Cemented carbide drill
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2024-12-12
- Publication Date
- 2025-07-03
AI Technical Summary
Existing drills struggle to effectively cool and prevent welding and chipping during machining of low thermal conductivity materials like stainless steel, particularly when using general-purpose machine tools without internal coolant supply mechanisms, leading to increased costs and reduced machining efficiency.
A tungsten carbide drill with multiple cutting edges, flank and rake face coatings, and twisted grooves for coolant delivery, along with precise chamfering angles on the flank and rake faces to enhance coolant reach and prevent welding and chipping.
The drill achieves effective cooling and chip breakage, preventing welding and chipping on low thermal conductivity materials, even with general-purpose machine tools, thereby maintaining machining stability and efficiency.
Abstract
Description
Carbide drill
[0001] The present invention relates to a drill made of cemented carbide having a sub-groove on the outer periphery for flowing cutting fluid (coolant).
[0002] Conventionally, when drilling holes using a drill, in order to cool the drill and the workpiece, a so-called external coolant supply method has been used, in which a coolant is applied to the drill and the workpiece from a machine tool. Also, as disclosed in Patent Document 1, grooves that allow the coolant to pass through can be provided on the outer periphery of the drill, so that the coolant supplied externally from the machine tool can be efficiently sent to the tip of the drill.
[0003] Furthermore, instead of the external oil supply system, the drill and workpiece can be cooled during drilling by using a drill with oil holes, which pumps coolant from the machine tool from the end to the tip of the drill as disclosed in Patent Document 2 and injects coolant from near the cutting edge.
[0004] Japanese Utility Model Publication No. 61-028654 Japanese Patent Application Laid-Open No. 2020-104253
[0005] However, with the drill disclosed in Patent Document 1, it is difficult to achieve a sufficient cooling effect on workpiece materials with low thermal conductivity, such as stainless steel, and welding to the drill's rake face is promoted, causing chipping, so it was necessary to lower (gentle) the machining conditions.
[0006] Furthermore, the drill disclosed in Patent Document 2 is limited to use with machine tools having a mechanism capable of pumping coolant into the drill, i.e., machine tools equipped with a so-called internal oil supply mechanism. In addition, drills with internal oil supply mechanisms (drills with oil holes) are more expensive than general-purpose drills.
[0007] Therefore, an object of the present invention is to provide a cemented carbide drill that can be used to drill workpieces with low thermal conductivity under normal drilling conditions using a general-purpose machine tool.
[0008] In order to solve the above-mentioned problems, the cemented carbide drill of the present invention has at least two or more cutting edges extending outward from the rotation axis O, flanks formed contiguous with these cutting edges, a first margin formed contiguous with the outer side of the flanks, and a main groove formed adjacent to the cutting edges, wherein the flanks and rake faces of the cutting edges are coated with a hard film, and a secondary groove formed parallel to the main groove is further provided on the rear side of the first margin in the direction of rotation, and a second margin formed on the rear side of the secondary groove in the direction of rotation, resulting in a cemented carbide drill having a first chamfered surface on the flank side at the tip of the cutting edge and a second chamfered surface on the rake face side.
[0009] In particular, the angle θ11 between the first chamfer surface and the rotation axis of the cemented carbide drill can be set to a range of 15° or more and 50° or less, and the angle θ12 between the second chamfer surface and the central axis of the cemented carbide drill can be set to a range of more than 0° and 15° or less.
[0010] The cemented carbide drill of the present invention has a plurality of different spiral flutes for the main and sub-floors, which allows coolant to reach the cutting edge of the cemented carbide drill tip while maintaining the drilling conditions of an external coolant supply system using a machine tool without an internal coolant supply mechanism. In addition, by applying minute chamfering to both the flank and rake face of the cutting edge, when the workpiece is a difficult-to-cut material such as stainless steel that has low thermal conductivity and tends to increase the cutting edge temperature, it is possible to suppress chip adhesion to the cutting edge (flank and rake face) and simultaneously improve chip breakability.
[0011] Fig. 4 is a front view of the cemented carbide drill 10 of the present invention. Fig. 5 is a plan view of the cemented carbide drill 10 of the present invention. Fig. 6 is a left side view of the cemented carbide drill 10 shown in Fig. 1. Fig. 7 is a view taken along arrow A of the cemented carbide drill 10 shown in Fig. 2. Fig. 4 is a view further showing a first chamfering amount e1 and a second chamfering amount e2 in Fig. 4.
[0012] An embodiment of the cemented carbide drill of the present invention will be described with reference to the drawings. Fig. 1 shows a front view of a cemented carbide drill 10 according to one embodiment of the present invention, Fig. 2 shows a plan view thereof, and Fig. 3 shows a left side view thereof. Fig. 4 shows a schematic enlarged view of the vicinity of the outer corner 4 of the cemented carbide drill 10 shown in Fig. 1. As shown in Figs. 1 to 3, the cemented carbide drill 10 of the present invention has two cutting edges 1, 1 at its tip portion, and on the forward side of each of these cutting edges 1, 1 in the direction of rotation RT, there are rake faces 3, 3 and two main flutes 7, 7 formed along the longitudinal direction (axial direction) of the cemented carbide drill 10.
[0013] Further, flanks 2, 2 are provided on the rear side of each cutting edge 1, 1 in the direction of rotation RT, and first margins (front margins) 5, 5 are provided on the outer periphery of these cutting edges 1, 1 along the circumferential direction of the cemented carbide drill 10 via outer corners 4, 4, and second margins (rear margins) 6, 6 are provided on the rear side in the direction of rotation RT. Furthermore, two sub-grooves 8, 8 are formed in a spiral shape from the tip side of the cemented carbide drill 10 toward the shank 20 side so as to be parallel to the two main grooves 7, 7 along the axial direction (longitudinal direction) of the cemented carbide drill 10 between the first margins (front margins) 5, 5 and the second margins (rear margins) 6, 6.
[0014] That is, as shown in Figures 1 to 3, these two sub-grooves 8, 8 are formed on the rear side of the main grooves 7, 7 in the rotational direction RT of the cemented carbide drill 10, and first margins (front margins) 5, 5 are provided on the rotational direction RT side of the sub-grooves 8, 8, and second margins (rear margins) 6, 6 are provided on the opposite side of the rotational direction RT.
[0015] Next, the shape of the cutting edge tip of the cemented carbide drill of the present invention will be described with reference to the drawings. Fig. 4 shows a view of the cemented carbide drill 10 shown in Fig. 2 as viewed from the arrow A. The tip of the cutting edge 1 of the cemented carbide drill 10 of this embodiment is chamfered on both the flank 2 side and the rake face 3 side. As shown in Fig. 4, the cemented carbide drill 10 of this embodiment has a first chamfered surface 11 chamfered on the flank 2 side and a second chamfered surface 12 chamfered on the rake face 3 side. Fig. 4 is a view of the vicinity of the outer corner 4 of the cemented carbide drill 10 as viewed from the direction of arrow A in Fig. 2. The direction of arrow A is the direction from the outermost position of the cutting edge 1 toward the center of the tool along the direction in which the cutting edge 1 extends. The arrow A' shown in Fig. 3 is the arrow drawn when the arrow A in Fig. 2 is projected in the direction of view in Fig. 3 (the direction as viewed from the left side of the cemented carbide drill 10 shown in Fig. 1), and is added to clearly explain that the position indicated by the arrow A is the direction in which the cutting edge 1 extends. Furthermore, for the sake of convenience, the cemented carbide drill 10 of the embodiment shown in Figs. 1 to 5 is described as having the cutting edge 1 extending linearly in the direction of the arrow A, but the present invention is not limited to this embodiment (in reality, machining errors and the like may occur, and such drills are not excluded from the scope of the present invention).
[0016] As shown in Fig. 4, the first chamfer surface 11 provided on the flank 2 side and the second chamfer surface 12 provided on the rake face 3 side form a predetermined angle with an imaginary line L0 parallel to the rotation axis O. In particular, for the first chamfer surface 11, the angle θ11 formed between the imaginary line L0 and an imaginary extension line L11 of the first chamfer surface 11 is preferably in the range of 15° to 50°, and for the second chamfer surface 12, the angle θ12 formed between the imaginary line L0 and an imaginary extension line L12 of the second chamfer surface 12 is preferably in the range of more than 0° to 15°. Note that the angle θ11 refers to the angle θ11 formed between the imaginary line L0 and an imaginary extension line L11 of the first chamfer surface 11 when viewing the vicinity of the outer corner 4 of the cemented carbide drill 10 from the direction of arrow A in Fig. 2. Similarly, the angle θ12 is the angle θ12 between the imaginary straight line L0 and the imaginary extension line L12 of the second chamfer surface 12 when viewing the vicinity of the outer corner 4 of the cemented carbide drill 10 from the direction of arrow A in Figure 2.
[0017] In order to confirm the effect of chamfering on the cutting edge of a cemented carbide drill, a cutting test (hereinafter referred to as "this test") was conducted, and the results of this test are described below. In this test, three types of cemented carbide drills were used: the cemented carbide drill of this embodiment shown in Figures 1 to 3 (hereinafter referred to as "invention product") and cemented carbide drills other than those of the present invention (hereinafter referred to as "conventional products 1" and "conventional products 2").
[0018] The chamfering of the invention product was performed with a first chamfer surface angle θ11 = 25° and a second chamfer surface angle θ12 = 8° as shown in Figure 4. In contrast, the chamfering of conventional product 1 was performed with a first chamfer surface angle θ11 = 25° and no second chamfer surface as shown in Figure 4, and the chamfering of conventional product 2 was performed with no first chamfer surface and a second chamfer surface angle θ12 = 8° as shown in Figure 4. The diameter of all three types of cemented carbide drills was 6 mm.
[0019] The cutting conditions for this test were as follows: cutting was stopped when a total of 100 holes had been drilled, and the condition of the cutting edge of the three types of cemented carbide drills, the invention product and conventional products 1 and 2, was checked. Cutting speed: 40 m / min. Feed rate: 0.15 mm / rev. Drilling depth: 30 mm. Workpiece material: austenitic stainless steel (SUS304).
[0020] As a result of this test, traces of chipping due to adhesion to the workpiece material were confirmed on the rake face side of the cutting edge tip of Conventional Product 1 when the number of holes machined reached 100. Furthermore, although the state of adhesion to the workpiece material on the rake face side of the cutting edge tip of Conventional Product 2 was improved compared to Conventional Product 1 when the number of holes machined reached 100, traces of chipping were still visible.
[0021] In contrast, the cutting edge of the invention showed no adhesion to the workpiece on either the rake face or flank face when the drilled number of holes reached 100, and no traces of chipping were observed.These test results show that by chamfering the cutting edge of a cemented carbide drill at a specified angle on both the rake face and flank face, it is possible to suppress the adhesion of chips to the flank and rake face of workpiece materials, particularly difficult-to-cut materials such as stainless steel.
[0022] In the above examples, it was confirmed that the inclusion of the first chamfer surface 11 and the second chamfer surface 12 is the minimum necessary technical condition from the viewpoint of chip adhesion, but in order to further narrow down more preferable embodiments from another evaluation viewpoint of the drill, the verification results of additional examples will be described below. The purpose of these additional examples is to determine more preferable chamfer conditions by adding additional conditions to the condition of the inclusion of the first chamfer surface 11 and the second chamfer surface 12 verified in the above examples as the highest priority condition, and to investigate in detail the effects that different condition settings for the chamfer shape have on chip formation and chipping of the cutting edge.
[0023] Here, the shape of the second chamfered surface 12 formed by chamfering on the rake face 3 side shown in FIG. 4 and the shape of the first chamfered surface 11 formed by chamfering on the flank face 2 side were evaluated separately.
[0024] <Evaluation of Chamfer Shape on the Rake Face> In this example, the chamfer shape on the rake face was first evaluated to investigate the effect of the chamfer angle on chip breakability. From this, an attempt was made to determine the optimal chamfer shape that can be expected to improve cutting stability.
[0025] Specifically, the cutting tests were conducted under the following conditions for the chamfer shape on the rake face side. First, the first chamfer amount e1 shown in FIG. 5 was set to 0.050 mm, the second chamfer amount e2 was set to 0.15 mm, and the chamfer angle (angle of the second chamfer surface) θ12 was set to three levels: 0°, 8°, and 16°. These tests were conducted under the following conditions: drill diameter: 6 mm, cutting speed: 40 m / min, feed rate: 0.15 mm / rev, hole drilling depth: 18 mm, and workpiece material: austenitic stainless steel (SUS304). The chamfer amounts e1 and e2 refer to the lengths of the chamfered surfaces 11 and 12 in the direction parallel to the virtual line L0. In this embodiment, the chamfered surfaces 11 and 12 are described as having constant chamfer amounts e1 and e2 across the entire width of the cutting edge 1, but in reality there will be some processing errors, so if the chamfered amounts e1 and e2 are not constant across the entire width of the cutting edge 1, the chamfered amounts e1 and e2 will be the longest lengths of the chamfered surfaces 11 and 12 in the direction parallel to the virtual straight line L0.
[0026] The evaluation item in this test was the breakability of chips. Specifically, elongated chips can cause chip clogging or wrap around the tool (drill), and adhesion of the workpiece material to the rake face can cause chipping or chipping of the cutting edge. The purpose of this test was to observe these and identify the optimal conditions for stable cutting.
[0027] The test results showed that a chamfer angle of 8° provided the best results. Under these conditions, chip breaking was excellent, and no chipping occurred even after drilling 225 holes, confirming that stable cutting was possible.
[0028] On the other hand, with a chamfer angle of 0°, after drilling 125 holes, the chips were generally broken and discharged, but they tended to elongate compared to when the chamfer angle was 8°. Furthermore, with a chamfer angle of 16°, some chips were elongated, and after drilling 125 holes, they began to tend to wrap around the main flute of the drill without breaking up. In other words, from the perspective of not only chip welding, which is the top priority, but also chip breakability, which is a more preferable condition, the optimal numerical range for the second chamfer angle θ12 is greater than 0° and less than 16°. In other words, the preferred range for the second chamfer angle θ12 is greater than 0° and less than 15°. Furthermore, given the good results with a chamfer angle of 8°, it can be inferred that the more preferred range for the second chamfer angle θ12 is between 4° and 12°. Furthermore, the results of this test also confirmed that the chamfering amount on the rake face side (second chamfering amount e2) is appropriate in the range of 0.10 mm to 0.20 mm, which is in the vicinity of 0.15 mm.
[0029] <Evaluation of chamfer shape on flank side> Next, the chamfer shape on the flank side was evaluated based on the conditions (chamfer amount 0.15 mm, chamfer angle 8°) that were considered to be optimal for the chamfer shape on the rake face side described above. The same cutting test was also carried out on the chamfer shape on the flank side, and the chip breaking ability and the presence or absence of chipping of the cutting edge were investigated.
[0030] Specifically, for the chamfer shape on the flank 2 side shown in FIG. 5 , the chamfer amount (first chamfer amount e1) was set to three levels: 0.030 mm, 0.050 mm, and 0.070 mm, and the chamfer angle (first chamfer surface angle: θ11) was set to three levels: 15°, 25°, and 40°. This test was also conducted under the same cutting conditions as the test for the chamfer shape on the flank side. The chamfer amounts e1 and e2 refer to the lengths of the chamfered surfaces 11 and 12 in a direction parallel to the virtual line L0. In this embodiment, the chamfered surfaces 11 and 12 are described as having constant chamfer amounts e1 and e2 across the entire width of the cutting edge 1. However, in reality, due to some machining error, if the chamfer amounts e1 and e2 are not constant across the entire width of the cutting edge 1, the longest length of the chamfered surfaces 11 and 12 in a direction parallel to the virtual line L0 is used as the chamfer amount e1 and e2.
[0031] The test results showed no difference in chip breakability depending on the chamfer amount and chamfer angle on the flank side. In other words, from the perspective of chip breakability, it was found that the first chamfer surface angle θ11 was not problematic when it was at least 15° or more and 40° or less. This range is merely a more preferable range, and it is presumed that the first chamfer surface angle θ11 would not be problematic from the perspective of chip breakability when it was slightly smaller than this range or slightly larger than this range, up to 50°. Next, as a separate technical evaluation item from chip welding and chip breakability, the preferable range for chipping of the cutting edge after long-term use was confirmed. Regarding chipping of the cutting edge, a chamfer angle of 25° and a chamfer amount of 0.050 mm showed the best results. Under these conditions, there was no chipping of the cutting edge after 225 holes were drilled, and stable machining was confirmed.
[0032] On the other hand, when the chamfer angle was 25° and the chamfer amount was 0.030 mm and 0.070 mm, slight chipping occurred on the cutting edge after drilling 225 holes, but welding was sufficiently reduced compared to the conventional shape (a shape without a first or second chamfer surface), so machining life was improved compared to the conventional shape. Also, when the chamfer angle was 15° and 40°, there was a tendency for slight chipping to occur at the corners of the cutting edge, but welding was sufficiently reduced compared to the conventional shape (a shape without a first or second chamfer surface), so machining life was improved compared to the conventional shape.
[0033] From the above results, it was found that, for the chamfer shape on the flank side, a first chamfer surface angle θ11 in the range of 15° to 50° improved welding properties and also provided excellent chip separation. Furthermore, from the perspective of evaluating chipping of the cutting edge over long-term use, a first chamfer surface angle of 25° and a chamfer amount of 0.050 mm were found to be optimal, suggesting that the first chamfer surface angle θ11 is more preferably in the range of 20° to 30°. Furthermore, it is more preferable that the magnitude of the first chamfer amount e1 be in the range of 0.040 mm to 0.060 mm, which is close to 0.050 mm. This more preferable condition range ensures stability during machining by suppressing chipping of the cutting edge and corner portions, and further improved cutting performance can be expected, even when the number of drilled holes is increased.
[0034] Summarizing the test results of this example, it was found that the preferred range of the second chamfer angle θ12 for improving machining stability is greater than 0° and less than 15°. It was also confirmed that the appropriate range for the second chamfer amount e2 is 0.10 mm or greater and 0.20 mm or less. It was also confirmed that the appropriate range for the first chamfer angle θ11 on the flank side is 15° or greater and 50° or less to improve adhesion reduction and chip breakability, and that a range of 20° or greater and 30° or less is more preferable from the perspective of durability. Furthermore, it was confirmed that the appropriate range for the first chamfer amount e1 is greater than 0.030 mm and less than 0.070 mm to improve adhesion reduction and chip breakability, and that a range of 0.040 mm or greater and 0.060 mm or less is more preferable from the perspective of durability.
[0035] 1 Cutting edge 2 Flank 3 Rake face 4 Peripheral corner 5 First margin (front margin) 6 Second margin (rear margin) 7 Main groove 8 Sub-groove 10 Carbide drill 11 First chamfered surface 12 Second chamfered surface 20 Shank L0 Imaginary straight line parallel to the rotation axis L11 Imaginary extension line of the first chamfered surface L12 Imaginary extension line of the second chamfered surface O Rotation axis RT Rotation direction θ11 Angle of the first chamfered surface θ12 Angle of the second chamfered surface e1 First chamfer amount e2 Second chamfer amount
Claims
1. A cemented carbide drill having at least two cutting edges applied outward from the rotation axis, a flank surface continuously formed on the cutting edge, a first margin continuously formed on the outer side of the flank surface, and a main groove formed adjacent to the cutting edge, wherein the flank surface and the rake surface of the cutting edge are coated with a hard film, a sub-groove formed parallel to the main groove on the rear side in the rotation direction of the first margin, and a second margin formed on the rear side in the rotation direction of the sub-groove are further provided, and the first chamfer surface on the flank surface side and the second chamfer surface on the rake surface side at the tip of the cutting edge are provided respectively. A cemented carbide drill characterized by this.
2. The cemented carbide drill according to claim 1, wherein the angle θ11 formed by the first chamfer surface and the rotation axis of the cemented carbide drill is in the range of 15° or more and 50° or less, and the angle θ12 formed by the second chamfer surface and the rotation axis of the cemented carbide drill exceeds 0° and is in the range of 15° or less.