JP2009255211A - Female screw machining tool and female screw machining method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a female screw machining tool and a female screw machining method using it, improving a female screw accuracy, and providing a long service life for the female screw machining tool by improving dischargeability of cutting chips, and reducing a load applied to the female screw machining tool when machining the female screw by the female screw machining tool. <P>SOLUTION: A multi-tap 1 includes an end mill section 10, a tap section 20, a shank section 30, a coolant supply hole 40, and a discharge groove 50 of which the groove bottom diameter W has slope that becomes gradually smaller toward the shank section 30 from an end of the end mill section 10. A center of the end of the end mill section 10 retracts toward a base end part side of the multi-tap 1 in relation to a circumferential edge part at the tip end of the end mill section 10, and the end surface (end cutting edge 12) of the end mill section 10 has a shape (recess shape) that is inclined toward the center from the circumferential edge part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a female thread machining tool and a thread machining method using the same, and more specifically, processing a pilot hole and a female thread (tapping) on a material (work) on which a cast hole is formed. The present invention relates to a so-called multi-tap configuration technique for performing in a process.

2. Description of the Related Art Conventionally, in an internal thread machining tool, an end mill blade that performs prepared hole processing on a workpiece to be processed, and a thread cutting blade that performs internal thread processing on a prepared hole formed by the end mill blade are provided. A technique is widely known in which, when machining, the feed amount per rotation of the female thread machining tool is the same as the screw pitch, and the female thread machining is performed simultaneously while making a pilot hole.
In addition, in order to reduce the cutting resistance when performing female threading using the female threading tool as described above, there is a technique in which a core hole is previously provided in a workpiece formed by casting as a pretreatment for female threading. Widely used.

However, in view of practicality, high accuracy is generally not required for the hole diameter and the hole position in order not to increase the burden of maintaining the accuracy of the punched hole in the casting process.
For this reason, when female threading is performed on the workpiece, it is necessary to use a separate special device such as a floating holder to hold the female threading tool and adjust the position with respect to the core hole. Furthermore, since the machining allowance increases due to the draft, there is a restriction that it can be applied only to a shallow cast hole. In such a case, it is necessary to form the workpiece by a high-precision casting method such as an aluminum die casting method, and to increase the position accuracy of the core hole, which increases the burden of maintaining the accuracy of the core hole. .

  In addition, when a floating holder or the like is not used as described above or when a casting method such as an aluminum die casting method is not used, the positional deviation between the position of the formed hole and the planned processing position of the female screw is within an allowable range. May be exceeded. When such a misalignment occurs, the female thread machining tool follows the cast hole, so that a large lateral load is applied to the female thread machining tool, so that the misalignment between the center position of the screw and the center position of the planned machining position occurs. There is a possibility that the position of the so-called female screw is poor. Furthermore, there is a possibility that the internal thread machining tool may be broken due to the lateral load.

As a means for solving the above problems, a technique such as Patent Document 1 shown below is disclosed.
In Patent Document 1, in a female thread machining tool having a biting portion whose crest diameter gradually decreases toward the tip and a complete crest continuous with the crest, a screw portion is provided below the tip surface of the biting portion. By forming the first cutting edge (end mill blade) for drilling, even if the axial center of the punched hole of the workpiece is misaligned, it is corrected by the first cutting edge formed on the front end surface of the biting section. However, a technique that enables female threading is disclosed.
Further, in Patent Document 1, a second blade portion (reamer blade) for finishing an inner diameter is formed by forming a length of one pitch or more on a part of the outer periphery of the complete mountain portion at the time of female thread processing. A technique that enables the inner diameter of the female thread to be finished within a tolerance is disclosed.

However, even the technique disclosed in Patent Document 1 can only be applied to machining a punched hole having a predetermined positional accuracy (for example, the amount of misalignment between the punched hole and the planned processing position is limited to 0.4 mm or less). Is a problem. Furthermore, when the positional accuracy cannot be ensured, it is necessary to reduce the diameter of the core hole. When the diameter of the core hole is reduced in this way, the lateral load applied to the internal thread machining tool increases. Therefore, there is a possibility that the internal thread machining tool may be broken, such as chipping of the first blade portion (end mill blade), or a female thread accuracy defect such as a taper is formed at the mouth of the female thread. there is a possibility. In addition, there is a possibility that the internal thread processing tool may be broken by clogging the thread portion (thread cutting blade) of the chip screw thread machining tool generated when the pilot hole is opened by the first blade section (end mill blade). is there.
In addition, chips generated as described above may enter between the second blade portion (reamer blade) and the internal thread of the female screw after processing, and may damage the thread surface of the thread portion. May cause inaccuracy.
JP-A-11-309624

  The present invention has been made in view of the circumstances as described above, and improves the chip discharge performance and reduces the load applied to the female thread machining tool when performing female thread machining with the female thread machining tool. It is an object of the present invention to provide a female thread machining tool capable of improving the accuracy of the above, and extending the life of the female thread machining tool, and a thread machining method using the same.

The internal thread machining tool according to claim 1, wherein a first blade portion for performing a pilot hole machining on a pre-formed hole formed in a workpiece is provided at a tip portion, and a pilot hole formed by the first blade portion. A second blade portion for subjecting female threading to the first blade portion is continuously provided coaxially with the first blade portion, a shank portion is provided at the base end portion, and the shaft extends from the shank portion to the tip of the first blade portion. A coolant supply hole penetrating in the direction, a female thread machining tool providing a spiral discharge groove on the outer peripheral portion over the entire axial length of the second blade portion from the tip of the first blade portion, The diameter of the groove bottom has a gradient that gradually decreases from the tip of the first blade portion toward the shank portion, and the center of the tip of the first blade portion is the peripheral edge of the tip of the first blade portion. And the distal end surface of the first blade portion is directed from the peripheral end toward the center. And it has a shape that inclines.
According to this, the cut generated when machining the pilot hole of the female thread using the female thread machining tool, depending on the diameter of the discharge groove formed in a spiral shape and the groove bottom formed in a reverse taper shape. Waste can be efficiently discharged outside the workpiece (cast hole). In this way, the chip discharge performance can be improved, so that the machining accuracy of the female thread by the first blade portion and the second blade portion of the female thread machining tool can be improved and the life of the female thread machining tool can be increased. .
Further, when the female thread machining tool comes into contact with the core hole, the concave shape at the tip of the first blade portion makes it easy to bite into the surface of the core hole, thereby reducing the lateral load on the female thread processing tool. Therefore, even when the position accuracy of the core hole is poor, the female thread machining tool does not follow the core hole, so that the formation position shift of the pilot hole can be prevented, and the position accuracy of the internal thread can be improved.

As described in claim 2, in the internal thread machining tool according to the present invention, it is preferable that the gradient of the diameter of the groove bottom from the tip is −1/100 or more and less than 0.
According to this, while ensuring the discharge | emission property of the said female thread processing tool, the intensity | strength, especially the intensity | strength with respect to a lateral load can also be ensured, and the lifetime improvement of the said female thread processing tool can be aimed at.

According to a third aspect of the present invention, in the internal thread machining tool according to the present invention, it is preferable that the watermark angle of the bottom blade of the first blade portion is 5 degrees to 15 degrees.
According to this, the strength of the blade provided at the tip of the first blade portion can be ensured while ensuring the biting property of the first blade portion with respect to the punched hole, and the first blade portion can be prevented from chipping. The service life of the tool can be improved, and as a result, the service life of the internal thread machining tool can be increased.

As described in claim 4, it is preferable that the internal thread machining tool according to the present invention is configured such that the minimum circumference of the second blade portion is larger than the maximum circumference of the first blade portion.
According to this, the internal diameter of a female screw can be finished with the 2nd blade part, and the precision of a female screw can be improved. Moreover, the internal cutting edge cutting blade provided in the conventional internal thread machining tool is not required, and the internal diameter of the internal thread of the internal thread can be reduced by inserting a chip between the internal cutting edge cutting blade and the internal thread in the middle of processing. It won't hurt.

As described in claim 5, the internal thread machining method according to the present invention uses a female thread machining tool according to any one of claims 1 to 4 to form a cast formed in advance on a workpiece. A method of machining a female screw, in which a female screw is subjected to a pilot hole machining and a female screw machining with respect to a punched hole, and the cast hole has a linear chamfered portion at an opening thereof.
According to this, it becomes easy for the female thread machining tool to bite against the chamfered portion of the cast hole formed in a linear shape, and the lateral load applied to the female thread machining tool can be reduced.

According to the sixth aspect of the present invention, in the internal thread machining method according to the present invention, the chamfering angle of the chamfered portion is set to 40 degrees to 60 degrees, and the diameter of the chamfered portion is set according to the accuracy of the cast hole. It is preferable to adjust.
According to this, even when the maximum misalignment occurs between the formation position of the core hole and the planned processing position of the female screw, it is possible to ensure the necessary chamfering and effective screw length for the female screw to be formed. .

According to the present invention, it is possible to provide a female thread machining tool capable of improving the precision of the female thread and extending the life of the female thread machining tool, and a thread machining method using the same.
Furthermore, since the coolant supplied through the coolant supply hole is distributed well to the first blade portion and the second blade portion through the discharge groove, it is possible to improve chip dischargeability, and the first blade portion and the second blade portion. Since the lubricity and cooling performance can be improved, high-speed rotation is possible and the processing time can be shortened.

  Below, with reference to FIGS. 1-5, the whole structure of the multi tap 1 which is one Embodiment of the internal thread machining tool which concerns on this invention is demonstrated.

  The multi-tap 1 is a female thread machining tool that performs a pilot hole machining of the female screw 4 and a female thread machining of the female screw 4 to a cored hole 3 formed in advance in the workpiece 2. As shown in FIG. 1, the multi-tap 1 mainly includes an end mill part 10, a tap part 20, a shank part 30, a coolant supply hole 40, a discharge groove 50, and the like.

  The workpiece 2 is an embodiment of the workpiece according to the present invention, and is a member that is cast and formed by a casting method. The workpiece 2 is a member such as an engine cylinder block or cylinder head made of an aluminum alloy, for example. In the present embodiment, machining of the female screw 4 by the multi-tap 1 is performed on a predetermined portion of the work 2.

  The cast hole 3 is an embodiment of the cast hole according to the present invention, and is a hole formed using a cast pin or the like in the casting process of the workpiece 2. Further, the diameter of the cast hole 3 is smaller than the diameter d2 of the female screw 4 processed by the multi-tap 1 and is a hole provided at a predetermined position of the workpiece 2 in order to reduce cutting resistance at the time of processing by the multi-tap 1. Yes, with a predetermined accuracy (for example, as shown in FIG. 2, the amount of misalignment D = 0.7 mm or less between the formation position A of the cast hole 3 and the planned processing position B of the female screw 4). ing.

As shown in FIG. 2, in the present embodiment, the cast hole 3 has a chamfered portion 3 a at the opening. The chamfer angle (θ2 shown in FIG. 2) is 40 degrees, and the chamfered shape (θ1 shown in FIG. 2) in a cross-sectional view is a linear shape of 100 degrees. Further, as shown in FIGS. 2 and 3, the chamfered diameter d1 of the chamfered portion 3a is larger than the diameter d2 of the female screw 4 to be processed, and after processing the female screw 4, a sufficient chamfered portion is formed around it. The size is set to remain. Specifically, the chamfered diameter d1 of the chamfered portion 3a is a value obtained by adding twice the maximum value of the misalignment amount D and a predetermined margin to the diameter d2 of the female screw 4.
In addition, the cast hole which concerns on this invention is not limited to the cast hole 3 of this embodiment, In chamfering part 3a, chamfering angle (theta) 2 and chamfering diameter d1 which can ensure sufficient chamfering amount after the process of the internal thread 4 are set. What is necessary is just to have. Further, from the viewpoint of reducing the lateral load applied to the multi-tap 1, the chamfer angle θ2 is preferably 40 ° to 60 ° (that is, the chamfered shape θ1 is 60 ° to 100 °), and is a female screw to be processed. From the viewpoint of securing the effective screw length and the chamfering amount of 4, the chamfering diameter d1 of the chamfered portion 3a is added to the diameter d2 of the female screw 4 by twice the maximum value of the misalignment amount D and a predetermined margin. (For example, when processing a female screw 4 having a nominal thread size of M8 × 1.25 and a screw hole diameter of 6.8 mm, it is preferably about 8 mm + 0.7 mm × 2 + 0.2 mm = 9.6 mm).
That is, it is preferable to adjust the chamfering diameter d1 of the chamfered portion 3a according to the positional accuracy of the cast hole 3 or the like.

The end mill portion 10 is an embodiment of the first blade portion according to the present invention, and is a portion that is provided at the distal end portion of the multi-tap 1 and performs a pilot hole machining of the female screw 4 on the core hole 3. . As shown in FIGS. 1 and 4, the end mill portion 10 is formed as an end mill blade having a plurality of blades (three blades in this embodiment), and mainly includes back taper portions 11, 11, 11, bottom blades 12, 12.12, cutting blades 13, 13, 13, discharge grooves 51, 51, 51, and the like.
As shown in FIGS. 1 and 4, the back taper portion 11 is formed in a spiral shape having a constant twist angle on the outer peripheral portion of the end mill portion 10. The bottom blade 12 protrudes in a radial direction from a center C arranged at a position retracted toward the base end side of the multi-tap 1 with respect to the peripheral end portion of the bottom portion at the bottom portion (tip surface) of the end mill portion 10. Is formed. Further, the bottom blade 12 is formed so as to be inclined by an angle θ from the peripheral end portion (corner portion) of the bottom portion in the end mill portion 10 toward the center C of the bottom portion (from the bottom to the top in the drawing). Yes. The cutting edge 13 is formed in an acute angle at a corner portion where the back taper portion 11 and the bottom blade 12 are continuous. Thus, in the end mill part 10, the bottom blade 12 and the cutting edge 13 form a so-called end mill blade.

Further, the discharge grooves 51, 51, 51 are outer peripheral portions of the end mill portion 10, and are formed between the end mill blades (strictly speaking, the bottom blades 12, 12, 12 and the cutting blades 13, 13, 13). It is a spiral groove provided so as to be continuous with the chip pockets 15, 15, 15.
As described above, in the end mill portion 10, the cutting edge 13, 13, 13 bites the surface of the workpiece 2 (the chamfered portion 3 a of the cast hole 3), and the bottom blade 12, 12, 12 cuts the workpiece 2. The pilot hole 5 is formed. Then, the cut chips are discharged through the discharge grooves 51, 51, 51 to the discharge grooves 52, 52, 52 provided on the outer periphery of the tap portion 20.

The tap portion 20 is an embodiment of the second blade portion according to the present invention. The tap portion 20 is coaxially connected to the end mill portion 10 in the multi-tap 1, and the diameter of the prepared hole 5 formed by the end mill portion 10 is set. While expanding, it is a site | part which performs the internal thread processing of the internal thread 4 with respect to the said prepared hole 5. FIG. As shown in FIG. 1, the tap portion 20 is formed as a so-called eccentric relief tap having an acute-angled thread cutting blade 21 over its entire length, and mainly includes the thread cutting blade 21, the discharge grooves 52, 52, 52, and the like. It has.
As shown in FIG. 1, the thread cutting blade 21 is formed over the entire length of the tap portion 20. As shown in FIG. 5, the diameter 21 b of the valley portion 21 a that is the minimum circumference of the thread cutting blade 21 is the maximum circumference drawn by the bottom blades 12, 12, and 12 of the end mill portion 10 (the two-dot chain line circle shown in FIG. 4). The outer diameter 12a is larger than the outer diameter 12a, and the lower hole 5 formed by the end mill 10 is widened by the valley 21a of the thread cutting blade 21 to form the lower screw hole 6, thereby reducing the diameter. While expanding, the internal diameter finishing of the internal thread 4 is performed.
According to this, the internal diameter of the female screw 4 can be finished satisfactorily, and as a result, the accuracy of the female screw 4 can be improved. In addition, a conventional internal thread machining cutting blade or the like provided in a conventional female thread machining tool is not required, and a chip is inserted between the internal diameter machining blade and the internal thread 4 in the middle of the machining process. No damage to the inner diameter of the.

Further, the discharge grooves 52, 52, 52 are spiral grooves formed on the outer peripheral portion of the tap portion 20 over the entire length of the tap portion 20, and are provided so as to divide the thread cutting blade 21. The discharge grooves 52, 52, 52 are provided so as to be continuous with the discharge grooves 51, 51, 51, respectively.
In this way, the chips cut by the thread cutting blade 21 are discharged through the discharge grooves 52, 52, 52. Further, the chips cut by the end mill 10 as described above also pass through the discharge grooves 51, 51, 51, and are discharged out of the work 2 through the discharge grooves 52, 52, 52. In the present embodiment, as shown in FIG. 1, the discharge grooves 52, 52, 52 are formed beyond the tap portion 20 in the axial direction of the multi-tap 1, and when processing the deep female screw 4. The discharge groove 52, 52, 52 can also be discharged out of the work 2.

  The shank portion 30 is an embodiment of the shank portion according to the present invention, and is provided at the base end portion of the multi-tap 1, and the base end portion 31 of the shank portion 30 is formed in a substantially rectangular cross section. The base end 31 is a part that is gripped and fixed to a machining center (not shown) or a spindle of a machine tool. As shown in FIG. 1, the shank portion 30 is provided at a position retracted from the tap portion 20 by a predetermined dimension so as to have a length that can be sufficiently grasped and fixed by the machining center or a spindle of a machine tool. Yes.

The coolant supply hole 40 is an embodiment of the coolant supply hole according to the present invention, and is a hole that is provided over the entire length of the multi-tap 1 in the axial direction and supplies coolant to the workpiece 2 to be processed. This coolant is used to remove chips generated when machining the internal thread 4 by the multi-tap 1 from the work site of the workpiece 2 (that is, in the vicinity of the cast hole 3) and to cool the tip of the end mill 10. Is. As shown in FIG. 1, the multi-tap 1 is provided through the center of rotation of the multi-tap 1 from the shank part 30 through the tap part 20 and the end mill part 10 to the center C of the bottom part of the end mill part 10.
Here, the high-pressure coolant supplied through the coolant supply hole 40 is fired from the center of the bottom of the end mill portion 10 toward the part to be processed of the workpiece 2, and from the tip pocket 15 (see FIG. 4) of the end mill portion 10. It flows along the discharge grooves 51 and 52. With this coolant, chips of the work 2 generated by cutting by the end mill 10 and the tap 20 are discharged.

The discharge grooves 50, 50, and 50 are one embodiment of the discharge groove according to the present invention, and are for discharging chips generated during machining of the female screw 4 by the multi-tap 1 to the outside of the workpiece 2. As shown in FIG. 1, the discharge groove 50 in the present embodiment is configured by a continuous groove including a discharge groove 51 and a discharge groove 52, and exceeds the total length of the tap portion 20 from the tip portion of the end mill 10. These outer peripheral portions are spirally provided at a predetermined twist angle (for example, 30 degrees).
These discharge grooves 50, 50, 50 are formed in a twist direction (right spiral) in which chips can be discharged in the direction opposite to the traveling direction of the multi-tap 1.

As described above, the multi-tap 1 according to the present embodiment is formed by the end mill portion 10 provided with the end mill portion 10 that performs the pilot hole processing on the punched hole 3 formed in advance on the workpiece 2 at the tip portion. A tap portion 20 for subjecting the prepared hole 5 to a female thread is continuously provided coaxially with the end mill portion 10, and an axial direction from a shank portion 30 provided at the base end portion to a bottom portion (tip end portion) of the end mill portion 10. A coolant supply hole 40 penetrating in the axial direction is provided over the entire length, and spiral discharge grooves 50, 50, 50 are formed on the outer peripheral portion from the bottom (tip portion) of the end mill 10 to the axial length of the tap portion 20. The center C of the bottom (tip) of the end mill 10 is set to a position retracted from the bottom toward the base end, and the bottom (tip) of the end mill 10 is moved from the peripheral end (corner) to the center C. Heading It is obtained by constituting the shape (concave shape recessed center portion) obliquely.
The multi-tap 1 is formed as a so-called spiral tap having the spiral discharge grooves 50, 50, 50 as described above. Thereby, the discharge performance of the chip | tip generated at the time of the process of the internal thread 4 improves. Therefore, wear of the multi-tap 1 can be reduced, chipping of the cutting edge due to chip biting can be reduced, and the life of the multi-tap 1 can be increased.
In the multitap 1, the diameter 21 b of the valley portion 21 a of the thread cutting blade 21 that is the minimum circumference of the tap portion 20 is configured to be larger than the outer diameter 12 a of the maximum circumference of the bottom blade 12 of the end mill portion 10. As a result, the inner diameter of the pilot hole 5 formed by the bottom blade 12 of the end mill portion 10 is enlarged and the inner diameter of the female screw 4 is finished by the valley portion 21a of the thread cutting blade 21 that describes the minimum circumference of the tap portion 20. Is possible. Accordingly, even when a deflection occurs in the multi-tap 1 due to a lateral load when the core misalignment amount D of the core hole 3 is large, the allowance by the thread cutting blade 21 is provided, so that the accuracy of the female screw 4 can be improved. At the same time, when finishing the inner diameter of the female screw 4, chips are not caught between the thread cutting blade 21 and the female screw 4 and the inner diameter of the female screw 4 is not damaged, and the accuracy of the female screw 4 can be improved.
In the multi-tap 1, a coating for improving lubricity is applied to the entire surface of the end mill 10 and the tap 20. This coating is made of, for example, DLC (Diamond-Like Carbon), TiCN (Titanium Carbonitride) or the like having a small friction coefficient, and is formed in an appropriate film thickness by a plasma CVD method or the like. Thereby, also when processing the internal thread 4 with respect to the workpiece | work 2 with high weldability, such as aluminum, welding is suppressed and the lifetime improvement of the multi tap 1 can be achieved.

Below, with reference to FIG. 6, the diameter W of the groove bottom of the multi tap 1 which concerns on this embodiment is demonstrated in detail. Here, the “groove bottom diameter” is the thickness of the core of the internal thread machining tool, that is, the diameter of an imaginary cone in contact with the bottom of the groove such as a bottom blade or a thread cutting blade. In the present embodiment, the diameter W of the groove bottom indicates the diameter of a virtual cone that is in contact with the bottom of the groove of the bottom blade 12 or the thread cutting blade 21.
As shown in FIG. 6A, in the conventional female thread machining tool 100, the groove bottom diameter X is formed in a tapered shape that gradually increases from the tip 110 toward the shank 120.
On the other hand, in the present embodiment, as shown in FIG. 6B, the groove bottom diameter W is formed in an inversely tapered shape having a gradually decreasing gradient from the tip of the multi-tap 1 toward the shank 30. ing. In other words, in the multi-tap 1, the female screw 4 formed by the multi-tap 1 and the multi-tap 1 (more precisely, the discharge groove) in the chip discharge direction (the direction opposite to the traveling direction of the multi-tap 1). 50) is formed to be larger.

Further, in this embodiment, the value of the gradient of the groove bottom diameter W is −1/150 (specifically, the groove bottom diameter W decreases by 1 mm as it advances 150 mm in the axial direction from the bottom of the end mill 10. Is set).
In addition, the value of the gradient of the diameter W of the groove bottom according to the present invention is not limited to that of the present embodiment, and in particular, the discharge of chips generated by cutting of the end mill portion 10 can be ensured, and the multi-tap 1 As long as the strength of the multi-tap 1 is sufficiently secured, specifically, it may be within a range not exceeding −1/100, which is the strength critical point of the multi-tap 1. Moreover, when the value of this gradient exceeds -1/100, it turns out that the intensity | strength with respect to the lateral load of the multi tap 1 falls rapidly, and from the viewpoint of intensity | strength, it is a gradient larger than -1/100 (that is, A value less than -1/100) is not preferable.

As described above, the diameter W of the groove bottom of the multi-tap 1 according to the present embodiment is formed in an inversely tapered shape having a gradually decreasing gradient from the tip of the multi-tap 1 toward the shank part 30. is there.
According to this, when machining the female screw 4 by the multi-tap 1, chips that are cut by the bottom blades 12, 12, 12 of the end mill 10 are discharged from the distal end side to the proximal end side of the multi-tap 1. It becomes easy to discharge through the grooves 50, 50, 50. Therefore, the chip discharging property of the multi-tap 1 can be improved, the internal thread 4 is damaged due to the biting of the chips into the bottom blades 12, 12, 12 or the thread cutting blade 21, and the chipping or multi-cutting of the cutting edge is performed. Since breakage of the tap 1 can be suppressed, the accuracy of the female screw 4 formed using the multi-tap 1 can be improved and the life of the multi-tap 1 can be increased.
Moreover, the value of the gradient of the diameter W of the groove bottom of the multi-tap 1 according to the present embodiment is set within a range of −1/100 or more and less than 0.
According to this, the intensity | strength with respect to the lateral load is securable, ensuring the discharge property of the multi tap 1. FIG. Therefore, breakage of the multi-tap 1 can be prevented, and the life of the multi-tap 1 can be further increased.

Below, with reference to FIG.7 and FIG.8, the angle (inclination angle of a bottom blade) (theta) of the bottom blade 12 which concerns on this embodiment is demonstrated in detail. Here, the “angle θ” is an inclination angle of the bottom blade of the female thread machining tool, and is an angle formed between a plane perpendicular to the axis of the female thread machining tool and the bottom blade. As shown in FIG. 7, in the present embodiment, the angle θ is set to 15 degrees.
Note that the angle θ of inclination of the bottom blade according to the present invention is not limited to that of the present embodiment, and the bottom blade 12 has sufficient biting property to the core hole 3 and sufficient strength of the bottom blade 12. More specifically, the angle θ does not exceed 15 degrees, which is the critical critical point of the bottom blade 12, and does not fall below 5 degrees, which is the critical point of biting ability of the bottom blade 12. It may be within the range.

Further, FIG. 8 shows that when the angle θ of the inclination of the bottom blade 12 is (1) 5 degrees, (2) when it is 10 degrees, and (3) when it is 15 degrees, the female thread 4 is attached by the multi-tap 1 respectively. The lateral load applied to the multi-tap 1 during processing and the position degree of the formed screw 4 are measured.
Here, the “lateral load applied to the multi-tap 1” is a value obtained by measuring the lateral load applied to the main spindle of the machine tool to which the multi-tap 1 is attached by an appropriate measuring method, Is a value obtained by measuring an amount of misalignment between the planned processing position B of the female screw 4 and the formation position of the female screw 4 by an appropriate measuring method.
As shown in FIG. 8, the larger the angle θ, the smaller the lateral load value and the smaller the degree of position (that is, the smaller the amount of misalignment). However, if the angle θ is too large, the possibility of chipping of the bottom blade 12 becomes high (for example, the strength of the blade edge is significantly reduced at 20 degrees). That is, the inclination angle θ of the bottom blade 12 is particularly preferably in the range of 5 degrees to 15 degrees.

As described above, the center C of the bottom of the end mill 10 is disposed at a position retracted from the bottom (tip) of the end mill 10, and the bottom blade 12 of the bottom of the end mill 10 is directed from the peripheral end to the center C of the bottom. It is formed in the concave shape which inclines.
According to this, when the bottom blades 12, 12, 12 come into contact with the core hole 3, it is easy to bite the surface, and the lateral load applied to the multi-tap 1 can be reduced. Even when the accuracy of the multi-tap is relatively low, the multi-tap 1 does not follow the cored hole 3, so that it is possible to prevent the displacement of the pilot hole processing of the female screw 4, thereby improving the accuracy of the female screw 4.
Further, the angle of inclination (bottom angle of the bottom blade) θ of the bottom blades 12, 12, 12 of the end mill portion 10 is set in the range of 5 to 15 degrees.
According to this, it is possible to ensure the strength of the blade while ensuring the biting property of the bottom blades 12, 12, 12 to the cored hole 3, preventing chipping and extending the life of the bottom blades 12, 12, 12, As a result, the lifetime of the multi-tap 1 can be increased.

In the following, referring to FIG. 9, the internal thread when the internal thread 4 is processed to the cored hole 3 using the multi-tap 1 which is an embodiment of the internal thread processing tool according to the present invention. The processing process will be described.
In the present embodiment, the female screw 4 formed using the multi-tap 1 is a metric screw having a nominal thread M8, a screw pitch of 1.25 mm, and a screw under hole diameter of 6.8 mm. 5 mm, hole depth 30 mm, chamfering angle θ2 is 40 degrees, chamfering diameter d1 is 9.6 mm, and the amount of misalignment D between the formation position A of the punched hole 3 and the planned processing position B of the female screw 4 is 0.7 mm. It is.

First, as shown in FIG. 9 (a), the multi-tap 1 is fed while being rotated in a direction approaching the cast hole 3 formed in the workpiece 2. The feed amount per rotation of the multi-tap 1 is the same as the screw pitch 1.25 mm.
Then, the bottom blades 12, 12, 12 of the end mill portion 10 bite into the chamfered portion 3 a of the cast hole 3, and the cast hole 3 is cut by the bottom blades 12, 12, 12 to form the prepared hole 5. The diameter of the pilot hole 5 formed by the end mill portion 10 is smaller than the diameter of the screw pilot hole 6 of the female screw 4 to be formed, and is 6.6 mm in this embodiment.
At this time, the lateral load applied to the multi-tap 1 is reduced by satisfactorily biting the chamfered portion 3a of the cast hole 3 by the bottom blades 12, 12, and 12 formed in a concave shape. Regardless of the misalignment amount D, the lateral force applied when contacting the chamfered portion 3a is reduced, so that the pilot hole 5 can be processed at a more accurate position. At the same time, the chamfered portion 3a of the cast hole 3 has a chamfering angle θ2 of 40 degrees, and the chamfered portion 3a of the bottom blades 12, 12, and 12 is made favorable.
In addition, the diameter W of the groove bottom of the multi-tap 1 is configured to have a gradually decreasing gradient from the end mill 10 toward the shank 30, so that the cutting cut by the bottom blades 12, 12, 12 is performed. Waste is discharged well through the discharge grooves 50, 50, 50 (discharge grooves 51, 51, 51) formed in a spiral shape.

Next, as shown in FIG. 9B, when the multi-tap 1 is fed toward the workpiece 2 in a direction closer to the work 2, the thread cutting blade 21 of the tap portion 20 is formed by the bottom blades 12, 12, and 12. Bit into hole 5.
Then, a female thread is formed in the pilot hole 5 by the screw cutting blade 21, and the diameter (6.6 mm) of the pilot hole 5 is expanded to the diameter of the screw pilot hole 6 by the valley portion 21 a of the screw cutting blade 21. In the present embodiment, the diameter of the screw prepared hole 6 after being enlarged by the valley portion 21a is 6.8 mm.
At this time, since the diameter 21b of the valley 21a of the thread cutting blade 21 is configured to be larger than the outer diameter 12a of the maximum circumference of the bottom blade 12, the diameter of the pilot hole 5 is increased by the valley 21a. The inner diameter of the screw 4 is finished. Thereby, the internal diameter of the internal thread 4 can be finished satisfactorily.
In addition, the diameter W of the groove bottom of the multi-tap 1 is configured to have a gradually decreasing gradient from the end mill 10 toward the shank 30, so that the cutting cut by the bottom blades 12, 12, 12 is performed. The chips and the chips cut by the thread cutting blade 21 are discharged well through the spirally formed discharge grooves 50, 50, 50 (discharge grooves 51, 51, 51 and discharge grooves 52, 52, 52). .

  After forming a female screw having a predetermined depth, the multi-tap 1 is pulled out while being rotated in a direction away from the work 2 as shown in FIG. The feed amount per rotation of the multi-tap 1 is the same as the screw pitch 1.25 mm.

In this way, the female screw 4 as shown in FIG.
At this time, the cored hole 3 has a linear chamfered portion 3a at its opening. This makes it easier for the multi-tap 1 to bite against the chamfered portion 3a of the cored hole 3 formed in a straight shape, compared to the biting of the internal thread machining tool for the conventional R-shaped chamfer. 1 can be reduced. Further, the chamfering angle θ2 is in the range of 40 degrees to 60 degrees (40 degrees in the present embodiment), and the chamfering diameter d1 is a value corresponding to the accuracy of the core hole 3, particularly the maximum value of the misalignment amount ( In this embodiment, it is set to 9.6 mm). Therefore, even when the maximum misalignment occurs between the formation position A of the core hole 3 and the planned processing position B of the female screw, the female screw 4 to be formed is formed. Necessary chamfering and effective thread length can be secured.
As described above, in this embodiment, when machining the female screw 4 using the multi-tap 1 with respect to the cast hole 3 that satisfies the predetermined condition, the formation position of the female screw 4 and the planned machining position B are It was confirmed that the degree of position (center misalignment) was 0.4 mm or less, and the accuracy of the female screw 4 was confirmed to satisfy JIS class 1.

It is a schematic front view which shows one Embodiment of the internal thread machining tool which concerns on this invention. It is a schematic diagram which shows one Embodiment of the internal thread processing tool and cast hole which concern on this invention. It is a top view which shows one Embodiment of the core hole which concerns on this invention. It is a bottom view which shows one Embodiment of the internal thread machining tool which concerns on this invention. It is a figure which shows the diameter of the 1st blade part of the internal thread machining tool which concerns on this invention, and a 2nd blade part. The figure which shows the diameter of the groove bottom of the internal thread processing tool which concerns on this invention, (a) is the conventional internal thread processing tool (b), The internal thread processing tool which concerns on this invention. It is the EE line expanded sectional view in FIG. It is a graph which shows the relationship between the inclination-angle of the front-end | tip of the 1st blade part which concerns on this invention, the lateral load concerning a female thread machining tool, and the internal thread formed. It is a figure which shows the manufacturing process of a screw in order to use the internal thread processing tool which concerns on this invention.

Explanation of symbols

1 Multi-tap (Female thread machining tool)
10 End mill (first blade)
20 Tap part (second blade part)
30 Shank 40 Coolant supply hole 50 Discharge groove 100 Conventional female thread machining tool A Cast hole formation position B Female thread planned machining position C Center of the bottom of the end mill D Alignment amount X Conventional female thread machining tool Groove bottom diameter W Groove bottom diameter

Claims (6)

A first blade portion is provided at the tip portion to perform prepared hole processing on a pre-formed punch hole in the workpiece,
A second blade portion for subjecting a pilot hole formed by the first blade portion to a female thread is continuously provided coaxially with the first blade portion,
A shank is provided at the base end,
From the shank part to the tip of the first blade part, a coolant supply hole penetrating in the axial direction is provided,
A female thread machining tool that provides a spiral discharge groove on the outer periphery over the entire length in the axial direction of the second blade from the tip of the first blade,
The diameter of the groove bottom has a slope that gradually decreases from the tip of the first blade portion toward the shank portion,
The center of the tip end of the first blade part is retracted toward the base end side with respect to the peripheral end part of the tip end of the first blade part, and the tip surface of the first blade part extends from the peripheral end part to the center. An internal thread machining tool characterized by having a shape inclined toward the center.   2. The female thread machining tool according to claim 1, wherein a gradient of the diameter of the groove bottom from the tip is −1/100 or more and less than 0. 3.   The internal thread machining tool according to claim 1 or 2, wherein a watermark angle of the bottom blade of the first blade portion is 5 degrees to 15 degrees.   The internal thread machining tool according to any one of claims 1 to 3, wherein a minimum circumference of the second blade portion is configured to be larger than a maximum circumference of the first blade portion. Using the female thread machining tool according to any one of claims 1 to 4, a female thread for performing a pilot hole machining and a female thread machining on a pre-formed hole formed in a workpiece. A processing method,
The method of processing a female screw, wherein the cast hole has a linear chamfered portion at an opening thereof.   6. The method for machining an internal thread according to claim 5, wherein the chamfering angle of the chamfered portion is set to 40 degrees to 60 degrees, and the diameter of the chamfered portion is adjusted according to the accuracy of the cast hole. .

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