JP2007144526A - Twist drill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high accuracy twist drill which can produce a beautiful finish of an inner surface without causing burrs, laminated layer separation, or residual fiber in a hole, even when a workpiece is made of high strength fiber composite material, by improving cutting performance by improving the structure of cutting edges, and which can improve its durability. <P>SOLUTION: The twist drill comprises land portions 3 having helical flutes 2, 2 for removing chips on the outer peripheral portion of a drill body 1 rotationally driven about the axis of the drill, and a pair of cutting edges 4, 4, a pair of flanks 5, 5, a pair of thinning edges 6, 6, and a pair of chisel edges 7, 7 formed on the tip end portion of the drill body 1 by a point angle α, wherein the outer peripheral shoulder portions 5a, 5a of the flanks are rounded so as to be curved surfaces R, R, and rake angle portions 21, 21 are provided at cutting edges and the helical flutes in the neighborhood of the shoulder portions, and the ridge lines of the cutting edges are formed so as to be composed of concave shape portions from the chisel edges toward the outer peripheral ends and curved lines following the concave shape portions, and as a result, the cutting edges are formed so as to be sharp cutting edges composed of S shape curved lines as a whole in the side view. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a twist drill, and more particularly to a twist drill suitable for drilling a high-strength fiber composite material. Specifically, a twist lead groove for discharging chips is formed in an outer peripheral portion of a drill body rotated around an axis. The present invention relates to an improvement of a twist drill including a pair of cutting blades and a flank formed by a tip angle.

In each industrial field, a high-strength fiber composite material is used for the purpose of reducing the weight and increasing the strength of equipment, and through-hole processing such as through holes, assembly holes, and mounting holes is performed. For example, in the electronic industry, double-sided copper foil glass fiber-containing epoxy substrates are frequently used as electronic circuit boards, and fine holes such as through holes and via holes are drilled in the composite substrate. In the aircraft industry, carbon fiber-containing epoxy substrates are used. A resin reinforced composite material (CFRP) is frequently used, and relatively large holes such as assembly holes and mounting holes are provided. The automobile industry is equipped with a millimeter-wave radar antenna as one of various safety measures. To secure high-speed vibration resistance as the antenna substrate, Teflon (registered trademark) with copper attached on both sides is used. ) A high-strength fiber composite material made of a base material or the like is used, and fine through-holes are perforated in order to form a multilayer millimeter-wave receiving circuit.
These composite materials are suitable for punching as punching because a hard region consisting of reinforcing fibers such as metal foil, carbon fiber, silicon carbide fiber, and glass fiber and a soft region such as resin as a matrix are mixed. Usually, drilling using a twist drill is often used.

Conventionally known twist drills are represented by the tip angle of the drill body as represented by FIG. 2 of Japanese Patent Laid-Open No. 61-109606 (Patent Document 1) and Japanese Utility Model Laid-Open No. 2-150112 (Patent Document 2). The pair of cutting blades formed is a twist drill for metal processing having a ridge line shape that is straight from the tip or chisel edge toward the outer peripheral end (hereinafter referred to as a general-purpose drill). As shown in FIG. 4, a cutting edge ridge line having a concave curve shape (inner concave shape) has also been proposed.
Further, as a twist drill for a composite material in which a hard region and a soft region are mixed, a proposal for improving the general-purpose drill has been made. For example, as disclosed in Japanese Patent Laid-Open No. 2-152708 (Patent Document 3), a twist angle is proposed. It has also been proposed to improve the ridge line shape of the cutting edge part from the chisel edge to the outer peripheral edge, such as selecting the (torsion lead angle) within a predetermined range, or making the cutting edge ridge line a concave curve (arc shape) Yes.

JP-A-61-109606 Japanese Utility Model Publication No. 2-150112 JP-A-2-152708

However, in recent drilling, in order to ensure the reliability of various devices, it is required to drill through holes or the like with high processing accuracy higher than before in a high-strength fiber composite material.
Specifically, the case of the antenna substrate of the millimeter wave radar antenna will be described as an example. In the drilling process using the general-purpose drill, the front and back copper foil surfaces are turned up (burrs), the inner layer is lifted up and delaminated. "Cross-section disorder" occurs, or the "fiber residue" that the reinforcing fiber is pulled out without being completely cut and protrudes into the hole is generated. Then, copper plating adheres to the fiber protruding into the hole, which becomes a defect of the millimeter wave receiving circuit and adversely affects the image conversion accuracy. For this reason, machining accuracy, that is, high cutting performance is required to completely prevent the above-mentioned “cross-sectional disorder” and “wrinkle remaining” state in the hole due to drilling.

  However, according to the above-mentioned Patent Document 3, although the conventional general-purpose drill is improved for composite materials, the cutting edge ridge line from the chisel edge to the outer peripheral end is simply made into a concave curve shape (arc shape). is there. Therefore, even if cutting resistance and cutting heat can be suppressed, the above-mentioned problems when drilling a recent high-strength fiber composite material, that is, "cross-sectional disorder" such as delamination between laminated layers, The cutting performance that can eliminate the state cannot be obtained.

  In order to solve the above-mentioned conventional problems, the present invention improves the cutting edge structure and enhances the cutting performance, so that even a high-strength fiber composite material does not have burrs, delamination between layers, or wrinkles remaining in holes An object of the present invention is to provide a twist drill with high machining accuracy that can achieve a smooth inner surface finish, and to improve the durability of the drill.

The twist drill of the present invention that solves the above-mentioned problems is a general-purpose drill that has been put to practical use, specifically, a twisted lead groove for chip discharge is formed in the outer peripheral portion of the drill body that rotates about the axis. A twist drill for forming a pair of cutting blades and flank formed by a tip angle at the tip portion, or a twist for discharging chips on an outer peripheral portion of a drill body rotated about an axis. A land portion having a lead groove is provided, and a tip portion is provided to improve a twist drill in which a pair of cutting blades, a flank surface, a thinning and a chisel edge formed by a tip angle are formed. The outer peripheral shoulder is a curved surface with a rounded chamfer, a scooping portion is provided in the cutting blade and the lead groove near the shoulder, and the ridge line of the cutting blade is directed from the tip or chisel edge to the outer peripheral end. It was concave-curved and curved subsequent, characterized in that the cutting edge was sharp edge shape composed of a side view S-shaped curve as a whole (claims 1 and 2).
The concave curve of the cutting edge ridge line is composed of a gradually decreasing curve portion from the tip or chisel edge to the concave bottom portion and a gradually increasing curve portion from the concave bottom portion to the outer peripheral end. The cutting pressure against the workpiece acts as a relatively small up-cut, and the gradually increasing curve portion acts as a large down-cut against the workpiece, and the curved ridge formed on the outer peripheral shoulder that continues to the gradually increasing curved portion is sharp. It is made to act as a curved blade part (Claim 3).

That is, the present invention not only makes the ridge line of the cutting edge a concave curve, but also provides a cutting edge by providing a scooping part in the lead groove, that is, a part where the tip part of the twisted lead groove is further scooped into a concave curved surface. A sharp blade edge is formed, and a sharp curved blade portion is newly formed on the outer peripheral shoulder of the flank by the curved surface (R surface) formed on the outer peripheral shoulder of the flank and the scooping portion. Accordingly, the cutting blade as a whole exhibits a three-dimensional S-shaped curve in a side view, and in particular, a new cutting blade portion formed on the outer peripheral shoulder also has a sharp curved razor-like curve. It becomes a blade part (R blade part).
The above-mentioned upcut refers to a cutting mode in which, for example, scooping is used to scoop up from the bottom, and the cutting pressing force of the cutting blade acts on the workpiece to be drilled relatively small. Further, the down cut refers to a cutting mode in which, for example, digging while pressing from above using a scissors, and the cutting pressing force of the cutting blade acts on the workpiece to be drilled.

Therefore, according to the twist drill of the present invention, centripetality is ensured in the initial cutting by the gradually decreasing curve portion of the cutting blade, cutting resistance is reduced by up-cutting due to rotation, and cutting is performed with a relatively small pressing force on the workpiece. The workpiece is cut with a sharp cutting blade while holding down the workpiece with a large pressing force by down-cutting by the gradually increasing curved portion of the cutting blade, and the outer peripheral portion of the hole drilled in the workpiece by the sharp R-blade following is completely Drilling proceeds continuously while cutting.
In particular, even when the workpiece is a composite material of a metal material and a fiber reinforced resin material as described above (Claim 4), deformation and peeling of the metal surface layer such as copper foil is prevented at the upcut stage, and the downcut The inner layer is prevented from lifting and delamination, and then the cutting edge of the cutting edge of the R-blade is used to prevent the fiber from being pulled out. A hole is obtained. Further, the curved surface formed on the outer peripheral shoulder portion of the flank provides a beautiful surface finish without generating burrs in the surface layer when the drill is pulled out after drilling.

  And about the shaping | molding method of the twist drill of the said form, if the cutting edge shape of the curved surface of a peripheral shoulder part, a scooping part, and the S-curve shape of a side view is formed, NC grinder will be used from the beginning of drill manufacture. Although it is optional to adopt a method of producing by a programmed polishing method or the like, preferably, a method of making an existing general-purpose drill that has been preformed by additional machining, that is, the curved surface of the outer peripheral shoulder is It is preferable that a general-purpose twist drill is formed by chamfering, and then a scooping process is performed to form the cutting edge shape of the S-curve when viewed from the side (Claim 5). According to this, it can be produced by subjecting an existing general-purpose drill to follow-up processing, and by applying scooping processing using a grindstone with a shaft or a disc-type grindstone, the scooping portion and the edge shape of the S-curve Can be formed simultaneously.

According to the present invention, the up-cut associated with the curved shape of the cutting blade is used to cut the workpiece without deforming or damaging it, and the drilling portion of the workpiece is completely cut by the down-cut and the curved razor blade following the drill. Since the generation of burrs at the time of drawing is prevented, the cutting performance is remarkably improved and the hole inner surface finish and surface finish of the workpiece are improved (claims 1 to 3).
In particular, even when the workpiece is a high-strength fiber composite material, it is possible to prevent “cross-sectional disorder” such as delamination of the surface layer and delamination and “wrinkle residue” in the hole, so that high processing accuracy is required. It is possible to provide a twist drill that can sufficiently cope with drilling of devices such as an electronic circuit board and a millimeter wave radar antenna board.
In addition, centripetality is ensured by the gradually decreasing curve part of the cutting edge, preventing drill bending at the beginning of cutting, improving straightness of drilling, and preventing breakage due to core blurring especially in the case of fine drills. Can be improved (claim 4).

  Furthermore, if the twist drill according to the present invention is manufactured by performing follow-up processing on a general-purpose drill, not only can the twist drill be provided easily and inexpensively, but also a change from the existing general-purpose drill can be used. (Claim 5).

  Embodiments of the present invention will be described with reference to the drawings. First, in order to make it easy to understand the characteristic configuration, one embodiment of a general-purpose drill that is a basic shape will be described. The manufacturing process will be described with reference to FIG.

In FIG. 1, (a) shows a general-purpose drill having a thinning and a chisel edge, (1) is a plan view, and (2) is a front view. This general-purpose drill 10 is made of cemented carbide or high-speed steel. The land portion 3 having two twisted lead grooves 2 for discharging chips is provided on the outer peripheral portion of the drill body 1, and the tip portion is provided with a tip angle α. A pair of cutting blades 4, 4 to be formed, flank surfaces 5, 5 that are continuous from each cutting blade in the circumferential direction, thinnings 6, 6 for facilitating discharge of chips, and chisel edges 7, 7 formed by thinning. Standard well-known shape with
Both the cutting edges 4 and 4 are linearly formed from each end of the chisel edge 7 toward the outer peripheral end, and more specifically, are substantially linear along the diameter line P passing through the center of the tip and are formed symmetrically. Further, the flank surfaces 5 and 5 are surfaces that are cut and polished along the tip angle α in order to define the cutting blades 4 and 4, and the outer peripheral shoulder portions 5a and 5a are not particularly processed. It is.
In this general-purpose drill 10, the chisel edges 7 and 7 substantially function as primary cutting edges, and the cutting edges 4 and 4 function as secondary cutting edges. Further, the symbol d in the figure is the diameter of the drill body 1 (drill diameter), and β is the lead angle (twist angle) of the twist lead groove 2.

FIG. 1B shows the intermediate drill 15 in a state where the general-purpose drill 10 is chamfered. The intermediate drill 15 is curved smoothly by chamfering the outer shoulder portions 5a, 5a of the flank surfaces 5, 5 by grinding and polishing with a grindstone or the like from the outer shoulder portions 5a, 5a to the land portion 3. The surface R is formed.
FIG. 1C shows a twist drill (hereinafter referred to as a drill) 20 according to the present invention, which is completed by further scooping the intermediate drill 15. The drill 20 forms a scooping portion 21 in the tip portion of the twisted lead grooves 2 and 2 of the intermediate drill 15, specifically the scribing portion 21 and the lead groove 2 in the vicinity of the curved surface R by scooping.
As shown in FIGS. 7 and 8, the scooping process is performed using a grinding apparatus (not shown) and a rotating drum wheel 16 with a rotating shaft (see FIG. 7) or a disk-type grinding wheel 17 (see FIG. 8). The twisted lead groove 2 of the intermediate drill 15 is pressed against the cutting edge 4 and the lead groove surface in the vicinity of the curved surface R is scraped into a curved shape, thereby forming the scooping portion 21 and at the same time the ridge line of the cutting blade 4 Are formed in a concave curve shape.
In FIGS. 1B and 1C, the shape of the general-purpose drill 10 is indicated by a two-dot chain line for comparison.

Details of the drill 20 will be described with reference to FIGS.
2 (1) and (2) are enlarged views of FIGS. 1 (c), (1), and (2), and FIG. 2 (3) is a side view as viewed from the arrow X in FIG. 2 (1). Moreover, the arrow Y in the figure is the rotation direction of the drill 20.
As shown in FIG. 2 (1), the drill 20 has a diameter line P ′ that passes through the center of the tip and connects the outer peripheral ends of the cutting blades 4, 4 slightly in the rotational direction from the position of the diameter line P of the general-purpose drill 10. The ridgeline of the cutting blades 4 and 4 is recessed with respect to the diameter line P ′. Specifically, the ridgeline of the cutting blades 4 and 4 is concave and drawn gradually from each end of each chisel edge 7 to the concave bottom of the substantially central portion. It has a concave curve shape that draws a gradually increasing curve portion 4b from the bottom toward the outer periphery. Moreover, since the lead groove surface in the vicinity of the cutting blades 4, 4 is scraped off by the scooping portion 21, each cutting blade 4 has a sharper edge shape than the general-purpose drill 10.
Further, the curved surface R formed on the outer peripheral shoulders 5a, 5a also has a sharp cutting edge shape because the adjacent lead groove surface is scraped off by the scooping portion 21, and thereby the curved surface R A curved R blade portion 22 newly formed continuously on the outer periphery of the cutting blade 4 is formed.
Therefore, the shape of the cutting edge of the drill 20 as a whole is formed into an S-shaped curve composed of the cutting blade 4 and the R blade portion 22 as shown in a side view of FIG.

FIG. 3 shows details of the cutting edge shapes of the cutting blade 4 and the R blade portion 22 formed by the scooping portion 21 as a cross-sectional plan view, and FIG. 3 (1) is the same as FIG. 2 (2). Is a front view for showing a cross-sectional line, and FIGS. 3 (2) to (5) are end views along the cross-sectional lines. In addition, the dashed-two dotted line in the figure has shown the shape of the general purpose drill 10 for the comparison. 3 (2) to (5), the symbol θ is the transverse edge angle at each part of the drill 20, and θ ′ is the transverse edge angle at each part of the corresponding general-purpose drill 10.
The drill 20 is a case where the drill diameter d is 0.3 mm, the tip angle α is 120 degrees, and the lead angle β is 30 degrees. Degrees, θ ′: 38 degrees, θ in section line BB: 32 degrees, θ ′: 65 degrees, θ in section line CC: 25 degrees, θ ′: 65 degrees, θ in section line DD: 36 degrees and θ ′: 65 degrees.
According to this illustration, it will be understood that the blade edge angle of the R blade portion 22 is the smallest and the shape is a sharp razor with the same portion curved.

FIG. 4 shows the details of the shape of the cutting edge 4 of the cutting blade 4 in the drill 20 as a longitudinal side view, FIG. 4 (1) is a plan view showing the cross-sectional line, and FIGS. It is a section side view which meets each longitudinal section line. 4 (2) to 4 (4), the symbol γ is the longitudinal cutting edge angle at each part of the drill 20, γ at the section line EE: 41 degrees, γ at the section line FF: 44 degrees, and the section line. Γ in GG: 43 degrees.
FIG. 5 shows the vertical cutting edge angle γ ′ at the same cross-sectional portion of the general-purpose drill 10 for comparison with the vertical cutting edge angle γ of the drill 20, γ at the cross-sectional line E′-E ′: 68 degrees, and the cross-sectional line F Γ ′ at “−F” is 59 degrees, and γ ′ at the section line G′-G ′ is 52 degrees.
It will be understood from this illustration that the cutting edge 4 of the drill 20 is sharper than the general-purpose drill 10 by the scooping portion 21. In particular, the cutting edge angle γ at the section line EE is extremely sharp at 41 degrees, so that the cutting resistance generated at the moment when the drill 20 bites into the workpiece can be reduced, and a stable drill point can be formed. Due to the synergistic effect with the subsequent down cut, drill breakage can be eliminated and drill breakage can be prevented. In addition, the reduction of the cutting edge angle γ (43 degrees) in the section line GG and the reduction of the cutting edge angle θ (25 degrees) in the section line CC of the R cutting section 22 are combined. The cutting property can be improved.

Thus, the case of drilling using the drill 20 will be described with reference to FIG. 6A. The workpiece 30 has a thickness of 0.5 mm, in which a high-strength fiber resin layer 31 is laminated and copper foil layers 32 are provided on both front and back surfaces. It is a composite material.
The drill 20 hits the surface copper foil layer 32 of the workpiece 30 by rotation and descending feed, and starts cutting. However, the up-cutting action by the gradually decreasing curve portions 4a and 4a of the cutting blades 4 and 4 ensures the centripetal force and the cutting resistance. Therefore, the copper foil layer 32 is not turned up and is perforated by a sharp blade edge.

Next, since the fiber resin layer 31 is pushed downward and cut by the down-cut action by the gradually increasing curved portions 4b and 4b of the cutting blades 4 and 4 and the sharp blade edge shape, the laminate is lifted and delamination does not occur. The high-strength fiber resin layer 31 is cut and perforated, and then proceeds while completely cutting the outer peripheral portion of the hole perforated by the cutting action of the sharp R-blade 22 so that the reinforcing fiber 31a is prevented from being pulled out and the inner surface of the hole is prevented. It is surely cut along.
Then, after drilling up to the back copper foil layer 32, the drill 20 is raised while being reversed and pulled out from the work 30, but since the outer peripheral shoulders 5a, 5a are formed on the curved surface R, delamination even at the time of ascent The occurrence of burrs can be prevented without turning up the surface copper foil layer 32.
Therefore, the inner surface of the drilled hole 33 is free from cross-sectional disturbance and wrinkle residue, and both the inner surface and the surface have a good finish (see FIG. 6 (2)).

(Other embodiments)
The drill 20 has been described and illustrated for the case where the tip angle α is 120 degrees and the lead angle β is 30 degrees. However, the drill 20 is not limited to this and is appropriately changed according to the material of the workpiece, the machinability, and the like. is there.
For example, the curved surface R formed by the chamfering process has a sharper R edge 22 as the amount of chamfering is increased even with the same scooping portion 21, so the amount of chamfering is increased for difficult-to-cut workpieces. It is intended to improve the machinability and make changes such as reducing the chamfering amount for sticky workpieces.

In addition, drills having various lead angles β are prepared so as to correspond to the types of workpieces, but the scooping portion 21 formed by scooping is changed according to the lead angle β, whereby the edge angle is changed. Change.
FIG. 9 illustrates the case where the scooping portion 21 changes corresponding to the lead angle β. In FIG. 9, (1) to (5) indicate the lead angle β of 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, respectively. The change of the ugly part is shown. Among them, (3) is the case of the drill 20 shown above, but in order to contrast the cross cutting edge angle Θ with FIG. 3, the drill 20 a (FIG. 9 (1)) with a lead angle β of 20 degrees, A drill 20b (FIG. 9 (5)) having a lead angle β of 40 degrees is shown in FIGS. 10 and 11 as a comparative example.

10, (2) to (5) are end views taken along the cross-sectional lines of the drill 20a shown in FIG. 10 (1), and θ at the cross-sectional line AA: 28 degrees, cross-sectional lines Θ in BB is 19 degrees, θ in section line CC is 17 degrees, and θ in section line DD is 12 degrees.
11, (2) to (5) are end views taken along the cross-sectional lines of the drill 20 b shown in FIG. 11 (1), and θ at the cross-sectional line AA is 56 degrees, the cross-sectional line Θ in BB is 47 degrees, θ in section line CC is 49 degrees, and θ in section line DD is 32 degrees.
By comparing FIG. 10, FIG. 11 and FIG. 3, it is understood that the smaller the lead angle β, the smaller the edge angle and the sharper the edge shape.
Therefore, in consideration of the lead angle β together with the degree of chamfering that forms the curved surface R, a drill with a cutting edge shape corresponding to the material of the workpiece, difficult-to-cut properties, etc. may be selected and used.

In the above-described embodiment, the fiber reinforced composite material is exemplified as the work. However, the present invention is not limited to this, and can be applied to drilling of soft materials, hard materials, and difficult-to-cut materials. Moreover, although the case where a fine hole using a drill diameter of 0.3 mm is drilled has been described, it is natural to change the drill diameter (for example, 1 to 30 mm) according to the type of workpiece and the desired drill hole diameter. In that case, it is optional to change the shape of the tip without departing from the spirit of the present invention.
In the above-described embodiment, the general-purpose drill having the thinning and the chisel edge is exemplified. However, it is obvious that the general-purpose drill can be applied to the general-purpose drill having no thinning and chisel edge.

It explains the process for producing the twist drill of the present invention, wherein (a) shows a general-purpose drill, (1) is a plan view, (2) is a front view, and (b) is a chamfer on the general-purpose drill. The processed intermediate drill is shown, (1) is a plan view, (2) is a front view, (c) is a twist drill of the present invention, (1) is a plan view, and (2) is a plan view. It is a front view. It is what expanded the twist drill of this invention, Comprising: The (1) is a top view, The same (2) is a front view, The same (3) is the side view seen from the arrow X in said (1). It explains the details of the cutting edge shape (transverse plan view) of the twist drill of the present invention, (1) is a front view, (2) is an end view along the line AA in (1), (3) is an end view along the BB line, (4) is an end view along the CC line, and (5) is an end view along the DD line. It explains the details of the cutting edge shape (vertical side view) of the twist drill of the present invention, (1) is a plan view, (2) is an end view along line EE in (1), (3) is an end view along the FF line, and (4) is an end view along the GG line. It explains the details of the cutting edge shape (vertical side view) of a general-purpose drill, (1) is a plan view, (2) is an end view along line E'-E 'in (1), (3) is an end view taken along line F′-F ′, and (4) is an end view taken along line G′-G ′. The drilling example using the twist drill of this invention is demonstrated, The (1) is sectional drawing in process, (2) is a notch perspective view which shows the drill hole surface of the drilled workpiece | work. (1) is a plan view, (2) is a front view, and (3) is a side view. Another example of scooping is shown, in which (1) is a plan view, (2) is a front view, and (3) is a side view. It is each front view which illustrated the case where a scoop part changes corresponding to a twist lead angle in the twist drill of the present invention. It explains the cutting edge shape (transverse plan view) of the twist drill of the present invention having a lead angle of 20 degrees, (1) is a front view, and (2) is an end surface along the line AA in (1). The figure (3) is an end view along the BB line, (4) is an end view along the CC line, and (5) is an end view along the DD line. It explains the cutting edge shape (transverse plan view) of the twist drill of the present invention having a lead angle of 40 degrees, (1) is a front view, and (2) is an end surface along the line AA in (1). The figure (3) is an end view along the BB line, (4) is an end view along the CC line, and (5) is an end view along the DD line.

Explanation of symbols

1: Drill body 2: Torsional lead groove 3: Land part 4: Cutting edge 4a: Gradually decreasing concave curve 4b: Gradually increasing concave curve 5: Flank 5a: Outer shoulder 6: Thinning 7: Chisel edge 10: General-purpose drill 15: Intermediate drill R: curved surfaces 20, 20a, 20b: drill (the drill of the present invention)
21: scooping part 22: R blade part

Claims (5)

Twist with a pair of cutting blades and flank formed by a tip angle at the tip portion provided with a land portion formed with a twist lead groove for discharging chips on the outer peripheral portion of the drill body rotated about the axis In the drill,
The outer peripheral shoulder portion of the flank is a curved surface with a rounded chamfer, a scooping portion is provided in the cutting blade and the lead groove in the vicinity of the shoulder portion, and a concave curved shape in which the ridge line of the cutting blade is directed from the tip portion to the outer peripheral end, and A twist drill characterized in that it has a curved shape, and the cutting blade as a whole has a sharp cutting edge shape consisting of an S-curve when viewed from the side. The outer periphery of the drill body that rotates about the axis is provided with a land part that has a twisted lead groove for discharging chips, and a pair of cutting edges, flank, thinning, and chisel edge formed by the tip angle are provided at the tip part. In the twist drill that is formed,
The outer peripheral shoulder portion of the flank is a curved surface that is chamfered, a scooping portion is provided in the cutting blade and the lead groove in the vicinity of the shoulder portion, and a concave curved shape with the ridge line of the cutting blade from the chisel edge toward the outer peripheral end and subsequent curvature A twist drill characterized in that the cutting blade as a whole has a sharp cutting edge shape composed of an S-curve when viewed from the side.   The gradually decreasing curve portion from the tip of the concave curved cutting edge ridge line or chisel edge to the bottom of the recess acts as an up-cut with a relatively small cutting pressure on the workpiece to be drilled, and the gradually increasing curve portion from the bottom of the recess to the outer peripheral edge is The cutting urging force acting on the workpiece acts as a large downcut, and the curved ridge formed on the outer peripheral shoulder continuous with the gradually increasing curved portion acts as a sharp curved blade portion. 2. The twist drill according to 2.   4. The twist drill according to claim 3, wherein the workpiece is a composite material of a metal material and a fiber reinforced resin material.   The curved surface of the outer peripheral shoulder is formed by chamfering a general-purpose twist drill, and then the edge shape of the S-curve in side view is formed by scooping. Item 3. A twist drill according to item 1 or 2.

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