Patent Application
20100285328
1. Field of the Invention
The invention relates to a press-forming method in which a desired portion of a formed part can be quenched, as well as a press-formed part using a plate manufactured according to this kind of press-forming method.
2. Description of the Related Art
Japanese Patent Application Publication No. 2007-75834 (JP-A-2007-75834) describes a hot press-forming die for press-forming metal plate. A coolant supply discharge port that opens on the side of the forming surface is formed in the hot press-forming die. This coolant discharge port is connected to a coolant supply conduit and is able to discharge coolant. Also, a concave portion that opens on the forming surface is formed on the hot press-forming die. The cooling effects from the coolant discharged from the coolant discharge port and the concave portion enable the strength of the hot press-formed part to be changed in steps.
However, the hot press-forming die described in JP-A-2007-75834 must be provided with a complex die cooling structure formed by the coolant supply conduit and the concave portion described above, and what is more, the hot press-forming die is only able to change the strength of the hot press-formed part in steps.
This invention thus provides a press-forming method which quenches a desired portion without making the die structure complex, as well as a press-formed part obtained by that press-forming method.
A first aspect of the invention relates to a press-forming method that includes i) a heating process of connecting an electrode to one end of a plate in a direction orthogonal to the thickness direction of the plate and connecting another electrode to the other end of the plate in the direction orthogonal to the thickness direction of the plate, and heating the plate by passing current from the one end to the other end, and controlling the temperature distribution of the plate while the current is passing through the plate by establishing, in the plate, a current density changing portion where the current density in the plate is different than the current density at another portion while current is passing through the plate; and ii) a forming process of forming the plate into a predetermined shape by pressing and cooling the plate which has been heated in the heating process.
With this press-forming method, in the heating process, an electrode is connected to one end of the plate in a direction orthogonal to the thickness direction of the plate and another electrode is connected to the other end of the plate in the direction orthogonal to the thickness direction of the plate, and current is passed through the plate. Passing current through the plate in this way heats the plate. The plate that has been heated in the heating process in this way is then formed into a desired shape by being pressed and cooled in a forming process.
Here, a current density changing portion where the current density is different than it is at another portion while the current is passing through the plate is established in the plate. As a result, the plate is not heated uniformly. Instead, the plate is heated with a temperature distribution corresponding to the region where the current density changing portion is established. When the plate that has been heated in this way is press-formed and cooled in the forming process, both a portion that has been so-called quenched corresponding to the region where the current density changing portion is established and a portion that has not been quenched are formed on the formed plate, i.e., the press-formed part (or that unfinished part).
As a result, the portion of the press-formed part to be strengthened is sufficiently heated in the heating process and quenched by cooling in the forming process. Portions that are to be welded or the like later or that are to be worked, e.g., bent or punched, are able to retain good characteristics for welding or working by either not being quenched as a result of being cooled in the forming process after not being sufficiently heated in the heating process, or being quenched to a lesser degree.
Moreover, the heating of the quenchable portion and the non-quenchable portion of the plate is controlled in the heating process prior to the forming process. Therefore, even if a complex cooling structure of the like for cooling only the predetermined region is not used in a die that is used in the forming process, the quenched portion and the non-quenched portion of the press-formed part can still be formed appropriately. As a result, the die cost and the like can be reduced.
As described above, the quenchable portion and the non-quenchable portion can be appropriately established in the plate in the heating process before the forming process where the press-forming and cooling take place. As a result, a complex die cooling structure is not necessary during forming so the die cost and the like can be reduced.
The heating process may be performed with a portion of the plate where the sectional area when the plate is cut in a direction orthogonal to the direction of current flow from the one end of the plate to the other end of the plate is different than the sectional area of another portion of the plate, serving as the current density changing portion.
The current density changing portion is established by making the sectional area at a portion of the plate, when the plate is cut in a direction orthogonal to the direction of current flow from one end to the other end of the plate, different from the sectional area at another portion of the plate. If the sectional area of the plate at the current density changing portion is smaller than the sectional area at the other portion of the plate, then when current is passed from one end to the other end of the plate in the heating process, the current density will basically become higher at the current density changing portion than it will at the other portion so the temperature at the current density changing portion will be higher than the temperature at the other portion. On the other hand, if the sectional area of the plate at the current density changing portion is larger than the sectional area at the other portion of the plate, then when current is passed from one end to the other end of the plate in the heating process, the current density will basically become lower at the current density changing portion than it will at the other portion so the temperature at the current density changing portion will be lower than the temperature at the other portion.
When the plate is press-formed and cooled in the forming-process after the heating process, the current density changing portion is quenched if the sectional area thereof is smaller than the sectional area of the other portion of the plate, and not quenched if the sectional area thereof is larger than the sectional area of the other portion of the plate. In this way, changing the shape of the plate such that the sectional area changes as described above in this way enables the current density changing portion to be easily established so that a quenchable portion and a non-quenchable portion can be incorporated into the plate before the forming portion.
The heating process may be performed with the current density changing portion established in a predetermined region of the plate in the direction of current flow by changing the width the plate orthogonal to both the direction of current flow from the one end of the plate to the other end of the plate and the thickness direction of the plate, in the direction of current flow.
The current density is increased by heating the plate by conduction in the heating process at a portion where the width of the plate narrows and an area near the corners formed on the plate by reducing the width of the plate. Accordingly, the temperature becomes higher there than it does at other portions. As a result, when the plate which has been through the heating process is press-formed and cooled in the forming process, the portion of the formed part where the current density is high in the plate is quenched and the portion where the current density is not high is not quenched. Therefore, the portion and the surrounding area of the formed part that is to be quenched can be made a quenchable portion in the heating process so that it can be quenched in the forming process, by shaping the plate so that the current density will become high at that portion before the plate reaches the forming process.
Changing the width of the plate in the direction of current flow makes it possible to ensure that a predetermined region of the plate in the direction of current flow is quenched and the rest of the plate is not quenched in the forming process after the heating process.
The heating process may be performed with the current density changing portion established in the plate by gradually reducing the width of the plate from one end side of the plate in the direction of current flow toward the other end side of the plate in the direction of current flow, such that the current density at the other end side is higher than the current density at the one end side.
In this case, when the plate is heated by conduction in the heating process, the heating temperature is lower at one end side of the plate in the direction of current flow and gradually increases toward the other end side. As a result, when the plate is press-formed and cooled in the forming process, the portion corresponding to the one end side of the plate of the formed part in the direction of current flow in the heating process is not quenched, or the region that is quenched can be reduced, and the portion corresponding to the other end side of the plate is quenched.
That is, the quenched region can be set.
The heating process may be performed with the current density changing portion established in the plate by forming a step in the width direction in the plate.
The current density changing portion is established in the plate by forming a step in the width direction of the plate in the plate. Therefore, when the plate is heated by conduction in the heating process, the current density increases near the corner of the plate at the portion where the step is formed, so the heating temperature at the area near this corner becomes locally high. As a result, when the plate is press-formed and cooled in the forming process, the area near the corner of the plate at the portion where the step is formed on the formed part can be locally quenched.
The heating process may be performed with the current density changing portion established in the plate by shaping an edge portion of the plate in the width direction that is toward the center portion with respect to both end sides of the plate in the direction of current flow so that the edge portion of the plate in the width direction is displaced toward the center of the plate in the width direction, such that the current density on the center portion side becomes higher than the current density on both end sides of the plate in the direction of current flow.
The edge portion in the width direction of the plate is bent or curved, for example, so that it is displaced toward the center portion side in the width direction, on the center portion side compared with both end sides of the plate in the direction of current flow. Therefore, a current density changing portion where the current density becomes higher on the edge portion side in the width direction that is bent or curved, as described above, and toward the center portion of the plate in the direction of current flow, is established in the plate.
Therefore, when the plate is heated by conduction in the heating process, the heating temperature is low on both end sides of the plate in the direction of current flow, and high on the center portion side of the plate in the direction of current flow (more specifically, on the center portion side of the plate in the direction of current flow and on the side of the edge portion in the width direction that is bent or curved as described above). As a result, when the plate is press-formed and cooled in the forming process, the portion of the formed part corresponding to both end sides of the plate in the direction of current flow is not quenched, or the region that is quenched can be reduced, and the portion of the formed part corresponding to the center portion side of the plate (more specifically, the portion corresponding to the center portion side of the plate in the direction of current flow and the side of the edge portion in the width direction that is bent or curved as described above) is quenched.
The heating process may be performed with the current density changing portion established in the plate by shaping an edge portion of the plate in the width direction that is toward the center portion with respect to both end sides of the plate in the direction of current flow so that the edge portion of the plate in the width direction is displaced toward the outside in the width direction of the plate, such that the current density on both end sides becomes higher than the current density on the center portion side of the plate in the direction of current flow.
The edge portion in the width direction of the plate is bent or curved, for example, so that it is displaced outward in the width direction on the center portion side compared with both end sides of the plate in the direction of current flow. Therefore, the current density changing portion where the current density is low on the center portion side in the direction of current flow of the plate and on the side of the edge portion in the width direction that is bent or curved as described above, is established in the plate.
Therefore, when the plate is heated by conduction in the heating process, the heating temperature is low on the center portion side of the plate in the direction of current flow (more specifically, on the center portion side of the plate in the direction of current flow and on the side of the edge portion in the width direction that is bent or curved as described above), and high on both end portion sides in the direction of current flow of the plate. As a result, when the plate is press-formed and cooled in the forming process, the portion of the formed part corresponding to the center portion side of the plate in the direction of current flow (more specifically, the portion corresponding to the center portion side of the plate in the direction of current flow and on the side of the edge portion in the width direction that is bent or curved as described above) is not quenched, or the region that is quenched can be reduced, and the portion of the formed part corresponding to the both end sides in the direction of current flow of the plate is quenched.
The heating process may be performed with the current density changing portion established in the plate by shaping the edge portions of the plate in the width direction so that the edge portions are displaced in the width direction in the direction of current flow, without changing the sectional area of the plate in the direction of current flow, when the plate is cut in a direction orthogonal to the direction of current flow from the one end of the plate to the other end of the plate.
The current density changing portion is established by shaping the plate such that the sectional area of the plate when it is cut in a direction orthogonal to the direction of current flow does not change, but the edge portions in the width direction of the plate change. As a result, the current density becomes higher on the side of the edge portion of the plate in the width direction that is displaced so as to curve inward in the width direction than it does on the side of the edge portion of the plate in the width direction that is displaced so as to bulge outward in the width direction.
Therefore, when the plate is heated by conduction in the heating process, the heating temperature of the plate is low on the side where the edge portion in the width direction bulges outward in the width direction, and is high on the side where the edge portion in the width direction curves inward in the width direction. As a result, when the plate is press-formed and cooled in the forming process, the portion of the formed part corresponding to the side where the edge portion of the plate bulges outward in the width direction is not quenched, or the region that is quenched can be reduced, and the portion of the formed part corresponding to the side where the edge portion of the plate in the width direction curves inward in the width direction is quenched.
The heating process may be performed with the current density changing portion established in the plate by making the thickness at one portion of the plate different from the thickness at another portion of the plate in the direction of current flow from the one end of the plate toward the other end of the plate.
The current density changing portion is established in the plate by making the thickness at one portion of the plate different than it is at another portion of the plate in the direction of current flow. Therefore, when the plate is heated by conduction in the heating process, the current density becomes higher at the portion where the plate is thinner than it does at the portion where the plate is thicker.
Therefore, the heating temperature of the plate can be locally increased by locally reducing the thickness of the plate and then heating the plate by conduction. Also, when the thickness of the plate is changed by gradually being reduced in the direction of current flow, the heating temperature of the plate can be gradually increased in the direction of current flow. As a result, when the plate is press-formed and cooled in the forming process, the portion of the formed part where the thickness of the plate has been reduced can be quenched.
Locally reducing the thickness of the plate enables the plate to be locally quenched in the forming process after the heating process. Also, gradually changing the thickness in the direction of current flow enables a predetermined region of the plate in the direction of current flow to be quenched in the forming process after the heating process.
The heating process may be performed with the density current changing portion established in the plate by forming a hole in the thickness direction through the plate.
A hole is formed in the plate, which reduces the sectional area of the plate at the portion where the hole is formed. Therefore, when the plate is heated by conduction in the heating process, the current density increases next to the hole in a direction orthogonal to both the thickness direction of the plate and the direction of current flow. As a result, the heating temperature of the plate increases at the portion beside the hole. Therefore, when the plate is press-formed and cooled in the forming process, only the portion of the formed part corresponding to the portion next to the hole and the portion near that portion is quenched.
A second aspect of the invention relates to a press-formed part i) which is formed by press-forming and cooling a plate which is connected to an electrode at one end in a direction orthogonal to the thickness direction and connected to another electrode at the other end in the direction orthogonal to the thickness direction and heated by passing current between the electrodes, and controlled to have a predetermined temperature distribution while the current is passing between the electrodes by establishing, at a predetermined portion between the electrodes, a portion where the current density is different than the current density at another portion, and ii) in which a portion where the current density is low is not quenched and a portion where the current density is high is quenched.
The plate used to form this press-formed part is connected to an electrode at one end in a direction orthogonal to the thickness direction and connected to another electrode at the other end in the direction orthogonal to the thickness direction, and then heated by passing current between the electrodes. Moreover, a portion where the current density is different than the current density at another portion is established at a predetermined portion of this plate between the electrodes. Therefore, when current is passing between the electrodes, the portion of the plate where the current density is high is heated to a high temperature, while the portion of the plate where the current density is low is not heated to a high temperature. In this way, the plate is heated with the desired temperature distribution, so a quenchable portion is formed at a desired portion of the plate and a non-quenchable portion is formed at another desired portion before press-forming.
Therefore, with the press-formed part that is formed by press-forming and cooling this kind of a plate, the desired portion is quenched, thereby improving the mechanical strength. Meanwhile, the other desired portion is not quenched, which makes it possible to take advantage of a portion that is not quenched, such as improved rust-proof performance when rust-proofing has been performed and improved weldability during welding. Moreover, the quenchable portion and the non-quenchable portion are incorporated into the plate before the plate is press-formed. As a result, a complex die cooling structure is not necessary during forming so the die cost and the like can be reduced.
The foregoing and further objects, features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:
An electrode 12 is connected to the lower base side of the flat metal plate 10, and an electrode 14 is connected to the upper base side of the flat metal plate 10. The electrode 12 is connected to a positive terminal of a power supply 18 of a quenching apparatus 16, and the electrode 14 is connected to a negative terminal of the power supply 18 of the quenching apparatus 16. Therefore, in the press-forming method according to this example embodiment, current flows from the lower base side toward the upper base side of the flat metal plate 10 which is trapezoidal when viewed from above.
Next, the operation and effects of this example embodiment will be described through a description of the processes in the press-forming method according to this example embodiment.
In the press-forming method according to this example embodiment, the flat metal plate 10 is heated by conduction in a heating process. As shown in
Here,
In this example embodiment, as described above, the width of the flat metal plate 10 gradually decreases in the direction in which the current flows through the flat metal plate 10, i.e., in the direction from the electrode 12 to the electrode 14, so the current density gradually increases in the direction from the electrode 12 to the electrode 14. In particular, when the portion where the current density increases to the point at which the flat metal plate 10 can be heated to between 850° C. and 950° C. is designated a current density changing portion 22 in this example embodiment, the hatched portion in
Here, in the example shown in
In contrast, in the example shown in
Also, In contrast, in the example shown in
In this way, with the flat metal plate 10 having a trapezoidal shape when viewed from above, the current density changing portion 22 is formed on the upper base side with respect to the center portion of the flat metal plate 10 in the direction in which current flows when current flows from the lower base side toward the upper base side of the flat metal plate 10 in the heating process. As a result, a quenchable portion is formed on the upper base side with respect to the center portion of the flat metal plate 10 in the direction in which current flows, and a non-quenchable portion is formed on the lower base side with respect to the center portion of the flat metal plate 10 in the direction in which current flows.
The flat metal plate 10 that has been heated by conduction as described above in the heating process is then press-formed into a predetermined shape in a forming process. In this forming process, the heated flat metal plate 10 is set into a die 24 as shown in
In this way, with the press-forming method according to this example embodiment, forming the flat metal plate 10 in a trapezoidal shape when viewed from above enables the quenchable region from the upper base side of the flat metal plate 10 to be set by the ratio of the widths of the flat metal plate 10 at the upper and lower base sides of the trapezoid when heating the flat, metal plate 10 by conduction in the heating process. Therefore, applying this example embodiment makes it possible to easily manufacture a press-formed part in which only a predetermined region to one side of the center portion in a direction orthogonal to the thickness direction of the flat metal plate 10 in the state shown in
Moreover, the flat metal plate 10 which has been heated by conduction in the heating process is press-formed in the forming process so the structure of the die 24, and more particularly, the cooling structure of the die 24, does not have to be complex, which enables the cost of the die and the like to be reduced.
Next, other example embodiments of the invention will be described. In the descriptions of these example embodiments, portions that are basically the same as portions in the first example embodiment described above will be denoted by the same reference characters and descriptions of those portions will be omitted. Also, in the second to the eighth example embodiments described below, the forming process is basically the same as it is in the first example embodiment described above so the description relating to the forming process will be omitted in the descriptions of the second to the eighth example embodiments.
However, the dimension D4 of the narrow portion 36 in the width direction of the flat metal plate 30 is set smaller than the dimension D3 of the wide portions 32 and 34 in the same direction. The end of the narrow portion 36 on the wide portion 32 side is connected to the end of the wide portion 32 on the narrow portion 36 side with the center of the end of the wide portion 32 in the width direction of the flat metal plate 30 substantially aligned with the center of the end of the narrow portion 36 in the width direction of the flat metal plate 30. Also, the end of the narrow portion 36 on the wide portion 34 side is connected to the end of the wide portion 34 on the narrow portion 36 side with the center of the end of the wide portion 34 in the width direction of the flat metal plate 30 substantially aligned with the center of the end of the narrow portion 36 in the width direction of the flat metal plate 30.
In this way, the electrode 12 is connected to the wide portion 32 of the flat metal plate 30, which is formed by the wide portions 32 and 34 and the narrow portion 36, and the electrode 14 is connected to the wide portion 34. Therefore, current flows from the wide portion 32 to the wide portion 34 through the narrow portion 36. Also, the boundary between the wide portion 32 and the narrow portion 36 of the flat metal plate 30 is designated as a current density changing portion 38, and the boundary between the wide portion 34 and the narrow portion 36 is designated as a current density changing portion 40. When the flat metal plate 30 is cut in the direction orthogonal to the direction in which current flows between the electrodes 12 and 14, the sectional area suddenly changes at the current density changing portions 38 and 40.
The electrodes 12 and 14 are connected to the flat metal plate 30 structured as described above and that flat metal plate 30 is then heated by conduction in a heating process. In this state, the flat metal plate 30 is heated by the electrical resistance of the flat metal plate 30 when current is made to flow from the electrode 12 toward the electrode 14 through the flat metal plate 30. Here, even though the thickness of the flat metal plate 30 is uniform, the narrow portion 36 positioned in the center portion of the flat metal plate 30 in the direction in which the current flows is narrower in the width direction of the flat metal plate 30 than the wide portion 32 where the electrode 12 is connected and the wide portion 34 where the electrode 14 is connected. Therefore, the sectional area of the narrow portion 36 cut in the direction orthogonal to the direction in which current flows is smaller than the sectional areas of the wide portions 32 and 34. Accordingly, the current density is higher at the narrow portion 36 than it is at the wide portions 32 and 34 so the temperature increases at the narrow portion 36 of the flat metal plate 30.
Moreover, the narrow portion 36 is connected to the wide portions 32 and 34 such that the center of the narrow portion 36 in the width direction of the flat metal plate 30 is substantially aligned with the centers of the wide portions 32 and 34 in the width direction of the flat metal plate 30. As a result, steps in the width direction of the flat metal plate 30 are formed at both ends in the width direction of the flat metal plate 30 at the current density changing portion 38 which is the boundary between the narrow portion 36 and the wide portion 32, and at the current density changing portion 40 which is the boundary between the narrow portion 36 and the wide portion 34. Accordingly, when current flows between the electrodes 12 and 14, the current density becomes particularly high on both end sides in the width direction of the flat metal plate 30 at the current density changing portions 38 and 40. As a result, the temperature becomes particularly high near the outside edge of each of the four corners of the narrow portion 36 in the width direction of the flat metal plate 30.
In
A steel sheet to be quenched that is 1.2 mm thick is used for each flat metal plate 30 shown in
With the flat metal plate 30 shown in
In contrast, with the flat metal plate 30 shown in
Furthermore, with the flat metal plate 30 shown in
In this way, with the press-forming method according to this example embodiment, forming the narrow portion 36 in the center of the flat metal plate 30 in the direction in which current flows when the flat metal plate 30 is heated by conduction in the heating process creates the current density changing portions 38 and 40 at the boundaries between the narrow portion 36 and the wide portions 32 and 34, respectively, during the heating process. As a result, quenchable portions can be established at and around the four corners of the narrow portion 36. Moreover, the regions of the quenchable portions at and around the four corners of the narrow portion 36 can be set by the ratio of the widths of the wide portions 32 and 34 in the width direction of the flat metal plate 30 to the width of the narrow portion 36 in the width direction of the flat metal plate 30. As a result, a press-formed part in which portions corresponding to predetermined regions at and around the four corners of the flat metal plate 30 have been quenched by press-forming and rapidly cooling the flat metal plate 30 in the forming process can easily be manufactured.
Moreover, the flat metal plate 30 that has been heated by conduction in the heating process is press-formed in the forming process so the structure of the die 24, and more particularly, the cooling structure of the die 24, does not have to be complex, which enables the cost of the die and the like to be reduced.
Next, a third example embodiment of the invention will be described.
Meanwhile, the flat metal plate 50 also has a trapezoidal portion 54 formed as a current density changing portion between the wide portion 34 and the narrow portion 36. The side of the trapezoidal portion 54 that is near the narrow portion 36 is parallel to the side of the trapezoidal portion 54 that is near the wide portion 34. The distance between the edges on both sides of the trapezoidal, portion 54 in the width direction of the flat metal plate 50 gradually becomes shorter from the side of the wide portion 34 toward the side of the narrow portion 36.
That is, in contrast to the flat metal plate 30 in the second example embodiment described above, in which the boundaries between the narrow portion 36 and the wide portions 32 and 34 are the current density changing portions 38 and 40, respectively, in this example embodiment the current density changing portions of the flat metal plate 50 (i.e., the trapezoidal portions 52 and 54) become wider farther away from the narrow portion 36. That is, in contrast to the flat metal plate 30, when the flat metal plate 50 is cut in a direction orthogonal to the direction of current flow, the sectional areas of the trapezoidal portions 52 and 54 gradually decrease from the side near the wide portions 32 and 34 toward the side near the narrow portion 36.
The electrodes 12 and 14 are connected to the flat metal plate 50 structured as described above and that flat metal plate 50 is then heated by conduction in a heating process. In this state, the sectional area of the flat metal plate 50 when the flat metal plate 50 is cut in a direction orthogonal to the direction of current flow is less at the narrow portion 36 than it is at the wide portions 32 and 34, just as it is with the flat metal plate 30 in the second example embodiment described above. Therefore, the current density is higher at the narrow portion 36 than it is at the wide portions 32 and 34, so the temperature of the flat metal plate 50 becomes higher at the narrow portion 36.
In addition, the dimensions of the trapezoidal portions 52 and 54 gradually become smaller toward the narrow portion 36 side. With this kind of structure, the temperature becomes higher particularly near both ends of the narrow portion 36 in the direction of current flow and near both ends of the narrow portion 36 in the width direction of the flat metal plate 50, just as with the flat metal plate 30 in the second example embodiment described above.
In
A steel sheet to be quenched that is 1.2 mm thick is used for each flat metal plate 50 shown in
Furthermore, with the flat metal plates 50 shown in
That is, with the flat metal plate 50 shown in
As described in the foregoing second example embodiment, with the structure shown in
In contrast, with the flat metal plate 50 shown in
Therefore, with the flat metal plate 50 shown in
Also, with the flat metal plate 50 shown in
In this way, with the press-forming method according to this example embodiment, when the flat metal plate 50 is heated by conduction in the heating process, the quenchable region at and around the four corners of the narrow portion 36 can be set by appropriately setting the inclination angle θ of the end portions in the width direction of the trapezoidal portions 52 and 54, even without changing the ratio of the sectional area of the narrow portion 36 to the sectional area of the wide portions 32 and 34. Therefore, the portions corresponding to the four corners and therearound of the narrow portion 36 of the flat metal plate 50 can be quenched by press-forming and rapidly cooling the flat metal plate 50 in the forming process. As a result, a press-formed part in which portions corresponding to the areas at and around the four corners of the flat metal plate 50 which is generally rectangular when viewed from above are quenched can be easily manufactured.
Moreover, the flat metal plate 50 which has been heated by conduction in the heating process is press-formed in the forming process so the structure of the die 24, and more particularly, the cooling structure of the die 24, does not have to be complex, which enables the cost of the die and the like to be reduced.
Next, a fourth example embodiment of the invention will be described.
Also, the other edge of the flat metal plate 70 in the width direction (i.e., the upper edge in
The electrodes 12 and 14 are connected to the flat metal plate 70 structured as described above and that flat metal plate 70 is then heated by conduction in a heating process. When current is passed through the flat metal plate 70, it flows along the shortest path from the electrode 12 to the electrode 14. In this case, the center of the flat metal plate 70 is offset from the ends where the electrodes 12 and 14 are attached as described above, so the current density along one edge of the flat metal plate 70 in the width direction gradually increases toward the center of the flat metal plate 70 in the length direction (i.e., in this example embodiment, the area of the flat metal plate 70 between the electrodes 12 and 14 serves as the current density changing portion). Therefore, when the flat metal plate 70 is heated by passing current through it, one side with respect to the center in the width direction of the flat metal plate 70 can be heated to a high temperature.
A steel sheet to be quenched that is 1.2 mm thick is used for each flat metal plate 70 shown in
However, the edges in the width directions of the flat metal plates 70 shown in
More specifically, with the flat metal plate 70 shown in
As shown in
Also, as shown in
In contrast, as shown in
In this way, with the press-forming method according to this example embodiment, a temperature change can be created in the flat metal plate 70 between one side of the flat metal plate 70 and the other side of the flat metal plate 70 in the width direction when heating the flat metal plate 70 by conduction in the heating process, by offsetting the center of the flat metal plate 70 in the length direction without changing the width of the flat metal plate 70. Therefore, a metal plate to be press-formed, which has a quenchable portion on one side in the width direction and a non-quenchable portion on the other side in the width direction, can be easily manufactured. Accordingly, a press-formed part of which a portion that corresponds to one side of the flat metal plate 70 in the width direction has been quenched by press-forming and rapidly cooling the flat metal plate 70 in the forming process can be easily manufactured.
Moreover, the flat metal plate 70 which has been heated by conduction in the heating process is press-formed in the forming process so the structure of the die 24, and more particularly, the cooling structure of the die 24, does not have to be complex, which enables the cost of the die and the like to be reduced. In this embodiment, the width of the center portion of the plate metal plate 70 may be narrower than that of the both end of the plate metal plate 70 on the electrodes 12 and 14 side.
Next, a fifth example embodiment of the invention will be described.
With this structure, the sectional area of the flat metal plate 90 cut in a direction orthogonal to the length direction of the flat metal plate 90 gradually decreases from the edges of the circular hole 92 in the length direction of the flat metal plate 90 toward the center. Therefore, the current density increases toward the center in the length direction of the flat metal plate 90 on the sides of the circular hole 92 in the width direction of the flat metal plate 90. That is, in this example embodiment, the side portions of the circular hole 92 in the width direction of the flat metal plate 90 serve as current density changing portions 94.
The electrodes 12 and 14 are connected to the flat metal plate 90 structured as described above and that flat metal plate 90 is then heated by conduction in a heating process. Basically, when current is passed through the flat metal plate 90, the current density is higher on the sides of the circular hole 92 in the width direction of the flat metal plate 90 than it is on the sides of the circular hole 92 in the length direction of the flat metal plate 90 because the sectional area of the flat metal plate 90 is less at the portions on the sides of the circular hole 92 (i.e., at the current density changing portion 94) in the width direction of the flat metal plate 90 than it is at the portions on the sides of the circular hole 92 in the length direction of the flat metal plate 90. Therefore, the temperature becomes higher on the sides of the circular hole 92 in the width direction of the flat metal plate 90 than it does on the sides of the circular hole 92 in the length direction of the flat metal plate 90.
Moreover, the sectional area of the flat metal plate 90 at the current density changing portions 94 becomes smaller toward the center of the circular hole 92 in the length direction of the flat metal plate 90 so the temperature becomes higher toward the center at the current density changing portion 94 than it does on both sides of the circular hole 92 in the length direction of the flat metal plate 90.
In this way, the portions corresponding to the sides of the circular hole 92 in the width direction of the flat metal plate 90 are quenched when the flat metal plate 90, which has been heated by conduction in the heating process, is press-formed and rapidly cooled in the forming process.
Forming the circular hole 92 next to a portion that is to be a quenchable portion in the width direction of the flat metal plate 90 enables a quenchable portion to be easily formed in a desired location. Also, quenchable portions of the flat metal plate 90 can easily be set by appropriately forming a plurality of circular holes 92 in the flat metal plate 90.
Moreover, the flat metal plate 90 which has been heated by conduction in the heating process is press-formed in the forming process so the structure of the die 24, and more particularly, the cooling structure of the die 24, does not have to be complex, which enables the cost of the die and the like to be reduced.
Incidentally, in this example embodiment, the current density changing portions 94 are created on the flat metal plate 90 by forming the circular hole 92 in the flat metal plate 90. Alternatively, however, a through-hole of any one of various shapes may be used instead of the circular hole 92.
Next, a sixth example embodiment of the invention will be described.
Therefore, with the flat metal plate 110, the sectional area of the flat metal plate 110 changes at the current density changing portion 112 by the thick plate portion 114 and the thin plate portion 116 even though the width of the flat metal plate 110 between the electrode 12 and the electrode 14 does not change. As a result, the current density becomes higher on the thin plate portion 116 side than it does on the thick plate portion 114 side.
The electrodes 12 and 14 are connected to the flat metal plate 110 structured as described above and that flat metal plate 110 is then heated by conduction in a heating process. When current is passed through the flat metal plate 110, the current density increases in the thin plate portion 116 as described above so the temperature is able to be higher at the thin plate portion 116 than it is at the thick plate portion 114. In particular, when the thin plate portion 116 is 1.2 mm thick and the thick plate portion 114 is changed between 1.4 mm thick (a 17% increase rate in the sectional area with respect to the think plate portion 116), 1.6 mm thick (a 33% increase rate in the sectional area with respect to the think plate portion 116), 1.8 mm thick (a 50% increase rate in the sectional area with respect to the think plate portion 116), and 2.3 mm thick (a 92% increase rate in the sectional area with respect to the think plate portion 116), it was confirmed that the temperature of the thick plate portion 114 was less than 850° C. in each case, even when the thin plate portion 116 was heated to a temperature of between 850° C. and 950° C.
In this way, it is possible to heat only the thin plate portion 116 of the flat metal plate 110 to a quenchable temperature without changing the width of the flat metal plate 110 in the heating process, by making the center portion in the length direction the current density changing portion 112 and changing the thickness of the flat metal plate 110 so that the side with the electrode 12 is a different thickness than the side with the electrode 14. Therefore, it is possible to quench the portion corresponding to the thin plate portion 16 of the flat metal plate 110 by press-forming and rapidly cooling the flat metal plate 110, which has been heated by conduction in the heating process, in the forming process.
Moreover, the flat metal plate 110 which has been heated by conduction in the heating process is press-formed in the forming process so the structure of the die 24, and more particularly, the cooling structure of the die 24, does not have to be complex, which enables the cost of the die and the like to be reduced.
Next, a seventh example embodiment of the invention will be described.
The electrodes 12 and 14 are connected to the flat metal plate 130 structured as described above and that flat metal plate 130 is then heated by conduction in a heating process. The flat metal plate 130 is similar to the flat metal plate 110 of the sixth example embodiment in that the thickness of the flat metal plate 130 on the electrode 12 side of the current density changing portion 132 that is in the center of the flat metal plate 130 in the length direction differs from the thickness of the flat metal plate 130 on the electrode 14 side of the current density changing portion 132. Therefore, when current is passed through the flat metal plate 130, the current density becomes higher at the thin plate portion 136 than it does at the thick plate portion 134, so the thin plate portion 136 is heated to a higher temperature than the thick plate portion 134 is. Meanwhile, the flat metal plate 130 has a trapezoidal shape when viewed from above, similar to the flat metal plate 10 of the first example embodiment.
Moreover, the current density changing portion 132 is parallel to both the end of the flat metal plate 130 on the electrode 12 side and the end of the flat metal plate 130 on the electrode 14 side, so the shape of the thin plate portion 136 when viewed from above is similar to the overall shape of the flat metal plate 130 when viewed from above, i.e., it is trapezoidal. Therefore, similar to the first example embodiment, the current density becomes higher on the shorter side, from among the two sides of the thin plate portion 136 that are parallel in the length direction, i.e., on the current density changing portion 132 side of the thin plate portion 136. Accordingly, the side of the thin plate portion 136 that is closer to the current density changing portion 132 is heated to a higher temperature than the side of the thin plate portion 136 that is closer to the electrode 12 in the length direction.
More specifically, when current flows through the plat metal plate 130 having the same shape as flat metal plate 110 shown in
In this way, it is possible to heat only the center portion on the electrode 12 side and the center portion on the electrode 14 side to the quenchable temperature by using the flat metal plate 130 that has a trapezoidal shape when viewed from above and has the current density changing portion 132 at the center portion in the length direction. Therefore, when the flat metal plate 130 which has been heated by conduction in the heating process is press-formed and rapidly cooled in the forming process, it is possible to quench only the portion corresponding to the center portion of the flat metal plate 130 on the electrode 12 side and the center portion of the flat metal plate 130 on the electrode 14 side.
Moreover, the flat metal plate 130 which has been heated by conduction in the heating process is press-formed in the forming process so the structure of the die 24, and more particularly, the cooling structure of the die 24, does not have to be complex, which enables the cost of the die and the like to be reduced.
Next, an eighth example embodiment of the invention will be described.
As shown in
Also, although not shown, the sectional shape of the current density changing portion 152 in the width direction of the flat metal plate 150 and the sectional shape of the current density changing portion 152 in the length direction of the flat metal plate 150, i.e., the sectional shape of the current density changing portion 152 cut along line 17-17 in
The electrodes 12 and 14 are connected to the flat metal plate 150 structured as described above and that flat metal plate 150 is then heated by conduction in a heating process. When current is passed through the flat metal plate 150, the current density becomes higher at the current density changing portion 152 because the sectional area of the flat metal plate 150 is less at the current density changing portion 152 which is circular when viewed from above than it is at other portions of the flat metal plate 150. Therefore, as shown in
Furthermore, as described above, the temperature becomes the highest at the center of the current density changing portion 152 when viewed from above, and that region extends out farther in the width direction of the flat metal plate 150 than it does in the length direction of the flat metal plate 150, i.e., in the direction in which the electrodes 12 and 14 oppose one another. Moreover, when the entire region of the current density changing portion 152 and the area therearound in the width direction of the flat metal plate 150 is heated to a quenchable temperature, i.e., between 850° C. and 950° C., the region of the quenchable temperature in the length direction of the flat metal plate 150 has been confirmed by the inventors to extend from the center of the current density changing portion 152 to a portion where the rate of change in the thickness compared with other portions of the current density changing portion 152 is up to approximately 10%.
Therefore, a desired portion of the flat metal plate 150 in the length direction can easily be heated to a quenchable temperature by forming the current density changing portion 152 by a punch or the like as described above. Therefore, the current density changing portion 152 of the flat metal plate 150 and the area around that current density changing portion 152 can be quenched by press-forming and rapidly cooling the flat metal plate 150, which has been heated by conduction in the heating process, in the forming process.
Moreover, the flat metal plate 150 which has been heated by conduction in the heating process is press-formed in the forming process so the structure of the die 24, and more particularly, the cooling structure of the die 24, does not have to be complex, which enables the cost of the die and the like to be reduced.
Next, example embodiments of a press-formed part based on the first to eighth example embodiments described above will be described as ninth and tenth example embodiments of the invention based on the example embodiments described above.
More specifically, as shown in
The press-formed part 310 having this kind of structure is formed by press-forming a flat metal plate 330 that serves as the plate shown in
When forming this press-formed part, the flat metal plate 330 is heated by passing current through the flat metal plate 330 in a heating process that corresponds to the heating process in the example embodiments described above. Here, for example, even if current is passed through the flat metal plate 330, the current density is lower at the portions that extend (bulge) outward in the width direction from the edges of the base portion 332 in the width direction where the electrodes 12 and 14 are attached, as described in the fourth example embodiment. That is, in the flat metal plate 330, even if the base portion 332 is heated to a quenchable temperature, such as between 850° C. and 950° C., the welded protrusions 318 will not reach the quenchable temperature.
Therefore, forming the press-formed part 310 by press-forming and rapidly cooling the flat metal plate 330, which has been heated by conduction in this way, in a forming process that corresponds to one of the forming processes in the example embodiments described above quenches the flat plate portion 312, the leg plate portions 314, and the flange portions 316, thereby dramatically improving the mechanical strength. Furthermore, even if the flat metal plate 330 is heated by conduction as described above, the welded protrusions 318 will not reach the quenchable temperature, so it is possible to effectively prevent or minimize a decrease in weld properties at the welded protrusions 318 that occurs due to quenching.
In this way, with this press-formed part 330, it is possible to quench the flat plate portion 312, the leg plate portions 314, and the flange portions 316 which together form a hat shape, without quenching the welded protrusions 318. Moreover, only the base portion 332 of the flat metal plate 330, which corresponds to the flat plate portion 312, the leg plate portions 314, and the flange portions 316 is heated to a quenchable temperature so localized cooling during press-forming is not necessary, obviating the need for a complex cooling structure.
More specifically, as shown in
Also, the press-formed part 350 structured as described above is formed by press-forming a flat metal plate 370 shown in
The electrode 12 is connected to a wide portion 374 on one side of the base portion 372 in the length direction, and the electrode 14 is connected to the wide portion 374 on the other side of the base portion 372. The curved portions 352, the flat plate portion 354, and the flange portions 356 are formed by press-forming this flat metal plate 370.
When forming this press-formed part 350, the flat metal plate 370 is heated by passing current through the flat metal plate 370 in a heating process that corresponds to the heating process in one of the example embodiments described above. Here, for example, just as described in the second example embodiment, the width of the base portion 372 is shorter than the widths of the wide portions 374 where the electrodes 12 and 14 are connected, so the current density becomes higher at the base portion 372. That is, even if the base portion 372 of the flat metal plate 370 is heated to a quenchable temperature, such as between 850° C. and 950° C., the wide portions 374 will not reach the quenchable temperature.
Therefore, when forming the press-formed part 350 by press-forming and rapidly cooling (i.e., cooling) the flat metal plate 370, which has been heated by conduction, in a forming process that corresponds to the forming process in one of the example embodiments described above in this way, the portions of the press-formed part 350 that correspond to the wide portions, i.e., a predetermined region of the press-formed part 350 from both ends in the length direction toward the center in the length direction, are not quenched, while the portion corresponding to the base portion 372 of the press-formed part 350 is quenched. As a result, the mechanical strength is dramatically improved at the portion excluding the predetermined region of the press-formed part 350 from both ends in the length direction toward the center in the length direction.
Moreover, as described above, even if the flat metal plate 370 is heated, the wide portions 374 will not be heated to the quenchable temperature. Therefore, because the portion of the press-formed part 350 that corresponds to the wide portions 374, i.e.; the predetermined region of the press-formed part 350 from both ends in the length direction toward the center in the length direction, is not quenched, that portion is able to be highly resistant to rusting.
In this way, with this press-formed part 350, the portion that has not been rust-proofed is quenched so that it has greater mechanical strength, and the portion that has been rust-proofed is not quenched. Moreover, only the base portion 372 of the flat metal plate 370, which corresponds to the curved portions 352, the flat plate portion 354, and the flange portions 356, is heated to the quenchable temperature. Therefore, localized cooling is not necessary during press-forming, so there is no need for a complex cooling structure.
While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the example embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the example embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-129784 | May 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2009/005606 | 5/14/2009 | WO | 00 | 6/30/2010 |
