JP7503263B2 - Cold forging joining method - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act, Proceedings of the 2019 Spring Conference on Plastic Processing, pp. 141 and 142, Japan Society for Technology of Plastic Processing

The present invention relates to a joining method using cold forging.

Patent Document 1 discloses a joining method using cold forging. In this joining method, cold forging is performed by pressing a member to be joined, which is a stack of multiple metal plates, with a punch. The portion of the member to be joined pressed by the punch undergoes plastic deformation, forming a concave portion on the pressure-actuated surface of the member to be joined that is pressed by the punch, and forming a convex portion on the back surface of the member to be joined opposite the pressure-actuated surface. The plastic deformation of the member to be joined causes new active surfaces that are not covered by oxide films and contaminant films to appear on the surfaces of the multiple metal plates. The newly active surfaces that appear are pressed against each other and come into close contact, and the multiple metal plates are joined by solid-state welding.

In this joining method, in order to increase the joining strength, a backing member is placed against the back surface of the joined parts, and the pressure application surface of the joined parts is pressed by a punch. The backing member is plastically deformed together with the joined parts by the pressure from the punch. Back pressure is applied from the backing member to the back surface of the joined parts.

Patent No. 6117411

In the conventional joining method described above, the backing material undergoes plastic deformation. This means that the backing material needs to be replaced every time processing is performed. This is an obstacle to improving productivity.

In order to solve this problem, the inventors have investigated a joining method using cold forging in which back pressure is applied by a back pressure punch. This back pressure punch is movably positioned relative to the die opening of the die in which the members to be joined are placed. When the pressure application surface of the members to be joined is pressed by the punch, this back pressure punch moves in the same direction as the pressing direction of the punch. For this reason, the back pressure punch does not deform due to the pressing force of the punch. Therefore, there is no need to replace the back pressure punch every time processing is performed. Then, when joining was performed while applying a constant back pressure with the back pressure punch, good joining was obtained.

However, in order to put the joining method that the inventors have developed into practical use, it is necessary to increase the joining strength.

In view of the above, the present invention aims to provide a method for joining workpieces by cold forging in which a back pressure punch applies back pressure while a punch applies a pressing force, and which can increase the joining strength.

In order to achieve the above object, according to the invention described in claim 1,
A cold forging joining method for joining a joined member (30) having a plurality of overlapping metal plate materials (31, 32) by cold forging, comprising:
a joining device (10) including a punch (12) for pressing a pressure operating surface (30a) of the workpiece (30), a die (14) on which the workpiece is placed and in which a die opening (14a) is formed at a portion facing the punch, a back pressure punch (18) arranged movably relative to the die opening and applying back pressure to a back surface (30b) of the workpiece opposite the pressure operating surface, and a back pressure adjustment unit (20, 22, 24) for adjusting the back pressure;
pressing the pressure application surface of the workpieces with a punch while applying back pressure to the back surface of the workpieces with a back pressure punch;
In pressing,
The portion of the workpiece pressed by the punch is plastically deformed, forming a concave portion (311) on the pressure acting surface and a convex portion (312) on the back surface.
The back pressure adjusting unit makes the maximum value of the back pressure in the latter half of the processing period from the start of pressing the punch to the end of pressing the punch greater than the maximum value of the back pressure in the first half of the processing period,
The plastic deformation causes the surfaces of the multiple metal plates to expand in area, and the newly active surfaces that appear on the surfaces are pressed together and adhered to each other by the pressing force of the punch and the back pressure of the back pressure punch, thereby solid-state joining the multiple metal plates.

According to this, the back pressure adjustment unit makes the maximum value of the back pressure in the latter half of the processing period greater than the maximum value of the back pressure in the first half of the processing period. Therefore, compared to when the magnitude of the back pressure during the entire processing period is constant at a small back pressure equal to or less than the maximum value of the back pressure during the first half of the processing period of the present invention, the force pressing the newly active surfaces against each other can be increased. Therefore, the bonding strength can be increased. Also, compared to when the magnitude of the back pressure during the entire processing period is constant at a large back pressure equal to the maximum value of the back pressure during the latter half of the processing period of the present invention, the amount of plastic deformation can be increased and the area of the newly active surfaces can be increased. Therefore, the bonding strength can be increased.

According to the invention described in claim 2,
A cold forging joining method for joining a joined member (30) having a plurality of overlapping metal plate materials (31, 32) by cold forging, comprising:
a joining device (10) including a punch (12) for pressing a pressure operating surface (30a) of the workpiece (30), a die (14) on which the workpiece is placed and in which a die opening (14a) is formed at a portion facing the punch, a back pressure punch (18) arranged movably relative to the die opening and applying back pressure to a back surface (30b) of the workpiece opposite the pressure operating surface, and a back pressure adjustment unit (20, 22, 24) for adjusting the back pressure;
pressing the pressure actuation surface of the workpieces with a punch while applying back pressure to the back surface of the workpieces with a back pressure punch;
In pressing,
The portion of the workpiece pressed by the punch is plastically deformed, forming a concave portion (311) on the pressure acting surface and a convex portion (312) on the back surface.
The back pressure adjusting unit makes the average value of the back pressure in the latter half of the processing period from the start of pressing the punch to the end of pressing the punch larger than the average value of the back pressure in the first half of the processing period,
The plastic deformation causes the surfaces of the multiple metal plates to expand in area, and the newly active surfaces that appear on the surfaces are pressed together and adhered to each other by the pressing force of the punch and the back pressure of the back pressure punch, thereby solid-state joining the multiple metal plates.

According to this, the back pressure adjustment unit makes the average value of the back pressure in the latter half of the processing period greater than the average value of the back pressure in the first half of the processing period. Therefore, compared to when the magnitude of the back pressure during the entire processing period is constant at a small back pressure equal to the back pressure at any time during the first half of the processing period of the present invention, the force pressing the newly active surfaces against each other can be increased. Therefore, the bonding strength can be increased. Also, compared to when the magnitude of the back pressure during the entire processing period is constant at a large back pressure equal to the back pressure at any time during the second half of the processing period of the present invention, the amount of plastic deformation can be increased and the area of the newly active surfaces can be increased. Therefore, the bonding strength can be increased.

According to the invention described in claim 4,
A cold forging joining method for joining a joined member (30) having a plurality of overlapping metal plate materials (31, 32) by cold forging, comprising:
a joining device (10) including a punch (12) for pressing a pressure operating surface (30a) of the workpiece (30), a die (14) on which the workpiece is placed and in which a die opening (14a) is formed at a portion facing the punch, a back pressure punch (18) arranged movably relative to the die opening and applying back pressure to a back surface (30b) of the workpiece opposite the pressure operating surface, and a back pressure adjustment unit (20, 22, 24) for adjusting the back pressure;
pressing the pressure actuation surface of the workpieces with a punch while applying back pressure to the back surface of the workpieces with a back pressure punch;
In pressing,
The portion of the workpiece pressed by the punch is plastically deformed, forming a concave portion (311) on the pressure acting surface and a convex portion (312) on the back surface.
As the back pressure punch, one is used in which at least a part of a portion of a tip surface (18a) of the back pressure punch that faces the tip surface (12a) of the punch in the axial direction of the punch has a rounded convex shape,
The plastic deformation causes the surfaces of the multiple metal plates to expand in area, and the newly active surfaces that appear on the surfaces are pressed together and adhered to each other by the pressing force of the punch and the back pressure of the back pressure punch, thereby solid-state joining the multiple metal plates.

This makes it possible to increase the surface expansion ratio in the portion of the workpieces that faces the punch in the axial direction of the punch, and to increase the number of newly active surfaces, compared to when the entire tip face of the back pressure punch is flat. Also, compared to when the entire tip face of the back pressure punch is flat, it is possible to increase the surface pressure at the joining interface in that portion of the workpieces, and to promote bonding between the newly active surfaces. As a result, the joining strength can be increased.

The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below.

FIG. 2 is a schematic cross-sectional view of the joining device according to the first embodiment. FIG. 2 is a top view of the joining apparatus of FIG. 1 . 2 is an enlarged cross-sectional view of the joining apparatus of FIG. 1 when members to be joined are joined using the joining apparatus; 4 is a graph showing a change in back pressure when members to be joined are joined using the joining apparatus of FIG. 1 . FIG. 11 is a schematic cross-sectional view of a joining device according to a second embodiment. FIG. 11 is a schematic cross-sectional view of a joining device according to a third embodiment. 13 is a graph showing a change in back pressure in the third embodiment. FIG. 13 is a cross-sectional view of a back pressure punch in a fourth embodiment. FIG. 13 is an enlarged cross-sectional view of a joining device according to a fourth embodiment. 13 is a graph showing the distribution of surface pressure at a joining interface when metal plate materials are joined together using the joining device of the fourth embodiment. 13 is a graph showing the distribution of surface expansion ratios when metal plate materials are joined together using the joining device of the fourth embodiment.

The following describes embodiments of the present invention with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are denoted by the same reference numerals.

First Embodiment
The joining method of the present embodiment is a method for joining a plurality of metal plate materials, which are members to be joined, by cold forging. Cold forging is a processing method in which pressure is applied to metal members in a room temperature environment to plastically deform the metal plate materials.

First, the joining device used in the joining method of this embodiment will be described. As shown in FIG. 1, the joining device 10 includes a punch 12, a die 14, a holding jig 16, a back pressure punch 18, and a spring 20. FIG. 1 shows a state in which the workpieces 30 are placed on the joining device 10.

The punch 12 is a male mold that presses the pressure operating surface 30a, which is the surface of the workpiece 30 facing the punch 12, by the force applied by a driving device (not shown). As shown in Figures 1 and 2, the punch 12 is a cylindrical pin. The tip surface 12a of the punch 12 facing the workpiece 30 is flat. As the driving device, a press machine used in general press processing, such as a servo press machine, other mechanical press machine, or hydraulic press machine, can be used.

The die 14 is a female die that corresponds to the punch 12. The workpiece 30 is placed on the surface of the die 14. That is, the die 14 is disposed on the opposite side of the workpiece 30 from the punch 12. A die opening 14a is formed in the portion of the die 14 that faces the punch 12 in the axial direction of the punch 12. The die opening 14a is a portion into which a protrusion formed on the workpiece 30 enters during processing. The opening shape of the die opening 14a is a circle. The diameter of the die opening 14a is larger than the diameter of the punch 12. That is, the maximum opening width of the die opening 14a is larger than the maximum width of the punch 12.

The pressing jig 16 presses the workpieces 30 by the force applied by the spring 17. The pressing jig 16 fixes the workpieces 30 to the die 14 and suppresses deformation of the surface of the workpieces 30 on the punch 12 side during processing. As shown in Figures 1 and 2, the pressing jig 16 is a cylindrical block. A jig opening 16a through which the punch 12 moves is formed in the center of the pressing jig 16. The pressing jig 16 can be the same jig as that used in general press processing.

The back pressure punch 18 is positioned on the opposite side of the workpiece 30 from the punch 12. The back pressure punch 18 applies back pressure to the workpiece 30 by the force of the spring 20. The back pressure is a pressure acting on the back surface 30b, which is the surface of the workpiece 30 opposite the punch 12 side. In other words, the back pressure punch 18 presses the back surface 30b of the workpiece 30. The back pressure punch 18 is not directly driven by the driving device of the punch 12.

The back pressure punch 18 is a cylindrical pin. The back pressure punch 18 is arranged to be movable relative to the die opening 14a. The back pressure punch 18 moves in the axial direction of the back pressure punch 18 through the die opening 14a. The back pressure punch 18 is arranged so that the axial center of the back pressure punch 18 coincides with the axial center of the punch 12. The diameter of the back pressure punch 18 is larger than the diameter of the punch 12. That is, as shown in FIG. 1, in a cross section of the joining device 10 cut along a plane including the axial center of the back pressure punch 18 and the axial center of the punch 12, the width of the back pressure punch 18 is larger than the width of the punch 12. In addition, the tip surface 18a of the back pressure punch 18 on the side of the joined member 30 is flat.

The spring 20 is a back pressure adjustment unit that adjusts the back pressure applied from the back pressure punch 18 to the workpiece 30. One end of the spring 20 is connected to the back pressure punch 18. The other end of the spring 20 is fixed to a fixed part (not shown). As described below, the workpiece 30 is deformed by the pressure from the punch 12, and the back pressure punch 18 moves in a direction that contracts the spring 20. When the spring 20 contracts due to the movement of the back pressure punch 18, a reaction force against the load that contracts the spring 20 is generated. This reaction force is applied as back pressure from the back pressure punch 18 to the workpiece 30. At this time, as the movement amount of the back pressure punch 18 increases, the contraction amount of the spring 20 increases and the reaction force increases. In this way, the spring 20 increases its back pressure as the movement amount of the back pressure punch 18 increases.

The members to be joined 30 are a first metal plate material 31 and a second metal plate material 32 that are stacked together. At least the joint locations of the first metal plate material 31 and the second metal plate material 32 are plate-shaped. In other words, only the joint locations of the first metal plate material 31 and the second metal plate material 32 may be plate-shaped, or the entirety of the first metal plate material 31 and the second metal plate material 32 may be plate-shaped.

The hardness of the first metal plate material 31 is higher than the hardness of the second metal plate material 32. The hardness of the first metal plate material 31 and the hardness of the second metal plate material 32 may be the same.

The first metal plate 31 and the second metal plate 32 are made of dissimilar metal materials, which are different types of metal materials. Dissimilar metal materials are materials in which at least some of the elements contained as components of the metal material are different, and materials in which the compositions are different even if all of the elements contained as components of the metal material are the same. Even if the elements contained as main components are the same, alloys with different compositions are dissimilar metal materials. Examples of metal materials include Al-based metals, iron-based metals, Cu-based metals, Ti-based metals, Mg-based metals, etc. Examples of combinations of dissimilar metal materials include combinations of Al-based metals and iron-based metals, combinations of Cu-based metals and Al-based metals, etc. Note that Al-based metals include pure aluminum and aluminum alloys. Iron-based metals include pure iron and iron alloys such as steel. Cu-based metals include pure copper and copper alloys. Ti-based metals include pure titanium and titanium alloys. Mg-based metals include magnesium alloys. Additionally, the first metal plate 31 and the second metal plate 32 may be made of the same metal material.

Next, the joining method and joining mechanism of the workpieces 30 using the joining device 10 will be described. First, as shown in FIG. 1, the workpieces 30 are placed on the joining device 10. At this time, the workpieces 30 are placed on the die 14 so that the first metal plate material 31, which has a higher hardness, faces the punch 12.

Then, the workpieces 30 are pressed down from above by the pressing jig 16. This fixes the workpieces 30 between the die 14 and the pressing jig 16. At this time, the back pressure punch 18 is in contact with the workpieces 30 and is pressing the workpieces 30 by the force applied by the spring 20. In other words, the back pressure punch 18 is applying back pressure to the back surface 30b of the workpieces 30. Note that the installation of the workpieces 30 and the pressing of the workpieces 30 by the pressing jig 16 may be performed simultaneously.

Next, in this state, the punch 12 moves through the jig opening 16a toward the workpiece 30. Furthermore, as shown in FIG. 3, the punch 12 moves from the position at the start of pressing to the position at the end of pressing. The left side of FIG. 3 shows the state of the workpiece 30 when the punch 12 starts pressing. The right side of FIG. 3 shows the state of the workpiece 30 when the punch 12 finishes pressing. The position at the start of pressing is the position of the punch 12 when the punch 12 starts pressing the workpiece 30, and is the position where the punch 12 contacts the workpiece 30. The position at the end of pressing is the position of the punch 12 when the punch 12 finishes pressing the workpiece 30. As a result, the punch 12 presses the pressure operating surface 30a of the workpiece 30 while the back pressure punch 18 applies back pressure to the back surface 30b of the workpiece 30.

When the punch 12 presses the workpiece 30, the part of the workpiece 30 pressed by the punch 12 undergoes plastic deformation, as shown in the right part of FIG. 3. Specifically, the part of the first metal sheet 31 facing the punch 12 is pressed by the punch 12 toward the second metal sheet 32, forming a recess 311 on the punch 12 side of the first metal sheet 31. A protrusion 312 is formed on the second metal sheet 32 side of the first metal sheet 31. The second metal sheet 32 is pressed by this protrusion 312, forming a recess 321 on the first metal sheet 32 side of the second metal sheet 32. A protrusion 322 is formed on the side of the second metal sheet 32 opposite the punch 12 side.

In this way, a recess 311 is formed on the punch side of the workpiece 30 by plastic deformation, and a protrusion 322 is formed on the opposite side of the workpiece 30 to the punch 12 side. The protrusion 322 of the workpiece 30 is located within the die opening 14a.

In the process of forming the convex portion 322 of the workpiece 30, the back pressure punch 18 is pressed by the convex portion 322, so that the back pressure punch 18 moves through the die opening 14a in the same direction as the movement direction of the punch 12 (i.e., the pressing direction of the punch 12). That is, the back pressure punch 18 moves through the die opening 14a in a direction that contracts the spring 20. At this time, as the movement amount of the back pressure punch 18 increases, the contraction amount of the spring 20 increases, and the reaction force against the load that contracts the spring 20 increases. Therefore, during the entire processing period from the start of pressing the workpiece 30 by the punch 12 to the end of pressing the workpiece 30 by the punch 12, as shown in FIG. 4, the back pressure applied by the back pressure punch 18 to the workpiece 30 increases as the movement amount of the back pressure punch 18 increases.

In this way, the joining method of this embodiment joins the workpieces 30 by cold forging, in which the back pressure punch 18 applies back pressure while the punch 12 applies a pressing force. In the process of plastically deforming the workpieces 30 by this cold forging, the surface areas of the first metal plate material 31 and the second metal plate material 32 are expanded. As a result, the oxide film and the contaminant film present on the surfaces of the first metal plate material 31 and the second metal plate material 32 are destroyed. On the surfaces of the first metal plate material 31 and the second metal plate material 32, active new surfaces that are not covered by the oxide film and the contaminant film appear. Furthermore, the pressing force of the punch 12 and the back pressure of the back pressure punch 18 press the active new surfaces together and make them adhere to each other. As a result, solid-phase bonding occurs, and metallic bonding is realized. That is, the first metal plate material 31 and the second metal plate material 32 are solid-phase bonded.

In the first half of the processing period, a small back pressure is applied, as shown by the arrow P1 in the left part of FIG. 3. The first half of the processing period is the period before the middle point of the processing period. The first half of the processing period includes the start of pressing. When the punch 12 starts pressing, the joined members 30 start to deform. Therefore, the start of pressing corresponds to the start of deformation of the joined members 30. If no back pressure is applied to the joined members 30 when the punch 12 presses, the joined members 30 will break. Therefore, the back pressure in the first half of the processing period is set to a level that does not break the joined members 30 due to the pressing of the punch 12, but allows the joined members 30 to plastically deform. This promotes the expansion of the surface area of the joining point due to plastic deformation.

In the latter half of the processing period, a back pressure greater than that in the first half of the processing period is applied, as indicated by arrow P2 on the right side of Figure 3. The latter half of the processing period is the period of the processing period that follows the middle point of the processing period. The latter half of the processing period includes the end of pressing. When the pressing of the punch 12 ends, the deformation of the joined members 30 ends. Therefore, the end of pressing corresponds to the end of the deformation of the joined members 30.

As shown in FIG. 4, the back pressure in the second half of the processing period is set to be greater at any time during the second half of the processing period than the back pressure at any time during the first half of the processing period. In this way, the maximum back pressure in the second half of the processing period is set to be greater than the maximum back pressure in the first half of the processing period. Also, the average back pressure in the second half of the processing period is set to be greater than the average back pressure in the first half of the processing period. Therefore, the surface pressure at the bonding interface is greater in the second half of the processing period than in the first half of the processing period, and the force pressing the newly active surfaces together increases.

In this embodiment, a spring 20 having a predetermined spring constant is selected so that the maximum back pressure in the first half of the processing period and the maximum back pressure in the second half of the processing period are each of the desired magnitudes. In other words, a spring 20 having a predetermined spring constant is selected so that the average back pressure in the first half of the processing period and the average back pressure in the second half of the processing period are each of the desired magnitudes.

As explained above, according to this embodiment, when the punch 12 is pressed against the pressure application surface 30a of the workpiece 30, the back pressure punch 18 applies back pressure to the back surface 30b of the workpiece 30. The back pressure punch 18 moves through the die opening 14a due to the pressing force of the punch 12. Therefore, the back pressure punch 18 is not deformed by the pressing force of the punch 12. Therefore, there is no need to replace the back pressure punch 18 every time processing is performed, and productivity is high.

Furthermore, according to this embodiment, the spring 20 makes the maximum value of the back pressure in the latter half of the processing period greater than the maximum value of the back pressure in the first half of the processing period. This increases the force pressing the newly active surfaces together, compared to when the magnitude of the back pressure during the entire processing period is constant at a small back pressure equal to or less than the maximum value of the back pressure during the first half of the processing period in this embodiment. This increases the bonding strength. Also, compared to when the magnitude of the back pressure during the entire processing period is constant at a large back pressure equal to the maximum value of the back pressure during the second half of the processing period in this embodiment, the amount of plastic deformation can be increased, and the area of the newly active surfaces can be increased. This increases the bonding strength.

In other words, according to this embodiment, the spring 20 makes the average value of the back pressure in the latter half of the processing period greater than the average value of the back pressure in the first half of the processing period. This increases the force pressing the newly active surfaces together, compared to when the magnitude of the back pressure during the entire processing period is constant at a small back pressure equal to the back pressure at any time during the first half of the processing period in this embodiment. This increases the bonding strength. Also, compared to when the magnitude of the back pressure during the entire processing period is constant at a large back pressure equal to the back pressure at any time during the second half of the processing period in this embodiment, the amount of plastic deformation can be increased, and the area of the newly active surfaces can be increased. This increases the bonding strength.

In this embodiment, the backpressure in the latter half of the processing period is set to be greater than the backpressure at any time during the first half of the processing period. However, if the maximum value of the backpressure in the latter half of the processing period is greater than the maximum value of the backpressure in the first half of the processing period, the backpressure in the latter half of the processing period may be temporarily smaller than the backpressure at any time during the first half of the processing period. Also, if the average value of the backpressure in the latter half of the processing period is greater than the average value of the backpressure in the first half of the processing period, the backpressure in the latter half of the processing period may be temporarily smaller than the backpressure at any time during the first half of the processing period.

Second Embodiment
5, this embodiment differs from the first embodiment in that the joining apparatus 10 includes an air cylinder 22 as a back pressure adjusting unit. The air cylinder 22 has a container 221 filled with air and a piston 222 disposed inside the container 221. The piston 222 changes the internal volume of the container 221. The piston 222 is linked to the back pressure punch 18.

The back pressure punch 18 moves through the workpieces 30 due to the pressure of the punch 12. This movement of the back pressure punch 18 compresses the air filled in the air cylinder 22. The compressed air generates a reaction force against the load compressing the air. As the movement of the back pressure punch 18 increases, the amount of compression of the air filled in the air cylinder 22 increases, and the reaction force increases. This reaction force is applied as back pressure from the back pressure punch 18 to the workpieces 30. In this way, the air cylinder 22 increases its back pressure as the movement of the back pressure punch 18 increases.

Other configurations of the joining device 10 and the joining method are the same as those of the first embodiment. Therefore, the same effects as those of the first embodiment can be obtained. In this embodiment, an air cylinder 22 in which air is filled inside the container 221 is used as the back pressure adjustment unit. However, a gas cylinder in which a gas other than air is filled inside the container 221 may also be used as the back pressure adjustment unit.

Third Embodiment
As shown in Fig. 6, this embodiment differs from the first embodiment in that the welding apparatus 10 includes a servo motor 24 as a back pressure adjustment unit. The servo motor 24 is an electric motor that drives the back pressure punch 18. The servo motor 24 can increase the back pressure applied from the back pressure punch 18 to the back surface 30b of the workpieces 30 in a stepwise and continuous manner. The other configurations of the welding apparatus 10 are the same as those of the first embodiment.

In the joining method of the present embodiment, the back pressure is controlled by the servo motor 24 during the period from when the pressing by the punch 12 starts to when the pressing is finished, as shown in FIG.
At the start of pressing, the back pressure is set to a small value, as in the first embodiment. From the start of pressing until a certain point, the back pressure gradually increases in order to promote plastic deformation. After that, at a certain point, the back pressure suddenly increases, and from the certain point until the end of pressing, the back pressure is kept constant at a large value.

In this manner, in the joining method of this embodiment, the servo motor 24 gradually increases the back pressure, so that the maximum back pressure in the latter half of the processing period is made greater than the maximum back pressure in the first half of the processing period, as shown in FIG. 7. In other words, the average back pressure in the latter half of the processing period is made greater than the average back pressure in the first half of the processing period. The joining method is the same as in the first embodiment, except for the adjustment of the back pressure. Therefore, the same effects as in the first embodiment can be obtained in this embodiment as well.

In this embodiment, the back pressure is suddenly increased at a point after the midpoint of the processing period. However, if the maximum value of the back pressure in the latter half of the processing period is greater than the maximum value of the back pressure in the first half of the processing period, the back pressure may be suddenly increased at a point before the midpoint. Also, if the average value of the back pressure in the latter half of the processing period is greater than the average value of the back pressure in the first half of the processing period, the back pressure may be suddenly increased at a point before the midpoint.

Fourth Embodiment
As shown in Fig. 8, this embodiment differs from the first embodiment in the shape of the tip surface 18a of the back pressure punch 18. The tip surface 18a has a convex shape in which the area facing the punch 12 is raised. More specifically, the tip surface 18a has a convex portion 18b and a flat portion 18c located around the convex portion 18b. The convex portion 18b is a convex spherical surface. The flat portion 18c is a flat surface.

As shown in FIG. 9, the convex portion 18b is located on the entire portion of the tip face 18a that faces the tip face 12a of the punch 12 in the axial direction of the punch 12. The portion of the tip face 18a that faces the tip face 12a of the punch 12 in the axial direction of the punch 12 is a portion that coincides with the entire projected tip face 12a of the punch 12 when the tip face 12a of the punch 12 is projected onto the tip face 18a of the back pressure punch 18 in the axial direction of the punch 12. Thus, in this embodiment, the entire portion of the tip face 18a that faces the tip face 12a of the punch 12 in the axial direction of the punch 12 is convex.

As shown in FIG. 9, this back pressure punch 18 is used to perform joining by cold forging, as in the first embodiment. The configuration of the joining device 10 and the joining method, other than the shape of the tip surface 18a, are the same as in the first embodiment. The left side of FIG. 9 shows a cross-sectional view of the joining area when pressing begins. The right side of FIG. 9 shows a cross-sectional view of the joining area when pressing ends.

According to this embodiment, the pressing force from the punch 12 is concentrated on the portion of the workpiece 30 that is sandwiched between the punch 12 and the protruding portion 18b of the back pressure punch 18. As a result, as shown in the right part of Figure 9, the material flows more in that portion and the portion becomes thinner compared to when the tip surface 18a of the back pressure punch 18 is flat.

As shown by the solid line in FIG. 10, the surface pressure at the bonding interface at this portion increases compared to when the tip surface 18a of the back pressure punch 18 is flat, as shown by the dashed line in FIG. 10. The vertical axis in FIG. 10 indicates the surface pressure at the bonding interface at the end of pressing. The horizontal axis in FIG. 10 indicates the distance r from the center position in the radial direction of the back pressure punch 18, as shown by the arrow in FIG. 9.

In addition, as shown by the solid line in FIG. 11, the surface expansion ratio of each of the first metal sheet material 31 and the second metal sheet material 32 at that portion increases compared to when the tip surface 18a of the back pressure punch 18 is flat, as shown by the dashed line in FIG. 11. The vertical axis in FIG. 11 indicates the surface expansion ratio of one of the first metal sheet material 31 and the second metal sheet material 32 at the end of pressing. The horizontal axis in FIG. 11 indicates the distance r from the center position in the radial direction of the back pressure punch 18, as shown by the arrow in FIG. 9.

As described above, according to this embodiment, a back pressure punch 18 is used in which the portion of the tip surface 18a of the back pressure punch 18 that faces the tip surface 12a of the punch 12 has a convex shape. Therefore, compared to when the entire tip surface 18a of the back pressure punch 18 is flat, the surface expansion ratio can be increased in the portion of the workpiece 30 that faces the punch 12 in the axial direction of the punch 12, and the number of newly active surfaces can be increased. Also, compared to when the entire tip surface 18a of the back pressure punch 18 is flat, the surface pressure of the joining interface in that portion of the workpiece 30 can be increased, and the bonding between the newly active surfaces can be promoted. As a result, the joining strength can be increased.

In this embodiment, the entire portion of the tip surface 18a of the back pressure punch 18 that faces the tip surface 12a of the punch 12 is convex. However, only a portion of the tip surface 18a of the back pressure punch 18 that faces the tip surface 12a of the punch 12 may be convex.

In addition, in this embodiment, only the portion of the tip surface 18a of the back pressure punch 18 that faces the tip surface 12a of the punch 12 is convex. However, the entire tip surface 18a of the back pressure punch 18 may be convex.

In addition, in this embodiment, the convex portion 18b is a convex spherical surface. However, the convex portion 18b may be a convex curved surface that is a curved surface other than a spherical surface. In other words, at least a portion of the tip surface 18a of the back pressure punch 18 that faces the tip surface 12a of the punch 12 may have a rounded convex shape.

Furthermore, in this embodiment, as in the first embodiment, the maximum value of the back pressure in the second half of the processing period is set to be greater than the maximum value of the back pressure in the first half of the processing period. In other words, the average value of the back pressure in the second half of the processing period is set to be greater than the average value of the back pressure in the first half of the processing period. However, the back pressure may be set to a constant value throughout the entire processing period. Even in this case, the effect of this embodiment can be obtained.

Other Embodiments
(1) A back pressure adjusting unit different from those in the above-described embodiments can be used. For example, when the back pressure punch 18 moves in the same direction as the pressing direction of the punch 12, a constant back pressure is applied from the back pressure punch 18 to the workpiece 30 by the hydraulic back pressure applying unit until the back pressure punch 18 reaches a fixing member that fixes the position of the back pressure punch 18. After the back pressure punch 18 reaches the fixing member, the back pressure is applied by a reaction force against the pressing force of the punch 12. As a result, the maximum value of the back pressure in the latter half of the processing period may be made larger than the maximum value of the back pressure in the first half of the processing period. In other words, the average value of the back pressure in the latter half of the processing period may be made larger than the average value of the back pressure in the first half of the processing period. In this case, the hydraulic back pressure applying unit and the fixing member constitute the back pressure adjusting unit.

(2) In each of the above-described embodiments, the punch 12 and the back pressure punch 18 are each a columnar pin and are shaped to press the workpieces 30 in a point-like manner. However, the punch 12 and the back pressure punch 18 may each have another shape. For example, the punch 12 and the back pressure punch 18 may each be shaped to press the workpieces 30 in a line-like manner. Also, the punch 12 and the back pressure punch 18 may each be shaped to press the workpieces 30 in a ring-like manner that continues in the circumferential direction.

(3) In each of the above-described embodiments, the members to be joined 30 are two metal plate materials. However, the members to be joined 30 may be three or more metal plate materials.

(4) The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the claims, and includes various modified examples and modifications within the equivalent scope. The above-described embodiments are not unrelated to each other, and can be combined as appropriate, except when the combination is clearly impossible. In the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except when they are specifically stated to be essential or when they are clearly considered to be essential in principle. In the above-described embodiments, when the numbers, values, amounts, ranges, etc. of the components of the embodiments are mentioned, they are not limited to the specific numbers, except when they are specifically stated to be essential or when they are clearly limited to a specific number in principle. In the above-described embodiments, when the materials, shapes, positional relationships, etc. of the components are mentioned, they are not limited to the materials, shapes, positional relationships, etc., except when they are specifically stated to be essential or when they are clearly limited to a specific material, shape, positional relationship, etc. in principle.

REFERENCE SIGNS LIST 10: joining device 12: punch 14: die 18: back pressure punch 20: spring 22: air cylinder 24: servo motor 30: member to be joined

Claims (4)

A cold forging joining method for joining a joined member (30) having a plurality of overlapping metal plate materials (31, 32) by cold forging, comprising:
placing the workpieces (30) on a joining device (10) including a punch (12) that presses a pressure operating surface (30a) of the workpieces (30); a die (14) on which the workpieces are placed and which has a die opening (14a) formed in a portion facing the punch; a back pressure punch (18) that is movably disposed relative to the die opening and applies back pressure to a back surface (30b) of the workpieces on the opposite side to the pressure operating surface; and a back pressure adjustment unit (20, 22, 24) that adjusts the back pressure;
pressing the pressure actuation surface of the workpieces with the back pressure punch while applying the back pressure to the back surface of the workpieces with the back pressure punch;
In the pressing,
A portion of the workpiece pressed by the punch is plastically deformed, so that a concave portion (311) is formed on the pressure acting surface and a convex portion (312) is formed on the back surface,
the back pressure adjusting unit makes the maximum value of the back pressure in a second half of a processing period from the start of pressing of the punch to the end of pressing of the punch greater than the maximum value of the back pressure in a first half of the processing period;
A cold forging joining method in which active new surfaces that appear on the surfaces of the multiple metal plate materials due to the expansion of the surface area of the surfaces caused by the plastic deformation are pressed against each other and adhered to each other by the pressing force of the punch and the back pressure of the back pressure punch, thereby solid-state joining the multiple metal plate materials. A cold forging joining method for joining a joined member (30) having a plurality of overlapping metal plate materials (31, 32) by cold forging, comprising:
placing the workpieces (30) on a joining device (10) including a punch (12) that presses a pressure operating surface (30a) of the workpieces (30); a die (14) on which the workpieces are placed and which has a die opening (14a) formed in a portion facing the punch; a back pressure punch (18) that is movably disposed relative to the die opening and applies back pressure to a back surface (30b) of the workpieces on the opposite side to the pressure operating surface; and a back pressure adjustment unit (20, 22, 24) that adjusts the back pressure;
pressing the pressure actuation surface of the workpieces with the back pressure punch while applying the back pressure to the back surface of the workpieces with the back pressure punch;
In the pressing,
A portion of the workpiece pressed by the punch is plastically deformed, so that a concave portion (311) is formed on the pressure acting surface and a convex portion (312) is formed on the back surface,
The back pressure adjusting unit makes an average value of the back pressure in a second half of a processing period from a start of pressing of the punch to an end of pressing of the punch larger than an average value of the back pressure in a first half of the processing period,
A cold forging joining method in which active new surfaces that appear on the surfaces of the multiple metal plate materials due to the expansion of the surface area of the surfaces caused by the plastic deformation are pressed against each other and adhered to each other by the pressing force of the punch and the back pressure of the back pressure punch, thereby solid-state joining the multiple metal plate materials. The cold forging joining method according to claim 1 or 2, in which at least a portion of the tip surface (18a) of the back pressure punch that faces the tip surface (12a) of the punch in the axial direction of the punch has a rounded convex shape. A cold forging joining method for joining a joined member (30) having a plurality of overlapping metal plate materials (31, 32) by cold forging, comprising:
placing the workpieces (30) on a joining device (10) including a punch (12) that presses a pressure operating surface (30a) of the workpieces (30); a die (14) on which the workpieces are placed and which has a die opening (14a) formed in a portion facing the punch; a back pressure punch (18) that is movably disposed relative to the die opening and applies back pressure to a back surface (30b) of the workpieces on the opposite side to the pressure operating surface; and a back pressure adjustment unit (20, 22, 24) that adjusts the back pressure;
pressing the pressure actuation surface of the workpieces with the back pressure punch while applying the back pressure to the back surface of the workpieces with the back pressure punch;
In the pressing,
A portion of the workpiece pressed by the punch is plastically deformed, so that a concave portion (311) is formed on the pressure acting surface and a convex portion (312) is formed on the back surface,
As the back pressure punch, one is used in which at least a part of a portion of a tip surface (18a) of the back pressure punch that faces the tip surface (12a) of the punch in the axial direction of the punch has a rounded convex shape,
A cold forging joining method in which active new surfaces that appear on the surfaces of the multiple metal plate materials due to the expansion of the surface area of the surfaces caused by the plastic deformation are pressed against each other and adhered to each other by the pressing force of the punch and the back pressure of the back pressure punch, thereby solid-state joining the multiple metal plate materials.

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