US20170361374A1

US20170361374A1 - Press forming method for a semi-solid metal material and press forming apparatus for a semi-solid metal material

Info

Publication number: US20170361374A1
Application number: US15/697,256
Authority: US
Inventors: Yuji Abe; Seiji Nakamura; Setsuo Toda
Original assignee: Aida Engineering Ltd
Current assignee: Aida Engineering Ltd
Priority date: 2014-05-27
Filing date: 2017-09-06
Publication date: 2017-12-21
Also published as: JP5936648B2; JP2015223603A; US20150343527A1

Abstract

Provided is a press forming method for a semi-solid material, including: a semi-solid material carrying step of carrying a semi-solid material into a lower die; a first press forming step of regulating, under a Z-direction regulation state in which a change in the Z direction's dimension corresponding to a pressing direction is regulated by an upper die, a change in one of the dimensions in X and Y directions by compressing the material with a transverse punch so that the one becomes equal to a dimension of the product, and then stopping the punch at a position of the compression; and a second press forming step of moving, under a state in which the change in the one is regulated in the above step, the upper die in the pressing direction to compress the material so that the Z direction's dimension becomes equal to the product's dimension.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser. No. 14/721,733, filed May 26, 2015, which claims priority from Japanese Patent Application No. 2014-109401, filed May 27, 2014. the contents of which are hereby incorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a press forming method for a semi-solid metal material and a press forming apparatus for a semi-solid metal material, which are configured to form mainly light metal, such as an aluminum alloy, and other kinds of metal under a semi-solid state.

BACKGROUND

Hitherto, as a technology of forming an aluminum alloy and the like, there has been used a casting method such as a die casting method, which involves injecting molten metal into a die under pressure so as to obtain a product having a predetermined shape. When the molten metal is used, there arise problems such as short lifetime of the die, and unsatisfactory quality of a product caused by generation of a shrinkage cavity or the like.
Accordingly, in recent years, as the die casting method, there has been used a casting method to be performed under high pressure using, as a metal material to be injected into the die instead of the molten metal, metal (semi-solid metal or semi-molten metal) assuming a semi-molten state in which a solid phase component and a liquid phase component coexist.
This method is distinguished from general die casting methods, and called a rheocasting method or a thixocasting method.
The rheocasting method is conducted in the following manner. Specifically, solidifying metal is forcibly stirred (or agitated) electromagnetically, mechanically, or by means of ultrasonic waves or the like, to thereby obtain semi-solid metal having a solid-liquid mixed phase in which fine spherical crystallites are dispersed homogeneously in a liquid phase. The semi-solid metal is injected under pressure into a mold of die-cast machine, to thereby form a product by casting.
The thixocasting method is conducted in the following manner. Specifically, semi-solid metal is obtained by forcibly stirring (or agitating) molten metal while cooling the molten metal. Then, the semi-solid metal is temporarily cooled quickly, and then completely solidified so as to form an ingot (billet) having a bar-like shape. When manufacturing a product, a piece of a necessary amount is cut out of the billet, and then the piece is reheated so as to assume a semi-molten state (semi-solid state). Through this procedure, a product is manufactured using a die-cast machine or the like similarly to the rheocasting method.
The both methods have an advantage and a disadvantage. The both methods are common in that the semi-solid metal (hereinafter also representing the semi-molten metal) is formed under pressure in the mold.
Incidentally, when injecting the metal material into the die under pressure by the above-mentioned methods, it is necessary to set the semi-solid metal in a casting sleeve and extrude (inject) the metal into the mold by a pressure device such as a plunger. However, at a stage of inserting the semi-solid metal in the sleeve, the metal is brought into contact with the sleeve, to thereby lose its heat. Thus, a solidified layer is liable to be generated. Accordingly, an inventive way is demanded for preventing the solidified layer from being contained in a product.
Further, while filling the semi-solid metal, the sleeve or the like requires a pressure portion called a biscuit sandwiched between the plunger and a terminal end of the sleeve, a runner (sprue runner) leading the semi-solid metal into the die, and the like similarly to die casing. Further, in order to control inflow rate (reduce the inflow rate), a runner having a large cross-sectional area is required. Those portions do not form a product, thereby leading to a cause of a large amount of wasted material, reduced yield, and increased manufacturing cost.
Further, the semi-solid metal has a higher coefficient of friction with respect to the sleeve and the die than the molten metal, and hence it is necessary to increase a force of pressing the plunger as compared to a case of the molten metal. Further, it is necessary to provide a device for generating a larger force of pressing the plunger as compared to the case of the molten metal, thereby causing a problem such as increased device cost, which is a cause of increased manufacturing cost.
In view of the above-mentioned circumstances, there has been developed a forming method involving inserting the semi-solid metal (or semi-molten metal) directly into a forming die.
For example, Patent Literature 1 discloses the following technology. Specifically, semi-solid metal held in a holding vessel is inverted and placed in a recess of a lower die, and an upper die is lowered so as to compress-deform the semi-solid metal softly into a basic shape. Then, the semi-solid metal is formed into a product, having a finished shape.
Further, Patent Literature 2 discloses the following method. Specifically, semi-molten metal (semi-solid metal) is charged into a cavity of a die (lower die) of a pressing machine, and an upper die is lowered. Primary forming is performed while applying pressure until a temperature of the metal in the cavity reaches a solidification finish temperature. Then, secondary forming of a product is performed by changing a shape of the cavity with a second pressure device.
Further, Patent Literature 3 discloses the following forming method. Specifically, semi-molten metal or semi-solid metal is charged into a die. First pressurizing (primary mold clamping) is performed on the die, and then second pressurizing (secondary mold clamping of forming a finished product) is performed.
Further, Patent Literature 4 discloses the following preventing method. Specifically, in order that a position of charging semi-solid metal can be corrected, the semi-solid metal is solidified so as to have a proper solid phase ratio, and thus a liquid phase component is reduced. Thus, dripping of the liquid phase component and crumble of the semi-solid metal are prevented, With this method, a satisfactory product can be obtained,
The four methods are common in that the semi-molten metal (semi-solid metal) is charged into the cavity of the die, and then pressure forming is performed.
Here, Patent Literature 1 corresponds to JP 2003-136223A, Patent Literature 2 corresponds to JP 2007-118030 A, Patent Literature 3 corresponds to JP 2011-67838 A, and Patent Literature 4 corresponds to JP 2014-18823 A.
It is considered that, when the above-mentioned forming methods disclosed in Patent. Literature 1, Patent Literature 2, Patent Literature 3, and Patent Literature 4 are used, a high-quality product having no shrinkage cavity can be manufactured at low cost using the semi-molten metal or the semi-solid metal.
Incidentally, in the method of manufacturing a product, under pressure after charging the semi-solid metal into the cavity of the die, the semi-solid metal is filled into the die while compressed under press pressure, and pressure having a certain intensity or more is applied to the semi-solid metal. In this manner, quality and accuracy of forming are increased.
Accordingly, application of the above-mentioned method is limited to the semi-solid metal having such dimensions that the semi-solid metal may be charged into the cavity of the lower die. Actually, the application is limited to a product having a dimension equal to or larger than a dimension of the semi-solid metal in a direction orthogonal to a compressive force generated along with compression under pressure by lowering of the upper die (or a slide).
Further, as a shape of the semi-solid metal for use in forming, there is adopted a shape having a side wall with a draft and a flat base continuous with the side wall through a chamfered portion as illustrated in FIG. 1 of Patent Literature 1, FIG. 2 of Patent Literature 2, or FIG. 8 of Patent Literature 4, Alternatively, there is adopted a shape having an inner wall continuous with a center of a base through a chamfered portion with a draft as illustrated in FIG. 2 of Patent Literature 4. All the shapes exhibit an axially symmetric shape (rotationally symmetric shape).
In addition, as illustrated in FIG. 4(a) of Patent Literature 3, there is adopted a shape obtained by cutting a columnar billet. The semi-solid metal having an axially symmetric shape is also used in Patent Literature 3. As described above, in all of Patent Literatures, the semi-solid metal having an axially symmetric shape is applied as a raw material for use in press forming.
This is because it is necessary to forcibly stir (or agitate) the semi-solid metal material so as to achieve homogeneity in an entire region of the semi-solid metal material, and also because the forming of the semi-solid metal material into such an axially symmetric shape that the semi-solid metal material may be stirred without, sediment is advantageous to produce a satisfactory raw material having homogeneity and stable quality.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a press forming method for a semi-solid metal material and a press forming apparatus for a semi-solid metal material, which are capable of manufacturing products having homogeneity, excellence in mechanical strength, and high quality while enhancing productivity when the products are manufactured using the semi-solid metal material having an axially symmetric shape. For example, the present invention has an object to provide satisfactory forming may be realized regardless of dimension of the product, even in a case where a widthwise dimension (X direction) and a lengthwise dimension (Y direction) of a product, which are orthogonal to a Z direction of pressing the product under pressure by lowering of the upper die (or the slide), are larger than dimensions of the semi-solid metal.
Therefore, according to one embodiment of the present invention, there is provided a press forming method for a semi-solid metal material, including:

a semi-solid metal material carrying step of carrying a semi-solid metal material, which is manufactured from molten metal of a metal material into an axially symmetric shape, into a recessed portion of a lower die, the recessed portion conforming to a shape of a press-formed product;
a first press forming step of regulating, under a Z-direction regulation state in which, among a dimension of the carried semi-solid metal material in an X direction, a dimension of the carried semi-solid metal material in a Y direction, and a dimension of the carried semi-solid metal material in a Z direction, a change in the dimension of the semi-solid metal material in the Z direction corresponding to a pressing direction is regulated by bringing the semi-solid metal material into abutment on an upper die, a change in one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction by compressing the semi-solid metal material with a transverse punch so that the one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction becomes equal to a dimension of the press-formed product, and then stopping the transverse punch at a position of the compression; and
a second press forming step of moving, under a state in which the change in the one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction is regulated in the first press forming step, the upper die in the pressing direction to compress the semi-solid metal material so that the dimension of the semi-solid metal material in the Z direction becomes equal to the dimension of the press-formed product.

According to the one embodiment of the present invention, the second press forming step may include simultaneously elongating the semi-solid metal material so that another one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction becomes equal to the dimension of the press-formed product.
According to the one embodiment of the present invention, the Z-direction regulation state in the first press forming step may be a state in which the upper die compresses the semi-solid metal material so that, among the dimension of the carried semi-solid metal material in the X direction, the dimension of the carried semi-solid metal material in the Y direction, and the dimension of the carried semi-solid metal material in the Z direction, the dimension of the semi-solid metal material in the Z direction corresponding to the pressing direction becomes a predetermined dimension, and then the upper die is stopped at the position, of the compression to regulate the change in the dimension of the semi-solid metal material in the Z direction.
According to the one embodiment of the present invention, the press forming method may further include, after the second press forming step, performing processing with a punch moving toward the semi-solid metal material under a state in which the upper die is stopped sit the position of the compression.
According to one embodiment of the present invention, there is provided a press forming apparatus for a semi-solid metal material, which is provided so as to press form a semi-solid metal material manufactured from molten metal of a metal material into an axially symmetric shape, the press forming apparatus being configured to:

carry the semi-solid metal material into a recessed portion of a lower die, the recessed portion conforming to a shape of a press-formed product;
regulate, under a Z-direction regulation state in which, among a dimension of the carried semi-solid metal material in an X direction, a dimension of the carried semi-solid metal material in a Y direction, and a dimension of the carried, semi-solid metal material in a Z direction, a change in the dimension of the semi-solid metal, material in the Z direction corresponding to a pressing direction is regulated by bringing the semi-solid metal material into abutment, on an upper die, a change in one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction by compressing the semi-solid metal material with a transverse punch so that the one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction becomes equal to a dimension of the press-formed product, and then stopping the transverse punch at a position of the compression; and
move, under a state in which the change in the one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction is regulated, the upper die in the pressing direction to compress the semi-solid metal material so that the dimension of the semi-solid metal material in the Z direction becomes equal to the dimension of the press-formed product.

According to the one embodiment of the present invention, the press forming apparatus for a semi-solid metal material may be configured to:

move, under the state in which the change in the one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction is regulated, the upper die in the pressing direction to compress the semi-solid metal material so that the dimension of the semi-solid metal material in the Z direction becomes equal to the dimension of the press-formed product; and
elongate the semi-solid metal material so that another one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction becomes equal to the dimension of the press-formed product.

According to the one embodiment of the present invention, in the press forming apparatus for a semi-solid metal material, the Z-direction regulation state may be a state in which the upper-die compresses the semi-solid metal material so that, among the dimension of the carried semi-solid metal material in the X direction, the dimension of the carried semi-solid metal material in the Y direction, and the dimension of the carried semi-solid metal material in the Z direction, the dimension of the semi-solid metal material in the Z direction corresponding to the pressing direction becomes a predetermined dimension, and then the upper die is stopped, at the position of the compression to regulate the change in the dimension of the semi-solid metal material in the Z direction.
According to the one embodiment of the present invention, in the press forming apparatus for a semi-solid metal material, after the press forming apparatus moves, under the state in which the change in the one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction is regulated, the upper die in the pressing direction to compress the semi-solid metal material so that the dimension of the semi-solid metal material in the Z direction becomes equal to the dimension of the press-formed product, and elongates the semi-solid metal material, so that the another one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction becomes equal to the dimension of the press-formed product, the press forming apparatus performs processing with a punch moving toward the semi-solid metal material under a state in which the upper die is stopped at the position of the compression.
According to the one embodiment of the present invention, it is possible to provide the press forming method for a semi-solid metal material and the press forming apparatus for a semi-solid metal material, which are capable of manufacturing the products having homogeneity, excellence in mechanical strength, and high quality while enhancing productivity when the products are manufactured using the semi-solid metal material having an axially symmetric shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a container and an electromagnetic stirring (or agitating) device for manufacturing a semi-solid metal material, which are used in an embodiment of the present invention.

FIG. 2A is a front view illustrating a shape of semi-solid metal slurry (semi-solid metal material) used in the embodiment of the present invention.

FIG. 2B is a right-hand side view of FIG. 2A.

FIG. 2C is a left-hand side view of FIG. 2A.

FIG. 3A is a front view illustrating a shape of a formed product according to the embodiment of the present invention, which is obtained after finish of forming.

FIG. 3B is a right-hand side view (sectional view) of FIG. 3A.

FIG. 3C is a sectional view taken along the arrow A-A of FIG. 3A.

FIG. 4A is a plan view illustrating a state in which the semi-solid metal slurry (semi-solid metal material) according to the embodiment of the present invention is charged (carried) into a lower die that is recessed so as to conform to a lower shape of a product.

FIG. 4B is a sectional view taken along the arrow B-B of FIG. 4A.

FIG. 4C is a sectional view taken along the arrow A-A of FIG. 4A.

FIG. 5A is a front view illustrating a state in which an upper die (slide) is lowered to slightly crush semi-solid slurry (semi-solid metal material) by an upper punch (in this case, crush by 4 mm), and the upper die (slide) is stopped at this position, FIG. 5B is a sectional view taken along the arrow A-A of FIG. 5A.

FIG. 6A is a front view illustrating a state in which pins, which are connected to actuators in the slide and placed in the upper die, push longitudinal cams of the lower die while repeating compression and stop so as to transmit a force to transverse cams, and then punches mounted to the transverse cams compress the semi-solid slurry (semi-solid metal material) in an X direction, thereby obtaining a formed product having a predetermined thickness.

FIG. 6B is a sectional view taken along the arrow A-A of FIG. 6A.

FIG. 7A is a view illustrating a state in which, after finish of forming in the X direction performed by the transverse cams, the transverse cams remain at the forming finish position, the upper die is lowered from a stop position (restarts compressing in a Z direction), and then the upper die (slide) reaches a bottom dead center so that the semi-solid metal slurry is compressed in a range surrounded by the lower die, to thereby flow only in a major axis Y direction.

FIG. 7B is a sectional view taken along the arrow A-A of FIG. 7A.

FIG. 8A is a front view illustrating a state in which a material contained in eyeglass-shaped portions formed at both end portions of the lower die in the major axis Y direction is pushed by columnar punches placed in the lower die, to thereby flow into holes of the upper punch and pad (or excess material) escape grooves formed on upper surface sides of the both end portions.

FIG. 8B is a sectional view taken along the arrow A-A of FIG. 8A.

FIG. 9 is a view illustrating a state in which a temperature of a formed product formed through a series of operations is reduced to room temperature, and then pads (or excess material portions), opening portions of the eyeglass-shaped portions, burrs, and the like are trimmed or pierced using a press die, thereby finishing the formed product into a desired product shape.

FIG. 10A is a plan view illustrating an example of a configuration in a case of employing servo actuators as structure for pushing the transverse punches.

FIG. 10B is a front view of FIG. 10A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, a press forming method for a semi-solid metal material and a press forming apparatus for a semi-solid metal material according to an embodiment of the present invention are described with reference to the attached drawings. Note that, the present, invention is not limited to the embodiment described below.
The inventors of the present invention have made a press forming method using a servo press machine and involving a first process of compressing a semi-solid metal material, which has a larger dimension than a product in one direction (X direction) of the product, up to a dimension equal to that of the product, and a second process of compressing the semi-solid metal material, which has a larger dimension than the product also in a second direction (Z direction) of the product, up to a dimension equal to that of the product.
In the following, the method is described with reference to a specific embodiment.
<Semi-Solid Metal Material Manufacturing (Producing) Process (Step)>
After a container 3 having a diameter (diameter of an upper end portion on an opening portion side) <φ of 70 mm, a length (height) of 70 mm, and a draft of 3° is carried into an electromagnetic stirring (or agitating) device 5, molten metal (such as an aluminum alloy) 1 scooped up from a melting furnace (not shown) by a molten metal feeding/injecting device (ladle) 4 is injected through a funnel 5 a into the container 3 made of metal (for example, made of non-magnetic SUS304) by tilting the molten metal feeding/injecting device 4 as illustrated in FIG. 1, and the molten metal in the container 3 is cooled while the molten metal is electromagnetically stirred by the electromagnetic stirring device 5 on which the container 3 is placed. In this manner, the semi-solid metal material (semi-solid material, semi-solid slurry) 2 having a solid phase ratio of 30 to 90% is manufactured (produced, obtained). (Electromagnetic stirring is performed from the point of start of injecting the molten metal.) As the semi-solid metal material, for example, an aluminum alloy may be employed, and another metal or another kind of alloy may also be employed.
This process corresponds to a semi-solid metal material manufacturing process (step).
Note that, as illustrated in FIGS. 2A to 2C, the semi-solid metal material 2 obtained in this step is formed into an axially symmetric shape (rotationally symmetric shape) having a diameter (diameter of an upper end portion on an opening portion side) φ of 70 mm, a length (height) of 70 mm, a draft of 3°, and a predetermined radius of curvature R (R=10 mm) at a bottom portion thereof. Note that, in this case, depending on a volume of a formed product, the semi-solid metal material 2 is set to have the above-mentioned dimensions, the radius of curvature R (R=10 mm) of a chamfered portion between a side wall and a bottom surface of the semi-solid metal material 2, and the draft of 3°. However, the dimensions of the semi-solid metal material 2 are determined in consideration of a volume of a formed product, easiness of manufacture of slurry, and the like.
Incidentally, this embodiment exemplifies, as a press-formed product obtained by press forming the semi-solid metal material 2, a link member 100 (such as a connecting rod) as illustrated in FIGS. 3A to 3C having a relatively long size and each end connected to a shaft or the like in a rotatable manner. In other words, as the product obtained by press forming (finished press-formed product), this embodiment exemplifies a member having small dimensions in the X direction and the Z direction, and a large dimension in a Y direction. Note that, in this embodiment, the Z direction is set as a pressing direction, and the X direction and the Y direction are set as a matter of convenience. Those directions may be set through appropriate interchange.
In a case where the semi-solid metal material is used as a raw material to be subjected to press forming, it is preferred that a composition, a structure, and the like of the semi-solid metal material used as the raw material be homogeneous in an entire region. Accordingly, in order to obtain the homogeneous semi-solid metal material using the electromagnetic stirring device 5, a shape of the semi-solid metal material is limited to an axially symmetric shape having, for example, a diameter (diameter of an upper end portion on an opening portion side) φ of 70 mm, a length (height) of 70 mm, and a chamfered bottom portion. Actually, it is inevitable to use the raw material having a shape relatively different from a shape of the finished press-formed product (see the link member 100 illustrated in FIGS. 3A to 3C).
In this embodiment, the above-mentioned raw material (semi-solid metal material) having an axially symmetric shape relatively considerably different from the shape of the finished press-formed product is press formed satisfactorily during one pressing stroke (one reciprocating sliding motion), thereby being capable of obtaining the finished press-formed product. Note that, the reason why press forming is completed during one pressing stroke (one reciprocating sliding motion) is as follows. Specifically, in a case where the semi-solid metal material is used as the raw material, when a time period for performing press forming is elongated, the raw material (semi-solid metal material) is cooled, and solidification of the raw material is locally accelerated to more than a predetermined degree. As a result, homogeneity cannot be secured in the entire region of the raw material (semi-solid metal material), thereby causing local fluctuations of a structure, a composition, and the like of the product,, and local lack of mechanical strength of the product, which brings difficulty in ensuring homogeneity and stable quality,
<Step 1>
As illustrated in FIGS. 4A to 4C, the semi-solid metal material 2 is charged (carried) into a cavity 21 of a lower die 20 so as to align, with a major axis Y of the lower die 20, at major axis Y of the semi-solid metal material 2 that is shaped to have the diameter (diameter of the upper end portion on the opening portion side) φ of 70 mm, the length (height) of 70 mm, the draft of 3°, and the predetermined radius of curvature R at the bottom portion thereof.
This step corresponds to a semi-solid metal material carrying step according to the present invention.
At this time, the lower die 20 has the cavity 21 that is shaped to enable the raw material (semi-solid metal material 2) to be charged (carried) into the cavity 21 so that, a position of a center axis of a recessed portion 20A of the lower die 20 and a position of a centroid C of the raw material (semi-solid metal material 2) (see FIG. 4C) are aligned with each other.
Note that, the recessed portion 20A conforming to a shape of the press-formed product (for example, the link member 100 illustrated in FIGS. 3A to 3C) is formed in the lower die 20.
Further, a group of dies including an upper die 7 and the lower die 20 is warmed to substantially 300 to 400° C. by a cartridge heater (electric heater) or the like, and a heat insulating material is provided between a die set and each die to prevent neat from being transferred to a body of the press machine.
Note that, it is only necessary to warm each die to a temperature of about 150 to 500° C. Further, a material of the die is equivalent to SKD61, and BN powder is applied to a surface of the die, thereby preventing adhesion between slurry and the die. The material of the die is determined depending on strength and hardness thereof at 500 to 600° C. and hence, for example, a sintered hard alloy may be adopted.
As illustrated in FIGS. 4A to 4C, the cavity 21 can accommodate the semi-solid metal material 2 therein, and is formed as a space defined by a part of the lower die 20, a pair of transverse cams 23 (transverse punches 23A mounted to distal ends of the transverse cams 23, respectively) pushed and moved in the X direction by a pair of longitudinal cams 22 arranged on the lower die 20 to be movable in the Z direction, and an inner bottom surface 20B of the lower die 20.
In other words, an upper plane of the cavity 21 in the Z direction is defined by an opening, and planes thereof in the X direction are defined by the pair of transverse cams 23 (transverse punches 23A) arranged so as to be opposed to each other. Planes of the cavity 21 in the Y direction are defined by the part of the lower die 20, and a lower plane thereof in the Z direction is defined by the inner bottom surface 20B of the lower die 20.
<Step 2>
After the raw material (semi-solid metal material 2) is charged (carried) into the cavity 21, as illustrated in FIGS. 5A and 5B, the upper die 7 (slide 6) is lowered immediately, and an upper punch 10 compresses the semi-solid metal material 2 in the Z direction (compresses by about 4 mm in this step). Then, the upper die 7 (slide 6) is stopped at a determined position. Note that, the upper die 7 includes, in addition to the upper punch 10, a pad 11 for preventing the raw material (semi-solid metal material 2) from moving in the Z direction. The pad 11 has such a mechanism as to be brought into contact with the lower die 20 before the upper punch 10 of the upper die 7 and the raw material (semi-solid metal material 2) are brought into contact with each other, and to be retained at the contact position while applying a constant force by a cushion 12 provided in the upper die 7 or the slide 6.
“A Z-direction regulation state according to the present invention in which, among dimensions of the carried semi-solid metal material in the X, Y, and Z directions, a change in the dimension of the semi-solid metal material in the Z direction corresponding to a pressing direction is regulated by bringing the semi-solid metal material into abutment on the upper die” corresponds to Step 2.
In this case, the upper punch 10 (corresponding to an upper die according to the present invention) compresses the semi-solid metal material 2 in the Z direction (compresses by about 4 mm in this step), but the present invention is not limited thereto. The upper punch 10 may compress the semi-solid metal material 2 further. Alternatively, for example, without compressing, the upper punch 10 (corresponding to the upper die according to the present invention) may be brought into abutment on the semi-solid metal material 2, to thereby regulate the change in the dimension of the semi-solid metal material 2 in the Z direction.
Note that, in Step 2, the raw material (semi-solid metal material 2) is restrained by the lower die 20, the upper punch 10, and the pad 11, and hence, the raw material cannot flow in the Z direction. Therefore, a portion of the raw material compressed in the Z direction is extruded in the X direction or the Y direction.
<Step 3>
After that, as illustrated in FIGS. 6A and 6B, while a position of the upper die 7 (slide 6) is stationary, pins 13 are pushed down in the Z direction, which can be moved by actuators 14 (hydraulic actuators) of a servo-driven type built in the upper die 7 or the slide 6, so as to push down the longitudinal cams 22 in the lower die 20 in the Z direction. Then, a force transmitted to the longitudinal cams 22 is transmitted to the pair of transverse cams 23 (transverse punches 23A) arranged so as to be opposed to each other. As a result, the raw material (semi-solid metal material 2) is compressed from both sides in the X direction, and then compressively deformed in the X direction. At this time, as illustrated in FIG. 6B, the raw material (semi-solid metal material 2) is expanded (elongated) in the Y direction, Note that, in order to prevent fracture of the raw material (semi-solid metal material 2), the raw material is restrained from flowing in the Z direction to flow only in the X direction and the Y direction.
This step corresponds to a first press forming step according to the present invention.
At this time, the pair of transverse cams 23 (transverse punches 23A) is controlled to advance while repeating compression and stop (or compression and return), and is stopped at the point in time when the dimension of the semi-solid metal material in the X direction reaches a predetermined thickness of 40 mm. Note that, depending on forming conditions, the transverse cams 23 (or the longitudinal cams 22 for driving the transverse cams 23) are sometimes moved at constant speed or under micro-vibration (approximately 1 to 100 Hz).
<Step 4>
Next, as illustrated in FIGS. 7A and 7B, the upper die 7, which has been stopped in Step 3, is lowered to compress the semi-solid metal material 2 until the dimension thereof in the Z direction reaches 24 mm at a center position of the semi-solid metal materials. At this time, the transverse cams 23 (transverse punches 23A) are not moved in the X direction (remain stationary). Therefore, a portion of the material (semi-solid metal material 2) compressed in the Z direction is moved in the Y direction (see FIG. 7B).
This step corresponds to a second press forming step according to the present invention.
Note that, in this case, the portion of the material (semi-solid metal material 2) compressed in the Z direction is moved in the Y direction. In this manner, the semi-solid metal material is elongated (expanded) so that the dimension of the semi-solid metal material in the Y direction becomes equal to that of the press-formed product, but the present invention is not limited thereto. The present invention is also applicable to a case where the semi-solid metal material is elongated (expanded) so that the dimension of the semi-solid metal material in the Y direction becomes equal to or larger than that of the press-formed product (for example, a case where pads (or the excess material portions) are removed in post-processing), or a case where there is adopted a forming step of performing forming until the dimension of the semi-solid metal material in the Y direction reaches a dimension nearly equal to that of the press-formed product, and then elongating (expanding) the semi-solid metal material to a dimension equal to that of the press-formed product in a post-process.
The upper die 7 (slide 6) is moved while repeating descent and stop (or descent and ascent), and is stopped at a predetermined position. When the upper die 7 is stopped at the predetermined position (the raw material reaches a predetermined thickness), a volume of the raw material is slightly larger than a volume of the formed product, and hence a part of the raw material flows into pad forming portions (or excess material portions) P. However, the pad forming portions (or excess material portions) P can absorb fluctuations in every volume of the raw material (semi-solid metal material 2).
Both end portions of the recessed portion 20A (recessed portion conforming to a shape of the press-formed product (link member 100)) of the lower die 20 are shaped as eyeglass-shaped portions 24 to conform to a contour of the press-formed product (ring-shaped portions 101, 102 of the link member 100). Pad escape grooves (or excess material escape grooves) (grooves into which the pads flow) are formed on upper surface sides of the both end portions, respectively. However, the pad escape grooves (or excess material escape grooves) may be formed on the upper die (upper punch 10) side.
At the time of finish of forming, the upper die 7 (slide 6) is stopped at a bottom dead center, whereas a force controlling cushion 6A provided in the slide 6 applies pressure to the formed product (semi-solid metal material 2 subjected to press forming) through the die (upper punch 10). Note that, depending on forming conditions, the upper die 7 (slide 6) is sometimes moved, instead of the repeat of descent, and stop (or descent and ascent), at constant speed or under micro-vibration (approximately 1 to 100 Hz). In a case of applying micro-vibration, the micro-vibration is transmitted to the entire cavity 21 of the lower die 20 through the upper punch 10, thereby being capable of reducing occurrence of adhesion between the die and the raw material.
<Step 5>
Subsequently, as illustrated in FIGS. 8A and 8B, even after finish of forming performed by the upper die 7, the press machine (slide 6) remains at the bottom dead center. Punches 30 provided in center portions of the eyeglass-shaped portions 24 of the lower die 20 are pushed upward in the Z direction by actuators 31 (hydraulic actuators) provided in the lower die 20 or a bolster, thereby forming center holes 101A, 102A (see FIGS. 3A to 3C) of the ring-shaped portions 101, 102 of the link member 100 serving as the press-formed product (semi-solid metal material 2 subjected to press forming). At this time, around center punched portions, thin-walled portions remain on distal ends of the punches 30, whereas pads (or excess material portions) flow into hole portions 10A (pads Q) of the upper punch 10 and the pad forming portions P formed in upper portions of the lower die 20.
<Step 6>
After finish of forming in Step 5, the slide 6 is raised to return to a top dead center, and a knockout mechanism 40 (see FIG. 8B) provided in the bolster pushes up the formed product (link member 100) to take (discharge) the formed product out of the lower die 20.
<Step 7>
After cooling the taken-out formed product (link member 100), overflow portions and burrs, such as the pads Q, the pad forming portions P, and the thin-walled portions formed near the center holes 101A, 102A of the ring-shaped portions 101, 102 (eyeglass-shaped portions) of the formed product (link member 100), are removed at room temperature by, for example, trimming or piercing using a press die in a next process (see FIG. 9).
With the above-mentioned forming method, the formed product 100 illustrated in FIGS. 3A to 3C is produced (manufactured).
Note that, normal die casting cannot produce the product having satisfactory mechanical properties such as strength and elongation, and hence the product is manufactured by hot forging. However, even when the product is manufactured with the above-mentioned method, the mechanical properties of the product can equal quality of hot forgings.
As described above, according to this embodiment, using the raw material (semi-solid metal material 2) having an axially symmetric shape (having substantially the same dimensions in the X, Y, and Z directions) relatively considerably different from a shape of the finished press-formed product, it is possible to obtain a press-formed product having small dimensions in the X and Z directions and a large dimension in the Y direction.
In this embodiment, using the raw material (semi-solid metal material) having an axially symmetric shape relatively considerably different from the shape of the finished press-formed product, press forming is performed satisfactorily during one pressing stroke (one reciprocating sliding motion). In this manner, the finished press-formed product can be obtained.
According to this embodiment, even using the raw material (semi-solid metal material) having an axially symmetric shape relatively considerably different from the shape of the finished press-formed product, press forming can be completed during one pressing stroke (one reciprocating sliding motion). Accordingly, as compared to the related art in which press forming is previously performed using another die or the like to form the raw material (semi-solid metal material) having an axially symmetric shape into a shape approximate to the shape of the finished press-formed product, and then final press forming is performed using still another die, a time period for performing press forming can be reduced. Thus, it is possible to avoid such a situation that the raw material (semi-solid metal material) is cooled, and solidification of the raw material is locally accelerated to more than a predetermined degree, with the result that homogeneity cannot be secured in the entire region of the raw material (semi-solid metal material), thereby causing local fluctuations of a structure, a composition, and the like of the product, and local lack of mechanical strength of the product, which brings difficulty in ensuring homogeneity and stable quality. Consequently, it is possible to obtain the press-formed product having homogeneity, excellence in mechanical strength, and high quality.
That is, according to this embodiment, it is possible to provide the press forming method for a semi-solid metal material and the press forming apparatus for a semi-solid metal material, which are capable of manufacturing the products having homogeneity, excellence in mechanical strength, and high quality while enhancing productivity when the products are manufactured using the semi-solid metal material having an axially symmetric shape.
Note that, this embodiment exemplifies a case where stirring is performed using the electromagnetic stirring device 5, but the present invention is not limited thereto. The present invention is also applicable to a case where the molten metal 1 is cooled while stirred by another method in order to produce the semi-solid metal material 2.
Further, this embodiment describes a configuration in which the transverse punches 23A are moved using the longitudinal cams 22 and the transverse cams 23, but the present invention is not limited thereto. As illustrated in FIGS. 10A and 10B, there may also be adopted structure in which the transverse punches 23A are pushed by a servo actuator using hydraulic action or the like.
The embodiment described above is merely an example for describing the present invention. It goes without saying that various modifications may be made without departing from the gist of the present invention.

Claims

What is claimed is:

1. A press forming method for a semi-solid metal material, comprising:

a semi-solid metal material carrying step of carrying a semi-solid metal material, which is manufactured from molten metal of a metal material into an axially symmetric shape, into a recessed portion of a lower die, the recessed portion conforming to a shape of a press-formed product;

a first press forming step of regulating, under a Z-direction regulation state in which, among a dimension of the carried semi-solid metal material in an X direction, a dimension of the carried semi-solid metal material in a Y direction, and 3-dimension of the carried semi-solid metal material in a Z direction, a change in the dimension of the semi-solid metal material in the Z direction corresponding to a pressing direction is regulated by bringing the semi-solid metal material into abutment on an upper die, a change in one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction by compressing the semi-solid metal material with a transverse punch so that the one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction becomes equal to a dimension of the press-formed product, and then stopping the transverse punch at a position of the compression; and

a second press forming step of moving, under a state in which the change in the one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction is regulated in the first press forming step, the upper die in the pressing direction to compress the semi-solid metal material so that the dimension of the semi-solid metal material in the Z direction becomes equal to the dimension of the press-formed product.

2. A press forming method for a semi-solid metal material according to claim 1, wherein the second press forming step comprises elongating the semi-solid metal material so that another one of the dimension of the semi-solid metal material in the X direction and the dimension of the semi-solid metal material in the Y direction becomes equal to the dimension of the press-formed product,

3. A press forming method for a semi-solid metal material according to claim 1, wherein the Z-direction regulation state in the first press forming step comprises a state in which the upper die compresses the semi-solid metal material so that, among the dimension of the carried semi-solid metal material in the X direction, the dimension of the carried semi-solid metal material in the Y direction, and the dimension of the carried semi-solid metal material in the Z direction, the dimension of the semi-solid metal material in the Z direction corresponding to the pressing direction becomes a predetermined dimension, and then the upper die is stopped at the position of the compression to regulate the change in the dimension of the semi-solid metal material in the Z direction.

4. A press forming method for a semi-solid metal material according to claim 1, further comprising, after the second press forming step, performing processing with a punch moving toward the semi-solid metal material under a state in which the upper die is stopped at the position of the compression.