 even in the portion of the peripheral cutting edge 24 closer to the base end 10b. Therefore, good chip discharge performance can be achieved even when a deep cutting depth is required, which makes the most of the cutting length of the peripheral cutting edge 24 (see Figure 5, etc.).

[0030] [Examples of main and sub groove shapes] For reference, an example of the cross-sectional shape of the end mill 1 at a position 50% of the tool diameter along the central axis 10A is shown in Figure 3. The shapes of the bottom surfaces of the main groove 31 and the sub-groove 32 are as shown in the figure (see Figure 3). In addition to the cross-sectional shape shown in Figure 3, a cross-sectional view comparing the shapes of the end mill 1 before and after forming the sub-groove 32 is shown in Figure 4 for reference.

[0031] [Twist angles α, β n Examples of specific examples: Twist angles α and β in the head 10 of this embodiment n Specific examples such as the above will be explained.

[0032] In the case of a so-called three-blade head 10 having an outer diameter of 10 mm and three cutting edges 20 (here, the three cutting edges 20 are referred to as the "first cutting edge," "second cutting edge," and "third cutting edge," respectively), suitable examples of the twist angle α of the main groove 31 and the twist angle β of the single secondary groove 32 are as follows: [Table 1]

[0033] When the peripheral cutting edge 24 is formed with a length that is 75% of the tool diameter from the tip surface S1 along the central axis 10A, it is preferable that the main groove 31 be formed with a length that is 90% of the tool diameter from the tip surface S1 along the central axis 10A. When the sub-groove 32 is formed with a length that is 110% of the tool diameter along the central axis 10A from the tip face S1, the recess of the sub-groove 32 should be arranged so that the core thickness CT is 30% of the tool diameter in a cross section that is 50% of the tool diameter along the central axis 10A from the tip face S1. Incidentally, when a test was conducted using a sample whose core thickness CT was 38% of the tool diameter, it was confirmed that good chip evacuation was not possible (see Figure 3). Length of the peripheral cutting edge 24≦length of the main groove 31<length of the sub-groove 32 nIt is also preferable that the groove length is such that: With this configuration, a wide cross-sectional area of ​​the chip discharge grooves 30 can be secured even at the base end of the peripheral cutting edge 24 (the end portion closer to the base end 10b of the head 10), and good chip discharge can be achieved even under cutting conditions with a large depth of cut.

[0034] The above-described embodiment is one example of a preferred embodiment of the present invention, but the present invention is not limited to this embodiment and various modifications are possible within the scope of the present invention. For example, as already mentioned, the present invention has been described so far as applied to an end mill, but it goes without saying that the present invention can also be applied to tools other than end mills as long as they are cutting tools that rotate around a central axis.

[0035] In the above-described embodiment, the minor groove 32 n Although the explanation has been given mainly on the case where the number of the minor grooves is one (n=1) or two, these are merely preferred examples, and the number is not limited. n The more the number of grooves is increased, the larger the area of ​​the chip discharge grooves 30 becomes, which acts to further improve the chip discharge performance. [Industrial Applicability]

[0036] The present invention is suitable for application to cutting tools such as end mills. [Explanation of symbols]

[0037] 1...End mill (cutting tool) 10...Head 10A…Center axis 10b…Proximal end 10s...peripheral side 10t...tip 20...(a set of) cutting edges 21…Bottom blade 21r...Scooping face 22...Corner cutting edge 24...Peripheral blade 24f...Flank face of peripheral cutting edge 25...Gash 30...Chip discharge groove 31…Main groove 32...Minor groove 32 n …nth minor groove 50...Shank T: Thickness formed by the main groove 31 forming the peripheral cutting edge 24 and the sub-groove 32 arranged behind the peripheral cutting edge 24 in the rotation direction CT…core thickness H: Line perpendicular to the central axis 10A S1…Tip surface α...(Main groove) helix angle β n …Twist angle (of the nth minor groove) θ 21 …Flatness of the bottom cutting edge

Claims

1. A cutting tool that rotates around a central axis, an end cutting edge formed to extend radially from the central axis side of the cutting tool in a tip end view of the cutting tool; a peripheral cutting edge extending from the tip end toward the base end of the cutting tool, the peripheral cutting edge forming a set of cutting edges together with the end cutting edge; a chip discharge groove provided around the central axis; It is equipped with the chip discharge groove is formed by two or more grooves including at least a main groove and a sub groove, the grooves having different helix angles; A cutting tool in which the twist angle of the main groove, which forms the peripheral cutting edge on a ridge line with the peripheral side surface of the cutting tool, is smallest, and the twist angle of the sub-groove, which is tangent to the main groove and positioned phase-shifted forward in the tool rotation direction from the main groove, is larger than the twist angle of the main groove.

2. 2. The cutting tool according to claim 1, wherein a helix angle of an (n+1)th sub-groove, which is tangent to an n-th (n is a natural number) sub-groove and is arranged further forward in phase with respect to the n-th sub-groove in terms of tool rotation, is larger than a helix angle of the n-th sub-groove.

3. The cutting tool according to claim 1 , wherein the bottom cutting edge and the peripheral cutting edge are connected by a corner cutting edge consisting of a curved cutting edge.

4. The cutting tool according to claim 1 , wherein the bottom cutting edge and the peripheral cutting edge are connected by a corner cutting edge consisting of a chamfered cutting edge.

5. A cutting tool according to any one of claims 1 to 4, wherein, when viewed from the side in a direction perpendicular to the central axis with the cutting surface of the bottom cutting edge facing forward, the bottom cutting edge retreats from the tip side to the base side as it moves from the outer periphery of the tool toward the center of the tool.

6. The cutting tool according to claim 1 , wherein the bottom cutting edge is formed in a shape that does not extend beyond a central axis when viewed from the tip end.

7. The cutting tool according to claim 1 , wherein the bottom cutting edge extends linearly in the radial direction when viewed from the tip end.

8. The cutting tool according to claim 1 , wherein the bottom cutting edge extends in a concave arc shape along the radial direction when viewed from the tip end.

9. The cutting tool according to claim 1 , wherein the head is detachably attached to the shank.

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