Patent Publication Number: US-2018029113-A1

Title: Direct squeeze casting

Description:
FIELD 
     The present disclosure relates to casting. More specifically, the present disclosure relates to direct squeeze casting. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Current manufacturing processes for producing engine components of a motor vehicle, for example, cylinder blocks include high pressure die cast (HPDC) processes. Typically, as molten metal is directed to a mold, HPDC high velocity fill processes entrain air, generate oxides and have difficulty addressing metal shrinkage from certain regions within the mold. Other processes include precision sand casting which employs a bonded sand core pack mold with a large thermal bulk head chill and head deck risers to achieve desired material properties. Precision sand casting, however, is a costly process reserved for components requiring high integrity and enhanced material properties. 
     Accordingly, there is a need in the art for a cost efficient casting process for producing high quality and performance cast components. 
     SUMMARY 
     The present invention provides a system to cast structural components. Accordingly, in one aspect of the present invention, a casting system includes a pour cup, a plurality of runners that receive molten metal from the pouring cup, a top mold and a bottom mold that receive the molten metal from the plurality of runners, and a plurality of slides positioned within the top mold and the bottom mold. The positioning of the plurality of slides applies direct pressure on the molten metal in the top mold and the bottom mold to form a high integrity casting component. 
     The foregoing aspect can be further characterized by one or any combination of the features described herein, such as: the pour cup is a gravity pour cup; the pour cup is a tilt pour cup; electromagnetic pump; low pressure dosing fill system; interior surfaces of the top mold and the bottom mold have a pressure sensitive coating; the pour cup introduces the molten metal to the plurality of runners with a pour velocity of less than 100 cm/sec, preferably less than 50 cm/s; the plurality of slides is four slides; each slide is an insert that reciprocates along a respective channel; the pour cup introduces molten metal to the runners so that the molten metal flows into the mold quiescently without turbulence; and the applied pressure is between about 60 psi and about 3000 psi. 
     Accordingly, pursuant to another aspect of the present invention, an apparatus to form a metal structural component includes a first mold, a second mold, the first mold and the second mold being configured to receive molten metal, and a plurality of slides positioned within the top mold and the bottom mold. Positioning of the plurality of slides applies direct pressure on the molten metal in the top mold and the bottom mold to form a high quality metal cast component. 
     The foregoing aspect can be further characterized by one or any combination of the features described herein, such as: interior surfaces of the first mold and the second mold have a pressure sensitive coating; the plurality of slides is four slides; each slide is an insert that reciprocates along a respective channel; and the applied pressure is between about 60 psi and about 3000 psi. 
     Accordingly, pursuant to yet another aspect of the present invention, a method of casting a quality metal component includes one or more of the following steps: pouring molten metal into an interior cavity defined by a first mold and a second mold, and exerting pressure on the molten metal to form a quality metal component. 
     The method of casting a structural component may be further characterized by one or any combination of the following features: interior surfaces of the first mold and the second mold have a pressure sensitive coating; the molten metal pours into the interior cavity with a velocity of less than 100 cm/sec, preferably less than 50 cm/s; exerting pressure is produced by a plurality of slides positioned in the first mold and the second mold; the molten metal flows into the interior cavity quiescently without turbulence assisting in pushing existing air from mold cavity; the applied pressure is between about 60 psi and about 3000 psi; the slides move outwards along respective channels to accommodate an overfill volume, and the slides move inward to compensate for metal shrinkage as the molten metal transitions to a solid, while the positioning of the slides maintain the desired pressure on the solidifying casting; and the slides are configured to move to apply direct pressure to the molten metal as it solidifies, and pressure is applied and controlled with use of one or more pressure punches applied to regions of interest of the solidifying casting, the slides and the one or more pressure punches operating simultaneously or independently of each other. 
     Further features, advantages, and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the drawings: 
         FIG. 1  illustrates a system for direct squeeze casting in accordance with the principles of the present invention; 
         FIG. 2  is cut-away view of the system; 
         FIG. 3  is a cut-away view of another direct squeeze casting system in accordance with the principles of the present invention; 
         FIG. 4  is a perspective view of a top mold and bottom mold for the direct squeeze casting system shown in  FIG. 1 ; 
         FIG. 5  is an interior view of the top and bottom molds; 
         FIG. 6  illustrates the top and bottom molds separately; 
         FIG. 7  is a schematic view of the system shown in  FIG. 1  in use molding a component. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     Referring now to the drawings, a direct squeeze system to cast structural components embodying the principles of the present invention is illustrated therein and designated at  10 . Turning in particular to  FIGS. 1 and 2 , the system  10  includes a pour cup  12  that communicates with a downsprue or downgate  14 , which, in turn, communicates with a runner  20 . The runner communicates with a set of molds  16  and  18  through a plurality of ingates  22 . 
     Referring to  FIG. 4 , there is shown the direct squeeze casting system  10  in use. Molten metal  11  is poured into the pour cup  12 . The molten metal flows down the downgate  12  through the runner  20  into the ingates  22 . Note that the runner  20  is not shown and only one ingate  22  is shown in  FIG. 4  for the sake of simplicity. It should be understood, that only one ingate  22  may be employed or any number of ingates that communicate with the runner  20  may be employed. For example,  FIGS. 1 and 2  show the system  10  with seven ingates  22 . Accordingly, the molten metal  11  flows through the one or more ingates  22  into the bottom mold  18 . The bottom mold  18  and the top mold  16  define a mold cavity or an interior region  28 . Hence, as the molten metal flows into the bottom mold  18 , the molten metal fills the interior region  28 . As the molten metal in the interior region  28  cools, it forms a structural component  30 . The top mold  16  includes a vent  29  to flush air from the mold cavity thereby relieving pressure within the interior regions  28 . Further, a direct pressure punch may be associated with the vent. That is, the punch may be controlled to vary the hydrostatic pressure in the molten metal as the component  30  solidifies. Note that more than one pressure punch may be employed to apply pressure to regions of interest of the solidifying casting, 
     Turning to  FIG. 3 , there is shown an alternative direct squeeze casting system  100 . Most of the components of the system  100  are the same as those of the system  10 . The system  100 , however, has a tilt cup  112  rather than the pour cup  12  and the downgate  14  arrangement. Accordingly, after the tilt cup  112  is filled with molten metal, the tilt cup, or entire cup and mold package  112  is tilted in the direction of the arrow  114  to pour the molten metal into the runner  20  such that that the molten metal fills the interior region  28  as described previously. Mold cavity fill can also be accomplished with other fill systems including; Electromagnetic pump, Low Pressure pumps and dosing systems. 
     In either system  10  or  100 , the molten metal is poured into the respective system with a slow pour velocity. For example, in some arrangements, the pour velocity through the ingates  22  is less than 100 cm/sec, preferably less than 50 cm/s. In contrast, in high pressure die cast (HPDC) systems, the pour velocity exceeds 2000 cm/sec, and, in some arrangements, approaches 3800 cm/sec. A particular benefit of the low speed pour velocity for the systems  10  or  100  is the quiescent flow of the molten metal as it flows into the molds  16  and  18 , which thereby reduces or eliminates turbulence in the flowing molten metal. In comparison to HPDC systems, the non-turbulent flow of the molten metal reduces the entrainment of air in the molten metal, which reduces the creation of structural voids in the structural component  30 . In some arrangements, the surface of the interior cavity  28  is coated with a pressure sensitive coating, which enhances heat transfer and directional solidification, since the coating has a high thermal resistance with no pressure and low or no thermal resistance with high pressure. An example of such a coating is Trabo™ available from REL, Inc. 
     Generally, molten metal shrinks as it cools. For example, aluminum shrinks about 6% as it solidifies. Another feature of the systems  10  and  100 , is the ability to compensate for the shrinkage of the molten metal as it cools and solidifies. Specifically, as shown in  FIGS. 5 and 6 , a set of inserts or slides  32 ,  34 ,  36  and  38  are positioned in the top and bottom molds  16  and  18 . The slides  32 ,  34 ,  36  and  38  are configured to reciprocate along channels  50 ,  52 ,  54  and  56  in the top mold  16  and corresponding channels  68 ,  70 ,  72  and  74  in the bottom mold  18  to accommodate material geometries of the component  30 . As such, as the molten metal flows into the interior region  28  defined by a cavity  60  of the top mold  16  and a cavity  62  of the bottom mold  18 , the slides  32 ,  34 ,  36  and  38  slide outwardly along their respective channels  50 ,  52 ,  54 ,  56  and  68 ,  70 ,  72 ,  74 , as indicated by the arrows  40 ,  42 ,  44  and  46  to accommodate an overfill volume of for example, 10%. As the molten metal cools and shrinks, the slides  32 ,  34 ,  36  and  38  slide inwardly to compensate for shrinkage of the molten metal as is cools and solidifies to form the quality metal component  30  (shown as a block for the sake of simplicity), while the positioning of the slides maintain the desired pressure on the solidifying casting. 
     Note also, that the positioning of the top mold  16  and the bottom mold  18  exerts or applies controlled direct pressure on the cooling molten metal as well. For example,  FIG. 7  schematically illustrates pressure being directly applied in a controlled manner from six directions (top and bottom and from the sides) to mold the mechanical component  30 . Specifically, the top mold  16  can be moved up and down as indicated by the arrow  66  and the bottom mold  18  can be moved up and down as indicated by the arrow  64 , in addition to the direct pressure applied by the slides  32 ,  34 ,  36  and  38  along the lines  40 ,  42 ,  44  and  46  to accommodate an overfill Further, the applied pressure can be controlled with the use of the aforementioned one or more pressure punches and the vent  29  to apply and control the pressure to regions of interest of the solidifying casting. The slides and the one or more pressure punches can operate simultaneously or independently of each other. 
     In sum, the mold cavity or interior region  28  is coated with a high thermal resistant-pressure activated coating. The molds  16  and  18  are closed and mechanically locked except for a direct pressure punch detail. Molten metal, such as, aluminum alloy quietly fills the mold cavity with approximately 10% overfill. The mold cavity is vented around the pressure punch or other locations. The direct pressure punch sequences shutting off the flow of molten metal through the downgate  14  and the ingates  22 . The desired pressure is set and held until the cast component  30  solidifies. The molds  16  and  18  are opened and the mechanical component is removed. 
     In various arrangements, the direct squeeze pressure applied to the metal by the system  10  or  100  as it forms the component  30  can vary between about 60 psi to 3000 psi. It should be understood, that the inserts  32 ,  34 ,  36  and  38  arrangement can be modified for creating different component geometries. The pressure can be applied directly to a strategic region of the mechanical component  30 , for example, the bulk head region of an engine block. As such, high integrity cylinder block castings can be heat treated to optimum tensile and fatigue strengths. Tensile and fatigue strengths of components produced with the system  10  or  100  can be at least double as compared to components produced with HPDC systems. Quiescent mold fill combined with low to medium squeeze pressure allows for the use of strong sand cores for internal passages and closed deck designs. Low to medium squeeze pressures can be used to drive molten metal infiltration of ceramic or metal reinforcement of local high stress regions of the component. Significantly lower casting pressures reduce tooling and press ruggedness requirements, which enables the use of simpler castings machines, hydraulic systems and controls compared to HPDC machinery. As such, simpler casting machines, hydraulics and controls and improved tool life lowers the cost per component compared to components made with HPDC systems. 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.