Extrusion die for forming hollow material

An extrusion die is provided with a male die through which a billet is extruded from an upstream side to a downstream side and, the male die adapted for forming an inside shape of a hollow material; and a female die for holding the male die and forming an outside shape of the hollow material. The male die is formed of a spider and a holder for holding the spider. The spider is formed of a mandrel and a plurality of bridge parts for supporting the mandrel, and enabling a distal-end outer peripheral surface to engage with a bridge-holding surface. The distal-end outer peripheral surface of each of the bridge parts and the bridge-holding surface of the holder are joined by shrink-fitting.

TECHNICAL FIELD

The present invention is related to a hollow material forming extrusion die for forming a hollow material constituted with a high-strength alloy, particularly with the so-called 7000-system maximum strength aluminum alloy.

BACKGROUND ART

In general, extrusion processing of aluminum alloy and the like is high in the versatility in terms of the sectional shapes and is excellent for acquiring a hollow material formed by extrusion. Thus, it is being widely employed in these days. Recently in particular, products manufactured by extrusion processing have come to be used broadly as strong members of structural materials, mechanical components, and the like. Thus, there are increasing demands for extruded members constituted with high-strength alloys, particularly with maximum strength aluminum alloys such as the so-called 7000-system, e.g., 7075, 7N01, and 7003.

As an example of a conventional extrusion die for forming a hollow material, there is known a hollow-material extrusion die constituted with the so-called a spider die in which a male die and a female die are mounted inside a die ring (see Patent Document 1, for example).

As shown inFIG. 20, a spider die100disclosed in Patent Document 1 is constituted by including: a male die101having a core (mandrel)110for forming an inside shape of a hollow material; and a female die102for forming an outside shape of the hollow material. The male die101is constituted by including the mandrel110and a male ring112that holds the mandrel110. Further, the mandrel110is formed with a forming projected part113and bridge legs111for holding the forming projected part113.

Further, a distal-end peripheral side surface115bof a distal-end115of the bridge leg111forms a slope surface that expands towards the tip side of the extrusion direction. The distal-end peripheral side surface115bis fitted with an inner peripheral surface112aof the male ring112.

The mandrel110includes, on the bottom side thereof, a part that forms the inside shape of the hollow material. In the outer periphery of the mandrel110, the bridge legs111in an X-letter shape, for example, i.e., extended in four directions, towards an inner periphery slope surface112aof the male ring112are provided. Further, a space surrounded by the four bridge legs111and the inner peripheral surface112aof the male ring112is a space S for introducing a billet formed with an aluminum alloy as a material.

The male die101is held by the female die102at the extrusion direction tip side shown with an arrow A. A forming hole part106to which the bottom part of the mandrel110is inserted and which is used for forming the outside shape of the hollow material is formed in the female die102. Further, a holding surface116for holding the bottom surfaces of the bridge legs111of the male die101is formed on the outer periphery side top surface of the female die102.

As described above, each of the bridge legs111in the spider die100disclosed in Patent Document 1 is formed as the slope surface in which the distal-end periphery side surface115bof the distal-end115becomes expanded towards the tip side of the extrusion direction. Thus, during the extrusion of the billet, the axial force works on each of the bridge legs111and the bending stress working on each of the bridge legs111is decreased. Thus, the flexure of each of the bridge legs111is suppressed, thereby providing a structure with which the holding state of the mandrel110during the extrusion becomes stable.Patent Document 1: Japanese Unexamined Patent Publication Hei 7-124633

In a case where a high-strength alloy, particularly the so-called 7000-system maximum strength aluminum alloy, is used as a material for forming a hollow material and an extruded material having a plurality of hollow parts such as a material in a sectional shape having a rectangle with two vertically parallel lines or the like is formed as a member for automobile dampers, for example, to be formed with the alloy, it is difficult to increase the speed of extrusion and to improve the life of the die since the deformation resistance thereof is higher than those of other alloy types so that the extrusion processing force becomes greater and the load for the die tools becomes greater as well.

For example, the hollow material extrusion die100disclosed in Patent Document 1 described above is so structured that the inner periphery slope surface112aof the male ring112and the distal-end periphery side surfaces115bof the bridge legs111are press-fitted to generate a compression stress to the bridge legs111in the direction orthogonal to the extrusion direction. The pressure stress and the extrusion force applied to the top surfaces of each of the bridge legs111when extrusion processing is executed, i.e., the tensile force for pulling towards the extrusion direction tip side generated in the shaping extrusion part113, are set off thereby to prevent damages of the bridge legs111and to prevent damages of the mandrel110as a result.

However, in the extrusion die100, the distal-end parts115of the bridge legs111are sloped in the direction spreading towards the tip side of the extrusion direction. Thus, the distance L between a base end part P1 held on the holding surface116of the female die102in the distal-end part115of the bridge leg111and the intersection point between the bridge leg111and the shaping extrusion part113, i.e., a working point P2 that may be broken by the tensile force, becomes larger, so that the moment is increased.

Therefore, when an extrusion force is applied to the mandrel100, a large weight is applied to the working point P2 so that the bridge legs111may be broken.

In order to overcome this issue, it is considered to increase the strength of the bridge legs111by increasing the size of the bridge legs111or to reduce the moment by shortening the distance L between the base end part P1 and the working point P2.

However, when the size of the bridge111is increased, the introduction space S of the billet to which the billet is guided and housed becomes smaller. Thus, the set amount of the billet cannot be secured. In order to secure the set amount of the billet, it is necessary to increase the inside diameter of the male ring112. To do so, the die becomes large-sized and the distance L is extended, so that the moment cannot be reduced as a result.

Further, when the distance L between the base end part P1 and the working point P2 is shortened, the space between the male ring112and each of the bridge legs111, i.e., the introduction space of the billet S, becomes small. This causes such issues that the extrusion amount of the billet is reduced, etc., so that there is naturally a limit in shortening the distance L.

As described above, with the spider die100designed to overcome the issues by offsetting the compression stress and the tensile stress, there is a possibility of breaking the bridge legs111as well as the mandrel110as a result. Thus, there is also a limit in extending the life of the die.

In order to overcome the issues, it is an object of the present invention to provide an extrusion die for forming a hollow material, which is capable of performing high-speed extrusion and preventing breakage of the mandrel at the same time so as to extend the life even when extrusion-forming a billet (an extruded material) constituted with a high-strength alloy with a high extrusion processing force, particularly constituted with the so-called 7000-system maximum strength aluminum alloy.

DISCLOSURE OF THE INVENTION

In order to achieve the foregoing object, the extrusion die for forming a hollow material according to the present invention is an extrusion die for forming a hollow material, which includes: a male die which forms an inside shape of the hollow material by extruding a billet constituted with an aluminum alloy fed from an upstream side towards a downstream side; and a female which holds the male die and forms an outside shape of the hollow material, wherein:the male die includes a spider which forms the inside shape and a holder which holds the spider;the spider includes a mandrel which corresponds to the inside shape of the hollow material, and a plurality of bridge parts provided in a unified manner with the mandrel and projected from a periphery of the mandrel towards outside; anddistal-end outer peripheral surfaces of each of the bridge parts and an inner peripheral surface part of the holder are bonded by shrink-fitting.

The extrusion die for forming the hollow material according to the present invention is structured in the manner described above, so that the distal-end outer peripheral surface of each bridge part of the spider and the inner peripheral surface of the holder are bonded and unified by shrink-fitting. Thus, the stress imposed upon the die can be received by the spider and the holder, so that the stress upon the stress concentrated part of each bridge part can be eased. This makes it possible to prevent the bridge parts of the spider from being broken.

As a result, it becomes possible to perform high-speed extrusion and to extend the life even when extrusion-forming a billet (an extruded material) constituted with a high-strength alloy with a high extrusion processing force, particularly constituted with the so-called 7000-system maximum strength aluminum alloy.

Further, even when the pressure for protruding the billet is applied to the mandrel and each bridge part of the spider, each of the bridge parts of the spider alone is not slightly shifted and is held stably since the distal-end outer peripheral surfaces of each bridge part of the spider and the inner peripheral surface of the holder are bonded and unified by shrink-fitting. As a result, it becomes possible to process the hollow material with a desired high precision.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, a first embodiment of an extrusion die10for forming a hollow material (referred simply to as an extrusion die hereinafter) according to the present invention will be described by referring toFIG. 1toFIG. 11.

The extrusion die10according to the first embodiment is of a spider die type, which forms a hollow material constituted with a high-strength alloy, particularly with the so-called 7000-system maximum strength aluminum alloy. The extrusion die10of the embodiment forms a hollow material1in a sectional shape having a rectangle with two vertically parallel lines as shown inFIG. 12, for example.

As shown inFIG. 2, the extrusion die10is structured by including: a male die20which forms an inside shape of the hollow material1by protruding a billet B constituted with an aluminum alloy fed from the upstream side of the extrusion direction towards the downstream side; a female die30which forms an outside shape of the hollow material1; and a back die40for holding the female die30.

The billet B is housed inside a billet extrusion device60constituted with a chamber and the like disposed on the upstream side of the male die20, and it is placed to be extruded out by the billet extrusion device60.

The male die20, the female die30, and the back die40are connected in a unified manner.

That is, after the male die20and the female die30are positioned via a knock pin47and two positioning pins46, for example, as shown inFIG. 1andFIG. 2, the male die20, the female die30, and the back die40are connected and fixed via two connecting bolts45, for example.

As shown inFIG. 1toFIG. 3, the male die20is constituted with a spider22for forming the inside shape of the hollow material1and a holder25for holding the outer periphery of the spider22. The holder25and the spider22are strongly bonded and unified by shrink-fitting. Further, a top surface22A of the spider22is formed as flat on the entire surface.

A mandrel23and the top surface22A of a bridge part24constituting the spider22when the spider22and the holder25are assembled in a unified manner are located at positions recessed from a top end surface (seal surface) of the holder25towards the extrusion downstream side in a prescribed length as shown inFIG. 2.

The spider22is constituted with: the mandrel23which corresponds to the inside shape of the hollow material1; and a plurality of bridge parts24which support the mandrel23and are projected in substantially X-letter shape towards the outer side from the periphery of the mandrel23, i.e., four pieces including a first bridge part24a, a second bridge part24b, a third bridge part24c, and a fourth bridge part24d. Spaces between each of the bridge parts24ato24dare introduction spaces S for the billets B.

Further, each of distal-end outer peripheral surfaces24C of those four pieces of the first bridge part24a, the second bridge part24b, the third bridge part24c, and the fourth bridge part24dis designed to be engaged with a bridge holding surface25C that is the inner periphery part of the holder25and bonded by shrink-fitting.

A sloping billet guide surface24E spreading wider towards the downstream side is formed in those first to fourth bridge parts24ato24din a prescribed height from the top surface part22A, so that the billets B extruded from the upstream side are extruded smoothly.

As described above, in the extrusion die10of the first embodiment, the distal-end outer peripheral surfaces24C of the first bridge part24a, the second bridge part24b, the third bridge part24c, and the fourth bridge part24dand a part of the bridge holding surface25C of the holder25constituting the spider22are strongly bonded by shrink-fitting.

Note here that shrink-fitting is a method for achieving strong bonding by using heat, and it is a fitting method with which a member such as a circular plate with holes are thermally expanded, shafts formed slightly larger than the diameter of the holes are fitted therein, and then cooled to be fixed. This method is used as fastening-type bonding. Then, the both (the circular plate and the shaft in the above case) are tightly fixed by shrink-fitting.

Any methods can be employed for applying heat at the time of shrink-fitting. However, it is preferable to apply heat by induction heating using a solid state power source, for example. This heating method is excellent in the reliability and reproducibility, so that high energy efficiency heating can be performed in a short period of time with no contact.

The state where the spider22and the holder25are bonded by shrink-fitting is shown inFIG. 2andFIG. 3.

FIG. 2andFIG. 3show the state where the distal-end outer peripheral surface24C of the second bridge24b, for example, of the spider22and the bridge holding surface25C of the holder25are strongly bonded by shrink-fitting. While the state where the distal-end outer peripheral surface24C of the second bridge24band the bridge holding surface25C of the holder25are strongly bonded is shown inFIG. 2andFIG. 3, the bonded state of the respective distal-end outer peripheral surface24C of the other first bridge part24a, the third bridge part24c, and the fourth bridge part24dand the bridge holding surface25C of the holder25is the same as the state shown inFIG. 2andFIG. 3.

FIG. 4shows a state before the spider22and the holder25are shrink-fitted.FIG. 4is a view showing a state where the male die30ofFIG. 2which shows a vertical sectional view taken along a line II-II ofFIG. 1is expanded while the spider22and the holder25are decomposed.

The holder25is formed in an overall circular plate in a prescribed thickness. The bridge holding surface25C thereof is formed with a sloping surface part25mthat is formed at a prescribed sloping angle α degree spreading from the distal-end inside diameter end part of the top end surface25A of the holder25towards the female die30side and a straight line part24nextended out straight to the bottom surface25B continuously from the distal-end of the sloping surface part25m.

Further, the sloping angle α degree of the slope surface part25mis set as 0.5 degree to 1 degree, for example.

Furthermore, the inside diameter N of the distal-end inside diameter end part on the top end surface25A of the slope surface part25mconstituting the bridge holding surface25C is the inside diameter before performing shrink-fitting, i.e., before the holder25is heated.

In the meantime, the distal-end outer peripheral surface24C of the second bridge part24bof the spider22is formed to correspond to the bridge holding surface25C.

That is, the distal-end outer peripheral surface24C of the spider22is formed with a sloping surface part24mthat is formed at a prescribed sloping angle α degree spreading from the outer periphery end part of the top end surface22A towards the female die30side and a straight line part24nextended out straight to the distal end of the slope surface part24mcontinuously. Further, the slope surface part24mis structured to correspond to the slope surface part25mof the bridge holding surface25C, and the straight line part24nis structured to correspond to the straight line part25nof the bridge holding surface25C.

Further, the sloping angle α degree of the slope surface part24mis set as 0.5 degree to 1 degree same as the sloping angle α degree of the slope surface part25mof the bridge holding surface25C.

As described above, the slope surface part25mand the slope surface part24mcorresponding to each other are formed in the bridge holding surface25C of the holder25and the distal-end outer peripheral surface24C of the spider22, respectively. Thus, the slope surface part24mcomes in a state of being guided to the slope surface part25mwhen the spider22is inserted into the holder25, so that insertion work can be done easily.

However, when the entire surface is a slope surface, a force in an inverted direction of the insertion direction, i.e., a force for slipping out the spider22from the holder25, is generated since the slope surface part25mand the slope surface part24mare sloping with respect to each other.

Thus, in order to prevent the spider22from being slipped out from the holder25, the straight line part25nand the straight line part24nare provided, respectively, in the distal-end parts of each of the slope surface part25mand the slope surface part24min the first embodiment. Therefore, there is a frictional force generated between the straight line part25nand the straight line part24n, so that it is possible to prevent the spider22from being slipped out from the holder25.

The external size of the spider22, i.e., a circumcircle to which the distal-ends of the first to fourth bridge parts24ato24dcome in contact, is set as an external size M. This external size M is formed larger by a prescribed amount than the inside diameter size of the bridge holding surface25C of the holder25before being heated.

In other words, the distal-end inside diameter size N of the bridge holding surface25C of the holder25before being heated is formed to be in a smaller size than the outside diameter size M of the circumcircle of each of the distal-end outer peripheral surfaces24C of the first to fourth bridge parts24ato24dof the spider22.

The sizes of the spider22and the holder25are set in the manner described above. Thus, at the time of shrink-fitting, as shown inFIG. 5, first, the holder25is heated to expand the bridge holding surface25C of the holder25to expand the inside diameter size N of the distal-end inside diameter end part of the bridge holding surface25C to be wider than the outside diameter size M of the spider22. Then, while grasping the spider22by a spider grasping module, not shown, the first to fourth bridge parts24ato24dare inserted to the bridge holding surface25C of the holder25along the insertion direction of the spider22shown with an arrow1inFIG. 4andFIG. 5, i.e., from the downstream side towards the upstream side.

Then, the fitted state of the both at accurate positions and the like is checked and then cooling is done thereon. Thereby, the bridge holding surface25C of the holder25is returned to the inside diameter size N that is in the state before being heated. Therefore, each of the distal-end external peripheral surfaces24C of the first to fourth bridge parts24ato24dis strongly bonded to the holder25. As a result, the spider22and the holder25are unified in a tightly fixed state.

InFIG. 4, the spider22is illustrated in the holder25with an imaginary line (a two-dot chain line). ThisFIG. 4shows the size of the spider22in a case of a state where the holder25is not heated.

In practice, as shown inFIG. 5, the holder25is heated to expand the bridge holding surface25C of the holder25to extend the inside diameter size N of the distal-end inside diameter end part of the bridge holding surface25C to be wider than the external size of the circumcircle of each of the distal-end outer peripheral surfaces24C of the first to fourth bridge parts24ato24dand cooled thereafter, so that the inside diameter size of the bridge holding surface25C of the holder25after being shrink-fitted becomes the same size as the external size M of the circumcircle of the first to fourth bridge parts24ato24d.

Note here that the shrink-fitting work of the spider22and the holder25can be done by placing the holder25on a shrink-fitting worktable90, for example, as shown inFIG. 5.

In this case, the positioning of the spider22and the holder25in the thickness direction can be done by abutting a bottom surface part22B of the spider22to a top end surface90A of the shrink-fitting worktable90.

When the spider22is inserted into the inner peripheral surface of the heated holder25and then cooled at the time of performing shrink-fitting, the first to fourth bridge parts24ato24dconstituting the spider22tend to be deformed in a contracting direction.

Thus, the first embodiment is structured to provide a bridge horizontal shaking prevention part24D in a part of the distal-ends of the two bridge parts24opposing to each other at the side surfaces on the downstream side so that the first to fourth bridge parts24ato24dare not deformed in a contracting direction.

That is, as shown inFIG. 6andFIG. 7, the above-described bridge horizontal shaking prevention part24D is provided in a part of the distal-ends of the first bridge part24aand the fourth bridge part24das well as the second bridge part24band the third bridge part24cat the side surfaces on the downstream side of the opposing to each other among the first to fourth bridge parts24ato24ddisposed to be in an X-letter shape on a plan view. Thus, the bridge horizontal shaking prevention part24D is provided at two points on the opposite sides from each other by sandwiching the mandrel23.

The bridge horizontal shaking prevention part24D is formed in substantially the same height as the height of the straight line part24nof the distal-end outer peripheral surface24C of the first to fourth bridge parts24ato24d. Further, the bridge horizontal shaking prevention part24D is formed in a straight line form that is in parallel to the straight line part24nof the distal-end outer peripheral surface24C.

Furthermore, the bridge horizontal shaking prevention part24D is placed on the edge part that forms a billet pool part30B to be described in details later (seeFIG. 2).

The first to fourth bridge parts24ato24dare placed in substantially an X-letter shape on a plan view as described above continuously with the mandrel23. As shown inFIG. 6, the intersection point P connecting the centers in the width direction of each of the bridge parts24ato24dis at a position different from the center O of the spider22and the X-letter shape is a deformed X-letter shape. Thus, the distances between the first bridge part24aand the fourth bridge part24dand between the second bridge part24band the third bridge part24care different by a prescribed amount with respect to the distances between the first bridge part24aand the second bridge part24band between the third bridge part24cand the fourth bridge part24d.

In this embodiment, the distance between the first bridge part24aand the fourth bridge part24dis longer than the distance between the first bridge part24aand the second bridge part24b.

When the distance between the neighboring bridge parts among the first to fourth bridge parts24ato24dis longer, the shape tends to be deformed, i.e., tends to be contracted. Thus, in the embodiment, the bridge horizontal shaking prevention part24D is provided between the first bridge part24aand the fourth bridge part24dand between the second bridge part24band the third bridge part24c, respectively, where the distances between the neighboring bridges are longer.

The spider22and the holder25are structured in the manner described above. Thus, when the spider22is inserted into the bridge holding ace25C of the heated holder25and the spider22is pushed in while being turned for fixing the first to fourth bridge parts24ato24dat prescribed positions at the time of shrink-fitting, deformation of the first to fourth bridge parts24ato24dcan be prevented since the bridge horizontal shaking prevention part24D is provided between the first bridge part24aand the fourth bridge part24dand between the second bridge part24band the third bridge part24c, respectively, and the bridge horizontal shaking prevention parts24D hold the side surface parts of each of the bridge parts24aand24din a mutually pressing state.

As shown inFIG. 1,FIG. 3, and the like, space connecting holes26connecting between the billet introduction spaces S formed between each of the bridge parts24ato24dare formed in the lower parts of each of the bridge parts24ato24d. Therefore, after the billet B fed from the upstream side is introduced into the billet introduction space S, the billet B is mixed with the billet B inside the billet introduction space S neighboring to each other via the space connecting hole26.

As shown inFIG. 2,FIG. 3,FIG. 8, and the like, an inside forming projected part23A formed on the downstream side end part of the flow of the billet B is provided in the mandrel23which constitutes the spider22.

The inside forming projected part23A is formed by being projected on the female die30side from the bottom end of the distal-end outer peripheral surfaces24C of each of the bridge parts24ato24d. Further, such inside forming projected part23A is constituted with a first inside piece part23B, a second inside piece part23C, and a third inside piece part23D which form three spaces1S,1S, and1S, of the hollow material1in a sectional shape having a rectangle with two vertically parallel lines, respectively, as shown with a virtual image (a two-dot chain line) inFIG. 8.

Note here that the hollow material1in a sectional shape having a rectangle with two vertically parallel lines is in a shape having a pair of long walls1A,1A, short walls1B,1B which connect the longitudinal-direction end parts of the long walls1A,1A to each other, and two partition walls1C,1C disposed equivalently between the short walls1B and1B as shown with a virtual line inFIG. 8andFIG. 9.

The inside forming projected part23A is projected out from the bottom ends of the distal-end outer peripheral surfaces24C of each of the bridge parts24ato24dtowards the female die30side as described above. This inside forming projected part23A is inserted into the billet pool part30B formed in the female die30and into a material forming hole part50continued therefrom as shown inFIG. 2.

Further, the billet pool part30B is formed to have an inside diameter that is substantially equivalent to the size of the inside diameter of the bridge horizontal shaking prevention part24D and to have a prescribed depth as shown inFIG. 2.

As shown inFIG. 10andFIG. 11, a holder receiving surface30A whose center part is recessed is formed on the top surface (the surface on the upstream side) of the female die30, so that the bottom surface25B of the holder25can be abutted against the holder receiving surface30A to hold the holder25.

Further, the billet pool part30B is formed on the holder receiving surface30A.

The material forming hole part50is formed substantially in the center part of the billet pool part30B, and it is formed with a prescribed sized space set between the outer shape of the inside forming projected part23A and an outside forming aperture part30C formed in the billet pool part30B. Further, the outside shape of the hollow material1shown with a virtual line (a two-dotted chain line) inFIG. 8andFIG. 9is formed with the billet B extruded out from the material forming hole part50.

As shown inFIG. 11, the outside forming aperture part30C includes a clearance part30aexpanded from a small-sized straight line part to the outer periphery direction of the female die30.

Thus, the billet B extruded out from the material forming hole part50is extruded without making a contact to the surrounding part at all.

Each of the first inside piece part23B, the second inside piece part23C, and the third inside piece part23D constituting the inside forming projected part23A is formed substantially in a quadrangular prism shape, and provided at the end part of the extrusion direction downstream side of the mandrel23as described above.

On the extrusion direction upstream side in each of the piece parts23B,23C, and23D, a band-like projected frame23E projected outside from the outer periphery of each of those is provided to be wrapped around each of the piece parts23B,23C, and23D, respectively.

The projected frames23E at the three points in the outer periphery of the first inside piece part23B and the third inside piece part23D and the projected frames23E at the two points in the outer periphery of the second inside piece part23C are opposing to the material shape forming aperture30C of the female die30, respectively, and each of the gaps constitutes the material forming hole part50for forming the long side walls1A,1A and the short side walls1B,1B.

Further, the long side walls1A,1A and the short side walls1B,1B of the hollow material1are formed by the billets B extruded out from the material forming hole parts50.

Further, the gap between the projected frame23E of the first piece part23B and the projected frame23E of the second piece part23C opposing to each other and the gap between the projected frame23E of the second piece part23C and the projected frame23E of the third piece part23D opposing to each other constitute the material forming hole parts51for forming the partition walls1C,1C.

Further, the partition walls1C and1C of the hollow material1are formed by the billets B extruded out from the material forming hole parts51.

A billet guide hole part24F is provided in a connected manner, respectively, to the gap between the projected frame23E of the first piece part23B and the projected frame23E of the second piece part23C and to the gap between the projected frame23E of the second piece part23C and the projected frame23E of the third piece part23D, respectively.

As shown with a dotted line inFIG. 6, the billet guide hole part24F is formed along the direction of the line connecting the first bridge part24ato the second bridge part24band the third bridge part24cto the fourth bridge part24d, and it is formed substantially in a rectangular tunnel shape as shown inFIG. 8.

Further, the billet B is pressed and guided into the billet guide hole part24F as shown in an arrow n from the billet introduction space S and extruded out via the material forming hole part51.

Furthermore, the billet B is pressed and guided as shown with an arrow m from the billet introduction space S to the gap between the projected frames23E of the first inside piece part23B and the third inside piece part23D and the material external shape aperture part30C of the female die30, i.e., to the material forming hole part50, and extruded out via the material forming hole part50.

The hollow material1extruded and formed by the die10constituted in the manner described above is shown inFIG. 12.

That is, as shown inFIG. 12, the above-described hollow material1is in a sectional shape having a rectangle with two vertically parallel lines in which both ends of a pair of long side parts1A are connected by the short sides1B, two partition walls1C are formed by connecting between the pair of long sides1A between those short side parts1B, so that there are three spaces1S,1S, and1S formed inside thereof.

Further, such hollow material1in a sectional shape having a rectangle with two vertically parallel lines is continuously extrusion-formed from the material forming hole parts50and51of the extrusion die10by corresponding to the supply amount of the billet B.

Next, a method for forming the hollow material1by using the extrusion die10in the above-described structure will be described.

When the billet B is extruded out from the billet extrusion device60provided on the upstream side of the extrusion direction of the billet B for the male die20, the billet B first is introduced into the billet introduction spaces S constituted by the gaps between each of bridge parts24ato24dconstituting the spider22and the holder25from the entrance of the bridge holding surface25C of the holder25.

The billets B introduced into the billet introduction spaces S are guided into the material forming hole part50via each of the billet guide surfaces24E of the first to fourth bridge parts24ato24dand the side surface of the mandrel23, and then extrusion-formed from the material forming hole parts50,51.

Then, the extrusion-formed hollow material1is fed out from a material send-out hole40A formed in the back die40and, thereafter, transported to a prescribed stockyard or the like by being held by a holding mechanism, not shown.

The extrusion die10according to the embodiment is structured in the manner described above, so that following effects can be acquired.

(1) The engaged surfaces between the distal-end outer peripheral surfaces24C of the first to fourth bridge parts24ato24dof the bridge part24constituting the spider22and the bridge holding surface25C of the holder25are unified by being strongly bonded by shrink-fitting, so that the stress imposed upon the die can be received by the spider22and the holder25. Thereby, the stress imposed upon the stress concentrated parts in each of the bridge parts24ato24dcan be eased, so that breakage of the bridge part24of the spider22can be prevented. As a result, it becomes possible to perform high-speed extrusion and to extend the life even when extrusion-forming the billet B constituted with a high-strength alloy with a high extrusion processing force, particularly constituted with the so-called 7000-system maximum strength aluminum alloy.

(2) Even when the pressure for extruding the billet B is applied to the mandrel23and each of the bridge parts24ato24dof the spider22, each of the bridge parts24ato24dalone of the spider22is not slightly shifted and is held stably since the distal-end outer peripheral surfaces of each of the bridge parts24ato24dof the spider22and the bridge holding surface25C of the holder25are bonded and unified by shrink-fitting. As a result, it becomes possible to process the hollow material1with a desired high precision.

(3) Each of the distal-end outer peripheral surfaces24C of the first to fourth bridge parts24ato24dis formed with the slope surface part24mand the straight line part24n, and the bridge holding surface25C of the holder25is formed with the slope surface part25mand the straight line part25n. Thus, after the spider22is inserted into the holder25, the bridge holding surface25C is contracted when being cooled. Therefore, a force for pushing out the spider22in the push-out direction works. However, there is a friction force generated between the respective straight line parts25nand24n, so that it is possible to prevent the spider22from being slipped out from the holder25.

(4) Each of the distal-end outer peripheral surfaces24C of the first to fourth bridge parts24ato24dis formed with the slope surface part24mand the straight line part24n, and the bridge holding surface25C of the holder25is formed with the slope surface part25mand the straight line part25n. Thus, the slope surface part24mcomes in a state of being guided to the slope surface part25mwhen the spider22is inserted into the holder25, so that insertion work can be done easily. As a result, it becomes easy to do the shrink-fitting work, so that the operability can be improved.

(5) The sloping guide surface24E in a prescribed height gradually widened from the top face part22A of each of the bridge parts24ato24dis formed in the mandrel23and the first to fourth bridge parts24ato24dof the spider22over a prescribed height. Thus, the billets B extruded from the upstream side can be smoothly extruded out into the billet introduction spaces S. As a result, the billets B can flow equivalently, so that the uniform hollow material1can be formed.

(6) Among the first to fourth bridge parts24ato24d, those with a longer distance between the neighboring bridges tend to be deformed easily. However, the bridge horizontal shaking prevention part24D is provided, respectively, between the first bridge part24aand the fourth bridge part24das well as between the second bridge part24band the third bridge part24c, and the bridge horizontal shaking prevention part24D holds them by pressing against the side surface parts of each of the bridge parts24a,24d, and the like. Therefore, it is possible to prevent deformation of the first to fourth bridge parts24ato24d.

Next, a second embodiment of the extrusion die according to the present invention will be described by referring toFIG. 14toFIG. 16.

An extrusion die10A according to the second embodiment is provided with: first to fourth bridge parts74ato74dcorresponding to the distal-end outer peripheral surfaces24C of the first to fourth bridge parts24ato24dof the extrusion die10according to the first embodiment; and an uneven structure77as well as a step structure78over a distal-end outer peripheral surface74C and a bridge holding surface75C of a holder75.

In the second embodiment, only the uneven structure77and the step structure78are different from the first embodiment and other structures are completely the same. Thus, same reference numerals are applied to the same structures and same members, and only the different points will be described.

As shown inFIG. 14andFIG. 15, the extrusion die10A of the second embodiment is structured by including a male die70which corresponds to the male die20. Further, the male die70is structured by including a spider72corresponding to the spider22and a holder75corresponding to the holder25.

As shown inFIG. 14andFIG. 15, the spider72is structured with: a mandrel73corresponding to the mandrel23; and a plurality of bridge parts74which support the mandrel73and are projected in substantially X-letter shape towards the outer side from the periphery of the mandrel73, i.e., four pieces including a first bridge part74a, a second bridge part74b, a third bridge part74c, and a fourth bridge part74d.

Further, the distal-end outer peripheral surfaces74C of the first bridge part74a, the second bridge part74b, the third bridge part74c, and the fourth bridge part74dare designed to be engaged with a bridge holding surface part75C of the holder75, and each of the distal-end outer peripheral surfaces74C of the first to fourth bridge parts74ato74dand the bridge holding surface part75C of the holder75are bonded by shrink-fitting.

The uneven structure77is constituted with: a protruded surface part74eprovided on each of the distal-end outer peripheral parts74C of the first bridge part74aand the fourth bridge part74d; and a recessed surface part75awhich is formed in the bridge holding surface part75C of the holder75to correspond to the protruded surface part74e.

The bridge holding surface part75C corresponds to the bridge holding surface part25C of the first embodiment, and it is formed with a slope surface part75mand a straight line part75nas in the case of the bridge holding surface part25C. Further, in the bridge holding surface part75C of the holder75, the recessed surface parts75acorresponding to the respective projected surface parts74eof the two bridge parts74aand74dare formed at positions somewhere on the slope surface part75m.

Furthermore, the distal-end outer peripheral surface part74C corresponds to the distal-end outer peripheral surface24C of the first embodiment, and it is formed with a slope surface part74mand a straight line part74nas in the case of the distal-end outer peripheral surface24C, and the projected surface part74eis formed at a position somewhere on the slope surface part74m.

Further, the step structure78is constituted with: a step surface part74fprovided in each of the distal-end outer peripheral surface parts74C of the second bridge part74band the third bridge part74c; and a step receiving surface part75bwhich is formed in the bridge holding surface part75C of the holder75to correspond to the step surface part74f. The step receiving surface part75bis formed in a straight line surface.

As shown inFIG. 15, the recessed surface part75C of the holder75which constitutes the uneven structure77is formed in a lower half part of the area acquired by connecting the point at 90 degrees and the point at 270 degrees, for example, on a plan view of the male die70. Further, the step receiving surface part75bof the holder75which constitutes the step structure78is formed in an upper half part of the area acquired by connecting the point at 90 degrees and the point at 270 degrees.

Therefore, when shrink-fitting the spider72and the holder75, it is necessary to insert and position the first bridge part74aand the fourth bridge part74dto be located at the lower half part sectioned by the line connecting between the point at 90 degrees and the point at 270 degrees inFIG. 15and to insert and position the second bridge part74band the third bridge part74cto be located at the upper half part sectioned by the line connecting between the point at 90 degrees and the point at 270 degrees inFIG. 15.

Further, in the embodiment, a position check mark65is applied to the spider72and the holder75for checking that each of the bridge parts74ato74dis disposed within the above-described range.

That is, the position check mark65is constituted with: a fixed side mark66applied to the holder75; and a moving side mark67applied to the first bridge part74awhich constitutes the bridge part74of the spider72as shown inFIG. 16in detail.

The fixed side mark66is formed with: a straight line mark66aapplied on the top surface of the holder75and on an extended line of the center line CL of the first bridge part74a; and a vertical mark66bextended vertically on the inner peripheral surface of the holder75from the distal end of the straight line mark66a.

The moving side mark67is applied on the distal-end outer peripheral surface and the top surface of the first bridge part74aon the center line CL of the first bridge part74a.

Further, it is preferable to apply those fixed side mark66and the moving side mark67by carving or the like.

The extrusion die10of the second embodiment is structured in the manner described above, so that following effects can be acquired in addition to the same effects as those described in (1), (4), and (5).

(6) The uneven structure77and the step structure78are provided over the distal-end outer peripheral surfaces74C of each of the bridge parts74ato74dof the spider72and the bridge holding surface75C of a holder75. Thus, when the holder75is cooled and contracted at the time of shrink-fitting the spider72and the holder75, each of the structures77and78functions as stoppers for the slip-out direction. As a result, it is possible to prevent the spider72from being slipped out from the holder75. Thereby, the both72and75can be bonded securely, which makes it possible to process still more highly precise hollow materials.

(7) The position check mark65constituted with the fixed side mark66and the moving side mark67is formed on the first bridge part74aof the spider72and the holder25, so that the fixed side mark66and the moving side mark67may simply be aligned when inserting the spider22to the heated and expanded holder25. Thus, each of the bridge parts74ato74dcan be easily disposed at prescribed positions.

Next, a third embodiment of the extrusion die according to the present invention will be described by referring toFIG. 17andFIG. 18.

An extrusion die10B according to the third embodiment is proposed in order to offset the pressure by bringing the surface that receives the pressure close to a position where there is a possibility of having a crack.

In the third embodiment, same reference numerals are applied to the same structures and the same members as those of the extrusion die10of the first embodiment, and only different points will be described.

FIG. 17shows bonding of a distal-end outer peripheral surface84C of a second bridge part84band a holder85.

As shown inFIG. 17, a spider82is structured by including a mandrel83and a bridge part84, and it is held by a holder85.

Further, each of the distal-end outer peripheral surfaces84C of the first to fourth bridge parts84ato84d(the second bridge part84binFIG. 17) constituting the bridge part84is formed with: a slope surface part84mwhich is spread from the upstream side towards the downstream side; and an inverse slope surface part84qwhich is formed at the end of the slope surface part84mon the downstream side in a shape tapered towards the center side of the holder85.

In the meantime, the bridge holding surface85C of the holder85is formed with: a slope surface part85mwhich corresponds to the slope surface part84mof each of the bridge parts84ato84d; and an inverse slope surface part85qwhich is formed at the distal end of the slope surface part85mby corresponding to the inverse slope surface part84q.

The part formed with the inverse slope surface part85qforms a bridge receiving surface part85A which receives the inverse slope surface part84qand also functions to prevent the spider82from being slipped out from the holder85.

As shown inFIG. 17andFIG. 18, the inverse slope surface part84qforming the distal-end outer peripheral surface84C of the second bridge part84bis tapered towards the center side of the holder85in a size H. In the meantime, the inverse slope surface part85qof the holder85is formed in a protrusion amount of the size H and formed in a prescribed width W as shown inFIG. 18. As described above, the inverse slope surface part85qis in a shape corresponding to the inverse slope surface part84qof each of the bridge parts84ato84d.

The inverse slope surface part85qof the holder85is tilted on the inverse slope surface84qside of the bridge part84at an angle α1 degree with respect to the slope surface part85mof the bridge holding surface85C. Further, this angle α1 degree is set as about 30 degrees, for example.

The first bridge part84a, the third bridge part84c, and the fourth bridge part84dare also in the same shape.

Note here that the distance between the base end point P1 of the bridge part84of the inverse slope surface part85qof the holder85and the working point P2 in the direction orthogonal to the extrusion direction in the mandrel83from the base end point P1 is set as the size L, and the surface receiving the pressure is brought close to the position where there is a possibility of having a crack.

Thus, the moment generated at the working point P2 of the mandrel83can be reduced, so that the strength of the bridge part84can be increased. Thereby, breakage of the bridge part84which constitutes the spider82can be prevented. As a result, it becomes possible to perform high-speed extrusion and to extend the life even when extrusion-forming the billet constituted with a high-strength alloy with a high extrusion processing force, particularly constituted with the so-called 7000-system maximum strength aluminum alloy.

As described above, the inverse slope surface parts85qare provided by corresponding to the respective inverse slope surface parts84qof each of the bridge parts84ato84d, so that positions of the both are required to be aligned when inserting the spider82into the holder85. Thus, in the third embodiment, the position check mark65is provided to the second bridge part84band the holder85, for example, among the four bridge parts84ato84d.

As a result, the fixed side mark66and the moving side mark67may simply be aligned when inserting the spider82to the heated and expanded holder85. Thus, each of the bridge parts84ato84dcan be easily disposed at prescribed positions.

The extrusion die10of the third embodiment is structured in the manner described above, so that following effects can be acquired in addition to the same effects as those described in (1), (4), (5) and (7).

(8) The distance between the base end point P1 of the bridge part84of the inverse slope surface part85qof the holder85and the working point P2 in the direction orthogonal to the extrusion direction in the mandrel83from the base end point P1 is set as the size L, and the surface receiving the pressure is brought close to the position where there is a possibility of having a crack.

Thus, the moment generated at the working point P2 of the mandrel83can be reduced, so that the strength of the bridge part84can be increased. Thereby, breakage of the first to fourth bridge parts24ato24dcan be prevented. As a result, it becomes possible to perform high-speed extrusion and to extend the life even when extrusion-forming the billet B constituted with a high-strength alloy with a high extrusion processing force, particularly constituted with the so-called 7000-system maximum strength aluminum alloy.

While the present invention has been described by referring to each of the embodiments, the present invention is not limited only to each of the embodiments described above. Various kinds of modifications and changes occurred to those skilled in the art can be applied to the structures and details of the present invention. Further, the present invention includes a part of or a whole part of the structures of each of the embodiments combined mutually as appropriate.

For example, while the hollow material1formed by the extrusion die10is in a sectional shape having a rectangle with two vertically parallel lines in the above-described embodiment, the shape is not limited to that. As shown inFIG. 13, it is possible to be used when forming a square sectional shape hollow material2.

In such case, first, a substantially quadrangular prism shaped piece part is provided to the end part of the mandrel for forming an inside space S2 of the square sectional shaped hollow material2instead of the first inside piece part23B, the second inside piece part23C, and the third inside piece part23D of the mandrel23of the spider22according to the embodiment. Further, a substantially square shaped external aperture corresponding to the substantially quadrangular prism shaped single piece part may be provided to the female die instead of the external shape aperture part30C of the female die30.

At this time, the engaged state and the tilt angle between the bridge distal-end outer peripheral surface24C of the spider22and the bridge holding surface25C of the holder25may be set as the same as the hollow material1in a sectional shape having a rectangle with two vertically parallel lines described above and the holder25can be used as it is. Therefore, it is possible to form a plurality of kinds of hollow materials with different sectional view shapes with a small number of use members.

Further, while the bridge horizontal shaking prevention parts24D are provided between each of the first bridge24aand the fourth bridge part24das well as between the second bridge part24band the third bridge part24cand the like constituting the spider22and the like in the first embodiment, the shape of the bridge horizontal shaking prevention part24D is not limited to that. For example, the structure shown inFIG. 19may be employed.

In the modification embodiment shown inFIG. 19, the bridge horizontal shaking prevention parts24D are provided in all the sections between each of the first to fourth bridge parts24ato24d. Further, in such modified mode, four bridge horizontal shaking prevention parts24D connecting the four bridge parts24ato24dare provided, so that more horizontal shaking prevention effect can be acquired.

Further, while the distal-end outer peripheral surface24C of each of the bridge parts24ato24dare formed with the slope surface part24mand the straight line part24nand the bridge holding surface25C is formed with the slope surface part25mand the straight line surface part25nin the first embodiment, the structures are not limited to that. For example, the entire surfaces of each of the distal-end outer peripheral surface24C and the bridge holding surface25C may be formed with the straight line surface parts. With such structure, it is also possible to insert each of the bridge parts24ato24dof the spider22into the bridge holding surface25C of the holder25since the inner peripheral surface inside diameter of the bridge holding surface25C is increased as a result of heating and expanding the holder25at the time of shrink-fitting.

With such modified mode, processing of the distal-end outer peripheral surface24C of each of the bridge parts24ato24dand the processing of the bridge holding surface25C can be done easily.

Further, while the uneven structure77is provided to the first bridge part74aand the fourth bridge part74das well as the holder75and the step structure78is provided to the second bridge part74band the third bridge part74cas well as the holder75, respectively, in the second embodiment, the structures are not limited only to that. For example, the uneven structure77in the same shape as that of the uneven structure77described above may be provided to all of the bridge parts74ato74dor the step structure78in the same shape as that of the step structure78described above may be provided to all of the bridge parts74ato74d.

Further, when the uneven structure77same as the uneven structure77is provided to all of the bridge parts74ato74d, the entire circumference of the bridge holding surface part75C of the holder75may be corresponded to the uneven structure77.

With such structure, a same kind of projected surface parts77aconstituting the uneven structure77may simply be formed in the distal-end outer periphery of the first to fourth bridge parts74ato74d, and a same kind of recessed surface parts77bmay simply be formed on the entire circumference of the bridge holding surface part75C of the holder75. Thus, the processing can be done more easily than the case of the second embodiment.

Further, when the step structure78same as the step structure78is provided to all of the bridge parts74ato74d, the entire circumference of the bridge holding surface part75C of the holder75may be corresponded to the step structure78.

With such structure, the step surface parts74fmay be simply be formed in the distal-end outer periphery of the first to fourth bridge parts74ato74d, and the step receiving surface parts75bmay simply be formed on the entire circumference of the bridge holding surface part75C of the holder75. Thus, the processing can be done more easily than the case of the second embodiment.

Further, while the uneven structure77and the strep structure78are formed at positions somewhere on the slope surface part74mand the straight line part74nis formed at the distal end thereof in the distal-end outer peripheral surface parts74C of all of the bridge parts74ato74din the second embodiment, the structures are not limited to that.

The uneven structure77and the step structure78are formed on the distal-end surface parts74C of each of the bridge parts74ato74d, and those uneven structure77and the step structure78are bonded to the bridge holding surface75Ca of the holder75by shrink-fitting. Thus, there is no risk that the spider72is slipped out from the bridge holding surface part75C of the holder75when extruding out the billet B. Therefore, unlike the second embodiment, it is not necessary to form the straight line part74nat the tip of the distal-end outer peripheral surface parts74C of the bridge parts74ato74d.

INDUSTRIAL APPLICABILITY

The extrusion die according to the present invention is used when forming a hollow material constituted with a high-strength alloy, particularly with the so-called 7000-system maximum strength aluminum alloy.

REFERENCE NUMERALS

1Hollow material in a sectional shape having a rectangle with two vertically parallel lines Hollow material forming extrusion die (first embodiment)

23B Inside forming projected part

24ato24dFirst to fourth bridges

24mSlope surface part

24nStraight line part

24C Bridge distal-end outer peripheral surface

25C Bridge holding surface

25mSlope surface part

25nStraight line part

30B Material external shape aperture

50Material forming hole part

51Material forming hole part

A Billet extrusion direction

B Billet

S Billet introduction space