JP5287565B2 - Steel pipe hot forming apparatus and method - Google Patents

Description

The present invention relates to a hot forming apparatus and method for forming a heated steel pipe using a mold and a shaft pressing device, and more particularly to a hot forming apparatus and method excellent in formability and shape freezing property.

  Metal tube press molding is highly productive, excellent in dimensional accuracy, and stable in quality with little variation in strength between pressed products, making it suitable for manufacturing automobiles, machinery, electrical equipment, transportation equipment, etc. It is the most common processing technique widely used.

  However, press products in recent years, especially automobile parts, have been required to have high strength from the viewpoint of weight reduction. This has led to a decrease in formability and a decrease in shape freezing due to the occurrence of springback, resulting in complicated shapes. It has become difficult to manufacture pressed products that have undergone the above.

For this reason, in recent years, hot press forming technology in which a material to be molded is heated to a high temperature in advance and the heated material to be pressed is molded with a mold (hot press forming of a metal plate material) has attracted attention. (For example, refer to Patent Documents 1 to 5).
Hot press molding press-molds a molding material heated to a high temperature, so the molding material with reduced material strength deforms straight along the molding surface of the mold, even if it has a complicated shape. It can be molded with excellent dimensional accuracy. Moreover, since it is cooled rapidly after the molding by the heat removal effect of the mold, no spring bag is generated and the shape freezing property is excellent.

  However, although it is a hot press molding technique that excels in moldability and shape freezeability, there is a limit to the moldability and shape freezeability. Although the molding material with reduced material strength deforms straight along the molding surface of the mold, the molding material is removed because it comes into contact with the molding surface of the mold. This is because the temperature of the molding material decreases and the material strength increases. Further, because the heat is removed during molding and the temperature of the material to be molded is lowered, the rapid cooling effect due to heat removal from the mold after molding is also reduced.

For this reason, the temperature of the material to be molded during molding, as well as the increase in material strength resulting from this, the reduction in the quenching effect due to heat removal from the mold after molding, and the reduction in moldability and shape freezing properties due to these. In order to prevent this, in Patent Documents 1 to 5, by forming a plurality of protrusions on the molding surface of the mold, the contact area between the mold and the metal plate material as the molding material is reduced, thereby solving the above problems. ing.
However, even if it is a protrusion with a small contact area that comes into contact with the material to be molded, the protrusion is also a part of a mold having heat removal capability, and its effect is only a matter of degree. Moreover, it does not fundamentally solve the above problem.
Note that the degree of processing and the processing time of press molding that affects the temperature drop of the material to be molded vary depending on the desired shape of the press product and the strength of the press material. Therefore, as long as the degree of processing and the processing time determined by the shape of the pressed product are in a range that does not affect the temperature decrease of the material to be molded and the decrease in formability and shape freezing property, those described in Patent Documents 1 to 5. The solution is beneficial even if it does not fundamentally solve the above problems. On the other hand, when the degree of processing and processing time determined according to the shape of the pressed product have an impact on the temperature drop of the material to be molded and the moldability and shape freezeability, the above solution was taken. Even so, there is a limit to formability and shape freezeability.

Here, the techniques disclosed in Patent Documents 1 to 5 are techniques for hot press-molding a metal plate material that is a plate material using a mold, and the technique is applied to a technique for forming a metal tube that is a pipe material. Has a problem to be solved.
Specifically, when the material to be molded is a metal plate material, forming is generally completed by a process of clamping the metal plate material using a mold, but when the material to be molded is a metal tube, Furthermore, it is common to perform a process of axially pushing the end of the metal tube clamped using a shaft pushing device, but when forming a metal plate using an upper mold and a lower mold, By mainly designing the mold in consideration of the vertical direction, setting the clearance, selecting the lubricant, etc., it is possible to suppress the thinning, breakage, buckling, etc. associated with the molding and to improve the moldability. However, since there is a shaft pushing process when forming metal pipes that are pipe materials, the design of molds and shaft pushing devices considering contact heat removal not only in the vertical direction but also in the horizontal direction (axial direction of the metal pipe) And so on.

  In other words, in the hot press molding technology, heat removal due to contact with the mold inevitably occurs, which leads to a decrease in the temperature of the material to be molded and, in turn, a decrease in moldability and shape freezing property. Even the hot press forming technology for metal plate materials by the die design etc. considering the vertical direction is not fundamentally solved, and this technology is not limited to the vertical direction but also the horizontal direction (the axial direction of the metal tube). It is extremely difficult to apply this as it is to the metal tube forming technology that requires the design of the mold and the shaft pushing device in consideration of the above. Moreover, even if it is applied, the formability and the shape freezeability are limited as in the case of the metal plate, and the extent to which the formability and the shape freezeability are reduced is more than that of the metal plate.

On the other hand, in the field of manufacturing automotive parts such as bumpers, pyralin forces, center pillars, and undercarriage parts, metal pipes are filled into molds and water pressure is applied to the metal pipes as a representative of metal tube molding technology. There is a hydroform molding technique in which a metal tube is formed by pushing the metal tube in the length direction at the same time as it is expanded.
Hydroform molding technology can integrally form parts that were previously welded and combined together, reducing the number of parts and omitting the welding process. It is an indispensable important technology.

However, hydroforms require complex and advanced control during molding. This is because there are many parameters to be controlled. In addition, hydroform molding is performed in a mold subjected to water pressure, so the deformation process cannot be confirmed.
For example, the metal tube may rupture or buckle if the hydraulic pressure or the shaft pressing timing is incorrect. Furthermore, appropriate conditions change when the material and lubrication change. In addition, the hydrofoam has a problem that wrinkles and cracks occur during molding when the amount of swelling is excessively increased. Similarly, when the amount of bulging is excessively increased, there is a problem that the wall thickness of the bulged portion is reduced, resulting in insufficient strength or breakage.

As a solution for preventing the occurrence of wrinkles and cracks associated with the above molding, a method of controlling the width of the bulging cavity by moving the mold is disclosed (for example, see Patent Document 6). In the method, a means for moving the mold is required, and a new problem arises that the apparatus configuration becomes more complicated and larger.
Alternatively, a numerical analysis technique using a finite element method (FEM) for simulating how a material to be deformed in a mold has been developed, and relatively accurate simulation is possible. In order to find suitable processing conditions, a large amount of data necessary for numerical analysis must be accumulated.

As described above, when applying the hot press forming technology to a metal tube, it is necessary to design a mold and a shaft pressing device in consideration of contact heat removal, and satisfy this. If this is not possible, the technical significance of preliminarily heating the material to be molded in order to obtain a rapid cooling effect due to a decrease in material strength during molding and heat removal from the mold after molding will be lost.
In addition, by adopting a multi-stage press that uses multiple dies / shaft pressing devices, it is possible to simplify the design of dies, etc., but fundamentally the problem of heat removal due to contact with dies, etc. It cannot be solved.
Furthermore, it is theoretically possible to fundamentally solve the above problems by incorporating a heat insulating material or heating means on the molding surface or inside of a mold or the like, but this leads to an increase in equipment cost and molding. The subsequent rapid cooling effect is discarded.
Alternatively, as a technique for forming a metal pipe, a hydroform forming technique using water pressure has been established and various improvements have been attempted, but complicated and sophisticated control is still required, and the apparatus configuration is also complicated.

JP 2006-192480 A JP 2006-198666 A JP 2006-212690 A JP 2007-075834 A JP 2007-075835 A Japanese Patent Laid-Open No. 2002-153917

  The problem to be solved by the present invention is the basic technology of the hot press forming technology represented by plate materials, in which excellent formability and shape freezing property are obtained by preheating the material to be molded at a high temperature. A new hot forming apparatus and method that does not exist in the prior art, which can fundamentally solve the above-mentioned problems that are manifested when applying the idea to forming metal pipes Is to provide.

In addition, automobile parts in recent years are required to have higher strength from the viewpoint of weight reduction. For example, by heating a metal tube to an austenite region and quenching it by a predetermined cooling process, the martensitic transformation is performed. Alternatively, it is required to achieve high strength by bainite transformation.
However, even with hydroform molding technology that is indispensable for increasing the strength and weight of the vehicle body, it can achieve the 980 MPa class with a closed cross-section, large R, and simple shape. It is currently difficult to ensure.
Moreover, in order to ensure the strength of the above class or more in the hydroform molding technique, a heat treatment process, which is another process, must be newly added after the molding process using water pressure. This is because in the hydroform molding technique using water pressure, a heat treatment process cannot be incorporated in the molding process. Furthermore, it cannot be assumed that the heat treatment process is carried out with the mold clamped after molding. This is because water must be drained from the mold after molding, and the productivity is significantly hindered.
That is, another problem to be solved by the present invention is a new feature that does not exist in the prior art, which is excellent in moldability and shape freezing property, and can increase the strength of a molded product without impairing productivity. It is to provide a hot forming apparatus and method.

  The present inventor obtained the following technical knowledge as a result of repeating various theoretical and experimental studies in order to solve the above two problems.

(A) Hot press forming technology, particularly hot pressing of a metal plate material, a metal plate material as a molding material is brought into contact with a molding surface of a mold, and the metal plate material is deformed along the molding surface. This is a method to finish a press product. The metal plate is sandwiched between the upper mold and the lower mold facing each other, and either or both of the upper mold and the lower mold slide toward the bottom stop point, so that the metal sheet is sandwiched between the upper mold and the lower mold. Undergoes plastic deformation such as bending, stretching, pulling and squeezing.
In other words, the plastic deformation in the hot press forming technology is mainly performed in a state where the metal plate material to be formed is sandwiched between the upper mold and the lower mold. In this method, the metal due to contact with the mold during molding is used. Heat removal from the plate is inevitable.
Therefore, in order to solve the above-mentioned problems, plastic deformation such as bending, stretching, pulling and squeezing must be given by a method completely different from the above method.

  Therefore, the present inventor has succeeded to the basic technical idea of the hot press forming technology of obtaining excellent formability and shape freezing property by heating the metal plate material to a high temperature in advance. As a result of various investigations on techniques for fundamentally avoiding heat removal problems caused by contact with molds, etc., which are manifested when applying the idea to metal tube forming, the following innovative forming technologies have been conceived. did.

(B) The epoch-making molding technique is not to plastically deform the metal tube by pressing the mold, but to bulge the metal tube mainly in the radial direction from the hollow portion inside. Then, the outer surface of the bulged metal tube is pressed along the molding surface of the mold so that the metal tube is plastically deformed without being brought into contact with the mold.

As is well known, in the metal tube forming method, the metal tube is clamped with a mold and the end of the clamped metal tube is closed with the molding surface of the shaft pressing device in the axial direction. A shaft pushing process is generally performed.
The epoch-making method which the present inventor has conceived is that, during this axial pushing process, a medium which is vaporized and expanded depending on the temperature of the metal tube is fed into the inside of the metal tube whose end is closed, that is, into the hollow portion. Then, using the force (vaporization expansion force) generated when the medium is vaporized and expanded inside the closed metal tube, the metal tube is bulged mainly in the radial direction from the hollow portion, and in the radial direction. The outer surface of the bulged metal tube is pressed against the molding surface of the mold by the action of the vaporizing expansion force, so that plastic deformation is applied to the metal tube.

(C) Also in this method, the metal tube before being set in the mold is heated to a high temperature in advance. Therefore, the material strength of the metal tube is reduced. Since the metal tube is expanded toward the outside by the pressure at which the medium vaporizes and expands inside the metal tube, the metal tube whose material strength is reduced bulges straight and is clamped. It deforms straight along the molding surface of the mold.
In other words, this ground-breaking method inherits the basic technical idea of hot press molding technology that obtains excellent formability by preheating the material to be molded at a high temperature. It is.

(D) Here, the method and function of the mold in this method is not to apply plastic deformation to the metal tube by contacting the molding surface of the mold but to bulge it by the vaporization expansion force of the medium. The shape is controlled by pressing the metal tube against the molding surface of the mold in the bulging direction, and its technical idea is close to that of hydroform.
However, in this epoch-making method, since the metal tube is heated to a high temperature in advance, the metal tube swelled by the vaporization expansion force of the medium is subjected to rapid cooling due to heat removal from the mold on the molding surface of the mold. Thus, a remarkable effect that no spring bag is generated can be obtained, and this point is greatly different from a hydrofoam which does not have a quenching effect due to heat removal from the mold.
In addition, this innovative method forms a metal tube whose material strength has been lowered by heating to a high temperature in advance, and this point is also very different from hydroform that does not manipulate the material strength of the metal tube. .
In other words, this revolutionary method inherits the basic technical idea of hot press forming technology that obtains excellent formability and shape freezing by heating the material to be molded at a high temperature in advance. That is why.

(E) Further, in this revolutionary method, the metal tube is expanded or pressed along the molding surface of the mold because of the vaporization expansion force of the medium. It is not due to the pressing of the mold. Therefore, in this method, the swelled metal tube does not receive heat removal due to contact with the mold before reaching the molding surface of the mold.
That is, in the hot press molding technology, heat removal due to contact with the mold inevitably occurs during the molding, and this leads to a decrease in the temperature of the material to be molded and, in turn, a decrease in moldability and shape freezeability. In an innovative method, the problem can be fundamentally solved.
The present invention, which does not exist in the prior art, is that the metal tube is expanded by the vaporization expansion force of the medium, and the metal tube is plastically deformed by pressing the expanded metal tube against the molding surface of the mold. This is a unique technical feature, and the fact that the bulging metal tube does not receive heat removal due to contact with the mold before reaching the molding surface of the mold is not present in the prior art. This is a technical effect unique to the invention.

(F) In addition, automobile parts in recent years have been required to have higher strength from the viewpoint of weight reduction. For example, by heating a metal tube to an austenite region and quenching it by a predetermined cooling process, martens can be obtained. Where it is required to achieve high strength by site transformation or bainite transformation, it is extremely easy to incorporate a cooling process for achieving this purpose into this innovative method.
In this epoch-making method, the metal tube is heated to a high temperature in advance, and heat removal due to contact with the mold does not occur during the molding. This is because the metal tube that has undergone plastic deformation is still in a high temperature state even when the shape control is completed by being along the molding surface of the mold. For this reason, the metal tube can be easily quenched by discharging the coolant toward the metal tube that has undergone plastic deformation.

For example, a plurality of refrigerant discharge ports are formed on the molding surface of the shaft pushing device, a refrigerant supply pipe communicating with each refrigerant discharge port is formed inside, and the refrigerant is supplied from the refrigerant supply pipe so that the inner surface of the metal pipe By being discharged onto the surface, the inner surface of the metal tube can be easily quenched.
Also, a plurality of refrigerant discharge ports are formed on the molding surface of the mold, a refrigerant supply pipe communicating with each refrigerant discharge port is formed inside, and the refrigerant is supplied from the refrigerant supply pipe to the outer surface of the metal pipe. By discharging, the outer surface of the metal tube can be easily quenched.
That is, in this epoch-making method, by adopting a shaft pressing device or a die having such a refrigerant discharge function, it is possible to perform the quenching process while the metal tube is clamped, In terms of productivity, it is extremely advantageous from the point of view of productivity over hydroforming in which a heat treatment process, which is another process, must be newly added after the forming process using water pressure. This is because in the hydroform molding technique using water pressure, a heat treatment process cannot be incorporated in the molding process.

Based on the above knowledge, the present inventor has obtained a basic hot press molding technique represented by a plate material that obtains excellent formability and shape freezing property by preheating the material to be molded at a high temperature. New hot forming that does not exist in the prior art, which can fundamentally solve the above-mentioned problems that are manifested when trying to apply the idea to forming metal pipes The device and method have been conceived.
Furthermore, the present inventor shall succeed to the basic technical idea of the hot press molding technology, and be excellent in moldability and shape freezing property, and increase the strength of the molded product without impairing productivity. The present inventors have come up with a new hot forming apparatus and method that do not exist in the prior art. The gist of these is as follows.

(1) A part of a heated steel pipe, a die steel mold that is clamped in linear contact with the longitudinal direction of the steel pipe, a medium supply port is formed on the molding surface, and the medium supply port is formed inside A communicating medium supply pipe is formed, connected to a die steel shaft pushing device that axially pushes the end of the clamped steel pipe with a molding surface, and a medium feeding pipe of the shaft pushing device, inside a steel tube which is closed with an end portion in the molding surface of the shaft pressing apparatus, the medium infeed means for feeding the medium to swell the steel pipe as vaporized and expanded to along the molding surface of the mold by the temperature of the steel pipe A hot forming apparatus for steel pipes, comprising:

(2) The apparatus according to (1), further comprising backflow prevention means connected to a medium supply pipe of the shaft pushing device and preventing the vaporized and expanded medium from flowing back from the inside of the steel pipe through the medium supply pipe. Steel pipe hot forming equipment.

(3) The apparatus according to (1) or (2), further comprising a degassing unit connected to a medium supply pipe of the shaft pushing device and discharging the vaporized and expanded medium from the inside of the steel pipe through the medium supply pipe. Steel pipe hot forming equipment.

(4) A plurality of refrigerant discharge ports are formed on the molding surface of the shaft pushing device, and refrigerant supply pipes communicating with the respective refrigerant discharge ports are formed inside (1) to (3) The hot forming apparatus for steel pipes according to any one of the above.

(5) A plurality of refrigerant discharge ports are formed on the molding surface of the mold, and refrigerant supply pipes communicating with the respective refrigerant discharge ports are formed inside (1) to (4). The hot forming apparatus for steel pipes according to any one of the above.

(6) A mold clamping step of clamping a part of the heated steel pipe with a die steel mold linearly in contact with the longitudinal direction of the steel pipe, and an end of the clamped steel pipe by a die steel shaft pressing device . the Jiku押step of axial pressing in the axial direction while closing the molding surface a hot forming method of the steel pipe to perform in this order, in about the axis押工, inside a steel tube which is closed with an end portion, the temperature of the steel tube A method of hot forming a steel pipe , wherein a medium that vaporizes and expands is fed, and the steel pipe is expanded along the molding surface of the mold.

(7) the medium supply port on the molding surface of the shaft pressing device is formed, the inside is formed with medium supply pipe communicating with the medium supply port, in about the axis押工, steel pipe from the medium supply pipe The method of hot forming a steel pipe according to (6), wherein a medium that vaporizes and expands depending on the temperature of the steel pipe is fed into the steel pipe .

(8) A mold clamping step of clamping a part of the heated steel pipe with a die steel mold linearly in contact with the longitudinal direction of the steel pipe, and an end portion of the clamped steel pipe of the die steel shaft pressing device the Jiku押step of axial pressing in the axial direction while closing the molding surface a hot forming method of the steel pipe to perform in this order, in about the axis押工, inside a steel tube which is closed with an end portion, the temperature of the steel tube by feeding medium vaporized and expanded, the steel pipe is bulged along the molding surface of the mold, then, subjected to degassing step of discharging the vaporized expanded medium from the interior of the steel pipe, then the refrigerant discharged to the steel tube A method of hot forming a steel pipe , characterized by performing a heat treatment step.

(9) the shaft medium supply opening to the molding surface of the press apparatus is formed in the inside are medium supply pipe communicating with the medium supply port formed in about the axis押工, steel pipe from the medium supply pipe The method of hot forming a steel pipe according to (8), wherein a medium that vaporizes and expands according to the temperature is fed into the steel pipe .

(10) The hot press forming method of a steel pipe according to (9), wherein the vaporized and expanded medium is discharged through the medium supply pipe in the degassing step.

(11) A plurality of refrigerant discharge ports are formed on the molding surface of the shaft pushing device, and refrigerant supply pipes communicating with the respective refrigerant discharge ports are formed inside, and in the heat treatment step, the refrigerant supply pipes are connected to the refrigerant supply pipes. The hot forming method for a steel pipe according to any one of (8) to (10), wherein the steel pipe is supplied and discharged onto the inner surface of the steel pipe .

(12) A plurality of refrigerant outlets are formed on the molding surface of the mold, and refrigerant supply pipes communicating with the respective refrigerant outlets are formed inside, and the refrigerant is supplied from the refrigerant supply pipes in the heat treatment step. characterized by discharging to the outer surface of the feed to the steel pipe (8) to hot forming method of the steel pipe according to any one of (11).

(A) In the hot forming apparatus and method (hereinafter referred to as the present invention) of a metal tube according to the present invention, the material to be formed is set in advance before being set in a mold, as in the hot press forming technique. The metal tube is heated to a high temperature, thereby ensuring excellent formability and shape freezing property.
However, the present invention does not apply plastic deformation to the material to be molded by pressing the metal mold as in the hot press molding technique, that is, by bringing the metal mold into contact with the material to be molded.
In the present invention, a medium that vaporizes and expands due to the temperature of the metal tube is fed into the metal tube closed by the shaft pushing device, and the metal tube is expanded mainly from the hollow portion in the radial direction by the vaporizing and expanding force of the medium. The metal tube is plastically deformed by pressing the outer surface of the metal tube bulged in the radial direction against the molding surface of the mold by the action of the vaporizing expansion force.
In the present invention, the metal tube is expanded and pressed against the molding surface of the mold because these are due to the vaporization expansion force of the medium, and before the bulging metal tube reaches the molding surface of the mold. Furthermore, it does not receive heat removal due to contact with the mold.
In other words, in the hot press molding technology, heat removal due to contact with the mold is inevitably generated during the molding, and this leads to a decrease in the temperature of the material to be molded and, in turn, a decrease in moldability and shape freezeability. In the invention, the problem can be fundamentally solved.
This is an effect peculiar to the present invention that arises from a technical feature peculiar to the present invention that does not exist in the prior art in which the metal pipe is plastically deformed by using the vaporization expansion force of the medium fed into the metal pipe. This is one of the most prominent effects far exceeding the foreseeableness of the contractor.

(B) As described above, in the present invention, since the problem of heat removal due to contact with the mold in the middle of molding can be fundamentally solved, the metal tube is still in place even after plastic deformation of the metal tube is completed. Maintains high temperature.
Thus, in the present invention, the mold clamping step of clamping the heated metal tube with a mold, and axially pushing the end of the clamped metal tube in the axial direction while closing the end of the mold with the molding surface of the shaft pushing device. In this order, the metal tube is plastically deformed by using the vaporization expansion force of the medium. In the present invention, the metal tube is moved from the top, bottom, left, and right by the mold and the shaft pressing device. The plastic deformation is completed in the surrounded state, and at this time, the metal tube is still in a high temperature state.
For this reason, in the present invention, by providing a coolant discharge mechanism in one or both of the mold and the shaft pressing device, the high-temperature metal tube that is still clamped by the mold and the shaft pressing device is used. The refrigerant can be discharged, whereby the metal tube that has undergone plastic deformation can be easily quenched.
That is, according to the present invention, it is excellent in moldability and shape freezing property, and the strength of the molded product can be easily increased without impairing productivity.
In addition, even with hydroform molding technology that has a proven track record as a metal tube molding technology, it is difficult to ensure a strength of 980 MPa class or higher, and in order to realize this, a new process is required after a molding process using water pressure. A heat treatment process has to be added, which significantly impedes productivity. According to the present invention, the metal tube can be moved from the forming process to the heat treatment process very easily with the mold clamped. This is a particularly remarkable effect that far exceeds the prediction of those skilled in the art.

It is a schematic diagram which shows the state which sets the heated metal tube to a metal mold | die, (a) is a top view, (b) is a front view, (A) AA sectional drawing, (c) is a side view FIG. It is a schematic diagram which shows the state which clamped the heated metal pipe with the metal mold | die, (a) is a top view, (b) is a front view, (a) BB sectional drawing, (c) is It is a side view. It is a schematic diagram which shows the axial pressing process which concerns on this invention, (a) is a top view, (b) is a front view, CC sectional drawing of (a), (c) is a side view. It is a schematic diagram which shows an example of the axial pushing apparatus in which the medium supply port and the medium supply pipe were formed, (a) is a perspective view, (b) is sectional drawing. It is a schematic diagram which shows an example of the hot forming apparatus which concerns on this invention provided with the medium feeding means. It is a schematic diagram which shows an example of the hot forming apparatus which concerns on this invention provided with the backflow prevention means. It is a schematic diagram which shows an example of the hot forming apparatus which concerns on this invention provided with the degassing means. It is a schematic diagram which shows an example of the hot forming apparatus which concerns on this invention provided with the refrigerant | coolant discharge mechanism.

Hereinafter, with reference to FIGS. 1-7, the 1st form which is the best form for implementing this invention is demonstrated.
In the present invention, as shown in FIGS. 1 and 2, a mold clamping step of clamping the heated metal tube 1 with a mold 2 and an end portion of the metal tube 1 clamped as shown in FIG. A shaft pushing process of pushing the shaft in the axial direction while closing the molding surface of the pushing device 3 is performed in this order.
Here, FIG. 1 is a schematic view showing a state in which the heated metal tube 1 is set in the mold 2, (a) is a plan view, (b) is a front view, and AA in (a). Sectional drawing and (c) are side views.
2A and 2B are schematic views showing a state in which the heated metal tube 1 is clamped with the mold 2, wherein FIG. 2A is a plan view, FIG. 2B is a front view, and BB in FIG. Sectional drawing and (c) are side views.

The material to be molded used in the present invention will be described. The material to be molded used in the present invention is a metal pipe 1 and can be applied to any steel pipe such as an Al-plated steel pipe, a Zn-plated steel pipe, a GI-plated steel pipe, a high-strength steel pipe, a normal steel pipe, and a stainless steel pipe.
Further, as will be described in the second embodiment of the present invention, if the steel pipe is subjected to martensitic transformation or bainite transformation, the strength can be increased by quenching by refrigerant discharge, so that martensitic transformation or bainite transformation is performed. Steel pipes are desirable. It is not always necessary to transform the refrigerant when it is discharged, and it may be transformed after molding.

Further, as the metal pipe 1 used in the present invention, (a) an electric-welded steel pipe in which a steel plate / strip steel is formed into a cylindrical shape and welded in parallel to the pipe axis direction, and (b) a thick plate is formed into a U shape by a U press After bending, UO steel pipe formed into a tubular shape by O-press and welded from the inner and outer surfaces of the seam, (c) Spiral steel pipe formed by winding a wide band steel into a tube while spirally winding and continuously welding the seam from inside and outside, (d ) Even after the steel strip is heated, even forged welded steel pipes that have been crimped at the edge of the plate while being drawn by roll forming, (e) after heating the billet to make a hole in the center, it was subjected to a rolling mill or drawing machine A seamless steel pipe may be used.
Needless to say, the cross-sectional shape of the metal tube 1 can be applied not only to a circular shape as shown in FIGS. Further, the present invention can also be applied to a metal tube whose cross-sectional shape changes along the longitudinal direction. Or it can apply also about a tailored tube. That is, the essential feature of the present invention resides in the metal tube forming method and bulging method, not in the shape of the metal tube.

The heating method and heating temperature of the metal tube 1 before being set in the mold 2 will be described. The method for heating the metal tube 1 is not particularly limited. If the method can heat the metal tube to the A1 transformation point or higher, heating in a heating furnace, electric furnace, gas furnace, flame heating, electric heating, Any heating method such as high-frequency heating or induction heating may be used.
Moreover, even if it is an aspect which heats the whole metal tube uniformly, the aspect which heats a part of metal tube may be sufficient. Here, the heating temperature of the metal tube is preferably 600 to 1000 ° C.

Although it is a mold clamping process, the mold 2 hardly contributes to the molding of the metal tube 1 in the example shown in FIGS. That is, as shown in FIG. 2, even if the mold 2 is clamped, the metal tube 1 is hardly deformed. In this example, the metal tube and the mold are in slight contact with each other in the lower mold portion.
This is because the greatest technical feature of the present invention is that the metal tube 1 is swelled by the vaporization expansion force of the medium fed into the metal tube 1 and the swelled metal tube 1 is formed on the molding surface of the mold 2. The metal mold or the mold clamping process illustrated in FIGS. 1 and 2 is an example that is schematically illustrated in order to briefly show the technical features of the present invention. is there.
Therefore, regardless of the example of FIGS. 1 and 2, in the mold clamping process, the metal tube 1 may be plastically deformed by pressing the metal tube 2 against the metal tube 1 or bringing it into contact with the metal tube 1. The greater the degree of processing in the mold clamping process and the longer the processing time, the greater the heat removal of the metal tube due to contact with the mold, which affects the plastic deformation in the next axial pressing process. That's what it means. In other words, the deformation method itself of the metal tube by the vaporization expansion force of the medium is within the range that the present invention contemplates, and the addition of plastic deformation due to the pressing of the mold does not affect the breadth of the scope of the present invention. .

  The shaft pressing process is a process in which the technical features of the present invention are exhibited. That is, in the axial pressing process of the metal tube according to the prior art, the end of the clamped metal tube 1 is blocked by the molding surface of the axial pressing device 3 and is axially pressed in the axial pressing direction to plasticize the metal tube. In the present invention, a medium that is vaporized and expanded depending on the temperature of the metal tube is fed into the metal tube closed by the shaft pushing device 3, and the metal tube is mainly hollowed out by the vapor expansion force of the medium. The metal tube is bulged in the radial direction from the portion, and the metal tube is plastically deformed by pressing the outer surface of the metal tube bulged in the radial direction against the molding surface of the mold 2 by the action of the vaporizing expansion force.

In the present invention, the metal tube is expanded and pressed against the molding surface of the mold because these are due to the vaporization expansion force of the medium, and before the bulging metal tube reaches the molding surface of the mold. Furthermore, it does not receive heat removal due to contact with the mold.
However, the shaft pressing process illustrated in FIG. 3 is an example schematically shown in order to briefly show the technical features of the present invention. In the shaft pressing process, the shaft pressing device 3 is pressed against a metal tube. Therefore, plastic deformation may be applied to the metal tube 1. The greater the degree of processing in the shaft pressing process, and the longer the processing time, the greater the heat removal of the metal tube 1 due to contact with the shaft pressing device 3, and the temperature of the metal tube decreases. Accordingly, the expansion output of the metal tube due to the vaporization expansion force of the medium and the pressing force against the mold forming surface due to the action of the vaporization expansion force are affected. That is, the deformation method itself of the metal tube by the vaporization expansion force of the medium is within the range that the present invention contemplates, and the plastic deformation caused by the pressing of the shaft pushing device affects the range of the present invention. is not.

  In the present invention, the mold clamping step and the shaft pressing step are performed in this order, but it is desirable to perform the shaft pressing step immediately after the mold clamping. Preferably, it is desirable to perform the shaft pressing process simultaneously with completion of mold clamping. This is because if the transition time from the mold clamping process to the shaft pressing process is long, the temperature of the metal tube is lowered, and the technical significance of heating the metal tube 1 to a high temperature in advance in order to obtain excellent formability is lost. .

  As for the timing of feeding the medium into the metal tube, it is desirable to feed it simultaneously with the start of the shaft pushing. When the metal tube undergoes plastic deformation, work hardening occurs. If the medium is fed simultaneously with the start of the axial push, the metal tube is not work hardened, and the metal tube is heated to a high temperature before processing. For this reason, the material strength of the metal tube is also reduced. Moreover, heat removal due to contact with the shaft pressing device also occurs. Therefore, the vaporization expansion force of the medium can be maximized by feeding the medium simultaneously with the start of the shaft pushing.

In order to feed the medium into the metal tube 1 whose end is closed by the shaft pushing device 3, a medium supply port 4 is provided on the molding surface of the shaft pushing device 3 as shown in FIG. Preferably, a medium supply pipe 5 communicating with the medium supply port 4 is formed. Needless to say, the number of the medium supply ports 4 and the medium supply pipes 5 communicating with the medium supply ports 4 does not affect the technical features of the present invention, and a plurality of medium supply ports 5 may be formed.
The medium supply port 4 and the medium supply pipe 5 communicating with the medium supply port 4 can be formed by mechanical drilling by a drill or drilling by electric discharge machining. As a material of the shaft pressing device 3 in this case, it is desirable to use hot working die steel from the viewpoint of hot strength. In addition, it is desirable to use die steel for hot working as the material of the mold 2.
In addition, since the medium supply pipe fulfills the medium feeding function if it communicates with the medium supply port, the outer surface of the shaft pushing device 3 can be changed from the inside of the shaft pushing device 3 instead of drilling the medium feeding port 4 or the medium supply tube 5 in the shaft pushing device. The medium supply pipe 5 may be connected to a porous metal having pores penetrating through the medium. In this case, it is desirable to use a porous metal having a plurality of holes having a diameter of 100 μm to 1 mm and a pitch of 100 μm to 10 mm penetrating in the thickness direction. Such a porous metal can be produced by unidirectional solidification in which the direction of the solidified structure is made constant by temperature control after sintering the powder after molding or by melting the metal.

In order to feed the medium into the metal tube 1 whose end is closed by the shaft pushing device 3, the medium feeding means 6 is connected to the medium feeding pipe 5 as shown in FIG. It is desirable to supply.
The medium feeding means 6 is not particularly limited as long as the medium can be fed into the metal pipe 1 through the medium supply pipe 5. For example, the medium feeding means 6 may be a compressor, an air cylinder, a pusher, a high water pressure generator (intensity generator). Fire) or the like can be used.

  As a medium to be sent into the inside of a metal tube, water, polyhydric alcohols, polyhydric alcohol aqueous solutions, polyglycol, mineral oil with a flash point of 120 ° C. or higher, synthetic ester, silicon oil, fluorine due to flame resistance and corrosiveness Any of oil, grease having a dropping point of 120 ° C. or higher, mineral oil, and a water emulsion in which a surfactant is mixed with a synthetic ester may be used, or a mixture thereof may be used. From the viewpoint of vaporization expansion force, it is desirable to use water.

The medium may be liquid, gas or solid. When a gas is used as the medium, the heat transfer coefficient is low, so that it is limited to a case where the processing is not severe or a martensitic transformation or a bainite transformation is not performed. Also, it is desirable to use nitrogen, CO ₂ , or inert gas with low activity in order to avoid surface oxidation. Further, when the medium is a gas, it does not remain attached to the molded product or the mold, so that there is an effect that unnecessary dirt and rust are hardly generated. Further, from the viewpoint of the vaporization expansion force of the medium, solids such as ice and dry ice can also be used.

As described above, in the present invention, the medium is sent into the closed metal tube, and the medium is plastically deformed by using the force by which the medium evaporates and expands inside the metal tube. In order not to escape, it is desirable to provide the backflow prevention means 7 as shown in FIG.
More specifically, the medium is preferably fed from the medium supply pipe 5 formed inside the shaft pushing device 3, and the medium vaporized and expanded inside the metal pipe flows back through the medium supply pipe 5. Since the possibility is the highest, it is desirable to connect the backflow prevention means 7 to the medium supply pipe 5.
The backflow prevention means 7 is not particularly limited as long as it prevents the vaporized and expanded medium from flowing back from the inside of the metal pipe through the medium supply pipe 5, and for example, a check valve, a check valve, an open / close A valve or the like can be used. Moreover, what combined these 2 or more may be used.

After the forming is completed, the shaft pushing device is removed and the metal tube subjected to the plastic deformation is taken out. However, since the inside of the metal tube 1 immediately after the plastic deformation is filled with the vaporized and expanded medium, the shaft pushing device is removed. When removed, sudden pressure fluctuations occur inside the metal tube, which can cause cracks and cracks in the metal tube. For this reason, when taking out the metal tube, it is preferable to gradually discharge the vaporized and expanded medium from the inside of the metal tube. For this purpose, it is desirable to provide a gas venting means 8 as shown in FIG.
Even in this case, since the medium supply pipe is already formed in the shaft pushing device, it is desirable to use this as a passage for venting gas. For this reason, the gas venting means 8 is connected to the medium feeding pipe 5. It is desirable to connect.
The gas venting means 8 is not particularly limited as long as the vaporized and expanded medium can be gradually discharged from the inside of the metal pipe through the medium supply pipe 5. For example, a pressure regulating valve, an on-off valve or the like can be used. it can. A combination of these may also be used.

As shown in FIGS. 1 to 7, in the present invention, a medium that is vaporized and expanded by the temperature of the metal tube is fed into the metal tube 1 closed by the shaft pushing device 3, and the metal is expanded by the vaporizing and expanding force of the medium. Plasticity of the metal tube is obtained by expanding the tube mainly in the radial direction from the hollow portion and pressing the outer surface of the metal tube expanded in the radial direction against the molding surface of the mold 2 by the action of the vaporizing expansion force. Perform deformation.
In the present invention, the metal tube is expanded and pressed against the molding surface of the mold because these are due to the vaporization expansion force of the medium, and before the bulging metal tube reaches the molding surface of the mold. Furthermore, it does not receive heat removal due to contact with the mold.
That is, in the hot press molding technology in which the present invention inherits the technical idea, heat removal inevitably occurs due to contact with the mold during the molding, and this is caused by a decrease in the temperature of the material to be molded and thus the formability / shape. When the freezing property is lowered, the present invention can fundamentally solve the problem.
This is a technical effect peculiar to the present invention that arises from a technical feature peculiar to the present invention that does not exist in the prior art in which the metal pipe is plastically deformed by using the vaporization expansion force of the medium fed into the metal pipe. This is one of the particularly remarkable effects far exceeding the prediction of those skilled in the art.

Next, a second embodiment according to the present invention will be described with reference to FIG.
As described above, in the first embodiment according to the present invention, since the problem of heat removal due to contact with the mold 2 during the molding can be solved, even after the plastic deformation of the metal tube 1 is completed, the metal tube No. 1 still maintains a high temperature state.
Thus, in the present invention, the mold clamping process of clamping the heated metal tube with the mold 2 and the axial direction while closing the end of the clamped metal tube with the molding surface of the shaft pressing device 3. A shaft pushing process for pushing the shaft is performed in this order, and in the shaft pushing process, plastic deformation of the metal tube is performed using the vaporization expansion force of the medium. In the present invention, the metal tube 1 is formed by the mold 2 and the shaft pushing device. The plastic deformation is completed in the state surrounded by the upper, lower, left, and right by 3, and at this time, the metal tube 1 is still in a high temperature state.
For this reason, in the present invention, either one or both of the shaft pressing device 3 and the mold 2 is provided with a refrigerant discharge mechanism, so that the high temperature of the mold 2 and the shaft pressing device 3 can be kept high. A predetermined refrigerant can be discharged to the metal tube 1, whereby the metal tube 1 subjected to plastic deformation can be easily quenched without impairing productivity.
In addition, if a heat treatment process is performed immediately after the shaft pressing process to discharge the refrigerant to the metal pipe using a predetermined refrigerant discharge mechanism, a sudden pressure fluctuation occurs inside the metal pipe, which causes cracks and cracks in the metal pipe. Therefore, it is desirable to perform the degassing step of discharging the medium vaporized and expanded from the inside of the metal tube 1 through the medium supply tube 5 using the degassing means 8 before the heat treatment step.

As an example of the refrigerant discharge mechanism, as shown in FIG. 8, a plurality of refrigerant discharge ports 10 are formed on the molding surface of the shaft pushing device 3, and the refrigerant communicating with each refrigerant discharge port 10 is formed inside the shaft pushing device 3. It is desirable to form the supply pipe 11. Accordingly, by supplying the refrigerant from the refrigerant supply pipe 11, the refrigerant can be easily discharged to the inner surface of the metal pipe.
Here, the refrigerant discharge ports 10 are formed so that the refrigerant discharge directions of the respective refrigerant discharge ports 10 are different so that the refrigerant discharged from the plurality of refrigerant discharge ports can cool the entire inner surface of the metal tube 1. desirable. In other words, it is desirable to form the refrigerant outlets so that their directions are different from each other. As a result, the strength of the entire inner surface of the metal tube 1 can be increased in a short time without damaging the productivity.
The refrigerant discharge port 10 and the refrigerant supply pipe 11 can be formed in the shaft pressing device 3 by the same method as the medium supply port 4 and the medium supply pipe 5.

As another example of the refrigerant discharge mechanism, as shown in FIG. 8, a plurality of refrigerant discharge ports 10 are formed on the molding surface of the mold 2, and the refrigerant communicated with each refrigerant discharge port 10 inside the mold 2. It is desirable to form the supply pipe 11. Thus, by supplying the refrigerant from the refrigerant supply pipe 11, the refrigerant can be easily discharged to the outer surface of the metal pipe.
Here, the coolant discharge port 10 may be formed on the upper mold or the lower mold, but it is desirable to form it on the molding surfaces of both molds. Moreover, it is desirable to form a plurality of refrigerant discharge ports 10 along the longitudinal direction so as to cover the entire longitudinal direction of the metal tube 1. Furthermore, it is desirable to form a plurality of refrigerant discharge ports so as to cover the outer surface of the metal tube so that the entire outer surface of the metal tube can be covered, that is, in the circumferential direction of the metal tube. As a result, the strength of the entire outer surface of the metal tube 1 can be increased in a short time with the mold clamped without impairing productivity.
The refrigerant discharge port 10 and the refrigerant supply pipe 11 can be formed in the mold 2 by the same method as the medium supply port 4 and the medium supply pipe 5.

As refrigerants for cooling metal pipes, water, polyhydric alcohols, polyhydric alcohol aqueous solutions, polyglycols, mineral oils with a flash point of 120 ° C or higher, synthetic esters, silicone oils, fluorine oils because of flame retardancy and corrosiveness , Any of greases having a dropping point of 120 ° C. or higher, mineral oils, and water emulsions obtained by blending a synthetic ester with a surfactant, or a mixture thereof may be used.
The refrigerant may be liquid or gas. When a gas is used as the refrigerant, the heat transfer coefficient is low, so that it is limited to cases where the processing is not relatively severe, or when martensitic transformation or bainite transformation is not performed. Also, it is desirable to use nitrogen, CO ₂ , or inert gas with low activity in order to avoid surface oxidation. Further, when the refrigerant is a gas, it does not remain attached to the molded product or the mold, so that there is an effect that unnecessary dirt and rust are hardly generated.

  In order to facilitate control of the refrigerant discharge amount, discharge flow rate, discharge pressure, discharge time, and discharge timing, the refrigerant supply pipe 11 is either one of an on-off valve, a flow rate adjustment valve, and a pressure adjustment valve (not shown). It is desirable to provide more than seeds.

DESCRIPTION OF SYMBOLS 1 Metal pipe 2 Mold 3 Axial pushing device 4 Medium supply port 5 Medium supply pipe 6 Medium feeding means 7 Backflow prevention means 8 Degassing means 10 Refrigerant discharge port 11 Refrigerant supply pipe 20 Cavity for swelling

Claims (12)

A part of the heated steel pipe and a die steel mold that is clamped in linear contact with the longitudinal direction of the steel pipe ;
A medium supply port is formed on the molding surface, a medium supply pipe communicating with the medium supply port is formed inside, and a die for axially pushing the end of the clamped steel pipe with the molding surface is axially pushed. A steel shaft pushing device ;
Is connected to the medium supply pipe of the shaft push device, in the interior of the shaft steel pipe which is closed with an end portion in the molding surface of the pressing device, the steel pipe as by vaporization and expansion by the temperature of steel pipe along the molding surface of the mold A hot forming apparatus for a steel pipe, characterized by comprising medium feeding means for feeding a medium for swelling the steel pipe. 2. The steel pipe according to claim 1, further comprising a backflow prevention unit connected to a medium supply pipe of the shaft pushing device and configured to prevent the vaporized and expanded medium from flowing back from the inside of the steel pipe through the medium supply pipe . Hot forming equipment. It is connected to the medium supply pipe of the shaft pressing device, between the vaporizing expanded medium steel pipe according to claim 1 or 2, characterized in that it comprises a degassing means for discharging from the interior of the steel pipe through the medium supply pipe heat Molding equipment. 4. A plurality of refrigerant discharge ports are formed on a molding surface of the shaft pushing device, and a refrigerant supply pipe communicating with each refrigerant discharge port is formed inside. The hot-forming apparatus of the steel pipe of description. 5. A plurality of coolant discharge ports are formed on the molding surface of the mold, and a coolant supply pipe communicating with each coolant discharge port is formed inside. The hot forming apparatus for steel pipes as described in 1. A mold clamping step of clamping with a part of the heated steel pipe and a die steel mold in linear contact with the longitudinal direction of the steel pipe ;
A hot forming method of a steel pipe that performs a shaft pressing step in this order while axially pushing the end of a clamped steel pipe with a molding surface of a die steel shaft pressing device ,
Steel pipe as the shaft押工, the inside of the steel tube which is closed ends, by feeding medium for vaporization and expansion by the temperature of the steel pipe, characterized thereby bulging the steel pipe along the molding surface of the mold Hot forming method. A medium supply port is formed on the molding surface of the shaft pressing device, and a medium supply pipe communicating with the medium supply port is formed inside,
In about said axis押工, hot forming method of the steel pipe according to claim 6, wherein the feeding to the interior of the steel pipe by supplying a medium to be vaporized and expanded by the temperature of the steel pipe from the medium supply pipe. A mold clamping step of clamping with a part of the heated steel pipe and a die steel mold in linear contact with the longitudinal direction of the steel pipe ;
A hot forming method of a steel pipe that performs a shaft pressing step in this order while axially pushing the end of a clamped steel pipe with a molding surface of a die steel shaft pressing device ,
In about said axis押工, inside a steel tube which is closed ends, by feeding medium for vaporization and expansion by the temperature of the steel pipe, it is bulged steel pipe along the molding surface of the mold,
Next, a degassing step of discharging the vaporized and expanded medium from the inside of the steel pipe is performed,
Then, hot forming method of the steel pipe, which comprises carrying out the heat treatment step of performing refrigerant discharge steel pipe. A medium supply port is formed on the molding surface of the shaft pressing device, and a medium supply pipe communicating with the medium supply port is formed inside,
In about said axis押工, hot forming method of the steel pipe according to claim 8, wherein the feeding to the interior of the steel pipe by supplying a medium to be vaporized and expanded by the temperature of the steel pipe from the medium supply pipe. 10. The hot press forming method of a steel pipe according to claim 9, wherein the vaporized and expanded medium is discharged through the medium supply pipe in a degassing step. A plurality of refrigerant discharge ports are formed on the molding surface of the shaft pushing device, and a refrigerant supply pipe communicating with each refrigerant discharge port is formed inside,
In the heat treatment step, hot forming method of the steel pipe according to any one of claims 8 to 10, characterized in that the discharge on the inner surface of the steel pipe by supplying a coolant from the coolant supply pipe. A plurality of refrigerant discharge ports are formed on the molding surface of the mold, and a refrigerant supply pipe communicating with each refrigerant discharge port is formed inside,
In the heat treatment step, hot forming method of the steel pipe according to any one of claims 8 to 11, characterized in that for discharging the outer surface of the steel pipe by supplying a coolant from the coolant supply pipe.

Images