JP2007007808A - Cemented carbide drill causing low work hardening - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve shortage of strength in the central part of the tip in the case of machining a large-diameter hole in a cemented carbide drill causing low work hardening, in which work hardening amount is comparatively smaller even in drilling an easy-to-quench material such as high carbon steel. <P>SOLUTION: The tip angle α1 of a chamfer blade part 54 provided inside the central part of a drill tip, that is, a predetermined boundary diameter dimension (d), ranges from 135° to 150°, and it is set larger than the tip angle α2 of the peripheral blade part 56, so that the strength of the central part is made higher without impairing the strength of a shoulder part 22, whereby even in a large-diameter cemented carbide drill for machining a large-diameter hole (e.g. a bore diameter 12 mm or more), which requires high load in drilling, loss of the cutting blade 52 of the tip central part, that is, the chamfer blade part 54 is restrained to obtain practically satisfactory durability. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cemented carbide drill, and more particularly to a low-work-hardening cemented carbide drill with a small work-hardening amount of a workpiece.

A cemented carbide drill made of cemented carbide is described in, for example, Patent Document 1 and the like, and in drilling a hub of an automobile, the tip angle is generally about 140 °, and the twist angle of the chip discharge groove Carbide drills of about 30 ° are used.
JP 2001-300808 A

  However, in drilling with a drill, it is inevitable that the inner peripheral surface of the drilled hole and the drill (leading edge) are in contact with each other due to the elasticity of the workpiece, and in the case of a material that is easy to quench, such as high carbon steel, The surface is work hardened by the quenching effect of frictional heat. For example, in the case of S55C carbon steel used for the hub or the like, the internal hardness is about 300 HV, but the surface of the processed hole may be 750 HV or more, and the tap life is shortened in the subsequent tap processing. Or press fitting such as bolts may become impossible. Such work hardening hardly becomes a problem with a new cemented carbide drill, but becomes noticeable particularly when the shoulder (the corner between the cutting edge and the leading edge) is worn or chipped by use. .

  On the other hand, although not yet known, the applicant of the present application described in Japanese Patent Application No. 2004-242446 filed earlier, the tip angle α is in the range of 125 ° to 135 °, and the twist angle β of the chip discharge groove is Low work hardening cemented carbide drill, characterized in that the axial rake angle γ of the cutting edge near the axial center formed by thinning is within the range of -5 ° to + 5 ° within the range of 20 ° to 30 °. Proposed. According to such a low work hardening carbide drill, since the tip angle α is smaller than the conventional 140 ° within the range of 125 ° to 135 °, the corner angle θ of the shoulder is increased accordingly. , Lack of shoulders and drooping are suppressed. Further, since the twist angle β is in the range of 20 ° to 30 ° and the axial rake angle γ of the cutting edge near the axis formed by thinning is in the range of −5 ° to + 5 °, the shoulder portion and The edge strength and sharpness of the cutting edge including the thinning portion are compatible, and a predetermined sharpness can be secured while suppressing chipping of the shoulder, cutting edge of the cutting edge, chipping, and the like. And since the chipping of the shoulder portion, chipping of the cutting edge, chipping and the like are suppressed in this way and a predetermined sharpness is obtained, excellent machining accuracy can be obtained over a long period of time, and the leading edge and Friction with the machining hole is reduced, and work hardening due to frictional heat is suppressed.

  However, in such a low work hardening cemented carbide drill with a relatively small tip angle α, for example, when machining a large-diameter hole having a hole diameter of 12 mm or more, the load (thrust load) during drilling becomes large. When the tip angle α is about 130 °, the strength is insufficient, and the cutting edge may be damaged early in the center of the tip, making it impossible to process.

  The present invention has been made against the background of the above circumstances, and the object of the present invention is a low work hardening carbide drill with a relatively small work hardening amount even in the drilling process for easily hardened materials such as high carbon steel. Is to improve the lack of strength at the center of the tip when machining a large-diameter hole.

  In order to achieve this object, the first invention is a cemented carbide drill in which at least the tip of the blade is made of cemented carbide, and (a) a tip angle α1 provided at the center of the drill tip. Biting blade portion within the range of 135 ° to 150 °, and (b) continuously provided on the outer peripheral side of the biting blade portion, and the tip angle α2 within the range of 125 ° to 135 ° and the above The cutting edge is configured to have a peripheral cutting edge smaller than the tip angle α1, and (c) the diameter d of the boundary between the biting cutting edge and the peripheral cutting edge is defined as a drill diameter D Is larger than 0.2D and smaller than 0.9D, while (d) the torsion angle β of the chip discharge groove is within the range of 20 ° to 30 °, and (e) near the axis formed by thinning. The axial rake angle γ of the cutting edge is in the range of −5 ° to + 5 °.

  The second invention is characterized in that, in the low work hardening cemented carbide drill of the first invention, the width dimension L of the negative land provided at the cutting edge of the cutting edge is in the range of 0.05 to 0.15 mm. .

  In such a low work hardening carbide drill, the tip angle α2 of the peripheral cutting edge provided at the outer peripheral portion of the tip of the drill is smaller than the conventional 140 ° within the range of 125 ° to 135 °. The corner angle θ of the shoulder portion (see FIG. 2) is increased by that amount, and shoulder chipping and shoulder slip are suppressed. Further, since the twist angle β is in the range of 20 ° to 30 ° and the axial rake angle γ of the cutting edge near the axis formed by thinning is in the range of −5 ° to + 5 °, the shoulder portion and The edge strength and sharpness of the cutting edge including the thinning portion are compatible, and a predetermined sharpness can be secured while suppressing chipping of the shoulder, cutting edge of the cutting edge, chipping, and the like. In addition, by suppressing the chipping of the shoulder portion, the chipping of the cutting edge, chipping, etc. and obtaining a predetermined sharpness, excellent machining accuracy can be obtained over a long period of time, and the leading edge and Friction with the machining hole is reduced, and work hardening due to frictional heat is suppressed.

  On the other hand, the center portion of the drill tip, that is, the tip of the biting blade provided inside the predetermined boundary diameter dimension d determined within a range larger than 0.2D and smaller than 0.9D with respect to the drill diameter D Since the angle α1 is larger than the tip angle α2 within the range of 135 ° to 150 °, the strength of the central portion can be increased without impairing the strength of the shoulder, Even in large-diameter carbide drills that process large-diameter holes with a large load (for example, a hole diameter of 12 mm or more), chipping of the cutting edge (cutting edge portion) at the center of the tip is suppressed, which is practically satisfactory. Durability can be obtained.

  In addition, when the tip angle is changed in the middle as described above, a corner portion is generated at the boundary portion based on the difference between the tip angles α1 and α2, and the tip angle α1 is within the range of 135 ° to 150 °. Since the angle α2 is in the range of 125 ° to 135 °, the crossing angle (outer angle) of the corner is 25 ° at the maximum, and defects due to stress concentration are suppressed. However, it is also possible to smoothly connect the biting blade portion and the peripheral blade portion with a predetermined arc, and in this case, the breakage of the boundary corner portion and the like can be more effectively prevented.

  In the second invention, the width L of the negative land provided at the cutting edge of the cutting edge by honing or the like is in the range of 0.05 to 0.15 mm. Thus, excellent processing accuracy can be obtained, and work hardening due to frictional heat is further suppressed.

  The low work hardening cemented carbide drill of the present invention, for example, the entire drill including the shank is integrally formed of cemented carbide, but the tip of the cemented carbide is made with the shank and the groove made of a material other than cemented carbide. The part may be integrally coupled by a coupling means such as brazing or shrink fitting. Although it is suitably applied to a two-blade carbide drill, it can also be applied to a three-blade or more drill.

  The present invention is suitably applied to a low work hardening cemented carbide drill having a large drill diameter D of 12 mm or more, but can also be applied to a low work hardening carbide drill smaller than 12 mm.

  If the tip angle α1 at the biting edge of the central portion is smaller than 135 °, insufficient strength at the central portion cannot be improved. On the other hand, if it is larger than 150 °, the biting property is deteriorated and the runout occurs. It becomes easy and the hole is enlarged or the work hardening amount is increased.

  When the tip angle α2 at the peripheral edge portion on the outer peripheral side is larger than 135 °, the corner angle θ is decreased, the strength of the shoulder portion is lowered, and shoulder chipping and shoulder swelling are likely to occur. Even if a chamfered blade portion having a tip angle α1 is provided, the strength of the central portion tends to be insufficient, and the intersection angle of the boundary portion with the chamfered blade portion becomes large, and the blade at the boundary corner portion Chipping and chipping are likely to occur. If the peripheral blade portion and the biting blade portion are smoothly connected with a predetermined arc, blade chipping or chipping at the boundary corner portion can be more effectively prevented.

  When the diameter d of the boundary between the cutting edge portion having a large tip angle α1 and the peripheral blade portion having a small tip angle α2 is 0.2 D or less, the effect obtained by providing the cutting blade portion having a large tip angle α1 is sufficiently obtained. Insufficient strength at the center portion cannot be sufficiently improved, but when it becomes 0.9D or more, the area of the peripheral blade portion with a small tip angle α2 becomes narrow, the strength of the shoulder portion becomes insufficient, and the shoulder portion is lost. Is likely to occur. The boundary diameter d may be in a range larger than 0.2D and smaller than 0.9D, but more preferably in a range of 0.3D to 0.7D. In addition, the position of the boundary diameter dimension d when the biting blade portion and the peripheral blade portion are smoothly connected by an arc is the position of the intersection where the linear biting blade portion and the peripheral blade portion are respectively extended.

  When the twist angle β of the chip discharge groove is larger than 30 °, the cutting edge strength of the cutting edge including the shoulder portion is reduced, and chipping, chipping and shoulder chipping are likely to occur. It becomes worse and durability performance and processing accuracy decrease.

  When the axial rake angle γ of the central cutting edge formed by thinning is larger than + 5 °, the strength of the blade edge is reduced and chipping and chipping are likely to occur, whereas when it is smaller than −5 °, the sharpness is poor. As a result, the cutting resistance increases and the processing accuracy decreases.

  If the width L of the negative land provided at the cutting edge of the cutting edge is larger than 0.15 mm, the sharpness is deteriorated and the machining accuracy is lowered. On the other hand, if the width dimension L is smaller than 0.05 mm, the cutting edge strength is lowered and the chipping or chipping is reduced. Is likely to occur. Honing is preferably used for forming (rounding) the negative land of the cutting edge.

  Further, the low work hardening cemented carbide drill of the present invention is provided with a hard coating such as TiAlN if necessary.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 2 is a diagram for explaining a low work hardening carbide drill 10 which is a premise of the present invention, and is a view showing a tip portion. (A) in the center is a front view seen from the drill tip side, and (( b) to (d) are side views as seen from the direction perpendicular to the axis O, respectively. The low work hardening cemented carbide drill 10 is integrally formed of a cemented carbide alloy, and a pair of chip discharge grooves 14 are provided on the outer peripheral surface. A cutting edge 16 is formed in each opening on the drill tip side. A thinning 18 is applied to the central portion of the cutting edge 16 to reach the vicinity of the axis O, and the cutting edge 16 is subjected to honing and a negative land 17 (see FIG. 3) is provided at the cutting edge. Yes.

  The tip angle α of the low work hardening carbide drill 10 is formed by the thinning 18 within a range of 125 ° to 135 °, and the twist angle β of the chip discharge groove 14 is within a range of 20 ° to 30 °. The rake angle γ in the axial direction of the cutting edge 16 near the center of the axis is in the range of −5 ° to + 5 ° (FIG. 2 shows a rake angle γ <0), and the negative land of the cutting edge 16 formed by honing. The width dimension (negative land width) L of 17 is in the range of 0.05 to 0.15 mm. The negative land width L is a relatively flat portion formed by honing at the intersection of the rake face 24 and the flank face 26 of the cutting edge 16 in a cross section perpendicular to the edge line of the cutting edge 16 as shown in FIG. Is the width dimension. The surface of the low work hardening cemented carbide drill 10 is coated with a hard coating 28 such as TiAlN with a thickness of several μm after honing, but the negative land width L is coated with the hard coating 28. It is the dimension in the later state.

  In such a low work hardening cemented carbide drill 10, the tip angle α is smaller than the conventional 140 ° within the range of 125 ° to 135 °, so that the cutting edge 16 and the leading edge 20 are correspondingly reduced. The corner angle θ of the intersecting shoulder portions 22 is increased, and loss of the shoulder portions 22 and minute chipping (shoulder missing), or the accompanying sagging (shouldering) of the shoulder portion 22 is suppressed. Further, since the twist angle β is in the range of 20 ° to 30 ° and the axial rake angle γ of the cutting edge 16 near the axis formed by the thinning 18 is in the range of −5 ° to + 5 °, the shoulder The cutting edge 16 including the portion 22 and the thinning portion has both cutting edge strength and sharpness, and a predetermined sharpness can be secured while suppressing chipping of the shoulder 22, cutting of the cutting edge 16, chipping, and the like. Furthermore, since the width dimension L of the negative land 17 of the cutting edge 16 of the cutting edge 16 formed by honing is in the range of 0.05 to 0.15 mm, the cutting edge strength and sharpness of the cutting edge 16 are compatible.

  As described above, the chipping of the shoulder portion 22, the chipping of the cutting edge 16, chipping and the like are suppressed and a predetermined sharpness is obtained, so that excellent processing accuracy can be obtained over a long period of time, leading edge Friction between 20 and the machining hole is reduced, and work hardening due to frictional heat is suppressed.

FIG. 4 is a diagram for explaining the results of drilling under the following processing conditions using 14 types of test products and examining the durability performance and the work hardening amount. Among the test products No1 to No14, 6 types of test products No4 to No7, No9, and No10 satisfy the specifications of each part of the low work hardening carbide drill 10 and are the test products that are the premise of the present invention (hereinafter referred to as the test products). Others are comparative products. Further, the tip angle α and the twist angle β of each test product are as shown in FIG. 4, but the axial rake angle γ of the thinning 18 and the width dimension L of the negative land 17 of the cutting edge 16 provided by honing. For all the test products, γ = 0 ° and L = 0.10 mm. In addition, invention premise products (test products No. 4 to No. 7, No. 9, and No. 10) satisfy the present invention except that the central portion of the drill tip is not provided with a biting blade portion having a tip angle α1 of 135 ° to 150 °. The tip angle α (= α2) of the outer peripheral side portion (peripheral blade portion) of the cutting edge 16 is in the range of 125 ° to 135 °, and the twist angle β of the chip discharge groove 14 is 20 ° to 30 °. In this range, the axial rake angle γ of the cutting edge 16 near the axis O formed by the thinning 18 is in the range of −5 ° to + 5 °.
(Processing conditions)
-Work material: S55C (carbon steel)
-Hole depth: 11mm through hole-Hole diameter: 10.8mm
・ Cutting speed: 70 m / min
・ Feeding amount: 0.25mm / rev

  In FIG. 4, “durability (number of holes)” is the number of holes until the end of the drill when the drill has reached the end of its life with a constant of 4000. As described in “Remarks”. The “work hardening amount (HV0.2)” is 1.96 N of the Vickers hardness X of the processed surface after drilling and the internal Vickers hardness Y after removing the work hardened surface layer portion. It is a value (XY) obtained by subtracting Y from X, each measured at a test load of (200 gf). “Initial” is a result of examining the machining hole at the beginning of machining, and “constant / lifetime” is When processing was performed up to 4000, the 4000th processing hole was examined, and the one that reached the end of its life was the result of examining the processing hole when that life was reached. FIG. 5 is a graph showing the amount of work hardening at “constant / lifetime” in relation to the number of processed holes (durability) for each of the test products No. 1 to No. 14 in FIG. The prerequisite product, “×” is a comparative product, and the numbers on the right side of them are the test product No.

  As is clear from FIGS. 4 and 5, all of the test prerequisites No. 4 to No. 7, No. 9 and No. 10 can be drilled to a constant of 4000. Regarding the work hardening amount, there is no great difference between the premise invention and the comparative product at the “initial” stage, but within the range of 191 to 259 at the stage where 4000 premise inventions were processed at the “constant / lifetime” stage. On the other hand, the work-curing amount of the 4000 processed comparative products (test products No. 12, 13, and 14) is 380 to 455, and the work-hardening amount of the invention premise product is reduced by 100 or more compared to the comparative product. For the test products No1 to No3 with the tip angle α = 120 °, the tip portion is chipped early, the hole accuracy is deteriorated, and sufficient durability cannot be obtained.

  Further, when tapping was performed on a processed hole formed using the invention premise product (test product No. 6) and the comparative product (test product No. 14), the comparative product had a tap life of about 1000 holes. In the invention premise product, it was possible to process 1250 holes or more, and it was confirmed that the tap life was improved by 25% or more.

  Further, according to another test result, at the stage of constant machining 3200 holes, the comparative product (tip angle α = 140 °, torsion angle β = 35 °) has a work hardening amount of 405 (HV 0.2) and is cured. Whereas the layer thickness was 0.02 mm, the precondition of the invention (tip angle α = 130 °, helix angle β = 25 °) had a work hardening amount of 162 (HV 0.2), and the cured layer thickness was The result was that the thickness was 0.01 mm, the work hardening amount was reduced by 240 (HV 0.2), and the cured layer thickness was halved. This is a numerical value equivalent to the initial work hardening.

  On the other hand, even in such a low work hardening carbide drill 10, for example, when machining a large diameter hole having a hole diameter of 12 mm or more, the load at the time of drilling becomes large, and the tip angle α is about 130 °. Insufficient strength sometimes caused the cutting edge 16 to break early in the center of the tip, making machining impossible. For this reason, in this embodiment, like the low work hardening carbide drill 50 shown in FIG. 1, a chamfered blade portion 54 having a tip angle α1 in the range of 135 ° to 150 ° is provided at the center of the tip of the drill. . The biting blade portion 54 is provided by grinding the flank (second surface) according to the tip angle α1 with respect to the invention premise product (low work hardening carbide drill 10) indicated by a dotted line, Thereafter, the thinning 18 and honing may be performed. The biting blade portion 54 is provided in the center side portion of a predetermined boundary diameter dimension d determined within a range larger than 0.2D and smaller than 0.9D with respect to the drill diameter D, and more than that. The tip angle α2 of the outer peripheral blade portion 56 is the same as the tip angle α of the low work hardening carbide drill 10, and the cutting edge 52 is constituted by the biting blade portion 54 and the peripheral blade portion 56. Yes. Moreover, it is the same structure as the said low work hardening cemented carbide drill 10 except the biting blade part 54 of big tip angle | corner (alpha) 1 (> (alpha) 2) being provided, and the same code | symbol is attached to a substantially common part. However, the twist angle β of the chip discharge groove 14 is in the range of 20 ° to 30 °, and the axial rake angle γ of the cutting edge 52 near the axis O formed by the thinning 18 is omitted. Is in the range of −5 ° to + 5 °, and the width dimension L of the negative land provided at the cutting edge of the cutting edge 52 by honing is in the range of 0.05 to 0.15 mm. FIG. 1 corresponds to (b) of FIG.

  And according to such a low work hardening cemented carbide drill 50 of a present Example, the front-end | tip angle (alpha) 1 of the biting blade part 54 provided inside the center part of the drill front-end | tip, ie, the boundary diameter dimension d, is 135 degrees-. Since it is larger than the tip angle α2 (= α) of the peripheral blade 56 within the range of 150 °, the strength of the central portion is increased without impairing the strength of the shoulder portion 22, and the load during drilling Even in large-diameter carbide drills that process large-diameter holes with a large diameter (for example, a hole diameter of 12 mm or more), chipping of the cutting edge 52 at the center of the tip, that is, the chamfered blade portion 54 is suppressed, and durability that can be satisfied in practice Sex can be obtained.

  In addition, when the tip angle is changed in the middle as described above, a corner portion is generated at the boundary portion based on the difference between the tip angles α1 and α2, and the tip angle α1 is within the range of 135 ° to 150 °. Since the angle α2 is in the range of 125 ° to 135 °, the crossing angle (outer angle) of the corner is 25 ° at the maximum, and defects due to stress concentration are suppressed. In particular, if the corner portion, that is, the boundary portion between the biting blade portion 54 and the peripheral blade portion 56 is connected smoothly by a convex arc having a radius R of about 0.02D to 0.3D with respect to the drill diameter D, for example. In addition, the loss of the boundary corner portion is prevented more effectively.

  Further, the axis formed by the thinning 18 is such that the tip angle α2 of the peripheral cutting edge 56 provided at the outer peripheral portion of the drill tip is in the range of 125 ° to 135 ° and the twist angle β is in the range of 20 ° to 30 °. The axial rake angle γ of the cutting edge 52 near the center is in the range of −5 ° to + 5 °, and the width dimension L of the negative land 17 at the cutting edge of the cutting edge 52 formed by honing is 0.05 to 0.15 mm. Since it is within the range, chipping of the shoulder portion 22, chipping of the cutting edge 52, chipping, etc. are suppressed and a predetermined sharpness is obtained, and excellent machining accuracy can be obtained over a long period of time, leading edge The point that the work hardening due to frictional heat is suppressed by reducing the friction between the work hole 20 and the work hole is the same as the low work hardening carbide drill 10.

Here, the tip angle α1 = 140 ° of the biting blade portion 54 and the tip angle α2 = 130 ° of the peripheral blade portion 56, and the boundary diameter dimension d thereof is 0.1D, 0.2D, 0.3D, Using six types of test products of 0.5D, 0.7D, and 0.9D, drilling was performed under the following processing conditions, and the drill life and work hardening amount were examined. The results shown in FIG. Obtained. The “diameter of 140 ° at the tip” in FIG. 6 means the boundary diameter dimension d. In addition, the torsion angle β = 25 ° of each test product, the axial rake angle γ = 0 ° of the thinning 18 and the width dimension L of the negative land 17 of the cutting edge 52 of the cutting edge 52 are L = 0.10 mm. The boundary with the blade 56 is smoothly connected by a convex arc having a radius R = 0.1D.
(Processing conditions)
-Work material: S55C (carbon steel)
-Hole depth: 11mm through hole-Hole diameter: 13.9mm
・ Cutting speed: 70 m / min
・ Feeding amount: 0.25mm / rev

  As can be seen from FIG. 6, when d = 0.1D, the effect of providing the biting blade portion 54 with the large tip angle α1 cannot be sufficiently obtained, and the cutting edge is cut early due to insufficient strength of the central portion. 52 is missing and cannot be processed. FIG. 7A is a photograph of the center portion of the drill tip at this time, and it can be seen that the center portion of the cutting edge 52 is completely crushed. In the case of d = 0.2D, it was possible to machine up to 3000 holes, but similarly, a chip was generated at the center portion of the cutting edge 52, the centripetality was deteriorated, and the amount of work hardening was increased due to the runout. Processing was not possible before drilling. When d = 0.3D, 0.5D, and 0.7D, any of 4000 holes or more can be drilled, and the amount of work hardening is small. FIG. 7B is a photograph of the center part of the drill tip when processing 4000 holes in the case of d = 0.5D, and almost no chipping is observed up to the center part. In the case of d = 0.9D, it was possible to process up to 3550 holes, but the strength of the shoulder portion 22 was insufficient and chipping occurred, the sharpness deteriorated and the processing accuracy decreased and the work hardening amount increased. Processing was not possible before processing 4000 holes. From this result, the boundary diameter dimension d needs to be larger than 0.2D and smaller than 0.9D.

Further, FIG. 8 shows that the peripheral edge 56 has a tip angle α2 = 130 °, a boundary diameter d = 0.5D, a torsion angle β = 25 °, an axial rake angle γ = 0 ° of the thinning 18, and the cutting edge 52 In the low work hardening carbide drill 50 having a width L of the cutting edge negative land 17 of 0.10 mm, the cutting edge 54 has a tip angle α1 of 135 °, 140 °, 145 °, 150 °, and 155 °. This is a result of examining the relationship between the number of holes to be drilled and the amount of expansion of holes by drilling with the following test conditions under the following processing conditions. In all the test products, the boundary between the biting blade portion 54 and the peripheral blade portion 56 is smoothly connected by a convex arc having a radius R = 0.1D.
(Processing conditions)
-Work material: S55C (carbon steel)
-Hole depth: 11mm through hole-Hole diameter: 13.9mm
・ Cutting speed: 70 m / min
・ Feeding amount: 0.25mm / rev

  In FIG. 8, in the case of α1 = 135 °, 140 °, 145 °, in the processing up to 1000 holes, the hole enlargement amount is 0.015 mm or less, high processing accuracy is obtained, and there is almost no runout due to the chipping of the blade. it is conceivable that. When α1 = 150 °, the biting property deteriorates and the load (thrust load) increases, the centripetality decreases due to wear or blade chipping, and the amount of hole expansion gradually increases with processing. In processing up to 1000 holes, the hole enlargement amount is 0.02 mm or less, which is practically acceptable. When α1 = 155 °, the bite resistance is poor and the load (thrust load) is large. Even in the initial processing of 1000 holes or less, the amount of expansion of the hole becomes 0.02 mm or more due to runout, which exceeds the allowable range. .

  As mentioned above, although the Example of this invention was described in detail based on drawing, this is an embodiment to the last, and this invention is implemented in the aspect which added various change and improvement based on the knowledge of those skilled in the art. Can do.

It is a figure explaining one Example of this invention, and is a figure equivalent to (b) of FIG. 2 which shows the low work hardening carbide drill used as a premise. It is a figure which shows the front-end | tip part shape of the low work hardening carbide drill used as the premise of this invention. It is sectional drawing explaining the negative land provided in the cutting blade by honing in the cemented carbide drill of FIG. It is a figure which shows the result of having investigated durability and the amount of work hardening about some test goods based on the cemented carbide drill of FIG. FIG. 5 is a graph showing the work hardening amount of “constant / lifetime” in FIG. 4 in relation to the number of processed holes. It is a figure which shows the result of having drilled using several test goods which changed the boundary diameter dimension d of a biting blade part and a peripheral blade part in FIG. 1, and having investigated the drill lifetime and work hardening amount. In FIG. 6, it is a photograph which shows the state of the cutting edge after drilling in case of d = 0.1D and 0.5D. It is a figure which shows the result of having drilled using some test goods which changed the front-end | tip angle (alpha) 1 of the biting blade part in FIG. 1, and having investigated the relationship between the number of process holes and a hole expansion amount.

Explanation of symbols

  14: Chip discharge groove 17: Negative land 18: Thinning 50: Low work hardening carbide drill 52: Cutting edge 54: Chamfering edge 56: Peripheral edge

Claims (2)

It is a carbide drill in which at least the tip of the blade is made of a cemented carbide,
A biting blade portion having a tip angle α1 provided at the center of the tip of the drill in a range of 135 ° to 150 °;
A peripheral blade portion continuously provided on the outer peripheral side of the biting blade portion and having a tip angle α2 within a range of 125 ° to 135 ° and smaller than the tip angle α1;
A cutting edge is formed, and a diameter d of a boundary between the biting blade and the peripheral blade is larger than 0.2D and smaller than 0.9D with respect to the drill diameter D. ,
The twist angle β of the chip discharge groove is in the range of 20 ° to 30 °,
A low work hardening carbide drill characterized in that the axial rake angle γ of the cutting edge near the axis formed by thinning is in the range of −5 ° to + 5 °. The low work hardening cemented carbide drill according to claim 1, wherein a width L of a negative land provided at a cutting edge of the cutting edge is in a range of 0.05 to 0.15 mm.

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