DRILL AND INSERT FOR DRILL HAVING IMPROVED CENTERING CAPABILITY AND CUTTING PERFORMANCE

Abstract

Disclosed are a drill and an insert for a drill having improved centering capability and cutting performance. In the drill of the present disclosure, central relief surfaces of cutting parts are processed as flat relief surfaces, and outer circumferential relief surfaces continuing from the center part to the outer circumferential surface of the drill are processed as curved relief surfaces, thereby enhancing the centering capability of the drill and minimizing the generation of drill vibration and burrs. In addition, in the drill of the present disclosure, the outer relief surfaces of the drill in contact with a hole to be drilled are processed such that an angle between the tangential lines of the outer relief surfaces is constant regardless of the size of the outer diameter of the drill, thereby achieving consistent performance of the drill despite change in the outer diameter of the drill.

Claims

1. A drill having a plurality of cutting parts and flutes formed alternately, the drill comprising: cutting parts comprising central relief surfaces being in contact with a chisel edge and processed as flat surfaces, and outer circumferential relief surfaces formed by extending from the central relief surfaces in directions toward an outer circumferential surface of the drill and configured as curved surfaces, each of the curved surfaces having at least one radius.

2. The drill of claim 1, wherein a point angle between the outer circumferential relief surfaces in contact with the central relief surfaces is the same as a central point angle between the central relief surfaces, wherein the central point angle is an angle defined by the central relief surfaces.

3. The drill of claim 2, wherein each of the central relief surfaces and each of the outer circumferential relief surfaces are divided into a first relief surface in contact with a cutting edge and a second relief surface extending from the first relief surface and having a relief angle larger than a relief angle of the first relief surface.

4. The drill of claim 1, wherein a central point angle between the central relief surfaces of the plurality of cutting parts is set to be 140° or less, and an outer circumferential point angle between the outer circumferential relief surfaces of the plurality of cutting parts is set to be 140° or more, wherein the outer circumferential point angle is defined by tangential lines of the outer circumferential relief surfaces meeting the outer circumferential surface.

5. The drill of claim 4, wherein despite change in a size of an outer diameter of the drill, the outer circumferential point angle is set to be constant by changing at least one selected from a radius of the curved surface of each of the outer circumferential relief surfaces and a length of each of the central relief surfaces in a direction toward the outer circumferential surface.

6. An insert mounted to an insert insertion part of a drill, the insert comprising: a plurality of cutting parts in contact with a chisel edge, wherein the cutting parts comprise central relief surfaces in contact with the chisel edge and processed as flat surfaces; and outer circumferential relief surfaces formed by extending from the central relief surfaces in directions toward an outer circumferential surface of the insert and configured as curved surfaces, each of the curved surfaces having at least one radius.

7. The insert of claim 6, wherein a point angle between the outer circumferential relief surfaces in contact with the central relief surfaces is the same as a central point angle between the central relief surfaces, wherein the central point angle is an angle defined by the central relief surfaces.

8. The insert of claim 6, wherein each of the central relief surfaces and each of the outer circumferential relief surfaces are divided into a first relief surface in contact with a cutting edge and a second relief surface extending from the first relief surface and having a relief angle larger than a relief angle of the first relief surface.

9. The insert of claim 6, wherein a central point angle between the central relief surfaces of the plurality of cutting parts is set to be 140° or less, and an outer circumferential point angle between the outer circumferential relief surfaces of the plurality of cutting parts is set to be 140° or more, wherein the outer circumferential point angle is defined by tangential lines of the outer circumferential relief surfaces meeting the outer circumferential surface.

10. The insert of claim 9, wherein despite change in a size of an outer diameter of the drill, the outer circumferential point angle is set to be constant by changing at least one selected from a radius of the curved surface of each of the outer circumferential relief surfaces and a length of each of the central relief surfaces in a direction toward the outer circumferential surface.

Description

DESCRIPTION OF DRAWINGS

[0022] FIG. 1 is a top plan view illustrating a drill tip part of a conventional drill;

[0023] FIGS. 2(a), 2(b), and 2(c) illustrate various examples of a section taken along line A-A of the drill tip part of the drill of FIG. 1;

[0024] FIGS. 3(a), 3(b), 3(c), and 3(d) are views illustrating examples of various kinds of drills to which the technology of the present disclosure is applied;

[0025] FIG. 4 is a perspective view of an insert for an indexable drill according an embodiment of the present disclosure;

[0026] FIG. 5 is a top plan view of the insert for each drill of FIGS. 3(a), 3(b), 3(c), and 3(d); and

[0027] FIG. 6 is a sectional view taken along line B-B of the insert for each of the drills of FIGS. 3(a), 3(b), 3(c), and 3(d).

MODE FOR INVENTION

[0028] Hereinbelow, the present disclosure will be described in detail with reference to the accompanying drawings.

[0029] The insert of the present disclosure is applied to a normal solid drill and an indexable drill. An insert for the indexable drill, like an insert for a spade drill, has a variety of shapes according to a fastening method thereof, but any shape of the indexable drill may be applied. FIG. 3(a) illustrates an example of a normal solid drill or a welding drill, FIG. 3(b) illustrates an example of the indexable drill, and FIGS. 3(c) and 3(d) illustrate examples of a spade drill.

[0030] Referring to FIGS. 3(a) and 3(b), the drill of the present disclosure includes a drill tip part 310 formed at a distal end thereof along a rotational axis X, and a spindle body 330 provided at a rear end of the drill tip part 310. The technology of the present disclosure may be applied in a drill itself due to an embodiment thereof embodied in the drill tip part 310 of the drill, and may be applied in the insert 350 for an indexable drill or in an insert such as an insert 371 or 373 for a spade drill. Meanwhile, the technology of the drill according to the present disclosure may be applied in the insert having two cutting parts like FIGS. 3(a), 3(b), 3(c), and 3(d), and may be applied even in an insert having at least three cutting parts.

[0031] The drill tip part 310 has a plurality of cutting parts and flutes 313 formed alternately. Generally, two or three cutting parts and flutes are arranged in the drill tip part, and FIGS. 3(a) and 3(b) illustrate a twist drill having two cutting parts 311a and 311b and two flutes 313. The plurality of cutting parts are arranged to be opposite to each other relative to the rotational axis of the drill and meet each other at a chisel edge, and are spaced apart from each other at the same intervals. For example, in FIGS. 3(a) and 3(b), the two cutting parts 311a and 311b of the insert 350 are arranged to be symmetrical to each other and are in contact with each other at the chisel edge.

[0032] Hereinbelow, the present disclosure will be described by focusing on the insert 350 for an indexable drill illustrated in FIG. 3(b), FIG. 4, and FIG. 6. First, referring to FIG. 3(b), an insert insertion part 331 to which the insert 350 can be inserted is provided in the spindle body 330 of the drill. To hold the insert 350 inserted to the insert insertion part 331, holding holes are formed in the spindle body 330 and the insert 350 such that the holding holes correspond to each other. A holding member 333 is inserted to the holding holes such that the holding member passes through the spindle body 330 and is inserted to the insert 350, and thus the insert 350 is fastened to the spindle body 330.

[0033] As described above, in the insert 350 of FIG. 4, the two cutting parts 311a and 311b are arranged symmetrically to each other and are in contact with each other at the chisel edge 401. Each of the cutting parts 311a and 311b has the same shape and configuration, and can be described in the same way.

[0034] Each of the two cutting parts 311a and 311b includes the central relief surface 407 or 409 and the outer circumferential relief surface 411 or 413 extending radially from the rotational axis X toward the outer circumferential surface 405 of the insert. A cutting edge 415 is formed at a side of the central relief surface 407 or 409 and the outer circumferential relief surface 411 or 413 which are in contact with the flute 313. The central relief surfaces 407 or 409 of the two cutting parts 311a and 311b become thinner toward the drill point due to a web thin arranged therebetween, and thus the center part of the drill is configured to have a pointed shape. The cutting edge 415 connected from the outer circumferential relief surface 411 or 413 to the central relief surface 407 or 409 is connected to a thinning edge 417 of the center part of the drill. In the thinning edge 417, the central relief surface 407 or 409 meets the web thin 421 arranged between the central relief surface 407 or 409 and a central relief surface 407 or 409 of another cutting part.

[0035] The central relief surface 407 or 409 and the outer circumferential relief surface 411 or 413 constitute “a relief of a cutting part” in contact with the entirety of the cutting edge 415. Meanwhile, as illustrated in FIG. 4, the relief of a cutting part may include a first relief surface 407 and 411 in contact with the cutting edge 415, and a second relief surface 409 and 413 connected to the first relief surface 407 and 411, relative to a boundary line 419 of crossing the central relief surfaces 407 and 409 and the outer circumferential relief surfaces 411 and 413 in a radial direction. The second relief surface 409 and 413 has a relief angle greater than the first relief surface 407 and 411, whereby in a process of cutting, the risk of the breakage of the cutting edge 415 is lowered and during the rapid rotation of the drill, a portion of the relief surfaces is prevented from being excessively in contact with a workpiece to be processed. Accordingly, each of the cutting parts 311a and 311b includes four relief surfaces 407, 409, 411, and 413 composed of a first central relief surface 407 and a second central relief surface 409 constituting the central relief surfaces 407 and 409 and a first outer circumferential relief surface 411 and a second outer circumferential relief surface 413 constituting the outer circumferential relief surfaces 411 and 413.

[0036] Meanwhile, a solid drill illustrated in FIG. 3(a) and the insert 371 or 373 for a spade drill illustrated in FIGS. 3(c) and 3(d) include the central relief surface and the outer circumferential relief surface. However, due to the characteristics of the spade insert, a chip breaker is formed on each of the relief surfaces.

[0037] As for the characteristics of the present disclosure, the central relief surface 407 or 409 in contact with the chisel edge 401 is configured as a flat surface, and the outer circumferential relief surface 411 or 413 extending from the central relief surface 407 or 409 in a direction toward the outer circumferential surface 405 is configured as a curved surface. Here, as illustrated in FIG. 6, the curved surface of the outer circumferential relief surface 411 or 413 means that a line continuing from the rotational axis X in the direction toward the outer circumferential surface 405 is a curve. Furthermore, generally, the curve of the outer circumferential relief surface 411 or 413 is a curve having one or a plurality of radii, but is not limited hereto. For example, the curve of the outer circumferential relief surface 411 or 413 includes a spiral of Archimedes, a cycloid spline, a spiral of a trochoid, a sine curve, or even a curved (that is, a free curve) which cannot be defined to have a plurality of radii like an involute curve. The same is applied even to a spade insert 371 or 373.

[0038] FIG. 6 illustrates a section (a section taken along line B-B of FIG. 5) crossing the central relief surfaces 407 and 409 and the outer circumferential relief surfaces 411 and 413 by crossing the rotational axis X of the insert 350, and allows whether the central relief surfaces 407 and 409 and the outer circumferential relief surfaces 411 and 413 are flat surfaces or curved surfaces to be seen. Referring to FIG. 6, since each of the central relief surfaces 407 and 409 is processed as a flat surface, the central relief surface section SR is represented as a straight line, and since each of the outer circumferential relief surfaces 411 and 413 is processed as a curved surface, the outer circumferential relief surface section CR is represented as a curved line.

[0039] The line B-B of FIG. 5 is in agreement with the boundary line 419, and when any one of the first relief surface 407 and 411 and/or the second relief surface 409 and 413 is taken in the direction of the rotational axis X, the central relief surface section SR is represented as a straight line and the outer circumferential relief surface section CR is represented as a curve. As described above, the curved surface of the outer circumferential relief surface 411 or 413 means that a line continuing from the rotational axis X to the outer circumferential surface 405 is a curve. Accordingly, the section of the outer circumferential relief surface 411 or 413 is represented as a straight line in a section taken along line C-C perpendicular to a section taken along line B-B.

[0040] The curve of the outer circumferential relief surface section CR may have one radius and may be designed as an arc, and may be designed as a curve having at least two radii. The radius of the curve of the outer circumferential relief surface section CR extending to the outer circumferential surface 405 increases according to the size of the outer diameter ØD of the drill, and is preferably approximately at least 1.5 times the outer diameter ØD of the drill.

[0041] Meanwhile, when seen in a direction perpendicular to the thickness surface 423 of the insert in FIG. 4, the shape of the thinning edge 417 and the shape of the cutting edge 415 of the insert 350 may not be the same as the shape of the straight line of the central relief surface section SR and the shape of the curved line of the outer circumferential relief surface section CR in FIG. 6, respectively, according to the shape of the flute 313 and the shape of the web thin 421.

[0042] Referring to FIG. 6, a central point angle θ3 defined by the central relief surfaces 407 or 409 and an outer circumferential point angle θ4 defined by the outer circumferential relief surfaces 411 or 413 are all designed as obtuse angles. Preferably, the central point angle θ3 is set to be 115° to 135° which is less than 140°, and the outer circumferential point angle θ4 is set to be an angle greater than 140°. Here, the central point angle θ3 is an angle defined by the central relief surfaces 407 or 409 relative to the rotational axis X, and the outer circumferential point angle θ4 is an angle defined by tangential lines at the outermost points of the outer circumferential relief surfaces 411 or 413 meeting the outer circumferential surface 405. If a drill is a drill (or an insert) having the two cutting parts 311a and 311b illustrated in FIG. 4, the central point angle θ3 of the drill is an angle between the central relief surfaces 407 or 409 of the two cutting parts 311a and 311b, and the outer circumferential point angle θ4 is an angle between the tangential lines at the outermost points of the outer circumferential relief surfaces 411 or 413 of the two cutting parts 311a and 311b. If a drill is a drill (or an insert) having at least three cutting parts, the central point angle θ3 of the drill is twice the unfolding angle of each of central relief surfaces relative to the rotational axis X, and the outer circumferential point angle θ4 of the drill is twice the unfolding angle of each of the tangential lines at the outermost points of the outer circumferential relief surfaces relative to the rotational axis X.

[0043] Since the central relief surface section SR is represented as a straight line, the central point angle θ3 is constant in the central relief surface section SR, and is formed to be less than 140°, so the centering capability of the drill can be maintained to be excellent as a whole.

[0044] On the other hand, since the outer circumferential relief surface section CR is represented as a curve, the outer circumferential point angle is not constant in the outer circumferential relief surface section CR. That is, the outer circumferential point angle gradually increases in a radial direction toward the outer circumferential surface 405 from the rotational axis X and becomes the largest angle when the outer circumferential relief surface section CR meets the outer circumferential surface 405. Accordingly, as illustrated in FIG. 6, the outer circumferential point angle θ4 can be obtained by an angle between the tangential lines of the outer circumferential relief surfaces 411 or 413 in contact with the outer circumferential surface 405. In the drill, the central point angle θ3 and the outer circumferential point angle θ4 are important factors which determine the performance of the drill. Accordingly, although the outer diameter ØD of the drill increases, the outer circumferential point angle θ4 is preferably set to be constant. To maintain the constancy of the outer circumferential point angle θ4 irrespective of the increase of the outer diameter ØD of the drill, the radius of the curve of the outer circumferential relief surface section CR and the length of the central relief surface 407 or 409 in the direction toward the outer circumferential surface may be changed according to the size of the outer diameter ØD of the drill.

[0045] The point angle between the outer circumferential relief surfaces 411 or 413 in contact with the central relief surfaces 407 or 409 is defined to be the same as the central point angle θ3, so difference between the point angle between the central relief surfaces 407 or 409 and the point angle between the outer circumferential relief surfaces 411 or 413 is not large. Accordingly, abrupt change in the torque and thrust of the drill does not occur. The outer circumferential point angle θ4 has an angle larger than 140°, so burrs produced in the penetrated hole can be minimized.

[0046] However, since the relief angle of the first relief surface 407 and 411 and the relief angle of the second relief surface 409 and 413 are different from each other, the outer circumferential point angle θ4 may be minutely changed even in the same insert 350 when the line B-B is located at a position different from the position of the boundary line 419.

[0047] Meanwhile, a part ranging from the chisel edge of the drill point to the outermost point of the cutting edge is preferably processed such that the height of the outermost point of the cutting edge is the same as the height of the outermost edge part of the drill of FIG. 2(a). This is because in the process of selecting the drill of the present disclosure, when a drill having the same outer diameter as the outer diameter of the conventional drill 10 is selected, a hole having the same depth and size can be drilled. Accordingly, although the drill of the present disclosure is selected in place of the conventional drill, there is no need to change other settings of a tool.

[0048] In the above, the exemplary embodiment of the present disclosure has been shown and described, but the present disclosure is not limited to the specific embodiment described above. Of course, various modifications of the embodiment can be implemented by a person with ordinary knowledge in the technical field to which the present disclosure belongs without departing from the gist of the present disclosure claimed in the claims. Such modified embodiments should not be understood individually from the technical idea or perspective of the present disclosure.