U.S. patent application number 09/845049 was filed with the patent office on 2001-12-20 for injection molding method of metal mold.
Invention is credited to Hayashi, Yuji, Koda, Toshiyasu, Miyagawa, Mamoru, Takizawa, Kiyoto.
Application Number | 20010052405 09/845049 |
Document ID | / |
Family ID | 18639838 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010052405 |
Kind Code |
A1 |
Takizawa, Kiyoto ; et
al. |
December 20, 2001 |
Injection molding method of metal mold
Abstract
The invention has an object to permit to mold metal molds having
a thixothropic structure by melting, agitating and weighing,
injection molten metal in a melting vessel by combining separately
functioning agitation means and injection means. The invention
consists in supply granular metal material in a fusion vessel 11
having a weighing chamber 17 by a cylinder of required length
communicating with a nozzle port at the extremity section,
including rotatively an agitation means 21 inside, and wherein an
injection means 22 whose extremity section is formed into an
injection plunger 30 is inserted advanceably and retractably into
the center section of this agitation means 21. The metal material
is heat melted by an external heat. The molten metal material is
accumulated in the fusion vessel by homogenizing by the agitation
means 21. A part of molten metal material is injection charged into
a die at a temperature equal or superior to the solid phase line
temperature and equal or inferior to the liquid phase line
temperature, and molded into a metal mold having a thixothropic
structure.
Inventors: |
Takizawa, Kiyoto;
(Nagano-ken, JP) ; Koda, Toshiyasu; (Nagano-ken,
JP) ; Hayashi, Yuji; (Nagano-ken, JP) ;
Miyagawa, Mamoru; (Nagano-ken, JP) |
Correspondence
Address: |
WEINGARTEN, SCHURGIN, GAGNEBIN
& HAYES, LLP
TEN POST OFFICE SQUARE
BOSTON
MA
02109
US
|
Family ID: |
18639838 |
Appl. No.: |
09/845049 |
Filed: |
April 27, 2001 |
Current U.S.
Class: |
164/113 ;
164/312 |
Current CPC
Class: |
B22D 17/007 20130101;
Y10S 164/90 20130101 |
Class at
Publication: |
164/113 ;
164/312 |
International
Class: |
B22D 017/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2000 |
JP |
2000-130,820 |
Claims
What is claimed is:
1. An injection molding method of metal mold, comprising steps of:
supply continuously or discontinuously granular metal material in a
cylindrical fusion vessel having a required length of weighing
chamber communicating with a nozzle port at the extremity section,
including rotatively an agitation means inside, and where an
injection means whose extremity section is formed into an injection
plunger is inserted retractably into the center section of this
agitation means, for engaging slidably said injection plunger into
the weighing chamber, heat melting the metal material to a
temperature equal or superior to the liquid phase line temperature
by an external heat and, at the same time, accumulating in the
fusion vessel by homogenizing by the aforementioned agitation
means, injecting and filling a die by cooling to a temperature
equal or superior to the solid phase line temperature and equal or
inferior to the liquid phase line temperature in the course from
the feed into the weighing chamber by the retraction of the
aforementioned injection plunger to the injection and filling of
the die, and forming into a metal mold having a thixothropic
structure.
2. An injection molding method of metal mold, comprising steps of:
supply continuously or discontinuously granular metal material in a
cylindrical fusion vessel having a required length of weighing
chamber communicating with a nozzle port at the extremity section,
including rotatively an agitation means inside, and where an
injection means whose extremity section is formed into an injection
plunger is inserted retractably into the center section of this
agitation means, for engaging slidably said injection plunger into
the weighing chamber, heat melting the metal material to a
temperature equal or superior to the solid phase line temperature
and equal or inferior to the liquid phase line temperature by an
external heat and, at the same time, accumulating in the fusion
vessel by agitating and maintaining melt metal material in a
semi-melt state (thixothropy state) by the aforementioned agitation
means, sending a part of this semi-melt state metal material into
the weighing chamber by the retraction of the aforementioned
injection plunger, injecting and filling by advancing the injection
plunger keeping the semi-melt state event after the weighing, and
forming into a metal mold having a thixothropic structure.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention concerns a method for injection
molding a metal mold by melting low fusion point metal materials
such as zinc, magnesium or their alloys.
[0003] 2. Detailed Description of the Prior Art
[0004] Die casting is adopted for casting low fusion point
nonferrous metal; however, die casting requires a smelter for
melting metal material completely, and the casting is performed by
pumping molten metal from this smelter, or by extruding by a
plunger. Therefore, granular metal material supplied from the rear
of a heating cylinder is being melt by transporting forward in the
heating cylinder by screw rotation, accumulated and weighed in a
heating cylinder antechamber, injected and charged into a die from
a nozzle at the heating cylinder extremity by screw advancement,
similarly as plastic material, without melting by a smelter.
[0005] Problems encountered in case of adopting such injection
molding for metal material are difficulty of melting and transport
of metal material by screw rotation and weighing instability.
[0006] Plastic material is melt mainly by shearing heat generation;
therefore, the screw diameter is formed to increase as approaching
the extremity section, and the screw groove forming the material
flow gap is formed relatively shallow. However, molten plastic is
transported smoothly forward by screw rotation even when the flow
gap is formed narrow, because of the difference of friction factor
at the interface surface of the heating cylinder inner wall.
[0007] On the other hand, the viscosity of metal material
completely molten to the liquid phase state being incomparably
lower than the plastic material, there is almost no difference of
friction factor at said two interface surfaces, so the transport
power by screw rotation as in case of molted plastic generates
hardly. In addition, in a low viscosity liquid phase state, a
pressure elevation so strong as pushing back the screw does not
generate, and the screw retraction by the material pressure hardly
occurs, and the accumulated amount in the antechamber differs only
by the screw rotation, making technically difficult to quantify the
injection filling quantity.
[0008] Therefore, it has been proposed to injection molding a metal
material in semi-molten state by limiting the melting temperature
to a temperature equal or superior to the solid phase line
temperature and equal or inferior to the liquid phase line
temperature , without melting the metal material completely. In
said temperature range, the structure of molten metal is supposed
to be in semi-molten state (thixothropic state), and in this state,
the flow resistance generates in the molten metal, allowing to
transport by the screw rotation and to weigh by its retraction.
Consequently, the molding of metal molds by the conventional
injection molding has been performed adopting such method.
[0009] However, such molding method is nothing but a straight
application of plastic material injection molding means, and it is
difficult to maintain the molten metal temperature in the heading
cylinder, as the metal is high in the heat conductivity different
from plastic material. Even in the metal material molding, the
heating cylinder keeps the set temperature being heated by an outer
periphery band heater. However, the screw side has no heating
means, and moreover, heat is easily radiated from the rear end
section. Consequently, the temperature of molten metal in the screw
grooves becomes easily irregular and this can not be preventing by
the agitation by screw rotation is assumed to be impossible,
because the screw per se serves as molten metal material transport
member, and provokes an excessive supply of material.
[0010] This invention devised to solve the aforementioned problems
in case of injection molding of metal material in semi-molten state
has an object to provide a novel injection molding method allowing
to agitate molten metal in a melting vessel by combining separately
functioning agitation means and injection means without adopting a
screw having triple functions of melting, transport and injection
supposed to be indispensable in the prior art, and to mold metal
molds having a thixothropic structure in a state where the metal
material melting temperature is kept within a set temperature range
by this.
SUMMARY OF THE INVENTION
[0011] For the aforementioned object, this invention consists in
supply continuously or discontinuously granular metal material in a
cylindrical fusion vessel having a required length of weighing
chamber communicating with a nozzle port at the extremity section,
including rotatively an agitation means inside, and where an
injection means whose extremity section is formed into an injection
plunger is inserted advanceably and retractably into the center
section of this agitation means, for engaging slidably said
injection plunger into the weighing chamber, heat melting the metal
material to a temperature equal or superior to the liquid phase
line temperature by an external heat and, at the same time,
accumulating in the fusion vessel by homogenizing by the
aforementioned agitation means, injecting and filling a die by
cooling to a temperature equal or superior to the solid phase line
temperature and equal or inferior to the liquid phase line
temperature in the course from the feed into the weighing chamber
by the retraction of the aforementioned injection plunger to the
injection and filling of the die, and forming into a metal mold
having a thixothropic structure.
[0012] Also, this invention consists in supply continuously or
discontinuously granular metal material in a cylindrical fusion
vessel having a required length of weighing chamber communicating
with a nozzle port at the extremity section, including rotatively
an agitation means inside, and where an injection means whose
extremity section is formed into an injection plunger is inserted
retractably into the center section of this agitation means, for
engaging slidably said injection plunger into the weighing chamber,
heat melting the metal material to a temperature equal or superior
to the solid phase line temperature and equal or inferior to the
liquid phase line temperature by an external heat and, at the same
time, accumulating in the fusion vessel by agitating and
maintaining melt metal material in a semi-melt state (thixothropy
state) by the aforementioned agitation means, sending a part of
this semi-melt state metal material into the weighing chamber by
the retraction of the aforementioned injection plunger, injecting
and filling by advancing the injection plunger keeping the
semi-melt state event after the weighing, and forming into a metal
mold having a thixothropic structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic longitudinal side view of a molding
machine allowing to realize the metal mold injection molding method
according to the present invention;
[0014] FIG. 2 is also a side view shown a partial longitudinal
section;
[0015] FIG. 3 is a longitudinal side view of the melting cylinder
extremity section when the injection plunger is retracted; and
[0016] FIG. 4 is a longitudinal side view of the melting cylinder
extremity section when the injection plunger is advanced.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] Drawing show one embodiment of molding machine allowing to
exert the metal mold injection molding method according to the
present invention.
[0018] In the drawing, 1 is an injection mechanism, 2 is a
compression mechanism, both installed on a top face of a base 3, 4
is a pedestal 4 installed movably forward and backward in respect
of the compression mechanism 2 and provided with a trestle 5 having
a slant top face and mounted rotatably on the rear section thereof,
and the aforementioned injection mechanism 1 is installed on this
trestle 5 so that the nozzle side can be positioned downwardly
slant in respect of the compression mechanism 2.
[0019] The aforementioned injection mechanism 1 comprises a
cylindrical melting cylinder 11 constituting the metal material
melting vessel, an agitation and injection means therein mentioned
below, a injection cylinder 12 provide at the rear end section of
the melting cylinder 11 with an interval, an electric motor 14 for
agitation attached to the support leg 13 at the rear end bottom of
the melting cylinder 11, and a delivery equipment 15 for supplying
granular metal material in the melting cylinder. This delivery
equipment 15 comprises a horizontal cylinder 15a and an inner screw
shaft 15c rotating by an electric motor 15b provide at the cylinder
end section. Though not shown in the drawing, it comprises a
structure allowing to mount a heater for material pre-heating
around the cylinder as necessary.
[0020] The aforementioned melting cylinder 11 is provided with a
nozzle member 10 at the extremity and a band heater 16 around the
outer periphery. The inside of the extremity section of the melting
cylinder 11 communicating with the aforementioned nozzle member 10
nozzle port is formed in a required length cylindrical weighing
chamber 17 whose diameter is reduced than the melting cylinder 11
inner diameter. In the illustrated example, the rear section inside
diameter of the nozzle member 10 attached to the melting cylinder
extremity by an extremity member 18 is reduced than the melting
cylinder inner diameter, and this rear section inside is formed as
a weighing chamber 17 in communication with the melting cylinder
inside; however, according to the case, a structure wherein the
extremity member 18 inner diameter is reduced to form the weighing
chamber 17, and a nozzle tip is attached to the extremity member 18
thereof.
[0021] A supply port 19 is opened at the middle top of the melting
cylinder 11 provided with such weighing chamber 17 at the
extremity, and the aforementioned delivery equipment 15 is arranged
at this supply port 19 by connecting a piping 20. The rear end of
the melting cylinder 11 is in the open state, and an agitation
member 21 and an injection member 22 composing the aforementioned
agitation and injection means is installed inside therefrom.
[0022] The aforementioned agitation member 21 is made of a rotation
shaft wherein a plurality of agitation fins 24, 24 are formed
continuously around the extremity section outer circumference of a
hollow shaft section 23 at the fixed position having a through port
in the middle. These agitation fins 24, 24 have an external
diameter substantially equal to the melting cylinder 11 inner
diameter. A partition flange 25 serving also as guide in contact
with the inner circumferential surface of the melting cylinder 11
is integrally formed around the shaft section backward of the
hollow shaft section 23 agitation fin 24.
[0023] A pulley 26 is affixed to the end section of the
aforementioned hollow shaft section 23 protruding from the opening
end of the melting cylinder 11, a timing belt 28 is engaged over
this pulley 26 and a pulley 27 at the driving shaft end of the
aforementioned electric motor 14, the agitation member 21 turns
unilaterally or reciprocally in the melting cylinder by the
electric motor 14, allowing to agitate the molten metal by the
aforementioned agitation fins 24, 24.
[0024] The aforementioned injection member 22 comprises an
injection rod 29 inserted into said hollow shaft section 23 through
port and provide slidably at the middle of the agitation member 21,
and an injection plunger 30 attached to the extremity thereof,
protruded from the front face of the agitation member 21 and fitted
with the aforementioned weighing chamber 17. This injection plunger
30 moves forward and backward without exiting the weighing chamber
inside by the injection rod 29. Rings 29a serving also to prevent
backflow of molten metal penetrated into the rod guide and
clearance are formed in several stages around the outer periphery
of the injection rod 29 above the aforementioned partition flange
25.
[0025] The aforementioned injection plunger 30 is made of an outer
diameter allowing to be inserted in the weighing chamber 17 with a
clearance for sliding and provided with a seal ring 31 around the
outer periphery thereof. This seal ring 31 comprises one adopting a
heat resistant piston ring made of special steel of the like as it
is. Though the detail is omitted in the drawing, the seal ring 31
is fitted to the annular groove around the plunger outer periphery
providing a required gap between the groove bottom and the groove
wall, so as to decrease the diameter during the weighing chamber
side negative pressure by the plunger retraction, thereby
increasing the aforementioned clearance to make suction transport
of molten metal material into the weighing chamber smooth and, on
the contrary, to prevent the backflow of molten metal from the
aforementioned clearance by expanding by the weighing chamber side
material pressure.
[0026] The aforementioned injection cylinder 12 includes integrally
a support leg 32 at the cylinder front end bottom, this injection
cylinder 12 is coupled integrally with the aforementioned melting
cylinder 11 by tie bars 33 arranged at both sides leaving an
interval, while the piston 34 is coupled with the aforementioned
injection rod 29 rear end protruding from the aforementioned hollow
shaft section 23 rear end, and moves forward and backward the
injection rod 29 with the injection plunger 30 at the
extremity.
[0027] Such injection cylinder 12 and the aforementioned melting
cylinder 11 insert the end section of the aforementioned support
legs 13, 32 protruding at respective lower both sides into support
shafts 40, 40 juxtaposed at both sides of the aforementioned
trestle 5 slant top surface and are mounted with the nozzle member
10 downward at the bottom, thereby composing the aforementioned
injection mechanism 1 installed slant to the aforementioned
compression mechanism 2.
[0028] Moreover, at both sides of the injection mechanism 1, a
nozzle touch equipment 44 by a hydraulic cylinder 42 and an
extended shaft rod 43 axially and rotatively attaches the rod 43
extremity to bearing members 46 at both sides of a nozzle touch
block 45 erected at the middle of the pedestal 4 extremity, while a
hydraulic cylinder 42 is bridged between the melting cylinder rear
end and the injection cylinder front end, and the cylinder rear end
is installed by rotatively affixing to the injection cylinder. This
nozzle touch equipment 44 functions also as retraction equipment
during repair or maintenance of the injection mechanism 1.
[0029] The aforementioned trestle 5 is formed into an inward slant
surface whose top face has an angle of around 45 and the
aforementioned support shaft 40 is attached to the top face thereof
by members 41, 41 at both sides. This trestle 5 is, though omitted
in the drawing, put on and fixed to a gate type reception base 6
installed on the aforementioned pedestal rest end section, and a
nozzle touch equipment 48 of a nozzle member 47 installed
horizontally by a member 52 on the nozzle touch block 45 front face
is arranged from the reception base 6 inside middle to the
aforementioned nozzle touch block 45.
[0030] A hydraulic cylinder 49 of this nozzle touch equipment 48 is
fixed to a reception member 50 at the center inside the pedestal 4
installed on the machine base 3, a rod member 51 coupled to an
inside piston rod (the drawing omitted) has an extremity coupled to
the aforementioned nozzle touch block 45, the pedestal 4 moves
forward and backward with the injection mechanism 1 on the trestle
4 top face by this rod member 51 forward and backward displacement,
performing the nozzle touch to a mold 7 of the aforementioned
nozzle member 47.
[0031] The inside upper section of the aforementioned nozzle touch
block 45 is formed on a slant rear face positioned normal to the
axial line of the aforementioned injection mechanism 1 nozzle
member 10, a gate for nozzle touch is opened on the slant rear
face. A hot runner 53 communicating the aforementioned nozzle
member 47 and the injection mechanism 1 nozzle member 10 is formed
in curvature inside the nozzle touch block 45, thereby preventing
molten metal from leaking during the injection filling, by
realizing a closely tight nozzle touch, even if the injection
mechanism 1 is installed slant to the composition mechanism 2.
[0032] In order to form a metal mold, for instance a mold of
magnesium (AZ91D) by a first injection molding method of the
present invention using a molding equipment of the aforementioned
composition, first the melting cylinder 11 is heated to a set
temperature equal or superior to the liquid line temperature
(620.degree. to 680.degree. C.) by a outer circumferential band
heater 16, to heat the inside to a hot temperature equal or
superior to the fusion temperature. On the other hand, the nozzle
touch block 45 and the nozzle member 47 are also preheated, though
omitted in the drawing, by an external heater to a temperature
equal or inferior to the solid phase line temperature (470.degree.
C.) and equal or inferior to the liquid phase line temperature
(595.degree. C.) while molten metal material passes through the
runner and is injected and charged in the mold 7. At this time, the
space area in the delivery equipment shall be inactive gas
atmosphere. This inactive gas can be supplied, though omitted in
the drawing, for instance by connecting a supply pipe of an
inactive gas cylinder to the aforementioned piping 20.
[0033] Next, the hollow shaft section 23 is rotated by the
aforementioned electric motor 14 at a set speed to realize the
agitation state. There, granular magnesium as metal material is
supplied into the melting cylinder 11 from the supply inlet 19 by
the aforementioned delivery equipment 15. As the melting cylinder
11 is slant downward, immediately the metal material melts in the
area of agitation fins 24, 24 rotating with the hollow shaft
section 23 becomes molten metal. Metal material supplied further
continuously falls into the molten metal accumulated therein, melts
by the heat of molten metal, and is mixed into the molten metal by
the agitation fins 24, 24. This allows to melt in an extremely
short time and, at the same time, the molten metal material is
homogenized.
[0034] When the injection plunger 30 is in its advance position,
the molten metal material is accumulated as it is in the front
section of the melting cylinder 11. This accumulation amount of 10
shots or so is enough, and a continuous molding can be executed
without problem by supplying material for one shot per molding.
[0035] When a predetermined amount of molten metal material is
accumulated, the aforementioned injection plunger 30 is retracted.
This retraction displacement is limited to a range where the seal
ring 31 remains in the weighing chamber 17, and a part of
accumulated molten metal material flows into the weighing chamber
17.
[0036] Molten metal material flows into the weighing chamber 17 by
the negative pressure generated by the retraction displacement of
the injection plunger 30 in the extremity member. This is because
the previous injection molten metal material cools down and sets at
the nozzle member 47 nozzle port, remains as cold plug, blocks the
weighing chamber 17 nozzle side and prevents from flowing in from
the nozzle port. In such a state, if a retraction force is applied
to the injection plunger 30 at the advance limit, a negative
pressure is generated in the weighing chamber 17 being expanded
according to the retraction displacement.
[0037] This negative pressure reduced the diameter of the injection
plunger 30 seal ring 31 and, at the same time, molten metal
material flows from the clearance around the seal ring into the
weighing chamber 17 being expanded by the suction effect of the
negative pressure and fills the chamber. This prevents such a high
negative pressure that the injection plunger 30 forced retraction
becomes difficult from generating in the weighing chamber 17,
allowing to weigh the material by a smooth retraction displacement
of the injection plunger 30.
[0038] Consequently, a set amount of molten metal material can
always be injected and charged in the die 7, by setting the
weighing completion position anticipating the backflow amount by
the advance displacement during the injection by the injection
plunger 30, thereafter, changing the process to the injection
filling, and advancing the injection plunger 30 to the advance
limit.
[0039] From such material weighing, molten metal material is
agitated continuously by the rotation of the aforementioned
agitation fins 24, 24 even during the injection filling, because
the aforementioned agitation member 21 and the injection member 22
are separate ones, thereby allowing to homogenize molten metal
material in the melting cylinder, even when new metal material is
supplied continuously or discontinuously into the melting cylinder
11.
[0040] It is unnecessary to make a large diameter injection rod as
the conventional screw taking the rotation torque into
consideration, because the injection member 22 does not rotate for
the purpose of metal material fusion, and gap between the melting
cylinder inner wall surface and the hollow shaft section outer
surface can be formed large, because the agitation member 21 also
does not melt by shearing heat, making thereby easier to
accumulated molten metal material for several shots that was
assumed to be difficult in case of adopting a screw, and further
improving the molten metal material temperature maintenance
effect.
[0041] Molten metal material after weighing is pressured by the
advance displacement of the injection plunger 30, drives the cold
plug blocking the nozzle member 47 nozzle port, passes through the
hot runner leading from the aforementioned nozzle touch block 45 to
inside the nozzle member 47, and injection charged in the mold 7
cavity.
[0042] In the course of weighing to injection, molten metal
material equal of superior to the liquid phase line temperature is
cooled down to semi-molten state while passing through the hot
runner 53 and being injection charged in the die 7 as the nozzle
touch block 45 and the nozzle member 47 are heated to and kept at a
temperature equal or superior to the solid phase line temperature
and equal or inferior to the liquid phase line temperature, and the
injection molded magnesium mold becomes a product having a
thixothropic composition, as a certain agitation is generated by a
flow disturbed by the flow resistance.
[0043] A second injection molding method of the present invention
consists in setting the temperature of all of the aforementioned
melting cylinder 11, nozzle touch block 45 and nozzle member 47 is
set so that the molten metal material temperature becomes equal or
superior to the solid phase line temperature and equal or inferior
to the liquid phase line temperature, heat melting the metal
material to a semi-molten state in this temperature range and, at
the same time, agitating to the thixothropic state by said
agitation member 21, and weighing and injection charging into the
aforementioned die 7 by the injection plunger 30 displacement all
the way keeping this state.
[0044] In any of the aforementioned first and second injection
molding methods, molten metal material is agitated continuously by
the rotation of the aforementioned agitation fins 24, 24 whether in
weighing or injection process, because the aforementioned agitation
member 21 and the injection member 22 are separate ones inside the
melting cylinder 11, thereby allowing to homogenize molten metal
material in the melting cylinder, even when new metal material is
supplied continuously or discontinuously into the melting cylinder
11.
[0045] It is unnecessary to make a large diameter injection rod as
the conventional screw taking the rotation torque into
consideration, because the injection member 22 does not rotate for
the purpose of metal material fusion, and gap between the melting
cylinder inner wall surface and the hollow shaft section outer
surface can be formed large, because the agitation member 21 also
does not melt by shearing heat, making thereby easier to
accumulated molten metal material for several shots that was
assumed to be difficult in case of adopting a screw, solving the
temperature irregularity of semi-molten metal material, and
allowing to injection molding easily thixothropic state metal molds
more excellent in molding accuracy that the conventional molding
methods.
* * * * *