Patent Publication Number: US-2018029112-A1

Title: Manufacturing apparatus for metal molded body

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a manufacturing apparatus for a metal molded body. More specifically, the present invention relates to an apparatus for suppressing growth of a metal crystal by electromagnetically stirring melted metal such as aluminum alloy, cooling the melted metal while discharging residual gas as a source of a mold cavity, and producing a tough metal molded body. 
     Description of Related Art 
     Description will be made by taking an example of aluminum as metal. In order to produce a precise aluminum material, it is essential that aluminum as a material has a fine crystal structure, and does not have defects such as a mold cavity therein. In order to produce such a material, molten aluminum is transferred to a die of a stirrer (manufacturing apparatus for a metal molded body), and growth of a crystal structure is prevented by stirring and cooling the molten aluminum in the die, so that a dense material is produced. Mechanical force is sometimes used as stirring force, but an electromagnetic force method capable of performing stirring in a non-contact manner is preferable in consideration of abrasion and the like of a stirring rod. 
     In order to perform stirring by electromagnetic force, a large number of coils are arranged along a wall surface (indicating an inner wall surface) of the die, a magnetic field which travels along the wall surface by a group of these coils is formed. An induced current is generated in the molten aluminum by the traveling magnetic field, electromagnetic force (Lorentz force) is generated by the current and the changing magnetic field, and the molten metal moves along the wall surface. Then, the movement of the molten metal along the wall surface reaches the center, so that stirring as a whole proceeds. This stirring work is continued until the metal is solidified. There are a case where the solidified metal is used as a final molded body with no change, and a case where the solidified metal is transposed to a press forming die to be pressurized and formed. The aluminum material thus completed has strong strength, and has less defects such as a mold cavity. Therefore, such an aluminum material is reliable as a part material. 
     In general, in an aluminum rabble furnace, a molten substance is stirred in a cylindrical melting pot, as described in JP 5352236 B1, JP 2009-74103 A, and JP 2007-144501 A. Therefore, the electromagnetic stirring apparatus has a cylindrical shape, similarly to a motor stator. However, for example, in a case where an elongated structure is made of aluminum, the shape of a stirring die is elongated. In the cylindrical rabble furnace, the volume of the furnace becomes huge, and huge excitation force is required, which is irrational. Therefore, a linear type stirring apparatus described in JP 2006-289448 A is known. 
     As a structure of a thrust section of a linear type stirring apparatus, JP 2006-289476 A, “Electromagnetic Coil Designed by Magneto-Hydro-Dynamic Simulation”, shinnittetsu giho vol. 379, and “Development of a Simulation Model for Electromagnetic Stirring in Melting Furnace, Furukawa-sky Review” No. 3, 2007” are known. 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     A vehicle body structure and the like are generally thin and long. In addition, such structures are often bent. Accordingly, in the circular stirring apparatus, as described above, the furnace volume is large, and excitation force (AT) for operation becomes extremely strong, and therefore handling is difficult. Therefore, such a linear type stirring apparatus described in JP 2006-289448 A, and JP 2006-289476 A, related to a continuous casting apparatus is applied. However, the linear type stirring apparatus has an elongated structure, and has a long acceleration distance (refer to  FIG. 1 ). Such a long acceleration distance increases the speed of molten metal, and a phenomenon that the molten metal runs on a wall surface of a die at a folded part or turning position having a small radius of curvature (refer to an end  18  of  FIG. 1 ), or runs over the wall surface to fall to the outside is generated. In particular, the die is provided with a draft angle, and therefore the molten metal more easily runs on the wall surface. 
     In order to suppress such a run-over phenomenon, when excitation force is reduced, traveling becomes moderate, and the run-over is suppressed. On the other hand, stirring efficiency is lowered, and a metal molded body formed of fine crystals cannot be efficiently manufactured. The present invention solves such a problem, and an object of the present invention is to provide a manufacturing apparatus for a metal molded body capable of performing efficient stirring by using an elongated die, and suppressing run-on or run-over of molten metal to a die wall surface. 
     Means to Solve the Problem 
     A manufacturing apparatus for a metal molded body of the present invention includes: a die having an elongated shape in plan view; and a plurality of pairs of thrust units disposed along a wall surface with the die disposed therebetween from both sides of the die, wherein the pairs of thrust units have electromagnetic coils that generate reverse traveling magnetic fields with each other and the thrust units arranged in a longitudinal direction are set so as to generate reverse traveling magnetic fields for each single thrust unit or each series composed of a plurality of the thrust units. 
     Such a manufacturing apparatus for a metal molded body may include a control circuit that switches the traveling magnetic fields of the electromagnetic coils such that the thrust units arranged in the longitudinal direction generate the reverse traveling magnetic fields for each desired number of the thrust units. Additionally, a whole or a part of the die may be curved in plan view. Furthermore, the manufacturing apparatus for a metal molded body preferably includes a thrust unit that causes an obliquely vertical traveling magnetic field, in addition to the thrust unit that causes a horizontal traveling magnetic field. 
     Effect of the Invention 
     In the manufacturing apparatus for a metal molded body of the present invention, a partial circulation flow of molten metal can be generated in the die by the traveling magnetic fields of the series composed of a pair of or a plurality of pairs of the thrust units disposed along the wall surface with the die disposed therebetween. That is, a flow in one direction is generated by the single or the plurality of thrust units disposed along one wall surface, and a flow in the other direction is generated by the single or the plurality of thrust units disposed along the other wall surface. Then, in an end of each series, a flow is generated in the die crossing direction. Therefore, a flow that circulates for each thrust unit is generated. The traveling direction of the magnetic field of a certain series of the thrust units, and the traveling direction of the magnetic field in the other series of the thrust units adjacent to the certain series of the thrust units are reversed from each other, and therefore the directions of the circulation flows are reversed. For example, when a clockwise circulation flow is generated in the series of the pair of thrust units, a counterclockwise circulation flow is generated in the other series of pair of thrust units in the adjacent to the series of the pair of thrust units. 
     Therefore, in each of the ends of the series of the thrust units, the flow along the wall surface is divided, and a node is formed in the flow. Therefore, an accelerated flow reduces the speed at a portion of the node or joint, and migration energy is converted into stirring energy. Therefore, running on the wall surface and running over the wall surface are suppressed. Additionally, at the portion of the node, the molten metal flowing from one of both sides collides with the molten metal flowing from the other side, or is divided, and therefore the molten metal is more efficiently stirred. 
     In a case where such a manufacturing apparatus for a metal molded body includes the control circuit that switches the directions of the traveling magnetic fields of the electromagnetic coils such that the thrust units arranged in the longitudinal direction generate the reverse traveling magnetic fields for each desired number of the thrust units, suitable stirring action and flow rate can be selected in accordance with the kind of metal. In a case where the die is curved in plan view, the curved metal molded body can be efficiently produced, and suppression of the above run-on and run-over can be attained similarly to the above. 
     In a case where the manufacturing apparatus includes the thrust unit that causes the obliquely vertical traveling magnetic field, in addition to the thrust unit that causes the horizontal traveling magnetic field, molten metal obliquely flows, and therefore a laminar flow commutates, and can be more efficiently stirred, and crystal grains can be made fine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view illustrating a manufacturing apparatus for a metal molded body according to an embodiment of the present invention, and  FIG. 1B  is an enlarged view of an essential part. 
         FIG. 2  is a II-II line sectional view of the manufacturing apparatus of  FIG. 1A . 
         FIG. 3A  and  FIG. 3B  are a schematic plan view and a schematic side view illustrating thrust units according to an embodiment (core back winding method) of the present invention, respectively. 
         FIG. 4A  and  FIG. 4B  are a schematic plan view and a coil connection diagram illustrating thrust units according to another embodiment (slot winding method) of the present invention, respectively. 
         FIG. 5  is a plan view illustrating an example of wire connection when a plurality of the thrust units of  FIG. 3A  and  FIG. 3B  are combined. 
         FIG. 6  is a plan view illustrating a manufacturing apparatus for a metal molded body according to another embodiment of the present invention. 
         FIG. 7A  and  FIG. 7B  are a front view and a plan view illustrating thrust unit that changes a flow of molten metal according to an embodiment of the present invention, respectively (illustration of the shapes of coil sides are omitted). 
         FIG. 8A  to  FIG. 8D  each are a plan view illustrating a manufacturing apparatus for a metal molded body according to yet another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A manufacturing apparatus (electromagnetic stirring apparatus)  10  for a metal molded body illustrated in  FIG. 1A  includes an elongated die  11  that is curved in an arc shape in plan view, and a plurality of pairs of thrust units  12  that are disposed along a wall surface of the die with the die disposed therebetween. Each thrust unit  12  includes cores  13 , and coils  14  that are wound around the cores  13 , as illustrated in  FIG. 1B . In this embodiment, two sets each obtained by winding the three coils  14  around the one core  13  are connected through a wedge shaped magnetic body  15  for curvature adjustment at an angle, and are made to be one unit. In  FIG. 1A , the wedge shaped magnetic bodies are omitted. 
     The die  11  has a substantially U-shaped cross-section including a bottom plate  16 , and side walls  17  rising from both ends of the bottom plate, as illustrated in  FIG. 2 , for example. In general, the depth of the die  11  is deeper than the width. Additionally, the side walls  17  are provided with draft angles, and expand toward upper ends. The die  11  is formed of metal having heat resistance enough to withstand a high temperature of molten metal, and having low magnetic permeability (for example, stainless steel), ceramics, or the like. The thrust units  12  are obliquely disposed in parallel to the wall surface with slight gaps G between the wall surface (inner wall surface) of the inclined side walls  17  and the thrust units  12 . 
     The size and the shape of the die  11  depend on the size and the shape of a member to be molded. As illustrated in  FIG. 1A , ends  18  of the die  11  each have an arc shape such that the direction of molten metal can be smoothly changed. In this embodiment, the right and left side walls  17  are each curved. The right and left side walls  17  have a common center of the curvature, and have almost the same width in the length direction. The thrust units  12  disposed along the side walls  17  are disposed so as to be curved or bent similarly, gaps G (refer to  FIG. 2 ) with the side walls (inner side walls)  17  are as small as possible, and are constant along the longitudinal direction. 
       FIG. 3A  and  FIG. 3B  each illustrate a thrust unit  12  by a “core back wounding method” among a basic shape. Each thrust unit  12  includes the core  13  having a comb-tooth shape, and the coils  14  that are wound between teeth of the core. The core  13  is composed of a rectangular column shaped yoke (core back)  19 , and teeth  21  having ends fixed to dovetail-shaped grooves  20  formed in the yoke. The number of the teeth  21  is seven, the number of the coils  14  to be wound around the yoke between the teeth is six, and all the coils are wound in the same direction. Therefore, in a case where a current enters from an initially wound coil, and a case where a current enters from a finally wound coil, the polarities are reverse. Slots  22  between the teeth  21  are filled with the coils (coil conductors)  14 . The slots  22  are opened toward the die  11  through slits  23  that are elongated openings. The yoke  19  and the teeth  21  are each formed by superimposing a large number of thin sheets of silicon steel sheets. The yoke and the teeth may be integrated. 
       FIG. 4A  and  FIG. 4B  illustrates a thrust unit  12 A by “inter-slot winding method” among a basic shape. In this method, the thrust unit  12 A includes the core  13  having a comb-teeth shape including the yoke  19  and a plurality of the teeth  21 , and the coils  14  each wound around a plurality of the teeth  21 . The slots  22   a  to  22   f  are filled with the coils (coil conductors)  14 . The coils  14  are composed of three kinds of coils  14   u ,  14   v ,  14   w  corresponding to a U-phase, a V-phase, and a W-phase of three-phase current (AC), respectively. A U-phase coil  14   u  passes through a leftmost slot  22   a  and a fourth slot  22   d  to be wound around three teeth between the leftmost slot and the fourth slot. 
     Similarly, a V-phase coil  14   v  passes through a third slot  22   c  and a sixth slot  22   f  to be wound around three teeth between the third slot and the sixth slot. A W-phase coil  14   w  passes through a second slot  22   b  and a fifth slot  22   e  to be wound around three teeth between the second slot and the fifth slot. These three kinds of coils  14   u ,  14   v ,  14   w  are overlapped to be intersect with each other on the lateral side of the core  13 , as illustrated in  FIG. 4B . Symbol  0  denotes a neutral point of a three-phase current. In the thrust unit  12 A by such an “inter-slot winding method”, the coils  14   u  to  14   w  are not wound the core back  19 , and therefore the core back  19  can be used to fix the thrust unit. 
       FIG. 5  illustrates wire connection in which three thrust units  12  are lined on one side of the die  11 . A power source is a three-phase current. Symbol  0  is a neutral point. When three-phase current U, W, V are sequentially connected to coils of terminal symbols R, S, T, a magnetic flux advances from the left to the right (refer to an arrow φ 1 ). When a phase order is changed and the three phase current are connected to the U-phase, the V-phase, the W-phase in order, a magnetic flux advances from the right to the left (the arrow φ 2  direction). That is, in  FIG. 5 , in a left end unit  12   a , the W-phase is connected to a winding finish end of a coil denoted by symbol w 1 −, and the V-phase is connected to a winding start end of a coil denoted by symbol v 1 +. In an central unit  12   b , the V-phase is connected to a winding finish end of a coil denoted by symbol w 3 −, the W-phase is connected to a winding start end of a coil denoted by symbol v 3 +, the V-phase and the W-phase are reverse. Furthermore, connection in a right end unit  12   c  is similar to the connection in the left end unit  12   a , and therefore a magnetic flux advances in the arrow φ 3  direction similar to the arrow φ 1 . 
     When such thrust units are disposed on both side of a pot, as illustrated in  FIG. 6 , the advancing directions of magnetic fluxes of units  12   a ,  12   b ,  12   c  on the near side of the die  11  and the advancing directions of magnetic fluxes of units  12   d ,  12   e ,  12   f  on the far side are made reverse. Consequently, in a case where the direction of a vortex Q 1  of molten metal caused by a pair of the left end units  12   a ,  12   d  is counterclockwise, a clockwise vortex Q 2  is generated in a pair of the central units  12   b ,  12   e . Furthermore, a counterclockwise vortex Q 3  is generated again in a pair of the right end units  12   c ,  12   f.    
     Therefore, the directions of the circulating vortexes are reverse for each set of the adjacent units, and therefore in the ends of the thrust units, a flow along the wall surface is divided, so that nodes  24   a ,  24   b  are formed in the flow. Therefore, an accelerated flow reduces the speed at portions of the node  24   a  and node  24   b , and migration energy is converted into stirring energy. Therefore, also when molten metal flows into the arc shapes of the ends, or also when the side walls  17  are curved as illustrated in  FIG. 1A , running onto the wall surface of the side walls  17 , and running over the side walls  17  are suppressed. Additionally, at the portions of the node  24   a  and the node  24   b , the molten metal flowing from one of the both sides collides with the molten metal flowing from the other side, and furthermore, an integrated flow is divided, and therefore the molten metal is more efficiently stirred. 
     In the embodiment, the thrust units are arranged in parallel to the inner side walls of the die (means that a void is uniform), a vortex generates horizontally. However, for example, as illustrated in  FIG. 7A  and  FIG. 7B , a thrust unit  25  that generates a vertically inclined flow P can be combined. Two slots  22  of the thrust unit  25  are formed with slits  23  provided with an inclined angle (skew) which retreats toward the lower part. By such skew, a vertical oblique flow P generates in the molten metal, and a laminar flow of the molten metal in the die commutates. Therefore residual gas venting is facilitated, more efficient stirring is attained, and therefore it is possible to make crystal grains fine. 
     Such skew can be formed by obliquely machining the slits  23 , when electromagnetic steel plates are stuck to perform machining on the slots  22  by wire cutting. The slots  22  are filled with the coils (coil conductor)  14 , but are omitted in  FIG. 7B . Reference numeral  26  in  FIG. 7B  denotes a wedge or plate for holding the coils  14  in the slot  22 . 
     In the embodiment, the advancing direction of the magnetic field is reversed for each thrust unit  12 , and the direction of vortexes Q 1 , Q 2  of molten metal are reversed for each pair of the thrust units  12  as illustrate in  FIG. 8A . However, the two or three thrust units as illustrated in  FIG. 8B  and  FIG. 8C , or the four or more thrust units as illustrated in  FIG. 8D  can form a “series” in which the advancing direction of a magnetic field is the same, and can be installed such that the vortexes are reversed for each series. In this case, the number or nodes are reduced, and therefore stirring action is reduced, but the speed of each vortex is increased. Accordingly, suitable stirring action and vortex speed can be set in accordance with the kind of metal to be manufactured. 
     Furthermore, a control circuit that switches, for each thrust unit, the direction of a current that flows into electromagnetic coils of the thrust unit may be provided, and the direction of the traveling magnetic field may be changed for every arbitrary n thrust units such as every single thrust unit, and every two thrust units, and the directions of vortexes may be able to be reversed. In such a manufacturing apparatus for a metal molded body capable of changing wiring of the coils of the thrust units, suitable stirring action and vortex speed can be selected in accordance with the kind of metal, and a metal molded body can be efficiently manufactured.