Abstract:
A mold includes a first groove part and a second groove part. The first groove part extends with a constant length or a constant width from a center part to an outer circumferential part of the mold. The second groove part extends from a terminal end of the first groove part on an outer circumferential part side of the first groove and merges with any portion of the first groove part. A molding manufacturing method includes manufacturing a preform by semimolten die casting or semisolid die casting using the mold. The method may also include removing a portion of the preform corresponding to the second groove part.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. National stage application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2008-162058, filed in Japan on Jun. 20, 2008, the entire contents of which are hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a mold for manufacturing a molding by a semimolten die casting method or a semisolid die casting method. In addition, the present invention relates to a method of using the mold to manufacture the molding by the semimolten die casting method or the semisolid die casting method. 
     BACKGROUND ART 
     In the conventional art, a molding manufacturing method wherein “a preform is formed by a semimolten die casting method into a near net shape, the preform is subject to ultraprecision finishing, and thereby a target molding is obtained” has been proposed (e.g., refer to Japanese Laid-open Patent Application Publication No. 2005-36693). Adopting this manufacturing method makes it possible to manufacture a molding that is stronger than the molding obtained by the casting method and, moreover, to reduce the cost of raw materials, machining, tool supplies, and the like as well as to reduce waste matter such as grinding waste material and machining waste liquid. 
     SUMMARY 
     Technical Problem 
     However, when manufacturing a molding by, for example, the semimolten die casting method or the semisolid die casting method, any grooves in the mold that extend from a center part to the outer circumferential part will suffer cracks in the vicinity of their end parts on the outer circumferential part side, and the number of molding shots will be significantly fewer than that normally expected during the life of the mold, which is a problem. 
     An object of the present invention is to increase the life of a mold when manufacturing a molding by a semimolten die casting method or a semisolid die casting method. 
     Solution to Problem 
     A mold according to a first aspect of the present invention is a mold that comprises a first groove part and a second groove part. The first groove part extends with a constant length or a constant width from a center part to an outer circumferential part. The second groove part extends from a terminal end of the first groove part on the outer circumferential part side and merges with any portion of the first groove part. Furthermore, a pouring gate is provided in the vicinity of the end part of the first groove part on the center side. 
     Incidentally, in a case where a conventional mold, which comprises only the first groove part, is used in semimolten die casting, semisolid die casting, or the like, when the high temperature semimolten metal is pressurized and fills the mold, a force is generated that presses against a groove wall in the vicinity of a groove end on the outer circumferential part side of the first groove part (hereinbelow, called an “outer circumferential end groove wall”). In other words, at this time, the outer circumferential end groove wall bears a tensile load. Meanwhile, when a molded part is removed from such a mold, the temperature of the mold decreases starting from the outer circumferential side. At this time, a large temperature differential arises between the center part and the outer circumferential part of the mold, and a compressive load owing to thermal expansion is generated in the outer circumferential end groove wall. Accordingly, in such a mold, the outer circumferential end groove wall alternately and repetitively bears a tensile load owing to pressurization and a compressive load owing to thermal expansion; as a result, stress amplitude is created in the outer circumferential end groove wall. Furthermore, if the stress amplitude exceeds the fatigue limit of the material of the mold, then a fatigue failure will occur and a crack will be created in the outer circumferential end groove wall. 
     However, in the mold according to the present invention, the second groove part is formed, and consequently the outer circumferential end groove wall does not exist. In other words, in this mold, the stress amplitude is not generated. Consequently, the mold according to the present invention has an increased lifespan. 
     Note that, to obtain the target molding, the portion corresponding to the second groove part should be removed from the preform using a technique such as cutting. 
     A mold according to a second aspect of the present invention is a mold according to the first aspect of the present invention wherein, the first groove part is a scroll shaped groove part that extends in one direction while maintaining a scroll shape. The second groove part extends from a scroll tail end of the scroll shaped groove part and merges with any portion of the scroll shaped groove part. Furthermore, the outer periphery of the second groove part is preferably either an arc or comprises an arc and a tangent that extends from an arbitrary point along the outer periphery of the scroll shaped groove part. In addition, in this mold, the scroll shaped groove part may extend in one direction from the end surface or may extend in one direction from a recessed part (i.e., a portion corresponding to an end plate). 
     In this mold, the first groove part is the scroll shaped groove part that extends in one direction while maintaining its scroll shape. Furthermore, the second groove part extends from the scroll tail of the scroll shaped groove part and merges with any portion of the scroll shaped groove part. Consequently, it is possible to increase the lifespan of a mold for a scroll member. 
     A mold according a third aspect of the present invention is the mold according to the second aspect of the present invention wherein, when the second groove part is viewed in the depth directions, an outer periphery of the second groove part is an arc. 
     In a case where the scroll shaped groove part is formed in the mold, if the outer periphery of the second groove part is made arcuate when the second groove part is viewed in the depth directions, then it is possible to prevent the groove wall of the second groove part from bearing the tensile load owing to pressurization and the compressive load owing to thermal expansion. Consequently, the lifespan of this mold increases. 
     A mold according to a fourth aspect of the present invention is the mold according to the second aspect of the present invention wherein, when the second groove part is viewed in the depth directions, an outer periphery of the second groove part has an arc and a tangent, which extends from an arbitrary point along the outer periphery of the scroll shaped groove part. 
     In a case where the scroll shaped groove part is formed in the mold, if the outer periphery of the second groove part comprises the arc and the tangent that extends from the arbitrary point along the outer periphery of the scroll shaped groove part when the second groove part is viewed in the depth directions, then it is possible to prevent the groove wall of the second groove part from bearing the tensile load owing to pressurization and the compressive load owing to thermal expansion. Consequently, the lifespan of this mold increases. 
     A mold according to a fifth aspect of the present invention is the mold according to the first aspect of the present invention wherein, the first groove part is a plurality of groove parts, the groove parts extending radially from the center part to the outer circumferential part. In addition, the second groove part merges with the terminal end portions of all of the first groove parts on the outer peripheral part sides. 
     In this mold, the first groove part is a plurality of groove parts, the groove parts extending radially from the center part to the outer circumferential part. Furthermore, the second groove part merges with the terminal end portions of all of the first groove parts on the outer peripheral part sides. Consequently, it is possible to increase the lifespan of a mold for a molded part that comprises radial reinforcing ribs and the like. 
     A molding manufacturing method according to a sixth aspect of the present invention comprises the step of: using a mold according to any one aspect of the first through fifth aspects of the invention to manufacture a preform by a semimolten die casting method or a semisolid die casting method. 
     Incidentally, in a case where a conventional mold, which comprises only the first groove part, is used in semimolten die casting, semisolid die casting, or the like, when the high temperature semimolten metal is pressurized and fills the mold, a force presses against the outer circumferential end groove wall of the first groove part. In other words, at this time, the outer circumferential end groove wall bears a tensile load. Meanwhile, when a molded part is removed from such a mold, the temperature of the mold decreases starting from the outer circumferential side. At this time, a large temperature differential arises between the center part and the outer circumferential part of the mold, and a compressive load owing to thermal expansion is generated in the outer circumferential end groove wall. Accordingly, in such a mold, the outer circumferential end groove wall alternately and repetitively bears a tensile load owing to pressurization and a compressive load owing to thermal expansion; as a result, stress amplitude is created in the outer circumferential end groove wall. Furthermore, if the stress amplitude exceeds the fatigue limit of the material of the mold, then a fatigue failure will occur and a crack will be created in the outer circumferential end groove wall. 
     However, in the mold according to the first through fifth aspects of the present invention, the second groove part is formed, and consequently the outer circumferential end groove wall does not exist. In other words, in this mold, the stress amplitude is not generated. Consequently, the mold according to the present invention has an increased lifespan. Accordingly, using this molding manufacturing method makes it possible to reduce the cost of the mold and to manufacture such a molding inexpensively. 
     A molding manufacturing method according to a seventh aspect of the present invention comprises a preform manufacturing process and an eliminating process. In the preform manufacturing process, a mold according to any one aspect of the first through fifth aspects of the invention is used to manufacture a preform by a semimolten die casting method or a semisolid die casting method. In the eliminating process, a portion corresponding to the second groove part of the preform is removed. 
     Incidentally, in a case where a conventional mold, which comprises only the first groove part, is used in semimolten die casting, semisolid die casting, or the like, when the high temperature semimolten metal is pressurized and fills the mold, a force presses against the outer circumferential end groove wall of the first groove part. In other words, at this time, the outer circumferential end groove wall bears a tensile load. Meanwhile, when a molded part is removed from such a mold, the temperature of the mold decreases starting from the outer circumferential side. At this time, a large temperature differential arises between the center part and the outer circumferential part of the mold, and a compressive load owing to thermal expansion is generated in the outer circumferential end groove wall. Accordingly, in such a mold, the outer circumferential end groove wall alternately and repetitively bears a tensile load owing to pressurization and a compressive load owing to thermal expansion; as a result, stress amplitude is created in the outer circumferential end groove wall. Furthermore, if the stress amplitude exceeds the fatigue limit of the material of the mold, then a fatigue failure will occur and a crack will be created in the outer circumferential end groove wall. 
     However, in the mold according to the first through fifth aspects of the present invention, the second groove part is formed, and consequently the outer circumferential end groove wall does not exist. In other words, in this mold, stress amplitude is not generated. Consequently, the mold according to the present invention has an increased lifespan. Accordingly, using this molding manufacturing method makes it possible to reduce the cost of the mold and to manufacture such a molding inexpensively. 
     Advantageous Effects of Invention 
     According to a first aspect of the invention, it is possible to increase the lifespan of a mold for semimolten die casting, semisolid die casting, or the like. 
     According to a second aspect of the invention, it is possible to increase the lifespan of a mold for a scroll member. 
     According to a third and fourth aspect of the invention, it is possible to increase the lifespan of a mold for semimolten die casting, semisolid die casting, or the like. 
     According to a fifth aspect of the invention, it is possible to increase the lifespan of a mold for a molded part that comprises radial ribs and the like. 
     The use of a molding manufacturing method according to a sixth aspect of the invention makes it possible to increase the lifespan of a mold as well as to reduce the cost of the mold and to manufacture a molding inexpensively. 
     The use of a molding manufacturing method according to a seventh aspect of the invention makes it possible to increase the lifespan of a mold as well as to reduce the cost of the mold and to manufacture a molding inexpensively. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal cross sectional view of a high/low pressure dome type scroll compressor according to an embodiment of the present invention. 
         FIG. 2  is a top view of a movable scroll that is incorporated into the high/low pressure dome type scroll compressor according to the embodiment of the present invention. 
         FIG. 3  is a cross sectional view taken along the V-V line of the movable scroll incorporated into the high/low pressure dome type scroll compressor according to the embodiment of the present invention. 
         FIG. 4  is a longitudinal cross sectional view of a mold, which is for manufacturing the movable scroll incorporated in the high/low pressure dome type scroll compressor according to an embodiment of the present invention, and a base of the movable scroll formed by semimolten die casting. 
         FIG. 5  is a bottom view of an end plate of the mold and a portion on a wrap forming side of the mold for manufacturing the movable scroll that is incorporated into the high/low pressure dome type scroll compressor according to the embodiment of the present invention. 
         FIG. 6  is a bottom view of an end plate and a portion on a wrap forming side of a conventional mold for manufacturing the movable scroll. 
         FIG. 7  is a graph that shows a time series of actually measured temperature values when the movable scroll is formed using a conventional mold. 
         FIG. 8  shows the analysis results of stress that occurs when pressure is applied to semimolten metal in the conventional mold. 
         FIG. 9  shows analysis results of stress that is generated by thermal deformation in the conventional mold. 
         FIG. 10  shows the results of using a thermoviewer to measure the temperature of the conventional mold. 
         FIG. 11  is a bottom view of the end plate and a portion of the mold on the wrap forming side according to a modified example (A). 
         FIG. 12  is a bottom view of the end plate and a portion of the mold on the wrap forming side according to the modified example (A). 
         FIG. 13  is a bottom view of the end plate and a portion of the mold on the wrap forming side according to the modified example (A). 
         FIG. 14  is a bottom view of the end plate and a portion of the mold on the wrap forming side according to the modified example (A). 
         FIG. 15  is a top view of a mold portion according to a modified example (B). 
         FIG. 16  is a top view of a portion of the mold—on the side whereon reinforcing ribs are formed—for manufacturing a housing according to the modified example (B). 
         FIG. 17  is a cross sectional view taken along the V-V line of the mold for manufacturing the housing according to the modified example (B). 
         FIG. 18  is a bottom view of the housing according to the modified example (B). 
         FIG. 19  is a cross sectional view taken along the line of the housing according to the modified example (B). 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The text below explains a compressor, wherein a sliding part is used, according to an embodiment of the present invention, using a high/low pressure dome type scroll compressor as an example. Furthermore, the high/low pressure dome type compressor according to the embodiment of the present invention is designed such that it can withstand the use of a high pressure refrigerant, such as carbon dioxide refrigerant (CO 2 ) or R410A. 
     A high/low pressure dome type scroll compressor  1  according to the embodiment of the present invention comprises an evaporator, a condenser, an expansion mechanism, and the like as well as a refrigerant circuit and serves to compress a gas refrigerant inside the refrigerant circuit; furthermore, as shown in  FIG. 1 , the high/low pressure dome type scroll compressor  1  principally comprises a cylindrical hermetic dome type casing  10 , a scroll compression mechanism  15 , an Oldham ring  39 , a drive motor  16 , a lower part main bearing  60 , a suction pipe  19 , and a discharge pipe  20 . The text below discusses the constituent parts of the high/low pressure dome type scroll compressor  1  in detail. 
     &lt;Details of Constituent Parts of the High/Low Pressure Dome Type Scroll Compressor&gt; 
     (1) Casing 
     The casing  10  is a hermetic container and principally comprises a substantially cylindrical trunk casing part  11 , a bowl shaped upper wall part  12 , and a bowl shaped bottom wall part  13 . The upper wall part  12  is welded to an upper end part of the trunk casing part  11 . The bottom wall part  13  is welded to a lower end part of the trunk casing part  11 . Furthermore, the casing  10  principally houses the scroll compression mechanism  15 , which compresses the gas refrigerant, and the drive motor  16 , which is disposed below the scroll compression mechanism  15 . The scroll compression mechanism  15  and the drive motor  16  are coupled by a crankshaft  17 , which is disposed inside the casing  10  such that it extends in the vertical directions. Furthermore, as a result, a gap space  18  is created between the scroll compression mechanism  15  and the drive motor  16 . 
     (2) Scroll Compression Mechanism 
     As shown in  FIG. 1 , the scroll compression mechanism  15  principally comprises: a housing  23 ; a fixed scroll  24 , which is disposed above the housing  23  in tight contact therewith; and a movable scroll  26 , which meshes with the fixed scroll  24 . The text below discusses the constituent parts of the scroll compression mechanism  15  in detail. 
     a) Housing 
     The housing  23  is press fitted and fixed, at its outer circumferential surface, to the trunk casing part  11  completely therearound in the circumferential directions. In other words, the trunk casing part  11  and the housing  23  are in close contact all the way around their circumferences. Consequently, the interior of the casing  10  is partitioned into a high pressure space  28  below the housing  23  and a low pressure space  29  above the housing  23 . In addition, the fixed scroll  24  is fastened and fixed to the housing  23  by a bolt  38  such that an upper end surface of the housing  23  is in close contact with a lower end surface of the fixed scroll  24 . In addition, in the housing  23 , a housing recessed part  31  is formed such that it provides a recess in the center of the upper surface of the housing  23 , and a bearing part  32  is formed such that it extends below the housing  23  from the center of the lower surface thereof. Furthermore, a bearing hole  33  is formed in the bearing part  32  such that it passes therethrough in the vertical directions, and a main shaft part  17   b  of the crankshaft  17  is rotatably inserted into the bearing hole  33  via a bearing  34 . 
     b) Fixed Scroll 
     As shown in  FIG. 1 , the fixed scroll  24  principally comprises: an end plate  24   a ; and a scroll shaped (i.e., involute) wrap  24   b , which extends downward from a mirror surface of the end plate  24   a  along a direction substantially orthogonal to the mirror surface. A discharge hole  41 , which communicates with a compression chamber  40  (discussed below), and an enlarged recessed part  42 , which communicates with the discharge hole  41 , are formed in the end plate  24   a . The discharge hole  41  is formed in a center portion of the end plate  24   a  such that it extends in the vertical directions. The enlarged recessed part  42  is formed in the upper surface of the end plate  24   a  such that it widens in the horizontal directions. 
     Furthermore, a cover body  44  is fastened and fixed to the upper surface of the fixed scroll  24  by a bolt  44   a  such that the cover body  44  covers the enlarged recessed part  42 . Furthermore, covering the enlarged recessed part  42  with the cover body  44  forms a muffler space  45 , which muffles the operation noise of the scroll compression mechanism  15 . Furthermore, the fixed scroll  24  and the cover body  44  are sealed to one another by being brought into tight contact with a gasket (not shown) interposed therebetween. 
     c) Movable Scroll 
     The movable scroll  26  is an outer drive type movable scroll and, as shown in  FIG. 1 ,  FIG. 2 , and  FIG. 3 , principally comprises: an end plate  26   a ; a scroll shaped (i.e., involute) wrap  26   b , which extends upward from a mirror surface  26 P of the end plate  26   a  in a direction substantially orthogonal to the mirror surface  26 P; a bearing part  26   c , which extends downward from a lower surface of the end plate  26   a  and fits an outer side of an eccentric shaft part  17   a  of the crankshaft  17 ; and groove parts  26   d  (refer to  FIG. 3 ), which are formed on opposite end parts of the end plate  26   a.    
     Furthermore, by fitting the Oldham ring  39  into the groove parts  26   d  (refer to  FIG. 1 ), the movable scroll  26  is supported by the housing  23 . In addition, the eccentric shaft part  17   a  of the crankshaft  17  is fitted into the bearing part  26   c . By incorporating the movable scroll  26  into the scroll compression mechanism  15  in this manner, the movable scroll  26  revolves inside the housing  23  without rotating on its own axis by the rotation of the crankshaft  17 . Furthermore, the wrap  26   b  of the movable scroll  26  is meshed with the wrap  24   b  of the fixed scroll  24 , and thereby the compression chamber  40  is formed between the parts at which the wraps  24   b ,  26   b  contact one another. Furthermore, the revolving of the movable scroll  26  displaces the compression chamber  40  toward its center, thereby shrinking the volume of the compression chamber  40 . In so doing, in the high/low pressure dome type scroll compressor  1 , the gas refrigerant that enters the compression chamber  40  is compressed. 
     d) Other 
     In addition, in the scroll compression mechanism  15 , a communicating passageway  46  is formed that spans the fixed scroll  24  and the housing  23 . The communicating passageway  46  comprises: a scroll side passageway  47 , which is formed as a notch in the fixed scroll  24 ; and a housing side passageway  48 , which is formed as a notch in the housing  23 . Furthermore, the upper end of the communicating passageway  46 , namely, the upper end of the scroll side passageway  47 , is open to the enlarged recessed part  42 ; furthermore, the lower end of the communicating passageway  46 , namely, the lower end of the housing side passageway  48 , is open to the lower end surface of the housing  23 . In other words, the lower end opening of the housing side passageway  48  constitutes a discharge port  49  wherethrough the refrigerant in the communicating passageway  46  flows out to the gap space  18 . 
     (3) Oldham Ring 
     The Oldham ring  39  is a member for preventing the movable scroll  26  from rotating about its own axis and is fitted into Oldham grooves (not shown), which are formed in the upper surface of the housing  23 . Furthermore, the Oldham grooves are elliptical and are provided and disposed in the housing  23  such that they oppose one another. 
     (4) Drive Motor 
     The drive motor  16  is a DC motor and principally comprises: an annular stator  51 , which is fixed to an inner wall surface of the casing  10 ; and a rotor  52 , which is rotatably housed on the inner side of the stator  51  with a small gap (i.e., an air gap passageway) therebetween. Furthermore, the drive motor  16  is disposed such that an upper end of a coil end  53 , which is formed in an upper side of the stator  51 , is at substantially the same height position as the lower end of the bearing part  32  of the housing  23 . 
     In the stator  51 , copper wire is wound around teeth parts, and the coil ends  53  are formed above and below the stator  51 . In addition, core cut parts, which are formed as notches in a plurality of locations with a prescribed spacing in circumferential directions and such that they span from the upper end surface to the lower end surface of the stator  51 , are provided in the outer circumferential surface of the stator  51 . Furthermore, the core cut parts form a motor cooling passageway  55 , which extends in the vertical directions between the trunk casing part  11  and the stator  51 . 
     The rotor  52  is drivably coupled to the movable scroll  26  of the scroll compression mechanism  15  via the crankshaft  17 , which is disposed at the axial center of the trunk casing part  11  such that it extends in the vertical directions. In addition, a guide plate  58 , which guides the refrigerant that flows out of the discharge port  49  of the communicating passageway  46  to the motor cooling passageway  55 , is provided and disposed in the gap space  18 . 
     (5) Crankshaft 
     The crankshaft  17  is a substantially columnar monolithically molded part, as shown in  FIG. 1 , and principally comprises the eccentric shaft part  17   a , the main shaft part  17   b , a balance weight part  17   c , and an auxiliary shaft part  17   d . The eccentric shaft part  17   a  is housed in the bearing part  26   c  of the movable scroll  26 . The main shaft part  17   b  is housed in the bearing hole  33  of the housing  23  via the bearing  34 . The auxiliary shaft part  17   d  is housed in the lower part main bearing  60 . 
     (6) Lower Part Main Bearing 
     The lower part main bearing  60  is provided and disposed in a lower space below the drive motor  16 . The lower part main bearing  60  is fixed to the trunk casing part  11 , constitutes a lower end side bearing of the crankshaft  17 , and houses the auxiliary shaft part  17   d  of the crankshaft  17 . 
     (7) Suction Pipe 
     The suction pipe  19  is for guiding the refrigerant in the refrigerant circuit to the scroll compression mechanism  15  and is hermetically fitted to the upper wall part  12  of the casing  10 . The suction pipe  19  passes through the low pressure space  29  in the vertical directions; furthermore, an inner end part of the suction pipe  19  is fitted into the fixed scroll  24 . 
     (8) Discharge Pipe 
     The discharge pipe  20  is for discharging the refrigerant inside the casing  10  to the outside of the casing  10  and is hermetically fitted to the trunk casing part  11  of the casing  10 . Furthermore, the discharge pipe  20  comprises an inner end part  36 , which is formed as a cylinder that extends in the vertical directions and is fixed to the lower end part of the housing  23 . Furthermore, the inner end opening, namely, the inflow port, of the discharge pipe  20  is open downward. 
     &lt;Operation of the High/Low Pressure Dome Type Scroll Compressor&gt; 
     Next, the operation of the high/low pressure dome type scroll compressor  1  will be explained in simple terms. First, when the drive motor  16  is driven, the crankshaft  17  rotates and the movable scroll  26  revolves without rotating about its axis. In so doing, low pressure gas refrigerant is suctioned from the circumferential edge side of the compression chamber  40  through the suction pipe  19  into the compression chamber  40 , is compressed as the volume of the compression chamber  40  changes, and thereby transitions to high pressure gas refrigerant. Furthermore, the high pressure gas refrigerant is discharged from a center part of the compression chamber  40  through the discharge hole  41  to the muffler space  45 , subsequently flows out to the gap space  18  through the communicating passageway  46 , the scroll side passageway  47 , the housing side passageway  48 , and the discharge port  49 , and flows toward the lower side between the guide plate  58  and an inner surface of the trunk casing part  11 . Furthermore, when the gas refrigerant flows toward the lower side between the guide plate  58  and the inner surface of the trunk casing part  11 , a portion of the gas refrigerant splits off and flows in the circumferential directions between the guide plate  58  and the drive motor  16 . Furthermore, at this time, lubricating oil that is mixed in the gas refrigerant separates out. Moreover, another portion of the split off gas refrigerant flows toward the lower side through the motor cooling passageway  55 , flows as far as a lower space of the motor, and subsequently reverses direction and flows upward through the air gap passageway between the stator  51  and the rotor  52  or through the motor cooling passageway  55  on the side opposing the communicating passageway  46  (in  FIG. 1 , the left side). Thereafter, the gas refrigerant that passes through the guide plate  58  and the gas refrigerant that flows through the air gap passageway or the motor cooling passageway  55  merge at the gap space  18 ; furthermore, the merged gas refrigerant flows from the inner end part  36  of the discharge pipe  20  into the discharge pipe  20  and is then discharged to the outside of the casing  10 . Furthermore, the gas refrigerant that discharges to the outside of the casing  10  circulates through the refrigerant circuit, subsequently passes through the suction pipe  19  once again, and is suctioned into and compressed by the scroll compression mechanism  15 . 
     &lt;Method of Manufacturing the Sliding Part&gt; 
     In the high/low pressure dome type scroll compressor  1  according to the embodiment of the present invention, the crankshaft  17 , the housing  23 , the fixed scroll  24 , the movable scroll  26 , the Oldham ring  39 , and the lower part main bearing  60  are the sliding parts, which are manufactured using the manufacturing method below. 
     (1) Raw Materials 
     A billet to which C, 2.2-2.5 wt %, Si: 1.8-2.2 wt %, Mn: 0.5-0.7 wt %, P: &lt;0.035 wt %, S: &lt;0.04 wt %, Cr: 0.00-0.50 wt %, Ni: 0.50-1.00 wt % has been added is used as the iron raw material, which is the raw material of the sliding parts in the embodiment of the present invention. Furthermore, the weight percentages herein apply to the entire amount of the material. In addition, “billet” herein means a raw material in a state after an iron raw material having the abovementioned composition is first melted in a melting furnace but before its final molding into a column using a continuous casting apparatus. Furthermore, here, the C content and the Si content are determined such that two conditions are satisfied: the tensile strength and the tensile modulus are greater than those in flake graphite cast iron; and a fluidity is provided that is appropriate to molding a sliding part base that has a complex shape. In addition, the Ni content is determined so as to constitute a metal composition that improves the toughness of the metallographic structure and is suited to preventing surface cracks during molding. 
     (2) Manufacturing Process 
     The sliding parts according to the embodiment of the present invention are manufactured by undergoing a semimolten die casting process, a heat treatment process, a finishing process, and a partial heat treatment process. The details of each of the processes are discussed below. 
     a) Semimolten Die Casting Process 
     In the semimolten die casting process, first, a billet is subjected to high frequency heating so that it transitions to a semimolten state. Next, the billet in the semimolten state is poured into a prescribed mold and molded into a desired shape while a die casting machine applies a prescribed pressure, and thereby the sliding part base is obtained. Furthermore, the sliding part base is quenched and solidified inside the mold, whereupon the metallographic structure of the sliding part base is entirely transformed into white cast iron. Furthermore, the sliding part base is slightly larger than the sliding part that is ultimately obtained, and the sliding part base becomes the final sliding part after the machining allowance is removed in a subsequent finishing process. 
     Furthermore, in the embodiment of the present invention, a base  126  of the movable scroll  26  is molded using a mold  80 , which is shown in  FIG. 4  and  FIG. 5 . 
     As shown in  FIG. 4 , the mold  80  for semimolten die casting the base  126  of the movable scroll  26  comprises a first mold portion  81  and a second mold portion  82 . Furthermore, a pouring gate (not shown) is disposed at substantially the center of a portion corresponding to the end plate. Furthermore, as shown in  FIG. 4  and  FIG. 5 , the following parts are formed in the second mold portion  82 : a recessed part  823 , which is for forming an upper part of the end plate  26   a ; a scroll shaped groove part  821 , which is for forming the wrap  26   b ; and a communicating groove part  822 , which is for providing communication from the scroll tail end to the inner circumferential side of the scroll shaped groove part  821 . Furthermore, to facilitate the removal of the base  126  of the movable scroll  26 , the scroll shaped groove part  821  is formed such that its width increases as one proceeds from the bottom part (i.e., the portion corresponding to the tip portion) to the recessed part  823 . Accordingly, in the base  126  of the movable scroll  26  formed using the mold  80 , the width of the portion corresponding to the wrap increases as one proceeds from the portion corresponding to the tip to the portion corresponding to the end plate. In addition, the portion formed by the communicating groove part  822  is removed in a subsequent finishing process. 
     b) Heat Treatment Process 
     In the heat treatment process, the sliding part base is heat treated after it has undergone the semimolten die casting process In the heat treatment process, the metallographic structure of the sliding part base changes from the white cast iron structure to a metallographic structure composed of a pearlite/ferrite and lump graphite. Furthermore, the transformation of the white cast iron structure to graphite and pearlite can be adjusted by adjusting the heat treatment temperature, the hold time, the cooling rate, and the like. As recited in, for example, an article entitled “Research on Technology for Semimolten Casting of Iron” published in the  Honda R &amp; D Technical Review  14(1), it is possible to obtain a metallographic structure with a tensile strength of approximately 500-700 MPa and a hardness in the range of approximately HB 150 (i.e., HRB 81, which is the converted value based on the SAE J 417 hardness conversion table) to HB 200 (i.e., HRB 96, which is the converted value based on the SAE J 417 hardness conversion table) by holding the temperature of the metal at 950° C. for 60 min. and then annealing the metal in the furnace at a cooling rate of 0.05-0.10° C./s. Such a metallographic structure is mainly ferrite and consequently is soft and has superior machinability; however, during machining, a built-up edge might be formed, which could reduce cutting tool life. In addition, by holding the metal at 1000° C. for 60 min., subsequently air cooling the metal, further holding the metal for a prescribed time at a temperature somewhat lower than the initial temperature, and then air cooling the metal, it is possible to obtain a metallographic structure with a tensile strength of approximately 600-900 MPa and a hardness in the range of approximately HB 200 (i.e., HRB 96, which is the converted value based on the SAE J 417 hardness conversion table) to HB 250 (i.e., HRB 105, HRC 26, which are the converted values based on the SAE J 417 hardness conversion table; note that HRB 105 is a reference value that is used in order to exceed the effective practical range of a test type). In such a metallographic structure, a composition with a hardness equivalent to that of flake graphite cast iron has a machinability equivalent to that of flake graphite cast iron and has superior machinability compared to that of nodular graphite cast iron having an equivalent ductility and toughness. In addition, by holding the metal at a temperature of 1000° C. for 60 min., subsequently oil cooling the metal, further holding the metal for a prescribed time at a temperature slightly lower than the initial temperature, and then air cooling the metal, it is possible to obtain a metallographic structure with a tensile strength of approximately 800-1300 MPa and a hardness in the range of approximately HB 250 (i.e., HRB 105, HRC 26, which are the converted values based on the SAE J 417 hardness conversion table; note that HRB 105 is a reference value that is used in order to exceed the effective practical range of a test type) to HB 350 (i.e., HRB 122, HRC 41, which are the converted values based on the SAE J 417 hardness conversion table; note that HRB 122 is a reference value that is used in order to exceed the effective practical range of a test type). Such a metallographic structure is mainly pearlite and consequently is hard and has poor machinability but superior abrasion resistance. However, the metal&#39;s excessive hardness might cause it to attack the sliding counterpart. 
     Note that, in the heat treatment process according to the embodiment of the present invention, heat treatment is performed under conditions such that the hardness of the sliding part base becomes greater than HRB 90 (i.e., HB 176, which is the converted value based on the SAE J 417 hardness conversion table) and less than HRB 100 (i.e., HB 219, which is the converted value based on the SAE J 417 hardness conversion table). 
     c) Finishing Process 
     In the finishing process, the sliding part base is machined, which completes the sliding part. 
     &lt;Mold Damaging Mechanism&gt; 
     The text below explains a case wherein a mold with a conventional second mold portion, as shown in  FIG. 6 , is used in semimolten die casting, semisolid die casting, and the like, referencing a mold damaging mechanism. Note that, a first mold portion is identical to the first mold portion discussed above. 
     First, while pressure is applied to semimolten metal at a high temperature in the mold  80 , a force is created that presses a groove wall (hereinbelow, called a “outer circumferential end groove wall”) in the vicinity of a scroll tail end (i.e., the end on the outer circumferential side) of a scroll shaped groove part  821 A of a second mold portion  82 A. In other words, at this time, the outer circumferential end groove wall bears a tensile load. Furthermore,  FIG. 8  shows the results (as a contour diagram) of analyzing the tensile stress exerted upon the outer circumferential end groove wall. 
     Next, the transfer of heat from the high temperature semimolten metal filling the mold  80  rapidly raises the temperature of the mold  80 ; after several seconds, when the molded part is removed, the temperature of the mold  80  falls starting from the outer circumferential side. Furthermore,  FIG. 7  shows a time series diagram of the actual measured temperatures at the center part groove wall and the outer circumferential end groove wall of the mold  80 . In addition,  FIG. 10  shows the results of using a thermoviewer to measure the temperature of the mold  80 . 
     Furthermore, when a large temperature differential arises between the center part groove wall and the outer circumferential end groove wall of the mold  80  in this manner, a compressive load owing to thermal expansion is exerted upon the outer circumferential end groove wall. Furthermore,  FIG. 9  shows the results (as a contour diagram) of analyzing the compressive stress exerted upon the outer circumferential end groove wall. 
     Accordingly, in such a mold  80 , the outer terminal end groove wall alternately and repetitively bears a tensile load owing to pressurization and a compressive load owing to thermal expansion; as a result, a stress of stress amplitude is created in the outer circumferential end groove wall. Furthermore, if the stress amplitude exceeds the fatigue limit of the material of the mold  80 , then a fatigue failure will occur and a crack CR will be created in the outer circumferential end groove wall. 
     &lt;Features of the Mold&gt; 
     The communicating groove part  822  is formed in the mold  80  according to the present embodiment. Consequently, the outer circumferential end groove wall, which exists in the conventional mold, does not exist in the mold  82 . Accordingly, in the mold  82 , it is possible to prevent the stress concentration on a part of the groove wall as well as to greatly reduce the magnitude of the stress amplitude. Thereby, if such a mold is used in semimolten die casting, semisolid die casting, or the like, it is possible to reduce the stress-induced load of the mold and, in turn, to extend the life span of the mold by tenfold or greater. 
     Modified Examples 
     (A) 
     In the mold  80  according to the above embodiment, the communicating groove part  822  of the second mold portion  82  is shaped as shown in  FIG. 5 , but the shape of the communicating groove part is not particularly limited thereto; for example, communicating groove parts  822 A,  822 B,  822 C,  822 D as shown in  FIG. 11  through  FIG. 14  may be formed. Furthermore, based on the results of stress analysis (taking into consideration the mean stress, the stress amplitude, a safety factor with respect to the fatigue limit, and the like), the shapes shown in  FIG. 13  and  FIG. 14 , namely, the shapes of the communicating groove parts  822 C,  822 D, are particularly preferable. In  FIG. 13 , the outer peripheries of the scroll shaped groove part  821  and the communicating groove part  822 C have a nearly arcuate shape in a bottom view. In addition, in  FIG. 14 , the outer periphery of the communicating groove part  822 D in a bottom view has an arc and a tangent, which extends from a point on the outer periphery of the scroll shaped groove part  821 . 
     (B) 
     In the above embodiment, the present invention is adapted to a mold for molding the movable scroll  26 , but the present invention may also be adapted to a mold for molding other components such as a fixed scroll or a housing. For example, a mold portion  100  as shown in  FIG. 15  may be used to mold a flat plate member. Note that, in such a case, a groove part  110  corresponds to a molded part portion and a groove part  120  is a communicating groove part and corresponds to a portion to be removed by machining and the like. In addition, a mold  200  as shown in  FIG. 16  and  FIG. 17  may be used to mold, for example, a housing  250  that comprises reinforcing ribs  251  as shown in  FIG. 18  and  FIG. 19 . Note that, in such a case, groove parts  210  correspond to the reinforcing ribs  251  and a groove part  220  is a communicating groove part and corresponds to a portion to be removed by machining and the like. 
     (C) 
     The above embodiment adopts a hermetic type compressor as the high/low pressure dome type scroll compressor  1 , but the high/low pressure dome type scroll compressor  1  may be a high pressure dome type compressor or a lower pressure dome type compressor. In addition, it may be a semihermetic type compressor or an open type compressor. 
     (D) 
     In the above embodiment, a billet to which C, 2.2-2.5 wt %, Si: 1.8-2.2 wt %, Mn: 0.5-0.7 wt %, P: &lt;0.035 wt %, S: &lt;0.04 wt %, Cr: 0.00-0.50 wt %, Ni: 0.50-1.00 wt % has been added is used as the iron raw material, but the percentages of the elements in the iron raw material can be determined arbitrarily as long as the percentages do not depart from the spirit of the invention. 
     (E) 
     In the above embodiment, the Oldham ring  39  is used as the rotation preventing mechanism, but any mechanism, such as a pin, a ball coupling, or a crank, may be used as the rotation preventing mechanism. 
     (F) 
     The above embodiment described an exemplary case wherein the scroll compressor  1  is used inside the refrigerant circuit, but the application of the scroll compressor  1  is not limited to air conditioning, and the present invention can also be adapted to a compressor, a fan, a supercharger, a pump, or the like—either as a standalone or embedded in a system. 
     (G) 
     In the scroll compressor  1  according to the above embodiment, lubricating oil is present, but the scroll compressor  1  may be an oilless or oil-free (i.e., with or without oil) type compressor, fan, supercharger, or pump. 
     (H) 
     The high/low pressure dome type scroll compressor  1  according to the above embodiment is an outer drive type scroll compressor but may be an inner drive type scroll compressor. 
     (I) 
     In the movable scroll  26  according to the above embodiment, the notches are formed by, for example, end milling, but a notch (i.e., counterbore) may be preformed by a semimolten die casting process in the center portion of the upper surface of the end plate  26   a  of the movable scroll  26  shown in  FIG. 5 . 
     (J) 
     In the above embodiment, iron raw material is used as the raw material of the sliding parts, but a metal material other than iron may be used as it does not depart from the spirit of the invention. 
     INDUSTRIAL APPLICABILITY 
     The mold according to the present invention features a long lifespan when used to manufacture a molding using a semimolten die casting method or a semisolid die casting method and is extremely useful when manufacturing a molded part by a semimolten die casting method or a semisolid die casting method.