JP4156748B2 - Metal injection molding method and apparatus, and molded product - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a metal injection molding method, an apparatus, and a molded product for injecting and molding a heat-melted metal into a molding die.
[0002]
[Prior art]
The thixotropic phenomenon is the appearance of molten metal in a solid-liquid coexistence state (semi-solid state) by adding vigorous stirring while cooling the liquid metal to a temperature lower than the liquidus temperature (the temperature at which everything becomes liquid). The injection molding method is known in the past to obtain a highly accurate molded product using a metal material such as magnesium alloy or aluminum alloy by utilizing this thixotropic phenomenon. (See U.S. Pat. No. 3,902,544).
[0003]
On the other hand, in Japan, a method for producing a thixotropic metal in one step by supplying a solid metal into an injection molding apparatus is known (see Patent Registration No. 1550760). Refer to FIG. 7 for this injection molding method. While explaining. FIG. 1 shows a conventional screw type injection molding apparatus. A metal material (not shown) such as a magnesium alloy or an aluminum alloy is chipped into a relatively small particle size convenient for melting, and is supplied into the cylinder 3 from the hopper 4 in the injection machine 1 through the throat 2. Is done. The metal material is heated by a heater 11 wound around the outside of the cylinder 3 while being transported along a screw groove 9 of a screw 8 that is rotationally driven by a motor 7 toward a nozzle 10 that is a front end outlet of the cylinder 3. Melt. The temperature of the cylinder 3 is measured by the thermocouple 12 attached to the outer peripheral surface of the cylinder 3, and the heater 11 is feedback-controlled based on the measured temperature, and is controlled to always maintain a predetermined value.
[0004]
Therefore, the metal material formed into a chip is sufficiently heated and melted by the heater 11 while being conveyed along the screw groove 9 to form a liquid, and then a shearing force is applied by the rotating screw 8 while the liquid is formed. The temperature is controlled to be lower than the phase line temperature. That is, the metal material melted in the cylinder 3 is lowered to a temperature range not lower than the solidus temperature and not higher than the liquidus temperature, and at least a part of the dendrite structure formed by the temperature drop is destroyed. Then, the metal is sheared with a sufficient shearing force and becomes a metal that exhibits thixotropic properties in the coexistence state of solid and liquid, and is injected from the nozzle 10 to the molding die 13. Therefore, when the metal material flows from the nozzle 10 into the spool flow path 18 of the fixed-side mold 14 in the molding die 13, the metal material is already below the liquidus temperature, and the fixed-side molding die 14 in the molding die 13. The cavity 20 is filled through a runner flow path 19 formed by closing these molds between the movable mold 17 and the movable mold 17.
[0005]
Unlike the molding in the liquid state, the molding with the metal material in the coexisting state of the thixotropic property as described above is a laminar flow because the fluid has a low viscosity, so the molding die 13 As a result, there is little occurrence of flow turbulence due to collisions with the inner walls of the flow paths 18 and 19 and collisions between the flowing molten metal, and the temperature of the injected molten metal is low, resulting in a small temperature difference until solidification. There is an advantage that defects such as shrinkage due to solidification shrinkage do not occur. Therefore, in the molding of the metal material as a melt in the coexisting state of solid and liquid, the transferability of the molding dies 14 and 17 to the molded product is extremely excellent, and thus the surface accuracy such as surface roughness and parallelism is very good. A molded product can be obtained. In addition, since the heat load applied to the molds 14 and 17 is small, there is an effect that the life of the molds 14 and 17 can be extended.
[0006]
[Problems to be solved by the invention]
However, in the molding of the metal material in the solid-liquid coexistence state as described above, since the temperature difference with respect to the solidus temperature of the metal material is small compared to the molding from the complete liquid phase state, the metal material becomes a solidified state. Is early. Therefore, when the cross-sectional area of the flow paths 18 and 19 is small and the flow paths 18 and 19 are long, the metal material in the solid-liquid coexistence state completely fills the entire flow paths 18 and 19 and the cavity 20. There is a problem that the molded product has been solidified before, and defects such as defects due to unfilling of the metal material are likely to occur in the molded product.
[0007]
Therefore, in order to avoid the above problems, a method of reducing the flow resistance of the metal material when filling the cavity 20 by increasing the thickness of the molded product itself, and the metal material from the nozzle 10 to the molding die The method of injecting to 13 at high speed can be considered. However, when the thickness of the molded product is increased, the size and weight of the entire molded product increase, and it is impossible to obtain a molded product that can sufficiently meet the recent needs for lightening. As for the flow lengths of the flow paths 18 and 19, when a metal material in the form of a conventional solid-liquid coexisting state is injected from the nozzle 10, the dimensional ratio of the flow length to the thickness of the molded product exceeds 200: 1. In some cases, molding becomes difficult, and if the length is shortened, the thickness of the molded product increases.
[0008]
On the other hand, when the metal material is injected at a high speed, when the molten metal material collides with the inner walls of the flow paths 18 and 19 of the molds 14 and 17, the metal material is scattered and entrains the atmospheric gas, resulting in voids in the molded product. Defects such as an increase in the rate and formation of nests in the molded product occur. Furthermore, the metal material injected at a high speed is likely to leak from the gaps in the molds 14 and 17 that are closed, so that a lot of burrs are generated in the molded product, resulting in a new problem that it takes time to work.
[0009]
Therefore, the present invention has been made in view of the above-described conventional problems. Provided is a metal injection molding method and apparatus and molded product capable of obtaining a molded product reduced as much as possible and obtaining a thin and large molded product with a molding die having a flow path with a long flow length. It is intended to do.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the metal injection molding method of the present invention injects a heated and melted metal material in a solid-liquid coexistence state into a spool flow path of a molding die , and the metal in the spool flow path. The material is allowed to flow while being heated to a temperature above the liquidus temperature, and the metal material is above the solidus temperature and below the liquidus temperature in the runner flow path between the spool flow path and the cavity in the molding die. The cooling is performed so that the temperature range is less than that of the runner channel cross-sectional area, and the gate part narrowed to a channel cross-sectional area that is smaller than the runner channel cross-sectional area is passed through, and the metal material flows into the cavity and is filled. Yes.
[0012]
In this metal injection molding method, the heated and melted metal material is cooled to a temperature range not lower than the solidus temperature and lower than the liquidus temperature when flowing through the runner flow path. compared to the cross-sectional area given a sufficient shear force when passing through a gate portion which is narrowed down to small flow passage cross-sectional area, is destroyed at least a portion of the dendritic crystal structure coming generated by the cooling. As a result, the metal material again exhibits thixotropic properties and flows into the cavity, so that the molded product hardly undergoes shrinkage at the time of cooling, and has excellent transferability to the molding die and high surface accuracy. It becomes.
[0013]
In addition, since the metal material flows as a laminar flow into the cavity in the coexistence state of solid and liquid, there is less entrainment of bubbles, resulting in a high-quality molded product with a low porosity, and further, the metal material is added to the mold. On the other hand, since it is injected as a laminar flow, almost no nests or burrs due to entrainment of gas occur in the molded product.
[0014]
In the molding method of the present invention, a shearing force is applied to the metal material by a protrusion protruding into the runner flow path at a location near the gate portion in the runner flow path of the molding die, and the metal material is absorbed through the protrusion. It is preferable to provide means for transferring the heat to the heat source for cooling.
[0015]
As a result, the metal material flows to the vicinity of the gate portion in the runner flow path while maintaining a predetermined temperature, and heat is transferred directly from the protrusion to the heat absorption source at this position to a temperature below the liquidus temperature. It is cooled efficiently, and the shear force is applied to the protrusions very effectively, so that at least a part of the dendrite structure generated by cooling is efficiently destroyed. Therefore, in addition to obtaining the same effect as the forming method of the above invention, cooling of the metal material and application of shearing force can be performed more effectively.
[0016]
On the other hand, in the molding method of the above invention, the metal material is caused to flow while being divided into a plurality of parallel flow paths along the flow direction in the vicinity of the gate portion in the runner flow path of the molding die. the can also configure to fill by flowing into the cavity.
[0017]
As a result, when the metal material is cooled in the runner channel so as to be in the temperature range above the solidus temperature and below the liquidus temperature, the dendrite structure generated by the cooling is sufficiently small. In addition to being given a shearing force by the gate section having a road cross-sectional area, the shearing force is more effectively applied by breaking the flow of the metal material, thereby efficiently destroying. . Therefore, in addition to obtaining the same effect as the forming method of the above invention, there is an advantage that the shearing force can be more effectively applied to the metal material.
[0018]
The metal injection molding apparatus according to the present invention is formed in a space corresponding to the shape of a molded product, an injection machine for injecting a metal material in a solid-liquid coexistence state from a nozzle, a spool channel and a runner channel communicating with the nozzle. A molding die having a cavity and a gate portion existing between the runner channel and the cavity, and the metal material in the spool channel is placed in the molding die at a liquidus temperature. Heating means for heating to the above, and cooling means for cooling the metal material flowing in the runner flow path and the gate portion to a temperature range not lower than the solidus temperature and not higher than the liquidus temperature, The gate portion is narrowed down to a flow passage cross-sectional area smaller than the runner flow passage cross-sectional area.
[0019]
This metal injection molding apparatus can faithfully embody the metal injection molding method of the present invention and reliably obtain the effects of the molding method.
[0020]
In the molding apparatus according to the above invention, each of the projecting pins includes a cooling unit body in which cooling means is incorporated in a molding die, and a plurality of projecting pins projecting from the cooling unit body in a state where heat can be transferred to the cooling means. It is preferable to attach a configuration in which the tip end portion of the runner channel is provided so as to protrude in a direction orthogonal to the flow direction of the metal material in the vicinity of the gate portion in the runner flow path.
[0021]
Thereby, in addition to obtaining the same effect as that of the metal injection molding apparatus of the present invention, it is possible to more effectively apply a shearing force to the metal material. A configuration in which a plurality of partition projecting walls extending along the flow direction of the metal material are provided in parallel with each other can be provided at a location in the vicinity of the gate portion in the runner flow path of the mold.
[0022]
Thereby, in addition to obtaining the same effect as that of the metal injection molding apparatus of the present invention, it is possible to more effectively apply a shearing force to the metal material.
[0023]
In addition, the molded product of the present invention which is injection-molded by any one of the metal injection molding methods of the present invention is almost free from defects, shrinkage, nests and burrs, and is a thin and large molded product. However, it is possible to reliably mold a product having high quality.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view of a main part showing a metal injection molding apparatus that embodies a metal injection molding method according to a first embodiment of the present invention. In FIG. Are given the same reference numerals. The molding die 21 includes a fixed side molding die 22 and a movable side molding die 23. The fixed-side mold 22 has a heater 27 embedded around the spool flow path 24 and a thermocouple 28 for measuring the temperature of the heater 27. On the other hand, the movable side mold 23 has a runner channel 29 formed between the fixed side mold 22 by closing the mold and a cooling pipe 32 embedded in one side of the gate portion 30, and a gate. A thermocouple 33 for measuring the temperature of the unit 30 is provided. The gate portion 30 provided between the runner flow path 29 and the cavity 31 is restricted to a flow path cross-sectional area that is sufficiently smaller than that of the runner flow path 29.
[0025]
Next, the operation of the metal injection molding apparatus will be described. The metal material that has developed thixotropy as a solid-liquid coexistence state in the cylinder 3 is injected from the nozzle 10 of the injection machine 1 into the spool flow path 24 of the fixed side mold 22 and heated by the heater 27. Feedback control is performed so that the temperature of the heater 27 becomes a predetermined value based on the measured temperature of the thermocouple 28 that measures the temperature, so that the gate portion in the runner flow path 29 is maintained while maintaining the predetermined temperature that is higher than the liquidus temperature. Therefore, even if the total flow length of the spool flow path 24 and the runner flow path 29 is increased, the fluid flows surely without solidifying to the gate portion 30 immediately before the cavity 31. . Therefore, the molded product is free from defects due to unfilling, and the flow length is set to be longer than that of the conventional product so that a desired thin and large molded product can be obtained.
[0026]
The metal material is cooled by the cooling pipe 32 when it next flows from the runner flow path 29 to the gate portion 30, and the temperature of the gate portion 30 becomes a predetermined value based on the measured temperature of the thermocouple 33 that measures the temperature. The feedback control is performed so that the temperature of the metal material is maintained at a predetermined temperature not lower than the solidus temperature and not higher than the liquidus temperature. Further, since the metal material is given a sufficient shearing force when passing through the gate portion 30 which is narrowed to a sufficiently small channel cross-sectional area as compared with the runner channel 29 as described above, At least a part of the dendrite structure formed by cooling is destroyed. As a result, the metal material is cooled to a predetermined temperature below the liquidus temperature and given a sufficient shearing force, so that the thixotropic property is expressed again and flows into the cavity 31. The shrinkage of the time hardly occurs and the transferability to the molding die 21 is excellent and the surface accuracy is high.
[0027]
Further, since the metal material flows as a laminar flow into the cavity 31 in the state of solid-liquid coexistence, there is little bubble entrainment, so that a high-quality molded product with a low porosity can be obtained.
[0028]
Furthermore, since the metal material is injected as a laminar flow from the nozzle 10 to the molding die 21, a molded product can be obtained in which almost no burrs or burrs are generated due to gas entrainment.
[0029]
FIG. 2 is a longitudinal sectional view of a main part showing a metal injection molding apparatus embodying a metal injection molding method according to the second embodiment of the present invention, and FIG. 3 is a diagram of a movable side mold 23 in the metal injection molding apparatus. It is a perspective view. In these drawings, the same or equivalent parts as those in FIG. This metal injection molding apparatus is different from that shown in FIG. 1 in that a cooling pipe 32 is provided at one side of the runner flow passage 29 of the movable mold 23 in FIG. The cooling unit body 37 in which the cooling pipe 34 is embedded, the tip portions of the plurality of projecting pins 38 integrally projecting from the cooling unit body 37, the flow direction of the metal material in the vicinity of the gate portion 30 in the runner channel 29. However, as an arrangement protruding in the orthogonal direction, only the configuration embedded in the movable mold 23 is used.
[0030]
Therefore, the metal material heated to a predetermined temperature equal to or higher than the liquidus temperature in the spool flow path 24 by the heater 27 flows without being cooled on the upstream side in the flow direction in the runner flow path 29 and maintains the predetermined temperature. As it is, it reaches the vicinity of the gate part 30 and is effectively absorbed by the cooling pipe 34 through the protruding pins 38 and the cooling unit body 37 at this point, so that it is efficiently cooled to a temperature below the liquidus temperature. At the same time, shear force is applied to each protruding pin 38 very effectively, and at least a part of the dendrite structure generated by the cooling is efficiently destroyed. Therefore, the cooling of the metal material and the application of the shearing force can be performed more effectively, and the same effect as in the first embodiment can be obtained more reliably.
[0031]
FIG. 4 shows a molded product 39 when both the molds 22 and 23 in the second embodiment are opened. In the residual molded portion 39b by the runner channel 29 following the product portion 39a of the molded product 39, FIG. A recess 39c is formed by the protruding pin 38. The molded product 39 is cut along a cutting line indicated by a two-dot chain line to remove the remaining molded portion 39b and the like, thereby obtaining a desired molded product including the product portion 39a. The molded product thus molded has significantly reduced defects due to solidification shrinkage and the transferability of the molding dies 22 and 23 is very good, so that the surface accuracy is very good. Even a relatively large size has a high quality with few defects.
[0032]
FIG. 5 is a perspective view showing a movable side mold 40 used in a metal injection molding apparatus that embodies the metal injection molding method according to the third embodiment of the present invention. The movable side mold 40 is movable as shown in FIG. When the side mold 23 is replaced, the metal injection molding apparatus of this embodiment is obtained. The movable side mold 40 is formed of a plurality of elongated pieces extending along the flow direction of the metal material (this embodiment) in the vicinity of the gate portion 30 in the runner flow path 29 formed when the mold is closed with the fixed side mold 22. In this embodiment, three partition projection walls 41 project in parallel with each other. The movable side mold 40 is not shown in the figure, like the movable side mold 23 of FIG. 1, but the cooling pipe 32 is embedded in the side portion of the runner flow path 29 and the temperature of the gate portion 30 is adjusted. A thermocouple 33 for measuring the temperature is provided.
[0033]
Next, the operation of the metal injection molding apparatus according to this embodiment will be described. The metal material injected from the nozzle 10 in the solid-liquid coexistence state is heated by the heater 27 in the spool flow path 24 and flows while maintaining a temperature equal to or higher than the liquidus temperature and flows into the runner flow path 29. In this case, the cooling pipe 32 is cooled to a predetermined temperature not lower than the solidus temperature and not higher than the liquidus temperature. The dendrite structure generated by this cooling is given a shearing force by the gate portion 30 having a sufficiently small channel cross-sectional area, and the flow of the metal material is divided by the partition projection walls 41. By effectively applying a shearing force, it is efficiently destroyed. Therefore, the shearing force can be more effectively applied to the metal material, and the same effect as that of the first embodiment can be more reliably obtained.
[0034]
FIG. 6 shows a molded product 42 in a state where both the molds 22 and 40 in the third embodiment are opened, and a partition projection wall 41 is formed in a residual molded part 42b by a runner channel 29 following the product part 42a. The groove part 42c by is formed. The molded product 42 is cut along a cutting line indicated by a two-dot chain line to remove the remaining molded portion 42b and the like, thereby obtaining a desired molded product including the product portion 42a. Since the molded product molded in this way is similar to the molded product molded according to the second embodiment, defects due to solidification shrinkage are remarkably reduced, and the transferability of the molds 22 and 40 is extremely good. The surface accuracy is very good. In particular, even a thin and relatively large-sized one has a high quality with few defects.
[0035]
【The invention's effect】
As described above, according to the metal injection molding method of the present invention, it is possible to destroy at least a portion of the dendritic crystal structure coming generated due to cooling, shrinkage during cooling hardly occur, and for the molding die A molded product having excellent transferability and high surface accuracy can be obtained. In addition, the low sky porosity high-quality molded articles can be obtained, further, to obtain a molded article such as a nest and burrs due to entrainment of gas is hardly generated.
[0036]
According to the metal injection molding apparatus of the present invention , the metal injection molding method of the present invention can be faithfully realized and the effects of the molding method can be reliably obtained.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a main part showing a metal injection molding apparatus embodying a metal injection molding method according to a first embodiment of the present invention.
FIG. 2 is a longitudinal sectional view of an essential part showing a metal injection molding apparatus embodying a metal injection molding method according to a second embodiment of the present invention.
FIG. 3 is a perspective view of a movable side mold in the apparatus.
FIG. 4 is a perspective view showing a molded product in a state where both molding dies of the molding die are opened after the molding described above.
FIG. 5 is a perspective view of a movable side mold used in a metal injection molding apparatus that embodies a metal injection molding method according to a third embodiment of the present invention.
FIG. 6 is a perspective view showing a molded product in a state in which both molding dies of the molding die are opened after the molding described above.
FIG. 7 is a longitudinal sectional view showing a conventional metal injection molding apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Injection machine 10 Nozzle 21 Mold 24 Spool flow path 27 Heater (heating means)
29 runner flow path 30 gate part 31 cavity 32, 34 cooling pipe (cooling means)
37 Cooling unit body 38 Projection pin (projection)
41 partitioning wall

Claims (6)

Injecting the heat-melted metal material in a solid-liquid coexistence state into the spool flow path of the molding die, and flowing the metal material in the spool flow path while heating to a temperature higher than the liquidus temperature ,
In the runner channel between the spool channel and the cavity in the molding die, the metal material is cooled to a temperature range not lower than the solidus temperature and not higher than the liquidus temperature. A metal injection molding method characterized in that a metal part is allowed to flow into the cavity and filled by passing through a gate portion narrowed to a smaller cross-sectional area of the flow path compared to the above.   In the vicinity of the gate portion of the runner channel of the molding die, a shearing force is applied to the metal material by the projection protruding into the runner channel, and the metal material is transferred to the heat absorption source through the projection and cooled. The metal injection molding method according to claim 1, wherein the metal injection molding method is performed.   The metal material is made to flow while being divided into a plurality of flow paths parallel to each other along the flow direction in the vicinity of the gate portion in the runner flow path of the molding die, and the metal material is caused to flow into the cavity for filling. Item 2. A metal injection molding method according to Item 1. An injection machine for injecting a metal material in a solid-liquid coexistence state from a nozzle;
A molding die having a spool channel and a runner channel communicating with the nozzle, a cavity formed in a space corresponding to the shape of a molded product, and a gate portion existing between the runner channel and the cavity And
Heating means for heating the metal material in the spool flow path to the liquidus temperature or higher, and the metal material flowing in the runner flow path and the gate portion at the solidus temperature or higher. And having a cooling means for cooling to a temperature range below the liquidus temperature,
The metal injection molding apparatus according to claim 1, wherein the gate portion is narrowed to a flow passage cross-sectional area smaller than the runner flow passage cross-sectional area.   A cooling unit body in which a cooling means is built in the molding die, and a plurality of projecting pins projecting from the cooling unit body in a state where heat can be transferred to the cooling means, and the tip of each projecting pin is a runner flow path The metal injection molding apparatus according to claim 4, wherein the metal injection molding apparatus is provided so as to protrude in a direction orthogonal to the flow direction of the metal material at a location in the vicinity of the gate portion.   5. The metal injection molding apparatus according to claim 4, wherein a plurality of partition projecting walls extending along the flow direction of the metal material are arranged in parallel with each other at a location near the gate portion in the runner flow path of the molding die. .

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