Abstract:
A shot sleeve assembly for a die casting process includes a housing defining a bore open at both a front end and a rear end and a pour opening for receiving molten material, the housing includes a first coefficient of thermal expansion. A core is received within the bore and includes a second coefficient of thermal expansion lower than the first coefficient of thermal expansion. Front and rear covers attached to the housing hold the core in place within the bore and accommodate differences in thermal expansion between the housing and core.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This subject of this disclosure was made with support from the Singapore government. 
       BACKGROUND 
       [0002]    This disclosure is generally directed to a shot sleeve for a die casting process. More specifically, this disclosure is generally directed to a shot sleeve formed of different materials. 
         [0003]    A die casting process utilizes a mold cavity defined between mold parts. Molten metal material is feed in to the cavity and held under pressure until the metal hardens. The mold parts are then separated and the cast part removed. In some processes a shot sleeve is utilized to hold molten material and introduce that material to the cavity. The shot sleeve includes an opening for introducing molten material into a bore that leads to the cavity. A plunger moves within the bore to inject the molten material into the cavity. The plunger is subsequently withdrawn and additional material-is-introduced into the plunger for fabricating another part within the same cavity. 
         [0004]    The shot sleeve experiences the very high temperatures of the molten metal material and therefore is fabricated of materials compatible with those high temperatures. However, materials that are compatible with the high temperatures encountered during the die casting process can be costly and difficult to machine. Accordingly, it is desirable to design and develop shot sleeves that can withstand the high temperatures while reducing cost and easing manufacturing. 
       SUMMARY 
       [0005]    A shot sleeve assembly for a die casting process according to an exemplary embodiment of this disclosure, among other possible things includes a housing defining a bore open at both a front end and a rear end and a pour opening for receiving molten material. The housing includes a material of a first coefficient of thermal expansion, a core received within the bore and extending from the front end to the rear end including a core opening aligned with the pour opening. The core including a material of a second coefficient of thermal expansion lower than the first coefficient of thermal expansion, a front cover attached to the front end of the housing, and a rear cover attached to the rear end of the housing, the rear cover forcing the core against the front cover holding the core within the bore of the housing. 
         [0006]    In a further embodiment of the foregoing shot sleeve assembly, the rear cover includes a nut threadingly received within the bore and rotatable to force the core against the front cover. 
         [0007]    In a further embodiment of any of the foregoing shot sleeve assemblies, the housing includes flats for holding rotation of the housing responsive to rotation of the rear cover. 
         [0008]    In a further embodiment of any of the foregoing shot sleeve assemblies, the front cover includes a shoulder against which the core abuts for holding the core within the bore. 
         [0009]    In a further embodiment of any of the foregoing shot sleeve assemblies, includes a plurality of fasteners extending through the front cover for securing the front cover to the front end of the housing. 
         [0010]    In a further embodiment of any of the foregoing shot sleeve assemblies, the front cover includes a plurality of threaded openings for receiving corresponding threaded fasteners for forcing the front cover from the housing. 
         [0011]    In a further embodiment of any of the foregoing shot sleeve assemblies, includes a key member disposed between the housing and the core for holding a position of the core relative to the housing. 
         [0012]    In a further embodiment of any of the foregoing shot sleeve assemblies, the core is fabricated from a refractory metal material. 
         [0013]    In a further embodiment of any of the foregoing shot sleeve assemblies, the core is fabricated form a ceramic material. 
         [0014]    A method of casting a cast article according to an exemplary embodiment of this disclosure, among other possible things includes defining a mold cavity between at least two mold parts, mounting a shot sleeve, heating a shot sleeve to a pre-heat temperature, tightening a rear cover threadingly received within a housing to force a core disposed within the housing into a front cover, pouring a quantity of molten material into the core through a pour opening in the housing, forcing the molten material into the mold cavity, and curing the molten material within the mold cavity. 
         [0015]    In a further embodiment of the foregoing method of casting a cast article as recited in claim  10 , includes loosening the rear cover prior to cooling the shot sleeve to room temperature that is less than the pre-heat temperature. 
         [0016]    In a further embodiment of any of the foregoing methods of casting a cast article, includes removing the front cover by inserting at least one threaded fastener through a threaded opening and threading the at least one fastener through the front cover and into engagement with a front end of the housing and forcing the front cover away from the housing by extending the threaded fastener from the front cover. 
         [0017]    In a further embodiment of any of the foregoing methods of casting a cast article, the core has a lower coefficient of thermal expansion than the housing. 
         [0018]    In a further embodiment of any of the foregoing methods of casting a cast article, includes extending a key through the housing against the core for preventing relative rotation between the core and the housing. 
         [0019]    A casting assembly according to an exemplary embodiment of this disclosure, among other possible things includes a mold includes at least one cavity for receiving molten material, and a shot sleeve mounted to the mold for injecting molten material into the cavity. The shot sleeve includes a housing defining a bore open at both a front end and a rear end and a pour opening for receiving molten material. The housing includes a material of a first coefficient of thermal expansion. A core received within the bore and extending from the front end to the rear end includes a core opening aligned with the pour opening. The core includes a material of a second coefficient of thermal expansion lower than the first coefficient of thermal expansion. A front cover attached to the front end of the housing, and a rear cover attached to the rear end of the housing. The rear cover forces the core against the front cover holding the core within the bore of the housing, and a plunger movable through the bore of the shot sleeve for forcing molten material through the core and into the at least one cavity. 
         [0020]    In a further embodiment of the foregoing casting assembly, the rear cover includes a nut threadingly received within the bore and rotatable to force the core against the front cover. 
         [0021]    In a further embodiment of any of the foregoing casting assemblies, the front cover includes a shoulder against which the core abuts for holding the core within the bore. 
         [0022]    In a further embodiment of any of the foregoing casting assemblies, includes a key member disposed between the housing and the core for holding a position of the core relative to the housing. 
         [0023]    Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
         [0024]    These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a schematic view an example mold assembly. 
           [0026]      FIG. 2  is a cross-section of an example shot sleeve. 
           [0027]      FIG. 3  is a perspective view of the example shot sleeve. 
           [0028]      FIG. 4  is a rear perspective view of the example shot sleeve. 
           [0029]      FIG. 5  is a schematic view of a method of utilizing the example shot sleeve. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIG. 1  schematically illustrates an example mold assembly  10  that includes a mold  12  having a first part  14  and a second part  16  that defines a cavity  18 . The example mold  12  includes an opening  20  that receives a shot sleeve  22 . The example shot sleeve  22  defines a bore  34  through which molten material  26  is injected into the cavity  18 . A plunger  24  is movable within the bore  34  to inject the molten material  26  into the cavity  18 . The molten material  26  is of a temperature in excess of 2000° F. (1093° C.). Accordingly, the material comprising the shot sleeve  22  must be compatible with the excessive temperatures of the molten material  26 . 
         [0031]    Referring to  FIGS. 2 ,  3  and  4 , the example shot sleeve  22  includes a housing  28  with a front end  30  and a rear end  32 . The bore  34  is disposed about a longitudinal axis  15  and extends from the front end  30  to the rear end  32 . The bore  34  is opened at both the front and rear ends  30 ,  32 . The housing  28  is comprised of common steel and/or alloys of steel with a coefficient of thermal expansion that causes significant thermal growth during operation. Moreover, it is not desirable to provide direct contact between the housing  28  and the molten material  26  within the bore  34 . 
         [0032]    A core  42  fabricated from a material with a much lower coefficient of thermal expansion than steel is provided to define the internal surfaces in direct contact with the molten material  26 . The core  42  is received within the bore  34  and provides an interior surface capable of withstanding the temperatures of the molten material  26  that can exceed 2000° F. (1093° C.). 
         [0033]    The example core  42  is comprised of a refractory metal material such as Anviloy or TZM. The core  42  may also be comprised of a ceramic material such as silicon nitride or silicon carbide that have low coefficients of thermal expansion. As appreciated, other high temperature compatible materials may be used and are within the contemplation of this disclosure. 
         [0034]    Although a low coefficient of thermal expansion is desirable, the shot sleeve assembly  22  must also be of a sufficient strength and thickness to withstand and prevent the shot sleeve  22  from bending upwards due to encountering the temperatures of the molten material. Molten material is poured ( FIG. 1 ) through an opening  36  defined in the housing  44  that is aligned with an opening  52  within the core  42 . Molten material therefore sits on a bottom surface  66  of the core  42  prior to being injected into the cavity  18 . Because the molten material  26  sits on the bottom surface  66  of the core  42 , the bottom portion of the housing  28  and the core  42  are heated more than the top surface and will expand more than the top portion causing the shot sleeve  22  to bend upwardly. The example housing  28  is of a sufficient thickness to overcome the upward bending caused by the differential temperatures between the bottom and top surfaces while also including the thinner core  42  that withstands the higher temperatures. 
         [0035]    The example shot sleeve  22  includes a front cover  44  that is attached to the housing  28  with a plurality of fasteners  56 . The example fasteners  56  are machine screws that extend through openings in the front cover  44  into threaded holes defined in the front end  30  of the housing  28 . The front cover  44  is fabricated from a material determined to withstand the impact and wear encountered due to interaction with the mold assembly  10 . 
         [0036]    The front cover  44  is a separate piece from the housing  28  and thereby may be removed and replaced without having to replace the entire housing  28 . The core  42  is fit within the bore  34  of the housing  28  such that it may be removed and replaced due to wear and if damaged without replacing the entire shot assembly  22 . 
         [0037]    The front cover  44  further includes threaded openings  58  that receive fasteners that extend through to engage the front surface  30  of the housing  28 . As appreciated, the fasteners  56  extend through clearance openings within the front cover  44  and are received within internally threaded openings in the housing  28 . In contrast, the openings  58  are threaded such that a fastener extending through the openings will abut the end surface  30  and upon further tightening, drive the front cover  44  away from the front end  30  of the housing  28 . In this way, the front cover  44  can be removed even if expansion or residual molten material makes it difficult to remove. The example front cover  44  also includes a shoulder  68  against which the core  42  abuts. 
         [0038]    A rear cover  46  is threadingly received within the bore  34  of the housing  28 . The rear cover  46  includes a threaded portion  48  that extends about the circumference of the core  42  and engages a threaded portion defined within the housing  28 . The rear cover  46  also defines an opening  50  through which the plunger  24  may extend to drive the molten metal material  26  through the shot assembly  22  and out an opening through the front cover  44 . The core  42  is sandwiched between the shoulder  68  of the front cover  44  and the rear cover  46  within the bore  34 . Accordingly, the bore  34  may comprise a slip fit with the core  42  to ease removal. 
         [0039]    A key  54  extends through the housing  58  and engages a surface of the core  42  to prevent rotation of the core  42  relative to the housing  28  and to maintain an alignment between the opening  52  of the core  42  and the opening  36  within the housing  28 . The example key  54  comprises a threaded bolt that extends through the housing  28  and engages a flat surface  55  defined on the outer surface of the core  42 . The flat surface  55  accommodates some longitudinal movement of the core  42  relative to the housing  28  as may occur due to differential thermal expansion during operation. 
         [0040]    The housing  28  further includes an integral collar portion  38 , including flats  40  that are utilized and provide for engagement of a tool. As appreciated, a tool can be utilized to engage the surfaces  40  to prevent rotation of the housing and thereby the shot sleeve  22  during tightening or loosening of the rear cover  46 . Additionally, the example housing  28  does not include a mounting flange that requires larger starting stock material that is simply machined away to define a mounting flange. 
         [0041]    Referring to  FIG. 5  with continued reference to  FIGS. 2-4 , the example shot sleeve  22  is installed within the mold assembly  10  and heated to a preheat temperature. The preheat temperature can range between 500° F. and 2000° F. (260-1093° C.) and provides for heating the shot sleeve  22  to a temperature closer to that of the molten metal material to eliminate excessively quick rises of temperature. 
         [0042]    The core  42  includes a thermal expansion coefficient schematically indicated at  64  that is much less than a thermal expansion coefficient of the housing  28  indicated at  62 . Accordingly, once the shot sleeve  22  is heated to the preheat temperature; the housing  28  will become longer than the core  42 . Because the housing  28  is longer than the core  42  a gap  60  may form between an end of housing  28  and the core  42 . In this example, the gap  60  is defined between the shoulder  68  of the front cover  44  and an end of the core  42 . Molten material poured within the bore  34  can become entrapped within the gap  60  and reduce effectiveness of the shot sleeve assembly  22 . Accordingly, the core  42  is movable longitudinally in response to tightening of the rear cover  46 . As appreciated, once the shot sleeve  22  is at the preheat temperature, the rear cover  46  is tightened such that it moves inwardly to push the core  42  forward against the shoulder  68  defined in the front cover  44 . The rear cover  46  is then tightened to a defined torque to maintain the desired interface between the front end of the core  42  and the shoulder  68  of the front cover  44 . 
         [0043]    The molding operation can then proceed as indicated and described in  FIG. 1  where molten material  26  poured through the opening  36  into the bore  34  defined by the core  42 . The plunger  24  is then pushed through the bore  34  to inject the molten material into the cavity  18 . 
         [0044]    Once molding has been completed, the shot sleeve  22  will cool to a much cooler temperature such as room temperature. At room temperature, the housing  28  will contract to a much larger degree than the core  42  thereby inducing stresses on the front cover  44  and the rear cover  46 . Therefore, prior to cooling of the shot sleeve assembly  22 , the rear cover  46  is loosened such that it moves longitudinally outward to provide additional space for the relative thermal contraction between the housing  28  and the core  42 . 
         [0045]    The example shot sleeve assembly  22  therefore includes modular components that can be replaced upon wear to reduce the expense of manufacture and accommodate relative thermal expansion between the core and the housing  28 . The allowances provided by the example modular shot sleeve assembly  22  provide for the use of temperature compatible materials in locations where it is required while also providing for the use of cheaper materials for the housing  28  to reduce costs and assembly. Additionally, the example shot sleeve assembly  22  provides a modular assembly that has the capability of preventing gaps between different thermally acting materials. 
         [0046]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the scope and content of this disclosure.