JP2007069229A - Tool for shock-plastic working metal for improving excellent fatigue-strength, and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tool for shock-plastic working and a working method with which a fatigue-strength of a corner part existing at the edge part of a metal is improved. <P>SOLUTION: In the enlarged diameter-state tool for shock-plastic working treatment, whose outer diameter is gradually enlarged from a head part 8 toward a tip end part; the tip end part 5 surface is formed as smooth curved surface and the shape of a side surface from the head part 8 to the tip end part 5 surface is formed as the enlarged diameter so as to become an exponential function-shape. At this time, the shape of the side surface 2 from the head part 8 to the tip end surface can be formed as the enlarged diameter so as to become the exponential function-shape, or can be formed so as to optimize the radius of the curvature on the tip end surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a structural member made of metal such as iron, aluminum, titanium, magnesium and alloys thereof used in automobiles, home appliances, building structures, ships, bridges, construction machines, various plants, penstocks, etc. The present invention relates to an impact plastic working tool and method for improving the fatigue strength of a corner portion of a metal end formed by shearing or the like.

  When metal (including both the base material and the parts subjected to processing such as welding and forming) is subjected to processing such as welding, pressing, cutting, and punching, and these parts are subjected to repeated loads, these processed parts Is the starting point of fatigue cracking due to the concentration of stress due to its shape and the presence of tensile residual stress, and reduces fatigue strength. Impact plastic processing methods such as shot peening, laser peening, water jet peening, hammer peening, needle peening, wire peening, and ultrasonic impact treatment have been used for the purpose of improving the durability of such parts. Yes. These impact plastic working methods impart plastic deformation by causing a tool, which is an energy medium that plastically deforms a metal structure, to collide with a workpiece.

  However, when processing corners of metal ends formed by shearing etc. using hammer peening, needle peening, wire peening, and ultrasonic impact treatment, which repeatedly strike a long and narrow bar-shaped tool, If the target position is slightly deviated, the position and reaction force of the tool and the impact plastic working device after the collision become unstable, and it is difficult to continue stable processing. Moreover, it takes much labor to manually control the position of the tool tip and the position and direction of the entire apparatus in order to maintain the collision of the tool with the corner. For this reason, in order to further improve the fatigue strength of the metal, it was necessary to devise a method and an apparatus capable of stably performing effective impact plastic working.

  For impact plastic working tools, Patent Document 1 discloses the shape and approximate curvature (about 0.5 mm to 3.0 mm) of the tool tip of ultrasonic impact treatment for the purpose of reducing the stress concentration of the metal member. ing. In the disclosed technique in Patent Document 1, based on the knowledge that the greater the amount of plastic deformation in the depth direction, the greater the introduced compressive force, the amount of plastic deformation formed by ultrasonic impact treatment, The fatigue improvement effect is related by the curvature of the tool.

  Further, Patent Literature 2 discloses a tool in which a frame portion is provided at a contact portion of a tip tool for the purpose of hitting a pile without causing lateral displacement as a pile driving tool. In the technique disclosed in Patent Document 2, the striking member covers the hitting side end portion of the pile, and therefore the striking member can be hit without being laterally displaced with respect to the pile.

  Furthermore, Patent Document 3 discloses a pneumatic tool in which a tip of a tool is rotatably attached for the purpose of driving a member having a complicated shape into another member.

  Furthermore, although it is not an impact plastic working device, the surface is formed by a plurality of continuous convex portions having a first radius of curvature and a second radius of curvature is formed from a line connecting the plurality of convex portions. A hardening roller burnishing tool is disclosed in Patent Document 4.

  Furthermore, Patent Document 5 and Patent Document 6 disclose methods for improving the fatigue strength of sheared surfaces, and Patent Document 5 discloses a method in which the amount of increase in hardness and the amount of coining is defined. Methods for defining the shot angle of shot peening and the ratio of burr height to width are disclosed.

Furthermore, as shown in FIG. 15, a tool called chisel for the purpose of hitting a metal manually is commercially available. The chisel is formed so that the front shape from the head 68 to the tip surface 65 for striking with a hammer or the like becomes wider from the middle, and the shape of the side surface is tapered from the middle. Yes.
JP 2003-113418 A JP 2002-317442 A Japanese Unexamined Patent Publication No. 8-150575 Japanese Patent Laid-Open No. 2003-145420 JP-A-6-57325 JP 2004-83927 A

  Among the disclosed technologies described above, Patent Document 1 discloses that the effect of improving the fatigue strength is high when the curvature radius of the curved surface at the tip of the tool is about 0.5 mm to 3.0 mm for the main purpose of improving the weld toe shape. Yes. However, there is no mention of the optimum overall shape of the tool in order to improve the fatigue strength of the corner of the metal end formed by shearing or the like.

  Further, Patent Document 2 only discloses a pile driving tool provided with a contact portion and a frame portion for driving a pile easily and quickly, and fatigue of a corner portion of a metal end which is a problem in the present invention is disclosed. There is nothing to keep in mind about the optimization of the shape of the tool in order to improve the strength.

  Furthermore, Patent Document 3 discloses a pneumatic tool in which a tool tip is rotatably attached, but is not configured to improve fatigue strength of a corner portion of a metal end portion. Similarly, Patent Documents 4 to 6 are different from the problems to be solved by the present invention, and no configuration is disclosed according to this.

  Furthermore, the chisel shown in FIG. 15 is a tool for an operator to hold in one hand and hit the head with a hammer or the like, and since the tip is flattened, this is attached to the corner of the metal end. When striking and striking, the corner is often recessed in an irregular shape, and it can be said that it is difficult to improve the fatigue strength.

  For this reason, in order to improve the fatigue strength at the corners of the metal edge formed by shearing or the like, no method or apparatus has been devised that can stably perform effective impact plastic working. Was the current situation.

  Therefore, the present invention has been devised in view of the above-described problems, and an object of the present invention is to provide an impact plastic working tool and a machining method for improving the fatigue strength of corner portions existing at metal end portions. Is to provide.

  In order to solve the above problems, the gist of the present invention is as follows.

(1) In an expanded impact plastic working tool whose outer diameter is gradually increased from the head toward the tip surface, the tip surface is formed of a smooth curved surface to improve fatigue strength. Excellent metal impact plastic processing tool,

(2) Impact metal working process of metal having excellent fatigue strength improvement as described in (1) above, wherein the shape of the side surface from the head to the tip surface is expanded so as to be an exponential function. Tools,

(3) In the method of impact plastic working a corner of a metal end using the impact plastic working tool described in (1) or (2) above, between the radius of curvature R formed by the corner, Impact plastic working of metal with excellent fatigue strength, characterized in that impact plastic working is performed by the impact plastic working tool having the tip surface having a radius of curvature r satisfying 0.5 ≦ r ≦ R. Is in the way.

  According to the present invention, a corner of a metal and an end of a member subjected to processing such as welding and plastic deformation are subjected to impact plastic working using a substantially trumpet-shaped tool, thereby forming the shape of the corner. Since stress concentration can be reduced by relaxation and compressive residual stress can be applied to further improve fatigue strength, it is possible to stably improve fatigue strength regardless of the type of material and target member. Industrial significance is great.

  Hereinafter, as a best mode for carrying out the invention, a method for impact plastic working of a metal excellent in improving fatigue strength will be described in detail with reference to the drawings.

  As shown in FIG. 6, the present inventor considered that a phenomenon in which the corner portion 9 at the end portion obtained by cutting the metal (material to be processed) 12 by shearing or the like is likely to be a starting point of fatigue failure, and the fatigue strength is reduced, is a shock plastic working method. Therefore, the shape of the tool 1 (1 ′) was examined. Usually, as shown in the longitudinal sectional view of FIG. 4 (a) and the side view of FIG. 4 (b), a cylindrical elongated tool 1 'in which the side surface 2 in the longitudinal section is composed of only the straight line 3 is used. When the position and direction of the tip of the tool 1 'and the impact plastic working device 7 are not controlled so that 9 can be processed well at the tip of the tool, the tool will move sideways and the device will swing, making stable processing difficult. Was in the situation.

  Incidentally, the impact plastic working device 7 has a tool 1 ′ attached to the protruding end of the piston rod 71, and reciprocates the piston rod 71 with a constant stroke at a high frequency using, for example, supply of air pressure. The impact force is applied to the corner portion 9 through the tool 1 ′.

  Even if the impact plastic working device 7 can be stably fixed with a jig or the like, since the area of the tip surface of the tool is small, the dent caused by one plastic deformation is narrow and deep, so that the corner portion is fixed. As shown in FIG. 9, the corner 9 'after the impact plastic working is performed on the corner 9 of the workpiece 12 using the conventional tool 1' as shown in FIG. In this way, it was found that a surface with unevenness was formed, and improvement in fatigue strength could not be expected. However, even when the diameter of the tool is simply increased or the shape thereof is complicated, the vibration energy from the vibration source in the impact plastic working apparatus 7 cannot be sufficiently transmitted to the workpiece, and sufficient plastic deformation is caused. There was a problem that could not be obtained. In particular, in the ultrasonic shock treatment method, it is necessary to suppress the attenuation of the transmitted ultrasonic wave as much as possible in order to achieve sufficient plastic deformation. Therefore, both the stability of impact plastic working at these corners and the impact plastic workability are compatible. It was necessary to study the tool shape to be used.

  As a result of intensive investigations on solutions for these conflicting phenomena, the present inventors have invented the tool 1 having the shape shown in FIGS. 1A to FIG. 3A show the front shape of the tool 1, and FIG. 1B to FIG. 3B show the side shape of the tool 1.

  That is, the tool 1 is an impact plastic working tool having an enlarged diameter in which the outer diameter is gradually increased from the head 8 toward the distal end surface 5. This tool 1 is a substantially trumpet-shaped tool having a tip outer diameter 13 larger than that of the head 8, and the tip surface 5 is a smooth curved surface. Incidentally, in FIG. 1 to FIG. 3, a substantially trumpet-shaped tool is taken as an example, but the tool is not limited to this, and may be configured in any expanded shape. In other words, a trumpet-shaped tool that gradually increases in diameter toward the tip can be configured to be wide while smoothing the tip surface 5, so that even if the tool is slightly displaced laterally, a large area can be obtained. The corner portion can be processed, and the shape of the side surface 2 from the head 8 to the distal end surface 5 is changed to a shape composed of the straight line 3 and / or the curved line 4, thereby reducing vibration energy and It is possible to suppress the attenuation of ultrasonic waves as much as possible in the sonic impact treatment.

  In the following description, impact plastic working means hammer peening, needle peening, wire peening, ultrasonic impact treatment, etc., using pneumatic pressure, ultrasonic vibration, etc. as an energy source, the tip tool is repeatedly fired at a frequency of 10 Hz to 50 KHz, It includes a method of imparting plastic deformation by causing it to collide with an object to be processed. Ultrasonic impact treatment means that 20-50 KHz ultrasonic vibration generated from an ultrasonic generator is pressed against an object through a tool such as a pin, and the surface shape is improved and residual stress is reduced by plastic deformation. A process for performing rearrangement or the like.

  The shape of the side surface 2 of the longitudinal section is only the curve 4 as shown in FIG. 3, whether it is a combination of the straight line 3 and the curve 4 as shown in FIGS. 1 and 2, or a straight line like a cone. However, even when they are smoothly combined, there is no problem.

  As shown in FIGS. 5 (a) and 5 (b), when the curve 4 'is particularly exponential, attenuation of the transmitted ultrasonic wave is further reduced in the case of ultrasonic impact processing.

  When the tool 1 having the shape to which the present invention is applied is used and the impact plastic working process is performed on the corner portion 9 as shown in FIG. 7, for example, the corner portion 9 after processing as shown in FIG. 'Can be made generally smooth. As a result, the stress concentration can be reduced, the residual stress can be compressed, and a high fatigue strength can be obtained.

  Further, the tip surface 5 needs to be a smooth curved surface in order to suppress vibration energy attenuation and ultrasonic wave attenuation in ultrasonic impact processing as much as possible.

The curvature radius 6 of the front end surface 5 is not particularly specified because it should be selected depending on the shape of the material to be treated 12. For example, as shown in FIG. 11, the radius of curvature 10 is R (mm) on the material to be treated 12. When the corner portion 9 is processed, when the radius of curvature 6 of the tip of the tool is r (mm),
0.5R ≦ r ≦ R (1)
When the tool is selected so as to satisfy the requirements and the impact plastic working is performed, in the case of the corner 9 as shown in FIG. 12, the corner 9 ′ after the treatment can be processed smoothly and smoothly as shown in FIG. I found. If r as the radius of curvature 6 of the tool tip is smaller than 0.5R, the width of the dent by one plastic deformation becomes narrow and deep, and it becomes difficult to process the corner continuously and smoothly, and r ≧ 0.5R is preferable. However, when r as the radius of curvature 6 of the tool tip is larger than the radius of curvature R of the punched portion of the material to be processed, a portion that does not contact the tip of the tool is generated among the corners having the curvature. It is difficult to give sufficient plastic deformation to the surface. Therefore, it is preferable to satisfy r ≦ R.

  The number of the tool of the present invention when attached to an impact plastic working device is not particularly limited, but when the corner of the punched portion is processed, the number of tools is preferably one and the radius of curvature is preferred. If the angle is large, that is, the corners are straight, more efficient processing can be performed by arranging a plurality of tools in parallel.

  In the present invention, the absolute value of the outer diameter 13 at the tip surface 5 of the tool is not particularly defined. However, when the outer diameter 13 is large, a large output device is required to give sufficient plastic deformation to the metal, It interferes with sex and portability. However, if the outer diameter 13 on the tip face 5 is small, the width and cross-sectional area that give plastic deformation also become small, and the unevenness of the treated surface becomes remarkable, so that stress concentration occurs and a sufficient fatigue strength improvement effect cannot be obtained. Therefore, from these practical viewpoints, the outer diameter 13 of the tool tip is preferably 10 mm to 40 mm in the case of hammer peening and 5 mm to 20 mm in the case of ultrasonic impact treatment.

  The curvature radius 6 of the tip is preferably a convex shape with a large curvature radius and smoothness. It may be a hemispherical tip formed with one radius of curvature or a spherical shell tip consisting of a plurality of curvature radii. When the tip portion has a plurality of curvature radii, the radius of curvature including the center portion of the tip surface is defined as r as the curvature radius 6 of the tool tip portion.

  Further, the material of the tool is not particularly specified, and any material having a hardness sufficient to give plastic working to the metal may be used, and tool steel, ceramics, etc. may be used.

  The object to which the impact plastic processing by the method for impact plastic processing according to the present invention is applied is not particularly specified, and metal base materials such as steel, aluminum and alloys thereof, titanium, magnesium and alloys thereof, and As long as they are processed by welding, shearing, plastic processing, etc., it is possible to apply to plates, pipes, profiles and members with complex shapes where fatigue failure is a problem. .

  The tool for impact plastic working according to the present invention is an enlarged, substantially trumpet-shaped tool, and preferably has an axial symmetry as shown in FIGS. 1 to 3 and FIG. If the cross section is elliptical as shown in FIGS. 19B and 19B, or if the cross section is smooth as shown in FIGS. Needless to say, the same effect can be obtained without this.

A plate-shaped test piece 30 having punched corners 31 shown in FIG. 14 was manufactured using a hot-rolled steel plate having the strength level and thickness shown in Table 1 as a test material.
[Table 1]

  The test piece 30 has a length in the longitudinal direction of 250 mm and a width of 90 mm, and the thickness is 2.3 mm or 3.2 mm. The test piece 30 is formed with punched portions 31 formed by punching the center portion. As shown in FIG. 14, the radius of curvature R of the punched corner portion 31 was 15 mm, and the punching clearance was 9% of the plate thickness.

  The punched corner portion 31 of the test piece 30 was subjected to impact plastic working using the tool shown in Table 1, and a fatigue test was performed to verify the effect. Table 1 shows which one of the shapes shown in FIGS. 1 and 3 to 5 is selected as the shape of the tool 1, the outer diameter on the head 8 side, the outer diameter on the tip surface 5 side, and the tip surface 5 of the tool 1. In addition, the radius of curvature 6 is expressed in mm, and the case where the equation (1) is satisfied is indicated by “◯”, and the case where the equation (1) is not satisfied is indicated by “X”.

  As impact plastic working treatment, hammer peening and ultrasonic impact treatment were selected and applied to the corners 9 on both the front and back sides of the punched hole. The frequencies were 100 Hz and 27 kHz, respectively. As the shape of the tool of the present invention, the shape shown in FIGS. 1, 3 and 5 was used. The tool 1 in FIG. 5 is a curved tool that is expanded in diameter so that the shape of the side surface from the head 8 to the tip surface 5 becomes an exponential function, and Examples No. 4 and No. 18 16 shows the tip tool 41 for hammer peening used in FIG. 16, and FIG. 17 shows the shape of the tip tool 42 for ultrasonic impact treatment used in Examples No. 14, 28, and 32. 16 (a) and 17 (a) are front views, and FIGS. 16 (b) and 17 (b) are side views.

  The tip tool 41 has an outer diameter on the head 8 side of 12 mm, an outer diameter on the tip surface 5 side of the tool of 30 mm, and a curvature radius r of the tip surface 5 of 15 mm. Further, as shown in FIG. 16, the shape of the side surface of the tip tool 41 is such that when the center of the head 8 is the origin 45 and the X axis and the Y axis are taken from the origin 45, the straight line 3 is Y = ± 2. 5 mm, and 0 ≦ x ≦ 17.3 mm, and the curve 4 is represented by Y = ± {6 + 0.5 * EXP (X-22.1)}.

  The tip tool 42 has an outer diameter on the head 8 side of 5 mm, an outer diameter on the tip surface 5 side of the tool of 20 mm, and a curvature radius r of the tip surface 5 of 15 mm. Further, as shown in FIG. 17, the shape of the side surface of the tip tool 43 is such that when the center of the head 8 is the origin 45 and the X and Y axes are taken from the origin 45, the straight line 3 is Y = ± 2. 5 mm, and 0 ≦ x ≦ 17.5 mm, and the curve 4 is expressed by Y = ± {2.5 + 0.5 * EXP (X−22.3)}.

  The impact plastic working time was 20 seconds per specimen. For comparison, a fatigue test was performed by manufacturing a test piece subjected to impact plastic working with a conventional tool shown in FIG. 4 and a test piece not subjected to impact plastic working at all.

  The fatigue test was carried out by a one-way load control fatigue test with a stress ratio (= minimum load / maximum load) of 0.1, and loaded in the longitudinal direction of the test piece in FIG. The fatigue life is a value obtained by dividing the load range where the fracture life is 2 million times by the cross-sectional area of the steel sheet (= plate thickness × test specimen width).

  The fatigue strength of each test piece is also shown in Table 1. When comparing fatigue strength with specimens of materials of the same plate thickness and strength level, for example, when focusing on 2.3mm thickness of 440 MPa class steel, the fatigue strength of No. 53 as punched (no treatment) No. 37 and 38 of hammer peening with conventional tools only improve the fatigue strength by about 15%, but No. 1 to 4 when using the tool of the present invention further improves the fatigue strength by 20% compared to conventional tools. ing.

  Among them, the tool No. 4 in FIG. 5 including the exponential function shape has improved fatigue strength by 15 MPa or more than the other present invention tools. Furthermore, if No. 1, 3 and 4 satisfying the formula (1) are satisfied, the fatigue strength is improved by 25%, and the present invention is effective for improving the fatigue strength of hammer peening to a 440 MPa class steel having a thickness of 2.3 mm. I understand that.

  In the case of ultrasonic impact treatment, No. 39 to 42 of the conventional tool is 20% better than No. 53 as punched, but when the tool of the present invention of No. 5 to 14 is used, it is more than the conventional tool. Furthermore, 16% fatigue strength is improved. The tool No. 14 in FIG. 5 including the exponential function shape has improved fatigue strength by 15 MPa or more than the other present invention tools. Furthermore, Nos. 6, 7, 8, 10, 13, and 14 satisfying equation (1) all showed 25% improvement in fatigue strength over conventional tools, and ultrasonic impact on 2.3 mm thick 440 MPa grade steel. It can be seen that the present invention is also effective in processing.

  Next, focusing on the 780MPa grade steel with a thickness of 2.3mm, the fatigue strength of 301MPa is shown in the case of No.54 as punched. When hammer peening with conventional tools is applied to this, an improvement of about 10% in fatigue strength is recognized as in No. 43 and 44. In the case of the present invention, as shown in Nos. 15 to 18, a 21% improvement in fatigue strength is recognized over the conventional tool. In addition, the tool No. 18 having an exponential function shape has improved fatigue strength by 20 MPa or more than the other tools of the present invention. Further, if the test pieces No. 15, 17, and 18 satisfying the formula (1) are limited, a margin of 27% improvement over the conventional tool is recognized, and the hammer peening of a 780 MPa class steel having a thickness of 2.3 mm is also possible according to the present invention. The tool and the method of formula (1) have proved effective.

  In addition, regarding ultrasonic shock treatment to 780 MPa class steel of 2.3 mm thickness, in the case of No. 45 to 48 of ultrasonic impact treatment with conventional tools, a 22% improvement in fatigue strength was observed compared to punching, By using the tool of the present invention, the fatigue strength was further improved by 17% as compared with the conventional tools as in Nos. 19 to 28. The tool No. 28 having an exponential function shape has improved fatigue strength by 20 MPa or more than the other tools of the present invention. No. 20, 21, 22, 24, 27, and 28 of the method (1) are 23% better than the conventional tool, and the tool of the present invention is also used for ultrasonic impact treatment on a 780 MPa class steel with a thickness of 2.3 mm. And the method of formula (1) proved to be effective.

  Furthermore, with regard to ultrasonic shock treatment to 440MPa class steel with a thickness of 3.2mm, in the case of No. 49 and 50 of the conventional tool treatment, the fatigue strength is improved by 27% compared to the fatigue strength of 177MPa in No. 55 as punched. Although recognized, Nos. 29 to 32 using the tool of the present invention had a further 15% improvement in fatigue strength than the conventional tool. Exponentially shaped tool No. 32 has a fatigue strength of 15 MPa or more higher than that of the other tool of the present invention, and further, No. 29, 31 and 32 of the method (1) are 19% of the conventional tool. It has improved. Thus, it was found that the tool of the present invention and the method of formula (1) are also effective for ultrasonic impact treatment on a 440 MPa class steel having a thickness of 3.2 mm.

  Furthermore, with regard to ultrasonic shock treatment to 780 MPa class steel with a thickness of 3.2 mm, in the case of No. 51 and 52 of the conventional tool treatment, the fatigue strength is improved by 24% compared to the fatigue strength of 296 MPa in No. 56 as punched. However, Nos. 33 to 36 using the tool of the present invention have a further 19% improvement in fatigue strength than the conventional tool. The tool No. 36 having an exponential function shape has improved fatigue strength by 20 MPa or more than the other tool of the present invention. In addition, No. 33, 35, and 36, which are the methods of formula (1), have 23% improvement over conventional tools. The ultrasonic shock treatment of 780 MPa class steel with a thickness of 3.2 mm is also possible with the tool of the present invention and ( It was found that the method of 1) is effective.

  As described above, the tool and method of the present invention showed a clear fatigue strength improvement effect with respect to the impact plastic working treatment of the metal shearing end corner.

It is the top view and side view which show the example of a shape of the tool of this invention. It is the top view and side view which show another example of a shape of the tool of this invention. It is the top view and side view which show another example of a shape of the tool of this invention. It is the top view and side view which show the shape of the conventional tool. It is the top view and side view which show another example of a shape of the tool of this invention. It is a figure which shows the state which performs an impact plastic working process to the corner | angular part of a to-be-processed material. It is a figure which shows the state which carries out the impact plastic working process of the corner | angular part of a shearing process part edge part with the tool of this invention. It is a figure which shows the corner | angular part of the edge part of a shearing process part processed by impact plastic working with the tool of this invention. It is a figure which shows the state which carries out the impact plastic working process of the corner | angular part of a shearing process part edge part with the conventional tool. It is a figure which shows the corner | angular part of the edge part of a shearing process part by which impact plastic processing was carried out with the conventional tool. It is a figure which shows the to-be-processed material which has a punching part. It is a figure which shows the state which carries out the impact plastic working process of the corner | angular part of a punching part with the tool of this invention. It is a figure which shows the corner | angular part of the edge part of a shearing process part processed by impact plastic working with the tool of this invention. It is a top view showing the shape and dimension of the fatigue test piece in the Example of this invention. It is the front view and side view which show the example of the conventional tool. It is the top view and side view which show the example of the shape of the tool in the Example of this invention. It is the top view and side view which show another example of the shape of the tool in the Example of this invention. It is the top view and side view which show another example of a shape of the tool of this invention. It is the top view and side view which show another example of a shape of the tool of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tool 2 Side surface 3 Straight line 4 Curve 5 Tip 6, 10 Radius of curvature 8 Head 9 Corner | angular part 11 Punching part 12 Material 13 Outer diameter

Claims (3)

In an expanded impact plastic processing tool whose outer diameter is gradually increased from the head toward the tip,
A metal impact plasticity processing tool excellent in improving fatigue strength, characterized in that the tip surface is a smooth curved surface. 2. The metal tool for impact plasticity processing with excellent fatigue strength improvement according to claim 1, wherein the diameter of the side surface from the head to the tip surface is expanded so as to be an exponential function. In the method of impact plastic working the corner of the metal end using the impact plastic working tool according to claim 1 or 2,
The impact plastic working is performed by the impact plastic working tool having the tip surface having the curvature radius r satisfying 0.5 ≦ r ≦ R between the curvature radius R formed by the corner portion. Metal impact plastic working method with excellent fatigue strength improvement.

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