JP2004330387A - Tap for screw cutting and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tap for screw cutting which realizes "burrless screw machining" without generation of burrs by slightly remodeling a new tap on the market. <P>SOLUTION: In this tap for screw cutting, a final shape of a female screw is machined by a non-synchronous system in which feed of the tap is not synchronized with rotation of a main shaft to perform screw machining within a mold of a progressive press die. A round chamfering surface 6g is formed by performing chamfering for a ridge line edge part of a peripheral direction in which a land surface 6a of a top part and flank surfaces 6b on both the sides are intersected for a trapezoidal blade part 6 formed on a screw thread of a biting part 3 of the tap. As a result, the "burrless screw machining" without generation of burrs (hair-like burrs) is realized on a machining surface of a workpiece. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a tap for thread cutting for machining a final shape of a female screw in a die such as a progressive press die, and a method for producing the tap.
[0002]
[Prior art]
A tap is generally used as a tool for machining a female screw on a work material. FIGS. 3 (a) and 3 (b) to FIG. 5 show the shape of a tap currently commercially available and the detailed structure of a blade portion thereof. In the figure, 1 is a shank for attaching a tap to a tap holder, 2 is a threaded portion, 3 is a biting portion, 4 is a completely threaded portion, and 5 is an axial direction so as to form, store and discharge chips and form cutting edges. Are formed at a plurality of positions (three positions in the illustrated example) on the circumference of the screw portion 4, and the bite portion 3 and the complete screw portion 4 have trapezoidal blade portions (threads) divided by the groove portion 5. 6) is formed.
[0003]
Here, for each of the trapezoidal blades 6, the top of the thread is referred to as a land surface 6a, and the left and right side surfaces of the land surface 6a are referred to as flank surfaces 6b, and the front and rear ends of the blade 6 divided by the groove 5 are cut. A blade 6c and a back blade 6d are formed. The commercially available new tap also has a sharp edge on the circumferential ridge line 6e (see FIG. 5) where the land surface 6a and the left and right flank surfaces 6b intersect.
The principle of thread cutting by the above tap is well known, and the blades 6 arranged on the biting portion 3 by cutting and rotating the tap share the predetermined cutting amount to cut the female screw. The whole forms a complete thread of the internal thread. On the other hand, the completely threaded portion 4 does not cut in principle, but engages with the thread of the internal thread cut by the biting portion 3 and plays a role of guiding the tap itself by its self-propelled action.
[0004]
On the other hand, tapping methods to cut female threads using taps are generally hand-operated by tapping, dedicated tapping machines, or machined by attaching to machine tools (lathes, machining centers, etc.). In addition, in order to manufacture parts with screw holes (for example, terminal fittings of circuit breakers) using progressive press dies, taps are provided in the dies, and a series of punching, drawing, and bending by the dies. Tapping in a mold is also practiced in combination with the above processing steps.
In addition, the tapping by manual operation is usually performed by sequentially using a set of three taps of a first tap, a second tap, and a third tap. The dedicated tapping machine is equipped with a synchro feed mechanism, and the threading is performed by completely synchronizing the rotation of the spindle and the feed pitch of the taps (synchro method).
[0005]
On the other hand, in the equipment that performs tapping in the progressive press die as described above, tapping is performed in accordance with the punching, drawing, and bending processes and the tact, so that the press die is moved up and down. The power is converted to rotational motion by a gear mechanism or the like to rotate the main shaft of the tap, and the bite of the tap to (work) is pressurized by another compression spring, and the subsequent tap feed is It adopts a system (non-synchro system) that performs by self-propelled action.
FIGS. 6 and 7 are explanatory views of the tapping method in the above-mentioned mold, where 7 is an upper die of a progressive press die, 8 is a lower die, and 9 is a punching, drawing, and bending process equipped on the press die. (Die set), 10 is a tap holder provided in the press die in parallel with the processing unit 9, 11 is a cutting tap, and 12 is a tap for pressing the tap 11 when the die is closed. A compression spring, in which a tap 11 for cutting a screw is attached to the tap holder 10, and punching and drawing are performed while pitch-feeding 13 (for example, a copper plate material) fed into the die according to the vertical movement of the press die. In parallel with the bending, the tap 11 is rotated and fed to the hole 13 having the prepared hole 13a by the above-mentioned non-synchronous feeding method to perform tapping.
[0006]
On the other hand, with regard to taps for thread cutting, various ideas have been proposed by tool manufacturers for the purpose of prolonging tool life, and as an example, the first and second taps of hand taps have been proposed. Also known is a chamfered edge at both ends of the trapezoidal blade at the biting portion to avoid chipping of the blade and partial wear of the edge caused by stress concentration during screw cutting and to improve the life of the tap. However, for taps of the type that cuts to the final shape of the internal thread with one tap, the trapezoidal blade portion of the thread is sharply polished as shown in FIGS. 3 to 5. Is sold as a commercial product.
[0007]
[Patent Document 1]
Japanese Utility Model Publication No. 60-67821 [0008]
[Problems to be solved by the invention]
By the way, a commercially available tap is mounted in the progressive press die described in FIG. 6 and FIG. 7, and the non-synchro system (rotation of the tap is performed by power, and feed is performed by the self-propelled action of the tap screw). When tapping is carried out at, a phenomenon that many whisker-like burrs (about 15 to 20 μm in thickness) cut off along the direction of tapping on the processed surface are observed.
Moreover, if the burrs formed on the threaded surface are left as they are, the terminal screws cannot be smoothly screwed into the screw holes of the product (for example, the terminal fitting of the circuit breaker), and the circuit breaker will cause a short circuit accident due to the burrs falling off. Since there is a possibility that burrs formed on the threaded surface of the work material must be removed as a post-process. In order to remove burrs, various methods such as double tapping, barrel polishing, electric discharge machining, etching, manual removal work, etc. can be used, but any of these methods requires extra equipment and processes for removing burrs. Increases the processing cost.
[0009]
Based on this, the inventors and others tried to find a measure to prevent burrs from being generated by tapping, and remodeled a commercially available new tap by changing the cutting edge rake angle of the cutting edge at the biting portion and the relief shape of the land surface in various ways. Further, cutting tests were attempted by changing tap processing conditions such as the spring pressure of an urging spring for pressing the tap against the work material, but none of them showed a sufficient improvement in burr generation. We also considered incorporating a tap-only synchro feed mechanism in the press die, but it was difficult to achieve the tact matching between punching, drawing, bending and tapping with the press die, and the overall equipment and structure It is not realistic due to problems such as complexity.
[0010]
On the other hand, the inventors investigated the cause of burr generation due to tapping in the above-described mold under the theme of reducing burr of tapping, and it was found that the cause was as follows. . That is, in the first half of the tapping for feeding the tap in the forward rotation, the sharp edge of the ridge line 6e extending in the circumferential direction from the cutting edge 6c of the blade portion 6 described in FIGS. 3 to 5 along both side edges of the land surface 6a. Bites into the work surface of the work material, roughens it into an uneven surface, and when the tap is reversely rotated in the latter half of tapping, the convex portion of the work surface is scraped off by the back blade 6 d of the blade portion 6, whereby the work surface A whisker-like burr occurs on the surface. By the way, when the tap is stopped at the descending point where the tap is forwarded, in this state, although the processed surface is roughened unevenly, no burrs are observed. In the tapping method in the mold described with reference to FIGS. 6 and 7, the biasing spring 12 (see FIG. 7) presses the tap 11 in the axial direction during the screw cutting, and the rotation of the tap is also performed by a special tapping. Severe tapping conditions, such as high-speed rotation compared to a machine, are also considered to be one of the factors that roughen the machined surface.
[0011]
Therefore, an object of the present invention is to provide a thread cutting that can realize “burr-less screw processing” without burr generation by slightly modifying a new tap on the market based on the investigation and consideration of the cause of burr generation described above. And a method of manufacturing the same.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, as in a processing facility for tapping in a die such as a progressive press die, the feed of the tap is not synchronized with the rotation of the spindle, and the final thread of the female screw is not synchronized. For a screw cutting tap for processing the shape, a ridge edge in the circumferential direction where the land surface on the top and the flanks on both sides intersect with the trapezoidal blade formed on the thread at the biting part of the tap An R-chamfered surface is formed (claim 1), and practically, it can be carried out in the following manner.
(1) The R-chamfered surface is formed only in the cutting edge side region of the blade portion (claim 2).
[0013]
(2) The R-chamfered surface is formed only in the back blade side region of the blade portion (claim 3).
(3) The R-chamfered surface is formed on both the cutting edge side and the back edge side of the blade portion.
As described above, by rounding corners at both ends of the trapezoidal blade at the biting portion of the tap (the circumferential ridge line where the land surface and the flank intersect), burrs on the machined surface are greatly reduced. Be improved. That is, by forming an R chamfered surface on the top side edge (ridge line portion) of the cutting edge side region of the blade portion, the cutting blade roughens the processed surface in the first half (forward rotation feed) of tapping. Nothing. On the other hand, if the R chamfer is formed in the region on the back blade side of the blade portion, the second half of the tapping process in which the tap is rotated in the reverse direction and the tap is pulled out even if the roughened surface is formed in the process of forward rotation of the tap. As a result, the back edge does not cut the convex portion of the processing surface, and as a result, no burr is generated on the processing surface. Thus, for the trapezoidal blade portion of the thread formed at the biting portion of the tap, the R chamfered surface is formed on either the cutting edge side or the back edge side, or on both the cutting edge side and the back edge side. By doing so, burr generation can be prevented. This has been confirmed from the cutting test of the test tap actually performed by the inventors.
[0014]
In addition, as a method of forming the above-mentioned chamfered surface on the tap, in the present invention, a commercially available new tap is modified by applying the following method.
That is, abrasive grains are blasted on the peripheral surface of the new tap to form an R-chamfered surface on the blade portion. In particular, when the R-chamfered surface is formed only on one of the cutting edge side and the back edge side of the blade portion as described in the above items (1) and (2), the non-chamfered region of the new tap is masked. Then, a method of blasting abrasive grains on the peripheral surface of the tap to form an R-chamfered surface on the blade portion (Claim 6), or after blasting abrasive grains on the entire peripheral surface of the new tap, a predetermined R-chamfered area And a method of re-polishing the remaining area (claim 7) is applied.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an enlarged cross-sectional view along the axial direction of a trapezoidal blade portion 6 formed on a biting portion 3 of a tap, and FIG. 2 is an explanatory diagram of a processing method for forming an R chamfer surface on a new tap. In each drawing, the same reference numerals are given to the portions corresponding to FIGS. 3 to 5 and the description thereof is omitted.
That is, in the tap of the embodiment shown in FIG. 1, the top land surface 6 a of the thread and the flanks on both sides of the trapezoidal blade portion 6 (see FIGS. 3 and 4) formed on the biting portion 3 of the tap. An R-chamfered surface 6g is formed on a circumferential ridgeline intersecting with the surface 6b. The method for forming the round chamfered surface 6g will be described later.
[0016]
Then, the tap manufactured by chamfering as described above was attached to the progressive press die described in FIG. 6 as a test tap, and the inside of the die was tapped to greatly reduce the occurrence of burrs on the processed surface. It was confirmed that it was possible. In this case, as the test tap, a round tapping surface 6g formed only in the cutting blade side region of the blade portion 6, a round tapping surface formed only in the back blade side region, and both the cutting blade side and the back blade side are used. When cutting tests were performed by preparing three types formed in the above-mentioned region, it was found that any of the three types had a large effect in suppressing the generation of burrs.
This effect is presumed to be due to the following reasons. That is, according to the analysis of the cause of the burr generation described above, by forming the R chamfered surface 6g on the cutting edge side of the blade portion 6, the cutting edge 6c makes the processed surface uneven in the first half (forward rotation feed) of tapping. No roughening. That is, the projections on the processed surface that cause burrs are not formed. Further, if the round chamfered surface 6g is formed in the back blade side region of the blade portion 6, even if the roughened surface is formed in the processing surface in the forward rotation feed process of the tap, the reverse rotation of the tap is performed in the process of the reverse rotation of the tap. The back blade does not cut the convex portion of the processing surface, and as a result, no burr occurs.
[0017]
Further, the chamfer amount on the above-mentioned round chamfered surface 6g is suitably about several μm to several tens μm.
In addition, according to the test tap, the tapping was repeatedly and continuously performed, and the durability (life) was examined. According to the result of the R chamfering, the tapping of the tap disappeared. The service life was extended by 2 to 5 times in comparison.
Next, a description will be given of a tap remodeling method implemented to form the R chamfered surface 6g on the tap with reference to FIG. That is, as shown in FIG. 2, a commercially available new tap (as described in FIGS. 3 to 5, the new tap has a sharp edge at the ridge of the top side edge of the blade 6). The compressed air 15 containing the abrasive grains 14 is blown from the air gun 13 to the peripheral surface of the tap 11 while rotating the tap 11 around the axis, and the air gun 13 is arranged on the side of the tap 11. 6 g of the R-chamfered surface shown in FIG. The chamfer amount was adjusted by the blast time.
[0018]
In the case where the R chamfered surface 6g is formed only on one of the cutting edge side region and the back edge side region of the blade portion 6 as described above, the non-chamfered region is masked in advance and the same as above. 2 or a method of blasting the entire area of the tap as shown in FIG. 2 and then re-polishing the non-chamfered area using a grindstone while leaving the specified chamfered area.
[0019]
【The invention's effect】
As described above, according to the present invention, the tap feed is formed on the thread of the biting portion of the tap in the thread cutting tap for processing the final shape of the internal thread in a non-synchronized manner in which the feed of the tap is not synchronized with the rotation of the main shaft. With respect to the trapezoidal blade portion, by forming an R chamfered surface at a circumferential ridge edge portion where the land surface at the top and the flank surfaces on both sides intersect, no burr is generated on the machined surface of the work material. This eliminates the need for an extra step of removing burrs generated on the machined surface as a post-processing step, thus reducing costs and reducing the cost. The effect of significantly extending the life of the tap was also obtained.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view in the axial direction of a tap blade portion according to an embodiment of the present invention. FIG. 2 is an explanatory view of a blasting method for forming an R-chamfered surface on the tap in FIG. 4A and 4B are side and end views of the entire tap, respectively. FIG. 4 is a sectional view taken along line XX in FIG. 3 and FIG. 5 is a partially enlarged view of FIG. Schematic configuration diagram of a progressive press die equipped with a tap in the die [FIG. 7] Enlarged view of the tap unit portion in FIG. 6 [Description of reference numerals]
2 Tap screw part 3 Tap biting part 4 Complete screw part 5 Groove part 6 Trapezoidal blade part 6a Land surface 6b Frank surface 6c Cutting blade 6d Back blade 6g R chamfered surface

Claims (7)

In the tap for thread cutting, the final shape of the internal thread is machined in a non-synchronous manner in which the feed of the tap is not synchronized with the rotation of the spindle.
For the trapezoidal blade formed on the thread of the biting part of the tap, a round chamfered surface is formed at the ridge edge in the circumferential direction where the land surface at the top and the flanks on both sides intersect. Tap for thread cutting. The tap according to claim 1, wherein the R-chamfered surface is formed only in a cutting edge side region of the blade portion. The tap for screw cutting according to claim 1, wherein the round chamfered surface is formed only in a region on the back blade side of the blade portion. The tap for screw cutting according to claim 1, wherein the R-chamfered surface is formed in a region on the cutting edge side and the back edge side of the blade portion. The method for manufacturing a tap for screw cutting according to claim 1, wherein abrasive grains are blasted on a peripheral surface of the new tap to form an R-chamfered surface on a blade portion. The screw according to any one of claims 2 or 3, wherein, after masking a non-chamfered area of the new tap, an abrasive is blasted on a peripheral surface of the tap to form an R chamfered surface on the blade portion. How to make taps for cutting. 4. The screw cutting device according to claim 2, wherein after blasting the abrasive grains on the entire peripheral surface of the new tap, the remaining region is polished while leaving the R chamfered region of the blade portion. 5. How to make taps.

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