Rotary cutting tools and tool bodies

Abstract

This achieves excellent chip removal performance and high rigidity of the tool body, and also provides a structure that makes it easy to form through holes that contribute to increasing the amount of coolant supplied. [Solution] A rotary cutting tool (1) having a cutting member (60) at its tip side (10t) and a cylindrical or approximately cylindrical shape, the rotary cutting tool (1) is provided with a chip discharge hole (30) that is formed from the tip side (10t) toward the base end side (10b) and at least a portion of a cross section perpendicular to the rotation center axis (10A) has a non-circular cross section having short sides and long sides.

Description

[Technical Field]

[0001] The present disclosure relates to rotary cutting tools and tool bodies. [Background technology]

[0002] When drilling holes using rotary cutting tools, such as tools for BTA (Boring & Trepanning Association) machining, it is necessary to supply coolant to the cutting edge of the cutting element provided at the tip (see, for example, Patent Documents 1 and 2). Conventional rotary cutting tools generally have a structure in which coolant is supplied to the cutting edge via an oil supply groove provided on the outer periphery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2003-502163 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-66678 Summary of the Invention [Problem to be solved by the invention]

[0004] However, because BTA tools are equipped with an opening (chip mouth) for discharging chips, much of the coolant supplied from the base end tends to be discharged from the chip mouth before reaching the tip of the tool. Furthermore, since highly viscous, water-insoluble cutting oil is often used as the coolant, it is difficult to supply sufficient coolant to the cutting edge.

[0005] To address this issue, the applicant has proposed a structure that allows sufficient coolant to be supplied to the tool tip by providing a through-hole extending from the outer circumferential surface of the tool body toward the tip as part of the coolant flow path. However, as a further improvement, there is a strong demand for a structure that makes it easy to form a through-hole that contributes to increasing the amount of coolant supplied while achieving both excellent chip evacuation performance and high rigidity (strength) of the tool body.

[0006] Therefore, the present disclosure has been made in consideration of the above circumstances, and aims to provide a tool body and a rotary cutting tool that can achieve excellent chip removal performance and high rigidity (strength) of the tool body, and further has a structure that makes it easy to form through holes that contribute to increasing the amount of coolant supplied. [Means for solving the problem]

[0007] [1] To solve the above problems, one example of a rotary cutting tool according to the present disclosure is a rotary cutting tool having a cutting member at its tip end and a cylindrical or approximately cylindrical shape, with a chip discharge hole that is formed from the tip end toward the base end and at least a portion of a cross section perpendicular to the central axis of rotation of the rotary cutting tool has a non-circular cross section having short and long sides (the cross section perpendicular to the central axis of rotation of the rotary cutting tool includes such a non-circular cross section). The "cutting member" may be a cutting insert that is attached to a mounting seat appropriately provided at the tip end of the rotary cutting tool, or a tip brazed to the tip end.

[0008] This configuration allows chip discharge holes to be formed from the tip end toward the base end of the rotary cutting tool (e.g., radially inward from the outer circumferential surface), and at least a portion of the chip discharge holes has a non-circular cross-sectional shape (e.g., a pseudo-rectangular shape), thereby ensuring a relatively large cross-sectional area between the outer circumferential surface and the long side of the chip discharge hole. This allows for an increased material thickness in that area, improving the rigidity of that area and the entire rotary cutting tool. As a result, the cutting force generated by the cutting edge of the cutting member can be primarily absorbed by this highly rigid area, contributing to reduced deformation of the rotary cutting tool and improved machining durability. Furthermore, rather than simply reducing the cross-sectional area of ​​the chip discharge holes to improve rigidity, adopting a non-circular cross-section with short and long sides ensures an appropriate chip flow path and maintains excellent discharge performance. Furthermore, increasing the material thickness facilitates the formation of a coolant passage with a through-hole, thereby increasing the amount of coolant supplied to the cutting edge.

[0009] [2] As a specific configuration for realizing a chip discharge hole having such characteristics, for example, when a predetermined two-dimensional coordinate system having the coordinate of the rotation center axis as the origin is defined in at least a part of the above cross section, the hole may be configured to satisfy the relationships shown in the following equations (1) and (2). d1≧D×0.8 …(1) d2≦D×0.7 …(2) D: Tool diameter of the rotary cutting tool d1: The maximum inner diameter of the non-circular cross section in the first and third quadrants, which mainly correspond to (include) the short side portions d2: The maximum inner diameter of the non-circular cross section in the second and fourth quadrants, which mainly correspond to (include) the long side portions.

[0010] Here, examples of the "two-dimensional coordinate system" include an "XY coordinate system in which the X axis is the direction connecting the rotation axis and the outermost end (outermost point) of the cutting edge of the cutting member" and, if the cutting member is a cutting insert, an "XY coordinate system in which the X axis is the direction parallel to the bottom surface of the mounting seat (insert seat) of the cutting insert in a cross section passing through the mounting seat." In this case, the quadrant located in front of the cutting edge of the cutting member in the "XY coordinate system" is the "first quadrant." Based on the "first quadrant," the "second quadrant," "third quadrant," and "fourth quadrant" are defined counterclockwise (same below). Note that "front" and "rear" here refer to "front and rear" in the direction of rotation of the rotary cutting tool. Furthermore, the "inner diameter" of a "non-circular cross section" refers to the diameter of a line segment passing through the above-mentioned "origin."

[0011] This configuration ensures a relatively large area between the outer peripheral surface of the rotary cutting tool and the long side of the chip discharge hole, thereby improving the rigidity of that area and the entire rotary cutting tool. Furthermore, since the chip flow path can be properly secured, stable and excellent chip discharge performance is achieved. Furthermore, since the through-hole can be easily formed as part of the coolant flow path, the amount of coolant supplied can be increased, improving lubrication and cooling performance.

[0012] [3] Similarly, when a predetermined two-dimensional coordinate system having the coordinate of the rotation center axis as the origin is defined in at least a part of the cross section, the structure may be configured to satisfy the relationship shown in the following formula (3). t1 <t2 …(3) t1: Thickness of the center of the short side in the first and third quadrants (including the short side) that mainly correspond to the above short side t2: Thickness of the center of the long side in the second and fourth quadrants (including the long side)

[0013] Here, "thickness" refers to the distance from the outer peripheral surface of the rotary cutting tool to the inner peripheral surface of the chip evacuation hole in the cross section, and its imaginary extension passes through the origin. By configuring the rotary cutting tool to satisfy the relationship of formula (3), the space in the first and third quadrants located in front of the cutting edge of the cutting member can be relatively enlarged to ensure chip evacuation performance, while the rigidity of the rotary cutting tool in the second and fourth quadrants located behind the cutting edge of the cutting member and primarily responsible for receiving cutting forces can be relatively increased. This makes it possible to simultaneously suppress deformation of the rotary cutting tool and improve chip evacuation performance.

[0014] [4] Similarly, it is also useful to configure at least a portion of the cross section so that when a predetermined two-dimensional coordinate system with the coordinates of the center of rotation as the origin is defined, the relationship shown in the following formula (4) is satisfied. s1 <s2 …(4) s1: Cross-sectional area of ​​the rotary cutting tool in the first and third quadrants that mainly correspond to (include) the short side portions s2: Cross-sectional area of ​​the rotary cutting tool in the second and fourth quadrants mainly corresponding to (including) the long side portion

[0015] Here, "cross-sectional area" refers to the area of ​​the material portion of the rotary cutting tool included in the region corresponding to each quadrant in the cross section. Satisfying the relationship of formula (4) makes it easy to ensure cross-sectional rigidity in the second and fourth quadrants, where large loads act during cutting. Furthermore, by setting cross-sectional area s2 larger than cross-sectional area s1, it becomes possible to design a structure in which structural support is concentrated in the second and fourth quadrants while ensuring space in the first and third quadrants for forming a chip evacuation path.

[0016] [5] In the above configuration, the inner peripheral surface of the chip discharge hole may be formed smooth at least in the chip discharge direction (from the tip side to the base side). In this disclosure, "smooth" refers to a state that satisfies at least one of the following conditions, at least in the chip discharge direction: (1) no sharp corners (edges) or discontinuous steps; (2) only continuous curved or flat surfaces; (3) no machining marks; and (4) no substantially visible machining marks from machining processes such as filleting, curved surface finishing, or polishing. This configuration can prevent chips from accumulating or adhering to steps or corners, further improving chip flow and ultimately increasing the overall efficiency of the cutting process.

[0017] [6] More specifically, the inner peripheral surface of the chip discharge hole may be configured to satisfy the relationship shown in the following formula (5). R≧0.1mm …(5) R: The minimum radius of curvature of the edge if the inner circumferential surface has an edge

[0018] Here, "minimum radius of curvature" refers to the minimum radius of curvature calculated based on edge (portion) profile data obtained using, for example, a contact or non-contact profile measuring instrument, in accordance with JIS B 0621:1984 "Definition and Display of Geometric Deviation." Even when the inner peripheral surface has an edge, setting the minimum radius of curvature R of that portion to the above value has the advantage of improving chip transportability and reducing friction. Furthermore, while it is not necessary to achieve a mirror-like smoothness, if the minimum radius of curvature R of the edge is less than 0.1 mm, chips may become caught or be poorly discharged.

[0019] [7] Furthermore, as mentioned above, the rotary cutting tool may be configured to have a coolant flow path with a through hole extending from the outer peripheral surface toward the tip side. In this way, coolant that may be sucked into the chip discharge hole can be directly and reliably supplied to the tip side of the rotary cutting tool via the through hole. This allows a sufficient amount of coolant to be supplied to the cutting edge of the cutting member attached to the tip side, further improving lubrication and cooling performance during cutting, especially around the cutting edge.

[0020] [8] More specifically, the coolant flow path may extend between the long side portion and the outer peripheral surface and penetrate all the way to the end face on the tip side. This avoids the need for a complex coolant flow path, reducing pressure loss and resistance of the coolant flowing through the through-hole, allowing a sufficient amount of coolant to be supplied to the cutting edge more smoothly. Furthermore, this configuration allows the coolant flow path to be formed as a relatively simple and linear path without unnecessary bending, effectively reducing pressure loss (pressure loss) and flow resistance of the coolant. This allows a sufficient amount of coolant to be supplied stably to the cutting edge, further improving the lubrication and cooling performance around the cutting edge during cutting.

[0021] [9] The tool body according to the present disclosure has a cylindrical or substantially cylindrical shape, a mounting seat provided at the tip end to which a cutting insert is attached, and a chip discharge hole formed from the tip end toward the base end, at least a portion of a cross section perpendicular to the central axis of rotation of the tool body having a non-circular cross section having short and long sides. Thus, the "tool body" according to the present disclosure corresponds to the portion of the "rotary cutting tool" according to the present disclosure excluding the cutting insert as a cutting member. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a perspective view schematically showing the overall configuration of a rotary cutting tool 1 according to a first embodiment. [Figure 2] FIG. 2 is a front view of the rotary cutting tool 1 shown in FIG. [Figure 3] FIG. 2 is a plan view of the rotary cutting tool 1 shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV (X axis) in FIG. [Figure 5] 4(A) to 4(C) are cross-sectional views taken along lines AA, BB, and CC in FIG. 3, respectively. [Figure 6] FIG. 10 is a perspective view schematically showing the overall configuration of a rotary cutting tool 2 according to a second embodiment. [Figure 7] FIG. 7 is a front view of the rotary cutting tool 2 shown in FIG. [Figure 8] FIG. 7 is a plan view of the rotary cutting tool 2 shown in FIG. [Figure 9] FIG. 8 is a cross-sectional view taken along line IX-IX (X axis) in FIG. [Figure 10] 9(A) to 9(C) are cross-sectional views taken along the lines DD, EE, and FF in FIG. 8, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. To facilitate understanding of the description, the same components in each drawing will be assigned the same reference numerals whenever possible, and redundant description will be omitted. Note that the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to only these embodiments. Furthermore, the present disclosure can be modified in various ways without departing from the gist thereof. Furthermore, a person skilled in the art can adopt embodiments in which the elements described below are replaced with equivalents, and such embodiments are also within the scope of the present disclosure.

[0024] First Embodiment Fig. 1 is a perspective view showing the overall configuration of a rotary cutting tool 1 according to this embodiment, and Fig. 2 and Fig. 3 are a front view and a plan view, respectively, of the rotary cutting tool 1 shown in Fig. 1. Also, Fig. 4 is a cross-sectional view taken along line IV-IV (X-axis) in Fig. 2.

[0025] 1 to 4, the rotary cutting tool 1 includes a tool body 10 (in other words, the portion of the rotary cutting tool 1 excluding the cutting insert 60) having a mounting seat 20 on a tip side 10t to which a cutting insert 60 is attached. The rotary cutting tool 1 has a generally cylindrical shape overall, and includes a connection portion 15, a tapered portion 16, and a large-diameter portion 17 from a base end side 10b of the tool body 10 to the tip end side 10t, and is formed to extend along a rotation center axis 10A (the Z-axis direction in FIG. 1 ) of the rotary cutting tool 1 and the tool body 10. In addition, a chip discharge hole 30 for discharging chips and coolant is defined from the tip end side 10t toward the base end side 10b of the tool body 10, radially inward of the outer circumferential surface 14.

[0026] The connecting portion 15 is a cylindrical portion located near the base end 10b of the tool body 10, and the large diameter portion 17 is located near the tip end 10t of the tool body 10 and has a larger diameter than the connecting portion 15. The tapered portion 16 connects the connecting portion 15 and the large diameter portion 17 and has a tapered outer peripheral surface. The connecting portion 15 is a portion to be connected to a drill pipe (not shown), and for example, a thread (not shown) that screws onto the drill pipe is formed on the outer peripheral surface of the connecting portion 15 (however, the present invention is not limited to this configuration).

[0027] The chip discharge hole 30 is formed as close as possible to the cutting edge of the cutting member. However, in this embodiment, in order to ensure space for replacing the cutting insert 60, the chip discharge hole 30 is formed radially inward from the vicinity of the mounting seat 20 provided on the tip side 10t toward the base side 10b, relative to the outer peripheral surface 14 of the tool body 10. The tip side 10t of the tool body 10 has a portion called a chip pocket, and openings 31 and 32 (also called "chip mouths") of the chip discharge hole 30 are provided at the rear end of this chip pocket.

[0028] The portion that opens to the outer periphery of the tool body 10 is a chip pocket, and the chip discharge hole 30 begins where a wall is formed on the outer periphery of the tool body 10. As will be described later, the rotary cutting tool 1 of this embodiment uses three cutting inserts 60, two of which face the same direction and the remaining one faces the opposite direction, so that chips are generated in two directions. For this reason, in this embodiment, two openings, one large and one small, are provided on the tip end face 12. The chip discharge holes 30 continuing from each of the two openings 31 and 32 that serve as chip inlets join at a position closer to the base end side 10b than the tip end face 12.

[0029] 5A to 5C are cross-sectional views taken along line AA (large diameter portion 17), line BB (tapered portion 16), and line CC (connecting portion 15) in FIG. 3, respectively. As shown in FIGS. 5A to 5C, the chip discharge hole 30 has cross sections perpendicular to the rotation axis 10A at the connecting portion 15, the tapered portion 16, and the large diameter portion 17, each having a different shape. Also, as shown in FIG. 4, the inner circumferential surface 30N of the chip discharge hole 30 is formed smoothly overall, without any steps or corners (edges), at least in the chip discharge direction (from the tip side 10t to the base side 10b) at the interconnection portion of the connecting portion 15, the tapered portion 16, and the large diameter portion 17. More specifically, the inner circumferential surface 30N of the chip discharge hole 30 is configured to satisfy the relationship shown in the following formula (5). In the formula, R indicates the minimum radius of curvature of the edge if the inner circumferential surface 30N has an edge. R≧0.1mm …(5)

[0030] Further, cutting inserts 60 and guide pads 80 are detachably attached to the tip side 10t of the tool body 10. The specific arrangement and form of these cutting inserts 60 and guide pads 80 are not particularly limited. For example, in this embodiment, two cutting inserts 60 are attached to the opening 31 of the chip discharge hole 30, and one cutting insert 60 is attached to the opening 32 with insert mounting screws 70. Furthermore, guide pads 80 are attached to the outer peripheral surface 14 near the tip side 10t, on the radially outer side (left side in FIG. 2 ) of the cutting inserts 60 at the opening 32 and on the radially outer side (downward in FIG. 2 ) perpendicular to the juxtaposition direction of the two cutting inserts 60 at the opening 31.

[0031] 5A to 5C, an XY coordinate system is defined in which the coordinate of the rotational center axis 10A of the rotary cutting tool 1 and the tool body 10 is defined as an origin G, and the direction connecting the origin G and the outermost end (outermost point) of the cutting edge 61 of the cutting insert 60 is defined as the X axis. In this embodiment, the origin G coincides with the center of an imaginary perfect circle C having the maximum outer diameter of the tool body 10 (including a part of the outer peripheral surface 14). In this XY coordinate system, the front of the cutting edges 61 of the two cutting inserts 60 arranged side by side (upper in FIG. 2) is a first quadrant 51 (X>0, Y>0). Furthermore, the front of the cutting edge 61 of another cutting insert 60 (lower in FIG. 2) is a third quadrant 53 (X<0, Y<0). Furthermore, the rear of the cutting edges 61 of the two cutting inserts 60 arranged side by side (lower in FIG. 2) is a fourth quadrant 54 (X>0, Y<0). Furthermore, the rear (upper in FIG. 2) of the cutting edge 61 of another cutting insert 60 is in the second quadrant 52 (X<0, Y>0).

[0032] The chip discharge hole 30 has a non-circular cross section at the large diameter portion 17 and the tapered portion 16 shown in FIGS. 5A and 5B (areas without diagonal hatching). These non-circular cross sections have short sides extending radially slightly inward along the outer peripheral surface 14, mainly in the first quadrant 51 and the third quadrant 53. The two-dimensional coordinate system in each cross section follows the XY cross section including the cutting edge 61 shown in FIG. 2 (the same applies below). Furthermore, these non-circular cross sections have long sides extending radially further inward in a substantially linear manner, mainly in the second quadrant 52 and the fourth quadrant 54. Meanwhile, the cross section of the chip discharge hole 30 at the connection portion 15 shown in FIG. 5C is a perfect circle. Thus, the cross sections shown in FIGS. 5A and 5B correspond to "at least a portion of a cross section perpendicular to the extension axis of the tool body" in this disclosure.

[0033] 5(A) and 5(B), the rotary cutting tool 1 and the tool body 10 are configured to satisfy the relationships shown in the following formulas (1) and (2): In the formulas, D represents the tool diameter of the rotary cutting tool 1, d1 represents the maximum inner diameter of the non-circular cross section of the chip discharge hole 30 in the first quadrant 51 and the third quadrant 53, and d2 represents the maximum inner diameter of the non-circular cross section of the chip discharge hole 30 in the second quadrant 52 and the fourth quadrant 54. d1≧D×0.8 …(1) d2≦D×0.7 …(2)

[0034] 5(A) and 5(B), the tool body 10 is configured to satisfy the relationships shown in the following formulas (3) and (4). In the formulas, t1 represents the thickness of the center of the short side in the first quadrant 51 and the third quadrant 53, and t2 represents the thickness of the center of the long side in the second quadrant 52 and the fourth quadrant 54. Furthermore, s1 represents the cross-sectional area of ​​the tool body 10 (shaded portion) in the first quadrant 51 and the third quadrant 53, and s2 represents the cross-sectional area of ​​the tool body 10 (shaded portion) in the second quadrant 52 and the fourth quadrant 54. t1 <t2 …(3) s1 <s2 …(4)

[0035] Furthermore, the tool body 10 is provided with a coolant flow passage 4 formed to supply coolant from the base end side 10b toward the tip end side 10t. The coolant flow passage 4 has through holes 4A, 4B penetrating the large diameter portion 17 from the outer peripheral surface 14 of the tool body 10 toward the tip end side 10t. Base end openings 4Ab, 4Bb of these through holes 4A, 4B are provided in the tapered portion 16, and tip end openings 4At, 4Bt of the through holes 4A, 4B are provided in the tip end surface 12 of the tool body 10. Of these, the base end openings 4Ab, 4Bb are preferably shaped to facilitate the introduction of coolant into the through holes 4A, 4B when the rotary cutting tool 1 is rotating and cutting. For example, the base end openings 4Ab, 4Bb may have a shape that is inclined while extending toward the tip end side 10t with respect to the rotation center axis 10A, and may also have a shape that extends in the circumferential direction.

[0036] 2 and 5, the through holes 4A, 4B are arranged side by side in the circumferential direction along the outer peripheral surface 14 and are provided in a portion of the tool body 10 where no chip discharge holes 30 exist, with the rotation center axis 10A sandwiched between them. That is, the through holes 4A, 4B pass between the outer peripheral surface 14 and the long sides of the chip discharge holes 30 in the second quadrant 52 and the fourth quadrant 54, penetrating all the way to the tip surface 12 of the tip side 10t. Furthermore, the tip side openings 4At, 4Bt of the through holes 4A, 4B are provided in a portion of the tip surface 12 where no openings 31, 32 of the chip discharge holes 30 exist, with the rotation center axis 10A sandwiched between them. In addition, the through hole 4B is shaped to branch into two branches midway toward the tip side 10t, and each branch is composed of two corresponding openings. In addition, the tip-side opening 4Bt of the through-hole 4B has an opening area smaller than the tip-side opening 4At of the through-hole 4A and is circular.

[0037] Second Embodiment FIG. 6 is a perspective view showing the overall configuration of the rotary cutting tool 2 according to this embodiment, and FIGS. 7 and 8 are a front view and a plan view, respectively, of the rotary cutting tool 2 shown in FIG. 6. FIG. 9 is a cross-sectional view taken along line XI-XI (X-axis) in FIG. 7. FIGS. 10A to 10C are cross-sectional views taken along line DD (large diameter portion 17), line EE (tapered portion 16), and line FF (connection portion 15), respectively, in FIG. 8. As shown in these figures, the rotary cutting tool 2 has the same configuration as the rotary cutting tool 1 according to the first embodiment, except that it includes a tool body 11 instead of the tool body 10. The tool body 11 has the same configuration as the tool body 10 according to the first embodiment, except that it does not include the through-holes 4A and 4B of the coolant flow passages 4.

[0038] Although the cross-sectional shapes of the tool body 11 of this rotary cutting tool 2 shown in Figures 10(A) and 10(B) are slightly different from the corresponding cross-sectional shapes of Figures 5(A) and 5(B), the tool body 11 is configured to satisfy the relationships shown in the following formulas (1) to (5) in the same manner as the tool body 10 of the rotary cutting tool 1. The parameters in the formulas are the same as those in the first embodiment. d1≧D×0.8 …(1) d2≦D×0.7 …(2) t1 <t2 …(3) s1 <s2 …(4) R≧0.1mm …(5)

[0039] <Effects of the embodiment> The rotary cutting tools 1, 2 and their respective tool bodies 10, 11 configured as described above provide the following advantageous effects. Specifically, the rotary cutting tools 1, 2 have chip discharge holes 30 radially inward from their outer peripheral surfaces 14, and at least a portion of the chip discharge holes 30 has a non-circular cross-sectional shape. This ensures a relatively large cross-sectional area s2 between the outer peripheral surface 14 and the long sides of the chip discharge holes 30, making it possible to increase the thickness t2 of the material in that area, thereby improving the rigidity of that area and of the rotary cutting tools 1, 2 as a whole.

[0040] Furthermore, the cutting force generated by the cutting edge 61 of the cutting insert 60 is greatest when the principal component (the force component perpendicular to the cutting edge 61 in the direction of rotation as viewed from the tip in FIG. 2 ) is the largest. In contrast, in the configuration employing the noncircular cross-section described above, the principal component of the cutting force can be absorbed mainly by the high-rigidity portions (portions corresponding to the second quadrant 52 and the fourth quadrant 54), thereby suppressing deformation of the rotary cutting tools 1 and 2 and improving their machining durability. Furthermore, rather than simply reducing the cross-sectional area of ​​the chip evacuation hole 30 to improve rigidity, employing a noncircular cross-section having short and long sides ensures an appropriate chip flow path, making it possible to maintain excellent evacuation performance.

[0041] Furthermore, increasing the material thickness facilitates the formation of through holes 4A, 4B, as in the tool body 10 of the rotary cutting tool 1, and these through holes 4A, 4B can be used to increase the amount of coolant supplied to the cutting edge 61. On the other hand, the tool body 11 of the rotary cutting tool 2 does not have through holes 4A, 4B, and therefore the cross-sectional area s2 between the long side of the non-circular cross section of the chip discharge hole 30 and the outer peripheral surface 14, and therefore the volume, can be easily increased. As a result, there is an advantage in that the rigidity of the portions (portions corresponding to the second quadrant 52 and the fourth quadrant 54) that receive the cutting force (particularly the principal component force) from the cutting edge 61 can be further increased.

[0042] In the cross sections shown in FIGS. 5(A) and 5(B) and 10(A) and 10(B), the following formulas (1) and (2) are used: d1≧D×0.8 …(1) d2≦D×0.7 …(2) Since the relationship shown in (a) is satisfied, a relatively large area is secured between the outer peripheral surface 14 and the long side of the chip discharge hole 30, thereby improving the rigidity of that portion and the entire rotary cutting tool 1, 2. This ensures an appropriate chip flow path, enabling stable and excellent chip discharge performance. Furthermore, since the tool body 10 of the rotary cutting tool 1 has through holes 4A, 4B as part of the coolant flow path 4, it is possible to increase the amount of coolant supplied to the cutting edge 61, thereby improving lubrication and cooling performance.

[0043] Furthermore, in the cross sections shown in FIGS. 5(A) and 5(B) and FIGS. 10(A) and 10(B), the following formula (3): t1 <t2 …(3) is satisfied, the spaces in the first and third quadrants 51 and 53 located in front of the cutting edge 61 of the cutting insert 60 can be relatively enlarged to ensure chip discharge performance, and the rigidity of the tool bodies 10 and 11 can be relatively increased in the second and fourth quadrants 52 and 54 that mainly contribute to receiving the cutting force (particularly the principal component force) behind the cutting edge 61 of the cutting insert 60. As a result, it is possible to suppress deformation of the rotary cutting tools 1 and 2 and improve chip discharge performance at the same time.

[0044] Furthermore, in the cross sections shown in FIGS. 5(A) and 5(B) and FIGS. 10(A) and 10(B), the following formula (4): s1 <s2 …(4) Since the relationship shown in the figure is satisfied, it is easy to ensure cross-sectional rigidity in the second quadrant 52 and the fourth quadrant 54, where a large load acts during cutting. Furthermore, by setting the cross-sectional area s2 larger than the cross-sectional area s1, it is possible to design the structure so that structural support is concentrated in the second quadrant 52 and the fourth quadrant 54, while ensuring space in the first quadrant 51 and the third quadrant 53 to form a chip discharge path.

[0045] Furthermore, the inner peripheral surface 30N of the chip discharge hole 30 is formed smoothly at least in the direction in which the chips are discharged (from the tip end to the base end), which prevents the chips from accumulating or adhering when there are steps or corners. This further improves the flow of chips, ultimately increasing the efficiency of the entire cutting process. More specifically, when the inner peripheral surface 30N of the chip discharge hole 30 satisfies the following formula (5): R≧0.1mm …(5) Since the relationship shown in is satisfied, the advantages of improved chip transport and reduced friction are obtained. In addition, although it is not necessary to achieve a smooth finish like a mirror finish, it is possible to suppress the chip getting caught and poor discharge that tend to occur when the minimum curvature radius R of the edge is smaller than 0.1 mm.

[0046] In order to form the chip discharge hole 30 having such a smooth inner peripheral surface 30N, additive manufacturing using a powder bed method using a metal 3D printer is effective, for example. In this case, from the viewpoint of maintaining the shape during manufacturing and ease of manufacturing, it is preferable to perform additive manufacturing from the base end side 10b of the rotary cutting tools 1, 2 toward the tip end side 10t, for example, that is, to use the end face of the base end side 10b as the reference surface (start surface of manufacturing) and to form the connecting portion 15, tapered portion 16, and large diameter portion 17 in that order perpendicular to that surface.

[0047] Furthermore, the rotary cutting tool 1 is provided with a coolant flow path 4 having through holes 4A, 4B extending from the outer circumferential surface 14 toward the tip side 10t, so that coolant that may be sucked into the chip discharge hole 30 can be supplied directly and reliably to the tip side 10t of the tool body 10 via the through holes 4A, 4B. This makes it possible to supply a sufficient amount of coolant to the cutting edge 61 of the cutting insert 60 attached to the tip side 10t, further improving lubrication and cooling performance during cutting, particularly around the cutting edge.

[0048] Furthermore, in the rotary cutting tool 1, the through holes 4A and 4B pass between the long side portion and the outer peripheral surface 14 and penetrate all the way to the tip surface 12 of the tip side 10t. This prevents the coolant flow path 4 from becoming complicated, reducing pressure loss and flow resistance of the coolant in the through holes 4A and 4B. This allows a sufficient amount of coolant to be supplied more smoothly to the cutting edge 61 of the cutting insert 60. This configuration also allows the coolant flow path 4 to be formed as a relatively simple and linear path without unnecessary bending, effectively reducing pressure loss and flow resistance of the coolant in the through holes 4A and 4B. As a result, a sufficient amount of coolant can be stably supplied to the cutting edge 61 of the cutting insert 60, further improving the lubrication and cooling performance around the cutting edge 61 during cutting.

[0049] Additionally, in the rotary cutting tools 1 and 2, three cutting inserts 60 are provided, and each cutting edge 61 is arranged in three locations, which tends to make it difficult to balance the cutting force using only those cutting edges 61. In contrast, in the rotary cutting tools 1 and 2, taking into consideration that the cutting force when two cutting inserts 60 are arranged is greater than when only one cutting insert 60 is arranged, the guide pads 80 are arranged in an approximately 270° direction (lower in FIGS. 2 and 7: fourth quadrant 54) and in an approximately 180° direction (left in FIGS. 2 and 7: a portion spanning the second quadrant 52 and the third quadrant 53) which stabilizes the cutting diameter, thereby making it possible to appropriately absorb the cutting force.

[0050] Furthermore, the through hole 4B constituting a part of the coolant flow path 4 is shaped to branch into two on the way to the tip side 10t of the rotary cutting tool 1, which makes it easier to increase the coolant flow rate while suppressing a decrease in tool rigidity at that location. Furthermore, the tip side opening 4Bt of the through hole 4B is smaller in opening area than the tip side opening 4At of the through hole 4A and is circular, which makes it possible to maintain a relatively higher strength in the fourth quadrant 54 where two cutting inserts 60 are arranged than in the second quadrant 52 where one cutting insert 60 is arranged.

[0051] The present embodiment has been described above with reference to specific examples. However, this is for the purpose of facilitating understanding of the present disclosure and is not intended to limit the present disclosure. In other words, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art are also encompassed within the technical scope of the present disclosure as long as they comprise the features of the present disclosure. Furthermore, unless otherwise specified, the elements, arrangements, materials, conditions, shapes, dimensions, sizes, scales, etc. of the above-described specific examples are not limited to those exemplified and can be modified as appropriate. Furthermore, the elements of the above-described specific examples can be combined as appropriate as long as no technical contradictions arise.

[0052] For example, the rotary cutting tools 1 and 2 described in the first and second embodiments are so-called indexable tools in which the cutting insert 60 can be detachably attached to the mounting seat 20 of the tool body 10 and 11. However, as described above, the present disclosure can also be applied to other tools. That is, the present disclosure can be suitably applied to the tool body 10 and 11 itself in a state in which the cutting insert 60 has been removed from the rotary cutting tool 1 and 2, or to rotary cutting tools of a type in which a tip such as a cemented carbide alloy is brazed. Furthermore, the through hole 4B may open to the tip surface 12 without bifurcating midway toward the tip side 10t. Furthermore, as described above, the specific arrangement and shape of the cutting insert 60 and the guide pad 80 are not particularly limited. In addition, the cutting edge 61 does not have to be straight, and even if it is straight, it does not have to be parallel to the X-axis. [Explanation of symbols]

[0053] 1,2...rotary cutting tool, 4...coolant passage, 4A,4B...through hole, 4Ab,4Bb...base end opening, 4At,4Bt...tip end opening, 4At,4Bt...tip end opening, 10,11...tool body, 10A...rotation axis, 10b...base end side, 10t...tip side, 12...tip surface, 14...outer surface, 15...connection portion, 16...tapered portion, 17...large diameter portion, 20...mounting seat, 30...chip evacuation hole, 30N...inner surface, 31,32...opening, 51...first quadrant, 52...second quadrant, 53...third quadrant, 54...fourth quadrant, 60...cutting insert, 61...cutting edge, 80...guide pad, C...virtual circle, d1,d2...maximum inner diameter, G...origin, t1,t2...wall thickness

Claims

1. A rotary cutting tool having a cutting member at a tip end side and having a cylindrical or substantially cylindrical shape, a chip discharge hole that is formed from the tip side toward the base side, and at least a part of a cross section perpendicular to a central axis of rotation of the rotary cutting tool has a four-sided non-circular cross section consisting of two opposing short sides and two opposing long sides; the short side portion includes a substantially arc-shaped curve along the outer periphery of the cross section, and the lengths of the two opposing short side portions are different from each other; the long side portion extends substantially linearly in the cross section, When a predetermined two-dimensional coordinate system having the coordinates of the rotation center axis as the origin is defined in at least a part of the cross section, the cross section is asymmetric with respect to an imaginary line that connects the two opposing short side portions, includes an inner diameter d1, and passes through the origin, and is also asymmetric with respect to an imaginary line that connects the two opposing long side portions, includes an inner diameter d2, and passes through the origin, where: d1 represents the maximum inner diameter of the non-circular cross section in the first and third quadrants corresponding mainly to the short side portions, d2 indicates the maximum inner diameter of the non-circular cross section in the second and fourth quadrants corresponding mainly to the long side portions, Rotary cutting tools.

2. The relationships shown in the following formulas (1) and (2) are satisfied: d1 ≧ D × 0.8 ... (1), d2≦D×0.7 ... (2), Here, D represents the tool diameter of the rotary cutting tool. The rotary cutting tool of claim 1 .

3. When a predetermined two-dimensional coordinate system having the coordinate of the rotation center axis as its origin is defined in at least a part of the cross section, the relationship shown in the following formula (3) is satisfied: t1<t2...(3), where: t1 represents the thickness of the central portion of the short side portion in the first and third quadrants corresponding mainly to the short side portion, t2 represents the thickness of the central portion of the long side portion in the second and fourth quadrants corresponding mainly to the long side portion, The rotary cutting tool of claim 1 .

4. When a predetermined two-dimensional coordinate system having the coordinate of the rotation center axis as its origin is defined in at least a part of the cross section, the relationship shown in the following formula (4) is satisfied: s1<s2...(4), where: s1 represents the cross-sectional area in the first and third quadrants corresponding mainly to the short side portions, s2 indicates the cross-sectional area in the second and fourth quadrants mainly corresponding to the long side portions, The rotary cutting tool of claim 1 .

5. The rotary cutting tool according to claim 1 , wherein an inner peripheral surface of the chip discharge hole is formed to be smooth at least in a direction in which the chips are discharged.

6. The chip discharge hole is formed to penetrate from the end surface on the tip end side to the end surface on the base end side, The inner peripheral surface of the chip discharge hole satisfies the relationship shown in the following formula (5): R≧0.1mm…(5), Here, R indicates the minimum radius of curvature of the edge if the inner circumferential surface has an edge. The rotary cutting tool of claim 5.

7. The rotary cutting tool according to claim 1 , further comprising a coolant passage having a through hole extending from an outer peripheral surface of the rotary cutting tool toward a tip side thereof.

8. The rotary cutting tool according to claim 7 , wherein the coolant flow passage passes between the long side portion and the outer circumferential surface and penetrates to the end face on the tip side.

9. It has a cylindrical or substantially cylindrical shape, a mounting seat provided on the tip side and on which the cutting insert is mounted; a chip discharge hole that is formed from the tip end side toward the base end side, and at least a part of a cross section perpendicular to the rotation central axis has a four-sided non-circular cross section consisting of two opposing short side portions and two opposing long side portions; Equipped with the short side portion includes a substantially arc-shaped curve along the outer periphery of the cross section, and the lengths of the two opposing short side portions are different from each other; the long side portion extends substantially linearly in the cross section, When a predetermined two-dimensional coordinate system having the coordinates of the rotation center axis as the origin is defined in at least a part of the cross section, the cross section is asymmetric with respect to an imaginary line that connects the two opposing short side portions, includes an inner diameter d1, and passes through the origin, and is also asymmetric with respect to an imaginary line that connects the two opposing long side portions, includes an inner diameter d2, and passes through the origin, where: d1 represents the maximum inner diameter of the non-circular cross section in the first and third quadrants corresponding mainly to the short side portions, d2 indicates the maximum inner diameter of the non-circular cross section in the second and fourth quadrants corresponding mainly to the long side portions, Tool body.

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