JP3927957B2 - Low melting point metal alloy forming method - Google Patents

Description

  The present invention relates to a method of injecting a low-melting-point metal alloy into a metal mold in a semi-solid state having thixotropic properties to form a metal product.

  As a method for forming a magnesium alloy, a metal material is dissolved in a liquid alloy at a temperature equal to or higher than the liquidus temperature, and the liquid alloy is allowed to flow down on the surface of the inclined cooling plate to rapidly cool it into a semi-molten state, which is stored in a storage tank. In this way, a metal slurry (semi-solid) with thixotropic properties is maintained by maintaining the temperature in the solid-liquid coexistence temperature range, and then cast into a metal material that potentially has thixotropy. It is heated into a metal mold and injected into a mold to form a metal product.

  As a method for producing a semi-molten hypereutectic aluminum alloy, the molten metal is caused to flow down on the surface of the inclined cooling plate and rapidly cooled to a semi-molten state, and this is put into a required number of heat insulating containers to obtain a predetermined liquid phase ratio. While maintaining the temperature in the solid-liquid coexistence temperature range for 5 seconds to 60 minutes, thereby generating a large number of fine spherical primary crystals and transferring the heat insulating container to the injection sleeve by a rotating disk, A semi-molten alloy in a container is pressure-molded into a metal product using a molding die.

In addition, as a forming means for magnesium alloy or the like, a heating means is provided on the outer periphery of a cylindrical body having a nozzle opening at the tip, and a measuring chamber connected to the nozzle opening is fixed to a molten metal holding cylinder formed in the tip by a reduced diameter. Some metal materials with thixotropic properties that are spheroidized are supplied and dissolved and accumulated, and the molten plunger held in the molten metal holding cylinder measures and melts and holds the molten metal that is injected into the mold. is there.
JP 2001-252759 A JP-A-9-10893 JP 2003-200409 A

  In the above molding method, the metal slurry having thixotropic properties generated by melting and quenching is cooled and solidified to form a metal material, and this metal material is re-melted and supplied to the mold. And the metal slurry is cooled and solidified into a metal material, which consumes a large amount of energy and requires a device for cooling the metal slurry and a device for cutting the metal material. Become. For this reason, there is a problem that the product cost is increased, and maintenance and management of the facilities are required.

  Also, in the molding method in which the rapidly cooled semi-molten alloy is put in a heat insulating container and kept at a temperature in the solid-liquid coexistence temperature range, and then supplied to the molding die and pressed into a metal product, the semi-molten alloy is remelted. Since it is pressure-formed without melting, it only needs to be melted once, and an apparatus for processing it into a metal material is not required, but in order to hold the semi-molten alloy in a heat-insulating container until a predetermined liquid phase ratio is obtained, continuous molding is performed. To do so, a large number of insulated containers are required. Further, a means for transferring the heat insulating container from the cooling jig to the injection sleeve and a device for transferring the semi-molten alloy to the injection sleeve are also required. Furthermore, since the insulated container also serves as a semi-molten alloy measuring container required for one molding, every time the product weight is changed, the molded container must be molded by changing to a insulated container having a volume suitable for the weight. The holding time until the phase ratio becomes shorter as the capacity becomes smaller. Therefore, it is difficult to adapt to the molding cycle time, and there is a problem that it is not suitable for molding a metal part having a product weight of 100 g or less. .

  In the above-mentioned conventional method, the thixotropic metal material with a solid phase spheroidized is dissolved and accumulated in the molten metal holding cylinder, and the accumulated molten metal is measured and injected into the mold by the forward and backward movement of the injection plunger. Since the molten metal accumulated in the molten metal holding cylinder is weighed and injected into the mold for each molding, the metering can be changed by adjusting the back and forth of the injection plunger, and the accumulated time becomes the holding time. There is no problem as in the case of holding the semi-molten alloy by the heat insulating container. However, the thixotropic metal materials used there are manufactured by material manufacturers, and the solid phase ratio (liquid phase ratio) often varies from production lot to production lot. Before starting, it is necessary to make a trial hit and set the accumulation amount, accumulation time, and holding temperature.

  This is a metal material with thixotropic properties, and when dissolved, it becomes a semi-molten metal (hereinafter referred to as semi-solid) in which the solid and liquid phases coexist, and the solid-liquid coexistence temperature range in order to maintain the fluidity of this semi-solid temperature This is because the solid phase grows over time and the solid phase ratio becomes higher than that at the time of dissolution. In the case of a metal material with a high solid phase ratio, if the accumulation time of the semi-solid is not set short, the fluidity deteriorates due to the solid phase grown during the accumulation, and the metering due to the backward movement of the injection plunger becomes unstable, and the product is good. It becomes difficult to perform continuous molding.

  The present invention has been conceived to solve the above-described conventional problems, and its purpose is to produce a semisolid having thixotropic properties from the dissolution of a cast normal metal material (dendritic crystals) and Accumulation and injection into the mold can be performed consistently, so that the solid phase ratio of semi-solid generated for each molding can be grasped and the allowable accumulation time (holding time) can be set from the solid phase ratio. At the same time, by setting the balance of the supply amount and accumulation amount of semi-solid, supply time and holding temperature, etc. based on the molding cycle time, all the accumulated amount of semi-solid is die within the allowable time continuously. It is an object of the present invention to provide a new method for forming a low-melting-point metal alloy that can be injected.

According to the above-described object, the present invention provides a step of melting a solid material of a low melting point metal alloy into a liquid alloy having a temperature equal to or higher than the liquidus temperature by a melting furnace, and the liquid alloy is disposed between the melting furnace and the generation tank. and the inclined quench cooling plate on the plate surface by flow down of, and stored the generated bath set to a temperature of solid-liquid coexisting temperature range, generated semisolid having thixotropic properties which the solid phase is finely spheroidized And a semi-solid for the required number of shots from the generation tank is supplied and accumulated in a heating and holding cylinder having a nozzle at the tip and a heating means on the outer periphery, and the temperature in the solid-liquid coexistence temperature region is stored by the heating and holding cylinder And the semi-solid accumulated in the heating and holding cylinder by the forced retraction of the injection plunger in the heating and holding cylinder within the time before the thixotropic properties are maintained and the fluidity deteriorates due to solid phase growth. 1 shot Weighed by minute, a step of forming an injection to a metal product in the mold from the nozzle by forced forward, it is that consist.

For the supply and accumulation of the semi-solid, the value obtained by dividing the allowable accumulation time by the molding cycle time is taken as the total number of shots in the accumulation time, and the total number of shots is equally divided into three or more equal parts. A semi-solid of one equivalent is newly supplied from the generation tank to the heating and holding cylinder every time required for injection of one equivalent, with the amount as the generation amount and the other as the accumulation amount. The method for forming a low melting point metal alloy according to claim 1.

The semi-solid is made of a magnesium alloy, and the injection of the semi-solid into the mold is performed within an accumulation time not exceeding 30 minutes after accumulating in the heating and holding cylinder. It consists of dendritic ingots and short columns that are cast by melting the alloy completely.

  In this invention, a semi-solid having a thixotropic property generated by dissolving a solid material is immediately accumulated in a heating and holding cylinder and injection molding of a metal product is continuously performed. Therefore, the semi-solid is processed into a solid material and molded. Compared to molding methods that re-melt with a machine, or semi-solids that are cooled and held until the desired solid phase ratio is transferred to the molding machine, less energy is consumed, and the molding machine is simplified, resulting in manufacturing costs. Can be reduced.

  Also, since the metal material is melted and semi-solidified at the time of molding, the solid phase ratio of the semi-solid can be grasped from the set temperature, and the accumulation time suitable for the molding cycle time is set from the solid phase ratio, and the semi-solid ratio is set. Since the supply amount and accumulation amount of solids can be balanced, even if semi-solids are accumulated in a heated holding cylinder and molded, deterioration of fluidity due to solid phase growth and poor measurement due to flow resistance Since the accumulated semi-solid is weighed and molded one shot at a time, it can be adapted to changes in product weight and metal parts with small product weight can be easily molded.

In the figure, reference numeral 1 denotes a metal forming machine, in which a heated holding cylinder 2 having a nozzle member 22 at the tip of a cylindrical body 21 and a solid material M ₁ of a metal alloy such as magnesium alloy are dissolved in a liquid alloy M ₂ , and then the thixotropic properties are obtained. It comprises a device ₃ that produces the semi-solid M ₃ and supplies it to the heating and holding cylinder 2 and an injection driving device 4 at the rear of the heating and holding cylinder 2.

The heating and holding cylinder 2 includes the semi-solid generating and supplying device 3 at a supply port provided in the middle upper side of the cylinder 21, and the temperature of the semi-solid M ₃ stored in the heating and holding cylinder 2 around the outer periphery of the cylinder is required. A heating means 24 using a band heater for heating and holding at a temperature is provided. Further, the rear end portion of the cylindrical body is attached to the support member 23 and is inclined at an angle of 45 ° with respect to the horizontal plane.

  The inside of the tip portion communicating with the nozzle opening of the nozzle member 22 is formed in a measuring chamber 25 having a required length reduced to a diameter of 8 to 15% smaller than the inner diameter of the cylindrical body. The injection plunger 26a at the front end of this is fitted so as to freely advance and retract.

  This injection plunger 26a is attached to the tip of a rod 26b, and is provided with a check valve 26c having a seal ring embedded in the outer peripheral surface thereof so as to be movable back and forth around the shaft portion. A flow path 26d is formed between the check valve 26c and the shaft portion, and the flow path 26d can be opened and closed by contacting and separating the rear end surface of the check valve 26c and the seat ring 26e at the rear portion of the injection plunger. Are inserted into the measuring chamber 25 so as to freely advance and retract.

  The inside of the cylindrical body 21 from the upper edge of the supply port to the upper part is close to the upper edge of the supply port and is closed by a closing member 27 provided in the cylindrical body. The closing member 27 is composed of a shaft member having a length extending from the vicinity of the upper edge of the supply port to the rear end of the cylinder, and is airtightly fixed by bolting the outer end to the rear end of the cylinder. A rod 26b of the injection means 26 is inserted in a through hole formed in the center so that the periphery thereof is hermetically sealed by a plurality of rings 28 so as to advance and retract. The rear end of the rod 26b is connected to the injection driving device 4.

The semi-solid production and supply apparatus 3 includes a melting furnace 31 having an outflow channel at the bottom, a cooling unit 33 having an inclined cooling plate 32 connected to the lower side of the melting furnace 31 and connected to the lower side of the melting furnace 31; A semi-solid M ₃ generation tank 34 having an upper opening connected to the cooling unit 33 and a supply pipe 35 connected to the bottom of the generation tank 34 are connected in a vertically long manner, and the supply pipe 35 is heated and retained. The melting furnace 31 is placed and fixed on the arm member 29 connected to the support member 23 at the rear of the cylinder, and is erected on the heating and holding cylinder 2. It is.

  Around the outer periphery of the melting furnace 31 and the generation tank 34, heating means 36 and 37 such as band heaters and induction heaters are respectively provided in a plurality of heating zones, and the outflow path and supply of the melting furnace 31 are provided. Valve devices 38 and 39 that are individually opened and closed are attached to the pipe line 35. Further, inert gas injection pipes 40 a and 40 b such as argon gas are provided from the lower part of the supply pipe 35 to the inside of the melting surface L of the heating and holding cylinder 2 and in the space above the supply pipe 35.

The heating means 36 of the melting furnace 31 is set to a temperature equal to or higher than the liquidus temperature of the low melting point metal alloy used as the solid material M ₁ , and the heating means 37 of the generation tank 34 and the heating means of the heating holding cylinder 2 are set. Both are set to a temperature in the solid-liquid coexistence temperature region between the liquidus temperature and the solidus temperature. The inclined cooling plate 33 is provided with a flow path 33a of the cooling medium therein, the liquid metal M ₁ flowing down over the plate surface from the melting furnace 31 by the cooling medium can be cooled to a temperature of solid-liquid coexisting temperature range It is like that.

  Regarding the forming of the low melting point metal alloy by the metal forming machine 1 having the above-described configuration, the case of a magnesium alloy (AZ91D) will be described as an example. First, the heating means 36 of the melting furnace 31 is set to a temperature higher than the liquidus temperature, for example, 600 °. The temperature is set to ˜700 ° C., and both the heating means 24 of the heating and holding cylinder 2 and the heating means 37 of the production tank 34 are set to a temperature in the solid-liquid coexistence temperature region, for example, 560 ° to 590 ° C. The temperature of the cooling medium inside the inclined cooling plate 33 is set to 5 ° to 50 ° C.

Next, the solid material M ₁ of the magnesium alloy is charged into the melting furnace 31 whose outflow path is closed by the valve device 38. The solid material M ₁ is made of an ingot or a short column formed by removing the molten magnesium alloy from the cold, and the metal structure is made of dendritic crystals.

The solid material M ₁ charged into the melting furnace 31 is heated to a temperature equal to or higher than the liquidus temperature and completely dissolved in the liquid alloy M ₂ . When the liquid alloy M ₂ in the melting furnace reaches a set amount, the outflow passage is opened and the liquid alloy M ₂ is poured onto the plate surface of the inclined cooling plate 33. The liquid alloy M ₂ is rapidly cooled by the inclined cooling plate 33 and flows into the production tank 34 in which the supply pipe 35 at the bottom is closed by the valve device 39 in a semi-molten state. The fine primary crystals generated while flowing down on the plate surface have a spherical shape, and the liquid phase and the spherical solid phase coexist in the production tank 34 set to a temperature in the solid-liquid coexistence temperature region. The resulting semi-solid M ₃ has thixotropic properties.

When the semi-solid M _{3 in the} production tank 34 reaches the set amount, the outflow passage of the melting furnace 31 is closed and the next solid material M ₁ is melted. Also, the supply line 35 is opened, and the semi-solid M ₃ in the production tank 34 flows out from the supply line 35 to the heated holding cylinder 2 heated to the temperature in the solid-liquid coexistence temperature region, and is supplied. The semi-solid M _{3 corresponding} to the required number of shots is accumulated until it is injected into a mold that does not. The accumulated temperature of the semi-solid M ₃ is maintained at a temperature in the solid-liquid coexistence temperature region until it is injected after weighing.

A part of the semi-solid M ₃ corresponding to the required number of shots accumulated in the heating and holding cylinder 2 flows into the measuring chamber 25 from the flow path 26d by the forced retraction of the injection plunger 26a, and enters the measuring chamber 25 for one shot. As stored. Since the amount of the semi-solid for one shot varies depending on the retracted position of the injection plunger 26a, it is possible to perform the measurement corresponding to the product weight regardless of the product weight only by the retracting operation of the injection plunger 26a. This weighing can be accurately performed even for metal parts having a small product weight. The semi-solid after the metering is injected from a nozzle 22 directly into a mold (not shown) or through a hot runner by a forced advance of an injection plunger 26a, and is formed into a metal product in a desired form.

The solid phase ratio of the semi-solid M ₃ varies depending on the temperature. In the case of the magnesium alloy, the solid phase ratio is around 65% at a set temperature of 570 ° C., and around 50% at 590 ° C., even if the temperature is in the solid-liquid coexistence temperature region, the solid phase becomes closer to the liquidus temperature. The rate is low. However, the spherical solid phase grows and grows with time regardless of the difference in solid-liquid coexistence temperature, and accordingly, the solid phase ratio increases and the density of the solid phase in the liquid phase also increases.

  3 and 4 are a semi-solid structure diagram (FIG. 3) in which the time at which the solid-liquid coexistence temperature is maintained is extremely short, and a semi-solid structure diagram (FIG. 4) held at 570 ° C. for 30 minutes. As is apparent from the figure, the solid fraction of the semi-solid has already reached 64% after production and has thixotropic properties. Although the solid phase ratio increases by 5% to 69% even in a state of being held for 30 minutes, the solid phase b in the liquid phase a is growing large overall. However, there are few things exceeding 200 μm, and the thixotropic properties are retained. When the holding time exceeds 30 minutes, the ratio of the solid phase b exceeding 200 μ increases, the solid phase ratio reaches 75%, and the fluidity decreases.

Therefore, the thixotropic property of the semi-solid M ₃ made of the magnesium alloy is maintained as long as the solid phase grows large if the proportion of the solid phase exceeding 200 μm is small, and the more the proportion of the solid phase exceeding 200 μ increases, the more difficult it becomes to flow. . Even with the semi-solid M ₃ accumulated in the heating and holding cylinder 2, if the accumulation time is within 30 minutes, metering by forced retraction of the injection plunger 26a and injection into the mold by forward movement can be performed smoothly. And the growth of the solid phase makes it difficult to pass through the flow path 26d of the injection plunger 26a, and the flow resistance and the decrease in flowability caused by the solid phase are combined to cause the backward movement of the injection plunger 26a. Feeding the semi-solid M _{3 into} the measuring chamber 25 becomes troublesome. For this reason, the weighing for each molding becomes unstable, and short shots are likely to occur due to a shortage of injection amount into the mold.

In order to avoid such a phenomenon, the semi-solid M ₃ accumulated in the heating and holding cylinder 2 is injected within a time before the thixotropy is lost due to the growth of the solid phase. If injection within sequential 30 min semisolid M ₃ accumulated in the heating holding cylinder 2 in the above magnesium alloys, continuously from the solid material M ₁ to the forming of production and accumulation and metal products semisolid M ₃ without trouble It can be carried out.

The ratio of the production amount of the semisolid M ₃ and the accumulation amount of the heating and holding cylinder 2 can be set from the accumulation time allowed from the solid phase rate and the molding cycle time. The value obtained by dividing the accumulation time by the molding cycle time (cooling-mold opening-product removal-mold closing and mold clamping-time required for completion of injection) is the total number of shots in the accumulation time. Divide evenly into equal parts or more to make 1 part as a production amount, and use the other as an accumulation quantity. Even if the storage time in the tank 34 is added as the accumulation time, the total amount of the semisolid M ₃ accumulated therein is continuously ejected within the time having the thixotropic property.

It is also possible to set several accumulation times at equal intervals, and form and accumulate semi-solid M ₃ suitable for those accumulation times. In this case, the number of shots for each accumulation time is divided equally with the number of shots of the accumulation time difference as a unit, and the same amount is generated in the same manner as described above, and the other is stored as the accumulated amount. If the supply and accumulation of the semisolid M _{3 is performed} every required time, the injection can be continuously performed within the accumulation time set there.

  For example, in the above magnesium alloy, the allowable storage time is 30 minutes or less with a solid phase ratio of 30 to 70%, so in the molding of a product weight of 50 to 100 g (one shot) that requires a molding cycle of 25 seconds, If several accumulation times are set within the allowable time at intervals of 5 minutes, 72 shots (3600-7200 g) at 30 minutes, 60 shots 3000-6000 g at 25 minutes, 48 shots (2400-4800 g at 20 minutes) ), It takes 36 shots (1800 to 3600 g) in 15 minutes.

Further, since the number of shots with a time difference of 5 minutes is 12 shots, the number of shots per accumulation time is equally divided into 6, 5, 4, and 3 units, respectively. If one unit is the amount of semi-solid M ₃ produced per time and the remaining 5, 4, 3, 2 units are accumulated amounts in the heated holding cylinder 2, the ratio of the generated amount to the accumulated amount is 1: 5. 1: 4, 1: 3, 1: 2.

Since the time required for injecting 12 shots in a molding cycle of 25 seconds is 5 minutes, 12 shots (600 to 1200 g) of semi-solid M ₃ are fed from the production tank 34 to the heating and holding cylinder 2 every 5 minutes. If supply and accumulation are performed, the semi-solid M ₃ accumulated in the heating and holding cylinder 2 within the set accumulation time can be sequentially injected into the mold even if the storage time in the production tank 34 is included. Further, since the generation amount and the supply time are constant with respect to any accumulation time, the accumulation time (accumulation amount) can be changed only by adding or subtracting the accumulation amount of the heating and holding cylinder 2 for each unit. Therefore, the accumulation amount can be arbitrarily set according to the volume of the heating and holding cylinder 2 and the product weight.

It is a vertical side view of the metal forming machine used for the forming method of the low melting point metal alloy according to the present invention. It is sectional drawing of an injection plunger with a check valve. It is a structure | tissue chart by the metallographic microscope after the production | generation of the semisolid which has the thixotropic property of a magnesium alloy (AZ91D). It is a structure | tissue figure by a metal microscope at the time of hold | maintaining the semisolid same as the above for 30 minutes at the temperature of a solid-liquid coexistence temperature range.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal molding machine 2 Heating holding cylinder 3 Semi-solid production | generation supply apparatus 21 Cylindrical body 22 Injection nozzle 24,36,37 Heating means 26 Injection means 26a Injection plunger 31 Melting furnace 32 Cooling part 33 Inclined cooling plate 34 Generation tank 35 Flow path 38 , 39 Valve device

Claims (4)

Melting a low melting point metal alloy solid material into a liquid alloy having a temperature equal to or higher than the liquidus temperature in a melting furnace;
The liquid alloy is rapidly cooled by flowing down on the surface of the inclined cooling plate disposed between the melting furnace and the generation tank, and stored in the generation tank set to a temperature in the solid-liquid coexistence temperature region. Producing a semisolid having thixotropic properties in which the phase is finely spheroidized;
A step of supplying and accumulating the required number of semi-solids from the generation tank to a heating and holding cylinder having a nozzle at the tip and a heating means on the outer periphery, and maintaining the temperature in the solid-liquid coexistence temperature region by the heating and holding cylinder. When,
The semi-solid accumulated in the heating and holding cylinder is measured one shot at a time by the forced retraction of the injection plunger in the heating and holding cylinder within the time before the fluidity deteriorates due to solid phase growth while maintaining thixotropic properties. , A process of injecting into the mold from the nozzle by forced advance and forming into a metal product;
An injection molding method for a low-melting-point metal alloy comprising: For the supply and accumulation of the semi-solid, the value obtained by dividing the allowable accumulation time by the molding cycle time is taken as the total number of shots in the accumulation time, and the total number of shots is equally divided into three or more equal parts. A semi-solid of one equivalent is newly supplied from the generation tank to the heating and holding cylinder every time required for injection of one equivalent, with the amount as the generation amount and the other as the accumulation amount. The method for forming a low melting point metal alloy according to claim 1.   2. The low melting point metal according to claim 1, wherein the semi-solid is made of a magnesium alloy, and the injection of the semi-solid into the mold is performed within an accumulation time not exceeding 30 minutes after accumulation in the heated holding cylinder. Alloy injection molding method.   2. The method of forming a low-melting-point metal alloy according to claim 1, wherein the solid material is composed of a dendritic crystal ingot and a short column that are cast by completely melting the low-melting-point metal alloy.

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