Extrusion screw tap

Abstract

A thread forming tap (1) is provided with a male thread section (3), a groove, and an inner diameter finishing blade (61). The cut-in section (31) of the male thread section (3) is provided continuously with the complete thread section (32), and the diameter of the cut-in section (31) becomes smaller toward the tip of the cut-in section (31). The groove is provided parallel to the axial center so as to extend across the complete thread section (32) and the cut-in section (31) so as to cut off the thread (71) of the male thread section (3). In the cut-in section (31) and the complete thread section (32), an inner diameter finishing blade (61) is provided along the open end of the groove on the opposite side from the direction of rotation of the thread tap (1). The inner diameter finishing blade (61) cuts and removes the top portion of the thread of the female thread formed on the surface layer of the bottom hole (90). The height of a first-stage finishing blade (611) of the inner diameter finishing blade (61), said first-stage finishing blade (611) being located in the cut-in section (31), is lower than the height of a second-stage finishing blade (612) of the inner diameter finishing blade (61), said second-stage finishing blade (612) being formed in a portion corresponding to a screw thread (71) at the most distal end of the complete thread section (32).

Description

Technical Field

[0001] The invention relates to an extrusion tap. Background Art

[0002] Patent document 1 discloses an extrusion tap with an inner diameter finishing blade (hereinafter referred to as an "extrusion tap"). The external thread portion of the extrusion tap has a complete tooth portion and a cutting portion. The cutting portion is arranged continuously with the complete tooth portion. The diameter of the cutting portion decreases as it moves toward the front end. The protrusion and the retreat portion are alternately arranged in the portion from the cutting portion to the first complete tooth. The first complete tooth is the frontmost thread tooth of the complete tooth portion. The protrusion bites into the inner circumferential surface of the bottom hole and plastically deforms the inner circumferential surface to form an internal thread. The extrusion tap has at least one groove. The groove cuts off the thread teeth of the external thread portion in the axial direction. The groove is parallel to the axis across the complete tooth portion and the cutting portion. The complete tooth portion has an inner diameter finishing blade. The inner diameter finishing blade makes the inner wall surface of the groove function as a rake face. The inner diameter finishing blade cuts off the top portion of the thread teeth of the internal thread.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 5362854 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] When the tapping machine reverses and returns after rolling the internal thread, friction occurs. The friction phenomenon is a phenomenon in which the inner diameter finishing blade contacts the inner diameter portion of the internal thread in a manner that rubs against the inner diameter portion from the opposite direction to the rake face. The inner diameter finishing blade may flatten or pull up the shape of the processed thread crest.

[0008] The friction phenomenon may intensify the wear of the back cutting edge of the inner diameter finishing blade. In the rolling of soft materials, the friction phenomenon may also cause the adhesion of the workpiece. The inner diameter finishing blade is sometimes formed with a slightly reverse cone shape in a manner that the diameter is approximately the same from the cutting portion at the front end of the extrusion tap. In this case, the inner diameter finishing blade that actually performs the finishing cutting of the inner diameter portion of the internal thread is the inner diameter finishing blade near the first complete tooth portion after the plastic deformation processing of the extrusion tap is completed. The inner diameter finishing blade of the cutting portion sometimes cuts the inner diameter portion at the midway stage of the thread tooth of the extruded internal thread. However, the inner diameter finishing blade of the cutting portion is not the inner diameter finishing blade that finishes the final size of the inner diameter portion. The diameter of the inner diameter finishing blade of the cutting portion is larger than the diameter of the complete tooth portion by the amount of the reverse cone shape. Therefore, when the extrusion tap reverses and returns, friction may occur in the state where the inner diameter finishing blade of the cutting portion is reversed.

[0009] An object of the present invention is to provide a screw forming tap capable of reducing deformation of the shape of the crest of an internal thread formed by roll forming.

[0010] Solutions for solving problems

[0011] A screw tap according to one technical solution of the present invention is an screw tap for forming an internal thread by plastically deforming a bottom hole of a workpiece, characterized in that the screw tap comprises: an external thread portion having a complete thread portion and a cut-in portion which is continuously provided with the complete thread portion and has a smaller diameter toward the front end; a groove which is provided parallel to the axis center across the complete thread portion and the cut-in portion in a manner to cut the thread teeth of the external thread portion; and an inner diameter finishing blade which is provided in the cut-in portion and the complete thread portion along the opening end of the groove on the side opposite to the rotation direction of the screw tap, and is used to cut and remove the top portion of the thread teeth of the internal thread, wherein, in the inner diameter finishing blade, when the distance from the axis of the screw tap is set as the height of the inner diameter finishing blade, the height of the cut-in portion side is lower than the height of the portion corresponding to the thread teeth at the front end of the complete thread portion. Therefore, when the screw tap is pulled out from the workpiece while being reversed, it is possible to reduce the interference of the portion of the inner diameter finishing blade located at the cut-in portion with the thread teeth of the formed internal thread and the deformation of the thread teeth.

[0012] Alternatively, in the inner diameter finishing blade, a step portion having a lower height on the cutting portion side than on the complete tooth portion side is provided between the thread tooth at the front end of the complete tooth portion and the cutting portion. Therefore, in the extruding tap, in the inner diameter finishing blade, the height of the portion on the cutting portion side can be easily made lower than the height of the portion corresponding to the thread tooth at the front end of the complete tooth portion.

[0013] Alternatively, the inner diameter finishing blade may be provided with an inclined portion whose height decreases as it moves from the frontmost thread of the complete thread portion toward the front end side of the cutting portion. Therefore, in the extruding tap, the height of the portion on the cutting portion side can be easily made lower than the height of the portion corresponding to the frontmost thread of the complete thread portion.

[0014] Alternatively, the inner diameter finishing blade may be provided with at least an inverted tapered shape whose height decreases from the portion corresponding to the frontmost thread of the complete thread portion toward the rear end side. Therefore, when the screw tap rotates forward or reversely, the friction between the screw tap and the workpiece can be reduced, thereby reducing the heat generated by the contact between the inner diameter finishing blade and the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a stereoscopic view of the screw extrusion tap 1.

[0016] Figure 2 It is a front view of the extrusion tap 1.

[0017] Figure 3 It is a rear view of the extrusion tap 1.

[0018] Figure 4 1 is a top view of the extrusion tap 1.

[0019] Figure 5 This is a cross-sectional perspective view obtained by cutting the front end side of the screw extrusion tap 1.

[0020] Figure 6 Viewed from the front side Figure 5 FIG. 1 shows a diagram of a screw forming tap.

[0021] Figure 7 yes Figure 1 A cross-sectional view taken along line II is shown.

[0022] Figure 8 This is a diagram showing a state before the bottom hole 90 is rolled by the screw forming tap 1 .

[0023] Fig. 9 This is a diagram showing a state where the screw pressing tap 1 is inserted into the bottom hole 90 .

[0024] Fig.10 This is a diagram showing a state where the screw forming tap 1 is extracted from the internal thread.

[0025] Fig.11 It is a diagram showing an inner diameter finishing cutting edge 65 formed on the external thread portion 3 of a screw tap 100 as a modified example.

[0026] Fig.12 These are photos showing the shape of existing products undergoing confirmation tests and the test results.

[0027] Fig.13 The following are photographs showing the shape of the product of the present invention during the confirmation test and the test results.

[0028] Fig.14 It is a figure which shows the blade shape of the screw tap 101 as a modification.

[0029] Fig.15 It is a figure which shows the blade shape of the screw tap 102 as a modification. DETAILED DESCRIPTION

[0030] An embodiment of the present invention is described below. Figure 1In the axial direction of the axis AX of the extrusion tap 1 shown, the side of the external thread portion 3 is set as the front end side, and the side of the shank portion 2 is set as the rear end side. For the convenience of explanation, the present embodiment uses the front (front end), rear (rear end), front (front), back (back), right, and left directions shown in the figure regarding the orientation of the extrusion tap 1. In order to make the explanation clear, there are parts in the drawings that are appropriately represented with a dimensional ratio different from the actual dimensional ratio. Therefore, the present invention is not to be interpreted as being limited to the shape of the drawings.

[0031] Reference Figure 1 to Figure 7 , illustrating the structure of the extrusion tap 1. Figure 1 The extrusion tap 1 shown in the drawing is provided with a bottom hole 90 (refer to Figure 8 ) is plastically deformed. The extrusion tap 1 forms an internal thread 40 in the bottom hole 90 (refer to Fig. 9 , Fig.10 When the extrusion tap 1 is viewed from the front end side, the extrusion tap 1 rotates counterclockwise around the axis AX (refer to Figure 1 , Figure 4 direction of rotation T as shown).

[0032] like Figure 1 to Figure 3 As shown, the extrusion tap 1 includes a shank 2, an external threaded portion 3, and four oil grooves 4 (see Figure 4 ) and a groove 6. The shank 2 is cylindrical with an axis AX. The material of the shank 2 is, for example, high-speed tool steel. The shank 2 has four corners 21 on the rear end side. The cross-section of the four corners 21 is roughly quadrilateral. Tool holders (not shown) are installed on the four corners 21. The tool holder supporting the extrusion tap 1 is installed on the spindle of the machine tool (not shown). Therefore, the extrusion tap 1 rotates integrally with the tool holder and the spindle. In the following description, "the extrusion tap 1 is installed on the spindle" means the same as "the tool holder supporting the extrusion tap 1 is installed on the spindle".

[0033] The external thread portion 3 is coaxial with the shank portion 2 and is formed integrally with the shank portion 2. The external thread portion 3 is substantially cylindrical. A thread ridge 71 and a root 72 are provided on the outer peripheral surface of the external thread portion 3. The height of the thread ridge 71 from the root 72 is substantially uniform. The thread ridge 71 is formed along a helical line with a predetermined thread lead angle.

[0034] The external thread portion 3 includes a cutting portion 31 and a complete tooth portion 32. The cutting portion 31 is provided on the front end side of the external thread portion 3. The diameter of the cutting portion 31 decreases as it moves toward the front end side on the axis AX. Therefore, the height of the thread teeth 71 of the cutting portion 31 from the axis AX is lower than the height of the thread teeth 71 of the complete tooth portion 32 from the axis AX. The cutting portion 31 bites into the surface layer of the bottom hole 90 provided in the workpiece W, causing the surface layer to plastically deform. The cutting portion 31 corresponds to several pitches of the external thread portion 3 from the front end side. The pitch refers to the distance between the centers of two adjacent thread teeth 71 in the axial direction. Several pitches are, for example, 2 to 5 pitches. The distance between the centers refers to Figure 1 , Figure 2 The distance P shown in .

[0035] The complete thread portion 32 is provided at the rear end side of the external thread portion 3. The diameter of the complete thread portion 32 is substantially constant on the axis AX. The shapes of the thread teeth 71 and the root 72 of the complete thread portion 32 are substantially consistent with the shapes of the thread teeth and the root 72 of the internal thread 40 to be rolled on the surface of the bottom hole 90 (refer to Fig.10 ). The complete thread portion 32 performs the surface finishing of the internal thread 40 during the rolling process and generates a driving force in the screwing direction.

[0036] like Figure 4 , Figure 6 As shown in FIG. 1 , five protrusions 51 to 55 are formed on a cross section of the thread 71 of the external thread portion 3. The protrusions 51 to 55 protrude radially outward and are arranged along the above-mentioned spiral line. Figure 4 As shown, when the extrusion tap 1 is viewed from the front end side, the protrusions 51 to 55 are arranged at about 240° (refer to Figure 4 The range of θ in the figure is arranged in a clockwise direction at equal intervals of 60°. Therefore, the protrusions 51 to 55 are adjacent to each other in a direction parallel to the axial direction for each lead of the helical line. One lead means one rotation.

[0037] The four oil grooves 4 are respectively provided between the protrusion 51 and the protrusion 52, between the protrusion 52 and the protrusion 53, between the protrusion 53 and the protrusion 54, and between the protrusion 54 and the protrusion 55. The oil grooves 4 are formed in a straight line parallel to the axis AX from the front end side to the rear end side of the extruding tap 1 across the full thread portion 32 and the cut portion 31 (see FIG. Figure 1 to Figure 3 The cross section of the oil groove 4 is roughly U-shaped (refer to Figure 6 The oil groove 4 supplies cutting fluid to the roll forming surface of the workpiece W. The cutting fluid improves the lubrication effect, cooling effect, etc. during the roll forming.

[0038] In the external thread portion 3, the interval between the protrusions 51 and 55 adjacent in the circumferential direction is 120° around the axis AX, which is wider than the interval between the other pair of protrusions adjacent in the circumferential direction (see Figure 4 , Figure 6 ). The grinding surface 60 is provided between the protrusions 51 and 55. The grinding surface 60 is a surface formed by removing the thread teeth between the protrusions 51 and 55 by plane cutting. The grinding surface 60 extends parallel to the axial direction. The grinding surface 60 is orthogonal to the radial direction of the external thread portion 3. The diameter of the rotation trajectory of the blade tip of the grinding surface 60 is consistent with the inner diameter of the internal thread 40 to be rolled.

[0039] like Figure 1 , Figure 3 As shown, in the grinding surface 60, the step portion 603 is provided at a position corresponding to the boundary between the cut-in portion 31 and the complete tooth portion 32. The first grinding surface 601 is formed at a position closer to the cut-in portion 31 side than the step portion 603. The second grinding surface 602 is formed at a position closer to the complete tooth portion 32 side than the step portion 603. The step portion 603 connects the rear end of the first grinding surface 601 with the front end of the second grinding surface 602 in the radial direction. The height of the first grinding surface 601 is lower than the height of the second grinding surface 602. The height of the grinding surface 60 is the distance from the axis AX. The height of the grinding surface 60 is the diameter of the rotation trajectory. The groove 6 is provided at a position of the grinding surface 60 adjacent to the protrusion 55. The groove 6 is an example of the "groove" of the present invention. The groove 6 is formed in a straight line parallel to the axis AX from the front end side to the rear end side of the external thread portion 3. The groove 6 has a substantially semicircular cross-sectional shape larger than the other oil grooves 4 (refer to Figure 6 ).

[0040] The inner diameter finishing blade 61 is formed on the ridgeline of the grinding surface 60 relative to the groove 6. The ridgeline of the grinding surface 60 relative to the groove 6 is also the open end of the groove 6 on the side opposite to the rotation direction T. Therefore, the inner diameter finishing blade 61 faces the rotation direction T side. The height of the inner diameter finishing blade 61 is the same as the height of the grinding surface 60. The height of the inner diameter finishing blade 61 refers to the distance in the radial direction from the axis AX. The top of the thread tooth of the internal thread 40 extruded by plastic deformation realized by the protrusions 51 to 55 is divided into an incomplete tooth shape. The inner diameter finishing blade 61 removes the incomplete tooth shape by cutting, thereby improving the inner diameter portion 41 (refer to Fig.10 The inner wall surface of the groove 6 functions as a "rake face" of the inner diameter finishing edge 61. The specific shape of the inner diameter finishing edge 61 will be described later.

[0041] like Figure 5 to Figure 7 As shown, the oil passage 7 is provided inside the extrusion tap 1. The oil passage 7 extends linearly along the axis AX, passing through the center of the rear end portion and the center of the front end portion of the extrusion tap 1 (see Figure 7The oil passage 7 opens in a circular shape at the center of the front end of the extrusion tap 1 (see Figure 3 ). The cutting fluid is supplied from the rear end side of the oil passage 7. The cutting fluid flows toward the front end side in the oil passage 7, and is ejected toward the surface layer of the bottom hole 90 from the opening of the front end portion.

[0042] Reference Figure 3 , Figure 8 , Fig. 9 , the shape of the inner diameter finishing edge 61 will be described in detail. Figure 8 , Fig. 9 A part of a cross section of the external thread portion 3 along the axis AX is shown. Figure 8 , Fig. 9 The height position of the inner diameter finishing blade 61 relative to the plurality of thread teeth 71 of the protruding portion 55 is shown. The inner diameter finishing blade 61 extends substantially linearly from the front end side toward the base end side of the external thread portion 3 when viewed from the front (see FIG. Figure 1 ). A slight inverted taper shape is applied to the inner diameter finishing blade 61. The inverted taper shape of the present embodiment refers to an inclination in which the diameter of the inner diameter finishing blade 61 becomes approximately the same from the cutting portion 31 side to the complete tooth portion 32 side as the height from the axis AX decreases from the cutting portion 31 side toward the complete tooth portion 32 side. Therefore, in the extrusion tap 1, the portion where the inner diameter finishing blade 61 contacts the inner diameter portion 41 of the internal thread 40 rolled on the surface of the bottom hole 90 can be reduced. Fig. 9 , Fig.10 , the height position Q indicated by the dotted line indicates the height of the inner diameter portion 41 of the internal thread 40. The inner diameter finishing blade 61 becomes lower relative to the height position Q as it approaches the complete thread portion 32. Therefore, when the screw tap 1 rotates forward and reversely, the friction caused by the contact between the inner diameter finishing blade 61 and the inner diameter portion 41 of the internal thread 40 can be reduced.

[0043] like Figure 3 , Figure 8 As shown, the inner diameter finishing edge 61 is a two-stage cutting edge corresponding to the step shape of the grinding surface 60. The inner diameter finishing edge 61 includes a first-stage finishing edge 611, a second-stage finishing edge 612, and a step portion 613. The first-stage finishing edge 611 is formed on the ridgeline of the first grinding surface 601 relative to the groove 6, corresponding to the cut-in portion 31. The axial length of the first-stage finishing edge 611 is substantially the same as the axial length of the cut-in portion 31. The second-stage finishing edge 612 is formed on the ridgeline of the second grinding surface 602 relative to the groove 6, corresponding to the complete tooth portion 32. The step portion 613 is formed on the ridgeline of the step portion 603 relative to the groove 6, corresponding to the boundary between the cut-in portion 31 and the complete tooth portion 32.

[0044] like Fig. 9As shown, the height of the first finishing edge 611 is set at a position lower than the height of the front end 615 of the complete thread portion 32. The front end 615 of the second finishing edge 612 is arranged corresponding to the portion closer to the cutting portion 31 than the vertex 711 of the most front thread 71A in the complete thread portion 32. The height of the front end 615 of the second finishing edge 612 is set at a position corresponding to the inner diameter of the internal thread 40 to be rolled (refer to Fig. 9 The step portion 613 connects the rear end of the first finishing edge 611 to the front end 615 of the second finishing edge 612 in the radial direction. The second finishing edge 612 gradually becomes lower as it moves from the step portion 613 toward the rear end side of the external thread portion 3 using an inverted tapered shape.

[0045] Reference Figure 8 to Figure 10 , illustrating a rolling method of an internal thread 40 realized by an extrusion tap 1. Figure 8 As shown in FIG. 1 , the bottom hole 90 is pre-formed in the workpiece W. The screw tap 1 is mounted on the main spindle of the machine tool (not shown). The machine tool positions the screw tap 1 at the preparation position in front of the bottom hole 90 by moving the main spindle. The machine tool and the main spindle start the normal rotation of the screw tap 1 integrally. The machine tool inserts the screw tap 1 from the preparation position into the bottom hole 90. Fig. 9 As shown, the cutting portion 31 of the extrusion tap 1 spirally advances relative to the surface layer of the bottom hole 90 of the workpiece W and bites into the surface layer of the bottom hole 90 of the workpiece W. The surface layer begins to plastically deform, and following the cutting portion 31, the complete thread portion 32 spirally advances further toward the surface layer of the bottom hole 90. Plastic deformation continues to occur, and the internal thread 40 is formed on the surface layer. The excess material 34 is squeezed out from the top of the thread of the internal thread 40 toward the inner circumference. Thereafter, the excess material 34 is cut off and removed by the passage of the inner diameter finishing blade 61. Therefore, the extrusion tap 1 can roll-form the internal thread 40 with a relatively high inner diameter accuracy on the workpiece W. After the rolling of the internal thread 40 is completed, the machine tool stops the rotation of the extrusion tap 1.

[0046] Next, in order to extract the screw tap 1 from the internal thread 40, the machine tool and the spindle integrally start reversing the screw tap 1. The screw tap 1 reverses and moves toward the preparation position. An inverted taper shape is applied to the inner diameter finishing edge 61. The first-level finishing edge 611 of the inner diameter finishing edge 61 is located at a position lower than the front end portion 615 of the second-level finishing edge 612. Therefore, in the process of reversing the screw tap 1 and returning to the preparation position, the first grinding surface 601 corresponding to the first-level finishing edge 611 does not interfere with the inner diameter portion 41 of the internal thread 40. The first grinding surface 601 is the portion of the first-level finishing edge 611 in the opposite direction to the front cutting edge. The front cutting edge 611 is the inner wall surface of the groove 6. The machine tool stops the spindle at the preparation position and stops the reversal of the screw tap 1 (refer to Fig.10When the screw tap 1 is reversed relative to the internal thread 40 formed on the workpiece W and then pulled out, the inner diameter finishing edge 61 does not interfere with the inner diameter portion 41 of the internal thread 40 from the direction opposite to the rake face. Therefore, the screw tap 1 can reduce the deformation of the inner diameter portion 41.

[0047] Reference Fig.11 , a modified example of the screw tap 1 is described. The inner diameter finishing edge 61 of the screw tap 1 is a two-stage cutting edge, and the portion corresponding to the boundary between the cutting portion 31 and the complete thread portion 32 is formed into a step shape. As long as the height of the inner diameter finishing edge of the portion corresponding to the cutting portion 31 is lower than the height of the inner diameter finishing edge formed in the portion corresponding to the thread thread at the front end of the complete thread portion 32, the inner diameter finishing edge is not limited to the step shape.

[0048] For example, Fig.11 The screw tap 100 shown is a modified example of the screw tap 1. The screw tap 100 includes an inner diameter finishing blade 65 instead of the inner diameter finishing blade 61. The inner diameter finishing blade 65 is substantially in the shape of an inverted letter V, with the boundary between the cutting portion 31 and the complete thread portion 32 as the vertex. The ground surface forming the inner diameter finishing blade 65 is formed to have a substantially inverted letter V cross-section corresponding to the shape of the inner diameter finishing blade 65.

[0049] The inner diameter finishing edge 65 includes a first finishing edge 651, a second finishing edge 652, and a top portion 653. The first finishing edge 651 corresponds to the cut-in portion 31. The second finishing edge 652 corresponds to the complete thread portion 32. The top portion 653 corresponds to the boundary between the cut-in portion 31 and the complete thread portion 32. The height position of the top portion 653 is set at a position corresponding to the inner diameter portion 41 of the internal thread 40 to be rolled. The position corresponding to the inner diameter portion 41 of the internal thread 40 to be rolled is Fig.11 The height position Q in the middle. The first-stage finishing edge 651 is inclined in a manner that becomes lower from the top 653 toward the front end side of the external thread portion 3. The second-stage finishing edge 652 is given the same inverted tapered shape as the inner diameter finishing edge 61. Therefore, the second finishing edge 652 is inclined in a manner that becomes lower from the top 653 toward the rear end side of the external thread portion 3. Alternatively, the same inverted tapered shape may be given to the first-stage finishing edge 651.

[0050] In such an inner diameter finishing edge 65, as in the inner diameter finishing edge 61 of the present embodiment, the first finishing edge 651 corresponding to the cutting portion 31 is located at a position lower than the tip 653 of the second finishing edge 652. Therefore, even if the screw tap 100 is reversed and pulled out from the internal thread 40, the ground surface (not shown) corresponding to the first finishing edge 651 does not interfere with the inner diameter portion 41 of the internal thread 40. Therefore, when the screw tap 100 is reversed and pulled out from the internal thread 40 formed on the workpiece W, the inner diameter finishing edge 65 does not interfere with the inner diameter portion 41 of the internal thread 40 from the direction opposite to the rake face. Therefore, the screw tap 100 can also reduce the deformation of the inner diameter portion 41.

[0051] Next, in order to confirm the effect of the product of the present invention, a confirmation test was conducted. In the confirmation test, the product of the present invention was used to roll the internal thread of the bottom hole pre-formed in the workpiece, and the quality of the internal thread after rolling was compared with that of the existing product. Fig.11 The screw forming tap 100 shown. In the conventional screw forming tap, only the linear inner diameter finishing edge 161 is provided with an inverted taper shape.

[0052] The processing environment is as follows.

[0053] Workpiece: ADC12 (plate thickness 10mm)

[0054] Thread size: M14×1

[0055] Machine tool: vertical machining center

[0056] Cutting oil: Water-soluble cutting oil (emulsion, dilution ratio 10 times, internal oil supply 3MPa)

[0057] Tool holder: milling chuck

[0058] Bottom hole: φ13.4mm (drill), measured = 13.395mm

[0059] Effective thread length: 10mm (through hole)

[0060] Cutting speed: 44m / min (1000min -1 )

[0061] Describe the results for existing products. Fig.12 (A) is a photograph of a part of the front end side of an existing product. The inner diameter finishing blade 161 is provided with an inverted taper shape (refer to Fig.12 The inverted tapered shape is formed so that the height decreases from the cut-in portion 31 side toward the complete tooth portion 32 side. Fig.12 (B) is an enlarged photo of the internal thread formed by rolling using the existing product. Fig.12 The screw forming tap is pulled out in the direction of arrow K shown in (B). Fig.12 The portion surrounded by a circle in (B) is a portion that contacts the inner diameter finishing cutting edge 161 from the side opposite to the rake face of the inner diameter finishing cutting edge 161 when the screw tap is reversed. Fig.12 (C) is to Fig.12 The enlarged photograph of the part surrounded by the circle in (B) is shown. Fig.12 As shown by the arrow in (C), it can be confirmed that the crest portion of the internal thread is flattened.

[0062] The results of the products of the present invention are described. Fig.13 (A) is a photograph of a part of the front end side of the product of the present invention. The first finishing edge 651 of the inner diameter finishing edge 65 is inclined downward from the top 653 toward the front end side. The second finishing edge 652 is inclined downward from the top 653 toward the rear end side. Fig.13 (B) is an enlarged photograph of the internal thread obtained by rolling the product of the present invention. Comparing the product of the present invention with the existing product, Fig.13 The portion surrounded by a circle in (B) is not flattened. The reason for this is that when the screw tap 100 is reversed, the portion of the first finishing edge 651 on the side opposite to the rake face does not interfere with the inner diameter portion of the rolled internal thread. The above results confirm that the product of the present invention can reduce the deformation of the thread teeth of the formed internal thread when the screw tap 100 is withdrawn from the rolled internal thread, compared with the conventional product.

[0063] As described above, the extrusion tap 1 of the present embodiment is a tool for forming an internal thread by plastically deforming the bottom hole 90 of the workpiece W. The extrusion tap 1 includes an external thread portion 3, a groove 6, and an inner diameter finishing blade 61. The external thread portion 3 includes a complete thread portion 32 and a cut-in portion 31. The cut-in portion 31 is provided continuously with the complete thread portion 32. The diameter of the cut-in portion 31 decreases toward the front end. The groove 6 is provided parallel to the axis across the complete thread portion 32 and the cut-in portion 31. The groove 6 cuts the thread ridge 71 of the external thread portion 3.

[0064] In the cut-in portion 31 and the complete thread portion 32, the inner diameter finishing blade 61 is provided along the open end of the groove 6 on the side opposite to the rotation direction T of the screw tap 1. The inner diameter finishing blade 61 removes the top portion of the thread crest of the internal thread formed on the surface layer of the bottom hole 90. When the distance from the axis AX of the screw tap 1 is defined as the height, the height of the first-stage finishing blade 611 of the inner diameter finishing blade 61 located in the cut-in portion 31 is lower than the height of the second-stage finishing blade 612 of the inner diameter finishing blade 61 formed in the portion corresponding to the thread crest 71 at the front end of the complete thread portion 32. Therefore, when the screw tap 1 is pulled out from the workpiece W during the reverse rotation, the portion of the inner diameter finishing blade 61 located in the cut-in portion 31 does not interfere with the thread crest of the formed internal thread. Therefore, the screw tap 1 can reduce the deformation of the thread crest of the internal thread formed in the bottom hole 90.

[0065] In the inner diameter finishing blade 61, the step portion 613 is provided between the thread ridge 71 at the front end of the complete thread portion 32 and the cut-in portion 31. At the step portion 613, the height on the cut-in portion 31 side is lower than the height on the complete thread portion 32 side. Therefore, the forming tap 1 can make the height of the portion of the inner diameter finishing blade 61 located at the cut-in portion 31 lower than the height of the portion of the inner diameter finishing blade 61 formed at the front end of the complete thread portion 32.

[0066] At least a reverse taper shape is provided on the inner diameter finishing blade 61. The reverse taper shape is formed so that the height becomes lower as it moves from the portion corresponding to the thread teeth 71 at the front end of the complete thread portion 32 toward the rear end. Therefore, the friction between the screw tap 1 and the workpiece can be reduced when the screw tap 1 rotates forward and reversely. Therefore, the screw tap 1 can reduce the heat generated by the contact between the inner diameter finishing blade 61 and the workpiece.

[0067] In addition, the present invention is not limited to the above-mentioned embodiment, and various changes can be made. The material of the shank 2 of the extrusion tap 1 can also be a material other than high-speed tool steel, for example, it can also be a superhard alloy. The reverse taper shape is applied to the entire portion of the inner diameter finishing edge 61, but it can also be applied only to the second-level finishing edge 612. In addition, the reverse taper shape may not be applied to the inner diameter finishing edge 61. The oil grooves 4 are not limited to four, and can be more or less. The oil grooves 4 and the oil passage 7 can also be omitted. The extrusion tap 1 is a left-handed tool that rotates counterclockwise when viewed from the front end side, but it can also be a right-handed tool that rotates clockwise.

[0068] The number of inner diameter finishing blades 61 of the extrusion tap 1 is one, but it may be two or more. Fig.14 The screw forming tap 101 shown includes four protrusions 15 , two oil grooves 14 , two grooves 16 , and two inner diameter finishing edges 161 in the external thread portion, and has a point-symmetrical shape centered on the axis AX. Fig.15The screw forming tap 102 shown in the figure includes three protrusions 15, three grooves 16, and three inner diameter finishing edges 161. The structures of these modified examples can also obtain the same effects as those of the above-described embodiment.

[0069] like Figure 8 As shown, in the axial direction, the step portion 613 is located closer to the cut portion 31 than the boundary between the cut portion 31 and the complete tooth portion 32 , but may also be located at the same position as the boundary between the cut portion 31 and the complete tooth portion 32 .

Claims

1. An extrusion tap, which plastically deforms the bottom hole of a workpiece to form an internal thread, characterized in that: The extrusion tap includes: An external thread portion having a complete thread portion and a cut-in portion which is continuously arranged with the complete thread portion and has a smaller diameter toward the front end; a groove arranged parallel to the axis across the full thread portion and the cut-in portion in a manner to cut off the thread teeth of the external thread portion; and An inner diameter finishing blade is provided in the cutting portion and the complete thread portion along the opening end of the groove on the side opposite to the rotation direction of the extrusion tap, and is used to cut and remove the top portion of the thread teeth of the internal thread. In the inner diameter finishing blade, when the distance from the axis of the screw forming tap is defined as the height of the inner diameter finishing blade, the height of the cutting portion side is lower than the height of a portion corresponding to the frontmost thread of the full thread portion.

2. The extrusion tap according to claim 1, characterized in that: In the inner diameter finishing blade, a step portion having a height on the cutting edge side being lower than that on the full thread portion side is provided between the thread thread at the leading end of the full thread portion and the cutting edge portion.

3. The extrusion tap according to claim 1, characterized in that: The inner diameter finishing blade is provided with an inclined portion whose height decreases from the thread crest at the front end of the full crest portion toward the front end side of the cutting portion.

4. The extrusion tap according to claim 1, characterized in that: The inner diameter finishing edge is provided with at least an inverted tapered shape whose height decreases from a portion corresponding to the thread crest at the front end of the full crest portion toward a rear end side.

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