Thread forming tap

Abstract

To provide a cold forming tap capable of spreading cooling liquid to a machining point of the cold forming tap even when thread machining is performed from the lateral direction of a workpiece.SOLUTION: In a cross-sectional view perpendicular to an axial direction of the thread forming tap 10, when a straight line L passing through an axial center O of the thread forming tap 10 and a bottom B of the oil groove 5 is a boundary, a cross-sectional area SB of the oil groove 5 at a rear side in a rotational direction R of the thread forming tap 10 is larger than a cross-sectional area SF of the oil groove 5 at a front side in the rotational direction R of the thread forming tap 10.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a thread forming tap for thread forming by rolling. [Background technology]

[0002] Most thread forming taps, which are used to thread steel or aluminum alloys by rolling, do not generate chips like those used in thread cutting, so there is no need to provide grooves such as helical or straight flutes.

[0003] However, in cases where thread cutting is performed while supplying coolant to the tap, there are thread forming taps (grooved thread forming taps) that have grooves to allow the coolant to reach the tip of the tap during thread cutting (see Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 60-153725 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-127027 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-314231 Summary of the Invention [Problem to be solved by the invention]

[0005] When threading from a vertical direction using a vertical machining center with a grooved thread forming tap, the coolant reaches the tip of the thread forming tap, so a cooling effect from the coolant can be expected.

[0006] However, when threading with a thread forming tap from the side (horizontal direction) of the workpiece using a horizontal processing machine (horizontal machining center), it is difficult for the coolant to reach the tip of the thread forming tap, which has the problem of shortening the tool life of the thread forming tap. This is due to the fact that the cross-sectional shape of the conventional thread forming tap 100 (see Figure 6) is symmetrical in the circumferential direction of the thread forming tap, and the groove and thread shapes are symmetrical in the circumferential direction of the thread forming tap.

[0007] Therefore, an object of the present invention is to provide a thread forming tap that allows coolant to reach the thread forming point of the thread forming tap even when thread forming is performed by plastic processing from the lateral direction of the workpiece. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the thread forming tap of the present invention is a thread forming tap having at least a thread portion for threading a workpiece, and a plurality of oil grooves formed in the thread portion, wherein the oil grooves are formed parallel to the axial direction of the thread forming tap, and when viewed in a cross section perpendicular to the axial direction of the thread portion, with the boundary being a straight line passing through the axis of the thread forming tap and the bottom of the oil groove, the cross-sectional area of ​​the oil groove on the rear side in the rotational direction of the thread forming tap is wider than the cross-sectional area of ​​the oil groove on the front side in the rotational direction, and the cross-sectional shape of the thread of the thread portion on the front side in the rotational direction has a portion that curves in a convex shape toward the front side in the rotational direction.

[0009] Furthermore, the cross-sectional shape of the oil groove is formed parallel to the axial direction of the forming tap, and when the outer diameter of the forming tap is D, the depth of the oil groove can be set in the range of outer diameter D of the forming tap × 0.20 to 0.25. [Effects of the Invention]

[0010] In the thread forming tap of the present invention, the cross section of the oil groove is wider on the rear side of rotation than in the normal oil groove cross section shown in Figure 6, so that the coolant reaches a larger area of ​​the thread portion on the rear side of rotation during thread cutting. As a result, the coolant reaches the cutting point of the thread forming tap not only when threads are cut vertically on the workpiece, but also when threads are cut horizontally. Therefore, the thread forming tap of the present invention has the effect of extending the tool life of the thread forming tap compared to conventional thread forming taps. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a front view of a thread forming tap 10 according to an embodiment of the present invention. [Figure 2] FIG. 2 is a left side view of the thread forming tap 10 shown in FIG. [Figure 3] FIG. 2 is a perspective view of the thread forming tap 10 shown in FIG. [Figure 4] 2 is a cross-sectional view of the thread forming tap 10 shown in FIG. 1 taken along the line AA. [Figure 5] FIG. 5 is a partially enlarged view of the thread forming tap 10 shown in FIG. [Figure 6] FIG. 1 is a schematic cross-sectional view of a conventional thread forming tap 100. DETAILED DESCRIPTION OF THE INVENTION

[0012] The form of the thread forming tap of the present invention will be described with reference to the drawings. Fig. 1 shows a front view of a thread forming tap 10 according to one embodiment of the present invention. Fig. 2 shows a left side view of the thread forming tap 10 shown in Fig. 1, and Fig. 3 shows a perspective view of the thread forming tap 10 shown in Fig. 1. The thread forming tap 10 of the present invention is broadly composed of a thread portion 1 at the front end and a shank 4 at the rear end. As shown in Figs. 1 and 3, the thread portion 1 includes a chamfering portion 2 that first forms a thread in the workpiece, a complete thread portion 3 formed continuous with the chamfering portion 2, and a plurality of oil grooves 5, 5 formed to divide the chamfering portion 2 and the complete thread portion 3, i.e., the thread portion 1, parallel to the axial direction of the thread forming tap 10.

[0013] As shown in Figure 2, when viewed from the tip of the thread portion 1 toward the rear end of the shank 4, the outer diameter of this thread forming tap 10 gradually increases from the chamfer 2 toward the full thread portion 3, and the outer diameter φD of the full thread portion 3 ultimately becomes the outer diameter of the thread forming tap 10. Furthermore, this thread forming tap 10 is rotated counterclockwise in the rotation direction R as shown in Figure 2. Note that the oil grooves 5, 5 of the thread forming tap 10 shown in Figures 1 to 3 are grooves (straight grooves) parallel to the axial direction (longitudinal direction) of the thread forming tap 10, but other oil groove configurations such as oil grooves formed spirally on the outer periphery of the thread forming tap 10 are also acceptable.

[0014] Next, the cross-sectional shape of this thread forming tap 10 will be described with reference to the drawings. Fig. 4 shows a cross-sectional view of the thread forming tap 10 taken along line AA in Fig. 1, and Fig. 5 shows an enlarged view of the upper portion of the thread forming tap 10 shown in Fig. 4. The fully threaded portion 3 of the thread forming tap 10 of this embodiment has eight threads 3A, 3B, 3C, 3D, etc., centered on the axis O, as shown in Fig. 4. Each of the threads 3A, 3B, 3C, 3D, etc. has a crest T1, T2, T3, T4, etc., formed by the overlap of the ridgelines of the inclined surfaces on the front and rear sides in the direction of rotation R. Furthermore, for example, an oil groove 5 having an oil groove bottom B1 is formed between two adjacent threads 3A, 3B.

[0015] Here, the circumscribing circle (imaginary circle) C1 that is centered on the axial center O and passes through the crests T1, T2, T3, T4... of the threads 3A, 3B, 3C, 3D... is the outer diameter φD of the thread forming tap 10. Furthermore, the inscribing circle (imaginary circle) C2 that is centered on the axial center O and passes through the oil groove bottoms B1, B2, B3, B4... of the oil grooves 5A, 5B, 5C... corresponds to the core thickness (core thickness) of the thread forming tap 10.

[0016] Next, the cross-sectional shape of the oil groove 5 of the thread forming tap 10 will be described with reference to the drawings. Fig. 5 is an enlarged partial view of the upper side from the axis O of the cross-sectional shape of the thread forming tap 10 shown in Fig. 4. For example, as shown in Fig. 5, the cross-sectional shape of the oil groove 5B of the thread forming tap 10 is asymmetrical at the front and rear in the direction of rotation R, with the boundary being a straight line L (imaginary line) that passes through the axis O and the oil groove bottom B2.

[0017] That is, in the circumferential direction of the thread forming tap 10, the groove cross section of the oil groove 5B formed between two adjacent threads 3B, 3C is defined as follows: B is the cross-sectional area S of the oil groove in front of the rotation direction R of the forming tap 10 F Make it wider than that.

[0018] Here, the cross-sectional area S of the oil groove at the rear of the rotation direction R B is the area surrounded by the straight line L shown in Figure 5, the ridgeline forming part of the thread 3C (the ridgeline from the oil groove bottom B2 to the top T3), and the circumscribed circle C1 mentioned above. Also, the cross-sectional area S of the oil groove at the front in the direction of rotation R is F is the area surrounded by the straight line L shown in FIG. 5, the ridgeline forming part of the thread 3B (the ridgeline from the oil groove bottom B2 to the top T2), and the circumscribing circle C1 mentioned above.

[0019] The depth h of the oil groove 5B of the thread forming tap 10 (the distance from the circumscribing circle C1 to the oil groove bottom B2) is preferably in the range of 20% to 25% of the outer diameter D of the thread forming tap 10 (h=0.20 to 0.25×D). [Example]

[0020] A thread forming test (hereinafter referred to as the "Test") was conducted using a thread forming tap according to the present invention (hereinafter referred to as the "Invention") and a conventional thread forming tap (hereinafter referred to as the "Conventional Product"), and the results of this test are described below. In this test, the Inventive Product and the Conventional Product were rotated and screwed into each workpiece to a predetermined position, and then the Inventive Product and the Conventional Product were removed from the workpiece by rotating them in the reverse direction, thereby completing a "single hole" thread. The test was also terminated when it was visually determined that any part of the tap had been damaged during thread forming.

[0021] The screw holes drilled into the workpiece were optionally measured with a gauge, and the total number of holes drilled until they were judged to be gauge-out was compared. In addition, if a drilled hole was judged to be gauge-out, the total number of holes drilled was calculated by investigating all consecutive holes until a hole that passed the gauge was confirmed.

[0022] Here, "gauge out" refers to the state when a GP gauge (through thread plug gauge) is used to manually screw in the specified fitting length without any difficulty, and the entire length of the screw cannot be threaded through (see Japanese Industrial Standards JIS B0251).

[0023] The inventive tap and conventional tap used in this test had common specifications: outer diameter (nominal) 12 mm (M12), pitch length 1.75 mm (1.75P), number of oil grooves 8, and the surface was coated with a TiCN-based hard film approximately 2 μm thick. The inventive tap used in this test had the same configuration as the thread forming tap shown in Figure 1, with an oil groove depth of 2.48 mm (0.21 times the thread diameter) and a cross-sectional area S of the oil groove on the front side in the direction of rotation. F When is set to 1, the cross-sectional area S of the oil groove on the rear side in the direction of rotation is B was set to 1.24.

[0024] In contrast, the conventional tap has the same shape as the forming tap shown in Figure 6, and the cross-sectional area S of the oil groove on the front side in the direction of rotation is F and the cross-sectional area S of the oil groove on the rear side in the direction of rotation B were considered to be the same. The thread processing conditions for this test are as follows: ·Work material: S50C (carbon steel) Machining speed: 30 m / min (converted to peripheral speed at the outer diameter of the forming tap) Processing type: blind hole (pre-drilled hole diameter: 11.2 mm) Coolant: Water-soluble cutting fluid ·Processing machine: horizontal machining center

[0025] As a result of this test, the conventional product reached gauge-out after 667 holes, at which point the test was terminated. In contrast, the inventive product reached gauge-out after 3,038 holes. These test results show that the inventive product achieved more than four times the number of holes drilled compared to the conventional product. Additionally, a rolling test was conducted using different nominal diameters of thread forming taps, using the same method as in this test. The results showed that, regardless of the outer diameter of the thread forming tap, making the cross-section of the oil groove wider on the rear side of the thread forming tap's rotation direction than on the front side was effective in improving thread forming performance through thread rolling. Table 1 lists the nominal diameters, pitch, number of grooves, cross-sectional areas of the oil grooves (front side SF and rear side SB), and the ratio of these cross-sectional areas (SB / SF).

[0026] [Table 1]

[0027] The above test results show that the inventive product has an oil groove cross section wider on the rear side of the rotation direction than on the front side in the direction of rotation when viewed in a cross section perpendicular to the axial direction, allowing the cutting oil to reach all the way to the tip and improving machining performance compared to conventional products. At the same time, it was also found that it is effective to set the cross section of the oil groove on the rear side of the thread forming tap's rotation direction to a range of 1.09 to 1.26 times the cross section of the oil groove on the front side of the rotation direction. [Explanation of symbols]

[0028] 1 Threaded part 2. Meal section 3 Completely mountainous 3A~3D Full thread section 4 shank 5(5A~5D) Oil groove 10,100 Filling Tap B(B1~B4) Oil groove bottom C1 Inscribed circle of forming tap C2 Circumscribed circle of forming tap D Outer diameter of forming tap L: An imaginary line connecting the axis of the forming tap and the bottom of the groove O Shaft center of forming tap R Rotation direction of forming tap S F ,S B Cross-sectional area of ​​oil groove T1~T4 Thread crest h Oil groove depth

Claims

1. At least a threaded portion for threading a workpiece; a plurality of oil grooves formed in the thread portion; A forming tap having The oil groove is formed parallel to the axial direction of the forming tap, In a cross-sectional view perpendicular to the axial direction of the threaded portion, When a line passing through the axis of the forming tap and the bottom of the oil groove is defined as a boundary, The cross-sectional area of ​​the oil groove on the rear side in the rotation direction of the forming tap is a cross-sectional area of ​​the oil groove on the front side in the rotational direction, a cross-sectional shape of the thread of the screw portion on the front side in the rotation direction has a portion that is curved convexly on the front side in the rotation direction; A forming tap characterized by:

2. When the cross-sectional area of ​​the oil groove on the front side in the rotation direction is 1, The cross-sectional area of ​​the oil groove on the rear side in the rotation direction is in the range of 1.09 to 1.

26.

2. The thread forming tap according to claim 1.

3. The depth of the oil groove is in the range of D × 0.20 to D × 0.25, where D is the outer diameter of the forming tap.

3. The thread forming tap according to claim 1 or 2.

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