Drill for prepared hole machining
By adopting three circumferentially spaced plugs and an optimized core shell exhaust and cooling design on the drill bit, the problem of low guide hole size and surface accuracy in the prior art is solved, and higher drilling accuracy and simplified processing flow is achieved.
Patent Information
- Application Number
- JP2023147546
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-09-12
- Publication Date
- 2025-03-25
AI Technical Summary
In the prior art, when drilling a drill bit is used, the guide holes (previous holes) formed before drilling are low in dimensional accuracy and surface accuracy, resulting in increased and complicated subsequent precision machining steps.
Design a drill bit, which uses three plugs (inner diameter plug, middle diameter plug and outer diameter plug) to be arranged in the circumferential direction during drilling, ensuring that the inner surface of the hole is supported by three points during drilling, thereby reducing the axial drift of the drill bit, and optimizing the core shell exhaust and cooling effect through special core shell exhaust trenches and cooling hole designs.
Through the three-point support design, the dimensional accuracy and surface accuracy of the guide hole are improved, the subsequent mid-processing steps are reduced, and the processing process is simplified. In addition, the optimized core shell exhaust and cooling design further improves the inner surface roughness and aperture accuracy of the hole.
Smart Images
Figure 2025040626000001_ABST
Abstract
Description
[Technical field]
[0001] The present invention relates to a pilot hole drill capable of drilling pilot holes with excellent dimensional accuracy and shape accuracy. [Background technology]
[0002] Generally, when forming a cylindrical hole with high finishing accuracy in a workpiece, a pilot hole (a hole before finishing machining) is first drilled into the workpiece, and then semi-finishing and finishing machining are performed in sequence on the inner surface of the pilot hole to finish it to the specified finishing dimensions (target dimensions).
[0003] Here, semi-finishing is a process in which the inner surface of a hole is cut while leaving a machining allowance (cut depth) for the finish machining so that the subsequent finish machining can be performed with high accuracy. In other words, pilot holes formed with a drill usually have low dimensional accuracy and shape accuracy of the inner surface of the hole, so if finish machining is performed directly on the inner surface of a pilot hole formed with a drill, the machining allowance of the inner surface of the hole will not be constant, and the hole cannot be finished with high accuracy. Therefore, in order to make the machining allowance of the inner surface of the hole in the finish machining constant and to finish the hole with high accuracy, semi-finishing (for example, boring using a balance cut boring bar) is performed before finish machining.
[0004] On the other hand, a drill for drilling holes in a workpiece is known, for example, from Patent Document 1. The drill in Patent Document 1 has a drill body that rotates about an axis and two insert tips attached to the axial front end of the drill body. The two insert tips are composed of an inner insert disposed at a radial position close to the axis and an outer insert disposed at a radial position far from the axis, and each has a cutting edge extending in the radial direction. The inner insert and the outer insert are disposed at a circumferential interval of about 180° as viewed from the axial direction. [Prior art documents] [Patent documents]
[0005] [Patent Document 1] JP 2018-079517 A Summary of the Invention [Problem to be solved by the invention]
[0006] The inventors of the present application believed that when forming a cylindrical hole with high finishing accuracy in a workpiece, conventionally, semi-finishing and finish machining were performed, in that order, on the inner surface of a pilot hole made with a drill. However, if it were possible to drill a pilot hole with excellent dimensional accuracy and shape accuracy when drilling the pilot hole, it would be possible to perform finish machining directly after drilling the pilot hole without performing semi-finishing machining, thereby reducing the number of machining steps.
[0007] In order to make it possible to drill pilot holes with excellent dimensional accuracy and shape accuracy, the inventors have studied the reasons why the dimensional accuracy and shape accuracy of the inner surface of pilot holes drilled with a conventional drill such as that of Patent Document 1 are low. As a result, the inventors have noticed that the drill of Patent Document 1 has two insert tips arranged at a circumferential interval of about 180° as viewed from the axial direction, so that the tip of the drill is supported by the inner surface of the hole during drilling at two points, which makes it easy for the axis of the drill body to run out, resulting in low dimensional accuracy and shape accuracy of the inner surface of the pilot hole formed by the drill. In addition, there is also a problem that the chips generated by each insert tip scratch the inner surface of the hole when they are discharged from the hole during drilling, which deteriorates the surface roughness of the inner surface of the pilot hole.
[0008] An object of the present invention is to provide a drill for drilling pilot holes that is capable of drilling pilot holes having excellent dimensional accuracy and shape accuracy. [Means for solving the problem]
[0009] In order to solve the above problems, the present invention provides a pilot hole drill having the following configuration. [Configuration 1] A drill body that is rotated about an axis; and three insert tips attached to an axial front end of the drill body, The three insert tips each have a cutting edge extending in the radial direction, The three insert tips include an inner insert disposed at a radial position closest to the axis, an outer insert disposed at a radial position farthest from the axis, and an intermediate insert disposed at a radial position intermediate between the inner insert and the outer insert, The inner diameter side insert, the intermediate insert and the outer diameter side insert are arranged at intervals from one another in the circumferential direction.
[0010] When this configuration is adopted, since the three insert chips (inner diameter insert, intermediate insert, outer diameter insert) are arranged at intervals from each other in the circumferential direction, the drill tip is supported by the inner surface of the hole during drilling at three points, and the axis of the drill body is less likely to run out. Therefore, it is possible to drill a pilot hole with excellent dimensional accuracy and shape accuracy. In addition, since the pilot hole is cut by dividing it into three parts in the radial direction using the three insert chips (inner diameter insert, intermediate insert, outer diameter insert), the width of the chips generated by each insert chip can be kept small. Therefore, when the chips generated by each insert chip are discharged from the hole during drilling, the inner surface of the hole is less likely to be damaged by the chips, and it is possible to drill a pilot hole with excellent surface roughness on the inner surface of the hole.
[0011] [Configuration 2] The countersink drill according to configuration 1, wherein three central angles, i.e., a central angle about the axis between the radial outer end of the cutting edge of the inner insert and the radial outer end of the cutting edge of the intermediate insert, a central angle about the axis between the radial outer end of the cutting edge of the intermediate insert and the radial outer end of the cutting edge of the outer insert, and a central angle about the axis between the radial outer end of the cutting edge of the outer insert and the radial outer end of the cutting edge of the inner insert, are each set in a range of 90° or more and 150° or less when viewed from the axial direction.
[0012] When this configuration is adopted, the central angles between the inner insert, intermediate insert, and outer insert are each in the range of 90° or more and 150° or less, so that the three-point support of the drill tip by the inner surface of the hole during drilling is well-balanced, and axial runout of the drill body can be effectively suppressed.
[0013] [Configuration 3] Three chip discharge flutes are formed at intervals in the circumferential direction on the outer periphery of the drill body, The inner diameter insert is attached to an inner diameter insert seat that is formed at an axial front end portion of a first chip discharge groove of the three chip discharge grooves and faces forward in a rotational direction, The intermediate insert is attached to an intermediate insert seat facing forward in the rotational direction, the intermediate insert seat being formed at an axial front end of a second chip discharge groove of the three chip discharge grooves; 3. The countersink drill according to claim 1, wherein the outer diameter side insert is attached to an outer diameter side insert seat facing forward in the direction of rotation and formed at an axial front end of a third chip discharge groove among the three chip discharge grooves.
[0014] By adopting this configuration, chips generated by the inner insert, the intermediate insert, and the outer insert during drilling can be smoothly discharged through the first chip discharge groove, the second chip discharge groove, and the third chip discharge groove, respectively.
[0015] [Configuration 4] 4. The countersink drill according to any one of configurations 1 to 3, wherein the diameter of the rotation path of the radially outer end of the cutting edge formed on the outer diameter side insert is set to 30 mm or more.
[0016] By adopting this configuration, it becomes possible to form pilot holes with a large diameter (specifically pilot holes with a diameter of 30 mm or more) with excellent dimensional accuracy and shape accuracy.
[0017] [Configuration 5] 5. The drill for drilling a countersink as described in any one of configurations 1 to 4, wherein the drill body has a coolant hole that extends axially inside the drill body and opens to an axial front end of the drill body.
[0018] By adopting this configuration, chips generated during drilling can be smoothly discharged by the coolant sprayed from the coolant hole, effectively preventing the chips from damaging the inner surface of the pilot hole. Effect of the Invention
[0019] The drill for drilling pilot holes of the present invention has three insert tips (inner diameter insert, intermediate insert, outer diameter insert) arranged at intervals from each other in the circumferential direction, so that the drill tip is supported by the inner surface of the hole during drilling at three points, and the axis of the drill body is less likely to run out. Therefore, pilot holes with excellent dimensional accuracy and shape accuracy can be drilled. In addition, the pilot hole is cut by dividing it into three parts in the radial direction using three insert tips (inner diameter insert, intermediate insert, outer diameter insert), so the width of the chips generated by each insert tip can be kept small. Therefore, when the chips generated by each insert tip are discharged from the hole during drilling, the inner surface of the hole is less likely to be damaged by the chips, and pilot holes with excellent surface roughness on the inner surface of the hole can be drilled. [Brief description of the drawings]
[0020] [Figure 1] FIG. 1 is a plan view showing a pilot hole drill according to an embodiment of the present invention; [Diagram 2] A partial cross-sectional view of the pilot hole drill of Figure 1, seen from the axial front end side. [Diagram 3] 3 is a perspective view of the vicinity of the axial front end of the pilot hole drill shown in FIG. [Figure 4] A diagram showing the relative positions of the three insert tips (inner diameter insert, middle insert, outer diameter insert) shown in Figure 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] A pilot hole drill according to an embodiment of the present invention is shown in Figure 1. This pilot hole drill has a shank 1 attached to the spindle of a machine tool (not shown), a drill body 2 extending axially forward (upward in the figure) from the shank 1, and three insert tips 3a, 3b, 3c attached to the axial front end of the drill body 2.
[0022] The drill body 2 is made of steel and is integral with the shank 1 so as to rotate about an axis O by the rotation of the shank 1. The three insert tips 3a, 3b, 3c are each made of a cemented carbide alloy.
[0023] 4, the three insert tips 3a, 3b, and 3c include an inner insert 3a arranged at a radial position closest to the axis O of the drill body 2, an outer insert 3c arranged at a radial position farthest from the axis O, and a middle insert 3b arranged at a radial position intermediate between the inner insert 3a and the outer insert 3c. The inner insert 3a, the middle insert 3b, and the outer insert 3c each have a cutting edge 4 extending in the radial direction.
[0024] 2 and 3, three chip discharge grooves 5a, 5b, and 5c are formed at intervals in the circumferential direction on the outer periphery of the drill body 2. Each of the three chip discharge grooves 5a, 5b, and 5c is formed to open at the axial front end of the drill body 2. In addition, the drill body 2 is formed with a coolant hole 6 that extends axially inside the drill body 2 and opens at the axial front end of the drill body 2.
[0025] As shown in Fig. 2, the inner insert 3a is detachably attached to an inner insert seat 7a, which is formed at the axial front end of the first chip discharge groove 5a of the three chip discharge grooves 5a, 5b, and 5c and faces forward in the direction of rotation, by a clamp screw 8. Similarly, the intermediate insert 3b is detachably attached to an intermediate insert seat 7b, which is formed at the axial front end of the second chip discharge groove 5b of the three chip discharge grooves 5a, 5b, and 5c and faces forward in the direction of rotation, by a clamp screw 8. Moreover, the outer insert 3c is detachably attached to an outer insert seat 7c, which is formed at the axial front end of the third chip discharge groove 5c of the three chip discharge grooves 5a, 5b, and 5c and faces forward in the direction of rotation, by a clamp screw 8.
[0026] 4, when viewed from the axial direction, the rotation trajectory of the radial outer end 9a of the cutting edge 4 of the inner insert 3a about the axis O intersects with the cutting edge 4 of the intermediate insert 3b, and the rotation trajectory of the radial outer end 9b of the cutting edge 4 of the intermediate insert 3b about the axis O intersects with the cutting edge 4 of the outer insert 3c. In the figure, the rotation trajectories are indicated by dashed lines.
[0027] Also, as viewed from the axial direction, the diameter of the rotation locus of the radial outer end 9a of the cutting edge 4 of the inner insert 3a about the axis O is set to 20% to 40% of the diameter of the rotation locus of the radial outer end 9c of the cutting edge 4 of the outer insert 3c about the axis O (i.e., the hole diameter of the pilot hole). Also, the diameter of the rotation locus of the radial outer end 9b of the cutting edge 4 of the intermediate insert 3b about the axis O is set to 60% to 80% of the diameter of the rotation locus of the radial outer end 9c of the cutting edge 4 of the outer insert 3c about the axis O (the hole diameter of the pilot hole). The diameter of the rotation locus of the radial outer end 9c of the cutting edge 4 of the outer insert 3c (the hole diameter of the pilot hole) is set to 30 mm or more.
[0028] The inner insert 3a, the intermediate insert 3b, and the outer insert 3c are arranged at intervals from each other in the circumferential direction. As viewed from the axial direction, the three central angles, i.e., the central angle about the axis O between the radial outer end 9a of the cutting edge 4 of the inner insert 3a and the radial outer end 9b of the cutting edge 4 of the intermediate insert 3b, the central angle about the axis O between the radial outer end 9b of the cutting edge 4 of the intermediate insert 3b and the radial outer end 9c of the cutting edge 4 of the outer insert 3c, and the central angle about the axis O between the radial outer end 9c of the cutting edge 4 of the outer insert 3c and the radial outer end 9a of the cutting edge 4 of the inner insert 3a, are each set in the range of 90° to 150°.
[0029] In Figure 4, the inner insert 3a, the intermediate insert 3b, and the outer insert 3c are arranged so that the cutting edge 4 coincides with a straight line extending radially through the axis O, but the cutting edge 4 may be arranged so that it is offset parallel to the straight line extending radially through the axis O toward the rear in the direction of rotation.
[0030] As shown in FIG. 4, this drill for drilling pilot holes has three insert tips 3a, 3b, and 3c arranged at intervals from each other in the circumferential direction, so that the drill tip is supported by the inner surface of the hole during drilling at three points, and the axis O of the drill body 2 is less likely to run out. Therefore, pilot holes with excellent dimensional accuracy (precision of the diameter of the pilot hole) and shape accuracy (cylindricity and roundness of the inner surface of the pilot hole, etc.) can be drilled. In addition, the pilot holes are cut by dividing them into three parts in the radial direction using the three insert tips 3a, 3b, and 3c, so that the width of the chips generated by each insert tip 3a, 3b, and 3c can be kept small. Therefore, when the chips generated by each insert tip 3a, 3b, and 3c are discharged from the hole during drilling through the chip discharge grooves 5a, 5b, and 5c, the inner surface of the hole is less likely to be damaged by the chips, and pilot holes with excellent surface roughness of the inner surface of the hole can be drilled. Therefore, after drilling a pilot hole with this pilot hole drilling drill, it is possible to perform finish machining directly without performing semi-finish machining.
[0031] For example, when forming a hole with a diameter of 40 mm after finishing, generally, a pilot hole with a diameter of about 39.0 mm is first drilled with a drill, then the inner surface of the pilot hole is semi-finished (such as boring with a balance cut boring bar) to make the hole diameter 39.8 mm (i.e., the hole diameter with 0.2 mm of finishing allowance remaining), and then the inner surface of the hole is finished with a finish boring bar to make the hole diameter 40.0 mm (target dimension). In contrast, if this pilot hole drill is used, a pilot hole with excellent dimensional accuracy, shape accuracy, and surface roughness can be made, so that a pilot hole with a diameter of 39.8 mm (i.e., the hole diameter with 0.2 mm of finishing allowance remaining) can be first drilled with a pilot hole drill, and then the inner surface of the hole is finished with a finish boring bar without semi-finishing to make the hole diameter 40.0 mm (target dimension).
[0032] As shown in FIG. 4, in this pilot hole drill, the central angles between the inner diameter insert 3a, the intermediate insert 3b, and the outer diameter insert 3c are each in the range of 90° or more and 150° or less. This provides a good balance in the three-point support of the drill tip by the inner surface of the hole during drilling, and effectively suppresses runout of the axis O of the drill body 2.
[0033] In addition, with this pilot hole drill, chips generated during drilling can be smoothly discharged through chip discharge grooves 5a, 5b, and 5c by coolant injected from coolant hole 6 shown in Figure 3, effectively preventing the inner surface of the pilot hole from being damaged by chips. [Explanation of symbols]
[0034] 2 Drill body 3a Inner diameter insert (insert tip) 3b Intermediate insert (insert tip) 3c Outer diameter insert (insert tip) 4 Cutting Edge 5a,5b,5c Chip discharge groove 6 Coolant Holes 7a Inner diameter insert seat 7b Intermediate insert seat 7c Outer diameter insert seat 9a, 9b, 9c Radial outer ends of cutting edges O axis
Claims
1. A drill body (2) that is rotated around an axis (O); and three insert tips (3a, 3b, 3c) attached to the axial front end of the drill body (2), The three insert tips (3a, 3b, 3c) each have a cutting edge (4) extending in a radial direction, The three insert tips (3a, 3b, 3c) are comprised of an inner diameter side insert (3a) arranged at a radial position closest to the axis (O), an outer diameter side insert (3c) arranged at a radial position farthest from the axis (O), and an intermediate insert (3b) arranged at a radial position intermediate between the inner diameter side insert (3a) and the outer diameter side insert (3c), The drill for drilling pilot holes, wherein the inner diameter side insert (3a), the intermediate insert (3b) and the outer diameter side insert (3c) are arranged at intervals from each other in the circumferential direction.
2. 2. The drill for countersinking according to claim 1, wherein three central angles, i.e., a central angle about the axis (O) between a radial outer end (9a) of the cutting edge (4) of the inner insert (3a) and a radial outer end (9b) of the cutting edge (4) of the intermediate insert (3b), a central angle about the axis (O) between a radial outer end (9b) of the cutting edge (4) of the intermediate insert (3b) and a radial outer end (9c) of the cutting edge (4) of the outer insert (3c), and a central angle about the axis (O) between a radial outer end (9c) of the cutting edge (4) of the outer insert (3c) and a radial outer end (9a) of the cutting edge (4) of the inner insert (3a), are each set in a range of 90° to 150° when viewed from the axial direction.
3. Three chip discharge grooves (5a, 5b, 5c) are formed at intervals in the circumferential direction on the outer periphery of the drill body (2), The inner diameter side insert (3a) is attached to an inner diameter side insert seat (7a) facing forward in the rotation direction, which is formed at an axial front end portion of a first chip discharge groove (5a) of the three chip discharge grooves (5a, 5b, 5c), The intermediate insert (3b) is attached to an intermediate insert seat (7b) facing forward in the rotational direction, which is formed at an axial front end portion of a second chip discharge groove (5b) of the three chip discharge grooves (5a, 5b, 5c); 3. The countersink drill according to claim 1, wherein the outer diameter side insert (3c) is attached to an outer diameter side insert seat (7c) facing forward in the direction of rotation and formed at an axial front end portion of a third chip discharge groove (5c) among the three chip discharge grooves (5a, 5b, 5c).
4. 3. The drill for drilling countersinks according to claim 1 or 2, wherein the diameter of the rotation path of the radially outer end (9c) of the cutting edge (4) formed on the outer diameter side insert (3c) is set to 30 mm or more.
5. 3. The drill for drilling a countersink as claimed in claim 1 or 2, wherein the drill body (2) is formed with a coolant hole (6) that extends axially inside the drill body (2) and opens to an axial front end of the drill body (2).
Citation Information
Patent Citations
Boring tool
JP2018079517A