Drill bit

Abstract

A drill bit (1), said drill bit (1) comprising:-a front end (2) comprising a drill tip (3) having an obtuse drill tip angle ([theta]); a rear end (4); -a central axis (C) extending from the front end (2) to the rear end (3); and-a peripheral surface (5) connecting the front end and the rear end wherein at least two flutes (6) are formed in the peripheral surface (5), each flute (6) extending helically around the central axis (C) from the front end (2) towards the rear end (4). For each flute (6), a cutting edge (7) is formed at the intersection between a rake face (8) located in the flute (6) and a flank face (9) located at the front end (2) of the drill bit. The radially outermost portion of the flank face (9) adjacent to the cutting edge (7) is a chamfered portion (91) in which, when viewed in a side view of the drill bit from a direction perpendicular to a plane containing the central axis and the radially outermost point of the cutting edge, the chamfered portion (91) is a chamfered portion (91). The portion of the cutting edge (7) bordering the chamfered portion (91) extends with respect to the central axis (C) at a chamfered angle (alpha) which is less than half of the drill tip angle (theta) by 5 DEG to 25 DEG. Furthermore, the radially outermost portion of the rake face (8) is a rake face reduction region (81) in which a reduced radial rake angle ([gamma] 2) is less than a preceding radial rake angle ([gamma] 1) of the rake face (8) in an adjacent region adjacent to the rake face reduction region (81) in a direction toward the central axis (C) by 20 DEG to 45 DEG.

Description

Technical Field

[0001] The present invention relates to metal cutting and, in particular, to drilling holes in heat-resistant superalloys. Background Art

[0002] Drilling is a common operation within the field of metal cutting. A common type of drill bit used for metal cutting is a twist drill bit, which has: two flutes; and cutting edges that extend radially from the tip of the drill bit to the outer circumference of the drill bit body. Such drill bits are typically made of high-speed steel or cemented carbide.

[0003] Machining in different materials involves different challenges. Heat-resistant superalloys (HRSA) are difficult to machine due to their strength retention at extremely high temperatures, often resulting in significant tool wear or damage. Edge chipping is the main failure mode seen in this application (specifically in the outer corner regions), so introducing features that can improve the structural integrity of these regions may be beneficial. In such cases, corner modification and / or edge preparation are sometimes used to strengthen the high-stress regions. However, drill bits according to the prior art generally do not adapt well to drilling in HRSA. That is, prior art drill bits that can drill high-quality holes in HRSA may suffer from poor or unpredictable tool life, and drill bits that include corner modifications for improving tool life may not be able to drill high-quality holes in HRSA.

[0004] Accordingly, there is a need for an improved drill bit for HRSA. Summary of the Invention

[0005] The object of the present invention is to mitigate the disadvantages of the prior art and to provide a drill bit having an increased tool life while maintaining hole quality when drilling in HRSA.

[0006] Accordingly, in a first aspect, the present invention relates to a drill bit comprising: - a front end including a drill tip having an obtuse drill tip angle; - a rear end; - a central axis extending from the front end to the rear end; and - an outer peripheral surface connecting the front end and the rear end, wherein at least two chip flutes are formed in the outer peripheral surface, each chip flute spirally extending around the central axis from the front end towards the rear end.

[0007] For each chip flute, a cutting edge is formed at the intersection between the rake face located in the chip flute and the flank face located at the front end of the drill bit. The radially outermost portion of the flank face adjacent to the cutting edge is a chamfered portion, wherein when viewed in a side view of the drill bit from a direction perpendicular to the plane containing the central axis and the radially outermost point of the cutting edge, the portion of the cutting edge bordering the chamfered portion extends relative to the central axis at a chamfer angle that is 5° to 25° less than half of the drill point angle. Further, the radially outermost portion of the rake face is a rake face reduction region, in which the reduced radial rake angle is 20° to 45° less than the previous radial rake angle in an adjacent region of the rake face adjoining the rake face reduction region in a direction toward the central axis.

[0008] The inventors have found that using a chamfered portion at the corner of the drill bit as specified above, in combination with a relatively aggressive “rake face correction” in the form of a rake face reduction region as specified above, significantly and unexpectedly improves the performance of the drill bit (both with respect to tool life and hole quality) when machining in HRSA, and has minimal exit burrs.

[0009] A common effect of machining HRSA materials is shrinkage of the material after machining, which increases the risk of friction between the edge of the drill bit and the machined surface. Accordingly, the cutting edges at the edge of the drill bit and the radially outermost portions of the cutting edges are particularly prone to chipping. The rake face reduction region and corner chamfer as proposed herein improve chipping resistance. It has been found that the radial rake angle in the rake face reduction region can be reduced quite significantly compared to the previous radial rake angle without significantly compromising the quality of the machined surface, and when combined with a corner chamfer on the flank face that is large enough to contribute sufficiently to improving chipping resistance but small enough not to increase exit burrs, this relatively aggressive modification of the outermost portion of the rake face results in a drill bit that can not only produce high-quality holes, but also exhibits very good overall chipping resistance and has an impressive tool life when drilling in 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 formed by the rake face in such a region with a radial line extending from the central axis to the region of the rake face, or more precisely with a point considering the region where the radial rake angle is located. If the point trails other portions of the rake face region located closer to the central axis with respect to the intended rotational direction of the drill bit, the radial rake angle is negative. Correspondingly, if the point leads such other portions of the rake face region located closer to the central axis, the radial rake angle is positive.

[0011] As used herein, a reduced radial rake angle that is less than a previous radial rake angle shall be understood to mean that the reduced radial rake angle is a smaller positive and / or a larger negative. In other words, if the previous radial rake angle is negative (or zero), then the reduced radial rake angle will also be negative. On the other hand, if the previous radial rake angle is positive, then the reduced radial rake angle will either be positive (but a positive smaller than the previous radial rake angle - i.e., closer to zero) or negative.

[0012] As used herein and as is known to those skilled in the art, the "point angle" of a drill bit is the included angle between the cutting edges at the drill point, and more specifically, for a conventional twist drill having two symmetrically arranged cutting edges, the "point angle" is the angle between the two cutting edges projected onto a plane containing the central axis of the drill bit and the respective radially outermost points of the cutting edges.

[0013] The transition between the chamfered and non-chamfered portions of the flank face and the transition between the reduced area of the rake face and the other portions of the rake face may be sharp or slightly rounded, i.e., formed by a small radius. For example, such a rounded transition may be the result of the manufacturing process used or may be intentionally applied to increase the strength of the boundary line between the areas. However, the transition will always constitute a clearly distinguishable boundary between the two respective surfaces.

[0014] The chamfered and non-chamfered portions of the flank face near the transition between the chamfered and non-chamfered portions of the flank face and the reduced area of the rake face and the other portions of the rake face near the transition between the reduced area of the rake face and the other portions of the rake face may extend linearly in a side view and a front view, respectively, or may at least have a curvature significantly less than that of the transition, such that the transition constitutes a clear boundary between the respective surfaces.

[0015] The flank face shall be formed to provide clearance relative to the surface being machined and may include one or more flat flank faces or facets, or may be formed by a convex curved surface that slopes away from the cutting edge.

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

[0017] According to some embodiments, the rake face reduction region has a linear or substantially linear extension in the radial direction. Accordingly, the reduced radial rake angle will not vary significantly along the rake face reduction region. In some embodiments, depending on the manufacturing method (i.e., the manner in which the rake face reduction region is ground), the rake face reduction region may not have a perfectly linear extension in the radial direction, but may actually have a very small curvature, i.e., a large radius (sometimes referred to as a "curvature error"). However, in such cases, it may generally be appropriate to approximate the small curvature by a straight line and consider the rake face reduction region to have a substantially linear extension in the radial direction.

[0018] According to some embodiments, the chamfer angle is constant or substantially constant along at least a majority of the cutting edge that interfaces with the chamfer portion. The chamfer portion on the flank face may be formed in such a way that the resulting chamfer angle is the same or substantially the same at all portions of the cutting edge that interface with the chamfer portion. Accordingly, when viewed in a side view from a direction perpendicular to the plane containing the central axis and the radially outermost point of the cutting edge, the portion of the cutting edge that interfaces with the chamfer portion may extend along a straight line.

[0019] According to some embodiments, the reduced radial rake angle is 30° to 40° less than the previous radial rake angle. When drilling in many types of HRSA materials, a reduced radial rake angle in this range may be particularly suitable. 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 previous radial rake angle.

[0020] According to some embodiments, the chamfer angle is 5° to 15° less than half of the drill point angle. When drilling in many types of HRSA materials, a chamfer angle in this range may be particularly suitable. The chamfer angle may be, for example, 10° or substantially 10° less than half of 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 rake angle is negative and the leading rake angle is positive. According to some embodiments, the reduced rake angle is between -25° and -5°. According to some embodiments, the leading rake angle is between 5° and 25°. As an example, the leading rake angle can be between 10° and 20° and can be, for example, 15°. A positive leading rake angle generally corresponds to a "hooked" flute shape which, in the absence of face relief, would introduce a weakness at the edge of the flute and thus be prone to chipping. Thus, for a positive leading rake angle between 5° and 25°, it may be advantageous, for the purpose of chipping resistance of the cutting edge, to apply a negative reduced rake angle (and in particular a reduced rake angle between -25° and -5°).

[0023] According to some embodiments, the radial extension of the portion of the cutting edge that interfaces with the chamfer portion, from the outer peripheral 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.

[0024] According to some embodiments, the radial extension of the face relief area, from the outer peripheral 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 that interfaces with the chamfer portion can be equal to the radial extension of the face relief area such that the transition to the chamfer angle and the transition 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 that interfaces with the chamfer portion can be greater than the radial extension of the face relief area or vice versa. Thus, the chamfer portion and the face relief area do not necessarily extend equally far in the radial direction.

[0026] According to some embodiments, most of the axial extension of the face relief area extends axially in the flute at the outer periphery of the drill. Even though the axial extension of the face relief area is not a critical parameter for the performance and tool life of the drill, this configuration is particularly advantageous for enabling the reconditioning of the drill.

[0027] According to some embodiments, each flute includes a web thinning and the cutting edge includes: - an auxiliary cutting edge formed at the intersection between the flank face and the web thinning; and - a main cutting edge extending from the radially outermost point of the auxiliary cutting edge to the outer peripheral surface of the drill.

[0028] The web thinning and the corresponding auxiliary cutting edge enable the maintenance of a sufficient total web thickness while limiting the chisel edge length.

[0029] According to some embodiments, the shortest distance between the first line and the second line is between 2% and 10% of the cutting diameter of the drill bit, - the first line extends from the radially outermost point of the auxiliary cutting edge to the radially innermost point of the portion of the cutting edge that interfaces with the rake face reduction zone, - the second line extends parallel to the first line through the central axis.

[0030] Such a configuration in which the cutting edge is positioned "over center" by only a small distance, in combination with the rake face reduction zone and the chamfered surface at the corner of the flank face, is considered to further improve the strength and chipping resistance of the drill bit.

[0031] According to a second aspect, the present invention relates to the use of a drill bit according to any of the embodiments described herein for drilling in heat-resistant superalloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The solution will now be described in more detail by means of exemplary embodiments and with reference to the drawings, in which:

[0033] Figure 1 is a perspective view of a drill bit according to an embodiment of the present invention, including an enlarged view of the drill bit tip.

[0034] Figure 2 is a side view of the drill bit as seen in the direction of the outer peripheral corner towards one of the cutting edges, including an enlarged view of the drill bit tip.

[0035] Figure 3 is another enlarged side view of the drill bit tip, corresponding to Figure 2 the enlarged view in, but rotated 90° about the central axis of the drill bit, i.e., as seen from a direction perpendicular to the plane containing the central axis of the drill bit and the radially outermost point of the cutting edge.

[0036] Figure 4 is a front view of the drill bit as seen from the direction IV as shown in Figure 2 .

[0037] Figure 5 shows a cross-section of the drill bit in the cross-section V-V as shown in Figure 2 .

[0038] All the drawings are schematic, not necessarily drawn to scale, and generally show only the components necessary to illustrate the corresponding embodiments, while other components may be omitted or merely suggested. Unless otherwise stated, the same reference numerals refer to the same components in different figures. DETAILED DESCRIPTION

[0039] Reference Figures 1 to 5 Now, drill bit 1 according to an embodiment of the present invention will be described.

[0040] The drill bit 1 includes a front end 2 and a rear end 4. The front end 2 includes a drill tip 3. A central axis C extends from the rear end 4 to the front end 2. An outer peripheral surface 5 extends between the rear end 4 and the front end 2 and is concentric with the central axis C. Two flutes 6 are formed in the outer peripheral surface, and the two flutes 6 extend axially from the front end 2 following a curved helical path around the longitudinal axis C. Accordingly, the outer peripheral surface 5 includes two land areas 18 that extend axially in a manner corresponding to the flutes 6.

[0041] The drill bit includes double edges 15, 16. Accordingly, each land area 18 includes: an edge 15 formed adjacent to the leading edge of the land area 18; and an edge 16 formed at the heel (i.e., the trailing edge of the land area 18). Adjacent to the rear end of the drill bit, the drill bit includes a shank 17.

[0042] The flutes 6 are symmetrically arranged and include corresponding features. For clarity, the drawings only include reference numerals for features related to one of these flutes 6. Figure 1 in

[0043] A cutting edge 7 is formed at the intersection between a rake face 8 located in each flute 6 and a flank face 9 located at the front end 2. The flank face 9 behind the cutting edge 7 is convexly curved and inclined away from the cutting edge 7, i.e., has an increasing clearance angle when moving away from the cutting edge 7.

[0044] The central region of each flute 6 includes a web thinning portion 10 in the form of a ground concave arched surface. Accordingly, the central portion of the rake face 8 is formed by the wall of the web thinning portion 10. Thus, the cutting edge 7 includes a secondary cutting edge 72 that extends along the rake face formed by the web thinning portion 10 from the chisel edge 13 at the center of the drill bit. The cutting edge 7 also includes a main cutting edge 71 that extends from the point 11 where the secondary cutting edge 72 terminates to the outer peripheral surface 5 of the drill bit.

[0045] The drill bit 1 has a drill point angle θ of 140° (see Figure 3 ). Accordingly, in a side view as shown in Figure 3 , each secondary cutting edge 72 forms an angle of 70° with the central axis C.

[0046] The drill bit 1 further includes two coolant channels that extend axially within the drill bit body and have outlets 14 located at the front end 2 of the drill bit.

[0047] The radially outermost portion of the flank face 9 adjacent to the main cutting edge 71 is chamfered with respect to the central axis C, thereby forming a chamfered portion 91 of the flank face 9. ReferenceFigure 3 When viewed in a side view of the drill bit in a direction perpendicular to a plane containing the central axis C and the radially outermost point of the cutting edge 7, the portion of the main cutting edge 71 that abuts the chamfer portion 91 extends relative to the central axis C at a chamfer angle α, which in the illustrated embodiment is 10° less than half of the drill point angle θ. Thus, in the case of a drill point angle θ of 140°, the chamfer angle α is 60°.

[0048] Further, the radially outermost portion of the rake face 8 located in the flute 6 is a rake face reduction region 81 in which the radial rake angle is a reduced radial rake angle γ2, which in the illustrated embodiment is approximately 35° less than the previous radial rake angle γ1 in an adjacent region of the rake face 8 that abuts the rake face reduction region 81 in a direction toward the central axis C.

[0049] As Figure 5 can be seen, the previous radial rake angle γ1 (i.e., the radial rake angle at a point on the rake face 8 immediately before transitioning to the rake face reduction region 81) is the angle between the radial rake face (or the radial tangent to the rake face 8 at that point) and the radial line r1 from the central axis C to that point. The reduced rake angle γ2 (i.e., the radial rake angle at the radially outermost point of the rake face reduction region 81) is the angle between the radial rake face of the rake face reduction region 81 and the radial line r2 from the central axis C to the radially outermost point of the rake face reduction region.

[0050] In the illustrated embodiment, as Figure 5 can be best seen, the previous radial rake angle γ1 is positive, approximately 15°, and the reduced radial rake angle γ2 at the outer periphery of the drill bit is negative, approximately -20°.

[0051] The rake face reduction region 81 has a linear extension in the radial direction, i.e., when viewed in a cross-section perpendicular to the central axis C, it extends along a straight line, as Figure 5 can be seen. However, the reduced radial rake angle will vary slightly along the radial extension of the rake face reduction region (as long as the radial rake angle is not zero). However, when the rake face reduction region has a relatively small radial extension relative to the cutting diameter of the drill bit, the variation of the radial rake angle over the rake face reduction region will be rather small, and in many cases, it may be appropriate to neglect this variation and consider the reduced radial rake angle to be substantially constant over the entire rake face reduction region (i.e., equal to γ2).

[0052] During the manufacturing process of the drill bit, the rake face reduction area 81 is created by grinding such that a major portion of the axial extension along the flute 6 forms a rake face reduction area that axially extends in the flute at the outer periphery of the drill bit. Such a ground surface is sometimes referred to as a "C-land". In other embodiments, for example, if a different manufacturing process is used, the area 81 may have a much smaller axial extension in the flute and may be located, for example, only near the cutting edge, adjacent to the cutting edge.

[0053] The rake face reduction area 81 and the chamfered portion 91 of the flank face 9 extend radially from the outer peripheral surface 5 of the drill bit. However, the respective radial extensions of these areas are not necessarily the same. The chamfered portion 91 has its maximum radial extension near the cutting edge. In the illustrated embodiment, the radial extension d1 from the outer peripheral surface 5 of the major cutting edge 71 that interfaces with the chamfered portion 91 is greater than the radial extension d2 from the outer peripheral surface 5 of the rake face reduction area 81, as Figure 3 shown. The radial extension d1 of the portion of the cutting edge that interfaces with the chamfered portion 91 is approximately 4% of the drill bit diameter D, and the radial extension d2 of the rake face reduction area is approximately 2% of the drill bit diameter D.

[0054] In the illustrated embodiment, the cutting edge 7 is positioned such that the shortest distance h between the parallel lines s1 and s2 ( Figure 4 shown) is approximately 5% of the cutting diameter D of the drill bit, where the line s1 extends from the radially outermost point 11 of the auxiliary cutting edge 72 to the radially innermost point 12 of the portion of the major cutting edge 71 that interfaces with the rake face reduction area 81, and the line s2 extends parallel to the first line s1 through the central axis C.

[0055] Although the above description contains many specificities, these should not be construed as limiting the scope of the concepts described herein, but rather as merely providing illustrations of some exemplary embodiments of the concepts described. It should be understood that the scope of the concepts currently described fully encompasses other embodiments that may be obvious to those skilled in the art, and the scope of the concepts currently described is therefore not limited.

Claims

1. A drill bit (1), comprising: - A front end (2), said front end (2) including a drill tip (3), said drill tip (3) having an obtuse drill tip angle (θ); - A rear end (4); - A central axis (C) extending from said front end (2) to said rear end (4); and - An outer peripheral surface (5), said outer peripheral surface (5) connecting said front end and said rear end, wherein at least two chip flutes (6) are formed in said outer peripheral surface (5), each chip flute (6) spirally extending from said front end (2) towards said rear end (4) around said central axis (C); Wherein, for each chip flute (6), a cutting edge (7) is formed at the intersection between the rake face (8) located in said chip flute (6) and the flank face (9) located at said front end (2) of said drill bit, and is characterized in that: - The radially outermost part of said flank face (9) adjacent to said cutting edge (7) is a chamfered part (91), wherein when viewed in a side view of said drill bit in a direction perpendicular to a plane containing said central axis (C) and the radially outermost point of said cutting edge (7), the part of said cutting edge (7) adjoining said chamfered part (91) extends relative to said central axis (C) at a chamfer angle (α), said chamfer angle (α) being 5° to 25° smaller than half of said drill tip angle (θ), and - The radially outermost part of said rake face (8) is a rake face reduction region (81), in said rake face reduction region (81), the reduced radial rake angle (γ2) is 20° to 45° smaller than the previous radial rake angle (γ1) in an adjacent region of said rake face (8) adjoining said rake face reduction region (81) in a direction towards said central axis (C).

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

3. The drill bit according to any one of the preceding claims, wherein said chamfer angle (α) is constant or substantially constant along at least most of the part of said cutting edge adjoining said chamfered part (91).

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

5. The drill bit according to any one of the preceding claims, wherein said chamfer angle (α) is 5° to 15° smaller than half of said drill tip angle (θ).

6. The drill bit according to any one of the preceding claims, wherein said drill tip angle (θ) is between 135° and 145°.

7. The drill bit according to any one of the preceding claims, wherein said reduced radial rake angle (γ2) is negative and said previous radial rake angle (γ1) is positive.

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

9. The drill bit according to any one of the preceding claims, wherein said previous radial rake angle (γ1) is positive and is between 5° and 25°.

10. The drill bit according to any one of the preceding claims, wherein a radial extension (d1) of the portion of the cutting edge (7) that abuts the chamfered portion (91), from the outer peripheral surface (5) towards the central axis (C), is between 1% and 10% of the cutting diameter (D) of the drill bit.

11. The drill bit according to any one of the preceding claims, wherein a radial extension (d2) of the rake face 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 bit.

12. The drill bit according to any one of the preceding claims, wherein the rake face reduction region (81) extends axially in the groove (6) along most of the axial extension of the groove (6) at the outer periphery of the drill bit.

13. The drill bit according to any one of the preceding claims, wherein the groove includes a web thinning portion (10), and the cutting edge (7) includes: - an auxiliary cutting edge (72) formed at the intersection between the flank face (9) and the web thinning portion (10); and - a main cutting edge (71) extending from the radially outermost point (11) of the auxiliary cutting edge (10) to the outer peripheral surface of the drill bit.

14. The drill bit according to claim 13, wherein, The shortest distance (h) between a first line (s1) and a second line (s2) is between 2% and 10% of the cutting diameter (D) of the drill bit, - the first line (s1) extends from the radially outermost point (11) of the auxiliary cutting edge (10) to the radially innermost point (12) of the portion of the cutting edge that abuts the rake face reduction region (81), - the second line (s2) extends parallel to the first line (s1) through the central axis (C).

15. Use of the drill bit according to any one of the preceding claims for drilling in a heat-resistant superalloy.

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