KR20210109285A - Apparatus and method for rapid and accurate mold making - Google Patents

Abstract

The present invention relates to an apparatus and a method for rapid and accurate manufacture of a mold, and the manufacturing apparatus includes a die set, a mold frame, a heating unit, a pressure plunger, a graphite insulating plate, and a pressure control unit. In addition, the manufacturing method includes forming a plurality of slits in a mold steel, heating the mold steel in which the slits are formed to a semi-molten state in which liquid and solid phases are mixed, filling the mold frame with the mold steel in the semi-molten state under pressure, and cooling the mold steel filling in the mold frame.

Description

Apparatus and method for rapid and accurate mold making

The present invention relates to an apparatus and method for manufacturing various types of molds essential for the production of various parts and products of industrial products, and more particularly, to an apparatus and method for rapidly and accurately manufacturing various types of molds.

In recent years, with the development of industry, consumers' desires for products are diversifying. Accordingly, the life cycle of the product is shortening, and the shape of the product in accordance with the taste of consumers often has a complex curved surface. Accordingly, the mold for producing these products also takes on a complex shape.

Products of such complex and various shapes are usually manufactured through molds such as injection molds, blowing molds, die-casting molds, and press molds, and these molds are manufactured through machining and electric discharge machining.

However, in the mold manufacturing technique such as mechanical cutting, in order to smoothly and accurately process a mold of a complex shape, a technique of modeling the shape of the mold more efficiently is required, and in addition, for example, mold processing In order not to cause problems such as interference with the tool, tool path planning and processing conditions according to mold machining should be calculated in advance from the above-described modeling information.

Therefore, in light of the recent trend of shorter product life cycles and complicated and diversified product shapes, it is difficult to keep up with the short life cycle of products due to the long time required for mold production, and It takes a lot of cost and becomes a factor that lowers the price competitiveness of the product.

The present invention has been devised in view of the above points, and an object of the present invention is to provide a mold making apparatus capable of producing a mold of higher quality, simply and quickly, and up to a mold of a large size.

Another object of the present invention is to provide a method for manufacturing a mold, and in particular to provide a method using the above-mentioned apparatus.

In the present invention as described above, since the semi-melting rapid forming method is applied to mold steel, particularly mold steel, instead of powder metal, the supply of raw materials is easy and the price is low. In addition, since the mold steel is used, the size of the graphite die set is small compared to the case of using powder metal, and thus the device can be miniaturized. In addition, since the mold is installed on the outside of the graphite die set, the mold can be replaced quickly and easily. In addition, since the semi-molten metal is pressed from only one side, it is easy to control the pressing force. In addition, by forming a plurality of slits in the mold steel, even a large-sized mold steel can be made more rapidly, repeatedly, and in a uniform semi-molten state. Therefore, even large-sized molds can be produced at low cost. In addition, more efficient uniform cooling can be realized in the modern mold manufacturing process with many curved surfaces by forming uniform cooling wiring matching the shape of the mold on the mold.

In the above, the present invention has been shown and described with respect to certain preferred embodiments. However, the present invention is not limited to the above-described embodiments, and those of ordinary skill in the art to which the present invention pertains within the scope not departing from the spirit of the present invention described in the claims below. can be changed in various ways.

1 is a cross-sectional view showing a mold manufacturing apparatus according to an embodiment of the present invention.
2 and 3 are enlarged views of the main parts of FIG. 1, and are operational state diagrams of a mold manufacturing apparatus for explaining a mold manufacturing method according to an embodiment of the present invention.
4A and 4C are views illustrating a mold steel in the form of a round bar having a slit according to an embodiment of the present invention.
5A and 5B are process diagrams respectively illustrating a manufacturing method for the formwork of the mold shown in Figs.
Figures 6a and 6b is a view showing the formwork of a conventional mold.
7A and 7B are views showing the formwork of a mold according to an embodiment of the present invention.

The above-described apparatus of the present invention includes: a die set having an upper and lower opening and a receiving portion in which a mold steel to be manufactured as a mold is accommodated; a mold of a mold having a shape corresponding to the shape of the mold, and mounted so as to seal and detach the opened upper side of the die set accommodating part; means for heating the mold steel so that the mold steel accommodated in the accommodating part is converted into a semi-molten state in which liquid and solid phases are mixed; a pressure plunger installed to be movable up and down through the lower opening surface of the receiving part, and pressurizing the mold steel in the semi-molten state upward so that the mold steel heated to a semi-molten state by the heating means is filled in the mold of the mold; a pressure control unit for improving the filling efficiency of the mold steel by creating a vacuum around the ceramic mold when the pressure plunger presses the mold steel; and the mold steel accommodated in the accommodating part is installed to be movable left and right between the mold steel and the mold frame, disposed on the mold steel accommodated during heating to keep the upper part of the heated mold steel insulated, and the progress direction of the mold steel in the semi-molten state during charging It includes a graphite heating plate that moves so as to be separated from it.

Here, the heating means includes a coil for induction heating installed around the accommodating part of the die set to heat the mold steel accommodated in the accommodating part, and a control unit for controlling the operation and heating temperature of the induction heating coil, The coil is installed so that it can be replaced with a high-frequency or medium-frequency coil according to the size of the mold steel accommodated in the accommodating part of the dieset.

The formwork of the mold includes, inside the formwork structure, cooling wiring selected from the group consisting of a cooling pipeline, a Zamak line of salt or Zn alloy, which generally coincides with the contour of the mold shape to be formed.

The mold steel is a round bar, and a plurality of slits are formed on the curved surface of the round bar in the longitudinal direction. The plurality of slits are symmetrical to each other about the axis of the round bar.

The mold manufacturing method of the present invention for manufacturing a mold using the mold manufacturing apparatus, (1) inserting the mold steel into the accommodating part and placing the graphite insulating plate on the upper part of the mold steel accommodated in the accommodating part, the mold steel charging (charging) ) step; (2) mounting the mold of the mold to seal the upper side of the accommodating part; (3) heating the metal so that the solid metal in the accommodating part is in a semi-molten state in which the liquid phase and the solid phase are mixed; (4) a semi-molten mold steel filling step, in which the heating plate is separated from the moving direction of the mold steel in the semi-molten state, and the metal material in the semi-molten state is pressed to fill the mold of the mold; and (5) cooling the mold steel filled in the formwork of the mold.

Here, the cooling in the cooling step may be an iterative process of separating the mold from the die set, cooling it separately, and starting a new mold manufacturing process using a new mold steel and a new mold mold.

The heating in step (3) is performed by induction heating. The mold steel is a round bar, and when the diameter is 150 PHI or less, high-frequency indirect induction heating can be used, and when the diameter is 100 PHI or more, mid-frequency direct induction heating can be used. In this case, the mold steel is formed with a plurality of slits in the longitudinal direction on the curved surface of the round bar. The plurality of slits are symmetrical to each other about the axis of the round bar.

The heating in step (3) is performed at a temperature of 1,200 to 1540° C. for 1 to 120 minutes.

In step (4), the liquid phase ratio of the mold steel in the semi-molten state is 1 to 90%, the applied pressure is 3 to 500 MPa, and the speed of pressing is 0.1 to 10 m/s.

The heating step, the charging step, and the cooling step are performed in a vacuum atmosphere or a gas atmosphere selected from argon, nitrogen and hydrogen.

The cooling in step (5) is performed at a cooling rate of 40° C./s or less.

After the cooling step, it may further include an annealing step or annealing after quenching.

The mold of the mold may be a ceramic mold formed through the step of forming a master pattern and the step of forming a mold formed of ceramic slurry to correspond to the master pattern. In this case, a silicon mold forming step is included between the master pattern forming step and the mold forming step to enable mass production of the mold.

In addition, in the mold manufacturing method of the present invention, a plurality of slits are formed in the mold steel, the mold steel in which the slits are formed is heated to a semi-molten state in which liquid and solid phases are mixed, and the mold steel in the semi-molten state is used as a mold of the mold. After pressure filling in the mold, it includes cooling the mold steel filled in the formwork of the mold.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view schematically illustrating a mold manufacturing apparatus according to an embodiment of the present invention.

As shown, the mold manufacturing apparatus according to an embodiment of the present invention includes, for example, a die set 10, a mold 20, a heating unit, a warming unit, a pressure plunger 41, and a pressure adjusting unit. .

The die set 10 is, for example, a graphite die set, which is fixed to the lower surface of the fixing plate 61, and forms, for example, a graphite or alumina material sleeve 12 that forms the receiving part 11 with the upper and lower sides open. And, it has a ceramic heat insulating material 13 and a ferrite material protective film 14 surrounding the outside of the sleeve 12 (see FIG. 2). A through hole 52 constituting a part of the receiving portion 11 is formed in the fixing plate 61 matching the opened upper side of the receiving portion 11 . A mold steel 80 to be manufactured as a mold, preferably, a mold steel is charged in the receiving part 11 .

A mold 20 of a mold made of, for example, ceramic or graphite material is mounted on the upper side of the fixing plate 61 . The formwork 20 seals the opened upper side of the accommodating part 11 and is detachably mounted. A filling part 21 forming the shape of a mold is formed on the surface in contact with the receiving part 11 of the mold. The mold 20 is made from a master pattern or a mock-up having the same size and shape as the mold to be manufactured.

The heating unit has an induction heating coil 31 installed to surround the sleeve 12 of the dieset 10 and a control unit (not shown) for controlling the operation and heating temperature of the coil 31 . Preferably, the coil 31 is installed so as to be replaceable together with the ferrite protective film 12 . When the coil 31 is installed to be replaceable in this way, a coil for high-frequency, medium-frequency or low-frequency induction heating can be selectively installed according to the size of the mold steel 80 accommodated in the accommodating part 11 .

The pressure plunger, the upper end of which is located inside the receiving portion 11 to seal the lower side of the receiving portion 11, can be moved up and down by the cylinder (42).

The heat insulating part 70 has a graphite heat insulating plate 71 installed so as to be movable from side to side by a cylinder 72 between the mold steel 80 and the mold housed in the accommodating part. Therefore, the graphite insulating plate 71 is disposed on the upper part of the mold steel accommodated during heating to keep the upper part of the heated mold steel, and during charging, it is separated from the moving direction of the heated mold steel in a semi-molten state that proceeds for charging. The graphite insulating plate 71 preferably has a gap of 1 to 10 cm from the charged mold steel. In addition, the thickness of the graphite insulating plate 71 is preferably 1 to 20 cm. By disposing the graphite insulating plate on the upper part of the heated mold steel, it is possible to not only prevent heat loss caused by radiation and convection, but also to further increase the temperature of the upper part of the mold steel due to the heat of the graphite. In addition, the temperature of the upper part of the mold steel can be controlled by adjusting the thickness of the graphite insulating plate and the distance between the graphite insulating plate and the mold steel according to the size of the mold steel.

The pressure control unit includes a mold 20 , a fixing plate 61 , a die set 10 , a vacuum chamber 51 accommodating the pressure plunger 41 , and a vacuum chamber at the upper and lower sides of the vacuum chamber 51 . It includes sealing plates 52 and 53 for sealing, and a vacuum pump 54 .

The upper sealing plate 53 is moved up and down by the lifting cylinder 62 installed on the upper part of the device, and the lower end of the lifting cylinder 62 grips the formwork 20 to mount and separate the fixing plate 61 . (63) is installed.

Further, as can be seen from Figs. 7A and 7B, the formwork of the mold has, inside the formwork structure, the cooling wiring 22 that generally coincides with the outline 23 that generally forms the shape of the mold to be formed. This cooling wiring 22 may be selected from the group consisting of cooling pipelines, Zamak lines of salt or Zn alloy. This is different from the existing mold 200 shown in FIGS. 6A and 6B having a straight cooling wiring 202 irrespective of the contour line 203 forming the shape of the mold to be formed, as shown in FIGS. 7A and 7B . The mold 20 of the present invention has uniform cooling wiring 22 that coincides with the contour 23 of the mold to be formed, so that more efficient uniform cooling can be achieved in modern mold manufacturing with many curved surfaces.

A mold manufacturing method using the mold manufacturing apparatus according to an embodiment of the present invention will be described.

First, a process of forming the mold 20 of the mold from the master pattern will be described with reference to FIGS. 5A to 5C .

In the case of a ceramic mold, as shown in FIG. 5A , first, a master pattern 1 or a mockup is formed using a Rapid Prototype device or a CNC device. At this time, the master pattern or mock-up should be processed in consideration of the shrinkage or expansion rate due to the thermal effect during the subsequent process. Then, the master pattern 1 is placed inside a molding box (not shown) such as a mold box, and ceramic in the form of a slurry is poured into the mold to solidify. Accordingly, a mold 20 of a ceramic material made of a ceramic material having a shape inverted from the shape of the master pattern 1 is formed. In the case of a graphite mold, it is directly processed using a CNC machine or the like.

In addition, referring to FIG. 5B , the master pattern 1 is formed in a state in which the shape of the object is engraved on both sides, unlike the case of FIG. 4A , and the master pattern 1 ′ is used in a plurality of molds using a mold. A silicone rubber mold 2 is formed. Next, the molds 20' of a plurality of molds are formed using each of the silicone rubber molds 2 . In the case of FIG. 5B , since the silicone rubber mold 2 can be mass-produced in a simple manner, it is advantageous when a plurality of molds having the same shape are to be manufactured.

4A and 4B, the steps of preparing the mold steel 80 and forming a plurality of slits 81 in the mold steel will be described.

The mold steel 80 is, for example, preferably a bar steel, and most preferably a round bar having a diameter of 40 PHI or more. Mold steel is manufactured by rolling or forging after the casting process of gravity casting or continuous casting. In addition, the manufacturing process of the round bar may include a heat treatment process for stress relief and solutionization, and all of the above-described processes may be continuously performed. In this case, the round bar preferably has a microstructure grain size of 0.5 to 300 μm. This round bar is cut to a size to be manufactured in a mold, and a plurality of slits 81 are formed on the curved surface. The slit 81 forms an appropriate number of slits 81 according to the diameter of the round bar used, and may be formed by cutting the curved surface of the round bar with a saw. The slits 81 are preferably formed in the axial direction (longitudinal direction), and are formed in a generally symmetrical structure about the axis A-A'. The depth of the slit 81 can be adjusted in the range of 2 to 10 cm depending on the size of the round bar. By forming a plurality of slits 81 in the round bar in this way, the current induced in the subsequent induction heating step can flow to the center of the mold steel. Therefore, the central part of the specimen is also heated almost simultaneously with the surface part, so that the temperature difference between the surface part and the central part of the mold steel can be minimized.

Next, a method for manufacturing a mold using the apparatus of the present invention will be described with reference to FIGS. 1 to 3 . The mold steel 80 to be manufactured as a mold is charged into the receiving part 11 of the die set 10 . The charging step includes inserting the mold steel 80 into the accommodating part 11 and arranging a graphite insulating plate on the mold steel. In the insertion of the mold steel, first the mold steel 80 is placed on the upper surface of the pressure plunger 41, and when the mold steel 80 is placed or placed, the pressure plunger 41 is the mold steel 80 is the receiving part ( 11) to be located in the center.

After the mold steel 80 is accommodated in the receiving part 11, the graphite insulating plate 71 is positioned on the upper part of the mold steel. The thermal insulation plate as described above is a graphite plate. Next, the cylinder 62 descends in a state in which the mold 20 of the mold is gripped by the gripper 63 to mount the mold 20 of the mold on the upper side of the fixing plate 61 . The mold 20 of the mounted mold is supported downward by the rod of the cylinder 62 in which the holding part 63 is installed.

Then, the vacuum pump 54 of the pressure control unit is operated to remove all of the air in the chamber (not shown) including the inside of the accommodation unit 11 to create a vacuum state.

After the inside of the accommodating part 11 is in a vacuum state, the mold steel 80 is heated so that the mold steel 80 accommodated in the accommodating part 11 is in a semi-melted state in which the solid and liquid phases are mixed. In this case, since the inside of the accommodating part 11 is in a vacuum state, a phenomenon in which the mold steel 80 is oxidized during heating does not occur. Instead of vacuum, the inside of the chamber including the accommodating portion may be in a gas atmosphere such as argon, nitrogen or hydrogen.

Possible heating methods include direct or indirect induction heating of high, medium and low frequencies. At this time, high-frequency indirect induction heating is used when the diameter of the mold steel 80 is 150 PHI or less so that the mold steel 80 can be uniformly melted regardless of the size of the mold steel 80, and when it is 100 PHI or more, medium frequency Direct induction heating is used. Preferably, when the diameter of the mold steel is 150 PHI or less, a high-frequency indirect induction heating method is used, and the sleeve 12 is formed of a graphite material.

Also, preferably, when the diameter of the mold steel is 100 PHI, a medium frequency direct induction heating method is used, the sleeve 12 is formed of an alumina material, and most preferably a plurality of slits 81 are formed in the mold steel 80 . do.

Induction heating is a method in which a strong magnetic field is formed around the mold steel to be heated and heated by the induction current induced in the specimen by this magnetic field. The induced current generates heat as it flows along the surface of the mold steel.

In the mold steel of the present invention, as shown in FIGS. 4A and 4B , since a plurality of slits 81 are formed, it is possible to flow along the slits 81 to the center. Therefore, heat is concentrated only on the surface, and the temperature shift between the surface and the center of the mold steel.

Unlike the conventional method with a large difference, the mold steel in which the slit 81 of the present invention is formed has almost no temperature deviation, and it is possible to reach a uniform semi-molten state more quickly. In addition, in the mold manufacturing method of the present invention, it is important to control the upper temperature of the mold steel. This is because the upper part of the mold steel is the first part that directly contacts the mold and is the biggest factor influencing the performance of the molded product during molding. Therefore, it is possible to block heat escaping by radiation and convection by disposing a thermal insulation plate made of graphite, which has a higher calorific value than general metal, on the upper part of the mold steel, and to further increase the upper temperature by the heat of the graphite.

As described above, the mold steel is heated to form a semi-molten state in which the solid and liquid phases are mixed. At this time, the heating rate and the temperature holding time are controlled by a heating pattern preset in the control unit so that the mold steel 80 in the semi-molten state has a fine and uniform structure. The temperature range is preferably 1200 to 1540° C., and the holding time is preferably 1 to 120 minutes.

During this heating step, when the liquid phase ratio of the mold steel 80 reaches approximately 1 to 90%, preferably 5 to 40%, the heat insulating plate 71 is moved away from the moving direction of the semi-molten mold steel, and then the pressure plunger ( 41) is advanced, and the semi-molten metal 80 is pressed into the filling part 21 of the mold and filled.

Reference numeral 80' denotes a filled mold steel in a semi-molten state. Here, the forward speed of the plunger 41 is 0.1 to 10 m/s, and the pressing force is 3 to 500 Mpa. In addition, it is preferable that the temperature is 25 to 500°C in the case of the ceramic mold during charging, and 100 to 700°C in the case of the graphite mold.

Finally, a mold having a predetermined shape can be obtained by cooling the mold steel 80 filled in the filling part 21 of the mold 20 . The cooling rate is preferably performed at a rate of about 40° C./s or less.

After cooling in this way, annealing treatment or annealing treatment after quenching may be performed. Annealing is preferably performed at a temperature of 450 to 650° C. for 1 to 180 minutes, and quenching is preferably performed at a temperature of 800 to 950° C. for 1 to 30 minutes.

If it is desired to manufacture a plurality of molds having the same shape, the molds 20 of a plurality of molds are manufactured using the method shown in FIG. 5B . Then, the semi-molten mold steel 80 is filled in the charging part 21 of the mold 20, and then the cylinder 62 is raised to separate the mold 20 from the holding part 63 and cooled separately, By accommodating the new mold steel 80 in the accommodating part 11, holding the new mold 20 in the holding part 63, and mounting it on the upper side of the fixing plate 61, the mold can be manufactured continuously and quickly.

10 ; Daiset 11 ; receptacle
12 ; sleeve 20 ; mold frame
21 ; charging part 31 ; coil for induction heating
41 ; pressure plunger 54 ; vacuum pump

Claims (22)

a die set having upper and lower sides opened and a receiving portion for accommodating a mold steel to be manufactured as a mold;
a mold having a shape corresponding to the shape of the mold and mounted so as to seal and detach the opened upper side of the die set accommodating part;
means for heating the mold steel so that the mold steel accommodated in the accommodating part is converted into a semi-molten state in which liquid and solid phases are mixed;
A pressure plunger installed so as to be movable up and down through the lower opening surface of the accommodating part and pressurizes the mold steel in the semi-molten state upward so that the mold steel heated to a semi-molten state by the heating means is filled in the mold of the mold. ;
a pressure adjusting unit for improving the filling efficiency of the mold steel by creating a vacuum around the ceramic mold when the pressure plunger presses the mold steel; and
It is installed so as to be movable left and right between the mold steel accommodated in the accommodating part and the mold of the mold, and is disposed on the upper part of the accommodated mold steel during the heating to keep the upper part of the heated mold steel, and the semi-melted state during the filling A mold making device including an installed graphite heating plate that can move away from the moving direction of the mold steel. The induction heating coil according to claim 1, wherein the heating means is installed around the accommodating part of the dieset to heat the mold steel accommodated in the accommodating part, and controls the operation and heating temperature of the induction heating coil. and a control unit, wherein the coil for induction heating is installed so as to be replaceable with a high-frequency or medium-frequency coil according to the size of the mold steel accommodated in the accommodating part of the die set. The mold manufacturing according to claim 1, wherein the mold of the mold includes a cooling wiring selected from the group consisting of a cooling pipeline, a salt or a Zamak line of a Zn alloy that generally coincides with the contour of the mold shape to be formed, inside the mold structure Device. The apparatus according to claim 1, wherein the mold steel is a round bar. [Claim 5] The apparatus of claim 4, wherein the mold steel has a plurality of slits formed on the curved surface of the round bar in the longitudinal direction. [Claim 6] The apparatus of claim 5, wherein the plurality of slits are symmetrical to each other about the axis of the round bar. As a method of manufacturing a mold using the mold manufacturing apparatus of claim 1,
(1) inserting the mold steel into the accommodating part and placing the graphite insulating plate on the upper part of the mold steel accommodated in the accommodating part, a mold steel charging step;
(2) mounting the mold of the mold to seal the upper side of the accommodating part;
(3) heating the metal so that the solid metal in the accommodating part is in a semi-molten state in which a liquid phase and a solid phase are mixed;
(4) a semi-molten mold steel filling step in which the insulating plate is separated from the moving direction of the mold steel in the semi-molten state, and the metal material in the semi-molten state is pressed to fill the mold of the mold; and
(5) A mold manufacturing method comprising the step of cooling the mold steel filled in the formwork of the mold. The mold manufacturing according to claim 7, wherein the cooling in the cooling step is an iterative process of separating the mold from the die set, cooling it separately, and starting a new mold manufacturing process using the new mold steel and the new mold mold. Way. The method according to claim 7, wherein the mold steel is a round bar. The method according to claim 9, wherein the heating in step (3) is by induction heating. The method according to claim 10, wherein the mold steel has a diameter of 150 PHI or less, and the heating in step (3) is high-frequency indirect induction heating. The method according to claim 10, wherein the mold steel has a diameter of 100 PHI or more, and the heating in step (3) is medium frequency direct induction heating. The method according to claim 12, wherein the mold steel has a plurality of slits formed on the curved surface of the round bar in the longitudinal direction. The method of claim 13 , wherein the plurality of slits are symmetrical with each other about the axis of the round bar. The method of claim 7 , wherein the heating in step (3) is performed at a temperature of 1,200 to 1540° C. for 1 to 120 minutes. The method according to claim 7, wherein in the step (4), the liquid phase ratio of the mold steel in the semi-molten state is 1 to 90%, the applied pressure is 3 to 500 MPa, and the speed of the pressing is 0.1 to 10 m/s. Mold manufacturing method, characterized in that. The method of claim 7 , wherein the heating step, the filling step, and the cooling step are performed in a vacuum atmosphere or a gas atmosphere selected from argon, nitrogen, and hydrogen. The method according to claim 7, wherein the cooling in step (5) is performed at a cooling rate of 40° C./s or less. The method according to claim 7, further comprising an annealing treatment after the cooling step or an annealing treatment step after quenching. The method of claim 7, wherein the mold of the mold is a ceramic mold formed through the step of forming a master pattern and the step of forming a mold formed of ceramic slurry to correspond to the master pattern. The mold manufacturing method according to claim 20, wherein a silicon mold forming step is included between the forming of the master pattern and the forming of the mold to enable mass production of the mold. A method of making a mold, comprising:
A plurality of slits are formed in the mold steel, the mold steel in which the slits are formed is heated to a semi-molten state in which a liquid and a solid phase are mixed, and the mold steel in the semi-molten state is pressure-filled in the mold of the mold, and then the mold A mold manufacturing method comprising cooling the mold steel filled in the mold of

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