WO2012053090A1

WO2012053090A1 - Three-bladed drill

Info

Publication number: WO2012053090A1
Application number: PCT/JP2010/068611
Authority: WO
Inventors: 一豊伊藤; 一輝高井
Original assignee: オーエスジー株式会社
Priority date: 2010-10-21
Filing date: 2010-10-21
Publication date: 2012-04-26

Abstract

Spiral flutes (18) are configured in such a manner that, with a straight line (AB) connecting a lowest point (A) on the inner peripheral side and an endpoint (B) on the heel side on the outer periphery in the cross sectional shape of the spiral flutes (18) in cross section perpendicular to a shaft center (O) of a shaft section (14) as a reference line, a maximum recessed amount (W) which is the maximum value in the distance between the reference line (AB) and the cross sectional shape falls within the range of 3 to 6% of drill diameter (D). This enables cutting chips to be divided even in the processing of a material to be cut which has relatively high viscosity, and also enables highly-efficient processing by high feeding even relative to the material to be cut, the processing of which has been difficult so far. More specifically, a three-bladed drill (10) for implementing excellent processing by suitably dividing the cutting chips can be provided in the highly-efficient processing by such high feeding as a feeding amount per turn exceeds 5% of the drill diameter (D).

Description

3-flute drill

The present invention relates to a three-blade drill in which three twist grooves are provided around a drill axis and three main cutting edges are provided corresponding to each twist groove, and particularly, high-efficiency machining by high feed is performed. It relates to improvements to make it possible.

A three-flute drill, in which three torsion grooves are provided around the drill axis O, and the main cutting edges are formed along the respective torsion grooves at portions where the torsion grooves open at the tip of the drill, is used for drilling. It is known as one form of a rotary cutting tool. For example, this is the drill described in Patent Document 1. According to this technique, in a drill in which a thinning is provided in the vicinity of the drill axis at the tip of the drill and a thinning blade is provided so as to be smoothly connected to the main cutting edge, In addition, the negative angle part in the range of the radial rake angle φ as viewed from the drill tip side in the range of −20 ° ≦ φ <0 ° is provided within the range of 0.1 D or less with respect to the drill diameter D from the outer corner. And the portion of the main cutting edge closer to the drill axis than the negative angle portion has a concave arc shape that is smoothly dented to the opposite side of the drill rotation direction in bottom view. High-efficiency machining is possible by high feed such that the feed amount per rotation exceeds 5% of the drill diameter D.

International Publication No. 2010/038279

However, in the conventional technique, the chips are not sufficiently divided, and the chips are connected for a long time, so that the twisted grooves are clogged with chips, and processing is difficult, or the durability of the drill is affected. There was a fear. In particular, in the processing of relatively viscous work materials such as carbon steel materials such as S25C (JIS G 4051) and rolled steel materials such as SS400 (JIS G 3101), the feed rate per rotation is relative to the drill diameter D. This tendency is remarkable when high-efficiency machining with high feed exceeding 0.05 D (5% of D) is performed. For this reason, in high-efficiency machining with high feed rate where the feed amount per rotation exceeds 5% of the drill diameter D, the development of a 3-flute drill that realizes good machining by suitably cutting chips is required. It was done.

The present invention has been made against the background of the above circumstances, and the object of the present invention is to perform cutting in high-efficiency machining with high feed such that the feed amount per revolution exceeds 5% of the drill diameter D. An object of the present invention is to provide a three-blade drill that suitably separates scraps to achieve good machining.

In order to achieve such an object, the gist of the present invention is that three torsion grooves are provided around the drill axis O, and the torsion grooves are formed along the respective torsion grooves at portions where the torsion grooves open at the drill tip. A three-edged drill in which a main cutting edge is formed, wherein the torsional groove is the lowest on the inner peripheral side in the cross-sectional shape with respect to the cross-sectional shape of the torsional groove in a cross section perpendicular to the axis O of the drill shaft. Using the straight line AB connecting the point A and the heel side end point B on the outer periphery as a reference line, the maximum dent W, which is the maximum value of the distance between the reference line AB and the cross-sectional shape, is 3% to 3% of the drill diameter D. It is characterized by being configured to be in the range of 6%.

In this way, the torsional groove has an inner peripheral lowermost point A in the cross-sectional shape and a heel side end point B on the outer periphery with respect to the cross-sectional shape of the torsional groove in the cross section perpendicular to the axis O of the drill shaft. The maximum dent W, which is the maximum value of the distance between the reference line AB and the cross-sectional shape, is within the range of 3% to 6% of the drill diameter D. Therefore, even when machining relatively viscous work materials, it is possible to divide chips, and high-efficiency machining with high feed even for such work materials that were difficult to machine. Is possible. That is, it is possible to provide a three-blade drill that achieves good machining by suitably dividing chips in high-efficiency machining with high feed such that the feed amount per rotation exceeds 5% of the drill diameter D. it can.

Here, preferably, the core thickness D2 of the three-blade drill is in the range of 20% to 50% of the drill diameter D. If it does in this way, chips can be divided suitably at the time of processing, guaranteeing sufficient endurance.

Further, preferably, a thinning is provided in the vicinity of the drill axis O at the tip of the drill, and a thinning blade is provided so as to be smoothly connected to the main cutting edge. The part has a negative angle part with a rake angle φ in the range of −20 ° ≦ φ <0 ° as viewed from the bottom when viewed from the drill tip side, which is 0.1 D or less from the outer corner to the drill diameter D. The portion of the main cutting edge closer to the drill axis O than the negative angle portion of the main cutting edge has a concave arc shape that is smoothly recessed toward the opposite side of the drill rotation direction in the bottom view. It is what. In this way, an increase in cutting resistance and thrust resistance due to the negative angle portion, or a decrease in sharpness is suppressed to a necessary minimum, and high-efficiency machining with high feed as a whole becomes possible. Further, since the portion closer to the drill axis O than the negative angle portion has a concave arc shape that is smoothly recessed in the direction opposite to the drill rotation direction, the curling of the chips is promoted and the cutting becomes easy to cut. The waste discharging performance is improved, the cutting edge length is longer than that of the straight cutting edge, the cutting load is dispersed, and further high-efficiency machining by high feed can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematically the 3 blade drill which is one Example of this invention, and is the front view seen from the direction perpendicular | vertical to the axial center. It is a front view which expands and shows the front-end | tip part in the 3-blade drill shown in FIG. 1 from the direction shown by arrow II, ie, the direction perpendicular | vertical to an axial center. It is a bottom view which expands and shows the front-end | tip part in the 3-blade drill shown in FIG. 1 from the direction shown by arrow III, ie, a front end side. FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 1 and showing a cross section perpendicular to the axis of the drill shaft. It is a figure which shows a cross section perpendicular | vertical to the axial center of the drill axial part in the conventional 3 blade drill for the comparison with the 3 blade drill of a present Example. It is a table | surface which shows the form and test result of each test article regarding the test which the present inventors etc. performed in order to verify the effect of the 3 blade drill of this invention. It is the photograph of the long connected chips discharged | emitted in the process of the test article which the result etc. were inferior in the test which the present inventors conducted in order to verify the effect of the 3 blade drill of this invention. In the test which the present inventors conducted in order to verify the effect of the 3 blade drill of the present invention, it is a photograph of the suitably divided chip discharged in the processing of the test product which had a good result. It is a figure which shows roughly the modification of the 3 blade drill of this invention, and is the front view seen from the direction perpendicular | vertical to the axial center.

In the three-blade drill of the present invention, high feed processing with a feed amount per revolution exceeding 5% of the drill diameter D is possible for steel, and feed per revolution for aluminum alloy. High feed processing with an amount exceeding 30% of the drill diameter D is possible. That is, it is particularly effective when the feed amount per rotation is 5% of the drill diameter D, and even when used at a high feed rate exceeding 10%, but the feed amount per rotation is 5% of the drill diameter D. It is also possible to use it for a normal drilling process that is less than 1. In addition, by improving the chip breaking property, it is effective for deep hole machining of about 10D with respect to the drill diameter D. In addition, drilling of various work materials such as drilling of cast iron and general steel, which require relatively high rigidity, and drilling of aluminum alloy, etc., which has relatively poor chip discharge performance. The three-blade drill of the invention is preferably used.

The twist groove is preferably twisted in the same direction as the drill rotation direction when viewed from the shank side, and is provided to discharge chips to the shank side, and the twist angle is in the range of about 10 ° to 50 °, for example. Is set as appropriate. As the material of the three-blade drill, various tool materials such as cemented carbide and high-speed tool steel can be used, and a hard coating such as TiAlN, TiCN, TiN, and diamond is coated as necessary. It is also possible to provide a fluid supply hole (oil hole) that passes through in the axial direction and opens to the flank at the tip.

In the torsion groove, when the maximum dent amount W, which is the maximum value in the distance between the reference line AB and the cross-sectional shape, is less than 3%, chips are clogged in the torsion groove, the load increases, and machining is difficult. The trouble that becomes. On the other hand, in the configuration in which the maximum dent W is larger than 6%, there is a risk of breakage due to a problem in durability due to insufficient rigidity of the tool. By configuring the maximum dent W to be in the range of 3% to 6% of the drill diameter D, chips can be cut even when machining relatively viscous work materials. Therefore, it is possible to perform high-efficiency machining by high feed even for such a work material that has been difficult to achieve.

In the configuration in which the core thickness D2 of the three-blade drill is less than 20% of the drill diameter D, that is, less than 0.2D, there is a problem in durability due to insufficient rigidity of the tool, which may cause breakage, for example. On the other hand, in the configuration in which the core thickness D2 is larger than 50% of the drill diameter D, that is, the configuration larger than 0.5D, the maximum dent amount W related to the torsion groove is 3% to 6% of the drill diameter D which is the preferred range. It is difficult to make it within the range, and as a result, the twisted groove is clogged with chips, increasing the load and causing a problem that machining becomes difficult. Accordingly, the core thickness D2 of the three-blade drill is preferably in the range of 20% to 50% of the drill diameter D, and more preferably in the range of 25% to 45% of the drill diameter D. It is configured to be inside. The core thickness D2 may be constant over the entire length of the drill body provided with the twist groove, but it is also possible to provide a back taper that decreases from the drill tip toward the shank side. .

With respect to the outer peripheral portion of the main cutting edge, when the radial rake angle φ as viewed from the bottom of the drill is less than −20 °, the cutting resistance and thrust resistance increase and the sharpness deteriorates. On the other hand, in the configuration in which the radial rake angle φ is 0 ° or more, chipping and chipping are likely to occur near the outer peripheral corner. Therefore, it is desirable that the negative angle portion has a rake angle φ in the radial direction as viewed from the drill tip side in a range of −20 ° ≦ φ <0 °. Further, if the negative angle range L exceeds 0.1D, the cutting resistance and thrust resistance increase and the sharpness deteriorates, so it is desirable that L ≦ 0.1D. The radial rake angle φ is, for example, substantially constant in the negative angle range L, and the main cutting edge may be substantially linear in a bottom view, but the diameter increases toward the inner side (tip side) from the outer peripheral corner. The main cutting edge may have a shape curved in a convex shape toward the drill rotation direction so that the direction rake angle φ gradually increases (increases gradually from a negative angle to 0 °). The negative angle range L is a linear distance in the direction from the outer corner to the drill axis O.

The main cutting edge preferably has a concave arc shape that is smoothly recessed toward the opposite side of the drill rotation direction in the bottom view at the portion closer to the drill axis O than the negative angle portion. The shape radius is preferably in the range of about 0.19D to 1.1D, for example. Note that the arc does not necessarily have a constant radius, and may have a shape corresponding to a curve whose curvature changes continuously. The concave arcuate portion has a positive radial rake angle φ at the outer peripheral portion connected to the negative angle portion, but gradually decreases toward the drill axis O (from positive angle to 0 °). For example, the inner peripheral side portion connected to the thinning blade is negative.

Regarding the drill shaft and the like, the ratio (land / groove ratio) θ ₁ : θ ₂ of the land width angle θ ₁ around the drill axis O and the groove width angle θ ₂ of the twisted groove is preferably 35: The range is from 65 to 65:35. When the ratio of the groove width angle θ ₂ is larger than the land / groove ratio θ ₁ : θ ₂ of 35:65, the land width angle θ ₁ is decreased and the durability and cutting edge strength of the tool are impaired. On the other hand, when the ratio of the groove width angle θ ₂ is smaller than the land / groove ratio θ ₁ : θ ₂ of 65:35, the chip discharging performance may be impaired. The twisted grooves are provided, for example, at equiangular intervals around the drill axis O, but can also be provided at unequal intervals. Even in this case, all land / groove ratios θ ₁ : θ ₂ are 35: 65˜ It is desirable to configure so that it falls within the range of 65:35.

The axial rake angle of the thinning blade is preferably in the range of −5 ° to 0 ° at the portion closest to the drill axis O, but 0 ° to + 15 ° at the connection with the main cutting edge. It is configured to increase smoothly and continuously as it goes from the drill axis O side to the connecting portion side so as to be within the range of. When the rake angle in the axial direction of the portion closest to the drill axis O of the thinning blade is smaller than −5 ° (large toward the negative side), cutting resistance and thrust resistance are increased. On the other hand, if the axial rake angle is larger than 0 °, that is, a positive angle, the blade edge strength may be impaired. Therefore, the range of −5 ° to 0 ° is desirable. When the angle is less than 0 °, that is, a negative angle, the cutting resistance increases at the connecting portion with the main cutting edge. On the other hand, when the angle exceeds + 15 °, the strength of the cutting edge may be impaired, so the range of 0 ° to + 15 °. The inside is desirable. The rake angle of the thinning blade does not necessarily have to be configured to increase smoothly and continuously from the drill axis O side toward the connecting portion side as described above, and takes a constant value. There may be.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings used for the following description, the dimensional ratios of the respective parts are not necessarily drawn accurately.

FIG. 1 is a view schematically showing a three-blade drill 10 which is an embodiment of the present invention, and is a front view seen from a direction perpendicular to the axis O. FIG. As shown in FIG. 1, the three-blade drill 10 of the present embodiment is a three-blade twist drill integrally formed of, for example, a cemented carbide that is a superhard tool material, and is held by a main shaft. The shank 12 to be rotationally driven, the shaft portion 14, and the tip portion 16 are provided coaxially in the axial direction. The dimensions of each part in the three-blade drill 10 of the present embodiment are such that the drill diameter (tool diameter) D is about 10 (mmφ), the diameter of the shaft portion 14 is about 9.85 (mmφ), and the shaft of the shank 12 is, for example. The directional dimension is, for example, about 60 (mm), the axial dimension of the drill body (shaft portion 14 and tip portion 16) is, for example, about 128 (mm), and the overall length of the drill is, for example, about 188 (mm). Preferably, the surfaces of the shaft portion 14 and the tip portion 16 are coated with a hard coating having a multilayer structure such as TiAlN. The shaft portion 14 and the tip portion 16 are provided with three twisted grooves 18 in a spiral shape at equiangular intervals clockwise around the drill axis O, and these twisted grooves 18 are opened at the tip of the drill in the tip portion 16. Main cutting edges 20 (see FIG. 2 and FIG. 3 and the like) are formed along the respective twist grooves 18 in the portions to be formed.

FIG. 2 is a front view showing the tip 16 of the three-blade drill 10 in an enlarged manner from the direction indicated by the arrow II in FIG. FIG. 3 is a bottom view showing the distal end portion 16 of the three-blade drill 10 in an enlarged manner from the direction indicated by the arrow III in FIG. 1, that is, from the distal end side. As shown in FIGS. 2 and 3, the torsion groove 18 is, for example, 10 ° in the same direction as the drill rotation direction (clockwise direction in this embodiment) when viewed from the shank 12 side, that is, from above in FIG. It is twisted at a predetermined twist angle (for example, about 30 °) within a range of about ˜50 °, and chips are discharged to the shank 12 side during processing. Preferably, the three-blade drill 10 is provided with a plurality of (three in this embodiment) fluid supply holes (three in this embodiment) that pass through in the axial direction from the rear end of the shank 12 and open to the flank. Oil hole) 22 is provided.

As shown in FIG. 3, in the vicinity of the drill axis O at the tip portion 16 of the three-blade drill 10, a thinning 24 is applied corresponding to each of the three main cutting edges 20. A thinning blade 26 is provided so as to be connected smoothly. The thinning blade 26 is preferably connected to the main cutting edge 20 so that the rake angle in the axial direction is within the range of −5 ° to 0 ° at the portion closest to the drill axis O. The portion is configured to be within a range of 0 ° to + 15 °, and the axial rake angle increases smoothly and continuously from the drill axis O side toward the connecting portion side ( Configured to be gradually increased from a negative angle to a positive angle). The rake angle of the thinning blade does not necessarily have to be configured to increase smoothly and continuously from the drill axis O side toward the connecting portion side as described above, and takes a constant value. There may be.

The outer peripheral portion of the main cutting edge 20 is provided with a negative angle portion 28 in which the radial rake angle φ is negative with respect to the bottom view seen from the drill tip side, that is, the form shown in FIG. The negative angle portion 28 corresponds to a portion where the radial rake angle φ in the outer peripheral portion of the main cutting edge 20 is within a range of −20 ° ≦ φ <0 °, and the negative angle range L is preferably The linear distance in the direction from the outer corner to the drill axis O is 0.1 D or less with respect to the drill diameter D. In this negative angle range L, the main cutting edge 20 has a shape that projects smoothly and protrudes in the direction of drill rotation, that is, in the counterclockwise direction around the drill axis O in FIG. The rake angle φ in the radial direction is the smallest at the outer peripheral corner (larger toward the negative side) and gradually increases toward the drill axis O side (the drill tip side) (from the negative angle gradually increases to 0 °). Configured). Also, the radial rake angle φ shown in FIG. 3 is an angle of the outermost outer peripheral corner portion. In the three-edged drill 10, the radial rake angle φ of this portion is preferably −20 ° ≦ φ. The predetermined angle is within a range of <0 °.

Further, the portion closer to the drill axis O than the negative angle portion 28 is a recess that is smoothly recessed in the direction opposite to the drill rotation direction in the bottom view shown in FIG. 3, that is, in the clockwise direction of the drill axis O in FIG. It is comprised so that circular arc shape may be comprised. The radius of the concave arc shape is preferably within a range of 0.19D to 1.1D with respect to the drill diameter D, for example, an arc shape having a constant radius of about 0.23D. Preferably, the radial rake angle φ is positive at the outer peripheral portion connected to the negative angle portion 28, but gradually decreases toward the drill axis O and becomes negative. A predetermined negative angle is set at the inner peripheral side portion connected to H.26. Further, the boundary between the negative angle portion 28 forming a convex shape and the concave arc shape is smoothly connected by a small convex arc.

Further, the core thickness D2 in the three-blade drill 10 of the present embodiment is preferably in the range of 20% to 50% of the drill diameter D, that is, in the range of 0.20D to 0.50D, and more preferably. Is in the range of 25% to 45% of the drill diameter, ie in the range of 0.25D to 0.45D. The core thickness D2 may be constant over the entire length of the drill body provided with the twisted groove 18, that is, the shaft portion 14. In the three-blade drill 10 of the present embodiment, FIG. A predetermined back taper is provided such that the drill diameter decreases from the tip of the drill toward the shank 12 at the tip 16 shown. Further, the back taper is not necessarily provided, and there is no difference in diameter between the shaft portion 14 and the tip portion 16. That is, as shown in FIG. 9, even a three-blade drill 10 ′ having a constant diameter (= drill diameter D) from the shank 12 to the tip 16 ′ (drill tip) can be used as shown in FIG. As with the three-blade drill 10 shown in FIG. In other words, the present invention is preferably applied to a three-blade drill having no neck.

4 is a cross-sectional view taken along the line IV-IV in FIG. 1, and is a diagram showing a cross-section perpendicular to the shaft 14 (cross section perpendicular to the axis O of the drill shaft) in the three-blade drill 10. As shown in FIG. 4, the torsion groove 18 opened to the tip end portion 16 is continuously provided from the tip end portion 16 to the drill body, that is, the shaft portion 14. Further, in the shaft portion 14, the land width angle θ ₁ around the drill axis O and the groove width of the torsion groove 18 with respect to the outer peripheral surface and the cross-sectional shape of the torsion groove 18 in a cross section perpendicular to the drill axis O. The land / groove ratio θ ₁ : θ ₂ , which is the ratio to the angle θ ₂ , is preferably in the range of 35:65 to 65:35.

Further, as shown in FIG. 4, the twist groove 18 has an inner peripheral lowermost point A and an outer periphery in the sectional shape of the twist groove 18 in a section perpendicular to the axis O of the drill shaft portion 14. With the straight line AB connecting the upper heel side end point B as a reference line, the maximum dent W, which is the maximum value of the distance between the reference line AB and the cross-sectional shape, is in the range of 3% to 6% of the drill diameter D. In other words, it is configured to be within the range of 0.03D to 0.06D. This innermost lowermost point A is the point closest to the axial center O in the twisted groove 18, in other words, the cross-sectional shape of the twisted groove 18 in the cross section perpendicular to the axial center O of the shaft portion 14. FIG. 4 is an intersection (a common contact point related to the same tangent line) with a circle corresponding to the core thickness (web) D2 indicated by a broken line in FIG. Further, the heel side end point B is an end point on the heel side, that is, the side opposite to the main cutting edge 20, of the outer peripheral surface side end points of the twist groove 18.

FIG. 5 is a diagram showing an axial straight section (a section perpendicular to the axis O of the drill shaft portion) of the shaft portion 100 in a conventional three-blade drill for comparison with the three-blade drill 10 of the present embodiment. It is. As shown in FIG. 5, in the conventional three-edged drill, the torsion groove 102 provided in the shaft portion 100 has a cross-sectional shape of the torsion groove 102 in a cross section perpendicular to the axis O of the shaft portion 100. With respect to the reference line A'B 'and the cross-sectional shape, the straight line A'B' connecting the innermost side lowest point A 'and the outer heel side end point B' in the cross-sectional shape is used as a reference line. The maximum dent amount W ′, which is the maximum value in distance, is configured to be, for example, about 1% of the drill diameter D, that is, about 0.01D. The core thickness D2 'is configured to be, for example, about 25% of the drill diameter D, that is, about 0.25D.

Hereinafter, a test conducted by the present inventors in order to verify the effect of the three-blade drill of the present invention will be described. In this test, the present inventors prepared 12 types of test products 1 to 12, which are three-edged drills having a tool diameter D = 10 (mm), with the core thickness D2 and the maximum dent W being changed. Then, a drilling test was performed under the following test conditions (processing conditions).

[Test conditions]
・ Work material: S25C (JIS G 4051)
・ Tool diameter: D = 10 (mm)
・ Cutting speed: 65 (m / min)
・ Rotation feed amount: 0.55 (mm / rev)
・ Processing depth: 50 (mm)
・ Water-soluble internal lubrication ・ Model machining center

FIG. 6 is a diagram showing the results of the above test, and the core thickness D2 (mm), the tool diameter ratio of each test product, that is, the ratio of the core thickness to the tool diameter (= D2 / D), and the maximum dent amount W (mm). ) And dent ratio (%), that is, the ratio between the maximum dent amount and the tool diameter (= W / D), and the result of the test relating to each test product is indicated by “good” or “bad”. As a result, “good” is the result related to the test product that was able to process 20 holes or more continuously on the work material, and other test products such as 1 to 2 holes were processed. The results relating to the test specimens for which further cutting is difficult are indicated by “defects”.

As shown in FIG. 6, in the test product 1 having a tool diameter ratio of 0.19D and a dent ratio of 1.8% (= 0.018D), breakage occurs in the processing of the first hole, and further processing is performed. The result was “bad”. Moreover, the test piece 2 whose tool diameter ratio is 0.20D and the dent ratio is 1.7% (= 0.177D), the tool diameter ratio is 0.25D, and the dent ratio is 1.4% (= 0.014D). Specimen 3 with a tool diameter ratio of 0.36D and a dent ratio of 1.1% (= 0.011D), Specimen 4 with a tool diameter ratio of 0.51D and a dent ratio of 0.7% ( = 0.007D) In the test product 5, the chips are not divided by the processing of about 1 to 2 holes but are connected as shown in FIG. 7, and the twisted grooves are clogged with chips, resulting in difficulty in processing. The result was “bad”. Further, in the test product 6 having a tool diameter ratio of 0.52D and a dent ratio of 0.7% (= 0.007D), the load is 100% or more in the processing of the second hole, and further processing is performed. The result was “bad”. Further, in the test product 7 having a tool diameter ratio of 0.19D and a dent ratio of 7.1% (= 0.071D), breakage occurs in the processing of the second hole, and further processing can be performed. The result was “bad”. Moreover, the test article 8 whose tool diameter ratio is 0.22D and the dent ratio is 5.9% (= 0.059D), the tool diameter ratio is 0.25D, and the dent ratio is 5.0% (= 0.050D). , Test product 9 with a tool diameter ratio of 0.36D and a dent ratio of 4.1% (= 0.041D), and a tool diameter ratio of 0.50D and a dent ratio of 3.2% ( = 0.032D) In the test product 11 in which processing was continued for 20 holes or more, the chips were appropriately divided as shown in FIG. 8, and the result was “good”. Further, in the test article 12 having a tool diameter ratio of 0.52D and a dent ratio of 2.2% (= 0.022D), the load is 100% or more in the processing of the second hole, and further processing is performed. The result was “bad”.

That is, as a result of this test, in the test products 8 to 11 in which the dent ratio is 3.2% to 5.9%, that is, the maximum dent amount W is 3.2% to 5.9% of the drill diameter D, FIG. As shown in FIG. 1, the chips were divided into about 1 curl or less, and good processing could be performed continuously for 20 holes or more. On the other hand, in the test products 1 to 6 and the test product 12 in which the dent ratio is less than 3%, as shown in FIG. In addition, machining has become difficult due to an increase in load. Further, in the test product 7 having a dent ratio larger than 6%, breakage occurred due to insufficient rigidity of the tool. Accordingly, in the test products 8 to 11 corresponding to the examples of the present invention configured so that the maximum dent W relating to the cross-sectional shape of the torsion groove 18 falls within the range of 3% to 6% of the drill diameter D. In high-efficiency machining with high feed such that the feed amount per rotation exceeds 5% of the drill diameter D, it was verified that good machining can be realized by suitably dividing the chips. That is, it has been clarified from the results of this test that it is preferable that the maximum dent amount W relating to the cross-sectional shape of the twisted groove 18 is in the range of 3% to 6% of the drill diameter D.

In addition, in the test products 8 to 11 corresponding to the examples of the present invention in which good results were obtained in this test, the tool diameter ratios are all in the range of 0.20D to 0.50D. In other words, the core thickness D2 is configured to be in the range of 20% to 50% of the drill diameter D. On the other hand, in the test product 1 and the test product 7 in which the core thickness D2 is less than 20% of the drill diameter D, that is, less than 0.2D, breakage occurs due to insufficient rigidity of the tool. Further, in the test product 5, the test product 6, and the test product 12 in which the core thickness D2 is larger than 50% of the drill diameter D, that is, larger than 0.5D, the twist is caused by the chips being connected for a long time without being sufficiently divided. The load increased due to clogging of chips in the groove, and it became difficult to perform continuous processing. This is because the core thickness D2 is configured to be larger than 50% of the drill diameter D, so that the maximum dent amount W relating to the twisted groove 18 is in the range of 3% to 6% of the drill diameter D, which is the preferred range. This is probably because it is difficult to configure the inside. That is, it has become clear from the results of this test that the core thickness D2 of the three-blade drill is preferably configured to be in the range of 20% to 50% of the drill diameter D.

Thus, according to the present embodiment, the twisted groove 18 is the innermost side lowermost point A in the cross-sectional shape with respect to the cross-sectional shape of the twisted groove 18 in the cross section perpendicular to the axis O of the shaft portion 14. The maximum dent W, which is the maximum value of the distance between the reference line AB and the cross-sectional shape, is 3% to 6% of the drill diameter D, with the straight line AB connecting the heel side end point B on the outer periphery as a reference line. Therefore, it is possible to divide chips even when processing a relatively viscous work material, which is difficult for conventional work materials. Even high-efficiency machining with high feed is possible. Further, since three main cutting edges 20 are provided at equal angular intervals around the drill axis O, the core thickness D2 is increased while ensuring a predetermined chip discharging performance as compared with the two-blade drill. In addition, the rigidity can be increased, centripetality is increased and core blurring is suppressed, and the machining hole diameter enlargement margin is reduced and the machining hole accuracy is improved. That is, to provide a three-blade drill 10 that achieves good machining by suitably dividing chips in high-efficiency machining with high feed such that the feed amount per rotation exceeds 5% of the drill diameter D. Can do.

Further, in this embodiment, since the core thickness D2 of the three-blade drill 10 is configured to be in the range of 0.20D to 0.50D with respect to the drill diameter D, the chip discharging performance is achieved. It is possible to ensure a good balance between the rigidity of the tool and the strength of the cutting edge, which is advantageous for high-efficiency machining with high feed.

In the present embodiment, the outer peripheral portion of the main cutting edge 14 is provided with a negative angle portion 28 having a negative radial rake angle φ, so that the cutting edge strength in the vicinity of the outer peripheral corner is increased. For example, even when drilling is performed at a high feed rate such that the feed amount per rotation exceeds 5% of the drill diameter D for steel and 30% of the drill diameter D for aluminum alloys, Chipping, chipping, and the like near the outer corner are suppressed, and high-efficiency machining with high feed can be performed.

Further, the rake angle φ in the radial direction of the negative angle portion 28 is in the range of −20 ° ≦ φ <0 °, and the range L of the negative angle portion 28 is set to 0.1 D or less from the outer corner. Further, an increase in cutting resistance and thrust resistance due to a negative angle, or a decrease in sharpness is suppressed to a necessary minimum, and high-efficiency machining with high feed as a whole becomes possible. Moreover, since the portion closer to the drill axis O than the negative angle portion 28 has a concave arc shape that is smoothly recessed in the direction opposite to the drill rotation direction, the curling of the chips is promoted, and it becomes easy to divide. The chip discharge performance is improved, and the cutting edge length is longer than that of the straight cutting edge and the cutting load is dispersed. This is also advantageous for high-efficiency machining with high feed.

In this embodiment, the ratio between the land width angle θ ₁ and the groove width angle θ ₂ , that is, the land / groove ratio θ ₁ : θ ₂ is in the range of 35:65 to 65:35. Therefore, it is possible to ensure a good balance between the chip discharge performance and the rigidity and cutting edge strength of the tool, which is advantageous for high-efficiency machining with high feed.

In the present embodiment, a thinning 24 is provided in the vicinity of the drill axis O of the tip portion 16, and a thinning blade 26 is provided so as to be smoothly connected to the main cutting edge 20. The rake angle in the axial direction is in the range of −5 ° to 0 ° at the portion closest to the drill axis O, but is in the range of 0 ° to + 15 ° at the connection with the main cutting edge 20. In addition, since it increases smoothly and continuously from the drill axis O side toward the connecting portion side, it is possible to ensure a predetermined cutting edge strength while suppressing an increase in cutting resistance and thrust resistance, The chipping of the connecting portion between the thinning blade 26 and the main cutting blade 20 is suppressed, and it is advantageous for high-efficiency machining by high feed. The rake angle of the thinning blade does not necessarily have to be configured to increase smoothly and continuously from the drill axis O side toward the connecting portion side as described above, and takes a constant value. There may be.

As described above, according to the three-blade drill 10 of the present embodiment, it is possible to divide chips even when processing a relatively high-viscosity work material. On the other hand, high-efficiency machining with high feed is possible, and high-efficiency drilling with high feed such that the feed amount per rotation exceeds, for example, 5% or even 10% of the drill diameter D becomes possible. . In addition, since high feed is possible in this way, the number of rotations per hole is reduced, and an improvement in tool life can be expected.

The preferred embodiments of the present invention have been described in detail with reference to the drawings. However, the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention. Is.

Industrial applicability

The three-blade drill of the present invention is provided with three twisted grooves around the drill axis O, and the main cutting edges are formed along the respective twisted grooves at portions where these twisted grooves open at the tip of the drill. In the single-edged drill, the torsional groove is related to the cross-sectional shape of the torsional groove in the cross section perpendicular to the axis O of the drill shaft, and the innermost side lowermost point A in the cross-sectional shape and the heel side end point on the outer periphery With a straight line AB connecting B as a reference line, the maximum dent W, which is the maximum value of the distance between the reference line AB and the cross-sectional shape, is in the range of 3% to 6% of the drill diameter D. Since it is configured, in high-efficiency machining with high feed such that the feed amount per revolution exceeds 5% of the drill diameter D, it is possible to achieve good machining by suitably dividing the chips. And relatively high rigidity Of cast iron and general steel is determined to the discharge is poor aluminum alloy of the chip, is suitably used in a hole drilled machining to various workpiece.

10: 3-flute drill 12: Shank 14: Shaft portion 16: Tip portion 18: Torsion groove 20: Main cutting edge 22: Fluid supply hole 24: Thinning 26: Thinning blade 28: Negative angle portion 100: Shaft portion (conventional technology) 102: Twisted groove (conventional technology) A: Inner peripheral side lowest point B: Heel side end point AB: Reference line D: Drill diameter L: Negative angle range O: Center axis W: Maximum dent amount φ: Radial rake angle θ ₁ : Land width angle θ ₂ : Groove width angle

Claims

A three-edged drill in which three twist grooves are provided around the drill axis O, and the main cutting edges are formed along the respective twist grooves in the portions where the twist grooves are open at the tip of the drill,
The twisted groove is a straight line AB connecting the innermost side lowermost point A and the heel side end point B on the outer circumference of the torsional groove in the cross section perpendicular to the axis O of the drill shaft. And the maximum dent amount W, which is the maximum value in the distance between the reference line AB and the cross-sectional shape, is within the range of 3% to 6% of the drill diameter D. A three-blade drill characterized by
The three-blade drill according to claim 1, wherein the core thickness D2 of the three-blade drill is in the range of 20% to 50% of the drill diameter D.
Thinning is performed in the vicinity of the drill axis O at the tip of the drill, and a thinning blade is provided so as to be smoothly connected to the main cutting edge,
The outer peripheral portion of the main cutting edge has a negative angle portion in the range of -20 ° ≦ φ <0 ° in the radial direction when viewed from the bottom of the drill with respect to the drill diameter D from the outer corner. And within a range L of 0.1D or less,
The portion closer to the drill axis O than the negative angle portion of the main cutting edge has a concave arc shape that is smoothly recessed toward the opposite side of the drill rotation direction in the bottom view. A three-blade drill according to 2.