drill

Abstract

The present invention relates to a drill (1), which comprises: a front end (2) including a drill tip (3) having an obtuse drill point angle (θ); ·Rear end (4); a central axis (C) extending from the front end (2) to the rear end (4); and The outer surface connecting the front end and the rear end (5) The drill has an outer peripheral surface (5) formed with at least two chip flutes (6), each extending spirally around a central axis (C) from the front end (2) to the rear end (4). A cutting edge (2) is formed for each chip flute (6) at the intersection of a rake face (8) of the chip flute (6) and a relief face (9) at the front end (2) of the drill. The radially outermost portion of the relief face (9) adjacent to the cutting edge (7) is a chamfer (91), and the portion of the cutting edge (7) that contacts the chamfer (91) extends at a chamfer angle (α) relative to the central axis (C) that is 5° to 25° less than half the drill point angle (θ), when viewed from the side of the drill in a direction perpendicular to a plane including the central axis (C) and the radially outermost point of the cutting edge (7). Furthermore, the radially outermost portion of the rake face (8) is a rake reduction region (81) in which the reduced radial rake angle (γ2) is 20° to 45° less in the direction toward the central axis (C) than the preceding radial rake angle (γ1) in the adjacent region of the rake face (81) adjacent to the rake reduction region (81).

Description

[Technical Field]

[0001] The present invention relates to metal cutting, particularly drilling in heat-resistant superalloys. [Background technology]

[0002] Drilling is a common operation in the field of metal cutting. A common type of drill for metal cutting is a twist drill with two flutes and a cutting edge that extends radially from the tip of the drill to the periphery of the drill body. Such drills are often made from high-speed steel or cemented carbide.

[0003] Machining various materials presents a variety of challenges. Heat-resistant superalloys (HRSAs) are difficult to machine because they retain their strength even at extreme heat, often resulting in significant tool wear or damage. Edge chipping is a major failure mode seen in this application, particularly in the outer corner region, so it can be beneficial to introduce features that can improve the structural integrity of this area. In this case, corner modifications and / or edge preparations may be used to strengthen the high-stress region. However, prior art drills are typically not suitable for drilling HRSAs. That is, conventional drills capable of drilling high-quality holes in HRSAs may have poor or unpredictable tool life, and drills incorporating corner modifications to improve tool life may not be able to drill high-quality holes in HRSAs.

[0004] Therefore, there is a need to improve HRSA drills.

[0005] overview It is an object of the present invention to provide a drill that alleviates the drawbacks of the prior art and provides extended tool life while maintaining hole quality when drilling with an HRSA.

[0006] Thus, according to a first aspect, the present invention relates to a drill, comprising: a front end including a drill tip with an obtuse drill point angle; ·Rear end; a central axis extending from the front end to the rear end; and The outer surface connecting the front and rear ends At least two chip flutes are formed on the outer peripheral surface, and each chip flute extends spirally around the central axis from the front end to the rear end.

[0007] For each chip flute, a cutting edge is formed at the intersection of the rake face at the chip flute and a clearance face at the leading end of the drill. The radially outermost portion of the clearance face adjacent to the cutting edge is a chamfer, and the portion of the cutting edge tangent to the chamfer extends at a chamfer angle relative to the central axis that is between 5° and 25° less than half the drill point angle when viewed on the side of the drill perpendicular to a plane containing the central axis and the radially outermost point of the cutting edge. Furthermore, the radially outermost portion of the rake face is a rake reduction region, where the reduced radial rake angle, in a direction toward the central axis, is between 20° and 45° less than the preceding radial rake angle in the adjacent region of the rake face adjacent to the rake reduction region.

[0008] The inventors have found that the use of chamfered corners on the drill as identified above, in combination with fairly aggressive "rake correction" in the form of the rake reduction areas identified above, significantly and unexpectedly improves the drill's performance in machining HRSA with minimal exit burrs, both in terms of tool life and drilled hole quality.

[0009] A common effect of machining HRSA materials is material shrinkage after machining, which increases the risk of friction between the drill margin and the machined surface. Therefore, the edges of the drill margin and the radially outermost part of the cutting edge are particularly susceptible to chipping. The proposed rake reduction region and corner chamfer improve chipping resistance. It has been found that the radial rake angle in the rake reduction region can be significantly smaller than the preceding radial rake angle without significantly compromising the quality of the machined surface, and that this relatively aggressive modification of the outermost part of the rake face, when combined with a relief surface corner chamfer large enough to contribute significantly to improved chipping resistance (but small enough not to increase exit burrs), not only produces high-quality holes, but also results in a drill with very good overall chipping resistance and excellent tool life when drilling HRSA materials.

[0010] The expression "radial rake angle," well known to those skilled in the art, is used herein with respect to different regions of the rake face at different radial positions along the flute surface and should be understood as the angle the rake face in such regions forms with a radial line extending radially from the central axis to the region of the rake face, or more precisely, to a point in the region for which the radial rake angle is considered. If the point in question traces a portion of the rake face region that is located relatively close to the central axis with respect to the intended drill rotation direction, the radial rake angle is negative. Correspondingly, if the point in question traces a portion of the rake face region that is located relatively close to the central axis, the radial rake angle is positive.

[0011] As used herein, a reduced radial rake angle being smaller than a leading radial rake angle should be understood to mean that the reduced radial rake angle is less positive and / or relatively negative. That is, if the leading radial rake angle is negative (or zero), the reduced radial rake angle will also be negative. On the other hand, if the leading radial rake angle is positive, the reduced radial rake angle will either be positive (but the leading radial rake angle is less positive, i.e., closer to zero), or negative.

[0012] As used herein, the "point angle" of a drill, which is well known to those skilled in the art, is the inclusive angle between the cutting edges at the tip of the drill, and more specifically, in the case of a conventional twist drill having two symmetrically arranged cutting edges, it is the angle between the two cutting edges projected onto a plane containing the central axis of the drill and the radially outermost point of each of the preceding cutting edges.

[0013] The transition between the chamfered and non-chamfered portions of the relief face, and between the rake reduction region and other portions of the rake face, may be sharp or slightly rounded, i.e., formed by a small radius. For example, such rounded transitions may be the result of the manufacturing process used or may be intentionally applied to increase the strength of the boundary between the regions. However, this transition always constitutes a clearly identifiable boundary between the two respective surfaces.

[0014] The chamfered and non-chamfered portions of the relief face near the transition, as well as the rake reduction region and other portions of the rake face near the transition, may extend linearly in side and front views, respectively, or may at least have a curvature significantly less than that of the transition, so that the transition constitutes a clear boundary between the surfaces.

[0015] The relief surface should be formed to provide clearance for the machined surface and may include one or more flat relief surfaces or facets, or may be formed by a convex curve that slopes away from the cutting edge.

[0016] The drill may be made of cemented carbide and may be uncoated or may include a coating.

[0017] According to some embodiments, the rake reduction region has a linear or substantially linear extension in the radial direction. Thus, the reduced radial rake angle does not vary significantly along the rake reduction region. In some embodiments, depending on the manufacturing method (i.e., the way in which the rake reduction region is cut), the rake reduction region may not extend perfectly linearly in the radial direction, but may actually have a very small curvature, i.e., a large radius (sometimes referred to as a "curvature error"). Nevertheless, in such cases, it may often be appropriate to approximate the small curvature with a straight line and consider the rake reduction region to extend substantially linearly in the radial direction.

[0018] According to some embodiments, the chamfer angle is constant or substantially constant along at least a major portion of the cutting edge that meets the chamfer. The relief chamfer may be formed such that the resulting chamfer angle is the same or substantially the same along all portions of the cutting edge that meet the chamfer. Thus, when viewed from the side in a direction perpendicular to a plane containing the central axis and the radially outermost point of the cutting edge, the portion of the cutting edge that meets the chamfer may extend along a straight line.

[0019] According to some embodiments, the reduced radial rake angle is between 30° and 40° less than the preceding radial rake angle. Reduced radial rake angles within this range may be particularly suitable when drilling many types of HRSA materials. The reduced radial rake angle at the radially outermost point of the cutting edge may be, for example, 35° or substantially 35° less than the preceding radial rake angle.

[0020] According to some embodiments, the chamfer angle is between 5° and 15° less than half the drill point angle. Chamfer angles within this range may be particularly suitable when drilling many types of HRSA materials. The chamfer angle may be, for example, 10° or substantially 10° less than half the drill point angle.

[0021] According to some embodiments, the drill point angle is between 135° and 145°. As an example, the drill point angle may be 140° or substantially 140°, resulting in a chamfer angle in the range of 45° to 65°.

[0022] According to some embodiments, the reduced radial rake angle is negative and the leading radial rake angle is positive. According to some embodiments, the reduced radial rake angle is between −25° and −5°. According to some embodiments, the leading radial rake angle is between 5° and 25°. By way of example, the leading radial rake angle may be between 10° and 20°, e.g., 15°. A positive leading radial rake angle typically corresponds to a “hook-like” flute shape, which, in the absence of rake compensation, leads to a weakened flute end, making it more susceptible to chipping. Thus, when the leading radial rake angle is positive between 5° and 25°, it may be advantageous to apply a reduced negative radial rake angle, particularly a radial rake angle between −25° and −5°, for chipping resistance at the end.

[0023] According to some embodiments, the radial extension of the cutting edge portion adjacent to the chamfer from the outer periphery towards the central axis is between 1% and 10% of the cutting diameter of the drill, for example between 2% and 6% of the cutting diameter of the drill.

[0024] According to some embodiments, the radial extension of the rake reduction region from the outer circumferential surface towards the central axis is between 1% and 10% of the cutting diameter of the drill, for example between 2% and 6% of the cutting diameter of the drill.

[0025] The radial extension of the portion of the cutting edge tangent to the chamfer may be equal to the radial extension of the rake reduction region, so that the transitions to the chamfer angle and to the reduced rake angle occur at the same point along the cutting edge. However, according to other embodiments, the radial extension of the portion of the cutting edge tangent to the chamfer may be greater than the radial extension of the rake reduction region, or vice versa. Thus, the chamfer and the rake reduction region do not necessarily need to extend equally far in the radial direction.

[0026] According to some embodiments, a rake reduction region extends axially in the peripheral flutes of the drill along the majority of the axial extension of the flutes. While the axial extension of the rake reduction region is not a critical parameter for drill performance and tool life, such a configuration is particularly advantageous for enabling reconditioning of the drill.

[0027] According to some embodiments, each flute includes a web thinning, the cutting edge being secondary cutting edges formed at the intersection of the flank and web thinnings, and The primary cutting edge extends from the radially outermost point of the secondary cutting edge to the outer periphery of the drill. The web thinning and corresponding secondary cutting edge make it possible to limit the length of the chisel edge while maintaining sufficient overall web thickness.

[0028] According to some embodiments, a first line extending from a radially outermost point about the secondary cutting edge to a radially innermost point of a portion of the cutting edge tangent to the rake reduction region; A second line extending parallel to the first line and through the central axis The shortest distance between the drill bit and the cutting diameter is between 2% and 10% of the drill bit diameter.

[0029] In this configuration, the cutting edge is located a small distance "off-center," which, combined with the rake reduction area and chamfered corners of the flank, is believed to further improve the strength and chipping resistance of the drill.

[0030] According to a second aspect, the present invention relates to the use of a drill according to any of the embodiments described herein for drilling holes in a heat-resistant superalloy.

[0031] The solution will now be explained in more detail by way of exemplary embodiments and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a perspective view of a drill according to an embodiment of the present invention, including an enlarged view of the drill tip. [Figure 2] FIG. 1 is a side view of the drill looking toward the outer corner of one of the cutting edges, including a close-up of the drill tip. [Figure 3] FIG. 2 is another enlarged side view of the drill tip, corresponding to the enlarged view of FIG. 2, but rotated 90° about the central axis of the drill, i.e., viewed from a direction perpendicular to a plane containing the central axis of the drill and the radially outermost point of the cutting edge. [Figure 4] FIG. 3 is a front view of the drill as seen from the direction IV shown in FIG. 2. [Figure 5] 3 shows a cross section of the drill taken along the VV cross section shown in FIG. 2.

[0033] All figures are schematic, not necessarily to scale, and generally show only what is necessary to clarify each embodiment, other parts may be omitted or merely suggested. Unless otherwise specified, like reference signs refer to like parts in different figures. DETAILED DESCRIPTION OF THE INVENTION

[0034] A drill 1 according to an embodiment of the present invention will be described below with reference to FIGS.

[0035] Drill 1 includes a front end 2 and a rear end 4. Front end 2 includes a drill point 3. A central axis C extends from rear end 4 to front end 2. An outer peripheral surface 5 extends between rear end 4 and front end 2 and is concentric with central axis C. Two flutes 6 are formed in the outer peripheral surface and extend axially from front end 2 following a curved, helical path about longitudinal axis C. Thus, outer peripheral surface 5 includes two lands 18 that extend axially corresponding to the flutes 6.

[0036] The drill includes double margins 15, 16. Thus, each land 18 includes a margin 15 formed adjacent the leading edge of the land 18 and a margin 16 formed at the heel (i.e., the trailing edge of the land 18). Adjacent to its rear end, the drill includes a shank 17.

[0037] The flutes 6 are symmetrically arranged and include corresponding features, and for clarity only the features relating to one of the flutes 6 are labeled in Figure 1.

[0038] The cutting edge 7 is formed at the intersection of the rake face 8 of each flute 6 and a relief surface 9 located at the front end 2. The relief surface 9 behind the cutting edge 7 is convexly curved and slopes away from the cutting edge 7, i.e., the relief angle increases with distance from the cutting edge 7.

[0039] The central region of each flute 6 includes a web thinning 10 in the form of a ground concavely arched surface, such that the central portion of the rake face 8 is formed by the wall of the web thinning 10. The cutting edge 7 thus includes a secondary cutting edge 72 that extends from the chisel edge 13 at the center of the drill, all along the rake face formed by the web thinning 10. The cutting edge 7 also includes a primary cutting edge 71 that extends from the point 11 where the secondary cutting edge 72 terminates to the peripheral surface 5 of the drill.

[0040] The drill 1 has a drill point angle θ (see FIG. 3) of 140°. Thus, in a side view as shown in FIG.

[0041] The drill 1 further includes two coolant channels extending axially within the drill body and having outlets 14 at the front end 2 of the drill.

[0042] The radially outermost portion of the relief surface 9 adjacent to the primary cutting edge 71 is chamfered relative to the central axis C to form a chamfered portion 91 of the relief surface 9. Referring to Figure 3, the portion of the primary cutting edge 71 tangent to the chamfered portion 91, when viewed from the side of the drill in a direction perpendicular to a plane containing the central axis C and the radially outermost point of the cutting edge 7, extends at a chamfer angle α relative to the central axis C, which in the illustrated embodiment is 10° less than half the drill point angle θ. Thus, when the drill point angle θ is 140°, the chamfer angle α is 60°.

[0043] Furthermore, the radially outermost portion of the rake face 8 of the flute 6 is a reduced rake region 81, where the radial rake angle is a reduced radial rake angle γ2, which in the illustrated embodiment is approximately 35° less than the preceding radial rake angle γ1 in the direction toward the central axis C in the adjacent region of the rake face 8 adjacent to the reduced rake region 81.

[0044] 5, the leading radial rake angle γ, i.e., the radial rake angle at a point on the rake face 8 immediately preceding the transition to the rake reduction region 81, is the angle between the radial rake face (or a radial tangent to the rake face 8 at that point) and a radial line r from the central axis C to that point. The reduced rake angle γ, i.e., the radial rake angle at the radially outermost point of the rake reduction region 81, is the angle between the radial rake face of the rake reduction region 81 and a radial line r from the central axis C to the radially outermost point of the rake reduction region.

[0045] In the illustrated embodiment, as best seen in FIG. 5, the leading radial rake angle γ is positive and approximately 15°, and the reduced radial rake angle γ at the periphery of the drill is negative and approximately −20°.

[0046] 5, the rake reduction region 81 has a linear extension in the radial direction, i.e., extends along a straight line when viewed in a cross section perpendicular to the central axis C. Nevertheless, the reduced radial rake angle varies slightly along the radial extension of the rake reduction region (unless the radial rake angle is zero). However, if the rake reduction region has a small radial extension relative to the cutting diameter of the drill, the change in radial rake angle across the rake reduction region will be very small, and in many cases it may be appropriate to ignore the change and consider the reduced radial rake angle to be substantially constant (i.e., equal to γ2) throughout the rake reduction region.

[0047] During the manufacturing process of the drill, the rake reduction region 81 is created by grinding to form an axially extending rake reduction region in the flutes at the periphery of the drill along the majority of the axial extension of the flutes 6. Such a ground surface is sometimes referred to as a "C-land." In other embodiments, for example using a different manufacturing process, the region 81 may have a much smaller axial extension in the flutes, for example located adjacent to and in close proximity to only the cutting edge.

[0048] The rake reduction region 81 and the chamfer 91 of the relief face 9 extend radially from the outer peripheral surface 5 of the drill. However, the radial extensions of these regions are not necessarily the same. The chamfer 91 has its greatest radial extension adjacent to the cutting edge. In the illustrated embodiment, as shown in FIG. 3 , the radial extension d1 of the primary cutting edge 71 tangent to the chamfer 91 from the outer peripheral surface 5 is greater than the radial extension d2 of the rake reduction region 81 from the outer peripheral surface 5. The radial extension d1 of the portion of the cutting edge tangent to the chamfer 91 is approximately 4% of the drill diameter D, and the radial extension d2 of the rake reduction region is approximately 2% of the drill diameter D.

[0049] In the illustrated embodiment, the cutting edges 7 are positioned such that the shortest distance h (shown in FIG. 4) between parallel lines s1 and s2 is approximately 5% of the cutting diameter D of the drill, where line S1 extends from the radially outermost point 11 of the secondary cutting edge 72 to the radially innermost point 12 of the portion of the primary cutting edge 71 that is tangent to the rake reduction region 81, and line S2 extends through the central axis C parallel to the first line S1.

[0050] While the above description contains a number of specificities, these should not be construed as limiting the scope of the concepts described herein, but merely as providing illustrations of some exemplary embodiments of the concepts described. It will be understood that the scope of the concepts described herein is not limited, as it fully encompasses other embodiments that may become apparent to those skilled in the art.

Claims

1. A drill (1) comprising: a front end (2) including a drill tip (3) with an obtuse drill point angle (θ); ・Rear end (4); a central axis (C) extending from the front end (2) to the rear end (4), and - An outer peripheral surface (5) connecting the front end and the rear end At least two chip flutes (6) are formed on the outer peripheral surface (5), and each chip flute (6) extends spirally around the central axis (C) from the front end (2) to the rear end (4), A drill in which a cutting edge (7) is formed at the intersection of a rake face (8) of each chip flute (6) and a relief face (9) at the front end (2) of the drill, The radially outermost portion of the relief surface (9) adjacent to the cutting edge (7) is a chamfered portion (91), and the portion of the cutting edge (7) in contact with the chamfered portion (91) extends at a chamfer angle (α) with respect to the central axis (C) that is smaller than half the drill point angle (θ) by between 5° and 25° when viewed from the side of the drill in a direction perpendicular to a plane including the central axis (C) and the radially outermost point of the cutting edge (7); The drill is characterized in that the radially outermost portion of the rake face (8) is a rake reduction region (81), in which the reduced radial rake angle (γ2) is between 20° and 45° smaller in the direction towards the central axis (C) than the preceding radial rake angle (γ1) in the adjacent region of the rake face (8) adjacent to the rake reduction region (81).

2. 2. The drill according to claim 1, wherein the rake reduction region (81) has a linear or substantially linear extension in the radial direction.

3. 3. A drill according to claim 1 or 2, wherein the chamfer angle (α) is constant or substantially constant along at least the major part of the cutting edge that is in contact with the chamfer (91).

4. 4. The drill according to any one of claims 1 to 3, wherein the reduced radial rake angle (γ2) is between 30° and 40° smaller than the preceding radial rake angle (γ1).

5. 5. The drill according to any one of claims 1 to 4, wherein the chamfer angle (α) is between 5° and 15° less than half the drill point angle (θ).

6. 6. The drill according to any one of claims 1 to 5, wherein the drill point angle (θ) is between 135° and 145°.

7. 7. The drill according to any one of claims 1 to 6, wherein the reduced radial rake angle (γ2) is negative and the leading radial rake angle (γ1) is positive.

8. The drill according to any one of claims 1 to 7, wherein the reduced radial rake angle (γ2) is negative and is between -25° and -5°.

9. 9. The drill according to any one of claims 1 to 8, wherein the leading radial rake angle (γ1) is positive and is between 5° and 25°.

10. 10. The drill according to claim 1, wherein the radial extension (d1) of the part of the cutting edge (7) that contacts the chamfer (91) from the outer circumferential surface (5) towards the central axis (C) is between 1% and 10% of the cutting diameter (D) of the drill.

11. 11. The drill according to any one of claims 1 to 10, wherein the radial extension (d2) of the rake reduction region (81) from the outer peripheral surface (5) towards the central axis (C) is between 1% and 10% of the cutting diameter (D) of the drill.

12. 12. The drill according to any one of claims 1 to 11, wherein the rake reduction region (81) extends axially in the flutes (6) at the periphery of the drill along the majority of the axial extension of the flutes (6).

13. The flute includes a web thinning (10) and the cutting edge (7) a secondary cutting edge (72) formed at the intersection of the flank (9) and the web thinning (10); and A primary cutting edge (71) extending from the radially outermost point (11) of the secondary cutting edge (10) to the outer peripheral surface of the drill. The drill according to any one of claims 1 to 12, comprising:

14. a first line (S1) extending from the radially outermost point (11) of the secondary cutting edge (10) to the radially innermost point (12) of the portion of the cutting edge tangent to the rake reduction region (81); A second line (s2) extending parallel to the first line (s1) and through the central axis (C).

14. The drill according to claim 13, wherein the shortest distance (h) between the cutting diameter (D) of the drill and the cutting edge (H) is between 2% and 10% of the cutting diameter (D) of the drill.

15. Use of a drill according to any one of claims 1 to 14 for drilling holes in heat-resistant superalloys.

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