U.S. patent application number 14/396382 was filed with the patent office on 2015-05-14 for high-density molding device and high-density molding method for mixed powder.
The applicant listed for this patent is AIDA ENGINEERING, LTD.. Invention is credited to Kazuhiro Hasegawa, Yoshiki Hirai.
Application Number | 20150132175 14/396382 |
Document ID | / |
Family ID | 49466532 |
Filed Date | 2015-05-14 |
United States Patent
Application |
20150132175 |
Kind Code |
A1 |
Hasegawa; Kazuhiro ; et
al. |
May 14, 2015 |
HIGH-DENSITY MOLDING DEVICE AND HIGH-DENSITY MOLDING METHOD FOR
MIXED POWDER
Abstract
A mixed powder placed in a container cavity is transferred to
the cavity of a first die. A first pressure is applied to the mixed
powder in the first die to form an intermediate green compact. The
first die and the intermediate green compact are heated to heat the
intermediate green compact to the melting point of a lubricant. The
heated intermediate green compact is transferred to the cavity of a
second die, and a second pressure is applied to the intermediate
green compact to form a high-density final green compact.
Inventors: |
Hasegawa; Kazuhiro;
(Sagamihara-shi, JP) ; Hirai; Yoshiki;
(Shibuya-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AIDA ENGINEERING, LTD. |
Kanagawa |
|
JP |
|
|
Family ID: |
49466532 |
Appl. No.: |
14/396382 |
Filed: |
April 22, 2013 |
PCT Filed: |
April 22, 2013 |
PCT NO: |
PCT/JP2013/061741 |
371 Date: |
October 22, 2014 |
Current U.S.
Class: |
419/38 ;
425/78 |
Current CPC
Class: |
B22F 3/004 20130101;
B22F 2003/145 20130101; B22F 2998/10 20130101; B22F 2003/023
20130101; B30B 11/10 20130101; B22F 3/16 20130101; C22C 45/00
20130101; B30B 15/34 20130101; B22F 2998/10 20130101; B22F 3/03
20130101; B22F 1/007 20130101; B22F 3/003 20130101; B30B 15/304
20130101; B30B 11/027 20130101; C22C 38/02 20130101; B30B 15/0011
20130101; C22C 38/00 20130101; H01F 41/0246 20130101; B22F 2003/023
20130101; C22C 33/02 20130101; C22C 45/02 20130101; B22F 2003/145
20130101 |
Class at
Publication: |
419/38 ;
425/78 |
International
Class: |
B22F 3/16 20060101
B22F003/16; B22F 3/00 20060101 B22F003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 23, 2012 |
JP |
2012-098060 |
Claims
1. A mixed powder high-density molding method comprising: filling a
container cavity of a container with a mixed powder that is a
mixture of a basic metal powder and a low-melting-point lubricant
powder; transferring the mixed powder in the container cavity to a
cavity of a first die that is positioned with respect to the
container; applying a first pressure to the mixed powder in the
cavity of the first die to form a mixed powder intermediate
compressed body; heating the first die and the mixed powder
intermediate compressed body to heat the mixed powder intermediate
compressed body to a melting point of the lubricant powder;
positioning the heated mixed powder intermediate compressed body
with respect to a second die together with the first die;
transferring the mixed powder intermediate compressed body in the
cavity of the first die to a cavity of the second die that is
positioned with respect to the first die; and applying a second
pressure to the mixed powder intermediate compressed body in the
cavity of the second die to form a high-density mixed powder final
compressed body.
2. The mixed powder high-density molding method as defined in claim
1, wherein the lubricant powder has a low melting point within a
range of 90 to 190.degree. C.
3. The mixed powder high-density molding method as defined in claim
1, wherein the second die is pre-heated before the mixed powder
intermediate compressed body is placed in the second die.
4. The mixed powder high-density molding method as defined in claim
1, wherein the first die is pre-heated after the mixed powder
intermediate compressed body has been molded.
5. The mixed powder high-density molding method as defined in claim
1, wherein the second pressure is selected to be equal to the first
pressure.
6. A mixed powder high-density molding system comprising: a mixed
powder feeding device that can fill a container cavity of a
container that is positioned at a mixed powder filling position
with a mixed powder that is a mixture of a basic metal powder and a
low-melting-point lubricant powder; a mixed powder transfer device
that transfers the mixed powder in the container cavity to a cavity
of a first die that is positioned with respect to the container; a
first press molding device that applies a first pressure to the
mixed powder in the cavity of the first die from a first punch to
form a mixed powder intermediate compressed body; a heating device
that heats the first die positioned at a heating position and the
mixed powder intermediate compressed body to heat the mixed powder
intermediate compressed body to a melting point of the lubricant
powder; an intermediate green compact transfer device that
transfers the mixed powder intermediate compressed body in the
cavity of the first die to a second die positioned at a transfer
relay position; a second press molding device that applies a second
pressure to the mixed powder intermediate compressed body in a
cavity of the second die positioned at a final compressed body
molding position to form a high-density mixed powder final
compressed body; and a product discharge device that is configured
to discharge the mixed powder final compressed body in the cavity
of the second die at a product discharge position.
7. The mixed powder high-density molding system as defined in claim
6, comprising: a first die transfer device that is configured to
transfer the first die to position the first die with respect to
the container that is positioned at the mixed powder filling
position; an unheated green compact transfer device that is
configured to transfer the first die from an intermediate green
compact molding position, to position the first die at the heating
position; a heated green compact transfer device that is configured
to transfer the first die that holds the mixed powder intermediate
compressed body from the heating position, to position the first
die at the transfer relay position; a second die transfer device
that is configured to transfer the second die that holds the mixed
powder intermediate compressed body from the transfer relay
position, to position the second die at the final green compact
molding position; a final green compact transfer device that is
configured to transfer the second die that holds the mixed powder
final compressed body from the final green compact molding
position, to position the second die at the product discharge
position; and a second die return transfer device that is
configured to transfer the second die that holds the mixed powder
final compressed body from the product discharge position, to
position the second die at a reception relay position.
8. The mixed powder high-density molding system as defined in claim
7, wherein the mixed powder filling position, the heating position,
and the transfer relay position are separately provided along a
first circular path defined around a first axis, and the reception
relay position, the final green compact molding position, and the
product discharge position are separately provided along a second
circular path defined around a second axis, the first die transfer
device, the unheated green compact transfer device, and the heated
green compact transfer device are implemented by utilizing a first
rotary table that can be rotated around the first axis, and the
second die transfer device, the final green compact transfer
device, and the second die return transfer device are implemented
by utilizing a second rotary table that can be rotated around the
second axis.
9. The mixed powder high-density molding system as defined in claim
6, further comprising: a first pre-heating device that pre-heats
the first die.
10. The mixed powder high-density molding system as defined in
claim 6, further comprising: a second pre-heating device that
pre-heats the second die.
Description
TECHNICAL FIELD
[0001] The present invention relates to a high-density molding
method and a high-density molding system that can form a green
compact having high density (e.g., 7.75 g/cm.sup.3) by pressing a
mixed powder twice.
BACKGROUND ART
[0002] Powder metallurgy is a technique that normally presses
(compresses) a metal powder to form a green compact having a given
shape, and heats the green compact to a temperature around the
melting point of the metal powder to promote intergranular coupling
(solidification) (i.e., sintering process). This makes it possible
to inexpensively produce a mechanical part that has a complex shape
and high dimensional accuracy.
[0003] An improvement in mechanical strength of a green compact has
been desired in order to deal with a demand for a further reduction
in size and weight of mechanical parts. When a green compact is
subjected to a high temperature, the magnetic properties of the
green compact may deteriorate. Therefore, the subsequent
high-temperature treatment (sintering process) may be omitted when
producing a magnetic-core green compact, for example. In other
words, a method that improves mechanical strength without
performing a high-temperature treatment (sintering process) has
been desired.
[0004] The mechanical strength of a green compact increases
significantly (hyperbolically) as the density of the green compact
increases. For example, a method that mixes a lubricant into a
metal powder, and press-molds the metal powder while achieving a
reduction in friction resistance has been proposed as a typical
high-density molding method (e.g., JP-A-1-219101 (Patent Literature
1)). A mixed powder prepared by mixing a lubricant with a basic
metal powder in a ratio of about 1 wt % is normally press-molded.
Various other methods have been proposed to achieve higher density.
These methods can be roughly classified into a method that improves
the lubricant and a method that improves the press
molding/sintering process.
[0005] Examples of the method that improves the lubricant include a
method that utilizes a composite of carbon molecules obtained by
combining a ball-like carbon molecule with a sheet-like carbon
molecule as the lubricant (e.g., JP-A-2009-280908 (Patent
Literature 2)), and a method that utilizes a lubricant having a
penetration at 25.degree. C. of 0.3 to 10 mm (e.g., JP-A-2010-37632
(Patent Literature 3)). These methods aim at reducing the friction
resistance between the metal powder particles, and the friction
resistance between the metal powder and a die.
[0006] Examples of the method that improves the press
molding/sintering process include a warm molding/sinter powder
metallurgical technique (e.g., JP-A-2-156002 (Patent Literature
4)), a facilitated handling warm molding powder metallurgical
technique (e.g., JP-A-2000-87104 (Patent Literature 5)), a double
press/double sinter powder metallurgical technique (e.g.,
JP-A-4-231404 (Patent Literature 6)), and a single press/sinter
powder metallurgical technique (e.g., JP-A-2001-181701 (Patent
Literature 7)).
[0007] According to the warm molding/sinter powder metallurgical
technique, a metal powder into which a solid lubricant and a liquid
lubricant are mixed is pre-heated to melt part or the entirety of
the lubricant, and disperse the lubricant between the metal powder
particles. This technique thus reduces the inter-particle friction
resistance and the friction resistance between the particles and a
die to improve formability. According to the facilitated handling
warm molding powder metallurgical technique, a mixed powder is
pressed before performing a warm molding step to form a primary
molded body having low density (e.g., density ratio: less than 76%)
that allows handling (primary molding step), and the primary formed
body is subjected to a secondary molding step at a temperature
lower than the temperature at which blue shortness occurs while
breaking the primary molded body to obtain a secondary molded body
(green compact). According to the double press/double sinter powder
metallurgical technique, an iron powder mixture that contains an
alloying component is compressed in a die to obtain a compressed
body, the compressed body (green compact) is presintered at
870.degree. C. for 5 minutes, and compressed to obtain a
presintered body, and the presintered body is sintered at
1000.degree. C. for 5 minutes to obtain a sintered body (part).
According to the single press/sinter powder metallurgical
technique, a die is pre-heated, and a lubricant is caused to
electrically adhere to the inner side of the die. The die is filled
with a heated iron-based powder mixture (iron-based
powder+lubricant powder), and the powder mixture is press-molded at
a given temperature to obtain an iron-based powder molded body. The
iron-based powder molded body is sintered, and subjected to bright
quenching and annealing to obtain an iron-based sintered body.
[0008] The density of the green compact achieved by the methods
that improve the lubricant and the methods that improve the press
molding/sintering process is about 7.4 g/cm.sup.3 (94% of the true
density) at a maximum. The green compact exhibits insufficient
mechanical strength when the density of the green compact is 7.4
g/cm.sup.3 or less. Since oxidation proceeds corresponding to the
temperature and the time when applying the sintering process
(high-temperature atmosphere), the lubricant coated with the powder
particles burns, and a residue occurs, whereby the quality of the
green compact obtained by press molding deteriorates. Therefore, it
is considered that the density of the green compact is 7.3
g/cm.sup.3 or less. The methods that improve the lubricant and the
methods that improve the press molding/sintering process are
complex, may increase cost, and have a problem in that handling of
the material is difficult or troublesome (i.e., it may be
impractical).
[0009] In particular, when producing a magnetic core for an
electromechanical device (e.g., motor or transformer) using a green
compact, a satisfactory magnetic core may not be produced when the
density of the green compact is 7.3 g/cm.sup.3 or less. It is
necessary to further increase the density of a green compact in
order to reduce loss (iron loss and hysteresis loss), and increase
magnetic flux density (see the document presented by Toyota Central
R & D Labs., Inc. in Autumn Meeting of Japan Society of Powder
and Powder Metallurgy, 2009). Even when the density of the magnetic
core is 7.5 g/cm.sup.3, for example, the magnetic properties and
the mechanical strength of the magnetic core may be insufficient in
practice.
[0010] A double molding/single sinter (anneal) powder metallurgical
technique (e.g., JP-A-2002-343657 (Patent Literature 8)) has been
proposed as a method for producing a magnetic-core green compact.
This powder metallurgical technique is based on the fact that a
magnetic metal powder that is coated with a coating that contains a
silicone resin and a pigment does not show a decrease in insulating
properties even if the magnetic metal powder is subjected to a
high-temperature treatment. Specifically, a dust core is produced
by pre-molding a magnetic metal powder that is coated with a
coating that contains a silicone resin and a pigment to obtain a
pre-molded body, subjecting the pre-molded body to a heat treatment
at 500.degree. C. or more to obtain a heat-treated body, and
compression-molding the heat-treated body. If the heat treatment
temperature is less than 500.degree. C., breakage may occur during
compression molding. If the heat treatment temperature is more than
1000.degree. C., the insulating coating may be decomposed (i.e.,
the insulating properties may be impaired). Therefore, the heat
treatment temperature is set to 500 to 1000.degree. C. The
high-temperature treatment is performed under vacuum, an inert gas
atmosphere, or a reducing gas atmosphere in order to prevent
oxidation of the pre-molded body. A dust core having a true density
of 98% (7.7 g/cm.sup.3) may be produced as described above.
SUMMARY OF THE INVENTION
Technical Problem
[0011] However, the double molding/single sinter powder
metallurgical technique (Patent Literature 8) is very complex,
individualized, and difficult to implement as compared with the
other techniques, and significantly increases the production cost.
The double molding/single sinter powder metallurgical technique
subjects the pre-molded body to a heat treatment at 500.degree. C.
or more. The heat treatment is performed under such an atmosphere
in order to prevent a situation in which the quality of the dust
core deteriorates. Therefore, the double molding/single sinter
powder metallurgical technique is not suitable for mass production.
In particular, when using a vitreous film-coated magnetic metal
powder, the vitreous material may be modified/melted.
[0012] The above methods and systems (Patent Literatures 1 to 8)
can implement a sintering process at a relatively high temperature.
However, the details of the press molding step achieved using the
above methods and systems are unclear. Moreover, attempts to
achieve a further improvement in connection with the specification
and the functions of the press molding device, the relationship
between pressure and density, and an analysis of the limitations
thereof, have not been made.
[0013] As described above, a further increase in mechanical
strength has been desired along with a reduction in size and weight
of mechanical parts and the like, and there is an urgent need to
develop a method and a system that can reliably, stably, and
inexpensively produce a high-density green compact (particularly a
magnetic-core high-density green compact).
[0014] An object of the invention is to provide a mixed powder
high-density molding method and a mixed powder high-density molding
system that can produce a high-density green compact while
significantly reducing the production cost by press-molding a mixed
powder twice with a heating step interposed therebetween.
Solution to Problem
[0015] A green compact has been normally produced by a powder
metallurgical technique, and subjected to a sintering process
performed at a high temperature (e.g., 800.degree. C. or more).
However, such a high-temperature sintering process consumes a large
amount of energy (i.e., increases cost), and is not desirable from
the viewpoint of environmental protection.
[0016] The press molding process molds a mixed powder to have a
specific shape, and has been considered to be a mechanical process
that is performed in the preceding stage of the high-temperature
sintering process. The high-temperature sintering process is
exceptionally omitted when producing a magnetic-core green compact
used for an electromagnetic device (e.g., motor or transformer).
This aims at preventing a deterioration in magnetic properties that
may occur when the green compact is subjected to a high-temperature
process. Specifically, the resulting product inevitably has
unsatisfactory mechanical strength. Since the density of the
product is insufficient when mechanical strength is insufficient,
the product also has insufficient magnetic properties.
[0017] It is possible to significantly promote industrial
utilization and widespread use of a green compact if a high-density
green compact can be formed only by the press molding process
without performing the high-temperature sintering process. The
invention was conceived to actual production, based on studies of
the effectiveness of a lubricant during pressing, the compression
limit when using a lubricant powder, the spatial distribution of a
lubricant powder in a mixed powder, the spatial distribution of a
basic metal powder and a lubricant powder, the behavior of a basic
metal powder and a lubricant powder, and the final disposition
state of a lubricant, so that the efficiency of the mixed powder
filling operation may be improved and a reduction in size and
weight of the first die, the second die, and the like may be
realized taking account of actual production. The invention was
also conceived based on analysis of the characteristics (e.g.,
compression limit) of a normal press molding device, and the
effects of the density of a green compact on strength and magnetic
properties.
[0018] Specifically, the invention may provide a method that
transfers a mixed powder placed in a container cavity to a first
die, forms a mixed powder intermediate compressed body in the first
die by performing a first pressing step while maintaining a
lubricant in a powdery state, liquefies the lubricant by heating to
change the state of the lubricant in the mixed powder intermediate
compressed body, transfers the heated mixed powder intermediate
compressed body to a second die, and molds a high-density final
green compact having a density close to the true density by
performing a second press molding step. In other words, the
invention may provide a novel powder metallurgical technique (i.e.,
a powder metallurgical technique that performs two press molding
steps with a lubricant liquefaction step interposed therebetween)
that differs from a known powder metallurgical technique that
necessarily requires a high-temperature sintering process, and may
provide an epoch-making and practical method and system that can
reliably and stably produce a high-density green compact at low
cost.
[0019] (1) According to a first aspect of the invention, a mixed
powder high-density molding method includes:
[0020] filling a container cavity of a container with a mixed
powder that is a mixture of a basic metal powder and a
low-melting-point lubricant powder;
[0021] transferring the mixed powder in the container cavity to a
cavity of a first die that is positioned with respect to the
container;
[0022] applying a first pressure to the mixed powder in the cavity
of the first die to form a mixed powder intermediate compressed
body;
[0023] heating the first die and the mixed powder intermediate
compressed body to heat the mixed powder intermediate compressed
body to a melting point of the lubricant powder;
[0024] positioning the heated mixed powder intermediate compressed
body with respect to a second die together with the first die;
[0025] transferring the mixed powder intermediate compressed body
in the cavity of the first die to a cavity of the second die that
is positioned with respect to the first die; and
[0026] applying a second pressure to the mixed powder intermediate
compressed body in the cavity of the second die to form a
high-density mixed powder final compressed body.
[0027] (2) In the mixed powder high-density molding method as
defined in (1), the lubricant powder may have a low melting point
within the range of 90 to 190.degree. C.
[0028] (3) In the mixed powder high-density molding method as
defined in (1) or (2), the second die may be pre-heated to the
melting point before the mixed powder intermediate compressed body
is placed in the second die.
[0029] (4) In the mixed powder high-density molding method as
defined in (1) or (2), the first die may be pre-heated after the
mixed powder intermediate compressed body has been molded.
[0030] (5) In the mixed powder high-density molding method as
defined in (1) or (2), the second pressure may be selected to be
equal to the first pressure.
[0031] (6) According to a second aspect of the invention, a mixed
powder high-density molding system includes:
[0032] a mixed powder feeding device that can fill a container
cavity of a container that is positioned at a mixed powder filling
position with a mixed powder that is a mixture of a basic metal
powder and a low-melting-point lubricant powder;
[0033] a mixed powder transfer device that transfers the mixed
powder in the container cavity to a cavity of a first die that is
positioned with respect to the container;
[0034] a first press molding device that applies a first pressure
to the mixed powder in the cavity of the first die from a first
punch to form a mixed powder intermediate compressed body;
[0035] a heating device that heats the first die positioned at a
heating position and the mixed powder intermediate compressed body
to heat the mixed powder intermediate compressed body to a melting
point of the lubricant powder;
[0036] an intermediate green compact transfer device that transfers
the mixed powder intermediate compressed body in the cavity of the
first die to a second die positioned at a transfer relay
position;
[0037] a second press molding device that applies a second pressure
to the mixed powder intermediate compressed body in a cavity of the
second die positioned at a final compressed body molding position
to form a high-density mixed powder final compressed body; and
[0038] a product discharge device that can discharge the mixed
powder final compressed body in the cavity of the second die at a
product discharge position.
[0039] (7) The mixed powder high-density molding system as defined
in (6) may include:
[0040] a first die transfer device that is configured to transfer
the first die to position the first die with respect to the
container that is positioned at the mixed powder filling
position;
[0041] an unheated green compact transfer device that is configured
to transfer the first die from an intermediate green compact
molding position, to position the first die at the heating
position;
[0042] a heated green compact transfer device that is configured to
transfer the first die that holds the mixed powder intermediate
compressed body from the heating position, to position the first
die at the transfer relay position;
[0043] a second die transfer device that is configured to transfer
the second die that holds the mixed powder intermediate compressed
body from the transfer relay position, to position the second die
at the final green compact molding position;
[0044] a final green compact transfer device that is configured to
transfer the second die that holds the mixed powder final
compressed body from the final green compact molding position, to
position the second die at the product discharge position; and
[0045] a second die return transfer device that is configured to
transfer the second die that holds the mixed powder final
compressed body from the product discharge position, to position
the second die at a reception relay position.
[0046] (8) In the mixed powder high-density molding system as
defined in (6), the mixed powder filling position, the heating
position, and the transfer relay position may be separately
provided along a first circular path defined around a first axis,
the reception relay position, the final green compact molding
position, and the product discharge position may be separately
provided along a second circular path defined around a second axis,
the first die transfer device, the unheated green compact transfer
device, and the heated green compact transfer device may be
implemented by utilizing a first rotary table that can be rotated
around the first axis, and the second die transfer device, the
final green compact transfer device, and the second die return
transfer device may be implemented by utilizing a second rotary
table that can be rotated around the second axis.
[0047] (9) The mixed powder high-density molding system as defined
in (6) or (7) may further include a first pre-heating device that
pre-heats the first die.
[0048] (10) The mixed powder high-density molding system as defined
in (6) or (7) may further include a second pre-heating device that
pre-heats the second die.
Advantageous Effects of the Invention
[0049] The mixed powder high-density molding method as defined in
(1) can reliably and stably produce a high-density green compact
while significantly reducing the production cost. It is also
possible to improve the efficiency of the mixed powder filling
operation, and implement a reduction in size and weight of the
first die, the second die, and the like taking account of actual
production.
[0050] The mixed powder high-density molding method as defined in
(2) makes it possible to ensure that the lubricant produces a
sufficient lubricating effect during the first press molding step.
It is also possible to selectively use a wide variety of
lubricants.
[0051] The mixed powder high-density molding method as defined in
(3) makes it possible to further improve the fluidity of the melted
lubricant in all directions during the second press molding step,
and significantly reduce the friction resistance between the basic
metal particles, and the friction resistance between the particles
and the second die.
[0052] The mixed powder high-density molding method as defined in
(4) can shorten the production cycle time including the mixed
powder intermediate compressed body heating time.
[0053] The mixed powder high-density molding method as defined in
(5) makes it possible to easily implement the press molding step,
facilitate handling, and indirectly reduce the green compact
production cost.
[0054] The mixed powder high-density molding system as defined in
(6) can reliably implement the mixed powder high-density molding
method as defined in any one of (1) to (5), can be easily
implemented at low cost, and facilitates handling.
[0055] The mixed powder high-density molding system as defined in
(7) makes it possible to simplify the system configuration, and
promptly and smoothly transfer the green compact as compared with
the configuration as defined in (6).
Further
[0056] The mixed powder high-density molding system as defined in
(8) makes it possible to simplify the system as compared with the
configuration as defined in (7). It is also possible to simplify
the production line, and further facilitate handling.
[0057] The mixed powder high-density molding system as defined in
(9) can shorten the production cycle time including the mixed
powder intermediate compressed body heating time.
[0058] The mixed powder high-density molding method as defined in
(10) makes it possible to further improve the fluidity of the
melted lubricant in all directions during the second press molding
step, and significantly reduce the friction resistance between the
basic metal particles, and the friction resistance between the
basic metal particles and the second die.
[0059] Further features and advantageous effects of the invention
will become apparent from the following description.
BRIEF DESCRIPTION OF DRAWINGS
[0060] FIG. 1 is a diagram illustrating a high-density molding
method according to one embodiment of the invention.
[0061] FIG. 2 is a plan view illustrating a high-density molding
system according to a first embodiment of the invention.
[0062] FIG. 3 is a vertical cross-sectional view illustrating a
process from a mixed powder filling operation to an operation that
positions an intermediate green compact at a transfer relay
position (first embodiment).
[0063] FIG. 4 is a vertical cross-sectional view illustrating a
process from an operation that receives an intermediate green
compact to an operation that discharges a final green compact
(product) at a product discharge position (first embodiment).
[0064] FIG. 5 is a graph illustrating the relationship between
pressure and density obtained at the pressure (first embodiment),
wherein a broken line (characteristics A) indicates a molding state
using a first die, and a solid line (characteristics B) indicates a
molding state using a second die.
[0065] FIG. 6A is an external perspective view illustrating a final
green compact (intermediate green compact) according to the first
embodiment of the invention having a ring-like shape.
[0066] FIG. 6B is an external perspective view illustrating a final
green compact (intermediate green compact) according to the first
embodiment of the invention having a cylindrical shape.
[0067] FIG. 6C is an external perspective view illustrating a final
green compact (intermediate green compact) according to the first
embodiment of the invention having a narrow round shaft shape.
[0068] FIG. 6D is an external perspective view illustrating a final
green compact (intermediate green compact) according to the first
embodiment of the invention having a disc-like shape.
[0069] FIG. 6E is an external perspective view illustrating a final
green compact (intermediate green compact) according to the first
embodiment of the invention having a complex shape.
[0070] FIG. 7 is a vertical cross-sectional view illustrating a
process from a mixed powder filling operation to an operation that
positions an intermediate green compact at a transfer relay
position (second embodiment).
[0071] FIG. 8 is a vertical cross-sectional view illustrating a
process from an operation that receives an intermediate green
compact to an operation that discharges a final green compact
(product) at a product discharge position (second embodiment).
DESCRIPTION OF EMBODIMENTS
[0072] Exemplary embodiments of the invention are described in
detail below with reference to the drawings.
First Embodiment
[0073] As illustrated in FIGS. 1 to 6E, a mixed powder high-density
molding system 1 includes a mixed powder feeding device 10, a
container 23, a mixed powder transfer device (lower punch 37), a
first press molding device 30, a heating device 40, an intermediate
green compact transfer device (extrusion rod 50), a second press
molding device 60, and a product discharge device 70, and stably
and reliably implements a mixed powder high-density molding method
that includes a mixed powder-filling step (PR1) that fills a
container 23 with a mixed powder 100, a mixed powder transfer step
(PR2) that transfers the mixed powder 100 to a first die 31, an
intermediate green compact-forming step (PR3) that applies a first
pressure P1 to the mixed powder in the first die 31 to form a mixed
powder intermediate compressed body (hereinafter may be referred to
as "intermediate green compact 110"), a heating step (PR4) that
heats the intermediate green compact 110 to the melting point of
the lubricant powder, an intermediate green compact transfer step
(PR5) that transfers the heated intermediate green compact 110 to a
second die 61, a final green compact-forming step (PR6) that
applies a second pressure P2 to the intermediate green compact 110
in the second die 61 to form a high-density mixed powder final
compressed body (hereinafter may be referred to as "final green
compact 120"), and a product discharge step (PR7) (see (A) in FIG.
1).
[0074] In the first embodiment, the die is promptly and smoothly
transferred by providing a first die transfer device (first die
return transfer device) 81, an unheated green compact transfer
device 82, and a heated green compact transfer device 83 for
transferring the first die 31 to a mixed powder filling position
(intermediate green compact molding position) Z11, a heating
position Z12, and a transfer relay position Z13, and a second die
transfer device 91, a final green compact transfer device 92, and a
second die return transfer device 93 for transferring the second
die 61 to a transfer relay position (reception relay position Z21)
Z13, a final green compact molding position Z22, and a product
discharge position Z23.
[0075] The configuration is significantly simplified by integrating
the first die transfer device 81, the unheated green compact
transfer device 82, and the heated green compact transfer device 83
utilizing a first rotary table 80 illustrated in FIG. 2, and
integrating the second die transfer device 91, the final green
compact transfer device 92, and the second die return transfer
device 93 utilizing a second rotary table 90 illustrated in FIG.
2.
[0076] The mixed powder 100 is a mixture of the basic metal powder
and the low-melting-point lubricant powder. The basic metal powder
may include only one type of main metal powder, or may be a mixture
of one type of main metal powder and one or more types of alloying
component powder. The expression "low melting point" used herein in
connection with the lubricant powder refers to a temperature
(melting point) that is significantly lower than the melting point
(temperature) of the basic metal powder, and can significantly
suppress oxidation of the basic metal powder.
[0077] In FIG. 3 that illustrates the high-density molding system
1, the mixed powder feeding device 10 situated at the mixed powder
filling position Z11 on the upstream side of a high-density molding
line fills the container 23 with the mixed powder 100. The mixed
powder feeding device 10 is used when performing the mixed
powder-filling step (PR1) illustrated in FIG. 1 (see (A)). The
mixed powder feeding device 10 has a function of storing a constant
amount of the mixed powder 100, and a function of feeding a
constant amount of the mixed powder 100. The mixed powder feeding
device 10 can selectively move between the initial position (i.e.,
the left position in FIGS. 2 and 3) and a container device 20.
[0078] The container device 20 includes a main body 21 that has a
hollow cylindrical shape, and includes a stopper 22 provided in the
upper part, a container 23 that includes a stopper 25 provided in
the lower part, and has a container cavity 24 having a hollow
cylindrical shape at the center, and a spring 26 that biases the
container 23 upward, and is positioned at the mixed powder filling
position Z11. The lower punch 37 included in the first press
molding device 30 (first die 31) is slidingly fitted into the
container cavity 24, and the amount of the mixed powder 100 with
which the container 23 is filled is determined by the relative
position of the lower punch 37 with respect to the container 23 in
the vertical direction. The container 23 is held at the initial
position in the vertical direction (see (A) in FIG. 3) in a state
in which the stopper 25 engages the stopper 22 due to the biasing
force applied by the spring 26.
[0079] When the container 23 (container cavity 24) is filled with
the mixed powder 100, and the mixed powder 100 is transferred to
the cavity 33 of the die 32 that forms the first die 31 of the
first press molding device 30, the cavity 33 can be filled with a
large amount of mixed powder 100 in a state in which the mixed
powder 100 is compressed to some extent due to preliminary pressing
as compared with the case of filling the cavity 33 directly with
the mixed powder 100. It is also possible to easily transfer the
first die 31 (die 32) to the delivery relay position (heating
position Z12) together with the mixed powder intermediate
compressed body 110. This makes it possible to significantly
simplify the structure as compared with a related-art example in
which only the workpiece (green compact) is removed from the first
die 31, and transferred to the second die. The preliminary pressing
is implemented by the function of the mixed powder transfer device
(lower punch 37) (described in detail later).
[0080] Since it is important to uniformly and sufficiently fill the
first die 31 (die 32) with the mixed powder 100 from the container
23, the mixed powder 100 must be in a dry state. Specifically, the
internal space (cavity 33) of the first die 31 (die 32) is formed
to have a shape corresponding to the shape of the product. It is
necessary to uniformly and sufficiently fill the first die with the
mixed powder 100 in order to ensure the dimensional accuracy of the
intermediate green compact 110, even if the product has a complex
shape, or has a narrow part.
[0081] The configuration (dimensions and shape) of the final green
compact 120 (intermediate green compact 110) is not particularly
limited. FIGS. 6A to 6E illustrate examples of the configuration
(dimensions and shape) of the final green compact 120 (intermediate
green compact 110). FIG. 6A illustrates the final green compact 120
(intermediate green compact 110) having a ring-like shape, FIG. 6B
illustrates the final green compact 120 (intermediate green compact
110) having a cylindrical shape, FIG. 6C illustrates the final
green compact 120 (intermediate green compact 110) having a narrow
round shaft shape, FIG. 6D illustrates the final green compact 120
(intermediate green compact 110) having a disc-like shape, and FIG.
6E illustrates the final green compact 120 (intermediate green
compact 110) having a complex shape. In the first embodiment, the
intermediate green compact 110 (final green compact 120) has a
cylindrical shape (see FIGS. 3 and 6B), and the internal space
(cavity 33) of the first die 31 has a shape (configuration)
corresponding to the shape of the intermediate green compact 110
(final green compact 120).
[0082] A solid lubricant that is in a dry state (fine particulate)
at room temperature is used as the lubricant that is used to reduce
the friction resistance between the basic metal particles (a larger
part of the basic metal powder), and the friction resistance
between the basic metal powder and the inner side of the die. For
example, since the mixed powder 100 exhibits high viscosity and low
fluidity when using a liquid lubricant, it is difficult to
uniformly and sufficiently fill the first die with the mixed powder
100.
[0083] It is also necessary for the lubricant to be solid and
stably maintain a given lubricating effect during the intermediate
green compact molding step that is performed using the first die 31
(cavity 33) at room temperature while applying the first pressure
P1. The lubricant must stably maintain a given lubricating effect
even if the temperature has increased to some extent as a result of
applying the first pressure P1.
[0084] On the other hand, the melting point of the lubricant powder
must be significantly lower than the melting point of the basic
metal powder from the viewpoint of the relationship with the
heating step (PR4) (see FIG. 1) that is selectively performed after
the intermediate green compact molding step, and suppression of
oxidation of the basic metal powder.
[0085] The lubricant powder has a low melting point within the
range of 90 to 190.degree. C., for example. The lower-limit
temperature (90.degree. C.) is selected to be higher to some extent
than the upper-limit temperature (e.g., 80.degree. C.) of a
temperature range (e.g., 70 to 80.degree. C.) that is not reached
even if the temperature has increased to some extent during the
intermediate green compact molding step, while taking account of
the melting point (e.g., 110.degree. C.) of other metallic soaps.
This prevents a situation in which the lubricant powder is melted
(liquefied) and flows out during the intermediate green compact
molding step.
[0086] The upper-limit temperature (190.degree. C.) is selected to
be a minimum value from the viewpoint of lubricant powder
selectivity, and is selected to be a maximum value from the
viewpoint of suppression of oxidation of the basic metal powder
during the heating step. Specifically, it should be understood that
the lower-limit temperature and the upper-limit temperature of the
above temperature range (e.g., 90 to 190.degree. C.) are not
threshold values, but are boundary values.
[0087] This makes it possible to selectively use an arbitrary
metallic soap (e.g., zinc stearate or magnesium stearate) as the
lubricant powder. Note that a viscous liquid such as zinc octylate
cannot be used since the lubricant must be in a powdery state.
[0088] In the first embodiment, a zinc stearate powder having a
melting point of 120.degree. C. is used as the lubricant powder.
Note that the invention does not employ a configuration in which a
lubricant having a melting point lower than the die temperature
during press molding is used, and the press molding step is
performed while melting (liquefying) the lubricant (see Patent
Literature 7). If the lubricant is melted and flows out before
completion of molding of the intermediate green compact 110,
lubrication tends to be insufficient during the molding step, and
sufficient press molding cannot be performed reliably and
stably.
[0089] The lubricant powder is used in an amount that is selected
based on an empirical rule determined by experiments and actual
production. The lubricant powder is used in an amount of 0.08 to
0.23 wt % based on the total amount of the mixed power taking
account of the relationship with the intermediate green
compact-forming step (PR3). When the amount of the lubricant powder
is 0.08 wt %, the lubricating effect can be maintained when molding
the intermediate green compact 110. When the amount of the
lubricant powder is 0.23 wt %, the desired compression ratio can be
obtained when forming the intermediate green compact 110 from the
mixed powder 100.
[0090] A practical amount of the lubricant powder must be
determined taking account of the true density ratio of the
intermediate green compact 110 that is molded in the first die 31
while applying the first pressure P1, and a sweating phenomenon
that occurs in the second die. It is also necessary to prevent
dripping (dripping phenomenon) of the liquefied lubricant from the
die toward the outside that causes a deterioration in the work
environment.
[0091] In the first embodiment, since the true density ratio (i.e.,
the ratio with respect to the true density (=100%)) of the
intermediate green compact 110 is set to 80 to 90%, the ratio
(amount) of the lubricant powder is set to 0.1 to 0.2 wt %. The
upper limit (0.2 wt %) is determined from the viewpoint of
preventing the dripping phenomenon, and the lower limit (0.1 wt %)
is determined from the viewpoint of ensuring a necessary and
sufficient sweating phenomenon. The ratio (amount) of the lubricant
powder is very small as compared with the related-art example (1 wt
%), and the industrial applicability can be significantly
improved.
[0092] It is very important to prevent the dripping phenomenon
during actual production. A large amount of lubricant powder tends
to be mixed in the planning stage and the research stage in order
to prevent a situation in which the lubricant powder runs short
from the viewpoint of reducing frictional resistance during
pressing. Since whether or not a high density of more than 7.3
g/cm.sup.3 can be achieved is determined by trial and error, for
example, a situation in which excess lubricant is liquefied and
flows out from the die is not taken into consideration. The
dripping phenomenon is also not taken into consideration. Since
dripping of the liquefied lubricant increases the lubricant cost,
decreases productivity due to a deterioration in the work
environment, and increases the burden imposed on the workers, it is
impossible to ensure practical and widespread use without
preventing the dripping phenomenon.
[0093] When the intermediate green compact 110 obtained by
compressing the mixed powder 100 including 0.2 wt % of the
lubricant powder to have a true density ratio of 80% is heated to
the melting point of the lubricant powder in the heating step
(PR3), the powder lubricant scattered in the intermediate green
compact 110 is melted to fill the voids between the metal powder
particles, passes through the voids between the metal powder
particles, and uniformly exudes through the surface of the
intermediate green compact 110. Specifically, the sweating
phenomenon occurs. When the intermediate green compact 11 is
compressed in the second die by applying the second pressure P2,
the frictional resistance between the basic metal powder and the
inner wall of the cavity is significantly reduced.
[0094] The sweating phenomenon similarly occurs when using the
intermediate green compact 110 obtained by compressing the mixed
powder 100 including 0.1 wt % of the lubricant powder to have a
true density ratio of 90%, or when using the intermediate green
compact 110 obtained by compressing the mixed powder 100 including
more than 0.1 wt % and less than 0.2 wt % of the lubricant powder
to have a true density ratio of more than 80% and less than 90%. It
is also possible to prevent the dripping phenomenon.
[0095] This makes it possible to produce a green compact (e.g.,
magnetic core) that can be molded to have high density, and has
sufficient magnetic properties and mechanical strength, and prevent
a situation in which the die breaks. Moreover, the consumption of
the lubricant can be significantly reduced, and a situation in
which the liquid lubricant drips from the die can be prevented, so
that a good work environment can be achieved. Since the green
compact production cost can be reduced while improving
productivity, the industrial applicability can be significantly
improved.
[0096] Note that Patent Literatures 1 to 8 are silent about the
relationship between the lubricant content and the compression
ratio of the mixed powder 100, and the dripping phenomenon and the
sweating phenomenon that may occur depending on the lubricant
content. Patent Literature 5 (warm powder metallurgical technique)
discloses producing a primary molded body having a density ratio of
less than 76% in order to facilitate handling. However, Patent
Literature 5 does not disclose technical grounds relating to
high-density molding and items that can be implemented. In Patent
Literature 5, the secondary molded body (final green compact) is
molded after breaking the primary molded body (intermediate green
compact 120).
[0097] The first press molding device 30 applies the first pressure
P1 to the mixed powder 100 with which the first die 31 (cavity 33)
has been filled using the mixed powder feeding device 10, to form
the mixed powder intermediate compressed body 110. In the first
embodiment, the first press molding device 30 has a press
structure.
[0098] As illustrated in FIG. 3 (see (A) and (B)), the first die 31
includes a lower die (die 32 and lower punch 37) situated on the
side of a bolster, and an upper die (upper punch 36) situated on
the side of a slide (not illustrated in FIG. 3). The cavity 33 of
the die 32 has a shape (hollow cylindrical shape) corresponding to
the shape (cylindrical shape) of the intermediate green compact 110
(see FIG. 6B). The shape of the cavity 33 corresponds to the shape
of the container cavity 24. The upper punch 36 is moved upward and
downward by the slide (not illustrated in FIG. 3). The upper part
of the cavity 33 can be closed by the lower side of the upper punch
36 having a planar shape. Specifically, the upper punch 36 comes in
contact with most of the upper side of the die 32.
[0099] When the intermediate green compact 110 has the shape
illustrated in FIG. 6A, 6C, 6D, or 6E, the cavity 33 of the lower
die 32 of the first press molding device 30 also have a shape
corresponding to the configuration (shape) of the intermediate
green compact 110. When the intermediate green compact 110 has the
ring-like shape illustrated in FIG. 6A, the cavity 33 has a
ring-like tubular shape. When the intermediate green compact 110
has the circular rod-like shape illustrated in FIG. 6C, the cavity
33 has a shape that is similar to the cylindrical shape illustrated
in FIG. 6B, but is long in the vertical direction. When the
intermediate green compact 110 has the disc-like shape illustrated
in FIG. 6D, the cavity 33 has a shape that is similar to the
cylindrical shape illustrated in FIG. 6B, but is short (thin) in
the vertical direction. When the intermediate green compact 110 has
the complex shape illustrated in FIG. 6E, the cavity 33 has the
corresponding complex shape. This also applies to the cavity 63 of
the die 62 of the second press molding device 60 (second die
61).
[0100] The mixed powder transfer device transfers the mixed powder
100 placed in the container cavity to the cavity 33 of the first
die 31 that is positioned with respect to the container 23. The
mixed powder transfer device includes the lower punch 37, and
transfers the mixed powder 100 in cooperation with the upper punch
36 and the die 32.
[0101] Specifically, the upper punch 36 moves downward, and comes
in contact with the upper side of the die 32 that is held on the
first rotary table 80 (die holding section 85) (see (A) in FIG. 3).
The die 32 is thus moved downward. Since the lower side of the die
32 comes in contact with the upper side of the container 23, the
container 23 is moved downward. The position of the lower punch 37
in the vertical direction does not change. Therefore, the mixed
powder 100 placed in the container cavity 24 is moved upward by the
lower punch 37, and transferred to the die 32 (cavity 33) of the
first die 31. Since the vertical dimension of the container cavity
24 is larger than the vertical dimension of the cavity 33, the
mixed powder 100 placed in the container cavity 24 is transferred
to the cavity 33 while being preliminarily compressed.
Specifically, the mixed powder transfer device (upper punch 36 and
lower punch 37) can transfer the mixed powder 100 placed in the
container cavity 24 to the cavity 33 of the first die 31 that is
positioned with respect to the container 23.
[0102] The upper punch 36 compresses the mixed powder 100 in
cooperation with the lower punch 37 in a state in which the upper
punch 36 has moved downward to the lower position (lower-limit
position) (see (B) in FIG. 3) to obtain the intermediate green
compact 110. Specifically, the first press molding device 30
applies the first pressure P1 to the mixed powder 100 placed in the
cavity 33 of the first die 31 from the first punch (upper punch 36)
to obtain the mixed powder intermediate compressed body
(intermediate green compact 110). Since the mixed powder transfer
device (lower punch 37) is provided, a large amount of mixed powder
100 can be fed, and compressed as compared with the case of filling
the cavity 33 directly with the mixed powder 100, and the density
of the intermediate green compact 110 can be easily increased. It
is also possible to increase the dimensional accuracy of the
intermediate green compact 110. The upper punch 36 moves upward to
the upper position (see (C) in FIG. 3) when the slide moves upward.
In this case, the first rotary table 80 moves upward to the
upper-limit position. The container 23 is returned to the original
position (see (A) in FIG. 3) due to the spring 26.
[0103] The relationship between the pressure P (first pressure P1)
applied by the first press molding device 30 and the true density
ratio (density .rho.) of the resulting intermediate green compact
110 is described below with reference to FIG. 5. The horizontal
axis indicates the pressure P using an index. In the first
embodiment, the maximum capacity (pressure P) is 10 tons/cm.sup.2
(horizontal axis index: 100). Reference sign Pb indicates the die
breakage pressure at which the horizontal axis index is 140 (14
tons/cm.sup.2). The vertical axis indicates the true density ratio
(density .rho.) using an index. A vertical axis index of 100
corresponds to a true density ratio (density .rho.) of 97% (7.6
g/cm.sup.3).
[0104] In the first embodiment, the basic metal powder is a
magnetic-core vitreous insulating film-coated iron powder, the
lubricant powder is a zinc stearate powder (0.1 to 0.2 wt %), and
the first pressure P1 is selected so that the mixed powder
intermediate compressed body (intermediate green compact 110) can
be compressed to have a true density ratio of 80 to 90%
corresponding to a vertical axis index of 82 to 92 (corresponding
to a density .rho. of 6.24 to 7.02 g/cm.sup.3).
[0105] A vertical axis index of 102 corresponds to a density .rho.
of 7.75 g/cm.sup.3 and a true density ratio (density .rho.) of
99%.
[0106] Note that the basic metal powder may be a magnetic-core
iron-based amorphous powder (magnetic-core Fe--Si alloy powder), a
magnetic-core iron-based amorphous powder, a magnetic-core Fe--Si
alloy powder, a pure iron powder for producing mechanical parts, or
the like.
[0107] The density .rho. achieved by the first press molding device
30 increases along the characteristics A (curve) indicated by the
broken line as the first pressure P1 increases. The density .rho.
reaches 7.6 g/cm.sup.3 when the horizontal axis index (first
pressure is P1) is 100. The true density ratio is 97%. The density
.rho. increases to only a small extent even if the first pressure
P1 is further increased. The die may break if the first pressure P1
is further increased.
[0108] When the density .rho. achieved by pressing at the maximum
capacity of the press molding device (press) is not satisfactory,
it has been necessary to provide a larger press. However, the
density .rho. increases to only a small extent even if the maximum
capacity is increased by a factor of 1.5, for example. Therefore,
it has been necessary to accept a low density .rho. (e.g., 7.5
g/cm.sup.3) when using an existing press.
[0109] It is possible to achieve a major breakthrough if the
vertical axis index can be increased from 100 (7.6 g/cm.sup.3) to
102 (7.75 g/cm.sup.3) by directly utilizing an existing press.
Specifically, it is possible to significantly (hyperbolically)
improve magnetic properties, and also significantly improve
mechanical strength if the density .rho. can be increased by 2%.
Moreover, since a sintering process at a high temperature can be
made unnecessary, oxidation of the green compact can be
significantly suppressed (i.e., a decrease in magnetic core
performance can be prevented). Note that a different machine having
a press function may also be used.
[0110] In order to achieve the above breakthrough, the high-density
molding system 1 is configured so that the intermediate green
compact 110 formed by the first press molding device 30 is heated
to promote melting (liquefaction) of the lubricant, and the second
press molding device 60 then performs the second press molding
process. A high density (7.75 g/cm.sup.3) .rho. that corresponds to
a vertical axis index of 102 (see the characteristics B (straight
line) indicated by the solid line in FIG. 5) can be achieved by
pressing the intermediate green compact 110 using the second press
molding device 60. The details thereof are described later in
connection with the second press molding device 60.
[0111] The heating device 40 heats the first die 31 positioned at
the heating position Z12 and the mixed powder intermediate
compressed body (intermediate green compact 110) to increase the
temperature of the intermediate green compact 110 to the melting
point of the lubricant powder (see (D) and (E) in FIG. 3). The
heating device 40 includes a main body 41 that has a hollow
cylindrical shape, and includes a stopper 42 provided in the upper
part, an elevating rod 43 that includes a stopper 45 provided in
the lower part, and has a receiving section 44 that is provided in
the upper part and receives a heater 47, and a spring 48 that
biases the elevating rod 43 upward. The elevating rod 43 is held at
the initial position (see (D) in FIG. 3) in a state in which the
stopper 45 is retained by the stopper 42 due to the biasing force
applied by the spring 48.
[0112] The first die 31 (die 32) is then placed on (positioned with
respect to) the receiving section 44, and the first rotary table 80
moves downward to the lower-limit position (see (E) in FIG. 3). The
heater 47 is then turned ON to heat the intermediate green compact
110. The timing at which the heater 47 is turned ON can be changed.
For example, the heater 47 may be turned ON at a timing at which
the intermediate green compact 110 is placed (see (D) in FIG. 3).
The heater 47 may be always turned ON when it is allowed from the
viewpoint of the power supply conditions, the production cycle, and
the like.
[0113] The technical significance of the low-temperature heat
treatment performed by the first press molding device 30 is
described below in connection with the relationship with the first
press molding process. The powder mixture 100 with which the first
die 31 (die 32) is filled has an area in which the lubricant powder
is relatively thinly present (thin area), and an area in which the
lubricant powder is relatively densely present (dense area) in
connection with the basic metal powder. The friction resistance
between the basic metal particles, and the friction resistance
between the basic metal powder and the inner side of the die can be
reduced in the dense area. In contrast, the friction resistance
between the basic metal particles, and the friction resistance
between the basic metal powder and the inner side of the die
increase in the thin area.
[0114] When the first press molding device 30 applies a pressure to
the mixed powder, compressibility is predominant (i.e., compression
easily occurs) in the dense area due to low friction. In contrast,
compressibility is poor (i.e., compression slowly occurs) in the
thin area due to high friction. Therefore, a compression difficulty
phenomenon corresponding to the preset first pressure P1 occurs
(i.e., compression limit). In this case, when the fracture surface
of the intermediate green compact 110 removed from the die 32 is
magnified, the basic metal powder is integrally pressure-welded in
the dense area. However, the lubricant powder is also present in
the dense area. In the thin area, small spaces remain in the
pressure-welded basic metal powder, and almost no lubricant powder
is observed in the thin area.
[0115] Therefore, it is possible to form compressible spaces by
removing the lubricant powder from the dense area, and improve the
compressibility of the thin area by supplying the lubricant to the
spaces formed in the thin area.
[0116] Specifically, the lubricant powder is melted (liquefied),
and increased in fluidity by heating the intermediate green compact
110 subjected to the first press molding process to the melting
point (e.g., 120.degree. C.) of the lubricant powder. The lubricant
that flows out from the dense area penetrates through the
peripheral area, and is supplied to the thin area. This makes it
possible to reduce the friction resistance between the basic metal
particles, and compress the spaces that have been occupied by the
lubricant powder. It is also possible to reduce the friction
resistance between the basic metal powder and the inner side of the
die. Specifically, the second press molding process is performed
while promoting liquefaction of the lubricant.
[0117] The intermediate green compact transfer device (extrusion
rod 50) transfers the intermediate green compact 110 in the cavity
33 of the first die 31 (die 32) to the cavity 63 of the second die
61 (die 62) positioned at the transfer relay position Z13.
[0118] The intermediate green compact transfer device includes the
extrusion rod 50 that is positioned at the transfer relay position
Z13, and a transfer relay stage 55 (see (F) in FIG. 3 and (G) in
FIG. 4). The extrusion rod 50 can move (reciprocate) upward and
downward between the upper-limit position illustrated in FIG. 3
(see (F)) and the lower-limit position illustrated in FIG. 4 (see
(G)). The diameter of the extrusion rod 50 may be equal to the
diameter of the upper punch 66 illustrated in FIG. 4 (see (H)), or
may be smaller to some extent than the diameter of the upper punch
66.
[0119] (F) in FIG. 3 illustrates a state in which the second die 61
has been positioned on the upper side of the transfer relay stage
55, and the first die 31 has been moved downward from the
upper-limit position to the lower-limit position, and placed on the
upper side of the second die 61. The mixed powder intermediate
compressed body 110 in the cavity 33 of the first die 31 can be
transferred to the cavity 63 of the second die 61 by moving the
extrusion rod 50 downward in this state.
[0120] Specifically, the intermediate green compact 110 can be
transferred from the first die 31 to the second die 61 at the
transfer relay position Z13 (see (G) in FIG. 4). In other words,
the second die 61 receives the intermediate green compact 110 from
the first die 31 at the reception relay position Z21. Specifically,
the transfer relay position Z13 is the same as the reception relay
position Z21.
[0121] The second press molding device 60 (see (H) in FIG. 4)
performs the second press molding process that applies the second
pressure P2 to the intermediate green compact 110 placed in the
second die 61 to form the high-density mixed powder final
compressed body (final green compact 120).
[0122] The second die 61 includes a lower die (die 62 and lower
punch stage 67) situated on the side of a bolster, and an upper die
(upper punch 66) situated on the side of a slide (not illustrated
in FIG. 4), and is positioned at the final green compact molding
position Z22. The shape of the cavity 63 of the die 62 corresponds
to the shape of the cavity 33 of the first die 31 (die 32).
Specifically, the cavity 63 has a shape (hollow cylindrical shape)
corresponding to the shape (cylindrical shape) of the final green
compact 120 (see FIG. 6B). The upper part of the die 62 is slightly
large as compared with the die 32 in order to easily receive the
intermediate green compact 110.
[0123] The upper punch 66 is pushed into the cavity by the slide
(not illustrated in FIG. 4) that can move upward and downward
between the upper position and the lower position, and applies the
second pressure P2 to the intermediate green compact 110 to form
the high-density final green compact 120 (see (H) in FIG. 4). The
lower punch stage 67 has the same structure as that of the transfer
relay stage 55, but the lower punch stage 67 may further include
the lower punch 37 (see (B) in FIG. 3).
[0124] In the first embodiment, the maximum capacity (pressure P)
of the second press molding device 60 is the same as that (10
tons/cm.sup.2) of the first press molding device 30. The first
press molding device 30 and the second press molding device 60 may
be configured as a single press so that the die 31 and the die 61
are moved upward and downward in synchronization using the common
slide. The above configuration is economical, and can reduce the
production cost of the final green compact 120.
[0125] The relationship between the pressure (second pressure P2)
applied by the second press molding device 60 and the density .rho.
of the resulting final green compact 120 is described below with
reference to FIG. 5.
[0126] The density .rho. achieved by the second press molding
device 60 has the characteristics B indicated by the solid line in
FIG. 5. Specifically, the density .rho. does not gradually increase
as the second pressure P2 increases, differing from the case of
using the first press molding device 30 (see the characteristics A
(broken line)). More specifically, the density .rho. does not
increase until the final first pressure P1 (e.g., horizontal axis
index: 50, 75, or 85) during the first press molding step (PR3) is
exceeded. The density .rho. increases rapidly when the second
pressure P2 has exceeded the final first pressure P1. This means
that the second press molding step is performed continuously with
the first press molding step.
[0127] Therefore, the first press molding step need not be
performed in a state in which the first pressure P1 is necessarily
increased to a value (horizontal axis index: 100) corresponding to
the maximum capacity. This makes it possible to prevent unnecessary
time and energy consumption that may occur when the first press
molding step is continued after the compression limit has been
reached. Therefore, the production cost can be reduced. Moreover,
since it is possible to avoid overloaded operation in which the
horizontal axis index exceeds 100, breakage of the die does not
occur. This makes it possible to ensure easy and stable
operation.
[0128] The product discharge device 70 discharges the final green
compact 120 in the cavity 63 of the second die 61 to the outside at
the product discharge position Z23. The product discharge device 70
includes a discharge rod 71 that is positioned at the product
discharge position Z23, and a chute 73 that is incorporated in a
discharge stage 77 (see (I) in FIG. 4). The product discharge
device 70 discharges the final green compact 120 by pushing the
discharge rod 71 into the cavity 63.
[0129] Specifically, the discharge rod 71 can move upward and
downward between the upper-limit position (not illustrated in FIG.
4) and the lower-limit position (see (I) in FIG. 4). The diameter
of the discharge rod 71 is equal to the diameter of the upper punch
66 illustrated in FIG. 4 (see (H)), or smaller to some extent than
the diameter of the upper punch 66. The final green compact 120 in
the cavity 63 of the die 62 included in the second die 61 can be
discharged to the chute 73 by moving the discharge rod 71 downward
to the lower-limit position after the second die 61 has been
positioned on the upper side of the discharge stage 77.
[0130] Since the green compact transfer method determines the
production cycle, it is important to select an appropriate green
compact transfer method. It is important to select an appropriate
configuration and structure taking account of the equipment cost,
handling/maintenance, and the production cost. Note that the
workpiece is normally transferred linearly in related-art
examples.
[0131] The embodiments of the invention employ a rotary transfer
method that utilizes the rotary tables 80 and 90. In FIG. 2, the
mixed powder filling position Z11, the heating position Z12, and
the transfer relay position Z13 are situated separately from each
other along a first circular path R1 defined around a first axis
Z1. The reception relay position Z21, the final green compact
molding position Z22, and the product discharge position Z23 are
situated separately from each other along a second circular path R2
defined around a second axis Z2. In the first embodiment, the mixed
powder filling position Z11, the heating position Z12, and the
transfer relay position Z13 are situated at equal angles
(120.degree.), and the reception relay position Z21, the final
green compact molding position Z22, and the product discharge
position Z23 are situated at equal angles (120.degree.). The
transfer device is configured to utilize the first rotary table 80
that can be rotated around the first axis Z1, and the second rotary
table 90 that can be rotated around the second axis Z2.
[0132] The interval between the first axis Z1 and the second axis
Z2 is determined so that the transfer relay position (vertical
axis) Z13 and the reception relay position (vertical axis) Z21
coincide with each other. The first rotary table 80 can be
intermittently rotated around the first axis Z1 in a DRL
(counterclockwise) direction so that the die holding section 85 can
be positioned (stopped) at the mixed powder filling position Z11,
the heating position Z12, and the transfer relay position Z13.
[0133] The first rotary table 80 can be moved upward and downward
between the upper-limit position and the lower-limit position, and
can be stopped at the upper-limit position and the lower-limit
position. The upper-limit position refers to a position at which
the state illustrated in (A), (C), (D), and (F) in FIG. 3 occurs,
and the lower-limit position refers to a position at which the
state illustrated in (B), (E), and (F) in FIG. 3 and (G) in FIG. 4
occurs. The first rotary table 80 generates a pressing force that
moves the elevating rod 43 downward to the lower-limit position
against the biasing force applied by the spring 48 (see (D) and (E)
in FIG. 3).
[0134] As illustrated in FIG. 2, the first rotary table 80 is
supported by a transfer drive shaft 87 (rotation drive shaft 88 and
elevation shaft 89). The rotation angle of the rotation drive shaft
88 can be controlled by a servo motor, and the rotation drive shaft
88 can stop the first rotary table 80 at the set angle. Therefore,
the die holding section 85 can be accurately positioned at the
positions Z11, Z12, and Z13. The elevation shaft 89 that is
spline-connected to the rotation drive shaft 88 can selectively
move (position) the first rotary table 80 upward or downward to the
upper-limit position or the lower-limit position using a cylinder
device. The first die 31 (die 32) is attached to the die holding
section 85.
[0135] The second rotary table 90 can be intermittently rotated
around the second axis Z2 in a DRR (clockwise) direction so that
the die holding section 95 can be positioned at the reception relay
position Z21, the final green compact molding position Z22, and the
product discharge position Z23. The second rotary table 90 can stop
the die holding section 95 at the reception relay position Z21, the
final green compact molding position Z22, and the product discharge
position Z23. The transfer rotary shaft 97 is used only for
rotation. In the first embodiment, the transfer rotary shaft 97
does not have an elevation function. Specifically, the second
rotary table 90 is maintained at a given height (i.e., see (F) in
FIG. 3 and (G), (H), and (I) in FIG. 4). The second die 61 (die 62)
is attached to the die holding section 95.
[0136] In the first embodiment, a plurality of (three) die holding
sections 85 are provided to the first rotary table 80 at equal
angles (120.degree.), and the first die 31 is attached to each die
holding section 85. Likewise, a plurality of (three) die holding
sections 95 are provided to the second rotary table 90 at equal
angles (120.degree.), and the second die 61 is attached to each die
holding section 95.
[0137] The rotary tables 80 and 90 are formed using a
large-diameter disc. Note that the rotary tables 80 and 90 may be
formed by disposing a plurality of bracket-like members at equal
angles (120.degree.) so that each bracket-like member can rotate
around the first axis Z1 or the second axis Z2 in
synchronization.
[0138] The first die transfer device 81, the unheated green compact
transfer device 82, and the heated green compact transfer device 83
are integrated using the first rotary table 80 (first die transfer
device 81, unheated green compact transfer device 82, and heated
green compact transfer device 83). The first die transfer device
81, the unheated green compact transfer device 82, and the heated
green compact transfer device 83 transfer the first die 31 while
transferring the die holding section 85 along the first circular
path R1 by utilizing intermittent rotation of the first rotary
table 80 around the first axis Z1 in the DRL direction. The first
rotary table 80 is moved upward and downward when the first die 31
is transferred.
[0139] The first die transfer device 81 transfers the first die 31
situated at the transfer relay position Z13 (see (F) in FIG. 3) to
the mixed powder filling position Z11 (see (A) in FIG. 3), and
positions the first die 31 relative to the container 23 situated at
the mixed powder filling position Z11. The first die transfer
device 81 moves the first die 31 upward from the lower-limit
position to the upper-limit position during the above transfer
operation. The first die transfer device 81 that returns the first
die 31 from the transfer relay position Z13 to the mixed powder
filling position Z11 may be referred to as "first die return
transfer device".
[0140] The unheated green compact transfer device 82 transfers the
first die 31 situated at the intermediate green compact molding
position (mixed powder filling position Z11) (see (B) in FIG. 3)
from the intermediate green compact molding position (mixed powder
filling position Z11) to the heating position Z12 (see (E) in FIG.
3), and positions the first die 31 at the heating position Z12. The
first die 31 is moved upward from the lower-limit position (see (B)
in FIG. 3) to the upper-limit position (see (C) in FIG. 3) during
the above operation. The first die 31 is then transferred to the
heating position Z12 (see (D) in FIG. 3) due to rotation of the
first rotary table 80. The first die 31 is placed (positioned) on
the receiving section 44 situated at the upper-limit position, and
moved downward to the lower-limit position due to downward movement
of the elevating rod 43.
[0141] The heated green compact transfer device 83 transfers the
first die 31 that holds the mixed powder intermediate compressed
body 110 from the heating position Z12 (see (E) in FIG. 3) to the
transfer relay position Z13 (see (F) in FIG. 3). The first die 31
is moved upward to the upper-limit position due to upward movement
of the first rotary table 80, positioned at the transfer relay
position Z13, and moved downward to the lower-limit position.
[0142] The second die transfer device 91, the final green compact
transfer device 92, and the second die return transfer device 93
are integrated using the second rotary table 90 (second die
transfer device 91, final green compact transfer device 92, and
second die return transfer device 93). The second die transfer
device 91, the final green compact transfer device 92, and the
second die return transfer device 93 transfer the second die 61
while transferring the die holding section 95 along the second
circular path R2 by utilizing intermittent rotation of the second
rotary table 90 around the second axis Z2 in the DRR direction.
[0143] The second die transfer device 91 transfers the second die
61 that is situated at the reception relay position Z21 (see (G) in
FIG. 4) and holds the intermediate green compact 110 to the final
green compact molding position Z22 (see (H) in FIG. 4), and
positions the second die 61 on the lower punch stage 67 situated at
the final green compact molding position Z22. The second rotary
table 90 is rotated by 120.degree..
[0144] The final green compact transfer device 92 transfers the
second die 61 that holds the final green compact 120 from the final
green compact molding position Z22 (see (H) in FIG. 4), and
positions the second die 61 at the product discharge position Z23
(see (I) in FIG. 4). The second rotary table 90 is rotated by
120.degree. in the DRR direction.
[0145] The second die return transfer device 93 transfers the
second die 61 that has discharged the final green compact 120 from
the product discharge position Z23 to the reception relay position
(product discharge position Z23) (see (F) in FIG. 3), and positions
the second die 61 at the reception relay position (product
discharge position Z23). Specifically, the second die 61 is
returned prior to the next cycle.
[0146] The green compact transfer device has the rotary table
structure, and transfers the green compact along the circular path.
The green compact is transferred directly from the first die 31 to
the second die 61 (see (F) in FIG. 3 and (G) in FIG. 4). According
to this rotary transfer/direct transfer method, it is possible to
prevent a situation in which the workpiece falls, prevent collision
of the workpiece with the slide or the die, and promptly and
accurately transfer the workpiece, as compared with a related-art
transfer method that linearly transfers the workpiece using a robot
or a transfer device. The mixed powder 100 is also transferred as
described above (see (A) and (B) in FIG. 3).
[0147] The mixed powder high-density molding system 1 according to
the first embodiment implements the high-density molding method as
described below. The process is described below referring to the
steps illustrated in (A) in FIG. 1 and the transfer operation
illustrated in (B) in FIG. 1. Note that the reference sign (e.g.,
Z22) in parentheses included in the block corresponding to each
step refers to the position (e.g., final green compact molding
position) at which each step is performed.
<Preparation of Mixed Powder>
[0148] The basic metal powder (magnetic-core vitreous insulating
film-coated iron powder) and the lubricant powder (zinc stearate
powder) (0.2 wt %) are mixed to prepare the mixed powder 100 in a
dry state. A given amount of the mixed powder 100 is fed to the
mixed powder feeding device 10 (step PR0 in FIG. 1).
<Filling with Mixed Powder>
[0149] The mixed powder feeding device 10 is moved from a given
position (not illustrated in the drawings) to a supply position
(indicated by the dotted line in FIG. 3 (see (A)) at a given
timing. The inlet of the mixed powder feeding device 10 is opened,
and the container device 20 (empty container cavity 24) is filled
with the mixed powder 100 (step PR1 in FIG. 1). The container
device 20 (empty container cavity 24) can be filled with the mixed
powder 100 within 2 seconds, for example. The inlet is closed after
the filling, and the mixed powder feeding device 10 is returned to
the given position. The first die transfer device 81 returns the
first die 31 (die 32) from the state illustrated in (F) in FIG. 3
to the state illustrated in (A) in FIG. 3.
<Transfer of Mixed Powder>
[0150] When the upper punch 36 is moved downward in the state
illustrated in (A) in FIG. 3, the first die 31 is moved downward
together with the first rotary table 80. The upper punch 36 moves
the first die 31 and the container 23 downward against the biasing
force applied by the spring 26. Since the lower punch 37 is
positioned at a given position, the mixed powder 100 in the
container 23 is transferred to the cavity 33 of the first die 31
(die 32) while being preliminarily compressed. Specifically, the
mixed powder transfer device (lower punch 37) operates.
<Molding of Intermediate Green Compact>
[0151] The upper punch 36 is moved downward to apply the first
pressure P1 to the mixed powder 100 in the die 32 (cavity 33). The
first press molding process (step PR3 in FIG. 1) is thus performed
(see (B) in FIG. 3). The powdery (solid) lubricant produces a
sufficient lubricating effect. The density .rho. of the compressed
intermediate green compact 110 increases along the characteristics
A (dotted line) illustrated in FIG. 5. When the first pressure P1
has reached a pressure (3.0 tons/cm.sup.2) corresponding to a
horizontal axis index of 30, for example, the true density ratio
increases to 85% (i.e., the density rho increases to 6.63
g/cm.sup.3) (vertical axis index: 87). The press molding process is
performed for 8 seconds, for example. The intermediate green
compact 110 thus obtained remains in the cavity 33 of the first die
31.
<Transfer of Intermediate Green Compact>
[0152] The unheated green compact transfer device 82 starts to
operate (see (C) in FIG. 3). After the upper punch 36 has been
moved upward to the upper position, the first die 31 that holds the
intermediate green compact 110 is moved upward to the upper-limit
position (i.e., a position lower than the upper position of the
upper punch 36). The first die 31 and the intermediate green
compact 110 are transferred from the intermediate green compact
molding position (mixed powder filling position Z11) to the heating
position Z12 (see (D) in FIG. 3). The first rotary table 80 is
rotated by 120.degree. in the DRL direction (see FIG. 2). The
container 23 is returned to the initial position (upper-limit
position) (see (A) in FIG. 3) from the lower-limit position for
performing the next cycle. The container 23 is returned by the
biasing force applied by the spring 26. The first die 31 is
positioned on the heating device 40 (receiving section 44) that is
situated at the heating position Z12 and set at the upper-limit
position (i.e., a position lower than the upper-limit position of
the first die 31) (see (D) in FIG. 3). The elevating rod 43 is
moved downward to position the first die 31 at the lower-limit
position (heating position) (see (E) in FIG. 3).
<Heating>
[0153] When the receiving section 44 has been moved downward to the
lower-limit position (i.e., a position lower than the lower-limit
position of the first die 31), the heating device 40 starts to
operate (i.e., the heater 47 is turned ON). The intermediate green
compact 110 in the die 32 is heated to the melting point (e.g.,
120.degree. C.) of the lubricant powder (step PR4 in FIG. 1).
Specifically, the lubricant is melted, and the distribution of the
lubricant in the intermediate green compact 110 becomes uniform.
The heating time is 8 to 10 seconds, for example. The timing at
which the heater 47 is turned ON can be changed. For example, the
heater 47 may be turned ON in the state illustrated in (D) in FIG.
3.
<Transfer/Reception of Heated Intermediate Green Compact>
[0154] The heated green compact transfer device 83 starts to
operate after completion of the heating step. The heated
intermediate green compact 110 is transferred from the heating
position Z12 to the transfer relay position Z13 in a state in which
the intermediate green compact 110 is placed in the first die 31
(see (E) and (F) in FIG. 3). Specifically, the first rotary table
80 is rotated by 120.degree. in the DRL direction (see FIG. 2).
Since the intermediate green compact 110 is transferred without
being exposed to the air, a decrease in the temperature of the
intermediate green compact 110 occurs to only a small extent. The
first die 31 is placed on the second die 61 that is positioned on
the transfer relay stage 55. The intermediate green compact
transfer device (extrusion rod 50) starts to operate. Specifically,
the extrusion rod 50 is moved downward from the upper position (see
(F) in FIG. 3) to transfer the heated intermediate green compact
110 placed in the first die 31 to the second die 61 (step PR5 in
FIG. 1). The extrusion rod 50 is returned to the upper position
after completion of transfer.
<Return Transfer of First Die>
[0155] When the intermediate green compact 110 has been transferred
from the first die 31 to the second die 61, the first die transfer
device 81 moves the first die 31 upward to the upper-limit position
(see (F) in FIG. 3), and returns the first die 31 from the transfer
relay position Z13 to the mixed powder filling position Z11 (see
(A) in FIG. 3). The first die 31 is thus positioned on the
container 23. In this case, the first rotary table 80 is rotated by
120.degree. in the DRL direction.
<Transfer of Intermediate Green Compact>
[0156] The second die transfer device 91 also starts to operate.
The second die transfer device 91 transfers the intermediate green
compact 110 received at the reception relay position Z21 (transfer
relay position Z13) (see (F) in FIG. 3) from the reception relay
position Z21 (see (G) in FIG. 4) to the final green compact molding
position Z22 (see (H) in FIG. 4). The intermediate green compact
110 is transferred in a state in which the intermediate green
compact 110 is placed in the second die 61. The second rotary table
90 is rotated by 120.degree. in the DRR direction (see FIG. 2).
<Molding of Final Green Compact>
[0157] The upper punch 66 is moved downward from the upper position
together with the slide (not illustrated in the drawings) (see (H)
in FIG. 4). The second pressure P2 is applied to the lower punch
stage 67 in a stationary state. Specifically, the second pressure
P2 is applied to the heated intermediate green compact 110 in the
die 62 (cavity 63). The liquid lubricant produces a sufficient
lubricating effect. The sweating phenomenon in which the lubricant
flows in all directions occurs during the press molding process. It
is also possible to efficiently reduce the friction resistance
between the basic metal particles, and the friction resistance
between the basic metal particles and the die. The density .rho. of
the compressed intermediate green compact 110 increases along the
characteristics B (solid line) illustrated in FIG. 5. Specifically,
when the second pressure P2 has exceeded a horizontal axis index of
30 (3.0 tons/cm.sup.2), for example, the density .rho. rapidly
increases from 6.63 g/cm.sup.3 to a value (7.75 g/cm.sup.3)
corresponding to a vertical axis index of 102. When the second
pressure P2 is increased to a horizontal axis index of 100 (10
tons/cm.sup.2), the density .rho. (7.75 g/cm.sup.3) becomes uniform
over the entire green compact. The second press molding process is
performed for 8 seconds, for example, to obtain the final green
compact 120 that has been molded in the die 41 (step PR6 in FIG.
1). The upper die 66 is then moved upward to the upper position
using the slide. The vitreous material included in the final green
compact 120 having a density .rho. of 7.75 g/cm.sup.3 corresponding
to a vertical axis index of 102 is not modified/melted since the
melting point of the lubricant powder was low. Therefore, a
high-quality magnetic-core green compact that can reduce eddy
current loss and improve magnetic flux density can be efficiently
produced.
<Transfer of Final Green Compact>
[0158] The final green compact transfer device 92 transfers the
second die 61 that holds the final green compact 120 from the final
green compact molding position Z22 (see (H) in FIG. 4) to the
product discharge position Z23 (see (I) in FIG. 4). The second die
61 is positioned at the product discharge position Z23 (discharge
stage 77). The discharge rod 71 stands by at the upper position
during this period. The second rotary table 90 is rotated by
120.degree. in the DRR direction.
<Product Discharge>
[0159] The product discharge device 70 starts to operate. The
discharge rod 71 is moved downward from the upper position to push
the final green compact 120 in the second die 61 into the chute 73
(see (I) in FIG. 4). The product is thus discharged (step PR7 in
FIG. 1). The discharge rod 71 is then moved upward to the upper
position, and stands by.
<Return Transfer of Second Die>
[0160] The second die return transfer device 93 transfers the
second die 61 from the product discharge position Z23 (see (I) in
FIG. 4) to the reception relay position Z21 (transfer relay
position Z13) (see (F) in FIG. 3). The second rotary table 90 is
rotated by 120.degree. in the DRR direction. Since the second
rotary table 90 is not moved upward and downward, prompt return
transfer can be implemented.
<Production Cycle>
[0161] According to the high-density molding method, since the
first press molding process, the heating process, and the second
press molding process can be performed in synchronization on the
metal powder 100 (mixed powder 100) that is sequentially fed, the
high-density green compact (final green compact 120) can be
produced in a cycle time of 12 to 14 seconds (i.e., maximum heating
time (10 seconds)+green compact transfer time (e.g., 2 to 4
seconds)). This makes it possible to remarkably reduce the
production time as compared with the related-art example
(high-temperature sintering time: 30 minutes or more). For example,
it is possible to ensure a stable supply of automotive parts that
have a reduced size and weight, a complex shape, and high
mechanical strength, or electromagnetic device parts that exhibit
excellent magnetic properties and mechanical strength, and
significantly reduce the production cost.
[0162] The high-density molding method according to the first
embodiment can reliably and stably produce a high-density green
compact while significantly reducing the production cost by filling
the container 23 with the mixed powder 100, transferring the mixed
powder 100 to the first die 31, applying the first pressure P1 to
the mixed powder 100 to form the intermediate green compact 110,
heating the intermediate green compact 110 to the melting point
(e.g., 120.degree. C.) of the lubricant powder, placing the
intermediate green compact 110 in the second die 61, and applying
the second pressure P2 to the intermediate green compact 110 to
form the final green compact 120. It is also possible to improve
the efficiency of the operation that fills the die with the mixed
powder 100, and reduce the weight of the first die 31 and the like
taking account of actual production.
[0163] Since a sintering process that is performed at a high
temperature for a long time can be made unnecessary, oxidation of
the green compacts 110 and 120 can be significantly suppressed
while minimizing energy consumption, and significantly reducing the
production cost. This is advantageous from the viewpoint of
environmental protection.
[0164] Since the lubricant powder has a low melting point within
the range of 90 to 190.degree. C., it is possible to ensure that
the lubricant powder produces a sufficient lubricating effect
during the first press molding step. It is also possible to
suppress oxidation, and enhance the selectivity of the
lubricant.
[0165] Since the second die 61 can be pre-heated to the melting
point of the lubricant powder before the second die 61 receives the
intermediate green compact 110, it is possible to improve the
fluidity of the melted lubricant in all directions during the
second press molding step. This makes it possible to significantly
reduce the friction resistance between the basic metal particles,
and the friction resistance between the basic metal particles and
the second die 61.
[0166] Since the first die 31 can be pre-heated after the
intermediate green compact 110 has been molded, it is possible to
shorten the production cycle time including the time in which the
intermediate green compact 110 is heated.
[0167] Since the second pressure P2 can be set to be equal to the
first pressure P1, it is possible to further improve the fluidity
of the melted lubricant in all directions during the press molding
step. This makes it possible to significantly reduce the friction
resistance between the basic metal particles, and the friction
resistance between the basic metal particles and the second die 61.
And it is possible to easily implement the press molding step,
facilitate handling, indirectly reduce the green compact production
cost, and easily implement the system based on a single press, for
example.
[0168] The high-density molding method according to the first
embodiment can efficiently and stably produce a magnetic core part
that exhibits magnetic properties corresponding to the type of
basic metal powder, using a magnetic-core vitreous insulating
film-coated iron powder, a magnetic-core iron-based amorphous
powder, or a magnetic-core Fe--Si alloy powder as the basic metal
powder.
[0169] It has been impossible to achieve a density equal to or
higher than that corresponding to a vertical axis index of 100,
taking account of the capacity (horizontal axis index=100 (see FIG.
5)) of a related-art system (e.g., press). According to the first
embodiment, however, it is possible to achieve a density equal to
or higher than that corresponding to a vertical axis index of 102
using an identical (existing) system. This fact achieves a major
breakthrough in the technical field.
[0170] Since the high-density molding system 1 includes the mixed
powder feeding device 10, the mixed powder transfer device (lower
punch 37), the first press molding device 30, the heating device
40, the intermediate green compact transfer device (extrusion rod
50), the second press molding device 60, and the product discharge
device 70, it is possible to reliably and stably implement the
high-density molding method. Moreover, the high-density molding
system 1 facilitates handling.
[0171] Since the high-density molding system 1 includes the first
die transfer device 81, the unheated green compact transfer device
82, and the heated green compact transfer device 83 that transfer
the first die 31, and also includes the second die transfer device
91, the final green compact transfer device 92, and the second die
return transfer device 93 that transfer the second die 61, the
system configuration can be simplified, and the green compact can
be transferred promptly and smoothly.
[0172] Since the mixed powder filling position Z11, the heating
position Z12, and the transfer relay position Z13 are separately
provided along the first circular path R1 defined around the first
axis Z1, the reception relay position Z21, the final green compact
molding position Z22, and the product discharge position Z23 are
separately provided along the second circular path R2 defined
around the second axis Z2, the first die transfer device 81, the
unheated green compact transfer device 82, and the heated green
compact transfer device 83 are implemented by utilizing the first
rotary table 80 that can be rotated around the first axis Z1, and
the second die transfer device 91, the final green compact transfer
device 92, and the second die return transfer device 93 are
implemented by utilizing the second rotary table 90 that can be
rotated around the second axis Z2, the system configuration can be
further simplified. It is also possible to simplify the production
line, and further facilitate handling. It is possible to implement
prompt transfer and a reduction in size and weight as compared with
a related-art linear transfer method.
Second Embodiment
[0173] FIGS. 7 and 8 illustrate a second embodiment of the
invention. The basic configuration and function are the same as
those described above in connection with the first embodiment (see
FIGS. 1 to 6E). In the second embodiment, a second pre-heating
device 64 is provided to the second die 61 (die 62) included in the
second press molding device 60, and a first pre-heating device 34
is provided to the first die 31 (die 32) included in the first
press molding device 30.
[0174] Specifically, a high-density molding system according to the
second embodiment is configured so that the second die 61 can be
pre-heated, and a decrease in temperature of the heated
intermediate green compact 110 can be prevented. Moreover, the
intermediate green compact 110 can be preliminarily heated while
pre-heating the first die 31. Although the first pre-heating device
34 and the second pre-heating device 64 are provided in the second
embodiment, only the first pre-heating device 34 or the second
pre-heating device 64 may be provided depending on the temperature
of the work environment and the like.
[0175] FIG. 7 (FIG. 8) corresponds to FIG. 3 (FIG. 4) according to
the first embodiment. FIGS. 1, 2, 5, and 6A to 6E are similarly
applied to the second embodiment.
[0176] The high-density molding method according to the invention
can be implemented without pre-heating the second die 61 as long as
the temperature of the heated intermediate green compact 110 has
not decreased to a low temperature outside a specific temperature
range until the second pressure P2 is applied to the intermediate
green compact 110 in the second die 61. It may be unnecessary to
preliminary heat the intermediate green compact 110 by pre-heating
the first die 31 before performing the heating step. In such a
case, a pre-heating function for pre-heating the second die 61 and
the first die 31 may not be provided.
[0177] However, the temperature of the heated intermediate green
compact 110 may decrease before molding the final green compact 120
when the heat capacity of the intermediate green compact 110 is
small, or when the transfer time or the transfer path until the
second die 61 is reached is long, or depending on the composition
of the mixed powder 100 or the configuration of the intermediate
green compact 110. In such a case, the desirable molding effect can
be obtained by pre-heating the second die 61.
[0178] As illustrated in FIG. 8, the second pre-heating device
(heater) 64 that can be adjusted in heating temperature is provided
to the second die 61 (die 62). The second pre-heating device 64
heats (pre-heats) the second die 61 to the melting point (e.g.,
120.degree. C.) of the lubricant powder (zinc stearate) before the
intermediate green compact 110 is received (placed). Therefore, the
heated intermediate green compact 110 can be placed in the second
die 61 without allowing the intermediate green compact 110 to cool.
This makes it possible to ensure a lubricating effect while
preventing a situation in which the lubricant that has been melted
(liquefied) solidifies.
[0179] The pre-heating step is performed before the final green
compact-forming step (PR6) described above in connection with the
first embodiment. The second pre-heating device 64 can heat the
second die 61 until the final green compact 120 is obtained.
Therefore, the fluidity of the melted lubricant in all directions
can be further improved during press molding, and the friction
resistance between the basic metal particles, and the friction
resistance between the basic metal particles and the second die 61
(die 62), can be significantly reduced.
[0180] When the composition of the mixed powder 100 or the
configuration of the intermediate green compact 110 is unique, or
when the heat capacity of the mixed powder intermediate compressed
body 110 is large, or when it is difficult to provide a large
heating device, or when the temperature of the work environment is
low, it may take time to heat the intermediate green compact 110.
In such a case, it is desirable to pre-heat the first die 31. In
the second embodiment, the first die 31 is pre-heated for the above
reason.
[0181] Therefore, the first pre-heating device (heater) 34 that can
be adjusted in heating temperature is provided to the first die 31
(die 32) so that the first die 31 can be pre-heated in the state
illustrated in (A) in FIG. 7 (corresponding to (A) in FIG. 3).
Specifically, the first pre-heating device 34 can be used as the
heating device 40. This makes it possible to reduce the heating
time of the heating device 40, and shorten the production cycle.
Specifically, since the outer circumferential surface and the lower
side of the intermediate green compact 110 can be heated by the
heaters 47 and 34 (see (D) and (E) in FIG. 7), the intermediate
green compact 110 can be promptly heated at an average
temperature.
[0182] The pre-heating step is performed after the intermediate
green compact-forming step (PR3) described above in connection with
the first embodiment. In the second embodiment, the intermediate
green compact 110 can be pre-heated until the intermediate green
compact 110 is transferred to the heating device 40.
[0183] In the second embodiment, the first pre-heating device 34
and the second pre-heating device 64 are implemented using an
electric heating method (electric heater). Note that the first
pre-heating device 34 and the second pre-heating device 64 may also
be implemented using a hot oil/hot water circulation heating device
or the like.
[0184] The second embodiment can thus achieve the same advantageous
effects as those achieved by the first embodiment. Moreover, since
the second die 61 can be pre-heated, it is possible to further
improve the fluidity of the melted lubricant in all directions
during the press molding step that applies the second pressure P2,
and significantly reduce the friction resistance between the basic
metal particles, and the friction resistance between the basic
metal particles and the second die 61.
[0185] Since the first die 31 can be pre-heated, it is possible to
reduce the load imposed on the heating device 40, and promptly
increase the temperature of the intermediate green compact 110 by
pre-heating the first die 31. This makes it possible to shorten the
production cycle.
REFERENCE SIGNS LIST
[0186] 1 High-density molding system [0187] 10 Mixed powder feeding
device [0188] 20 Container device [0189] 23 Container [0190] 30
First press molding device [0191] 31 First die [0192] 34 First
pre-heating device [0193] 37 Lower punch (mixed powder transfer
device) [0194] 40 Heating device [0195] 50 Extrusion rod
(intermediate green compact transfer device) [0196] 60 Second press
molding device [0197] 61 Second die [0198] 64 Second pre-heating
device [0199] 70 Workpiece discharge device [0200] 80 First rotary
table (first die transfer device, unheated green compact transfer
device, and heated green compact transfer device) [0201] 90 Second
rotary table (second die transfer device, final green compact
transfer device, and second die return transfer device) [0202] 100
Mixed powder [0203] 110 Intermediate green compact (mixed powder
intermediate compressed body) [0204] 120 Final green compact (mixed
powder final compressed body)
* * * * *