Method of and apparatus for manufacturing joined body

Abstract

Electrodes are embedded respectively in a first die and a second die. A metal workpiece is placed in a cavity defined between the first die and the second die which mate with each other. Then, a molten metal is poured through a passage into the cavity. The molten metal is solidified into a casting, forming a contact region of the metal workpiece and the casting. Thereafter, an electric current is supplied from a power supply between the electrodes across the contact region. The supplied electric current breaks an oxide film that is present on the surface of the metal workpiece, and joins the metal workpiece and the casting in the contact region.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of and an apparatus for manufacturing a joined body which comprises a metal workpiece and a casting that are joined to each other.

[0003] 2. Description of the Related Art

[0004] Pressing is advantageous in that the time required to process workpieces is short, but it is not easy to press workpieces into complex shapes. For pressing a workpiece into a complex shape, it has been customary to press individual workpieces into members of a final product and then join the pressed members by welding or the like.

[0005] The conventional process, however, is disadvantageous in that it requires separate dies having different shapes for pressing individual workpiece, and hence large investments for pressing facilities. Furthermore, since a separate joining process such as a welding process is needed, it takes a long period of time until the final product is obtained, and it is not easy to increase the efficiency with which the final products are manufactured.

[0006] Products may be manufactured by a casting process which employs a reduced number of dies or molds and which does not require a welding process. However, it is relatively time-consuming to cast a product by pouring and then solidifying a molten metal. The casting process must wait until the cast product is sufficiently cooled before it can be removed from the die. It is thus not easy to manufacture products efficiently according to the casting process.

[0007] The above shortcomings may be eliminated by casting a product around a pressed workpiece as disclosed in Japanese Laid-Open Patent Publication No. 57-146464, for example. Specifically, the pressed workpiece is placed as a core in a cavity of a casting die, and then a molten metal is poured into the cavity.

[0008] The poured molten metal flows around the workpiece and adheres to the workpiece, and then the molten metal is solidified by being cooled. When the molten metal that has adhered to the workpiece is solidified, the workpiece and the cast product are joined to each other.

[0009] The casting process makes it possible to manufacture complexly shaped products. The casting process as described above dispenses with a joining process.

[0010] Japanese Laid-Open Patent Publication No. 57-146464 discloses a process of applying an electric current to the workpiece in advance to promote fused joining between the workpiece and the cast product. According to the disclosed process, however, it is difficult to join a workpiece with an oxide film (passive film) on its surface, such as an aluminum workpiece or the like, to the cast product by way of fused joining. The reasons are that since both of energizing electrodes are held in contact with only the workpiece, the current flows only through the workpiece, as shown in FIGS. 1 and 2 of Japanese Laid-Open Patent Publication No. 57-146464. Specifically, because the oxide film is an insulation, the current finds it extremely difficult to flow transversely across the oxide film into the molten metal or the cast product, and hence fails to accelerate fused joining.

[0011] Even if the workpiece is preliminarily energized with a current before the molten metal is cast around the workpiece with the oxide film being present on the surface, it is difficult to join the workpiece and the cast product to each other by way of fused joining.

SUMMARY OF THE INVENTION

[0012] It is a general object of the present invention to provide a method of manufacturing a joined body which comprises a metal workpiece and a casting, by allowing the metal workpiece to be easily joined to the casting regardless of the material of the metal workpiece.

[0013] A principal object of the present invention is to provide a method of manufacturing a joined body which comprises a metal workpiece and a casting, by allowing the metal workpiece to be highly easily joined to the casting even if an oxide film is present on the surface of the metal workpiece.

[0014] Another object of the present invention is to provide a joined body manufacturing apparatus for joining a metal workpiece and a casting to each other.

[0015] According to an aspect of the present invention, there is provided a method of manufacturing a joined body having a first member and a second member which are joined to each other, comprising the steps of placing the first member in a cavity defined between dies, pouring a molten metal into the cavity for forming the second member, and supplying an electric current between the first member and the second member. In this case, an electric current is preferably supplied between the first and second members in the dies.

[0016] According to another aspect of the present invention, there is provided a method of manufacturing a joined body having a metal workpiece and a casting which are joined to each other, comprising the steps of placing the metal workpiece in a cavity defined between a first die and a second die with electrodes disposed on respective molding surfaces thereof, pouring a molten metal into the cavity to form a contact region of the molten metal and the metal workpiece or a contact region of a casting produced when the molten metal is solidified and the metal workpiece, between the electrode on the first die and the electrode on the second die, and supplying an electric current between the electrodes to join the contact region to produce a joined body.

[0017] According to the present invention, an electric current flows between the molten metal or the casting and the metal workpiece to join them. When an oxide film is present on the surface of the metal workpiece, as the electrodes are disposed across the metal workpiece in the thickness direction such that the electric current flows between the electrodes transversely across the metal workpiece, the oxide film that is broken.

[0018] The metal workpiece with the oxide film being broken thereon can easily be joined to the molten metal or the casting. Therefore, the joined body can easily be produced.

[0019] The temperature of the metal workpiece rises due to the heat of the molten metal. The metal workpiece is efficiently heated, and hence the value of the electric current that is required to break the oxide film may be small. Therefore, the method is highly advantageous in terms of cost.

[0020] According to the present invention, the dies for pressing the metal workpiece may be the same as the dies for casting the pressed workpiece. Specifically, after the metal workpiece is pressed by the first die and the second die, the molten metal may be poured into the cavity that is defined between the first die and the second die. Therefore, the period of time required until the joined body is produced is shortened, and the number of dies to be prepared in advance is small. Consequently, the joined body can be manufactured efficiently, and the investments for pressing facilities are small.

[0021] The electrodes should preferably be made of a material having a resistivity value higher than those of the metal workpiece and the casting and a melting point higher than the boiling point of the metal workpiece and the casting. Thus the contact region is heated efficiently. In addition, the electrodes and the metal workpiece or the casting are prevented from being alloyed due to solid diffusion therebetween.

[0022] According to a further aspect of the present invention, there is also provided an apparatus for manufacturing a joined body having a first member and a second member which are joined to each other, comprising dies having a housing section for housing the first member and a molding section for forming the second member, and a power supply electrically connected to the dies.

[0023] In this case, it is preferable to electrically connect the dies to the power supply so as to make an electric current flow through the housing section and the molding section for easy joint of the first and second members.

[0024] According to a still further aspect of the present invention, there is also provided an apparatus for manufacturing a joined body having a metal workpiece and a casting which are joined to each other, comprising a first die and a second die with electrodes disposed on respective molding surfaces thereof, a power supply electrically connected to the electrode on the first die and the electrode on the second die, and a passage for introducing a molten metal into a cavity defined between the first die and the second die.

[0025] In the apparatus, an electric current flows between the molding surfaces of the dies for casting the molten metal. As a result, an electric current flows through a contacting region where the molten metal or a casting produced when the molten metal is solidified or semi-solidified and the metal workpiece contacts each other so as to form a joined body. That is, an electric current flows through a contacting region between the molten metal and the metal workpiece, or between the casting and the metal workpiece.

[0026] According to the present invention, the electric current flows through the metal workpiece and the molten metal or the casting, thereby easily joining the contact region.

[0027] The first and second dies of the apparatus may double as dies for pressing the metal workpiece, as mentioned above. Specifically, the first and second dies are brought together to press the metal workpiece, and the electric current is supplied to flow through the deformed metal workpiece and the molten metal or the casting.

[0028] For the reasons described above, the electrodes should preferably be made of a material having a resistivity value higher than those of the metal workpiece and the casting and a melting point higher than the boiling point of the metal workpiece and the casting.

[0029] The casting herein includes a semi-solidified molten metal.

[0030] The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is a cross-sectional view of main part of a joined body manufacturing apparatus according to an embodiment of the present invention;

[0032] FIG. 2 is an enlarged fragmentary cross-sectional view of a joined region of a joined body manufactured by the joined body manufacturing apparatus; and

[0033] FIG. 3 is a schematic perspective view of a joined body manufacturing apparatus according to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] A method of manufacturing a joined body according to preferred embodiments of the present invention and apparatus for carrying out the method will be described in detail below with reference to the accompanying drawings.

[0035] FIG. 1 shows in cross section a joined body manufacturing apparatus 10 according to an embodiment of the present invention. As shown in FIG. 1, the joined body manufacturing apparatus 10 has a first machining center 12 and a second machining center 14 which can movable toward and away from each other, and a first die 16 and a second die 18 which are mounted respectively on the first machining center 12 and the second machining center 14. The first die 16 and the second die 18 are disposed in confronting relation to each other, and jointly define a cavity 19 therebetween when they are combined with each other.

[0036] An electrode 20a is embedded in the first die 16 so as to lie flush with a molding surface which faces the cavity 19. The electrode 20a is made of a material having a resistivity value higher than those of a metal workpiece MW and a molten metal, to be described later, and a boiling point higher than the melting points of the metal workpiece MW and the molten metal. For example, if the metal workpiece MW is made of aluminum, aluminum alloy, magnesium, magnesium alloy, cast iron, stainless steel, or the like, and the molten metal is aluminum, cast iron, or the like, then the electrode 20a is made of tungsten, molybdenum, niobium, or an alloy of two or more of these materials.

[0037] The first die 16 has an insertion hole 22a of a substantial inverted L shape including a vertical extension and a horizontal extension. An energizing post 24a is inserted in the vertical extension of the insertion hole 22a, and an electrode support 26a with the electrode 20a embedded therein is inserted in the horizontal extension of the insertion hole 22a. The energizing post 24a and the electrode support 26a are made of copper. The energizing post 24a has a side surface held in abutment against the bottom surface of the electrode support 26a.

[0038] A coolant passage 28a is continuously defined in the energizing post 24a and the electrode support 26a, and has an end portion disposed near the electrode 20a. A coolant supply tube 30a and a coolant discharge tube 32a are connected respectively to ends of the coolant passage 28a in the energizing post 24a. A coolant supplied from the coolant supply tube 30a into the coolant passage 28a flows through the energizing post 24a into the electrode support 26a, and then flows back through the energizing post 24a, after which the coolant is discharged from the coolant discharge tube 32a.

[0039] An insulation 33a is interposed between the first die 16 and the energizing post 24a, the electrode support 26a.

[0040] The second die 18 is essentially identical in structure to the first die 16. Components of the second die 18 which are identical to those of the first die 16 are denoted by identical reference numerals with a suffix "b" rather than "a", and will not be described in detail below. The second die 18 additionally has a passageway 34 defined therein for introducing the molten metal into the cavity 19.

[0041] A power supply 38 is electrically connected to the energizing posts 24a, 24b by respective leads 36a, 36b. An electric current supplied from the power supply 38 flows through the energizing post 24a, the electrode support 26a, the electrode 20a, the metal workpiece MW, a casting CM, the electrode 20b, the electrode support 26b, and the energizing post 24b.

[0042] The joined body manufacturing apparatus 10 according to the present embodiment is basically constructed as described above. Operation and advantages of the joined body manufacturing apparatus 10 will be described below.

[0043] First, the molding surfaces of the first die 16 and the second die 18 except where the electrodes 20a, 20b are exposed are coated with a release agent. Then, the metal workpiece MW is held against the molding surface of the first die 16. At this time, the electrode 20a is held in contact with an end face of the metal workpiece MW.

[0044] As described above, the metal workpiece MW is made of a material having a resistivity value lower than those of the electrodes 20a, 20b and a melting point lower than the boiling point of the electrodes 20a, 20b. If the electrodes 20a, 20b are made of tungsten, molybdenum, niobium, or an alloy of two or more of these materials, then the metal workpiece MW may be made of aluminum, aluminum alloy, magnesium, magnesium alloy, cast iron, stainless steel, or the like. When the metal workpiece MW of such a material is in contact with oxygen in the atmosphere, an oxide film is formed spontaneously on the metal workpiece MW. In the present embodiment, the metal workpiece MW is in the form of a plate.

[0045] Then, the first die 16 and the second die 18 are brought toward each other until they mate with each other by operating the first machining center 12 and the second machining center 14. The cavity 19 is now formed between the first die 16 and the second die 18. Even after the cavity 19 is formed, a predetermined pressure remains applied to the first die 16 and the second die 18.

[0046] When the first die 16 and the second die 18 are combined with each other, the electrodes 20a, 20b are positioned across the oxide film from each other.

[0047] Then, a molten metal is poured into the cavity 19 through the passageway 34. The molten metal is also made of a material having a resistivity value lower than those of the electrodes 20a, 20b and a melting point lower than the boiling point of the electrodes 20a, 20b. Preferably, the molten metal should be made of aluminum, aluminum alloy, or cast iron.

[0048] Part of the poured molten metal is brought into contact with the metal workpiece MW in the cavity 19. Then, the molten metal is cooled and solidified, producing a casting CM that is complementary in shape to the cavity 19. A laminated region L where the metal workpiece MW and the casting CM are partly superposed on each other is formed in the area where the molten metal contacted the metal workpiece MW.

[0049] Thereafter, while the predetermined pressure is being continuously applied to the first die 16 and the second die 18 and the casting CM remains heated at a high temperature, an electric current is supplied from the power supply 38. The current flows through the lead 36a, the energizing post 24a and the electrode support 26a into the electrode 20a.

[0050] The oxide film is present on the surface of the metal workpiece MW. Therefore, the power supply 38 supplies an electric current having a value large enough to break the oxide film on the metal workpiece MW in the laminated region L.

[0051] According to the present embodiment, as described above, the current is supplied while the predetermined pressure is being continuously applied to the first die 16 and the second die 18. Therefore, the electrode 20a is pressed against the metal workpiece MW and the electrode 20b is pressed against the casting CM, allowing the current to flow easily therethrough. Consequently, the value of the current may be lowered.

[0052] Since the casting CM remains heated at a high temperature, the heat of the casing CM is transferred to the metal workpiece MW. Therefore, the oxide film on the metal workpiece MW can easily be broken even if the current flowing therethrough is of a low value.

[0053] Because the electrodes 20a, 20b are made of a material having a relatively high resistivity value, heat tends to be generated not only in an area where the metal workpiece MW and the casting CM are held against each other, but also in an area where the electrode 20a and the metal workpiece MW are held against each other and an area where the casting CM and the electrode 20b are held against each other. Accordingly, the laminated region L is efficiently heated, thereby making it easy for the oxide film on the metal workpiece MW to be broken.

[0054] Inasmuch as the metal workpiece MW is efficiently heated, the value of the current supplied to break the oxide film can be lowered.

[0055] The value of the current may be about 10000 A. This current value is much lower than a current ranging from 20000 to 40000 A which is required to break an oxide film when an aluminum alloy is welded.

[0056] According to the present embodiment, therefore, the value of the current supplied to break the oxide film for welding purposes can greatly be lowered. Therefore, the joined body manufacturing apparatus 10 is highly advantageous in terms of cost.

[0057] When the current flows from the metal workpiece MW to the casting CM, the oxide film that is present on the surface of the metal workpiece MW is finally broken. In other words, no oxide film is interposed between the base material of the metal workpiece MW and the casting CM. As the oxide film is broken, the exposed base material of the metal workpiece MW is held in contact with the casting CM so that the metal workpiece MW and the casting CM will firmly be joined to each other. The current flows from the electrode 20b through the electrode support 26b, the energizing post 24b, and the lead 36b back to the power supply 38.

[0058] Since the molding surfaces of the first die 16 and the second die 18 are coated with the insulative release agent, the current is not diffused in the molding surfaces. Furthermore, the current is not diffused in the first die 16 or the second die 18 because the insulations 33a, 33b are interposed between the energizing posts 24a, 24b and the first and second dies 16, 18, and the electrode supports 26a, 26b and the first and second dies 16, 18.

[0059] Inasmuch as the electrodes 20a, 20b are made of a material having a melting point higher than the boiling points of the molten metal, the electrode 20a and the metal workpiece MW or the casting CM and the electrode 20b are prevented from being alloyed due to solid diffusion therebetween while the current is flowing therethrough.

[0060] When the current flows as described above, the metal workpiece MW and the casting CM are joined to each other in the laminated region L, producing a joined body. While the current is flowing, the coolant such as cooling water or the like flows through the coolant passages 28a, 28b to prevent the energizing posts 24a, 24b of copper and the electrode supports 26a, 26b of copper from excessively rising temperature.

[0061] FIG. 2 shows the joined region of the joined body. In FIG. 2, current has flowed through the region that is shown cross-hatched, between the electrodes 20a, 20b.

[0062] The laminated region L that is sandwiched between the electrodes 20a, 20b is a region where the metal workpiece MW and the casting CM are integrally joined to each other with no interface therebetween. This indicates that the oxide film is removed from the metal workpiece MW by the current flowing therethrough and the metal workpiece MW is firmly joined to the casting CM.

[0063] In the above embodiment, the current starts being supplied after the molten metal is solidified into the casting CM. However, the current may start being supplied before the molten metal is solidified after it has ended being poured.

[0064] In the present embodiment, the casting CM is joined to the plate-like metal workpiece MW which has not been plastically deformed. However, the metal workpiece MW may be plastically deformed by being pressed, and then the deformed metal workpiece MW and the casting CM may be joined to each other. Such a modification will be described below as another embodiment with reference to FIG. 3.

[0065] FIG. 3 shows in perspective a joined body manufacturing apparatus 50 according to another embodiment of the present invention. As shown in FIG. 3, the joined body manufacturing apparatus 50 comprises a base 52 with passages 51 defined therein, first and second dies 54, 56 that are movable toward and away from each other by machining centers, not shown, a rear die 58 disposed behind the first and second dies 54, 56 away from the viewer of FIG. 3, and a front die, not shown, positioned in front of the first and second dies 54, 56. The first and second dies 54, 56 are sandwiched between the rear die 58 and the front die, jointly defining a cavity 60 therebetween.

[0066] Electrodes 62a, 62b are mounted on the molding surfaces of the first and second dies 54, 56. The electrodes 62a, 62b are made of tungsten, molybdenum, niobium, or an alloy of two or more of these materials. The electrodes 62a, 62b are electrically connected to a power supply 66 via respective leads 64a, 64b.

[0067] An insulation, not shown, is interposed between the electrodes 62a, 62b and the first and second dies 54, 56 for preventing an electric current from flowing from the electrodes 62a, 62b to the first and second dies 54, 56.

[0068] The joined body manufacturing apparatus 50 operates as follows: A metal workpiece MW in the form of a plate made of aluminum or aluminum alloy is supported on the first die 54. The machining centers are operated to bring the first and second dies 54, 56 toward each other until they mate with each other. The plate-like metal workpiece MW is now pressed into a bent body having two bent portions.

[0069] Then, a molten metal such as aluminum, aluminum alloy, or the like is poured through the passages 51 into the cavity 60. The molten metal is poured until the level of the introduced molten metal touches an end of the deformed metal workpiece MW.

[0070] Thereafter, the molten metal is cooled and solidified, producing a casting CM that is complementary in shape to the cavity 60. A laminated region L where the metal workpiece MW and the casting CM are partly superposed on each other is formed in the area where the molten metal contacted the metal workpiece MW.

[0071] Subsequently, an electric current is supplied from the power supply 66 to break the oxide film on the metal workpiece MW and join the metal workpiece MW and the casting CM in the laminated region L. Therefore, the joined region of the joined body as shown in FIG. 2 is produced. The value of the supplied current may be about 10000 A. The electrodes 62a, 62b and the laminated region L are prevented from being alloyed.

[0072] According to the present embodiment, the dies for pressing the metal workpiece MW double as the dies for casting the casting CM since the number of dies to be prepared in advance is small, the investments for pressing facilities of the joined body manufacturing apparatus 50 are small. Furthermore, since the period of time required until the joined body is produced is shortened, the joined body can be manufactured efficiently.

[0073] In the present embodiment, the electrodes 62a, 62b may be embedded in the first and second dies 54, 56, and may be electrically connected to the power supply 66 by conductors, not shown, and the leads 64a, 64b, as with the first embodiment. An insulation may be interposed between the electrodes 62a, 62b and the conductors, and the first and second dies 54, 56.

[0074] In the present embodiment, the current may start being supplied before the molten metal is solidified.

[0075] The principles of the present invention are applicable to not only joining the metal workpiece MW with the oxide film being present thereon, but also joining metal workpieces of various materials.

[0076] When a joined body is manufactured, the first and second dies 16, 18, 54, 56 may be electrically connected to the external power supply to flow current to the first and second dies 16, 18, 54, 56 without the electrodes 20a, 20b, 62a, 62b embedded in the first and second dies 16, 18, 54, 56.

[0077] Although certain preferred embodiments of the present invention have been described above, it should be understood that various changes and modifications may be made therein without departing the scope of the attached claims.

Claims

1. A method of manufacturing a joined body having a metal workpiece and a casting which are joined to each other, comprising the steps of: placing the metal workpiece in a cavity defined between a first die and a second die with electrodes disposed on respective molding surfaces thereof; pouring a molten metal into said cavity to form a contact region of said molten metal and said metal workpiece or a contact region of a casting produced when the molten metal is solidified or semi-solidified and said metal workpiece, between the electrode on said first die and the electrode on said second die; and supplying an electric current between said electrodes to join said contact region to produce a joined body.

2. A method according to claim 1, further comprising the step of before said molten metal is poured into said cavity, pressing said metal workpiece between said first die and said second die.

3. A method according to claim 1, wherein said electrodes are made of a material having a resistivity value higher than those of said metal workpiece and said casting and a melting point higher than the boiling point of said metal workpiece and the boiling point of said casting.

4. A method according to claim 1, wherein said metal workpiece has an oxide film on a surface thereof.

5. A method according to claim 4, wherein the electric current is supplied to said electrodes for flowing the electric current transversely across said oxide film.

6. An apparatus for manufacturing a joined body having a metal workpiece and a casting which are joined to each other, comprising: a first die and a second die with electrodes disposed on respective molding surfaces thereof; a power supply electrically connected to the electrode on said first die and the electrode on said second die; and a passage for introducing a molten metal into a cavity defined between said first die and said second die.

7. An apparatus according to claim 6, wherein said first die and said second die double as dies for pressing said metal workpiece.

8. An apparatus according to claim 6, wherein said electrodes are made of a material having a resistivity value higher than those of said metal workpiece and said casting and a melting point higher than the boiling point of said metal workpiece and the boiling point of said casting.

9. An apparatus according to claim 6, wherein said metal workpiece has an oxide film on a surface thereof.

10. An apparatus according to claim 9, wherein said electrodes are disposed in respective positions for supplying an electric current transversely across said oxide film.

11. A method of manufacturing a joined body having a first member and a second member which are joined to each other, comprising the steps of: placing the first member in a cavity defined between dies; pouring a molten metal into the cavity for forming the second member; and supplying an electric current between the first member and the second member.

12. A method according to claim 11, wherein an electric current is supplied between the first and second members in the dies.

13. An apparatus for manufacturing a joined body having a first member and a second member which are joined to each other, comprising: dies having a housing section for housing the first member and a molding section for forming the second member; and a power supply electrically connected to the dies.

14. An apparatus according to claim 13, wherein the power supply is electrically connected such that an electric current flows through the housing section and the molding section.