JP2007007831A - Stepped drill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a stepped cutting edge from cracking and wearing while securing its machining accuracy to improve durability. <P>SOLUTION: A part extending from a step 18 to a large diameter part 16 is ground by a blade, whereby a tilt angle θ of the stepped cutting edge 54 is made within a range of 10-25°, and becomes smaller than a torsion angle β of a helical flute 22 so that the cutting edge 54 gets stronger and its breakage is suppressed. In addition, since the tilt angle θ corresponds to an axial rake angle, the cutting edge gets sharper than cases where the edge has a straight edge with a rake angle of 0° or a chamfer is provided. Thus, better machining accuracy can be attained and also abrasion can be suppressed, thereby obtaining better durability by a combination with the mentioned suppression of the breakage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a step drill, and more particularly, to a technique for improving durability by suppressing chipping and wear while ensuring processing accuracy of a stepped cutting edge.

(a) a large-diameter portion, and (b) a small-diameter portion provided coaxially with the large-diameter portion on the distal end side of the large-diameter portion via a step portion in which the diameter dimension is continuously reduced, (c) A twist groove for discharging chips continuously provided over the large diameter portion and the small diameter portion, and (d) a tip provided at a portion where the twist groove opens at the tip of the small diameter portion. A step drill having a cutting edge and (e) a stepped cutting edge provided at a side edge of the torsion groove in the stepped part is described in, for example, Patent Document 1.
No. 3-5371

  The step drill 10 of FIG. 4 is an example, (a) is a front view seen from a direction perpendicular to the axis O, and (b) is a view of the stepped cutting edge 26 seen from a direction perpendicular to the axis O. It is an enlarged view. The step drill 10 is a two-blade twist drill integrally formed of cemented carbide, and includes a shank 12 and a body 14 integrally in the axial direction, and the body 14 includes a large-diameter portion 16. And a small-diameter portion 20 provided coaxially on the distal end side of the large-diameter portion 16 via a step portion 18 whose diameter dimension is continuously reduced. Then, a pair of twisting grooves 22 for discharging chips are provided continuously across the large-diameter portion 16 and the small-diameter portion 20, and the twisting groove 22 is formed in a portion that opens at the tip of the small-diameter portion 20. A tip cutting edge 24 is formed, and a stepped cutting edge 26 is formed at the side edge of the twisted groove 22 in the stepped part 18. The tip cutting edge 24 and the stepped cutting edge 26 are both provided such that the diameter dimension changes linearly in the axial direction, and each has a tapered surface shape with a predetermined taper angle (for example, 120 °, 60 °). Perform cutting.

  This step drill 10 performs cutting by being rotated clockwise about the axis O as viewed from the shank 12 side, and the twist groove 22 is provided clockwise, and the tip cutting edge 24, Chips cut out by the stepped cutting edge 26 are discharged to the shank 12 through the twisted groove 22. The torsion groove 22 is provided with a constant lead, and the torsion angle in the large diameter portion 16 is larger than that in the small diameter portion 20, for example, about 30 °. The tip cutting edge 24 and the stepped cutting edge 26 are provided with relief surfaces 28 and 30, respectively, and margins 34 and 36 are left on the outer peripheral surfaces of the large diameter portion 16 and the small diameter portion 20, respectively. The second number is given.

  And, according to such a step drill 10, for example, as shown in FIG. 5 (a), a step hole 100 whose diameter is changing in the middle or an opening as shown in FIG. 5 (b). Each of the chamfered holes 104 provided with the chamfer 102 in the part can be processed at a time. That is, the small diameter hole portion 100 a of the stepped hole 100 is formed by the tip cutting edge 24, and the large diameter hole portion 100 b is formed by the stepped cutting edge 26. Further, the hole portion of the chamfering hole 104 is formed by the tip cutting edge 24, and the chamfering 102 is formed by the stepped cutting edge 26.

  However, in such a step drill, since the load of the stepped cutting edge having a high peripheral speed is increased, for example, when drilling a steel material such as S50C, particularly in the vicinity of the outer peripheral corner of the stepped cutting edge. (Refer to reference numeral 26c in FIG. 4), chipping is likely to occur, and there is a problem that the roughness of the processed surface is deteriorated and the tool life is shortened. In order to prevent chipping, it is conceivable to provide a chamfer on the stepped cutting edge, or make the chip discharge groove parallel to the shaft center and make it a straight blade, but in each case the cutting quality deteriorates and the processing accuracy is impaired As a result, the cutting force is increased, wear is promoted, and the machined surface is peeled off to shorten the tool life.

  The present invention has been made against the background of the above circumstances, and its object is to improve the durability by suppressing chipping and wear while ensuring the processing accuracy of the stepped cutting edge.

  In order to achieve such an object, the first invention provides (a) a large-diameter portion and (b) a large-diameter portion on the distal end side of the large-diameter portion via a stepped portion whose diameter is continuously reduced. A small-diameter portion provided coaxially with (c) a twist groove for chip discharge provided continuously over the large-diameter portion and the small-diameter portion, and (d) the twist groove In a step drill having a tip cutting edge provided at a portion opening at the tip of the small diameter portion, and (e) a step cutting edge provided at a side edge of the torsion groove in the step portion, (f ) Side edge of the twisted groove on the side where the stepped cutting edge is formed, and a portion straddling the large diameter portion from the stepped portion is subjected to blade contact grinding in a straight line, The stepped cutting edge is inclined with respect to the axis O at a predetermined inclination angle θ that is smaller than the torsion angle of the torsion groove and is set within a range of 10 ° to 25 °. And wherein the are.

  The second invention is characterized in that, in the stepped drill of the first invention, an axial grinding dimension t in which the large-diameter portion is ground by the blade contact grinding exceeds 1 mm.

  In such a step drill, by applying blade contact grinding to a portion extending from the step portion to the large diameter portion, the inclination angle θ of the step portion cutting edge is set within a range of 10 ° to 25 °. Since the twist angle is smaller than the twist angle of the twist groove, the strength of the stepped cutting edge is increased accordingly, and chipping is suppressed. In addition, since the inclination angle θ corresponds to the rake angle in the axial direction, the sharpness is better than when a rake angle is 0 ° or a chamfer is provided, and excellent machining accuracy is obtained and wear is achieved. In combination with the above-mentioned chipping suppression, excellent durability can be obtained.

  In the second invention, since the grinding dimension t in the axial direction where the large-diameter portion is ground by the blade contact grinding exceeds 1 mm, even in the outer peripheral corner portion of the stepped cutting blade having the fastest peripheral speed and severe processing conditions. Predetermined strength can be obtained, chipping can be prevented more reliably, and durability can be improved.

  The present invention is suitably applied to a step drill made of a hard material such as a cemented carbide that has high hardness and is likely to be chipped, and is also suitably applied when the twist angle of the twist groove is greater than 25 °. However, it can also be applied to other step drills. It is also possible to coat a hard film such as TiAlN if necessary.

  Further, although the present invention is suitably applied to a two-blade stepped drill having two twisted grooves, it can also be applied to a single-blade or three-blade drill. The twist groove may be provided so that the lead is constant, but can also be provided so that the twist angle is constant regardless of the difference in diameter.

  The tip cutting edge and the stepped cutting edge, for example, are provided so that the diameter dimension changes linearly in the axial direction, and are configured to cut into a tapered surface shape with a predetermined taper angle. In this case, various modes in which the diameter dimension changes continuously such as a convex curve shape or a concave curve shape are possible.

  The present invention only needs to include at least one small-diameter portion and one large-diameter portion, and can be applied to a step drill in which the diameter is changed in three or more stages.

  The linear blade contact grinding provided from the stepped portion to the large diameter portion is made to approach the stepped drill in a posture in which the grinding wheel is inclined with respect to the drill axis by the inclination angle θ, or the inclination angle. It can be applied by relative movement in the inclination direction of θ, but the grinding wheel is rotated relative to the axial direction of the drill while rotating the stepped drill around the axis in a posture where the grinding wheel is inclined by the inclination angle θ. Various modes are possible, such as movement (lead feeding). In other words, the blade contact grinding need not be a complete straight line, but may be a substantially straight one twisted around the drill axis, and the inclination angle of the stepped cutting edge varies continuously depending on the grinding mode. However, it is sufficient that the average value of the inclination angles of the entire region of the stepped cutting edge is within the requirement of θ, that is, within the range of 10 ° to 25 °.

  The axial grinding dimension t in which the large-diameter portion is ground by blade contact grinding is preferably more than 1 mm, and more preferably 2 mm or more, or 3 mm or more, but the grinding dimension t is 1 mm or less. Even if it exists, it should just have reached the large diameter part at least. The upper limit of the grinding dimension t of the large-diameter portion is not particularly limited, but about 5 mm to 7 mm is sufficient to increase the strength of the stepped cutting edge. After all, the grinding dimension t is in the range of about 2 to 7 mm. Is appropriate.

  Further, the blade contact grinding is performed, for example, outside the margin of the small-diameter portion so that it is applied to the entire portion of the stepped cutting edge that actually contributes to the cutting process, that is, the portion having a larger diameter than the tip cutting edge. Although it is performed with a cut size that reaches the diameter, grinding may be performed with a cut size deeper than the outer diameter of the margin.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The step drill 50 of FIG. 1 is a case where the present invention is applied to the step drill 10 of FIG. 4, and the portion provided with the step portion cutting edge 26 is changed from the step portion 18 to the large diameter portion 16. The point is that the blade contact grinding is performed in a straight line and the stepped cutting edge 54 is provided along the blade contact grinding part 52, but the other configuration is the same as that of the step drill 10. Therefore, the same reference numerals are given and detailed description is omitted. Note that (a) and (b) in FIG. 1 correspond to (a) and (b) in FIG. 4, respectively.

  In the blade contact grinding, for example, the grinding wheel is approached to the stepped drill 50 in a posture inclined by a predetermined inclination angle θ with respect to the axis O, or is relatively moved in the inclination direction of the inclination angle θ. However, the grinding wheel may be relatively moved in the axial direction of the drill (lead feed) while the stepped drill 50 is rotated about the axis in a posture in which the grinding wheel is inclined by the inclination angle θ. good. Therefore, strictly speaking, the inclination angle θ of the stepped cutting edge 54 may vary continuously in the axial direction, but the average value of the inclination angle θ over the entire region of the stepped cutting edge 54 is 10 ° to 25 °. It is within the range. The torsion groove 22 is provided with a constant lead, the torsion angle β at the large-diameter portion 16 is about 30 °, and the inclination angle θ of the stepped cutting edge 54 is the torsion angle at the large-diameter portion 16. It is smaller than β.

  In addition, the blade contact grinding is performed with the cutting dimension reaching the outer diameter of the margin 36 in the small diameter portion 20 so that the blade contact grinding portion 52 is substantially flush with the margin 36 in this embodiment. Moreover, it is given so that it may reach the large diameter part 16 from the step part 18, and the axial grinding dimension t in the large diameter part 16 exceeds 1 mm, and is set to the range of 2-7 mm in a present Example.

  In such a stepped drill 50, by applying blade contact grinding to a portion extending from the step portion 18 to the large diameter portion 16, the inclination angle θ of the step portion cutting edge 54 is 10 ° to 25 °. Since it is within the range and is smaller than the twist angle β of the twist groove 22, the strength of the stepped cutting edge 54 is increased accordingly, and chipping is suppressed. In addition, since the inclination angle θ corresponds to the rake angle in the axial direction, the sharpness is better than when a rake angle is 0 ° or a chamfer is provided, and excellent machining accuracy is obtained and wear is achieved. In combination with the above-mentioned chipping suppression, excellent durability can be obtained.

  Moreover, since the axial grinding dimension t in which the large-diameter portion 16 is ground by the blade contact grinding exceeds 1 mm and falls within the range of 2 to 7 mm, the step speed is the fastest and the cutting conditions are severe. A predetermined strength can be obtained also at the outer peripheral corner 54c of the blade 54, so that chipping can be prevented more reliably and durability can be improved.

FIG. 2 is an improved product obtained by performing blade contact grinding like the conventional product (step drill 10) shown in FIG. 4 and the step drill 50 shown in FIG. This is a result of examining durability by preparing holes at 25 °, 20 °, 10 °, 5 °, and 0 ° and performing drilling under the following processing conditions. In the conventional product, the twist angle of the twist groove 22 in the large diameter portion 16 is about 30 °, and the inclination angle of the stepped cutting edge 26 is also about 30 °. The improved products have three grinding dimensions t of the blade contact grinding at the large-diameter portion 16 of 5 mm and the inclination angles θ of 25 °, 20 °, and 10 ° are the products of the present invention.
(Processing conditions)
Work Material: S50C (Carbon Steel for Machine Structure)
Drilled hole size: φ20 × φ30 stepped hole Hole depth: 25mm
Cutting speed V: 70 m / min
Feed amount f: 0.20 mm / rev
Cutting fluid: water-soluble cutting oil

  As is apparent from FIG. 2, the conventional product that does not perform blade contact grinding has chipped at the stepped cutting edge 26 in the drilling process of about 100 holes, and the machining surface roughness has deteriorated, making machining impossible. On the other hand, the improved product (the product of the present invention) in which the inclination angle θ of the stepped cutting edge 54 formed by blade contact grinding is 25 ° can be drilled to nearly 500 holes, and the stepped cutting blade 54 wear forms were normal normal wear. The improved product (invention product) having an inclination angle θ of 20 ° could still be used even after drilling up to 500 holes. The improved product (invention product) with an inclination angle θ of 10 ° can be drilled up to about 350 holes, and the wear form of the stepped cutting edge 54 was normal normal wear. The improved products with the inclination angle θ of 5 ° and 0 ° were not able to be machined because the wear of the stepped cutting edge 54 exceeded the allowable amount in the drilling of about 100 holes. Therefore, even in an improved product in which the inclination angle θ of the stepped cutting edge 54 is appropriately set by performing blade contact grinding, excellent durability can be obtained when the inclination angle θ is in the range of 10 ° to 25 °. I understand.

  Further, FIG. 3 shows a step drill 50 shown in FIG. 1 in which the inclination angle θ is 20 ° and the blade contact width of the blade contact grinding in the large diameter portion 16, that is, the grinding dimension t is 1 mm, 3 mm, 5 mm, and 7 mm. 4 shows the results of preparing the four types of test products and examining the durability by drilling under the same processing conditions as in FIG. As is clear from the test results of FIG. 3, when the blade pad width (grinding dimension t) was 3 mm, 5 mm, and 7 mm, the continuous use was still possible even after drilling up to 500 holes. On the other hand, when the blade contact width (grinding dimension t) was 1 mm, the stepped cutting edge 54 was chipped during the drilling process of about 200 holes, making the machining impossible. Therefore, it is desirable to perform blade contact grinding so that the blade contact width (grinding dimension t) in the large diameter portion 18 exceeds 1 mm.

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

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the step drill which is one Example of this invention, (a) is a front view, (b) is the enlarged view which looked at the part in which the step part cutting blade was provided from the direction orthogonal to the axis O FIG. The figure which shows the result which carried out drilling processing using the conventional product which does not perform blade contact grinding, and a plurality of improved products in which the inclination angle θ of the stepped cutting edge formed by blade contact grinding is examined. It is. It is a figure which shows the result of having drilled using the some improved goods from which the blade contact width | variety (grinding dimension t) of a large diameter part differs, and investigated durability. It is a figure which shows an example of the conventional step drill, and is a figure corresponding to FIG. It is a figure which shows the step hole and chamfering hole which can be processed with the step drill of FIG. 1, FIG.

Explanation of symbols

  16: Large diameter portion 18: Step portion 20: Small diameter portion 22: Twist groove 24: Tip cutting edge 50: Step drill 52: Blade contact grinding portion 54: Step portion cutting blade θ: Inclination angle of step portion cutting blade β: Twist angle of torsion groove t: Grinding dimension of large diameter part

Claims (2)

A large diameter part,
A small-diameter portion provided coaxially with the large-diameter portion on the distal end side of the large-diameter portion, through a step portion in which the diameter dimension is continuously reduced;
A twisted groove for discharging chips provided continuously across the large diameter portion and the small diameter portion;
A tip cutting edge provided at a portion where the twist groove opens at the tip of the small diameter portion;
A stepped cutting edge provided at a side edge of the twisted groove in the stepped portion;
In a step drill having
A side edge on the side where the stepped cutting edge is formed in the twisted groove, and a portion straddling the large diameter portion from the stepped portion is subjected to blade contact grinding linearly, The stepped cutting edge is inclined with respect to the axis O at a predetermined inclination angle θ which is smaller than the torsion angle of the torsion groove and is set within a range of 10 ° to 25 °. Step drill. The stepped drill according to claim 1, wherein a grinding dimension t in an axial direction in which the large-diameter portion is ground by the blade contact grinding exceeds 1 mm.

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