JP4428581B1 - Forging tool design method and forging tool - Google Patents

Abstract

Provided is a forging tool which can be used continuously for a long time with a low-price and simple configuration, which suppresses punch breakage.
A forging tool includes a die 10 having a forming hole for a forged product formed by forging;
A punch 30 disposed opposite to the die 10, the forged material 40 is disposed in the forming hole of the die 10, and the forged product is formed by pressing the material 40 by the punch pressing portion 30 a of the punch 30. In this process, the space 50 for dispersing and absorbing the stress caused by the impact during forging was formed inside the punch 30 by actively accelerating the elastic deformation of the punch pressing portion 30a.
[Selection] Figure 1

Description

  The present invention relates to a forging tool used for forging.

  Conventionally, fastening parts such as screws and bolts are forged using tools called a punch (upper die) and a die (lower die). Stresses such as compression, tension, and shear are repeatedly applied to the punch, and sometimes these stresses are shocked. In addition, the requirements for the shape and dimensional accuracy of parts are becoming stricter year by year, and the use of special materials such as high-strength steel is increasing, which necessitates high-risk molding conditions and reduces tool life due to fatigue failure. There was a problem.

  Therefore, as a result of studying the prior art that addresses such problems, a method of forming a hard layer on the surface of the tool by surface coating (Patent Documents 1 and 2), and a method of improving the tool life by a special heat treatment (patent) Documents 3 and 4) were found.

  However, in any of the methods, the purpose is to improve the tool surface hardness, and it is necessary to perform a special treatment in addition to the normal tool production, resulting in an inconvenience that the tool manufacturing cost increases.

  In addition to the above, there is a method (Patent Documents 5 and 6) for dividing the stress concentration portion in advance. However, these techniques also have a disadvantage that the number of tools becomes plural and the tool manufacturing cost increases.

JP2003-112229A JP 2000-054108 A JP 08-300066 JP 07-173572 A JP 2006-26709 A JP 2000-627 A

  If the tool life is reduced, parts such as punches must be replaced frequently, resulting in an increase in the cost of replacement parts, and the continuous operation of the forging machine becomes impossible, leading to reduced production efficiency. It was.

The present invention has been made in view of such circumstances, and provides a forging tool design method and a forging tool capable of suppressing punch fatigue failure and enabling continuous use for a long time with an inexpensive and simple configuration. The purpose is to do.

  In order to solve the above-described problems and achieve the object, the present invention is configured as follows.

The invention according to claim 1 is a die having a forming hole of a forged product formed by forging;
A punch disposed opposite the die;
With
Place the material of the forged product in the forming hole of the die,
A forging tool design method for forming the forged product by pressing the material with a punch pressing portion of the punch ,
The interior of the punch, the punch press part of actively promoting the elastic deformation, bending by forming a space portion in which stress is dispersed and absorbed by the impact during forging,
The amount of deflection of the punch pressing part is evaluated with an equivalent stress value,
The forging tool design method is characterized in that the equivalent stress value at the breaking point of the punch pressing portion is set smaller than the equivalent stress value of the punch pressing portion of the forging tool not provided with the space portion .

The invention according to claim 2 is characterized in that the amount of deflection evaluated by the equivalent stress value is quantified by numerical analysis or model experiment using a model material for plastic working. This is a tool design method.

The invention according to claim 3 is a forging tool manufactured by the design method according to claim 1 or claim 2 .

  With the above configuration, the present invention has the following effects.

In this invention, when forming a forged product, the elastic deformation of the punch pressing part is actively promoted by the space formed inside the punch, and the stress caused by the impact during forging is dispersed and absorbed by bending. As a result, fatigue damage of the punch can be suppressed and durability can be improved, so that continuous use for a long time is possible.

It is a figure which shows the assembly drawing of the cold forging tool before the cold forging in main forming. It is a figure which shows the assembly drawing of the cold forging tool after the cold forging in main forming. Fig. 3 (a) is a plan view and Fig. 3 (b) is a front view. It is a figure which shows the finite element method analysis model at the time of the preforming by cold heading. It is a figure which shows the finite element method analysis model at the time of the main shaping | molding by cold heading. It is a figure which shows the relationship between the processing load and stroke of the main shaping | molding punch. It is a figure which shows the analysis result when not providing the space of main shaping | molding. It is a figure explaining the analysis conditions of this invention. It is an analysis result and is a figure which shows the change of the process load when changing the bottom thickness and internal diameter of a hole which are the cylindrical space parts of FIG.8 (c). It is a figure which shows the change of the stress distribution for every site | part at the time of changing bottom thickness when a hole space part is 3 mm in internal diameter. It is a figure which shows the change of the stress distribution for every site | part at the time of changing bottom thickness when a hole space part is internal diameter 6mm. It is a figure which shows the change of the stress distribution for every site | part at the time of changing bottom thickness when a hole space part is 9 mm in internal diameter. It is a figure which shows the change of stress distribution at the time of changing the internal diameter and bottom thickness of a space part about A point. It is a figure which shows the change of stress distribution at the time of changing the internal diameter and bottom thickness of a space part about B point. It is a figure which shows the change of the stress distribution at the time of changing the internal diameter and bottom thickness of a space part about C point. A punch is a figure which shows the analysis conditions of embodiment which formed the space part with the integral member which has a cylindrical hole, and changed the shape of the bottom of a hole. A punch is a figure which shows the analysis conditions of embodiment which formed the space part of the column-shaped hole with the member of a separate body of a cylindrical member and a cover member, and changed the shape of the bottom of a hole. It is a figure which shows an analysis result about the analysis conditions of embodiment which changed the shape of the bottom of a hole.

Embodiments of a forging tool design method and forging tool according to the present invention will be described below. This embodiment is a method for designing a cold forging tool for a screw and a cold forging tool, and shows a preferred embodiment of the present invention, but the present invention is not limited to this.

  An embodiment of the present invention will be described with reference to FIGS. Cold forging of screws consists of two steps: preforming to form an intermediate shape from a material and main forming to form a head with a cross hole. FIG. 1 is a diagram showing a set of cold forging tools before cold forging in main molding, FIG. 2 is a diagram showing a set of cold forging tools after cold forging, FIG. 3 is a diagram showing forged products, 3 (a) is a plan view and FIG. 3 (b) is a front view.

  The cold forging tool 1 includes a die 10 having a forming hole 10a for a forged product formed by cold forging, a holder 20 disposed to face the die 10, and a slidable movement on the holder 20. A punch 30 is provided. The material 40 of the forged product is disposed in the molding hole 10 a below the head of the die 10. The forming hole 10a has a shape for forming a cross hole screw. A punch 30 is slidably provided in the slide hole 20 a of the holder 20.

  The forged product 41 is formed by sliding the punch 30 and pressing the material 40 by the punch pressing portion 30a. The front end surface 30a1 of the punch pressing part 30a is shaped to protrude from the peripheral edge 30a2 at the axial center. That is, in this embodiment, the front end surface 30a1 is projected in a cross shape, and a cross hole of a cross hole screw is formed.

  The material 40 is obtained by cutting a rod-shaped member into a predetermined length. As shown in FIG. 3, the forged product 41 is a screw part before being thread-rolled, and includes a shaft portion 41a and a head portion 41b that are thread-rolled. A cross hole 41b1 is formed in the head 41b by making the tip surface 30a1 of the punch pressing portion 30a project in a cross shape with an axial center from the peripheral edge 30a2.

In the punch 30, a space 50 is formed that actively promotes elastic deformation of the punch pressing portion 30 a during cold forging and disperses and absorbs stress caused by impact during forging. ing. Space 50 is a hole in the cylindrical, in the pressing direction, a region where the position of the bottom of the hole reaches the stress due to impact during forging are formed at positions that do not collapse during the forging. In addition, the cross-sectional area S <b> 1 in the direction orthogonal to the pressing direction of the space 50 is formed larger than the cross-sectional area S <b> 2 in the direction orthogonal to the pressing direction of the material 40. Hole cylindrical forming the space portion 50, the shape of the bottom, a plane orthogonal to the axis of the hole, the corners are square.

In the cold forging tool 1, as shown in FIG. 1, the material 40 of the forged product 41 is disposed in the forming hole 10 a of the die 10. Then, as shown in FIG. 2, the punch 30 is slid and the material 40 is pressed and plastically processed by the punch pressing portion 30a, and the forged product 41 having the cross hole 41b1 is cold forged. When the forged product 41 is formed, the space portion 50 formed inside the punch pressing portion 30a actively promotes elastic deformation of the punch pressing portion 30a and is bent to forge the punch pressing portion 30a. It is possible to disperse and absorb the stress caused by the impact of time. Therefore, fatigue breakage occurring in the punch pressing portion 30a can be suppressed and durability is improved, so that the punch 30, the die 10, and the holder 20 can be used continuously for a long time.

  Next, the effect of providing a space inside the punch will be described based on numerical analysis examples based on the finite element method shown in FIGS. Forging analysis by the finite element method is a continuous process of the preforming analysis model of FIG. 4 and the main forming analysis model of FIG. 5, and the result obtained by the preforming analysis is used as material data of the main forming analysis. Therefore, the analysis was performed with high accuracy.

  FIG. 4 shows an analysis model of preforming, and the analysis was performed by placing the material on the die and pressing the material with a punch that slides in the holder. The punch was an elastic body and was divided into 30,000 elements for analysis. This punch is a cemented carbide and has a Young's modulus of 540000 MPa and a Poisson's ratio of 0.22. The material was a rigid plastic and was divided into 20,000 elements for analysis.

  FIG. 5 shows a main molding analysis model, in which a punch is pressed by a ram and a material that is the molded product of FIG. 4 is pressed by the punch. In the forging analysis for the main molding, the influence of work hardening of the material in the preforming analysis of FIG. 4 is considered. The punch was divided into 30,000 elements for analysis. The punch used was a conventional punch that did not provide a space.

  FIG. 6 is a diagram showing the relationship between the processing load and stroke of the main forming punch, and shows a comparison between the analysis and the actual phenomenon. The horizontal axis shows the punch stroke, and the vertical axis shows the punch processing load. The relationship between the punch processing load and stroke based on the main forming analysis, and the relationship between the punch processing load and stroke based on actual measurement values. Gave almost similar results. This confirmed the reliability of the analysis.

FIG. 7 shows the analysis result of the main forming, FIG. 7A shows the formation state at the end of the analysis, and FIG. 7B is a longitudinal sectional view showing the stress distribution of the punch. FIGS. 7C and 7D are enlarged vertical sectional views of the stress distribution near the punch pressing portion. Points A, B, and C indicate stress concentration points. As shown in FIG. 7A, a cross hole is formed in the forged product by a tip surface protruding in a cross shape with an axial center from the periphery of the punch pressing portion. As shown in FIG. 7 (b), the stress of the punch by the analysis is shown in the stress range of 0.000 to 1000 (MPa) and divided into eight stages shown in the figure. That is, the stress of the punch pressing portion is distributed in a circular arc shape from the portion corresponding to the tip surface protruding in a cross shape, and the portion corresponding to the tip surface protruding in a cross shape is 876-1000 ( MPa), and the stress is the largest. In the portion where the stress is the largest, a very large surface pressure is generated in the punch pressing portion, which causes fatigue failure in the punch pressing portion.

Next, FIG. 8 is a diagram for explaining the analysis conditions of the present invention. 8 (a) is a perspective view showing a punch press of the punch, and FIG. 8 (b) is an enlarged perspective view showing the punch press part, FIG. 8 (c) inner and bottom positions of the holes of the cylindrical forming space The intersection of D and H in the figure indicates the inner diameter of the hole and the position of the bottom, and all 18 conditions were analyzed. In the embodiment of the present invention, the front end surface of the punch pressing portion is shaped so as to protrude from the periphery of the periphery, and in this embodiment, the punch is slid and the material is pressed by the punch pressing portion to produce the forged product. When molding, as shown in FIGS. 9 to 15, by providing a space inside the punch, stress due to impact could be dispersed and absorbed. In the tip surface protruding in a cross shape of the punch pressing portion, the portion where the stress is concentrated is indicated by points A, B, and C in FIG. 8B.

FIG. 9 shows the analysis results, and is a diagram showing the relationship between the bottom thickness of the hole, which is the cylindrical space portion of FIG. 8C, and the change in the processing load when the inner diameter is changed. In FIG. 8C, the punch is
A cylindrical shape having a length of 10 mm and an outer diameter of 12 mm was used, and the space was formed by a cylindrical hole. For example, in FIG. 8C, the position indicated by P1 is a space having an inner diameter of 6 mm and a bottom thickness of H4 mm. 9, shows the processing load in the case of not forming the space portion by a dotted line, square marks in FIG. 8 (c), the case of the punch tip 100 with an inner diameter 3mm of the space with varying bottom thickness H The circle indicates the processing load for the space portion in which the bottom thickness H is changed from the punch tip 100 with an inner diameter of 6 mm, and the triangle indicates the punch tip 100 with an inner diameter of 9 mm. The processing load about the case of the space part which changed bottom thickness H from is shown. The space D3 of the inner diameter 3 mm, obtained when the punches of the tip 100 in 3 mm around the bottom thickness H is, processing load is smallest, the results of the other bottom thickness H in the processing load tends to increase the It was. The space D6 of inner diameter 6 mm, when the bottom thickness H of approximately 6 mm from the punch tip 100 with the results of the tendency of processing load is smallest bloom. In the space portion D9 having an inner diameter of 9 mm, when the bottom thickness H is about 3 mm from the tip end portion 100 of the punch, the processing load becomes the smallest, and as the bottom thickness H becomes 1 mm from the tip end portion 100 of the punch, As a result, the processing load tends to increase with the bottom thickness H. The processing load of the space portion D3 having an inner diameter of 3 mm is smaller than the processing load of the space portion D3 having an inner diameter of 3 mm, and the processing load of the space portion D9 having an inner diameter of 9 mm tends to be smaller than the processing load of the space portion D3 having an inner diameter of 3 mm . .

  10 to 12 show changes in the stress distribution by changing the inner diameter and bottom thickness of the space. In FIG. 10, when the stress distribution is obtained by changing the bottom thickness H in the space D3 having an inner diameter of 3 mm, the stress at the point C is 974, 1270, 1270 (MPa) when the bottom thickness H is 1 mm, 2 mm, and 3 mm. Thus, the stress was smaller than the stress at point C when the space of FIG. 7 was not provided. In FIG. 11, when the stress distribution is obtained by changing the bottom thickness H in the space D6 having an inner diameter of 6 mm, the stress at the point C is 1330, 1050, 1240 (MPa) when the bottom thickness H is 1 mm, 2 mm, and 3 mm. Thus, the stress was smaller than the stress at point C when the space of FIG. 7 was not provided. In FIG. 12, when the stress distribution is obtained by changing the bottom thickness H in the space D9 having an inner diameter of 9 mm, the stress at the point A is 775 (MPa) and the stress at the point B is 894 (when the bottom thickness H is 2 mm. The stress at point C is 707 (MPa), the stress at point A is 638 (MPa) at 3 mm, the stress at point C is 1010 (MPa), and the stress at point A is 785 (MPa) at 4 mm. The stress at point C is 1170 (MPa), the stress at point A is 875 (MPa), the stress at point C is 1360 (MPa) at 6 mm, the stress at point C is 1280 (MPa) at 8 mm, It became smaller than the stress of the corresponding point when not providing the space of FIG.

FIGS. 13 to 15 show changes in stress distribution by changing the inner diameter and bottom thickness of the space at points A, B, and C. FIG. In FIG. 13, with respect to point A, the inner thickness of the cylindrical space is 3 mm, 6 mm, and 9 mm, and the bottom thickness H is changed. For the inner diameters of 3 and 6 mm, the case where the bottom thickness H was about 2 mm to 4 mm was equivalent to the stress when the corresponding point A space in FIG. 7 was not provided. When the inner diameter was 9 mm, the case where the bottom thickness H was about 2 mm to 6 mm was smaller than the stress when the corresponding point A space in FIG. 7 was not provided.

In FIG. 14, with respect to point B, the inner thickness of the cylindrical space is 3 mm, 6 mm, and 9 mm, and the bottom thickness H is changed. In an inner diameter 3mm, in bottom thickness H is 3mm around, the stress when not provided a space corresponding point B in FIG. 7 becomes small. The inner diameter of 6 mm, with bottom thickness H is 3 mm to 6 mm, never be less than the stress when not provided a space corresponding point B in FIG. When the inner diameter was 9 mm, the case where the bottom thickness H was about 2 mm to 8 mm was smaller than the stress when the corresponding point B space in FIG. 7 was not provided.

In FIG. 15, with respect to point C, the inner thickness of the cylindrical space is 3 mm, 6 mm, and 9 mm, and the bottom thickness H is changed. When the inner diameter was 3 mm, the case where the bottom thickness H was about 1 mm to 4 mm was smaller than the stress at the corresponding point C in FIG. When the inner diameter was 6 mm, the case where the bottom thickness H was about 1 mm to 4 mm was smaller than the stress when the space at the corresponding point C in FIG. 7 was not provided.
When the inner diameter was 9 mm, the case where the bottom thickness H was about 2 mm to 5 mm was smaller than the stress when the space at the corresponding point C in FIG. 7 was not provided.

In this way, when forming a forged product by analysis, the space formed inside the punch actively promotes elastic deformation of the punch pressing part, and by bending it absorbs stress due to impact during forging. It was proved that the processing load or stress was reduced by dispersion. In the analysis, it was found that the stress was reduced most at the points A, B and C when the inner diameter was 9 mm and the bottom pressure was 2 mm as compared with the conventional type.

  In the embodiment shown in FIGS. 1 to 15, the punch has a space formed by an integral member having a cylindrical hole, and can be manufactured at low cost by forming the punch by an integral member. The shape of the bottom of the hole is a corner and a center is a plane, but the shape of the bottom of the hole can be formed as shown in FIG. In FIG. 16, analysis number 1 is a comparative example, in which a linear hole is formed by wire cutting or the like, and the shape of the hole is a slit shape. Analysis numbers 2 to 8 show the embodiment, and a space portion D9 having an inner diameter of 9 mm is formed in a punch having an outer diameter of 12 mm that was most effective in the analysis of the embodiment of FIGS. The shape of the bottom of the hole was changed on the basis of the bottom thickness H of about 2 mm.

  Analysis No. 2 is the shape of the bottom of the hole, the center is a plane and the corner is a corner, Analysis No. 3 is a curved surface with the center being a plane and a corner being concave, and Analysis No. 4 is the center being a plane and the corner is convex It is a curved surface. In addition, analysis number 5 is a convex curved surface with a corner at the center and corners are corners, and analysis number 6 is a convex curved surface with the center at a vertex and concave corners. . Analysis number 7 is a concave curved surface with a corner at the center and corners are corners, and analysis number 6 is a concave curved surface with a shaft at the top and concave corners. . The bottom shape of the punch hole may be a convex curved surface with a convex center and a convex corner at the center, or a concave curved surface with the central point at the center and a convex corner. It may be a curved surface.

  In addition, as shown in FIG. 17, the punch fixes the lid member to the end of the cylindrical member, forms a cylindrical hole space by a separate member of the cylindrical member and the lid member, A punch pressing part is comprised and the intensity | strength of a cover member can be changed according to the raw material of a forge product. In FIG. 17, analysis number 9 is obtained by fixing a lid member having a stepped portion at the end to the end of the cylindrical member, and the shape of the bottom of the hole is a plane at the center and corners are corners. In analysis number 10, a lid member having a middle step at the end is fixed to the end of the cylindrical member. The shape of the bottom of the hole is flat at the center and corners are corners. In analysis number 11, a lid member having a lower stepped portion at the end is fixed to the end of the cylindrical member. The shape of the bottom of the hole is a plane at the center and corners are corners. In this embodiment, the shape of the bottom of the hole may be a convex curved surface with the central axis at the center, or a concave curved surface with the axial center at the top. Further, the shape of the bottom of the hole may be a curved surface with a concave corner or a convex curved surface.

In analysis number 12, a small-diameter columnar chip-shaped lid member is fixed to the end of the cylindrical member. The shape of the bottom of the hole is flat at the center and corners are corners. In analysis number 13, a large-diameter columnar chip-shaped lid member is fixed to the end of the cylindrical member. The shape of the bottom of the hole is flat at the center and corners are corners. In this embodiment, the shape of the bottom of the hole may be a convex curved surface with the central axis at the center, or a concave curved surface with the axial center at the top. Further, the shape of the bottom of the hole may be a curved surface having a concave corner or a convex curved surface.

FIG. 18 shows the analysis results at the final processing stage for the analysis numbers 1 to 13 shown in FIGS. 16 and 17 and the conventional punch without holes. FIG. 18 shows the stress distribution and the stress at points A and B shown in the embodiment of FIGS. As a result of analysis, in analysis number 1 of the comparative example, the stress distribution was asymmetric, the stresses at points A and B were both large, and the processing load was also large . In this embodiment, the values of analysis number 2 and points A and B of analysis number 5 are smaller than the values of stress and processing load at point A and B of the conventional punch, Good results. In addition, in the analysis numbers 3 and 6, the stresses at the points A and B are both smaller than the stress values at the points A and B of the conventional punch. Further, the stress at a point B of the analysis number 4, 11, the value of the processing load, the stress of the conventional punch point B, are I both smaller kuna than the value of the processing load. The value of the stress at the point B of the analysis number 7 to 10, 12, 13 are both Ru smaller kuna Ttei than the value of the stress of the conventional punch point B.

  In particular, when forming the cross hole of the cross hole screw, the stress due to the impact concentrated on the front end surface of the punch pressing portion can be dispersed and reduced. In this analysis, the case of forming a cross hole of a cross hole screw was explained as an example of forming a forged product. However, the present invention is not limited to this, and examples of forming various forged products should be proved by the same analysis. Can do.

The present invention can be applied to a forging tool design method and forging tool used when forging a forged product, and can be used continuously for a long time with a low-price and simple configuration, suppressing fatigue fracture of the punch. To do.

DESCRIPTION OF SYMBOLS 1 Cold forging tool 10 Die 10a Forming hole of forged product 20 Holder 20a Sliding hole 30 Punch 30a Punch press part 30a1 End surface of punch press part 30a 30a2 Periphery of punch press part 30a 40 Forging material 41 Forging 41a shaft Portion 41b Head 50 Space S1 Cross-sectional area orthogonal to the pressing direction of the space 50 S2 Cross-sectional area orthogonal to the pressing direction of the material 40

Claims (3)

A die having a forming hole of a forged product formed by forging;
A punch disposed opposite the die;
With
Place the material of the forged product in the forming hole of the die,
A forging tool design method for forming the forged product by pressing the material with a punch pressing portion of the punch ,
The interior of the punch, the punch press part of actively promoting the elastic deformation, bending by forming a space portion in which stress is dispersed and absorbed by the impact during forging,
The amount of deflection of the punch pressing part is evaluated with an equivalent stress value,
A method for designing a forging tool , wherein the equivalent stress value at the breaking point of the punch pressing portion is set smaller than an equivalent stress value of a punch pressing portion of a forging tool not provided with the space portion . The forging tool design method according to claim 1, wherein the deflection amount evaluated by the equivalent stress value is quantified by a numerical analysis or a model experiment using a model material for plastic working. A forging tool manufactured by the design method according to claim 1.