GB2379180A

GB2379180A - Metallic member forming method

Info

Publication number: GB2379180A
Application number: GB0220482A
Authority: GB
Inventors: Haruo Watanabe; Hiroyuki Iseki
Original assignee: Aisin Takaoka Co Ltd
Current assignee: Aisin Takaoka Co Ltd
Priority date: 2001-09-04
Filing date: 2002-09-04
Publication date: 2003-03-05
Anticipated expiration: 2022-09-04
Also published as: JP3761820B2; GB2379180A8; GB0220482D0; US20040040636A1; GB2379180B; DE10240876A1; JP2003154415A; DE10240876B4

Abstract

A metallic member forming method capable of achieving both formability of a metallic member and highly strengthening same. Cylindrical metallic member 1 having a hollow space 10 and forming die 3 having a forming face 31 are used. Metallic member 1 is heated up to a temperature range capable of quench-hardening (e.g., not less than A1 transformation point). By increasing the internal pressure of gas contained in the hollow space 10 of the metallic member 1 a wall 1a of the metallic member 1 is bulged and/or deformed, and the bulged, deformed wall 1a of the metallic member 1 is deformed by bringing it into intimate contact with the forming face 31 of the forming die concurrently with quench-hardening it. High strengthening of the metallic member 1 is achieved. The forming die 3 may comprise curling means 33.

Description

2379 1 80

METALLIC MEMBER FORMING METHOD

[ O O 0 1]

FIELD OF THE INVENTION

This invention relates to a metallic member forming method capable of enhancing formability of a metallic member and highly strengthening the same.

BACKGROUN D

As a metallic member forming method, a hydro-forming method is known. The hydro-forming method is a technique of using a tubular or cylindrical metallic member having a hollow space and a forming die having a forming face designed to have a target shape. Water is fed into the hollow space of the metallic member to bulge and deform the wall of the metallic member, and to form the wall by bringing it into intimate contact (i.e., contact closelyorwithout clearance) with the forming face of the forming die.

According to the aforementioned hydro-forming method, the wall of the metallic member becomes bulged and deformed by feeding water into the hollow space of the metallic member, and consequently, forming the wall can be realized. However, there are limitations for satisfying both the formability of a metallic member and highly strengthening the same.

t0004] In automotive parts and the like, it is often a requirement to reduce the thickness of the materialto reduce weight. The forming force required for forming a metallic member is less, but there are limitations with respect to highly strengthening the metallic member.

In the case where the material is iron-based, it is sometimes required to improve the tensile strength of the material (i.e., produce high tensile steel) by increasing the consent of en alloy clement while reducingits thickness.

Although the tensile strength of the material is improved in such a way, the decreasing elongation of the material canimpairthe, formabilityofthematerial,andaccordingly, there is a fear of causing cracks and other defects in the course of bulging and deforming the metallic member when using the hydro-forming method.

WO 01/23116 A1(5 April 2001) discloses a method of forming an elongated Lubularblankinto a tubular structural component by applying high pressure gas so as to conform totheinnersurfaceoftheshellinwhichthetubularcomponent is heated by inductively heating the shell. The resultant product is further brought to a separate quench station.

However, the quenching cannot be carried out simultaneously with the forming step, and there is much to be desired for

further improvement.

SUMMARY OF THE DISCLOSURE

The present invention has been made under such circumstances as described above. It is an object of the present invention is to provide a metallic member-forming method capable of achieving both formability of and highly strengthening a metallic member.

According to a first aspect of the present invention thereisprovidedametallicmemberformingmethodcomprising the steps of: providing and using a (typically cylindrical or tubular (herein termed "cylindrical'' comprehensively)) metallic member having a hollow space and forming die having a forming face; and performing a forming and quench-reinforcing step by increasing an internal pressure of gas contained in the hollow space of the metallic member heated up to a temperature range capable of reinforcing by quenching (i.e., quenchreinforcing) to bulge and/or deform a wall of the metallic member, wherein forming of the bulged, deformedwallofthemetallicmember is performed by bringing the same wall into intimate contact with the forming face of the forming die accompanied by simultaneous quench- reinforcing of the wall.

According to the metallic member-forming method of the invention, at first, a metallic member is heated up to a temperature range capable of quench-reinforcing. Then, in a forming end quench-reinforcing step,a wall ofthemetallic member is changed into a bulged and/or deformed state by increasing internalpressureof the gas containedina hollow space of the metallic member. During this span of time, the metallic member can be maintained at a significantly high temperature ascomparedwiththecasewherewateris contained in the hollow space of the metallic member as the case with the hydro-forming method.

[ O O O 9]

Besides,accordingtothemetallicmemberformingmethod oftheinvention, the wallof the metallic die, bulged and/or deformed as above described, is formed by bringing it into intimate contact with a forming face of a forming die, and thereupon simultaneous quench-reinforcing takes place. In bulging and/or deforming the metallic member in this way, elongation of the metallic member can be ensured, since the metallic member has been heated up to a temperature range capable of quench-reinforcing. As a result, plastic deformability of the metallic member can be improved, and also bulged deformability and/or formability of the metallic member can be enhanced.

The term "bulge'' used herein does not mean that the

workpiece is "bulged" in its entirety, but encompasses the case of partial bulging, i.e., a case where only part of a workpiece is bulged or deformed under the applied high pressure within the internal hollow space of the workpiece.

[ O 0 1 0]

In addition, in the above described forming and quench-reinforcing step, the metallic member can be quenched andreinforcedbybringingthebulgedand/ordeformedmetallic member into intimate contact with a forming face of a forming die to realize high strengthening of the metallic member.

According to a second aspect of the present invention, there is provided a method for forming metallic member comprising the steps of: (a) placing a cylindrical metallic member having a hollow space in a forming die assembly, (b) heating said metallic member placed in the forming die assembly, (c) bringing a prescribed surface of said metallic member into intimate contact with a prescribed face of the forming die assembly by introducing a pressured gas into said hollow space of themetallicmemberheatedinthe formingdie assembly, to thereby plastically deform said metallic member, and, (d) quenching said metallic member immediately following the deformation of the metallic member through cooling said

metallic member in a state of being placed in the forming die assembly. By this method, the heating, deformation and cooling are carried out consecutively or continuously within the die assembly. That is the formation and heat treatment of the metallic member are performed continuously in situ, resulting in an improved operation.

According to a third aspect of the present invention, there is provided a method for forming metallic member comprising the steps of: (a) heating a cylindrical metallic member having a hollow space, (b) placing said heated metallic member into a forming die assembly' (c) bringing said heated metallic member into intimate contact with a prescribed face of the forming die assembly by introducing a pressurizing gas into the hollow space of said metallic member, to thereby plastically deform said metallic member, (d) quenching said metallic member immediately following the deformation ofsaidmetallic member through cooling said forming die assembly, in a state that said metallic member is placed in the forming die assembly. By this method, the deformation and cooling of the metallic member are carried outcontinuouslywithinthedieassembly. Thatis the forming

and heat treatment of the metallic member are performed continuously in situ.

According to a fourth aspect, there is provided a metallic member product produced according to the method as defined in any one of preceding aspects.

According to a fifth aspect, there is provided an apparatus for forming metallic member comprising: a forming die assembly for placing a cylindrical metallic member having a hollow space into a cavity of the forming die assembly, a gas supply device for supplying a pressurizing gas into the hollow space of said metallic member heated within the forming die assembly, and, a cooling device for cooling said forming die assembly configured to quench-hardenimg said metallic member place end plastically deformed in said forming die assembly. The apparatus further comprises a control unit for controlling saidgassupplydevicesoastoperformbulgingand/ordeforming of said metallic member together with quench-hardening the same. According to this apparatus, the deformation and quenchingarecarriedoutcontinuouslywithinthedieassembly. Thatis the forming end heat treatment of the metallicmember are performed continuously in situ.

The apparatus may further comprise a heating device for selectively heating the metallic member placed in the cavity of said forming die assembly.

BRIEF EXPLANATION OF DRAWINGS

Fig.1 is a perspective view associated with a first example of the invention showing schematically a process of forming an expended pert at both endsofametallicmember end placing the same in a furnace chamber of a furnace respectively.

Fig.2 is a cross-sectional view associated with the first example of the invention showingschematically a state of placing the heated metallic member in a forming die.

Fig.3 is a cross-sectional view associated with the first example oftheinvention showing Schematically a state of feeding gas into a hollow space of the metallic member end swelling awallofthemetallicmember under the condition that the heated metallic member is placed in the forming die. Fig.4isacross-sectionalviewassociatedwithasecond example of the invention showing schematically a state of heating a metallic member facing a forming die.

Fig.5 is a cross-sectional view associated with the second example oftheinvention showing schematically a state immediately before feeding gas into a hollow space of the heated metallic member placed so es to face the forming die.

Fig.6is across-sectionalview associated with a third example of the invention showing schematically a state of heating a metallic member facing a forming die.

Fig.7 is a cross-sectional view associated with the third example of the invention showing schematically a state immediately before feeding gas into a hollow space of the heated metallic member placed so as to face the formingdie.

Fig.8isacross-sectionalviewassociatedwithafourth example of the invention showing schematically a state of heating a metallic member facing a forming die.

Fig.9 is a cross-sectional view associated with the fourth example oftheinvention showing schematically a state immediately before feeding gas into a hollow space of the heated metallic member placed so as to face the forming die.

Fig.10 is a perspective view showing a first applied example of the invention.

Fig.11 is a perspective view showing a second applied example of the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

According to a metallic member forming method of the invention, at least one of the following embodiments can He employed.

A metallic member is in a cylindrical form that has

a hollow space. As the cylindrical (or tubular) form, those of a circular or an angularly (i.e., polygonal or square) or any cross sectionmaybeemployedwhere the metallicmember before executing a forming and quench-reinforcing step may have a straightly cylindrical form or a cylindrical form that has atleast one ofourved,concave end convex portions.

The metallic member maybe a unitary formed (shaped) article or a joint product of plural materials.

With regard to a material of the metallic member, an embodimentcanbeemployedafthatthematerialisaniron-based materialincludingan alloy steelsuchas high tension steer, stainless steel or the like, a titanium-based material, an aluminumbasedmaterialoracupper-basedmaterial.However, it is unnecessary to restrict the material of the metallic membertothoseexemplifiedmaterials. Theterm"hightension steel"means high tensile strength steelmade ofsteelhaving alargetensilestrength.Asthehightensionsteel,iron-based metal having a tensile strength of not less than 500MPa ( 50kgf/mm2), iron-based metal having a tensile strength of not less than 600Mpa, iron- based metal having a tensile strength of not less than 800Mpa, iron-based metal having a tensile strength of not less than 1,OOOMpa, or iron-based metal having a tensile strength of not less than 1,500Mpa may be employed. In general, high-tension steel has a high

strength, but does not necessarily have sufficient plastic deformability. According to the invention, these metallic members are heated before being quenched and reinforced so that the plastic deformability of the metallic member can beimproved.Asaresult, bulgeddeformabilityandformability of the metallic member can tee entranced even in the case where plastic deformability ofthemetallicmemberisinsufficient as is in the case where a material of the metallic member is in a high tension state. Consequently, in the case where formed shapes of metallic members are different from each other and also in the that where formation degree of a metalliomemberislarge, formabilityofeachmetallicmember can be well secured.

[ O 0 1 9]

In regard of heating a metallic member, an embodiment can be employed where the heating is executed by at least one of operation for maintaining the metallic member in a furnace chamber of a heating furnace, induction heating operation for induction-heating the metallic member, and resistance heating operation for energizing the metallic member. At least two of these operations may be employed in a combined state. In other words, after executing the operation for maintaining the metallic member in the furnace chamber of the furnace, the induction heating operation for induction-heating the metallic member may be performed.

Alternatively,afterexecutingtheoperationformaintaining the metallic member in the furnace chamber of the furnace, the resistance heating operation for energizing the metallic member may be performed. If not so, without performing the operation for maintaining the metallicmemberin the furnace chamber of the furnace, the induction heating operation and the resistance heating operation (generally, electrical heating) may be performed. The induction heating operation and the resistance heating operation can be performed simultaneously or successively.

With regard to the operation for maintaining the metallic member in the furnace chamber of the furnace, an embodiment can be employed where this operation is executed under the condition that the furnace chamber of the furnace has a non-oxidizing atmosphere. As the non-oxidizing atmosphere, at least one of vacuum atmosphere, reducing atmosphereandinertatmospheremaybeemployed.Thereducing gasmaybeatleast one of CO gas atmosphere and CO-containing gas atmosphere. The inert gas atmosphere may be a nitrogen atmosphere or a rare gas atmosphere of argon or the like.

For theinduction heating operation, en embodiment can be employed wherein this operation is put into practice by applyinganalternatingaurrenttoanelectricallyconductive

member for induction heating in a state of placing the conductive member close to (preferably within the hollow space of) the metallic member disposed within the forming die in order to induction-heat the metallic member (selectively, as much as possible). The conductive member for induction heating may be coil-shaped or plate-shaped.

Basically, the conductive member has any shape if it can induction-heat the metallic member. The frequency of the alternating current to be applied to the conductive member may be selected properly within a frequency range capable of induction-heating the metallic member taking into account of material of themetallicmember, equipment cost, induction heating ability and the like, and accordingly, low frequency region, middle frequency region or high frequency region may be applied depending on circumstances. Applicable frequencies may range, for example, from 0.5 to 5,000kHz, especially, 1 to 2,000kHz. However, the applicable frequency range is not restricted to these exemplified frequencies.

In the case of applying a high frequency alternating current to the conductive member to induction-heat the metallic member, a surface layer of the metallic member can be heated efficiently since the proximity effect capable of heating efficiently the surface layer positioned near the conductive member in the metallic member, and also the

skineffectresultingfromanelectriccurrentrunningthrough the surface layer of the metallic member, can be expected.

In the resistance heating operation for energizing the metallic member, an embodiment can be employed where this operation is executed by energizing the metallic member from energizing terminals in a state ofoonnecting the energizing terminals to the metallic member facing a forming face of a forming die to heat the metallic member by Joule heat.

An electric current for energizing the metallic member from the energizing terminals may be a direct current or an alternating current (AC). in the of applying the alternating current, its frequency may be in a low, middle or high frequency region depending on circumstances taking into account of material of the metallic member, equipment cost, induction heating ability and the like. The frequency may be in a range of, for example, from 0.5 to 5,000kHz, especially, from 1 to 2,000kHz. However, the frequency is not restricted Lo these exemplifiedfrequencies. In the case of applying a high frequency alternating current to the metallicmemberfromoneoftheenergizingterminalsFasurface layer of the metallic member can tee treated efficiently since the skin effect resulting from running an electric current through the surface layer of the metallic member can be expected.

The metallic member may be made of an iron-based material, and an embodiment can be employed where the metallic member is heated up to a temperature range of not less than the Al transformation point "temperature capable of hardening). The term"notless than the Al transformation point', means a temperature range higher than an austenite generation temperature. As the case may be, an embodiment also can be employed where the metallic member is heated up to a temperature range of not less than the A3 transformation point. It is preferable to set the maximum heating temperature ofthemetallicmemberat a liquid phase generation temperature of a matrix of the metallic member.

In the forming and quench-reinforcing step, at least a part of the metallic member can be hardened to provide an accelerated transformation into a martensite state by bringing a wall ofthe metalllcmemberintointimate contact with a forming face of a forming die. Hardening in this way canpromisetostrengthenthemetallicmember. Aconstitution ofOeneratingtroostite,sorbiteorthelikeisalsopermissive together with or in place ofmartensite.Troostiteorsorbite is liable to be generated when the cooling rate is lower than that required for generating martensite.

In the case where the metallic member is iron-based, it may contain an alloy element having a high multiplying factor for the purpose of enhancing the hardening property.

The alloy element having a high multiplying factor includes carbon, manganese, silicon, nickel, chromiumandmolybJenum, and at least one of these alloy elements may be contained in the metallic member. In the case where the metallic member is of an iron-based material, there are many cases where the content of at least one alloy element described above is increased for transforming the material into a high tension one. [0027]

As for a forming die, an embodiment can be employed wherein the forming die has a cooling device for cooling the forming die. With regard to the cooling device, at least one of the following systems may be employed: a system wherein a cooling passage inside the forming die is formed and a coolant such as cooling water, refrigerant gas or the like is passed through the cooling passage) and a system wherein a coolant such as cooling water, refrigerant gas or the like is brought into intimate contact with the forming face of the forming die. A material of the forming die includes a metal having a good thermal conductivity as well as good durability such as carbon steel, alloy steel and the like.

i0028]

According to the present inventive method, a wall of the metallic member is bulged and/or deformed to come into contact with the forming face of the forming die byincreasing the internal pressure of a gas contained in a hollow space of the metallic member. For an operation for increasing the internal pressure, an embodiment can be employed in which an operation is performed by feeding gas into the hollow space of the metallic member. The gas to be fed into the hollow space may be at least one of air, nitrogen gas, nitrogen-rich gas, argon gas and argon-rich gas. The term "nitrogen-rich gas" means a gas having a high nitrogen concentration. The term "argon-rich gas''means a gas having a high argon concentration.

With regard to the operation for feeding gas into the hollow space of the metallic member, an embodiment can be employed in which an operation is performed from a high-pressure gas supply capable of feeding a highpressure gas. Taking into consideration the formability of the metallic member, it is preferable that the pressure of the high-pressure gas is rather high. The pressure of the high-pressure gas can be set at, for example, not less than lOMPa, not less than 15MPa, not less than 20MPa, or not less than 30MPa. However, taking into consideration of applications, it is preferablyin a range offrom15 to25MPa,

from 17 to 23MPa, or from 19 to 21MPa; or otherwise set at 20MPa. An exemplary high-pressure gas supply sourceincludes a canister, factory air supply line and the like.

For the metallic member, an embodiment canbeemployed in which the metallic member has an opening communicating with its hollow space and formed by a tapered open (e.g., conical)wallface.Inthiscase, anembodimentcanbeemployed inwhichanopeningofthemetalliamemberissealedbyapplying directly or indirectly a sealant, having a taper angle corresponding to that of the tapered open wall face, to the tapered open wall face.In this case, a good sealis realized since the sealant is applied to the tapered open wall face.

As an embodiment of the method for forming a metallic member, the following method may be employed. Namely the method comprises the steps of:placingacylindricalmetallic member having a hollow spaceinaformingdicassembly;heating said metallic member placed in the forming die assembly; bringing a prescribed surface of said metallic member into intimate contact with a prescribed face of the forming die assembly by introducing a pressured gas into said hollow space of themetalliamember heatedinthe formingdieassembly, to thereby plastically deform said metallic member; and, quenching said metallic member immediately following the

deformation of the metallic member through cooling said metallic member in a state of being placed in the forming die assembly.

Also the following method for forming metallic member may be employed. That is, the method comprises the steps of: heating a cylindrical metallic member having a hollow space; placing said heated metallic member into a forming die assembly; bringing said heated metallic member into intimate contact with a prescribed face of the forming die assembly by introducing a pressurizing gas into the hollow space of said metallic member,totherebyplasticallydeform said metallic member; and quenching said metallic member immediatelyfollowingthedeformationofsaidmetallicmember through cooling said forming die assembly, in a state that said metallic member is placed in the forming die assembly.

A metallic member product having a desired shape may be produced according to any one of the methods es mentioned hereinbefore. By employing any one of the aforementioned methods, both the forming and high-reinforcement of the metallic member can be achieved.

As an apparatus for forming metallic member, the followingapparatusmaybeemployed. Theapparatuscomprises

a forming die assembly for placing a cylindrical metallic member having a hollow space into a cavity of the forming die assembly;agassupplydevice for supplyinga pressurizing gas into the hollow space of said metallic member heated within the forming die assembly; and, a cooling device for cooling said forming die assembly configured to quenchhardeningsaidmetallicmemberplacedandplastically deformed in said forming die assembly.

The apparatus further comprises a control unit for controlling said gas supply device so as to perform bulging and/or deforming of said metallic member together with quench-hardening the same. As a gas supply means, a high pressure gas supply source (or line system) may be used, which comprises a bomb, valve, supply lines etc. [0035]

The apparatus may further comprise a heating device for selectively heating said metallic member placed in the cavityofsaidformingdicassembly. Inthiscase,induction heatingorresistanceheatingmaybeutilizedastheselective heating device for the metallic member.

t0036] [EXAMPLES]

(1st example)

Afirstexampleofthepresentinventionwillbeexplained below in reference to Figs 1 to 3. This example is an example

of applying a reinforcing by quench-hardening method, which is a typical quench-reinforcing method, to a metallic member 1. The metallic member 1 used in the forming method of this example has a cylindrical (tubular) form having a hollow space 10 and is made of an iron-based metal. The iron-based metal before hardening is in the condition of a high tension, i.e., has been changed into high tensile strength steel, and has a tensile strength of not less than 600MPa ( 60kgf/m2), so that plastic deformability is not necessarily sufficient.

According to this example, as shown in Fig. 1, Openings at either end of the metallic member are expanded or flared, so that a respective expanded part 12 is formed beforehand.

A tapered open wall face 13, which is an inner wall face of the expanded part 12, configures an opening 13x communicating with the hollow space 10.

At first, in a heating step, the metallic member 1 is maintained in a furnace chamber 20 of a furnace 2 for a predeterminedtimeandheateduptoa temperature range capable of quench-reinforcing, i.e., temperature range of not less than the Al transformation point. In this case, the metallic member may be heated up to a temperature range of not less than the AS transformation point if necessary. Thereby all or partial me/allographic structure of the metallic member

1 is changed into an austenite state. Because of maintaining the furnace chamber 20 of the furnace 2 in a non-oxidizing atmosphere, oxidation and decarburization of the metallic member 1 can be suppressed. As the nonoxidizing atmosphere, a vacuum atmosphere, a reducing atmosphere, an inert gas atmosphere of, e.g., argon gas, or the like may be employed depending on circumstances.

t0039] Then, the metallic member 1 heated up to a target temperature range as described above is taken out of the furnace chamber 20, and as shown in Fig. 2, is placed in a forming die 3. The forming die 3 is made of a steel-based material that is one of typical metallic materials, and has a forming face 31 designed so as to have a target shape.

In this case, it is preferable to initially place the metallic member 1 so as not to bring a reinforcement-requiring portion of a wall of the metallic member 1 in contact with the forming face 31 of the forming die 3. In the forming die 3, a cooling passage 33 through which a coolant such as cooling water, coolant gas or the like flows is formed as a cooling device.

When a coolant such as cooling water, coolant gas or the like flows through the cooling passage 33, the forming die 3 will be cooled and become capable of quenching a formed product of the metallic member 1 onthe forming face (cavity surface) 31 of the forming die 3. It is preferable to cool

the forming die 3 by flowing a coolant such es cooling wafer, coolant gas or the like through the cooling passage 33 of the forming die 3 before or during (or in the midway) of the aforementioned heating step.

In the forming and quench-reinforcing step of this example, as shown in Fig. 2, one set of two sealants 40, 41 each having a sealing face 44 with a taper angle slant corresponding to that of the tapered open wall face 13 of the expanded part 12 of the metallic member 1 are used. The sealants 40, 41 may tee mace of metal or a refectory materiel.

One sealant 40 has a passage 40a to be connected to a high-pressure gas supply source 5. The other sealant 41 has a sealing function but never connects with the high-pressure gas supply source 5. The high-pressure gas supply source 5 is used for feeding high-pressure gas and has a canister 50 having high-pressure gas enclosed therein,valve52 having an opening/shutting valve 51 for opening and shutting the canister 50, pressure indicator 53 functioning as pressure detection means for detecting pressure of gas enclosed in the bomb 50 and flexible feed pipe54 functioning es a feeding passage of gas discharged from the valve 52.

Then, asshowninFig.2, sealant40,41arerespectively fixed in openings 13 positioned at both ends of the metallic

member 1, and sealing is performed by applying the sealing face 44 to the tapered open wall face 13 of the expanded partl2Ofthemetallicmemberldirectlyorindirectlythrough a non-illustrated intermediate member. In this case, a void space W is intervenient between the wall la of the metallic member 1 and the forming face 31.

In the forming and quench-reinforcing step of this example, high-pressure gas (of, e.g., 20MPa) of the high-pressure gas supply source 5 is fed into the hollow space lOof the metallic memberlkeeping the state of sealing the sealants 40, 41 on the tapered open wall face 13 of the expended pert 12cfthemetallicmember las above described.

More specifically, the opening/shutting valve 51 of the high-pressure gas supply source 5 is opened to feed a high-pressure gas contained in the canister 50 of the high-pressure gas supply source 5 through the feed pipe 54 and the passage 40a formed through the one sealant 40 to the hollow space 10 of the metallic member 1.

Thereby, the internal pressure of the gas contained in the hollow space 10 of the metallic member 1 is increased to bulge and/or deform the wall la of the metallic member 1 outwardly in the radial direction. Consequently, the wall la is brought into intimate contact with the forming face

31 of the forming die 3. Thereby, the wall la is deformed along a profile of the forming face 31 as shown in Fig. 3.

In addition, the wall la is quenched by the forming face 31 of the forming die 3 concurrently with deformation, so that the wall la is hardened.

It is favorable to flow a coolant such as cooling water, coolant gas or the like through a cooling passage 33 formed through the forming die 3 and cool the forming die 3 directly before or during (or in the middle of) the forming and quench-reinforcing step of this example in order to enhance the hardening property.

As for the gas to be fed into the hollow space 10 of the metallic member 1, at least one of air, nitrogen gas, nitrogen-richgas,argon gas andargonrichgasmaybe employed depending on circumstances. Taking into consideration of cost reduction, airmaybe employed. Taking intoconsideration of suppressing oxidation, nitrogen gas, nitrogen-rich gas, argon gas or argon-rich gas, each of which has little or no oxidizing ability, may be employed. After finishing the deforming and the hardening of the metallic member 1 as above described, themetallicmemberlisseparatedfromthesealants 40, 41 and from the forming die 3.

As explained above, according to this example, the metallic member 1 is heated up to a high-temperature range in the course of the deformation/bulging. Accordingly, plasticdeformabilityofthemetallicmemberlcanbeimproved even in case of using the metallic member 1 composed of a high-tension metallic material and having low plastic deformability. As a result, plastic deformability, and accordingly, formability of the metallic member 1 can be enhanced. [0047]

Further, according to this example, the bulged and deformed wall la of the metallic member 1 is brought into intimate contact with the forming face 31 of the forming die3.Accordingly, takingheatawayfromandtherebyhardening the wall la of the metallic member 1 can be realized.

Consequently, the wall la of the metallic member 1 can be reinforced. Therefore, as described above, according to the method applied in this example, improvement in the deformability of the wall la of the metallic member 1 and highly strengthening the-same can be achieved at the same time. [0048]

According to this example in which the metallic member 1 can be reinforced in such a way as disclosed above, in spite of using the metallic memberl mace of iron-based metal

having a tensile strength before hardening of not less than 600MPa (60kgf/mm2), the iron-based metal constituting the metallicmemberlcanbe reinforced to have a tensile strength of not less than 1,OOOMPa (. lOOkgf/mm2) or of not less than 1,200MPa, or of not less than 1,500MPa as the case may be.

According to this example, as aforementioned, in the forming and quenchreinforcing step, the wall la of the metallic member 1 is hardened and reinforced by bringing the bulged and deformed wall la of the metallic member 1 into intimate contact with the forming face 31 of the forming die3.Accordingly,iftheheatingtemperatureofthemetallic member 1 and cooling ability of the forming face 31 of the forming die 3 are controlled properly, with regard to the thickness direction of the wall la of the metallic member 1, acoolingrateofonesurfacelayerlcfacingandinintimate contact with the forming face 31 of the forming die 3 (outer surface layer) can be made larger than that of the other surfacelayerldbackfacingtheformingface31Oftheforming die 3 (inner surface layer).

In other words, in terms of the thickness direction of the wall la of the metallic member 1, the cooling rate of the surface layer Id (inner surface layer) can be made smaller than that of the surface layer lo (outer surface

layer). Accordingly, in respect of the thickness direction of the wall la of the metallic member 1, a hardening property of the surface layer lc (outer surface layer) can be enhanced to strengthen highly this portion, and a hardening property of the surface layer Id (inner surface layer) also can be suppressed to ensure a toughness of this portion. Namely, in the thickness direction of the wall la of the metallic member 1, the degree of hardening and reinforcing can be changed, and an effect of enhancing both strength and impact resistance of the metallic member 1 also can be expected.

In addition, according to this example, sealing the opening 13x of the metallic member 1 is performed by using: the sealants 40, 41 each having the sealing face 44 with a taper angle corresponding to that of the tapered open wall face 13 of the expanded part 12 of the metallic member li and pressing the sealants 40, 41 to the tapered open wall face 13 of the expanded part 12 of the metallic member 1.

Accordingly, good sealing property of a boundary region between the metallic member 1 and the sealants 40, 41 can be ensured respectively. Consequently, changing the hollow space 10 of the metallic member 1 into a high-pressure state can be achieved effectively. Therefore, bulging and/or deforming ability of the wall la of the metallic member 1 can be enhanced.

According to this example, if the expanded part 12 positionedateitherendofthemetalliamemberlisunnecessary afterhardening, theexpandedpart12mayberemovedbyCutting. Or otherwise, if the expanded part 12 is necessary, it may be left as it is.

(2nd example)

A second example of the present invention will be explained below with reference to Figs 4 and 5. The constitution,workandeffectof this example are essentially the same as those of the first example. Explanation of this example will be made as follows focusing on difference from the first example. This example is an example of applying a reinforcing by hardening method, which is a typical quench-reinforcing method, to a metallic member 1 in the same way as disclosed in the first example. The metallic member used in a forming method of this example has a cylindrical form having a hollow space 10 and made of an iron-based metal capable of hardening. Theiron-based metal ismadetohaveahightension,i.e., changedintohightensile strength steel, for highly strengthening so that plastic deformability is not necessarily sufficient.

At first, in a heating step, the metallic member 1 is

placed in a forming die 3 so that a wall la of the metallic member 1 faces a forming face 31 of the forming die 3. In this case, it is preferable to place the metallic member 1 so that a reinforcement- requiring part of the wall la of the metallic member 1 does not come into contact with the forming face 31 of the forming die 3. Then, as shown in Fig. 4, an electrically conductive member 6 of a coil form for induction heating is placed in the hollow space 10 of the metallic member 1. Namely, the conductive member 6 for induction heating is mace to close with the metallic member 1 facing the forming face 31 of the forming die 3. In this heating step, it is preferable that the forming die 3 and the metallic member 1 are maintained in no contact state with each other in order to avoid raising a temperature of the forming die 3 and also lowering the temperature of the metallic member 1.

As described above, the metallic member 1 is induction-heated by applying a high-frequency alternating current to the conductive member 6 in a state of placing theconductivemember6forinductionheatingnearthemetallic member 1 in the hollow space 10 of the metallic member 1.

The alternating current for energizing the conductive member 6 should have frequency end current values which are capable of induction-heating a reinforcement-requiring part in the

wall la of the metallic member 1 up to a temperature range of not less than the Al or A3 transformation point. In the case of induction-heating the wall la of the metallic member 1 by applying a high-frequency alternating current to the conductive member6in this way, a surface layer of the wall la of the metallic member 1 can be heated efficiently since the proximity effect capable of heating efficiently the surface layer positioned near the electrically conductive memberinthemetallicmemberandalsotheskineffectresulting from an electric current flowing through the surface layer the metallic member can be expected. As a result of such aninductionheating, allorpartialmetallographicstructure of the metallic member 1 is changed into an austenite state in a short time.

According to this example, raising a temperature of the forming face 31 of the forming die 3 is suppressed in the heating step for induction- heating the metallic member 1, so that a heat insulating member 9 may be placed between the forming face 31 of the forming die 3 and the metallic memberl as showninFig.4if necessary. The heat insulating member 9 preferably has high thermal insulating property and also high magnetic flux-shielding property. It is favorable to flow a coolant such as cooling water, coolant gas or the like through a cooling passage 33 of the forming

die 3 and cool the forming die 3 thereby before or in the middle of the above described heating step.

Then, after completing the heating step, in the case of using the heat insulating member 9, the heat insulating member9is separated from the forming die 3.Aftercompleting the above-described heating step, a forming and quench-reinforcing step is performed. Namely, the forming face 31 of the forming die 3 is placed near the metallic member 1. In this case, as shown in Fig. 5, a void space Wis intervenient between the wall la of the metallic member 1 and the forming face 31. Further, in the same way of the first example, as shown in Fig. 5, using sealants 40, 41 each having a taper angle corresponding to that of a tapered openwallface13Ofthemetallicmemberl,sealingisperformed by applying the sealants 40, 41 to the tapered open wall face13Of the metallic member directly or indirectly through an intermediate member.

Keepingasealedstatebyapplyingthesealants(sealing members)40, 41tothetaperedopenwallfacel3Oftheexpanded part 12 of the metallic member 1 in a way as described above, highpressuregascontainedinacanister50Ofahigh-pressure gas supply 5 is fed through feed pipe 59 and passage 40a of the sealant 40 to the hollow space 10 of the metallic

memberlbyopeninganopening/shuttingvalve51.Asaresult, internal pressure of gas contained in the hollow space 10 of the metallic member 1 is increased, and consequently, thewalllaofthemetalliamemberlbecomesbulgedanddeformed in its radial direction to be in intimate contact with the forming face 31 of the forming die 3. Thereby the wall la of the metallic member 1 is deformed along the forming face 31 of the forming die 3 to complete a forming and quench-reinforcing step.

It is preferable to cool the forming die 3 by flowing a coolant such as cooling water, coolant gas or the like through the cooling passage 33 of the forming die 3 before or in the middle of the forming and quenchreinforcing step of this example in order to enhance a hardening property.

As explained above, according to this example, the metallic member 1 is made of iron-based metal that has not necessarily sufficient plastic deformability because of being changed into a high-tension state (or high tensile strength steel). However, the metallic member 1 is heated up to a high temperature range in the course of deformation by swelling, so that plastic deformability of the metallic memberlcanbeimproved, andthatthebulgingand/ordeforming ability and accordingly formability of the metallic member

1 can be enhanced.

Further, according to this example, the wall la of the metallic member 1 induction-heated up to not less than a hardening temperatureis bulged and/or deformed Lo be brought into contact with the forming face 31 of the forming die 3 in the forming and quench-reinforcing step. As a result, the wall la of the metallic member 1 can be hardened.

Accordingly, the metallic member 1 can be reinforced.

Consequently, in this example, in the same way of the first example, both formability of the wall la of the metallic member 1 and highly strengthening the same can be achieved at the same time.

Furthermore, induction-heating the metallic member 1 isperformedbyapplyingahigh-frequencyalternatinDcurrent to the conductivemember Gina stateofplacingthe conductive member for induction heating near the wall la of the metallic member 1 facing the forming face 31 of the forming die 3.

Accordingly, the wall la of the metallic member 1 can be bulged and/or deformed to be formed by opening an opening/shutting valve 51 of a valve control unit 52 immediately after heating the walllaof the metallic member 1 up to a target temperature range end feeding high-pressure gas contained in the canister 50 of the high-pressure gas

supply 5 into the hollow space 10 of the metallic member 1.Consequently, astepof taking the metallicmemberlheated up to the target temperature range out of a furnace 2 and then carrying it into the forming die 3 can be eliminated, and lowering a temperature of the metallic member can be suppressed. Therefore, immediatelybeforethestepofforming and hardening the metallic member 1, the temperature of the wall la of the metallic member 1 can be maintained as high aspossible, sothatbothformingandhardeningofthemetallic member 1 can be performed well. The valve control unit 52 controls the gas pressure end timing of opening/closing the valve 51. The valve controlunit52 operates in cooperation with or under control of a central control unit (not shown) for controlling the entire process of the forming method including closing/opening movement of the die assembly, energizing of heating means (i.e., supplying electric current), supplying cooling medium, placing/removing the metallic member, and inserting/retracting of an insulator, controlling the temperature of respective portions, etc. [0063]

In addition, according to this example, hardening-reinforcement bytheformingface31Of the forming die 3 can be performed at the time when the wall la of the metallic member 1 comes into contact with the forming face 31 of the forming die 3.

In this example, sealing is performed by applying the sealants 40, 41 to the tapered open (e.g., conical) wall face 13 of the metallic member 1 after executing the heating step of heating the metallic member 1. However, sealing is not restrictive to this way, and the sealants 40, 41 may be applied to the tapered open wall face 13 of the metallic memberlin the middle of or before the heating step of heating the metallic member 1.

(3rd example)

A third example of the present invention will be illustrated concretely as follows in reference to Figs 6 and 7. Essentially the same constitution, work and effect of the second example are employed in this example. This example will be explained below focusing on difference from the second example. In a heating step, a metallic member 1 is placed in the cavity of a forming die 3 so that a wall la of the metallicmemberlfacesa forming face of the forming die 3. In this case, it is favorable to place the metallic member 1 in such a way that a reinforcement-requiring part of the metallic member 1 does not come into contact with the forming face 13 of the forming die 3.

Then,themetalliamemberlisheatedupto a temperature

range of not less than the Al or AS transformation point byapplyingaresistance-heatingoperation.Namely,asshown inFig.6, energizing terminals d are connected Lo an expanded part 12 that is a peripheral portion of the metallic member 1 facing to the forming face 13 of the forming die 3, and keeping this state, the wall la of the metallic member 1 is heated up to a temperature range of not less than the Al or A3 transformation point by Joule heat by energizing the metallic member 1 from the energizing terminals Respective energizing terminal may be made of good electrically conductive metal such as cupper-based, aluminumbased, titanium-based or iron-based metal or the like.An electric current for energizing the metallicmember lfromtheenergizingterminals7maybedirectoralternating. [0067]

In the case of energizing the metallic member 1 by applying an alternating current through the energizing terminals 7, its frequency may be in a low, middle or high frequency region depending on circumstances. In the case of energizing the metallic member 1 by applying a high- frequency alternating current through the energizing terminals 7, a surface layer of the wall la of the metallic memberlcanbeheatedefficientlysinceaskineffectresulting from an electric current flowing through the surface layer of the metallic member can be expected.

Also in this example, sealants 40, 41 each having a taper angle corresponding to that of a tapered open wall face 13 of an expanded part 12 of the metallic member 1 are used in a forming and quench-reinforcing step as shown in Fig. 7. Then, sealing is performed by applying the sealants 40, 41 to the tapered open wall face 13 of the expanded part 12 of the metallic part directly or indirectly through an intermediate member. Keeping a state of sealing by applying the sealants 40, 41 to the tapered open wall face 13 of the metallic member 1 in this way, an opening/shutting valve 51 is opened Lo feed high-pressure gas containedina canister 50 of a high-pressure gas supply 5 through feed pipe 54 and passage 40a formed through the sealant40 into a hollow space 10 of the metallic member 1. Accordingly, internal pressure of gas containedin the hollow spacelOof the metallic member 1 is increased, and the wall la of the metallic member 1 is bulged and deformed racially tocomeintointimate contact with the forming face 31 of the forming die 3. Consequently, the wall la of the metallic member 1 is deformed along (and corresponding to an inner profile of) the forming die 31.

Loo6s] As explained above, according to this example, the metallic member 1 is heated up to a high-temperature range in the course of deformation by bulging in the same way of

the first and second examples, plastic deformability of the metallicmemberlcanbeimproved and also bulging/deforming abilityandformabilityofthemetallicmemberlcanbeenhanced even in the case where the metallic member 1 is made of iron-based metal changed into a high tension state.

Further, according to this example, the wall la of the metallic member 1 can be hardened and reinforced thereby by deforming/bulging the wall la of the metallic member 1 induction-heated up to a hardening temperature or more to come in intimate contact with the forming face 31 of the forming dies. Consequently,accordingtothisexample, both formability of the walllaof the metallicmemberl end highly strengthening the same can be achieved.

L0071]

Still further, according to this example, the metallic memberlisheatedbyenergizingfromtheenergizingterminals 7 in a state of connecting the terminals 7 to the metallic member 1 facing the forming face 31 of the forming die 3.

Accordingly, the wall la of the metallic member 1 can be bulged and deformed by feeding high-pressure gas into the hollow space 10 of the metallic member 1 immediately after heating the wall la of the metallic member 1. Consequently, a step of taking the metallic member 1 heated up to a target temperature range out of afurnace2 and carrying the metallic

member to the forming die 3 can be omitted, and lowering a temperature of the metallic member 1 can be suppressed.

Therefore, a temperature of the metallic member 1 can be maintained high in a state immediately before the steps of forming and hardening the metallic member 1. Thereby, both formingandhardeningofthemetallicmemberlcanbeperformed well while a temperature drop of the heated metallic member 1 is suppressed.

Further more, according to this example, in order to suppresstemperatureriseoftheformlngface310ftheforming die 3 in the heating step, a heat insulating member 9 may be placed between the forming face 31 of the forming die 3 and the metallic member 1 as shown in Fig.6 depending on need. A favorable heat insulating member 9 is ones having high thermal insulating and magnetic flux-shielding properties. [0073]

(4th example)

A fourth example of the present invention will be explained concretely below with reference to Figs 8 and 9.

Constitution, function and effect of this example are essentially the same with those of the second example. This example willbeillustratedae follows focusing on difference from the second example. Also in this example, a metallic

member 1 is preferably placed so as not to bring a reinforcementrequiring part of a metallic member 1 into contact with a forming facel30fa forming die Sin a heating step. In this case, a wall la of the metallic member 1 faces the forming face 31 of the forming die 3.

Also in this example, the metallic member 1 is heated up to a temperature range of not less than the Al or A3 transformation point by a resistanceheating operation.

Namely,asshowninFig.8,energizingterminals7areconnected to an expanded (e. g., tapered or conical) part 12 that is a peripheral portion of the metallic member 1 facing to the forming face 13 of the formingdie3, and keeping this state, the wall la of the metallic member 1 is heated by Joule heat by energizing the metallic member 1 from the energizing terminals 7. Further, an electrically conductive member 6 for induction heating is placed in a hollow space 10 of the metallic member 1 and then a high-frequency alternating current is applied to the conductive member 6. Thereby the wall la of the metallic member 1 is induction-heated.

In this way, resistance heating by energizing in use of the energizing terminals 7 and induction heating in use of the conductive member 6 for induction heating are applied in combination for heating the metallic member 1 according

to this example, so that the metallic member 1 can be heated efficiently. In particular, the conductive member 6 for induction heating is placed near a part requiring the highest deformation degree or a part most requiring reinforcement by hardening of the wall la of the metallic member 1, so that either part can be heated up to a high-temperature range efficiently, and that plastic deformability and hardening property of the part can be enhanced. As seen from Fig.9, the forming/quench- hardening step is carried out in the present example likewise in the second Example.

(Applied example) Fig. 10 shows an applied example 1 of the present invention. In this applied example 1, a metallic member 1B of a straightly tubular form is used. To the metallic member 1B having a straightly tubular form, heating step and forming and quench-reinforcing step are applied which are the same with those of any example described above. Fig. 11 shows an applied example 2 of the invention. In this applied example 2, a tubular metallic member 1C is used which results from forming a (crank-like) curved part Is beforehand e.g., by mechanical press working. Further, in this metallic, member lC, a groove Is is formed by stamping etc. Then, to the grooved metallic member 1C, heating step and forming and quench-reinforcing step are applied substantially according

toanyofexamplesdescribedabove.Inthepresent invention, a metallic member 1 may be applied to form a beam for use in a vehicle suspension mechanism, a suspension member, or a bumper-reinforce to be attached to a bumper. Otherwise, it may be applied also to a center pillar placed between frontandbackseatsofavehicle,oracenterpillar-reinforce to be attached to a center pillar for reinforcing the same.

It should be noted that the bulging/quench-hardening processing is best suited as a unified processing for the forming/reinforcement stage.

(Others) According to the above-described first example, an expanded part 12 is formed at both ends of a metallic member 1. However, sealants 40, 41 may be attached to the both ends of the metallic member 1 without forming the expanded part 12. Further, the expanded part 12 of the metallic member 1 does not need to be formed before heating and may be formed concurrently with sealing after heating. A sealing face 44 of the sealants 40, 41 has a taper angle of a conical face shape according to the above-described first example, but is not restrictive to this type, and may be cylindrical.

According to the first example, one sealant 40 has a passage 40a to be connected to a high-pressure gas supply

5, the other sealant 41 has a sealing function, and is not connected to the high-pressure gas supply 5. This is not restrictive, andapassagetobeconnectedtothehigh-pressure gas supply 5 may be formed also in the other sealant 40.

In this case, high-pressure gas is fed from the both ends of the metallic member 1.

Further,accordingtothelstexample,thehigh-pressure gas supply 5 has a canister 50 having high-pressure gas enclosed therein, valve control unit 52 having an opening/shutting valve 51 for opening and shutting the canister 50, pressure indicator 53 functioning as pressure detection means for detecting pressure of gas enclosed in the bomb 50 and flexible feedpipe54 functioning as a feeding passage of gas discharged from the valve control unit 52. However, this is not restrictive, end that of bulging and/or deforming the

metallic member 1 instantly by gas having a highpressurestatemaybeused.Basically,itisonlyrequired for the high-pressure gas supply source 5 have the ability of feeding gas into a hollow space 10 of the metallic member 1 and deforming/bulging the metallic member 1 thereby.

Still further, according to the first example, iron-based metal constituting the metallic member 1 before hardeningischangedintoa hightension state or high tensile

strength steel, and has a tensile strength of not less than 600MPa ( 60kgf/mm2), but this is not restrictive. A material constituting the metallic member 1 may be usual carbon steel or alloy steel, and basically has only to be able to be quenched and reinforced by a forming face 31 of a forming die 3.

[ 0 0 8 1]

Furthermore, according to the first example, a heating step for heating the metallicmember 1 is performed separately from a forming and quenchreinforcing step for bulging/deforming a wall la of the metallic member 1, but this is not restrictive. The metallic member 1 may be heated in the middle of the forming and quench-reinforcing step as the case may be. For instance, the metallic member may be heated at an early stage or a middle stage of bulging/deforming the wall la of the metallic member 1.

[ 0 0 8 2]

According to the third example shown in Fig. 6, energizing terminals 7 are connected to an end of the metallic member 1 respectively. Structure and material of the respective energizingmember 7 maybe selecteddepending on circumstances.

Basically, the energizing members 7 have only to be able to energize and thereby resistance-heat the metallic member 1. According to the third example, the respective energizing member 7 is connected to the end of the metallic member 1, but this is not restrictive, and the energizing member 1

r may be connected Lo a middle position of the metallic member [0083]

According to the above-described second and third examples, the forming die 3 and the metallic member 1 are in no contact with each other, but this is not restrictive.

The forming dies may be in partial contact with the metallic member 1 in the heating step for the purpose of holding the metallic member 1 and the like. Also in other aspects, the present invention is not limited to the above-described examples only, and modifications falling within the spirit and scope of the invention may be made depending on circumstances. [0084]

(Appendix) The following technicalideas can tee reed from the above description.

* (Appendant item 1) A metallic member forming method including the steps of: using cylindrical metallic member, having a hollow space and made of iron-based metal of a high-tensionstate, andformingdieassemblyhaving(acavity with) a forming face; and performing a forming and quench-reinforcing step of increasing internal pressure of gas contained in the hollow space of the metallic member heateduptoatemperaturerangecapableofquench-reinforcing

- to bulge and/or deform the metallic member' s wall, forming the bulged and/or deformed wall by bringing the same into intimate contact with the forming face and quench-reinforcing the wall. In this case, the metallic member made of iron-based metal of a high-tension state can be reinforced still more while its formability is ensured.

(Appendant item 2) Ametallic member forming method including the steps of: using cylindrical metallic member having a hollow space and forming die assembly having a (cavity with a) forming face; and performing heating step of heating the metallic member up to a temperature range capable of quench-reinforcing and forming and quench-reinforcing step of increasing internal pressure of gas contained in the hollow space of the heated metallic member to bulge and/or deform themetallicmember'swall, formingthebulgedand/ordeformed wall by bringing the same wall into intimate contact with the forming face of the forming die and quenchreinforcing the wall.

(Appendant item 3) A formingmethod of forming a center pillar reinforce including the steps of: using cylindrical metallic member, to be applied to a center pillar reinforce for reinforcing a center pillar of a vehicle, having a hollow space, and forming die assembly having a forming face; and performing a forming and quench-reinforcing step of increasing internal pressure of gas contained in the hollow

space of the metallic member heated up to a temperature range capable of quench-reinforcingtobulgeanddeformthemetallic member' s wall, forming the bulged and/or deformed wall by bringing the same wall into intimate contact with the forming face and quench-reinforcing the wall. In this case, high strengthening of the center pillar reinforce can be realized while formability of the same is ensured to enhance resistance to side-on collisions of a vehicle.

(Appendant item 4) Ametallic member forming method according to any appended claim or any preceding item, wherein heating the metallic member is performed under the condition that the metallic member is placed within the cavity the forming die. [0085]

The meritorious effects of the present invention are summarized as follows.

According to a metallic member forming method of the invention, a metallic member is heated up to a temperature range capable of quench- reinforcing. Then, in a forming and quench-reinforcing step, a wall of the metallic member is bulged and deformed by increasing internal pressure of gas contained in a hollow space of the metallic member, forming the bulged and/or deformed wall of the metallic member by bringing the same wall into intimate contact with a forming face of a forming die and c uench-reinforcing the wall. The

-' metallic member is in a heated state during the bulging/deformation, so that plastic deformability of the metallic member becomes improved and also bulging and deforming abilityand accordingly formabilityofthe metallic member becomes enhanced. Further, in the forming and quenchreinforcing step, the metallic member is quenched and reinforced by bringing the bulged and/or deformed wall of the metallic member into intimate contact with the forming face of the forming die. Accordingly, both formability of the metallic member and high strengthening of the same can be achieved at the same time.

According to the metallic member forming method of the invention, if heating temperature of the metallic member in a heating step, thickness of the metallic member, cooling ability of the forming face of the forming die are controlled properly, with regard to the thickness direction of the wall of the metallic member 1, a cooling rate of one surface layer facing and in intimate contact with the forming face of the forming die can be made larger than that of the other surface layer disposed opposite to the forming face of the forming die. Accordingly, in respect of the thickness direction of the wall of themetallicmember, entrancing a hardening property of one surface layer facing and in intimate contact with the forming face of the forming die to highly strengthen

this portion,a hardening properly of the other surfacelayer disposed opposite to the forming face of the forming die also can be suppressed Lo ensure toughness of this portion.

According to the metallic member-forming method, the resultant metallic member product and the metallic member-formingapparatus, theheattreatmentofthemetallic member(i.e.,thecooling(quenching) orheatingandcooling) can be carried out under the state of holding the metallic member within the die (assembly). For instance, surface hardening of the metallic member may be achieved by quench-hardening caused by the cooled die. Accordingly, a metallicmemberforwhichtheformingprocessingisdifficult, can be efficiently formed by means of formation using the pressurized gasmedium, simultaneously achieving efficient reinforcement of the same due to quench-hardening occurring within the die cavity caused by cooled die.

It should be noted that other objects, features and aspects of the present invention will become apparent in the entire disclosure and that modifications may be done

without departing the gist end scope of the presentinvention as disclosed herein and claimed as appended herewith.

Also it should be noted that any combination of the disclosed and/or claimed elements, matters and/or items may

fall under the modifications aforementioned.

Claims

CLAIMS:

1. A method for forming a metallic member comprising the steps of: providing a metallic member having a hollow space and a forming die having a forming faces and performing a forming and quench-reinforcing step by increasing aninternalpressureof gas containedinthC hollow space of the metallicmember treated up to a temperature range capable of quenchreinforcing to bulge and/or deform the well of the metallic member, wherein forming of the bulged and/or deformed wall is performed by bringing the well of the metallic member into intimate contact with the forming face of the forming die accompanied by simultaneous quenchreinforcing of the wall.

2. A method according to claim 1, wherein the step of increasing the internal pressure of gas contained in the hollow space of the metallic member is performed by feeding a gas into the hollow space of the metallic member.

3. A method according to claim 1 or 2, wherein the step of heating the metallic member is performed by maintaining themetalliamemberina furnace chamber ofaheating furnace, carrying out an induction heating operation for induction-heating the metallic member, and/or carrying out a resistance heating operation for energizing the metallic member.

4. A method according to claim 3, wherein the operation for maintaining the metallic member in the furnace chamber of the furnaceis performed under a condition that the furnace chamber has a non-oxidizing atmosphere.

5. A method according to claim 3 or claim 4, wherein the induction heating operation is performed by applying an alternating current to an electrically conductive member for induction heatingin a state of placing the electrically conductive member in proximity of the metallic member disposedwithintheformingdietoinduction-heatthemetallic member.

6. A method according to any of claims 3 to 5, wherein the resistance heating operation is performed by energizing the metallic member from energizing terminals in a state of connecting the energizing terminals to the metallic member disposed within the forming die to heat the metallic member by Joule heat.

7. A method according to any preceding claim wherein the metallic member is made of an iron-based material, a titanium-based material, an aluminumbased material or a cupper-based material.

8. A method according to any preceding claim wherein the metallic member is made of an iron-based material and is heated up to a temperature of not less than the Al transformationpoint,andtheformingandquench- reinforcing

step further comprises bringing the wall of the metallic member into intimate contact with the forming face of the forming die to harden atleasta pert of the metallic member.

9. A method according to any preceding claim wherein the forming die has a cooling device for cooling the forming die at least a part thereof corresponding to a part of the metallic member to be quench-hardened.

10. A method according to any preceding claim wherein the gas to befedinto the hollow space of the metallic member is at least one selected from the group consisting of air, nitrogen gas, nitrogen-rich gas, argon gas and argon-rich gas.

11. A method according to any of claims 2 to 10, wherein an operation for feeding gas into the hollow space of the metallic memberis performed from a high-pressure gas supply source capable of feeding high pressure gas.

12. A method according to any preceding claim, wherein the metallic member has at least one opening communicating with the hollow space end formed by a tapered open wall face, and wherein the opening is sealed by applying directly or indirectly a sealant, which has a taper angle corresponding to that of the tapered open wallface of the metallic member, to the tapered open wall face of the metallic member.

13. A method for forming 9metallic member comprising the steps of:

(a) placing a metallic member having a hollow space in a forming die assembly, (b) heating the metallic member placed in the forming die assembly, (c) bringing a prescribed surface of the metallic member into intimate contact with a prescribed face of the forming die assembly by introducing a pressured gas into the hollow space ofthemetallicmemberheatedinthe formingdie assembly, to thereby plastically deform the metallic member, and, (d) quenching the metallic member immediately following the deformation of the metallic member by cooling the metallic member in a state of being placed in the forming die assembly.

14. A method according to claim 13, wherein the heating of step(b) is performed within en opened space of the forming die assembly.

15. A method according to claim 13 or claim 14, wherein the heatingstep(b) isperformedunderathermallyinsulated condition.

16. A method according to claim 15, wherein said thermally insulated condition is provided by a thermal insulator positioned betweenthedieformingassembly end the metallic member,theinsulatorbeingremovedbeforeclosingtheforming die assembly.

17. A method according to any claims 13-16, wherein the

heating step(b) is carried out by induction heating by an induction conductor disposed within the hollow space of the metallic member.

18. A method for forming a metallic member comprising the steps of: (a) heating a metallic member having a hollow space, (b) placing the heated metallic member into a forming die assembly, (c) bringing a prescribed surface of the treated metallic member into intimate contact with a prescribed face of the forming die assembly by introducing a pressurized gas into the hollow space of the metallic member, to thereby plastically deform the metallic member, and (d) quenching the metallic member immediately following thedeformationof the metalllamember by cooling the forming die assembly, in a state that the metallic member is placed in the forming die assembly.

19. A metallic member product produced according to the method as defined in any preceding claim.

20. An apparatus for formingametallicmembercomprising: a forming die assembly having a cavity for receiving a metallic member having a hollow space a gas supply device for supplying a pressurized gas into the hollow space of the metallic member a cooling device for cooling the forming die assembly

configured to quench-harden ng the metallic member placed and plastically deformed in the forming die assembly,and a control unit for controlling the gas supply device so as to perform bulging and/or deforming of the metallic member together with quench-hardening the metallic member.

21. An apparatus according to claim 20, comprising a heating device for selectively heating the metallic member placed in the cavity of the forming die assembly.

22.Anapparatusaccordingtoclaim21, further comprising a retractable thermal insulator for insulating the metallic member to be heated from the die assembly, these insulator being retracted after heating.