Tap

Abstract

The present invention provides a tap having a back taper and having an improved breaking strength and improved torsional rigidity.　A tap 10 has a biting part 18 and a complete thread part 16. In the complete thread part 16, the angle θ1 of the thread changes. The decreasing amount of the valley diameter in the complete thread part 16 due to the change in the angle θ1 of the thread is configured to be smaller than the decreasing amount of the outside diameter. With this configuration, while the complete thread part is formed to have a back taper shape, it is possible to increase a self-guiding property and to improve breaking strength and torsional rigidity.

Description

Tap

[0001] The present invention relates to a tap, and more particularly to a technique for improving tool life while providing a shape of a back taper in a full thread portion.

[0002] A tap having a biting portion for forming a female thread and a full thread portion for guiding during threading is known, and is used for forming a female thread in a pilot hole. In the biting portion, a predetermined number of threads are provided for each type of tap, and each thread performs cutting or plastic working by a predetermined amount. On the other hand, in the full thread portion, threads having a shape corresponding to the female thread to be formed are provided, and engage with the female thread formed by the biting portion to guide the tap itself.

[0003] Also, in the full thread portion, it is known to provide a back taper processed so that the diameter of the tap becomes thinner from the biting portion side toward the shank side. According to such a back taper, the contact between the full thread portion smaller than the first full thread and the female thread is reduced, so that the torque during threading can be reduced.

[0004] Patent Document 1 and Patent Document 2 disclose taps having a back taper.

[0005] Japanese Patent Application Laid-Open No. 2004-174607 International Publication No. 2009 / 116178 Problems to be Solved by the Invention

[0006] By the way, the back taper is formed simultaneously with the full thread portion, and the formation of the full thread portion may be performed using a grinding wheel. In such a case, when trying to form a back taper, as the outer diameter (the diameter of the top of the thread) of the full thread portion becomes smaller, the diameter of the valley also becomes smaller by the same amount.

[0007] Figure 9 shows a cross-section of a complete thread section 116 of a comparative example including such a back taper. Figure 9(a) shows five threads in the complete thread section, and Figure 9(b) shows a magnified view of one of those threads. As shown in the example in Figure 9(a), the thread angle θ1 of the complete thread section is the same as the thread angle θ0 of the first complete thread. A back taper is created by reducing the outer diameter and root diameter of the thread from the first complete thread at the right end of Figure 9(a) toward the shank side at the left end of Figure 9(a), in other words, by bringing the position of the root closer to the axis. In Figure 9(a), θ1_1, θ1_2, θ1_3, and θ1_4 each indicate the values ​​of the thread angle θ1 of the complete thread section 116 that appear in the cross-section of Figure 9(a). In Figure 9(a), the thread angle θ1 does not change in the complete thread portion 116, so θ1 = θ1_1 = θ1_2 = θ1_3 = θ1_4. In Figure 9(a), the dashed line LT11 is a straight line connecting the peaks of the complete thread portion 116, i.e., the outer diameter of the complete thread portion 116, and the dashed line LV2 is a straight line connecting the roots of the internal threads. The dashed line LV2 is parallel to the axis of the tap, while the dashed line LT11 is inclined to approach the axis of the tap as it moves towards the shank side, which is the left side of the figure. The dotted line LV11 is a straight line connecting the roots of the complete thread portion 116, and is inclined to approach the axis of the tap as it moves towards the shank side, which is the left side of the figure, and LT11 and LV11 are parallel. The dashed line LV0 is included for reference and is a straight line parallel to the axis passing through the position of the root of the first complete thread. In this configuration, as shown in Figure 9(b), the flank surface of the tap's threads and the corresponding flank surface of the internal thread become parallel, and the clearance gap 11 between the peaks of the tap's threads and the internal thread 30 becomes approximately equal to the clearance gap 12 between the external thread and the internal thread 30 near the root of the external thread. Therefore, in the back taper section, the threads on the shank side of the first complete thread do not contact the internal thread formed throughout the circumferential direction and may not contribute to the self-guiding action of the tap.

[0008] Furthermore, because the diameter of the tap's root is relatively small, stress is inherently concentrated there. Adding a back taper further reduces the root diameter, potentially lowering the fracture strength and torsional rigidity.

[0009] The present invention was made against the above circumstances, and its objective is to increase the self-guiding properties and further improve the fracture strength and torsional rigidity of a tap having a back taper.

[0010] To achieve this objective, the first invention is characterized by (a) a tap having a cutting portion and a full thread portion, (b) the angle of the thread in the full thread portion being variable, and (c) the decrease in the root diameter due to the change in the thread angle being smaller than the decrease in the outer diameter.

[0011] According to the first invention, the thread angle θ1 in the complete thread portion changes, and the decrease in the root diameter can be made smaller than the decrease in the outer diameter.

[0012] Preferably, the second invention is characterized in that, in the tap of the first invention, the diameter of the thread valley in the complete thread portion is equal to or greater than the diameter of the first complete thread valley. In this way, the diameter of the thread valley in the complete thread portion is not made smaller than the diameter of the first complete thread valley, and fracture strength and torsional rigidity can be improved.

[0013] Preferably, the third invention is a tap of the first or second invention wherein the thread angle θ1 in the complete thread portion is greater than or equal to the thread angle θ0 of the first complete thread, and satisfies the following equation (1), This is a key feature. In this way, a tap is obtained that has less resistance during threading and improved self-guiding properties, fracture strength, and torsional rigidity.

[0014] Preferably, the fourth invention is characterized in that, in the tap of the first invention, the angle of the thread in the complete thread portion changes so that it increases as it moves toward the shank side. In this way, in the complete thread portion, the angle of the thread can be changed so that it increases as it moves toward the shank side from the first complete thread.

[0015] This figure illustrates a tap that is one embodiment of the present invention. This is a cross-sectional view illustrating a cross-section of the tap 10 in Figure 1 that includes the axis of the complete thread portion. Figure 2(a) shows the five threads in the complete thread portion, and Figure 2(b) shows an enlarged view of one of those threads. This figure shows the back taper of this embodiment and the back taper of the comparative example superimposed. Figure 3(a) shows the five threads in the complete thread portion, and Figure 3(b) shows an enlarged view of one of those threads. This figure illustrates the variables that define the shape of the thread. Figure 5(a) shows the torque and thrust force during threading for the comparative example, and Figure 5(b) shows the torque and thrust force during threading for the tap of the present invention. Figure 6(a) shows the torque and thrust force during threading for the comparative example, and Figure 6(b) shows the torque and thrust force during threading for the tap of the present invention, and shows the results when a tap of a different size than that in Figure 5 is used. This figure shows the number of machinable holes for the tap of the present invention and the tap of the comparative example, respectively. This figure illustrates the relationship between the range of change of the thread angle θ1 and the performance of the tap. This is a cross-sectional view illustrating the cross-section of the tap of the comparative example, including the axis of the complete thread portion. Figure 9(a) shows the five threads of the complete thread portion, and Figure 9(b) shows an enlarged view of one of those threads.

[0016] The embodiments of the present invention will be described in detail below with reference to the drawings. Note that in the following embodiments, the drawings illustrate the essential parts related to the invention, and the dimensions and shapes are not necessarily depicted accurately.

[0017] Figure 1 is a diagram illustrating a tap 10, which is one embodiment of the present invention, and is a front view taken from a direction perpendicular to the axis O. This tap 10 has a shank 12 and a threaded portion 14 integrally mounted coaxially. The threaded portion 14 is provided with dimensions corresponding to the internal thread 30 to be machined (see Figure 2, etc.), and includes a complete threaded portion 16 with a substantially constant diameter and a cutting portion 18 whose diameter gradually decreases towards the tip, and the threads are provided spanning the cutting portion 18 and the complete threaded portion 16.

[0018] Figure 2 is a cross-sectional view illustrating the cross-section of the tap 10 in Figure 1, including the axis of the complete thread portion 16. Figure 2(a) shows the five threads of the external screw in the complete thread portion 16, and Figure 2(b) shows a magnified view of one of those threads. As shown in Figure 2(a), the thread angle θ0 in the first complete thread is 60°, while the thread angle of the complete thread portion 16 is assumed to change continuously, gradually increasing as it moves towards the shank side. Therefore, in Figure 2(a), the thread angle θ0 of the first complete thread is 60°, and the thread angles θ11, θ12, θ13, and θ14 in the back taper adjacent to the left side, i.e., the shank side, are 61.81°, 63.72°, 65.73°, and 67.83°, respectively. On the other hand, the diameter of the thread valleys in the back taper is assumed to be the same as that of the first complete thread.

[0019] In Figure 2(a), the dashed line LT1 is a straight line connecting the peaks of the complete thread section 16, and LV2 is a straight line connecting the roots of the female thread 30. Thus, a back taper is provided in the complete thread section 16. Furthermore, the dashed line LV1 is a straight line connecting the roots of the complete thread section 16, and since this line is parallel to the axis of the tap 10, it can be seen that in the complete thread section 16, the roots do not change depending on the axial direction of the tap 10.

[0020] Figure 2(b) is a magnified view of one of the threads in Figure 2(a). As shown in Figure 2(a), in the tap 10 of this embodiment, the thread angle θ1 increases as it approaches the shank. In Figure 2(a), θ1_1, θ1_2, θ1_3, and θ1_4 each represent the values ​​of the thread angle θ1 of the complete thread portion 16 that appear in the cross-section of Figure 2(a). In Figure 2(a), since the thread angle θ1 changes in the complete thread portion 16, θ1_1, θ1_2, θ1_3, and θ1_4 can each be different values. In this embodiment, as shown in the cross-section of Figure 2(a), four threads corresponding to θ1 are provided in the complete thread portion 16, but this number is not limited to four. In other words, the length of the threads in the complete thread portion 16 in this invention is not limited. As a result, the outer diameter of the complete thread crest becomes smaller, while the diameter of the valley remains unchanged. However, the clearance gap 1 near the crest (see Figure 9(b)), that is, the distance between the crest of the tap 10 and the valley of the internal thread, is set in the same way as the back taper illustrated in Figure 9(a).

[0021] On the other hand, the clearance gap 2 near the root of the thread is smaller than the gap 1 because, as shown in Figure 2(b), it gradually decreases from the crest to the root. The thread angle of the female thread 30 is approximately equal to the thread angle θ0 of the first complete crest that forms the female thread 30. Therefore, when the thread angle θ1 in the complete crest portion 16 becomes larger than the thread angle of the female thread 30, the clearance gap 2 near the root of the thread becomes smaller than the clearance gap 1 near the crest.

[0022] Figure 3 is a diagram showing the back taper of this embodiment superimposed on the back taper of the comparative example for comparison. Figure 3(a) shows the five threads of the complete thread portion 16 and corresponds to Figures 2(a) and 9(a). Figure 3(b) corresponds to Figures 2(b) and 9(b). In Figures 3(a) and 3(b), the threads of this embodiment are shown by solid lines, and the threads of the comparative example are shown by dotted lines. As shown in Figure 3(a), the back taper of this embodiment has a first characteristic compared to the comparative example in how the clearance with the internal thread 30 is provided. That is, in the comparative example, the clearance is set to be the same size both near the crest (outer diameter) of the tap's thread and near the root of the thread. On the other hand, in this embodiment, sufficient clearance is provided near the crest of the tap's thread to suppress the increase in torque and wear during threading, while the clearance value is reduced on the flank surface near the root of the thread to promote contact with the internal thread. This increases the self-guiding ability of the tap 10.

[0023] Furthermore, the back taper of this embodiment has a second characteristic compared to the comparative example: the size of the valley diameter. In the comparative example, a back taper is created in which the outer diameter of the complete crest and the valley diameter decrease by the same amount, and the valley diameter gradually decreases from the first complete crest toward the shank side. On the other hand, in this embodiment, the valley diameter of the complete crest 16 is the same size as the valley diameter of the first complete crest throughout the entire back taper. As a result, the fracture strength and torsional rigidity of the tap 10 can be improved by making the valley diameter larger compared to the comparative example.

[0024] Furthermore, as shown in Figure 3(b), in the comparative example, the thread angle θ1 of the complete thread section 16 is the same for all threads in the back taper (θ1 = 60°), whereas in this embodiment, the thread angle θ1 of the complete thread section 16 gradually increases in the back taper from the first complete thread (θ0 = 60°) toward the shank side. Here, as the thread angle θ1 increases, the angle of the root (the angle of adjacent flanks that make up the root) φa also increases. Therefore, in this embodiment, the angle of the root φa increases toward the shank side in the back taper, and as a result, stress concentration can be reduced and fracture strength can be improved. On the other hand, in the comparative example, the angle of the root φb is constant, and the diameter of the root decreases toward the shank side.

[0025] In this embodiment, the thread angle θ1 of the back taper is calculated as shown in equation (1) below. In equation (1), P is the pitch (mm), L is the thread length (mm), Tc is the cut height at the crest (mm), and Tr is the cut height at the valley (mm). Figures 4(a) and 4(b) illustrate these relationships.

[0026] Figure 4(a) shows the definitions of each variable of the thread that constitutes the back taper. In Figure 4(a), the solid line S0 shows the shape of the thread, and the dotted line S' extends the adjacent flanks at the crest and root of the thread. Figure 4(b) shows the shape of the first complete thread S0, shown by the solid line, and one of the shapes S1 of the thread that constitutes the back taper, shown by the dashed line, superimposed on the shapes in the cross-sectional view of Figure 2, for comparison of the thread angle θ1. As shown in Figure 4(b), the outer diameter of the first complete thread and the thread that constitutes the back taper is smaller by a height h. Furthermore, the axial length WV at the root of the thread and the axial length WT of the tap 10 at the cut portion of the crest are also the same for both.

[0027] Next, we will describe experimental examples conducted by the inventors of the present invention to demonstrate the effects of the present invention.

[0028] Figures 5 and 6 are diagrams for comparing the torque and thrust force when threading with the tap 10 of the present invention and a conventional tap used as a comparative example. Figure 5 shows the results of an experiment using a tap of size M1 x 0.25. The machining conditions are as follows: Size M1 x 0.25 Workpiece material SUS304 Machining speed 10 m / min Threading length 2 mm Pilot hole diameter 0.91 mm Hole shape Blind hole Coolant Water-soluble cutting fluid Machine Vertical machining center

[0029] Figure 5(a) shows the changes in torque and thrust force during threading when using a conventional tap, and Figure 5(b) shows the changes in torque and thrust force when using the tap 10 of this embodiment. Comparing Figures 5(a) and 5(b), it can be seen that the thrust force is lower when using the tap 10 of this embodiment than when using the comparative example tap. This is because the tap 10 of this embodiment has improved self-guiding properties and suppressed pitch deviation.

[0030] Figure 6 shows the results of an experiment using a tap with size M3 x 0.5. The machining conditions were as follows: Size M3 x 0.5 Workpiece material SUS304 Machining speed 10 m / min Threading length 6 mm Pilot hole diameter 2.8 mm Hole shape Through hole Coolant Water-soluble cutting fluid Machine Vertical machining center

[0031] Figure 6(a) shows the changes in torque and thrust force during machining when using a conventional tap, and Figure 6(b) shows the changes in torque and thrust force when using the tap 10 of this embodiment. Comparing Figure 6(a) and Figure 6(b), it can be seen that, as with Figure 5, the thrust force is lower when using the tap 10 of this embodiment than when using the comparative example tap.

[0032] Next, we will explain the experimental results regarding tool life. Figure 7 shows the results of a tapping test conducted on tap 10 of this embodiment and three each of two conventional products, Conventional Product A and Conventional Product B, for comparison. In this test, the condition of the tap was evaluated every 100 holes of internal threading to determine whether it was possible to continue machining. Conventional Product A and Conventional Product B have the structure shown in Figure 9. The machining conditions at that time were as follows: Size M1.4 x 0.3 Workpiece material SUS304 Machining speed 10 m / min Tapping length 2.8 mm Pilot hole diameter 1.28 mm Hole shape Blind hole Coolant Water-soluble cutting fluid Machine Vertical machining center

[0033] As shown in Figure 7, with conventional product A, one tap showed chipping after machining 400 holes and another after machining 700 holes, and another tap was able to machine 100 holes but broke during subsequent machining. With conventional product B, one tap showed chipping after machining 700 holes, and one tap was able to machine 1 hole and another after machining 5 holes but broke during subsequent machining. On the other hand, all taps 10 of this embodiment were able to continue machining even after completing 2000 holes. It can be seen that taps 10 of this embodiment are less prone to breakage and chipping than conventional products, and have a significantly longer tool life.

[0034] Next, the inventor will explain the experimental results regarding the method for selecting the thread angle θ1 in the complete thread portion 16. Figure 8 is a diagram illustrating the preferred range of the thread angle θ1 that constitutes the back taper for each of the taps 10 with sizes M1 × 0.25, M3 × 0.5, and M6 × 1.

[0035] In this experimental example, for the three sizes of taps described above, a back taper was constructed by changing the thread angle θ1 of the complete thread portion within the range shown in the "Variation Range of Thread Angle θ1 [°]" column in Figure 8. More specifically, the thread angle θ0 of the first complete thread of the complete thread portion 16 was set to 60°, and the thread angle θ1 of the thread on the shank side of the complete thread portion 16 (i.e., the leftmost thread in Figure 2(a)) was set to the upper limit of the range, and the thread angle θ1 increased as it moved towards the shank side. Note that the taps corresponding to the rows where the "Variation Range of Thread Angle θ1" column in Figure 8 shows 60 have a thread angle θ1 of 60° for all threads in the complete thread portion 16, but in this invention, since the diameter of the root does not change in the complete thread portion 16, this is a comparative example in which a back taper is not provided.

[0036] Using the tap 10 of this embodiment, configured according to the conditions shown in each row of Figure 8, threading tests were performed under the following conditions: • Size M1 x 0.25, Workpiece material SUS304, Machining speed 10 m / min, Threading length 2 mm, Pilot hole diameter 0.91 mm, Hole shape blind hole, Coolant water-soluble cutting fluid, Machine vertical machining center • Size M3 x 0.5, Workpiece material SUS304, Machining speed 10 m / min, Threading length 6 mm, Pilot hole diameter 2.8 mm, Hole shape through hole, Coolant water-soluble cutting fluid, Machine vertical machining center • Size M6 x 1, Workpiece material S45C, Machining speed 15 m / min, Threading length 12 mm, Pilot hole diameter 5.52 mm, Hole shape through hole, Coolant water-soluble cutting fluid, Machine horizontal machining center

[0037] In the results of these threading tests, taps with a large thrust force during threading are marked with a "△" in Figure 8. More specifically, "△" indicates that machining with a large thrust force is possible, but the thrust force generated is relatively larger than that of taps marked with a "○". Furthermore, taps that produced internal threads that exceeded the gauge (those that did not meet the standard dimensions according to the gauge test) are marked with a "×". All other taps, i.e., those with a suitable thrust force and that produced suitable internal threads, are marked with a "○".

[0038] As shown in Fig. 8, it can be seen that for any of the taps of M1×0.25, M3×0.5, and M6×1, by having the configuration of this embodiment, the effect of reducing the thrust force can be obtained. On the other hand, depending on the size of the tap, the range of change in the thread angle θ1 of the suitable full thread portion differs.

[0039] According to the tap 10 of this embodiment, it has a biting portion 18 and a full thread portion 16, and the thread angle θ1 of the full thread portion 16 changes. The decrease in the diameter of the valley in the full thread portion 16 accompanying the change in the thread angle θ1 can be made smaller than the decrease in the outer diameter, and the breakage strength and torsional rigidity can be improved.

[0040] Further, according to the tap 10 of this embodiment, the diameter of the valley of the thread in the full thread portion 16 is equal to or larger than the diameter of the valley of the first full thread, and the diameter of the valley in the full thread portion 16 does not become smaller than the diameter of the valley of the first full thread. Therefore, the occurrence of a portion where stress concentrates is avoided.

[0041] Further, according to the tap 10 of this embodiment, the thread angle θ1 of the thread in the full thread portion 16 is not less than the thread angle θ0 of the first full thread and satisfies the above formula (1). Therefore, a tap with less thrust force during threading, improved self-guiding property, breakage strength, and torsional rigidity can be obtained.

[0042] Further, according to the tap 10 of this embodiment, the thread angle θ1 of the thread in the full thread portion 16 changes so as to increase toward the shank side. Therefore, in the full thread portion 16, the thread angle θ1 can be changed to increase as it goes from the first full thread toward the shank side.

[0043] As described above, the embodiments of the present invention have been described in detail based on the drawings, but these are merely one embodiment, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art.

[0044] For example, in the above-described embodiment, the tap 10 was a raised tap, but it is not limited thereto, and for example, it may be a cutting tap.

[0045] Furthermore, although the above-described embodiment used a screw with a thread angle (thread angle θ0 of the first complete thread) of 60°, the present invention is not limited to this, and can also be applied to taps with screws having a thread angle of 55° or the like.

[0046] 10: Tap, 12: Shank, 16: Complete thread, 18: Cutting edge, θ0: Thread angle of the first complete thread, θ1: Thread angle at the complete thread.

Claims

1. A tap having a cutting portion and a full thread portion, characterized in that the angle of the thread in the full thread portion changes, and the amount of decrease in the root diameter due to the change in the thread angle is smaller than the amount of decrease in the outer diameter.

2. The tap according to claim 1, characterized in that the diameter of the thread valley in the complete thread portion is equal to or greater than the diameter of the first complete thread valley.

3. The thread angle θ1 in the complete thread section is greater than or equal to the thread angle θ0 of the first complete thread, and satisfies the following equation (1): The tap according to claim 1 or 2, characterized by the following:

4. The tap according to claim 1, characterized in that the angle of the thread in the complete thread portion changes so that it becomes larger as it approaches the shank side.

Images