Abstract:
An apparatus for casting material has a die for receiving a compressive force, the die having a shaped-opening for receiving a die insert. The die insert has an exterior shape that is adapted to cooperate with and be received in the opening such that compressive forces impinging upon the die are focused upon the die insert such that tensile forces within the die and impinging upon the die insert are minimized.

Description:
BACKGROUND 
     Investment casting is an industrial process based on one of the oldest metal forming techniques. This process is capable of producing complicated shapes that would be difficult or impossible (particularly with high melting temperature alloys) with die casting. Investment casting produces parts that usually require little surface finishing and only minor machining Usually, the process begins with fabrication of a sacrificial ceramic pattern with the same basic shape as the finished cast part. Patterns are made wax that is injected into a metal injection die. Fabricating the injection die is expensive and can take months of lead time. 
     Once a wax pattern is produced, it is then dipped in a ceramic slurry, covered with a particulate material, and allowed to dry. Once dried, the pattern is placed in an autoclave to remove the wax. After autoclaving, any remaining wax is burned out in a furnace during which the ceramic shell is also hardened. The mold is then preheated and filled with molten metal, creating the metal casting. Once the casting has cooled sufficiently, the mold shell is chipped away from the casting. 
     Die casting, on the other hand, is the process of forcing molten metal under high pressure into mold cavities that are machined into dies. Most die castings are made from nonferrous and relatively low melting temperature metals specifically zinc, copper, aluminum, magnesium, lead, and tin-based alloys, although ferrous metal die casts are possible. After the die is filled, and the material therein has solidified, the part for casting is ejected usually by ejector pins. Thereafter, any scrap, which includes gate runners and flash etc. must be separated from the castings. 
     The dies used in die casting are usually made out of hardest tool steels because cast iron cannot withstand the high pressures involved. Due to this, dies are expensive and may have high start-up costs. 
     SUMMARY 
     According to an embodiment disclosed herein, an apparatus for casting material has a die for receiving a compressive force, the die having a shaped-opening for receiving a die insert. The die insert has an exterior shape that is adapted to cooperate with and be received in the opening such that compressive forces impinging upon the die are focused upon the die insert such that tensile forces within the die and impinging upon the die insert are minimized. 
     According to a feature of the embodiment, the die insert and the shaped opening have a plurality of shaped sides or a continuous side that compressive forces impinging upon the die are focused upon the die insert such that tensile forces within the die and impinging upon the die insert are minimized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
         FIG. 1  is a side view of a die having a pair of inserts disclosed therein. 
         FIG. 2A  shows top and side views of a second embodiment of a die insert of  FIG. 1 . 
         FIG. 2B  shows top and side views of a third embodiment of a die insert of  FIG. 1 . 
         FIG. 2C  shows top and side views of a fourth embodiment of a die insert of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1  the embodiment of a die  10  is shown. The embodiment includes a top die  15 , a bottom die  20 , a top die insert  25 , a bottom die insert  30 . Both dies are driven by a press indicated by arrows  35  that supplies clamping forces that exert high pressure forces on the die inserts  25  and  30  as are known in the art. The use of 150 ton presses and greater are known to be used though lesser tonnage may be used depending on the size of a part  40  to be die cast. 
     In the instant application, the part  40  created by using the dies and die inserts is made of a high temperature nickel alloy that has a melting point around 2800° F.-2900° F. though other high temperature and low temperature alloys may be used herein. The die inserts are typically made of a ceramic material like silicon nitride which can withstand temperatures up to 5000° F. Silicon nitride has enviable properties like high strength over a wide temperature range, fracture toughness, high hardness, outstanding wear resistance, thermal shock resistance and chemical resistance. However other materials are known and are contemplated for use herein. 
     The upper and lower die inserts  25 ,  30  fit very snuggly within the upper and lower dies  15 ,  20  and have tapered or contoured sides  42  so that operation of the presses force the top die and the bottom die to provide the uniform compressive forces indicated by arrows  45  upon the upper and lower die inserts  25 ,  30 . Ceramic materials, like silicon nitride, have very low ductility and compressive forces are ideally tolerated by the material while tensile forces are not as well tolerated. By providing the uniform compressive force caused by the contoured sides on the die inserts, which focus the compressive forces on the upper and lower die inserts  25 ,  30 , any tensile forces, which might damage the die inserts  15 ,  20 , on the die inserts are minimized and die life is therefore maximized. 
     Referring now to  FIG. 2 , several alternative embodiments of the die inserts  2 A,  2 B and  2 C a side view of lower die  20  and lower die insert  30 , and a bottom view of the top die insert  25  are shown. 
     In  FIG. 2A , the upper die insert  25  has a rectangular top portion  50 , a rectangular bottom portion  55  and four angled side surfaces  60  that attach the top portion  50  to the bottom portion  55 . Similarly, the lower die insert  30  mirrors the upper die insert  25 . 
     In  FIG. 2B , upper die insert has a circular top portion  65 , a circular bottom portion  70  and a conical side surface  75  joining the top portion  65  to the bottom portion  70  so that the die looks like a truncated cone. Similarly, the lower die insert  30  mirrors the upper die insert  25 . 
     In  FIG. 2C , upper die insert has a bowl-shaped top and side portion  80  and a circular face portion  85  so that the die looks like a bowl. Similarly, the lower die insert  30  mirrors the upper die insert  25 . 
     Ideally the side surface forms an angle α that is greater than 90° between the side surface  60  and the top surface  50  (see  FIG. 2A ). 
     Each upper and lower die insert in  FIGS. 2A ,  2 B, and  2 C have a pair of shoulders  90  in a mating surface  95  thereof and a side surface  60 ,  75 ,  80  thereof so that a screw  100  will mate with the top surface and the side surface to hold the upper and lower die insert  25 ,  30  in the upper and lower dies  15 ,  20  respectively. 
     Screw  100  has a large head  105  in which a counter sink  110  is disposed therein. In the embodiment shown, the counter sink  110  is hexagonally-shaped to receive a hexagonally-shaped pin  115  that extends radially from the large head  105  and locates the upper die  15  atop the lower die  20 . The screws mate with holes  120  within the upper and lower dies  15 ,  20 . 
     Alternatively, the pins  115  may be set or manufactured within the screw  105  so that one screw  105  disposed in the bottom die  20  would, for instance, mate with the screw counter sink  110  in the upper die  15  or vice-versa. Other locating devices and other shaped countersinks are contemplated for use herein. 
     In operation, the upper die insert  25  is inserted into a top die  15  and a bottom die insert  30  is placed in the bottom die  20 . The inserts are secured to the dies by screws  100  that fit into holes  120  and the enlarged screw head  100  holds the shoulders  90  of the upper and lower die inserts  25 ,  30  securely in the upper and lower dies  15 ,  20 . The top die insert and the bottom die insert are then aligned via the pins  115  that are inserted into countersinks  110 . Liquid metal is then injected at high temperature between the dies into the die cavity to create a part  40 . 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.