JP2006231430A - Centering drill and machining method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centering drill machining a center hole to enhance biting stability of a drill to be used for drilling and enhanced in rigidity of a drill main body. <P>SOLUTION: In this centering drill 1, the biting stability of the drill 100 for drilling can be enhanced since a tip end angle θ1 of a first cutting edge 5a provided in an inner peripheral part of a cutting edge 5 is set to be in the range of 145° to 155°. In the centering drill 1, the rigidity of the drill main body 2 is enhanced since a groove length L of a chip discharge groove 3 is set to be in the range of 0.5 to 1.5 times of a drill diameter D, and thereby machining accuracy and tool service life in chamfering become extremely excellent. Since a diameter D1 of the first cutting edge 5a is set to be in the range of 45% to 70% of the drill diameter D, the diameter of the center hole is made larger to further enhance the biting stability of the drill 100. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a centering drill used for center hole machining and chamfering and a machining method thereof.

Usually, in drilling with HSS (high speed tool steel) drill and deep hole machining with L / D (working hole depth / working hole diameter) exceeding 11, in order to improve the hole position accuracy and hole bending of the machined hole, There is a case where center hole processing called centering processing, countersink processing or leading processing is performed before drilling. When drilling with an L / D of 11 or less with a carbide drill, the problems of hole position accuracy and hole bending are less likely to occur, but the biting surface is processed like drilling at the center of the work material in turning. When there is a residue, when drilling into a cast product with a flatness of the biting surface or when drilling into an inclined surface, the above-mentioned center hole processing is performed regardless of the drill material and processing hole depth. Done.

Generally, in the above-described center hole machining, a drill called a centering drill or a leading drill with a relatively short chip discharge groove length is used, and the tip angle of this type of drill is generally It is set in the range of 120 ° to 140 °. Moreover, the same kind as the centering drill of this invention which can perform a center hole process and the chamfering with respect to the drilled hole is also conventionally known.

A conventional centering drill capable of processing a center hole and chamfering will be described below. The centering drill illustrated in FIG. 6 is intended to prevent swinging, and an n-sided pyramid (n>) is provided at the tip of the shaft-shaped tool body (11) rotated about the axis (O). 2) A shaped cutting edge (12) is formed (see, for example, Patent Document 1).

In the centering drill shown in FIG. 7, the tip angle of the cutting edge is set to a two-stage angle of around 120 ° and around 90 ° to enable center hole machining and chamfering (see, for example, Patent Document 2).

The centering drill shown in FIG. 8 has a tip angle set in the range of 60 ° to 120 ° and a chamfered thinning surface (8) having a substantially triangular shape at the center of the tip (for example, Patent Document 3). reference).

The centering drill shown in FIG. 9 has a drill body (1) provided with a first cutting edge (5a) having a tip angle of 120 ° to 140 °, and a tip angle of 60 ° to 120 ° continuous with the first cutting blade (5a). A second cutting edge (5b) is provided (for example, see Patent Document 4).

JP 2003-326410 A Japanese Utility Model Publication No. 62-174809 Japanese Utility Model Publication No. 2-135111 Japanese Utility Model Publication No. 5-63718

However, the conical angle of the center hole having a concave conical taper shape obtained by the centering drill disclosed in Patent Documents 1 to 3 is a general tip angle of a drill for drilling (the tip angle of a cemented carbide drill is 140). In addition, since the difference between the cone angle and the tip angle is large, the drilling drilling starts to bite from the outer peripheral edge of the cutting blade, so that the contact is likely to occur. Abnormal damage tends to occur at the outer peripheral edge of the blade. Moreover, since the cutting distance and the cutting time from the start of biting of the drill until the entire cutting edge bites, that is, the unstable cutting state is long, cutting performance and tool life may be deteriorated. Further, in the above unstable cutting state, the width of the chip (the width in the direction along the cutting edge) is small, so that there is a problem that the chip is easily stretched and sometimes entangled with the drill body.

Furthermore, since the centering drill disclosed in Patent Document 1 does not have a chisel edge formed at the tip shaft center portion and the tip angle of the cutting edge is small, the strength of the tip shaft center portion is reduced, resulting in a satisfactory tool life. There was a possibility that it could not be obtained.

In the centering drills disclosed in Patent Document 2 and Patent Document 4, the diameter of the inner peripheral cutting edge having a large tip angle is smaller than the drill diameter. Due to the long cutting state, cutting performance and tool life may be deteriorated.

In the centering drills disclosed in Patent Literature 3 and Patent Literature 4, the length of the chip discharge groove is longer than the diameter of the drill, and the rigidity of the drill is reduced. Therefore, the cutting performance and tool life due to the unstable cutting state described above. The drill body is likely to bend in the chamfering process in which the cutting resistance in the direction perpendicular to the axis increases. For this reason, there is a possibility that the accuracy of the chamfered surface is deteriorated due to tool chatter and chipping or chipping of the cutting edge occurs.

The present invention has been made in view of the above problems, and provides a centering drill that improves the bite stability of a drill used for drilling, and has improved the rigidity of the drill body during chamfering, and the centering drill. It aims at providing the processing method using this.

In order to solve the above-described problems and achieve such an object, the centering drill of the present invention has an outer peripheral surface of a drill body rotated about an axial center from a tip flank of the tip of the drill body. A pair of chip discharge grooves extending toward the rear end side are formed, and a pair of cutting edges are formed on the intersecting ridge line portion between the wall surface facing the rotation direction of the chip discharge grooves and the tip flank, and machining a center hole In the centering drill, the cutting blade is formed on the inner peripheral portion thereof, and the first cutting blade whose tip angle (θ1) is set in the range of 145 ° to 155 ° is continuous with the first cutting blade. And a second cutting edge whose tip angle (θ2) is set in the range of 60 ° to 120 °, and the groove length (L) of the chip discharge groove is a drill diameter ( D) must be set within the range of 0.5 to 1.5 times A centering drill which is characterized.

In the centering drill, the diameter (D1) of the first cutting edge is set in a range of 45% to 70% of the drill diameter (D), and the tip core thickness portion of the drill body is thinned, A thinning blade extending linearly or curvedly from the axial center or from both ends of the chisel edge is formed at the intersection ridge line portion of the thinning surface facing the rotation direction and the tip flank surface by this thinning. It is preferable that

In the centering drill provided with the above-mentioned thinning, the valley line intersecting the wall surface facing the front side and the wall surface facing the rear side in the rotation direction of the chip discharge groove extends from the axial center to the outer peripheral side as it goes from the front end to the rear end side. A thinning surface that is inclined at an inclination angle (α1) with respect to the axial center so as to be gradually separated from each other, and that intersects with the tip clearance surface and faces the rotation direction, and a tip sharpening surface that extends to the outer peripheral side connected to the thinning surface Is inclined with an inclination angle (α2) with respect to the axial center so that the valley line intersects the axial center and gradually separates toward the outer peripheral side toward the rear end side, and further, the inclination angle (α1) Is preferably set smaller than the inclination angle (α2), the inclination angle (α1) is set in a range of 20 ° to 45 °, and the inclination angle (α2) is set in a range of 40 ° to 60 °. Setting And more preferably it is.

Further, the included angle (β1) formed by the front wall surface and the rear wall surface in the rotation direction of the chip discharge groove is connected to the thinning blade and faces the rotation direction, and extends to the outer peripheral side connected to the thinning surface. The included angle (β2) is preferably set smaller than the included angle (β2) formed with the tip sharpened surface, and the included angle (β1) is set in the range of 80 ° to 120 °, and the included angle (β2) is set to 90 ° to 140. More preferably, it is set in the range of °.

Further, the machining method of the present invention is formed by the process of machining the center hole using only the first cutting edge, the process of drilling using the drill for drilling after this process, and the above drill for drilling. And a chamfering process with the second cutting edge of the centering drill at the peripheral edge of the processed hole.

In the said processing method, it is preferable that the diameter (Da) of a center hole exists in the range of 60%-95% of the drill diameter (Db) of the said drill for drilling.

According to the centering drill of the present invention, the tip angle (θ1) of the first cutting edge formed on the inner peripheral portion of the cutting edge is set in a range of 145 ° to 155 ° larger than that of the conventional centering drill. Since the conical angle of the center hole having a conical tapered shape formed by the first cutting edge is substantially equal to the tip angle (θ1), the difference from the tip angle of the drill for drilling is very small. The cutting distance and the cutting time from the start of biting until the entire cutting edge bites can be shortened. Therefore, since the stability at the time of biting of the drill is increased, the hole position accuracy and hole bending of the processed hole and the tool life of the drill can be improved. Furthermore, since the chip | tip with the narrow width | variety (width | variety along the direction of a cutting edge) produced | generated in the unstable cutting state until the whole cutting edge bites is reduced as much as possible, it can prevent the entanglement of the chip to a drill main body. . When the conical angle of the center hole becomes larger than the tip angle of the drill for drilling, the drill bites from the tip axial center, so that the centripetality is further increased, and the hole position accuracy, the hole bending, and the tool life of the drill are improved. The improvement effect becomes extremely high. When the tip angle (θ1) of the first cutting edge is less than 145 ° or exceeds 155 °, the cutting distance and the cutting time in the unstable cutting state from the start of biting of the drill until the whole cutting blade bites are long. There is a risk of chipping or chipping on the cutting edge of the drill, and when it exceeds 155 °, the thrust of the centering drill becomes high and the cutting performance may be deteriorated. Furthermore, since the groove length (L) of the chip discharge groove is limited to a range of 0.5 to 1.5 times the drill diameter (D) and the rigidity of the drill body is increased, the cutting resistance in the direction perpendicular to the axis is large. In the chamfering process with the second cutting edge, the deflection of the drill body is greatly reduced, and the machining accuracy and tool life are extremely good. If the groove length (L) of the chip discharge groove is less than 0.5 times the drill diameter (D), the chips during center hole processing may not be discharged smoothly. As a result, the rigidity of the drill body is lowered, and the effect of preventing the deflection of the drill body in the chamfering process cannot be obtained.

When the diameter (D1) of the first cutting edge is set in the range of 45 to 70% of the drill diameter (D), the diameter of the mouth that is the maximum diameter of the center hole is larger than that of the conventional centering drill. Therefore, the cutting distance and the cutting time from the start of biting of the drill for drilling until the entire cutting edge bites are further reduced, and the biting stability of the drill becomes extremely high. When the diameter (D1) of the first cutting edge is less than 45% of the drill diameter (D), there is a possibility that the effect of improving the biting stability of the drill may not be obtained. Besides, there is a possibility that the thrust at the time of processing the center hole of the centering drill becomes large, and since the length of the second cutting edge is shortened, the size or shape of the chamfer that can be processed at one time is restricted.

By thinning the tip core portion of the drill body, a thinning blade extending linearly from the axial center and continuing to the first cutting blade is formed at the intersecting ridge line portion between the thinning surface facing the rotation direction and the tip flank surface. This improves the discharge of chips generated from the thinning blade without lowering the rigidity of the drill body, and reduces or eliminates the chisel edge that is inferior in sharpness to prevent biting around and prevent centripetality. Greatly enhanced.

In the centering drill provided with the above-mentioned thinning, the valley line intersecting the wall surface facing the front side and the wall surface facing the rear side in the rotation direction of the chip discharge groove extends from the axial center to the outer peripheral side as it goes from the front end to the rear end side. A thinning surface that is inclined at an inclination angle (α1) with respect to the axial center so as to be gradually separated from each other, and that intersects with the tip clearance surface and faces the rotation direction, and a tip sharpening surface that extends to the outer peripheral side connected to the thinning surface Is inclined with an inclination angle (α2) with respect to the axial center so that the valley line intersects the axial center and gradually separates toward the outer peripheral side toward the rear end side, and further, the inclination angle (α1) Is set smaller than the inclination angle (α2), the rigidity of the drill body increases as it goes to the rear end side of the chip discharge groove, and thinning near the tip axis is cut. Stiffness of the tip axis near since it is inclined further toward the outer circumferential side of the discharge groove is improved. If the inclination angle (α1) in the chip discharge groove is less than 20 °, the effect of improving the rigidity of the drill body may not be obtained, and if it exceeds 45 °, the chip discharge property may be deteriorated. The angle (α1) is preferably set in the range of 20 ° to 45 °. On the other hand, if the inclination angle (α2) in thinning is less than 40 °, the effect of improving the rigidity in the vicinity of the tip axis of the drill body may not be obtained. The inclination angle (α2) is preferably set in the range of 40 ° to 60 °.

In the centering drill provided with the above-mentioned thinning, a thinning surface in which the included angle (β1) formed between the wall surface on the front side and the rear side wall in the rotation direction of the chip discharge groove is connected to the thinning blade and faces the rotation direction, and the thinning surface Since it is set to be smaller than the included angle (β2) formed with the tip sharpening surface that extends to the outer peripheral side, it is generated from the thinning blade while preventing a reduction in the rigidity of the drill body due to the chip discharge groove. Chip discharge is improved. If the included angle (β1) in the chip discharge groove is less than 80 °, the chip discharge property may be deteriorated, and if it exceeds 120 °, the effect of improving the rigidity of the drill body may not be obtained. The included angle (β1) is preferably set in the range of 80 ° to 120 °. On the other hand, if the included angle (β2) in the thinning is less than 90 °, there is a concern that the discharge of chips generated from the thinning blade may be deteriorated, and if it exceeds 140 °, the rigidity of the portion subjected to the thinning is lowered. For this reason, the included angle (β2) is preferably set in the range of 90 ° to 140 °.

Further, according to the above-described machining method using the centering drill, in the center hole drilling process prior to the drilling process, only the concave conical tapered center hole whose cone angle is in the range of 145 ° to 155 ° is machined. Therefore, the unstable state of drill biting during drilling is further shortened, so the stability of the above drill biting increases, so tool life is greatly improved and the entire cutting edge bites. During this period, the generation amount of chips with a narrow width (width in the direction along the cutting edge) is reduced, so that the entanglement of the chips of the drill can be prevented. Furthermore, the chamfering process in the post-drilling process is a single chamfering process with the second cutting edge, so the cutting resistance is greatly reduced compared to machining in the same process of the center hole and chamfering, and the chamfer finish surface accuracy and The surface roughness is extremely good. Here, when the tip angle (θ1) of the first cutting edge is set to be larger than the tip angle of the drill for drilling, biting starts from the tip axial center portion of the drill and the whole cutting blade bites immediately. Since it is attached, drilling with high centripetality and very little swing is possible. When the diameter (Da) of the center hole is less than 60% of the drill diameter (Db) of the drill for drilling, it becomes difficult to obtain the effect of improving the stability of the drill. There is a possibility that a part of the center hole may remain at the end of the processed hole.

Next, an embodiment of a centering drill to which the present invention is applied will be described with reference to the drawings. 1 and 2 are a front view and a front view side view of the centering drill, respectively. FIG. 3 is an enlarged perspective view of the tip of the centering drill shown in FIG. 4 and 5 are diagrams for explaining the machining state of the centering drill.

As shown in FIG. 1, the centering drill (1) is formed on the outer peripheral surface of a drill body (2) having a substantially round bar shape rotated about an axis (CL) at the tip of the drill body (2). A pair of chip discharge grooves (3) extending from the tip end flank (4) toward the rear end side are formed symmetrically with respect to the axis (CL), and these chip discharge grooves (3) and the tip flank A pair of cutting edges (5) are formed at the intersection ridge line with (4). These cutting edges (5) are provided in contrast with the axis (CL) as a reference, and have an action of maintaining a balance of cutting resistance received by the drill body (2) when machining the center hole. At least the cutting edge (5) is made of a hard material such as cemented carbide, cermet, ceramic, or diamond and / or cubic boron nitride sintered body, and enables machining with a high cutting speed. The centering drill (1) as a whole is preferably made of the hard material, but a cutting blade (5) made of the hard material may be brazed to a drill body (2) made of steel or the like.

As shown in FIG. 1, the cutting edge (5) has a first cutting edge (5a) whose tip angle (θ1) is set in the range of 145 ° to 155 ° on the inner periphery thereof, and the first cutting edge. It is comprised from the 2nd cutting blade (5b) extended to the outer peripheral edge part continuously to (5a), and the front-end | tip angle ((theta) 2) set to the range of 60 degrees-120 degrees. Furthermore, the first cutting edge (5a) is formed such that its diameter (D1) is in the range of 45% to 75% of the drill diameter (D), which is the outermost diameter of the cutting edge (5). The first cutting edge (5a) is for machining a concave conical tapered center hole that serves as a guide for the drilling drill (100), and the second cutting edge (5b) is opened by the drill for drilling. The chamfering is processed at the peripheral edge portion of the processed hole. As a center hole machining method using the centering drill (1), as a preceding process prior to drilling, the center hole machining by the first cutting edge (5a) and the chamfering machining by the second cutting edge (5b) are performed. A method performed in one step, a center hole machining (first step) using only the first cutting edge (5a), which is a pre-process of drilling, and a first process to the peripheral edge of the machined hole, which is a post-process of the above-described drilling. There is a method in which chamfering processing (second step) using only two cutting edges (5b) is divided and performed in two steps. In the chamfering process by the second cutting edge (5b), it is not limited to the peripheral edge part of the hole of the processing hole, but the end milling process is performed along a linear and / or curved ridge line part where adjacent surfaces intersect each other. Thus, chamfering may be performed.

The centering drill (1) has a tip angle (θ1) of the first cutting edge (5a) larger than the tip angle of the conventional centering drill. The difference between the tip angle of the drill (100) becomes small, and the cutting distance and the cutting time (hereinafter referred to as “biting failure”) from when the cutting edge of the drill (100) starts to bite until the whole cutting edge bites. "Stable state") can be shortened. Therefore, the stability of the drill (100) when it bites increases, so that the tool life can be prevented from being deteriorated, and the width of the chip (width in the direction along the cutting edge) is reduced until the entire cutting edge bites. Since the generation amount is reduced, the entanglement of the chips of the drill (100) can be prevented. In the method of dividing the center hole machining method into the above-described two steps, since only the center hole having a conical tapered shape with a large cone angle is formed in the previous step, the biting unstable state of the drilling drill (100) is formed. Is very preferable because it will be further shortened. When the tip angle (θ1) of the first cutting edge (5a) is set larger than the tip angle of the drilling drill (100), the biting starts from the tip axial center of the drill (100) and is quick. Since the entire cutting edge bites into the hole, drilling with high centripetality and very little swing is possible. When the tip angle (θ1) of the first cutting edge (5a) is less than 145 ° or exceeds 155 °, the difference between the cone angle of the center hole and the tip angle of the drilling drill (100) becomes large, and the drill (100 ) Cannot be shortened, and chipping or chipping may occur in the cutting edge of the drill (100), or entanglement of chips may occur in the drill (100). When the tip angle (θ1) of the first cutting edge (5a) exceeds 155 °, the thrust of the centering drill (1) becomes high, which may cause tool chatter and abnormal damage to the cutting edge (5). Furthermore, in this centering drill (1), since the diameter (D1) of the first cutting edge (5a) is set in the range of 45 to 70% of the drill diameter (D), the cone angle is 145 ° to 155 °. Since the diameter of the center hole (Da) of the center hole having a conical tapered shape in the range of can be increased, the biting instability state of the drilling drill (100) is further shortened. The stability when the drill (100) bites is extremely high. When the diameter (D1) of the first cutting edge (5a) is less than 45% of the drill diameter (D), the effect of improving the biting stability of the drill (100) may not be obtained. If the ratio exceeds 50%, the thrust of the centering drill (1) may be increased, and the length of the second cutting edge (5b) will be shortened, limiting the size or shape of the chamfer that can be processed at one time. End up.

Thinning (6) is applied to the tip core thickness portion of the drill body (2), so that the axial center is located at the intersection ridge line portion of the thinning surface (6b) facing the rotation direction (K) and the tip flank (4). A pair of thinning blades (6a) are formed symmetrically with respect to (CL). As shown in FIG. 2, each thinning blade (6 a) intersects the shaft center (CL) and extends linearly to the outer peripheral side and intersects the first cutting blade (5 a) at an obtuse angle when viewed from the front end in the axial direction. Then they are connected. Note that the thinning blade (6a) does not necessarily need to intersect the axis (CL), and a thinning blade (6a) that is connected to both ends of the chisel edge may be formed by leaving a slight chisel edge at the tip axial center. At this time, the length of the chisel edge is preferably set in the range of 0.1 mm to 1.0 mm, more preferably in the range of 0.2 mm to 0.5 mm, from the viewpoint of ease of manufacturing and reduction of thrust during processing. . Moreover, you may form a cross | intersection part in a curve shape so that the thinning blade (6a) and the 1st cutting blade (5a) may be connected smoothly. Moreover, you may form the whole thinning blade (6a) in the shape of a curve. By applying the thinning (6), it is possible to improve the discharge of chips generated from the thinning blade (6a) without reducing the rigidity of the drill body (2), and to reduce or eliminate the chisel edge that is inferior in sharpness. As a result, biting-out swinging is suppressed and centripetality is greatly enhanced.

As can be seen from FIG. 1, the chip discharge groove (3) is formed so that the groove length (L) is in the range of 0.5 to 1.5 times the drill diameter (D). The rigidity of the main body (2) is increased. Therefore, in the chamfering by the second cutting edge (5b) in which the cutting force in the direction perpendicular to the axis (CL) increases, the deflection of the drill body (2) is greatly reduced, and the chamfering accuracy and the centering drill (1) The tool life is extremely good. If the groove length (L) of the chip discharge groove (3) is less than 0.5 times the drill diameter (D), the center hole and the chips during the chamfering process may not be discharged smoothly. In the case of exceeding, the rigidity of the drill body (2) is lowered, the effect of preventing the deflection of the drill body (2) at the center hole and chamfering processing is not obtained, and tool chattering occurs or chipping of the cutting edge (5) There is a risk of damage.

In each chip discharge groove (3), as the valley line intersecting the wall surface (3a) facing the front side in the rotational direction (K) and the wall surface (3b) facing the rear side goes from the front end to the rear end side. It inclines with respect to the said axial center (CL) so that it may gradually distance from an axial center (CL) to an outer peripheral side, The inclination angle ((alpha) 1) is set to the range of 20 degrees-45 degrees. The inclination angle (α1) is not limited to a certain value, and may change midway as long as it is within the above range. The wall surfaces (3a, 3b) constituting the chip discharge groove (3) are not limited to flat surfaces but may be curved surfaces. On the other hand, in the thinning (6), the valley line intersecting the thinning surface (6b) and the tip sharpening surface (6c) adjacent to the thinning surface (6b) and extending to the outer peripheral side goes from the tip to the rear end. Accordingly, it is inclined with respect to the axis (CL) so as to gradually move away from the axis (CL) to the outer peripheral side, and the inclination angle (α2) is set in the range of 40 ° to 60 °. The inclination angle (α2) is not limited to a fixed value, and may change midway as long as it is within the above range. Further, the inclination angle (α1) of the valley line of the chip discharge groove (3) is set to be smaller than the inclination angle (α2) of the valley line of the thinning (6), and the rigidity of the drill body (2) is set. Since it is gradually raised toward the rear end side of the chip discharge groove (3), and the thinning (6) is inclined further toward the outer peripheral side than the chip discharge groove (3), the vicinity of the tip axial center The rigidity is improved. The reason why the inclination angle (α1) of the valley line of the chip discharge groove (3) is limited to the range of 20 ° to 45 ° is that the rigidity of the drill body (2) is improved when the inclination angle (α1) is less than 20 °. This is because the effect may not be obtained, and if it exceeds 45 °, the chip dischargeability may deteriorate. On the other hand, the reason why the inclination angle (α2) of the valley line of the thinning (6) is limited to the range of 40 ° to 60 ° is that when the inclination angle (α2) is less than 40 °, the tip axis of the drill body (2) This is because the effect of improving the rigidity in the vicinity may not be obtained, and if it exceeds 60 °, the chip dischargeability of the thinning blade (6a) may be deteriorated.

As understood from FIG. 3, the included angle (β1) formed by the wall surface (3a) facing the rotation direction (K) front side and the wall surface (3b) facing the rear side of the chip discharge groove (3) is 80 ° to The range is set to 120 °. On the other hand, the included angle (β2) formed by the thinning surface (6b) constituting the thinning (6) and the tip sharpening surface (6c) is set in the range of 90 ° to 140 °, and further, the chip discharge groove (6) Since the included angle (β1) is set smaller than the included angle (β2) of the thinning (6), the drill body (2) is prevented from being lowered in rigidity due to the chip discharge groove (3), and the thinning blade ( The discharge property of the chips generated from 6a) is improved. The reason why the included angle (β1) in the chip discharge groove (3) is limited to the range of 80 ° to 120 ° is that if the included angle (β1) is less than 80 °, the chip discharge property may be deteriorated. If the angle exceeds 120 °, the effect of improving the rigidity of the drill body (2) may not be obtained. On the other hand, the reason for limiting the included angle (β2) in the range of 90 ° to 140 ° in the thinning (6) is that the chips generated from the thinning blade (6a) when the included angle (β2) is less than 90 °. This is because the discharge performance may be deteriorated, and if it exceeds 140 °, the rigidity in the vicinity of the tip axis of the drill body (2) subjected to the thinning (6) may be lowered.

As the center hole and chamfering processing method using the centering drill (1), as shown in FIGS. 4 (a) and (b), the centering drill (1) is used as a pre-process for drilling. As shown in FIGS. 5A to 5C in addition to the method of performing the center hole machining by the first cutting edge (5a) and the chamfering machining by the second cutting edge (5b) in the same process. In addition, as a pre-process of drilling (see FIG. 5B), processing of the center hole by only the first cutting edge (5a) of the centering drill (1) (first process, see FIG. 5A) As a post-process, there is a method in which the chamfering process (see the second process, FIG. 5C) of the peripheral edge of the processing hole by only the second cutting edge (5b) of the centering drill (1) is performed in a separate process. is there. When the center hole machining and the chamfering process are divided into two steps of the first step and the second step before and after the drilling as in this machining method, the cone angle is 145 ° in the center hole machining in the first step. Since only the concave conical taper-shaped center hole in the range of ˜155 ° is machined, the bite instability of the drill (100) in the drilling process is further shortened, so that the bite of the drill (100) is In addition to greatly improving tool life due to increased stability at the time, the amount of chips generated with a narrow width (width in the direction along the cutting edge) is reduced until the entire cutting edge bites. 100) of the chips can be prevented. Furthermore, the chamfering process in the second step is a single chamfering process using the second cutting edge (5b), so that the cutting resistance is greatly reduced compared to the machining in the same process of chamfering with the center hole, and the chamfering finish surface accuracy. And surface roughness becomes very good. The chamfering process is not limited to the peripheral edge of the hole of the machining hole, but may be performed like end milling along a linear and / or curved ridge line where adjacent surfaces intersect each other.

In both the method of performing the center hole and chamfering process in the same process as described above and the method of performing the process in a separate process, the diameter (Da) of the center hole is greater than the drill diameter (Db) of the drill for drilling (100). Is also formed to be small. When the diameter (Da) of the center hole is less than 60% of the drill diameter (Db) of the drill for drilling (100), it becomes difficult to obtain the effect of improving the stability of the drill (100), and exceeds 95%. Since there is a possibility that part of the center hole may remain at the end of the drilled hole, the center hole diameter (Da) is 60 to 95% of the drill diameter (Db) of the drill for drilling (100). It is preferable that it is the range of these.

Examples of center hole processing and chamfering processing by the centering drill (1) will be described below. The drill (100) used for drilling is a two-blade drill having a drill diameter (Db) of 8.5 mm and a tip angle of 140 °. The cutting conditions of the drill (100) were a cutting speed of 50 m / min and a feed of 0.1 mm / rev. The centering drill (hereinafter referred to as the present invention product) has a drill diameter (D) of 12.0 mm, a tip angle (θ1) of the first cutting edge (5a) of 145 °, and a tip of the second cutting edge (5b). This is a two-blade centering drill having an angle (θ2) of 90 °, a diameter (D1) of the first cutting edge (5a) of 6.0 mm and 50% of the drill diameter (D). One of the comparative centering drills (hereinafter referred to as “comparative product 1”) is the same as the product of the present invention except that the tip angle (θ1) of the first cutting edge (5a) is 120 °. Another comparative centering drill (hereinafter referred to as comparative product 2) has a drill diameter (D) of 12.0 mm, a tip angle (θ1) of the first cutting edge (5a) of 120 °, and a second cutting edge. A two-blade centering drill in which the tip angle (θ2) of the blade (5b) is 90 °, the diameter (D1) of the first cutting blade (5a) is 2.5 mm, and 20.8% of the drill diameter (D). It is. Still another centering drill for comparison (hereinafter referred to as comparative product 3) is a two-blade centering drill having a drill diameter (D) of 12.0 mm and a constant tip angle of 90 °.

In order to obtain a processed hole with C1.0 chamfered at the peripheral edge of the hole with a hole diameter of 8.5 mm, the center hole drilling and chamfering are performed in the same process using each centering drill. The cutting distance and the cutting time in the axial direction from when the drill for drilling (100) started to bite until the entire cutting edge bites were compared.

In comparative product 1, the cutting distance was 3.0 mm (cutting time: 1.0 second), and in comparative product 2, the cutting distance was 3.7 mm (cutting time: 1.2 seconds). In the product of the present invention, the tip angle (θ1) of the first cutting edge (5a) is larger than that of the comparative product 1 and the diameter (D1) of the first cutting blade (5a) is larger than that of the comparative product 2. Was 2.2 mm (cutting time 0.7 seconds), and the biting and unstable state of the drilling drill (100) was shortened. In the comparative product 3 having the smallest cutting edge angle, the cutting distance was 4.3 mm (cutting time: 1.4 seconds), and the biting unstable state of the drilling drill (100) was the longest. As shown in this result, in the centering drill (1), since the tip angle (θ1) and the diameter (D1) of the first cutting edge (5a) are set larger than those of the conventional centering drill, the drill for drilling (100) It is possible to shorten the unstable state of biting, and to improve the cutting performance and tool life of the drill (100) and the entanglement of chips.

It is a front view of this centering drill. FIG. 2 is a side view of the centering drill shown in FIG. It is an expansion perspective view of the front-end | tip part of the centering drill shown in FIG. It is a figure explaining a processing method, (a) is a figure which shows the state of the center hole and chamfering process by this centering drill, (b) is a figure which shows the state of drilling. It is a figure explaining a processing method, (a) is a figure which shows the state of the center hole processing by this centering drill, (b) is a figure which shows the state of drilling, (c) is a figure by this centering drill It is a figure which shows a chamfering process. It is a figure which shows the centering drill disclosed by patent document 1. FIG. It is a figure which shows the centering drill disclosed by patent document 2. FIG. It is a figure which shows the centering drill disclosed by patent document 3. FIG. It is a figure which shows the centering drill disclosed by patent document 4. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Centering drill 2 Drill main body 3 Chip discharge groove 4 Tip flank 5 Cutting blade 5a First cutting blade 5b Second cutting blade 6 Thinning 6a Thinning blade 6b Thinning surface 6c Tip sharpening surface 100 Drill used for drilling (for drilling Drill)
CL shaft center D drill diameter D1 first cutting edge diameter L flute length of the chip discharge groove θ1 first cutting edge angle θ2 second cutting edge angle α1 inclination angle α2 of the chip discharging groove valley with respect to the axial center Tilting angle β1 of the thinning line with respect to the axial center Tilting angle β2 of the chip discharge groove Dinning angle Da of the thinning Db Diameter of the center hole mouth Db Drill diameter of the drill for drilling

Claims (9)

A pair of chip discharge grooves extending from the tip flank at the front end of the drill body toward the rear end side are formed on the outer peripheral surface of the drill main body rotated about the axis, and facing the rotation direction of the chip discharge grooves. In the centering drill for processing the center hole, a pair of cutting blades are formed at the intersecting ridge line part of the wall surface and the tip flank,
The cutting edge has a first cutting edge formed on an inner peripheral portion thereof and having a tip angle (θ1) set in a range of 145 ° to 155 °, and extends to the outer peripheral end portion continuously to the first cutting blade. And the tip angle (θ2) is composed of a second cutting edge set in the range of 60 ° to 120 °, and the groove length (L) of the chip discharge groove is 0.5 to the drill diameter (D). A centering drill characterized by being set in a range of 1.5 times. The centering drill according to claim 1, wherein a diameter (D1) of the first cutting edge is set in a range of 45% to 70% of a drill diameter (D). Thinning is applied to the tip core thickness part of the drill body, and the crossing ridge line part of the thinning surface facing the rotation direction by the thinning and the tip flank surface is linear or curved from the axis or from both ends of the chisel edge. The centering drill according to claim 1, wherein a thinning blade extending to the first cutting blade and extending to the first cutting blade is formed. In the shaft center, the valley line intersecting the wall surface facing the front side and the wall surface facing the rear side in the rotational direction of the chip discharge groove is gradually separated from the shaft center to the outer peripheral side as it goes from the front end to the rear end side. The trough line of the thinning surface that is inclined with respect to the inclination angle (α1) and intersects the tip clearance surface and faces the rotation direction and the tip sharpening surface that extends to the outer peripheral side and extends to the thinning surface intersects the axis. In addition, as it goes to the rear end side, it is inclined at an inclination angle (α2) with respect to the axial center so as to be gradually separated toward the outer peripheral side, and further, the inclination angle (α1) is smaller than the inclination angle (α2). The centering drill according to claim 3, wherein the centering drill is set. The tip angle sharpening (β1) formed between the wall surface on the front side and the rear side wall in the rotation direction of the chip discharge groove is connected to the thinning blade and faces the rotation direction, and the tip sharpening extends to the outer peripheral side connected to the thinning surface. The centering drill according to claim 3 or 4, wherein the centering drill is set smaller than an included angle (β2) with the surface. The centering drill according to claim 4, wherein the inclination angle (α1) is set in a range of 20 ° to 45 ° and the inclination angle (α2) is set in a range of 40 ° to 60 °. 6. The centering drill according to claim 5, wherein the included angle (β1) is set in a range of 80 ° to 120 ° and the included angle (β2) is set in a range of 90 ° to 140 °. In the processing method using the centering drill in any one of Claims 1-7, the process of processing a center hole using only a 1st cutting blade, and the process of drilling using a drill for drilling after this process And a step of chamfering with a second cutting edge of the centering drill on the peripheral edge of the hole formed by the drill for drilling. 9. The processing method according to claim 8, wherein a diameter (Da) of the center hole is in a range of 60% to 95% of a drill diameter (Db) of the drill for drilling.

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