Patent Publication Number: US-2004045693-A1

Title: Mold for casting forged material, and method for casting forged material

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT  
       [0001] The present invention relates to a mold for casting a forged material, and a method for casting a forged material, both of which are usable for casting a molten forged material. More particularly, the present invention relates to a mold for casting a forged material usable for manufacturing a metal product produced via forging process, such as, for example, a vehicle suspension part for an automobile or the like, and is capable of casting a forged material having poor castability so as to prevent an internal defect, and a method for casting a forged material using the mold.  
       [0002] The reduction in fuel consumption of an automobile is required on a global scale to prevent global warming that is one of global environmental problems. To reduce the fuel consumption, weight reduction techniques of an automobile are considered to be the most significant. It is because an automobile having lightened weight can reduce a load on a power source to allow reduction of fuel consumption in not only a gasoline engine but also any power source. A most approachable weight lightening technique is to switch a material to be used to a lightweight material. Typically, using an aluminum alloy material, many automobile parts such as an engine cylinder head or an engine cylinder block have been manufactured and used.  
       [0003] However, almost all of the parts are what is called cast products. The cast products have merit in the point that they are easy to manufacture, but there is a limit in improvement of the mechanical strength thereof. Thus, it is difficult to use the cast products for automobile parts such as suspension parts that are required to be less corrosive, have a sufficient strength and a good extending property, and have fewer defects, and that significantly relate to safety. Instead, forged products or squeeze cast products (low speed injection molded products) have been manufactured and used for such a usage.  
       [0004] However, the forged products or the squeeze cast products have a problem to be solved of high cost, and applications thereof are extremely limited at present. The reason why a conventional aluminum forged product wherein A6061 alloy or the like is used, and is preferably employed as the suspension part for the automobile is high in cost is mainly that the forged material per se is high in cost, and also that it requires a large number of manufacturing steps. Further, for example, since a squeeze cast product using an AC4CH alloy requires a large number of manufacturing steps and is low in injection speed, the cost reduction thereof can not be attained due to the low productivity.  
       [0005] On the other hand, it is clear that the application of general cast products to the suspension part used in hostile environments is difficult, even if one devotes oneself to reduce the occurrence of defects by cleaning a molten metal.  
       [0006] Thus, there have been increasing demands to reduce costs by reviewing a manufacturing process of the forged product having a higher mechanical strength. Usually, when an aluminum product is manufactured by forging, a material to be used for forging, such as a wrought material in the form of a round bar, having high plasticity and toughness appropriate for forging is bought, cut into a length according to a metal product to be produced, and then, forged with a die to separate the product and burrs. However, the burrs having not been used for the product account for appropriately 30% of a starting material prepared for the die forging. That is, only 70% of the material are used for a forged product, and this brings a big waste. Thus, it is considered that the reduction of this waste would reduce costs.  
       [0007] However, as described above, it is the standard practice among those skilled in the art that the forged material is supplied in the form of the round bar. If a supplier is required to provide a material having a shape similar to a shape of a product to be produced in order to minimize the amount of unnecessary burrs to forging, the manufacture of such a material having a particular and non-standard shape by forging, even if possible, would bring too significant increase in cost for the manufacturers to afford it only by restraining the amount of burrs to be produced. To produce a material having the shape similar to the shape of the product by forging would lower a forging ratio, and disturb the improvement in mechanical properties. This would result in losing the superiority of the forging process, and thus remain the problem unsolved.  
       [0008] Therefore, it has been required to use repeatedly the burrs generated by forging as a starting material for a metal product produced via forging process, with application of forging-press and the like after the molding of forged material by dissolving burrs and casting the resultant.  
       [0009] However, the property required for a material to be forged is plasticity or toughness as described above, and the molten metal of the forged material has poor fluidity or a poor solidification shrinkage property relating to casting ability. Thus, casting defects such as a shrinkage cavity are observed when it is cast and molded, and mechanical properties of a metal product obtained thereafter by forging are deteriorated. Consequently, since the products are not stable in the quality, it is difficult to use machining scrap such as the burrs for a raw material for the forged metal product having good mechanical properties and higher quality, even if the scrap is originally a forged material. Thus, the scrap has not been actually used. Accordingly, the machining scrap such as the burrs is used only as a raw material for miscellaneous cast products in which a high mechanical strength is not required.  
       [0010] Thus, a metal product being low in cost and having quality stability has been required as a forged metal product that requires good mechanical properties like strength and extension, like a vehicle suspension part for an automobile or the like used under the severe conditions. However, there have been proposed no appropriate metal product for such a use.  
       SUMMARY OF THE INVENTION  
       [0011] The present invention has been made, in view of the above-described conventional problems. The object of the present invention is to achieve the reduction in the cost for producing a metal product by forging, by utilizing again, for the production of a metal product having good mechanical properties being provided by forging, unnecessary machining scrap such as a burr that is a forged material being poor in the cast ability, with keeping high and stable quality equal to or higher than quality, compared with the one produced by forging using a newly forged material.  
       [0012] Further, another object is to use, for example, an aluminum alloy as metal to provide a light and strong vehicle suspension part for an automobile at lower cost, thereby the fuel cost of the automobile, and resultantly the amount of discharged carbon dioxide are reduced. Thus, the present invention is contributed to environmental protection measures such as preventing global warming.  
       [0013] The present inventors have studied casting processes and casting apparatuses, and performed casting using molten metal that is a molten forged material as a starting material to solve the above described problems. They have found that, with trial and error studies, the above described objects can be achieved by continuously cooling a mold from one end to the other end thereof to solidify a molten metal in a mold in a specified direction, thereby a metal product is obtainable by forging a preform made of a forged material that is free from internal defects by concentrating the defects in a gate riser part, even if in the case where few defects occur.  
       [0014] Namely, according to the present invention, there is provided a mold for casting a molten forged material, which comprises a first divided mold part and a second divided mold part, an open gate located on one end of the mold, a cavity for a riser connecting through said gate, and a cavity connecting through said cavity for riser and formed between said first and second divided mold parts; said mold being equipped with a shaft for inclining the mold so as to solidify a molten metal in the cavity in a specified direction from one end opposite to said gate to another end located on said gate side. It is preferable that said mold is equipped with a mechanism capable of passing a coolant through a plural number of hollow paths formed therein so as to cool a molten metal with some time difference from the one end opposite to said gate to the other end located on said gate side. The coolant usable at this time is preferably a cooling water or a cooling gas of temperature of 40° C. or below.  
       [0015] According to the present invention, it is preferred to use a mold of which first and second divided mold parts are made of a metal having high thermal conductivity of 100 to 400 W/m·K. An aluminum alloy or a copper alloy can be preferably used as a metal having such a high thermal conductivity.  
       [0016] In the case of the mold for casting a forged material according to the present invention, the cavity has preferably such a shape that a forging ratio between a material obtained by casting a molten forged material with the mold to a metal product obtained by forging the cast-forged material is approximately 10:1 to 2:1. For example, it is preferred that a forged material after casing has an approximately simple cylindrical shape.  
       [0017] A vehicle suspension part can be preferably produced as the metal product. Further, in the present invention, an aluminum alloy can be preferably used as a forged material to be used as a starting material for casting.  
       [0018] According to the present invention, there is provided a method for casting a forged material, which comprises:  
       [0019] a step of melting a forged material, and  
       [0020] a step of charging a molten forged material into a cavity of a mold to cast a cast-forged material,  
       [0021] wherein the mold used is one which comprises a first divided mold part and a second divided mold part, an open gate located on one end of the mold, a cavity for a riser connecting through said gate, a cavity connecting through said cavity for riser and formed between said first and second divided mold parts; and a mechanism capable of cooling a molten metal in the cavity; said mechanism being formed in at least one of said first divided mold part and said second divided mold part, and,  
       [0022] a step of cooling stepwise the molten forged material from one end at any one end of the mold to another end located on opposite to said one end at any one end of the mold with some time difference, thereby the molten forged material charged into the mold is solidified in a specified direction.  
       [0023] Here, it is preferred that the mechanism for cooling is a mechanism comprising a plural number of hollow paths installed in at least one of the said first and second divided mold parts, and a means for passing a coolant through said plural number of hollow paths one by one from one end of either said first divided mold part or said second divided mold part to an opposite end thereof with some time difference. It is preferred that said one end is the end on the gate side.  
       [0024] According to the present invention, there is further provided a method for casting a forged material, which comprises:  
       [0025] a step of melting a forged material, and  
       [0026] a step of charging a molten forged material into a cavity of a mold to cast a cast-forged material for a gate of the mold,  
       [0027] wherein the mold used is one which comprises a first divided mold part and a second divided mold part, an open gate located on one end of the mold, a cavity for a riser connecting through said gate, a cavity connecting through said cavity for riser and formed between said first and second divided mold parts; and a mechanism capable of inclining the mold, and,  
       [0028] a step of rotating the mold by operating said mechanism capable of inclining the mold within a predetermined time in such manner that the charging of the molten forged material is initiated when the mold is kept in a horizontal state, and the charging is completed when the mold is turned in vertical state with the gate upward, thereby the molten forged material charged into the mold is solidified in a specified direction. A metal having high thermal conductivity of approximately 100 to 400 W/m·K can be preferably used as a material for producing the mold in this case.  
       [0029] In the method for casting forged material according to the present invention, an inner surface of the mold is preferably coated with a mold wash. Moreover, it is preferable that said forged material is an aluminum alloy.  
       [0030] It is also preferable to cast an approximately cylindrical shape cast article. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0031]FIG. 1 is a sectional view of an embodiment of a mold for casting a forged material according to the present invention.  
     [0032] FIGS.  2 ( a ) to ( d ) shows an example of a flow of the casting processing according to the present invention by using an embodiment of an apparatus for casting a forged material of the present invention.  
     [0033]FIG. 3 shows a block flow of an example of a system constitution wherein the apparatus for casting a forged material according to the present invention is set, and by which a waste of the forged material is recycled.  
     [0034]FIG. 4 shows a perspective view of an example of a preform made of cast-forged material by using an embodiment of a mold for casting a forged material of the present invention.  
     [0035]FIG. 5 shows a perspective view of an example of a finished metal product produced by forging a cast-forged material that is cast by using an embodiment of a mold for casting a forged material of the present invention.  
     [0036]FIG. 6 shows a top view of another example of a preform made of cast-forged material produced by the method for casting a forged material according to the present invention.  
     [0037]FIG. 7 shows a top view of another example of a finished metal product produced by using an embodiment of the mold for casting a forged material of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT  
     [0038] Now, embodiments of a mold for casting a forged material, an apparatus for casting a forged material and a method for casting a forged material according to the invention will be described in detail. The invention is not limited to the embodiments, but various changes, modifications, and improvements may be made based on knowledge of those skilled in the art within the scope of the invention.  
     [0039] For example, an aluminum product that is produced by forging an aluminum alloy will be described as a typical metal product in the detailed description hereinafter. However, the present invention relates to a mold for casting a forged material, an apparatus for a casting forged material, and a method for casting a forged material capable of obtaining, by casting, a preform made of forged material having less internal defects and stable quality from a molten metal of a forged material having poor fluidity and a poor solidification shrinkage property relating to castability, in such a case that casting is done by melting a starting material that is originally a forged material having the above-mentioned properties, represented by the case where scraps like burrs produced during forging is effectively used. Thus, the term “metal usable as a forged material” means a forged material having a high plasticity sufficient for forging in the next step and capable of being formed into a metal product after the substantial forging processing. Thus, there is no special restriction as far as it meets the requirements. For example, the metal may include carbon steel (such as S40C) or special steel (such as chrome molybdenum steel) as an iron based alloy, or a magnesium alloy, other than the aluminum alloy (A6061).  
     [0040] The invention relates to the mold for casting a forged material, the apparatus casting for a forged material, and the method for casting a forged material adapted such that the poor castability of the forged material in a casting process does not result in the deterioration in the quality of a finished product obtained by forging even if, for example, an unnecessary burr (hereinafter also referred to as a burr material) generated in forging processing is molten and then cast to be repeatedly used as a material for forging.  
     [0041] The invention is preferably used when charging the molten forged material into the mold to cast, and the invention has a feature of causing solidification in a specified direction of the molten forged material charged into the mold by either of the following methods.  
     [0042] 1) By using a mold having a mechanism for cooling, the molten metal is cooled from one end of the mold, preferably the hollow path located on a parting surface side opposite to a gate toward the other end of the mold, preferably the hollow path located at the end of the gate side, with some time difference, preferably continuously. It is preferred to pass a coolant such as a cooling water or a cooling gas through a plural number of the hollow paths one by one, with some time difference. The mold may be cooled from outside from one end toward the other end with some time difference without passing the coolant into the mold, however, the installation of a means capable of more rapid cooling contributes to improvement in throughput, and allows easier solidification in a specified direction.  
     [0043] 2) By using a mold capable of inclining, the mold is turned in a predetermined time, preferably continuously in such a manner that the charging is initiated from the gate when the mold is in a substantially horizontal state, and the charging is completed when the mold is in a substantially vertical state with the gate upward.  
     [0044] The term “solidification in a specified direction” is well known as a method for concentrating internal defects in the cast material positioned at a riser portion by using occurrence of the internal defects such as shrinkage holes or pores at a final solidification position, for example, by solidifying the riser portion of the cast material from a particular direction as the final solidification position in general casting, and is generally performed with a cooling metal. A parting surface generally refers to a split surface of a mold, but the parting surface herein refers to a portion where an upper mold and a lower mold having no cavity and riser cavity completely contact with each other, that is, a portion opposite the gate or the riser cavity seen from the cavity. In the following description as to the accompanied drawings, the first mold part is called as an upper mold, and the second mold part is called as a lower mold, however, these expressions do not mean automatically the physical positioning in the respective mold parts.  
     [0045] In the preform made of forged material obtained by solidification in a specified direction according to the above method, a portion that solidifies latest becomes the end on the gate side, that is, the riser, and internal defects such as shrinkage cavities caused by the forged material having poor castability can be concentrated in the riser to form. The riser is outside a portion for die forging. Thus, any internal defect in casting the molten forged material does not significantly affect on the quality of the finished metal product.  
     [0046] Now, the mold for casting a forged material, the apparatus for casting a forged material, and the method for casting a forged material according to the present invention will be described in detailed with reference to the drawings.  
     [0047] First, the mold for casting a forged material, and the apparatus for casting a forged material will be described.  
     [0048]FIG. 1 is a sectional view of an embodiment of the mold for casting a forged material, and the apparatus for casting a forged material according to the invention. An apparatus for casting a forged material  93  includes a mold for casting a forged material  84  having an upper mold  85  and a lower mold  86  as a main component element, each of the upper mold  85  and the lower mold  86  has, as a mechanism for cooling, a plural number of hollow paths  94  therein capable of rapidly cooling a molten forged material, that is, molten metal charged into the mold, bypassing a coolant such as cooling water or cooling gas. The upper mold  85  and the lower mold  86  form a cavity  98  to be a mold for a preform made of a forged material, and there are provided a gate  88  from which the molten metal is poured into the cavity  98 , and the cavity for a riser  97  connected to the gate  88 .  
     [0049] A metal having high thermal conductivity of 100 to 400 W/m·K is applied as a material of the mold for casting a forged material  84 . This is because more rapid heat dissipation increases throughput, and ensures and facilitates control of solidification in a specified direction of the molten metal. For example, an aluminum alloy or a copper alloy can be used as the metal having high thermal conductivity.  
     [0050] The molten metal may be automatically poured into the cavity  98  by pressurization or suction, but in this embodiment, the molten metal is poured thereinto by a basic pumping. A pool  90  into which the molten metal pumped from a holding furnace or the like is poured can be separated from a receptacle  91  on the lower mold  86 . The lower mold  86  also is provided with a shaft  92  for inclining the mold, and around the shaft  92  for inclining the mold, the mold for casting a forged material  84  can rotate 90° from a substantially horizontal state in FIG. 1 to the state with the gate  88  upward.  
     [0051] In the invention, effective solidification in a specified direction of the molten metal that is the molten forged material poured into the cavity is significant. Thus, typical preferable aspects of the apparatus casting a forged material according to the present invention are that:  
     [0052] a) a metal having high thermal conductivity and capable of rapidly dissipating heat is used as the material for the mold for casting a forged material, and a direction of the mold for casting a forged material can be changed from at least the substantially horizontal state to a substantially vertical state, and that  
     [0053] b) the mold for casting a forged material can be cooled from one end toward the other end with some time difference and in a short time. A means capable of achieving either of the above may be provided, but a means capable of achieving both of the above like the apparatus for casting a forged material  93  shown in FIG. 1 is preferably provided.  
     [0054] Cooling the mold for casting a forged material  84  from one end toward the other end with some time difference in a short time can be achieved without installing a plural number of the hollow paths  94  in the mold for casting a forged material  84 , by applying cold air or a cooling metal to an outer surface of the mold for casting a forged material  84  from one direction to the other direction. However, for more reliable solidification in a specified direction, it is preferable to provide a means that has a plural number of the hollow paths  94  in the mold for casting a forged material  84  per se and can forcefully cool an intended particular portion of the mold for casting a forged material  84  by passing the coolant. The mechanism for cooling, for example, the plural number of hollow paths  94  may be provided on either of the upper mold  85  and the lower mold  86  only, but preferably provided on both of the upper mold  85  or the lower mold  86 . Any number of hollow paths  94  may be provided unless strength degradation of the mold for casting a forged material  84  occurs. The number and arrangement thereof are selected according to a size of the cavity  98 . It is particularly preferable to install a mechanism for passing a coolant through the plural number of the hollow paths with some time difference from an end of either one of the upper and lower molds, preferably the end opposite to the gate  88  toward another end thereof, preferably the end of the gate side with some time difference.  
     [0055] To facilitate controlling cooling of the mold for casting a forged material  84 , the temperature of the coolant such as cooling water or cooling gas passed through the hollow paths  94  is preferably at 40 20  C. or below.  
     [0056] Next, the preform made of forged material produced by using the apparatus for casting a forged material of the present invention, and forged with a die by a forging apparatus will be described. The preform made of forged material refers to a previously formed forged material, and means a cast-forged material of a predetermined size.  
     [0057] A cast material obtained by casting the molten forged material with the mold for casting a forged material, that is, a preform made of forged material preferably has a shape such that a forging ratio of the preform made of forged material to a metal product obtained by forging the preform made of forged material is approximately 10:1 to 2:1, and the mold for casting a forged material preferably has a shape capable of molding such a preform made of forged material.  
     [0058] Specifically, the preform made of forged material has a simpler shape. Even if the preform made of forged material has an extremely simple shape, when a vehicle suspension part for an automobile is taken as an example of the metal product, the forging ratio of the preform made of forged material to the metal product is approximately 10:1 or below in most cases. Thus, the shape is applicable to a manufacturing process for casting and forging the forged material as a starting material. The extremely simple shape refers to a cylinder, a cube, or a sheet with a considerable thickness, or the like, but is preferably a cylinder that is a general shape of available wrought materials.  
     [0059] When producing a metal product having a very complex shape such that the forging ratio of the preform made of forged material to the metal product exceeds 10:1, it is preferable to make the shape of a preform made of forged material more similar to the shape of the metal product to have the forging ratio of 10:1 or below. It is because this reduces the number of die forging operations in die forging by pressing, increases throughput, and reduces manufacturing costs.  
     [0060] The reason why the forging ratio of the preform made of forged material to the metal product obtained by forging the preform made of forged material is preferably about 2:1 or more is that the forged material to be cast is not always appropriate for casting in view of its fluidity or solidification shrinkage property. That is, the raw material has poor castability. Main properties required for the forged material are plasticity and toughness, and the forged material superior in such properties is likely to cause internal defects such as shrinkage cavities when cast and formed. Thus, the metal product obtained by forging the preform made of forged material having such detects does not have desirable mechanical properties.  
     [0061] Therefore, it is preferable to cause the solidification in a specified direction as described above when solidifying the molten forged material in the mold to obtain the preform made of forged material so as not to affect the finished metal product, and to form the preform made of forged material obtained by the mold for casting a forged material into a simpler shape to prevent casting defects such as the shrinkage cavities even if the molten forged material having poor fluidity is the raw material.  
     [0062] The forging ratio of the preform made of forged material to the metal product of approximately 2:1 or below is not preferable because effects such that plasticity deformation by forging provides good mechanical properties are hard to obtain.  
     [0063] The forging ratio refers to a ratio of a cross-sectional area of the preform made of forged material before forging to a cross-sectional area of the metal product after forging. The forging ratios are naturally different depending on parts, when the preform made of forged material having the simpler shape is forged with the die to obtain a metal product having a more complex shape. As described above, the shape such that the forging ratio of the preform made of forged material to the metal product is approximately 10:1 to 2:1 is preferable. This means that the metal product after forging preferably has, at any part thereof, the cross-sectional area of ½ to {fraction (1/10)} of the cross-sectional area of the preform made of forged material before forging, and the preform made of forged material and the metal product are desirably designed to have such shapes. For example, in the vehicle suspension part for the automobile generally used as the metal product, more specifically, a knuckle steering, a lower arm, or the like, the preform made of forged material satisfies the above described condition of the forging ratio even if the material has the simplest cylindrical shape.  
     [0064] The vehicle suspension part for the automobile such as the knuckle steering or the lower arm is an appropriate metal product obtained by using the apparatus for casting a forged material according to the present invention, and then performing forging and heat treatment, or the like. Conventional metal products having good mechanical properties and manufactured by forging have been too expensive to be widely used, though it has been understood that the products are appropriate for the vehicle suspension parts requiring higher strength. However, the present invention allows to produce the metal product having good mechanical properties provided by forging, from the preform made of forged material obtained by casting the molten forged material, similarly as when a virgin forged material is used as the starting material. Thus, the unnecessary machining scrap such as the burrs that are originally the forged material can be recycled to reduce costs and facilitate wide use of forged products with high performance.  
     [0065] A lighter vehicle suspension part for the automobile is preferable, and in the present invention, the aluminum alloy can be preferably used as the molten forged material that is the starting material, thus sufficiently achieving reduction in weight. If the same aluminum alloy having high thermal conductivity is used as the mold for casting a forged material, an oxide film is formed on the mold, and the mold is coated with the mold wash used in casting. Thus, if the hot molten metal of the same material is charged, a problem that the mold is molten to prevent molding does not occur. Separating the preform made of forged material from the mold is easy.  
     [0066]FIG. 4 shows an example of a shape of a preform made of forged material obtained by using the mold for casting a forged material according to the present invention, and FIG. 5 shows an example of a shape of a finished metal product obtained by forging the preform made of forged material. The product is a delivery pipe used as an automobile part. FIG. 4 is a perspective view of an example of the preform made of forged material  41 , and FIG. 5 is a perspective view of an example of the metal product  51 . In this example, the metal product  51  has no thin portion, so that the preform made of forged material  41  has a simple cylindrical shape to obtain an effect of improvement in mechanical properties by forging.  
     [0067]FIG. 6 shows another example of a shape of a preform made of forged material obtained by using the mold for casting a forged material according to the present invention, and FIG. 7 shows another example of a shape of a finished metal product obtained by forging the preform made of forged material. The product is a knuckle steering used similarly as an automobile part. FIG. 6 is a top view of an example of the preform made of forged material  61 , and FIG. 7 is a top view of an example of the metal product  71  (with a burr). In this example, the metal product  71  has a thin portion, so that the preform made of forged material  61  has a shape similar to a shape of the product so as not to increase the number of die forging operations to obtain an effect of improvement in mechanical properties by forging.  
     [0068] Next, main two embodiments of a method for casting a forged material according to the present invention will be described.  
     [0069] Either method allows solidification in a specified direction of the molten forged material charged into the mold. In these embodiments, the mold is made of the wrought material that is the aluminum alloy having high thermal conductivity, and the aluminum alloy A6061 appropriate for forging is used as the molten forged material, that is, the molten metal raw material.  
     [0070] A first method for casting includes using the forged material casting apparatus  93  shown in cross section in FIG. 1, and using, for example, the cooling water as the coolant to forcefully cool the mold from one end toward the other end continuously.  
     [0071] The mold for casting a forged material  84  is heated up to 50 to 150° C., the molten metal of 680 to 780° C. is supplied into the pool  90  by an unshown ladle, and when the mold for casting a forged material  84  is tilted, the molten metal is poured form the gate  88  into the mold for casting a forged material  84 , and charged into the cavity  98  via the riser cavity  97 . When the cavity  98  is filled with the molten metal, the cooling water of 10° C. is soon passed through hollow paths  94 (F) on the upper mold  85  and the lower mold  86 . It is preferable to cool the upper mold  85  and lower mold  86  simultaneously. Then, after 0.01 to 1.0 seconds, the cooling water is passed through next hollow paths  94 (E). This step is repeated at certain intervals, and the cooling water is passed to hollow paths  94 (A) at an end in a direction of the gate  88  to cool the molten metal. This causes solidification in a specified direction of the molten metal from a downstream side toward the gate  88  in a short time. A portion that solidifies latest is the molten metal charged into the riser cavity  97 . After the solidification, the upper mold  85  and the lower mold  86  are separated to take out the preform made of forged material.  
     [0072] A second method for casting a forged material includes, as shown in FIGS.  2 ( a ) to ( d ), using the apparatus for casting a forged material  93 , rotating the mold for casting a forged material  84  from a substantially horizontal state to a substantially vertical state, and continuously cooling the mold from one end toward the other end by air cooling.  
     [0073] FIGS.  2 ( a ) to ( d ) illustrate an example of a flow of casting processing. The molten metal  89  is pumped from the holding furnace  82  in which the molten metal  89  is heated, into the pool  90  by the unshown ladle. The mold for casting a forged material  84  is previously heated up to 50 to 150° C., and the molten metal  89  of 680 to 780° C. is supplied into the pool  90 . The pool  90  starts tilting around the tilting shaft  92  together with the mold for casting a forged material  84 , and as the pool  90  tilts from the substantially horizontal state to the substantially vertical state, preferably continuously, the molten metal  89  in the pool  90  moves from the gate  88  to the riser cavity  97 , and further to the cavity  98  at the back, and is charged from a tip, that is, a downstream side of the cavity  98  that forms a forged metal product, and into the entire cavity  98 , then charged into the riser cavity  97  that does not form the metal product. When the molten metal  89  is charged up to near the gate  88 , the pool  90  becomes empty of the molten metal  89 .  
     [0074] At this time, heat is dissipated from the mold for casting a forged material  84  to start solidification successively from the downstream side of the cavity  98  where the molten metal  89  is first charged, and in a short time, cause solidification in a specified direction from the downstream side toward an upstream side, that is, the riser cavity  97 . The time required for tilting from the substantially horizontal state to the substantially vertical state is preferably about 20 to 90 seconds. Then, the pool  90  is returned to the horizontal state to separate the upper mold  85  and the lower mold  86  and to take out the preform made of forged material.  
     [0075] The first method for casting a forged material and the second method for casting a forged material may be separately implemented, or may be implemented together for solidification in a specified direction. For solidification in a specified direction by air cooling without the first method for casting a forged material, it is desirable to provide a cooling fin such as in an air cooling motorcycle engine on an outer surface of the mold to increase an air contact area and increase an air cooling effect.  
     [0076] In the method for casting a forged material according to the present invention, the molten metal  89  is supplied into the pool  90  by the ladle (not depicted), but the pool  90  may be used as a detachable supply vessel to pump and pour the molten metal  89  by the pool  90 . It is because changes in the volume of the pool  90  and variation in the amount of poured molten metal by a formed oxide film can be prevented.  
     [0077] In the method for casting a forged material according to the present invention, an inner surface of the mold for casting a forged material  84  is preferably coated with the mold wash. The mold wash protects the inner surface of the mold to improve fluidity of the molten metal and removability after solidification.  
     [0078] Next, a forged material recycling system that includes the apparatus for casting a forged material according to the present invention and allows recycling the forged material.  
     [0079]FIG. 3 shows a block flow of an embodiment of the forged material recycling system. The forged material recycling system  1  including the apparatus for casting a forged material  93  of the present invention comprises, for example, a melting furnace  11  for melting the forged material to obtain the molten metal  89 , the apparatus  93  for casting the molten metal  89  to obtain a preform made of forged material  6 , a forging apparatus  16  for forging the preform made of forged material  6  to obtain a forged product  4 , and a trimming apparatus  18  for trimming the forged product  4  to be a pre product, and is a system in which a casting process and a forging process can be successively performed.  
     [0080] In addition, it is preferable to provide a cooling apparatus  15  for cooling the preform made of forged material  6  produced by the apparatus  93  for casting a forged material down to a temperature appropriate for the forging apparatus  16 , an analyzer  20  for confirming a component of the molten metal  89  obtained by melting the forged material containing burr materials  5 , a cleaning apparatus  12  for removing impurities in the molten metal  89 , a heat treatment apparatus  19  for improving mechanical properties of the forged and trimmed pre-product to obtain a metal product  7 , or the like.  
     [0081] In a mixing bath  10 , the burr materials  5  separated from the forged product  4  by the trimming apparatus  18  are collected, a virgin material  8  that is a forged material is added, and micro-metals  9  are mixed as required to be a staring material. The mixed starting material is molten in the next melting furnace  11  to be a molten metal  89 .  
     [0082] The first starting material with no burr material  5  contains the virgin material  8  only, but if, for example, a certain amount of burr material  5  is continuously recycled to be contained in the starting material, composition of the starting material may gradually change. Thus, the component of the molten metal  89  is analyzed by the analyzer  20  described later, and according to the result, the micro-metals  9  are mixed as required to stabilize quality by matching the composition of the starting material to such as the composition of the virgin material  8 . Generally, the micro-metals  9  are mixed in the mixing bath  10 , but may be directly charged into the melting furnace  11 .  
     [0083] Intentionally changing a mixing ratio of the micro-metals  9  allows a thermal refining operation that provides a different property from the original starting material. Such an operation also causes the analyzer  20  described later to clearly record the mixture of the forged material, so that changing the provided property causes no quality degradation or variation.  
     [0084] The melting furnace  11  is a furnace for heating the forged material together with the burr material  5  that is a solid metal to be liquid metal, that is, the molten metal  89 . A fuel for heating may be any of liquid, solid, or gas. An electrical heating source such as electrical resistance, electrical induction, or an arc, or an electronic heating method such as laser or electronic beam may be used.  
     [0085] Then, the molten metal  89  is moved to the cleaning apparatus  12  for removing the impurities. From the melting furnace  11  to the apparatus for casting a forged material  93 , the molten metal that is the liquid metal is handled, so that it is preferable to use automatic conveying/pouring means for conveying the molten metal in view of productivity and safety.  
     [0086] The analyzer  20  analyzes the component of the molten metal  89 , and is preferably provided after the melting furnace  11  and before the apparatus casting a forged material  93  for quality control. The analyzer  20  can take a sample of the molten metal  89  from the melting furnace  11  to obtain a composition ratio of the metal contained in the molten metal  89 , and monitor and measure whether the quality of the molten metal  89  has no problem. Monitoring the quality of the molten metal  89  by the analyzer  20  facilitates recycling using not only the burr material  5  generated from the system and the added virgin material  8 , but also scrap such as burrs generated from other systems as starting material.  
     [0087] The cleaning apparatus  12  removes inclusion or impure gas by, for example, degassing, deoxidizing, and filtering, with the understanding that increasing purity of the molten metal is essential to prevention of the internal defects of the product and improvement in mechanical strength.  
     [0088] The holding furnace  82  is a furnace for holding a temperature of the molten metal  89  cleaned by the cleaning apparatus  12  until the molten metal  89  is sent to the apparatus for casting a forged material  93 , and usually includes a heater. The type of the heater is not limited, but it is preferable to use an immersion heater capable of directly transferring heat to the molten metal  89 , and place the heater so as to achieve even heat distribution.  
     [0089] The apparatus for casting a forged material  93  pours the molten metal  89  into the mold as described above, and after the solidification in a specified direction, obtains the cast product, that is, the preform made of forged material  6  as solid metal.  
     [0090] It is also preferable in terms of the quality control to provide an inspection apparatus  21  after the apparatus for casting a forged material  93  to inspect the internal defects of the preform made of forged material  6 . The inspection apparatus  21  can include, for example, a magnetic detector or an ultrasonic detector.  
     [0091] Then, the temperature of the preform made of forged material  6  is lowered, in the cooling apparatus  15 , to the temperature appropriate for the forging apparatus  16 , and for example, forging pressing of the preform made of forged material  6  is performed by the forging apparatus  16  to obtain the forged product  4 .  
     [0092] The forged product  4  is cooled by a cooling apparatus  17 , and then separated into the pre-product and the burr material  5  by the trimming apparatus  18 . The pre-product is subjected to solution heat and aging treatment such as T 3  to T 6  by the heat treatment apparatus  19  to improve the mechanical properties, thus becoming the finished metal product  7 .  
     [0093] The burr material  5  separated by the trimming apparatus  18  is returned to the mixing bath  10  and mixed with a virgin material  8 , and then recycled as the forged material. Thus, the burr material  5  is effectively used as the metal product  7  produced by forging, thereby reducing starting material costs that form a large proportion of total costs for forged products to reduce manufacturing costs. Not only the burr material  5  separated by the trimming apparatus  18 , but also burr receivers or defectives can be recycled.  
     [0094] As described above, the invention allows keeping high quality of the metal product obtained by casting and then forging the starting material that is the forged material having poor castability. Specifically, the metal product having good mechanical properties provided by forging can be produced from the preform made of forged material obtained by casting the molten forged material similarly to the case where the virgin forged material is used as the starting material. Thus, the unnecessary machining scrap such as the burr can be recycled, thereby reducing costs of the forged metal product that has not been widely used because of the high costs though there is high potential demand, and meeting market needs.  
     [0095] Using, for example, the aluminum alloy as a metal to provide the light vehicle suspension part at lower cost achieves reduction in fuel cost of the automobile to reduce discharged carbon dioxide that is a problem on a global scale and to contribute to environmental protection measures such as preventing global warming.