Closed shot die casting

Abstract: A method and apparatus for closed shot die casting in which a molten metal filling cylinder (52;90) is provided which intersects but is laterally offset from a shot sleeve (50;86) in fluid communication with a filling hole (60;96) in the shot sleeve. Molten metal is introduced into the filling cylinder. The molten metal passes from the filling cylinder through the filling hole into the shot sleeve until the shot sleeve is completely filled with molten metal. The filling cylinder includes a piston-like, reciprocating internal valve (66;92) which moves into position to seal off the filling hole. As a result, the shot sleeve is completely filled with molten metal and pressure-sealed prior to the advancement of the shot plunger (26;84).

Description: The present invention relates to a method and apparatus for die casting molten material, and more particularly, to a method and apparatus for injecting a shot of molten material into the cavity of a die. Die casting is frequently used as a method for forming articles from molten material. The present invention will be described in terms of casting molten metal; however, it should be understood the invention may be practised with other materials which may be cast from an initially liquid state. Typically, two or more die parts are provided such that, when brought together, they form a cavity which defines the shape of the article to be cast. Molten metal is introduced into the cavity and allowed to cool. If desired, the metal may be squeeze cast under high pressure to yield a heat treatable or weldable casting. The die parts are opened and the cast article is removed. In the past, molten metal has been introduced into a die by means of a shot sleeve. Fig. 1 shows a horizontal die casting apparatus with a shot sleeve arrangement according to the prior art. The die 10 includes an ejector die 12 mounted to a movable platen 14 and a cover die 16 mounted to a stationary platen 18. Together, the dies 12 and 16 form a cavity 19 into which a shot of molten metal will be introduced. A cylindrical shot sleeve 20 is disposed passing axially through the stationary platen 18 and the cover die 16 in fluid communication with the cavity 19. The upper surface of the outer wall near the end of the shot sleeve 20 is penetrated by an open pouring or filling hole 22. Molten metal 24 is ladled through the filling hole 22 into the interior of the shot sleeve 20. A plunger 26 seals off the outer end of the shot cylinder and reciprocates within the shot cylinder 20 to inject the molten metal into the die. The plunger 26 is connected axially to a plunger rod 28, crosshead adapter 30, and shot cylinder 32. The shot cylinder 32 is typically an hydraulic cylinder having a reciprocating shot cylinder rod 34 which causes the plunger 26 to advance toward the die 10 and withdraw therefrom. The outer end of the shot cylinder rod has threads 36 to allow for adjustment of the shot size and stroke length. Die casting methods and apparatus according to the prior art are subject to problems arising from the open filling hole 22 of the shot sleeve 20. The molten metal within the shot sleeve 20 is free to exit through the filling hole 22 until the plunger 26 advances past the filling hole. If the shot sleeve were entirely filled with molten metal, the beginning of plunger stroke would cause molten metal to spurt out of the filling hole 22. Therefore, as shown in Fig. 1, the shot sleeve 20 can only be partially filled with molten metal prior to the injection stroke of the plunger 26. Since the shot sleeve 20 can only be partially filled with molten metal, the diameter of the sleeve must be enlarged to provide an air space as well as for the necessary volume of molten metal. This enlargement of the shot sleeve diameter reduces the mechanical advantage of the shot cylinder 32, making the apparatus less suitable for squeeze casting. Fig. 2 shows the effect of the injection stroke of the plunger 26 on the molten metal 24. Since the molten metal does not completely fill the interior of the shot sleeve 20, a rolling, turbulent wave 40 of molten metal is created. Such turbulence in turn causes the formation of air bubbles 42 within the molten metal. The air bubbles ultimately cause unwanted porosity in the castings. Accordingly, there is a heretofore unmet need for a die casting method and apparatus that prevents molten metal from exiting the filling hole of the shot cylinder. EP-A-0226830 discloses a die casting apparatus comprising a die having a die cavity; a shot sleeve having an axial internal in fluid communication with the die cavity and a filling hole in fluid communication with the internal bore, a plunger disposed in the internal bore of the shot sleeve for reciprocating axial movement therein, and a filling cylinder having an axial internal bore disposed with its axis angularly offset with respect to the axis of the shot sleeve such that both of the said internal bores are in overlapping fluid communication with each other through the said filling hole, the filling cylinder further having an opening for the introduction of molten material into the internal bore of the filling cylinder. GB-A-475543 also discloses these features. EP-A-0226830 discloses the features of the pre-characterising portions of the independent claims hereto. According to a first aspect of the present invention, a die casting apparatus is characterised by the features of the characterising portion of claim 1. According to a second aspect of the present invention, a method for closed shot die casting is characterised by the features of the characterising portion of claim 9. According to a third aspect of the present invention, an apparatus for injecting a shot of molten material into the cavity of a die is characterised by the features of the characterising portion of claim 10. The present invention satisfies the aforementioned need by making it possible for the shot sleeve to be completely filled with molten metal and pressure sealed prior to the advancement of the plunger. Thus it is possible to eliminate air entrainment and resultant porosity. The diameter of the shot sleeve and the plunger may be minimized so that mechanical advantage and shot pressure may be increased for squeeze casting. The invention is suitable for use with both horizontal and vertical die casting and may be applied to existing die casting equipment. The invention may be carried into practice in various ways but two examples of die casting apparatus and their method of operation in accordance with the invention will now be described by way of example with reference to the accompanying drawings which also show an example of the prior art as already described. In the drawings: Fig. 1 is a sectional, side elevational view of a die casting apparatus according to the prior art; Fig. 2 is a an enlarged, sectional elevational view of the prior art apparatus of Fig. 1 illustrating the effects of the advancement of the plunger in the shot sleeve partially filled with molten metal; Fig. 3 is a side elevational view, with parts in vertical section of a die casting apparatus according to the principles of the invention; Fig. 4 is a perspective view of the intersecting shot sleeve and filling cylinder; Fig. 5 is a sectional view taken substantially along the line 5-5 of Fig. 3; Fig. 5a is a fragmentary, sectional view of the outer end of the filling cylinder similar to Fig. 5 but with the slide valve in the closed position; and Fig. 6 is a side elevational view, with parts in vertical section of a vertical die casting apparatus according to an alternative embodiment of the invention. The closed shot die casting apparatus which is shown in Fig. 3 includes in its general organization a die 10 having ejector and cover dies 12 and 16, movable and stationary platens 14 and 18, cavity 19, hydraulic shot cylinder 32, adjustment threads 36, rod 34, crosshead adapter 30, plunger rod 28, and plunger 26. Thus, the die, hydraulic shot cylinder, and plunger are substantially the same as described above with respect to the prior art shown in Fig. 1. The apparatus of Fig. 3 further includes a shot sleeve 50, filling cylinder 52, and hydraulic cylinder 54. Shot sleeve 50 is similar to the shot sleeve 20 according to the prior art, but may be formed with a smaller diameter. Referring additionally to Figs. 4 and 5, it may be seen that the shot sleeve 50 and filling cylinder 52 are so arranged that a central extent of the filling cylinder overlaps the shot sleeve with their longitudinal axes perpendicular to and offset to one another. The axis of the filling cylinder 52 crosses above the axis of the shot sleeve 50. Thus, as best shown in Fig. 5, the spacing of the axes is such that the internal bore 56 of the shot sleeve 50 and the internal bore 58 of the filling cylinder 52 partially intersect. This intersection coincides with a filling hole 60 formed through the outer wall of the shot sleeve adjacent the outer end of the shot sleeve by which the shot sleeve and filling cylinder are in fluid communication. As shown in Fig. 4, the shot sleeve 50 and filling cylinder 52 are clamped together at their intersection in fluid-tight relationship by U-bolts 62. Hydraulic cylinder 54 is mounted by a suitable base 63 and includes a reciprocating rod 64. The outer end of rod 64 is coaxially coupled to a piston-like slide valve 66. Slide valve 66 thus moves reciprocatingly within the bore of the filling cylinder 52 actuated by hydraulic cylinder 52. In Fig. 5, slide valve 66 is shown in its retracted, or filling, position. In this position, the filling hole 60 is open and in fluid communication with the bore 58 of the filling cylinder. When the slide valve is in the filling position and the shot plunger 28 withdrawn, molten metal is poured into the open outer end 68 of the filling cylinder 52. Pouring may be accomplished by ladling directly into the open end, through a funnel, or other suitable means. As best shown in Fig. 5, the filling cylinder 52 is tilted so that the molten metal runs down to the shot sleeve. The molten metal passes down the bore 58 of the filling cylinder, through the filling hole 60, and into the bore 56 of the shot sleeve 50. The shot sleeve is filled to overflowing such that the molten metal 24 covers the filling hole 60. Hydraulic cylinder 54 is then actuated to extend the rod 64 and move the slide valve 66 toward the hole 60. When hydraulic cylinder 54 is fully extended, as shown in Fig. 5a, the slide valve 66 overlies the filling hole 60 and makes a fluid tight seal therewith to prevent pressurized molten metal from exiting the filling hole when the plunger 26 is actuated. The sealing end of the slide valve 66 is formed with a recess 70 in the form of a segment of a cylinder complementary in shape to the bore of the shot sleeve 50. The recess 70 permits the plunger 26 to reciprocate within the shot sleeve past the filling hole 60 without interference from the slide valve 66. As shown in Fig. 5, a receptacle 72 may be provided beneath the open outer end 68 to catch any molten metal pushed out of the filling cylinder 52 by the slide valve 66. An operating cycle of the apparatus of shown in Figs. 3-5a is described as follows: Initially, die parts 12 and 16 are separated, and hydraulic cylinders 32 and 54 are extended. Die parts 12, 16 are brought together to form a cavity 19 in fluid communication with the inner end of the shot sleeve 50. Hydraulic cylinder 32 is retracted to withdraw the plunger 26 to the position shown in Fig. 3. Next, hydraulic cylinder 54 is retracted to withdraw the slide valve 66 to the position of Fig. 5. Molten metal is poured into the open end 68 of the filling cylinder until interior of the shot sleeve 50 is filled to overflowing with molten metal. Next, hydraulic cylinder 54 is extended so that slide valve 66 moves into the position of Fig. 5a to seal off the filling hole 60 and contain the molten metal within the shot sleeve 50. Cylinder 32 is then actuated to forcibly extend the plunger 26 and drive the molten metal from the shot sleeve into the mold cavity. No air is entrained in the metal. High pressures may be developed in the metal for squeeze casting. Finally, the die parts are separated and the casting is removed. An alternative embodiment of the invention in a vertical die casting system is show in Fig. 6. In a manner similar to the embodiment of Fig. 3, the vertical system includes a die 80, a hydraulic shot cylinder 82, plunger 84, shot sleeve 86, hydraulic cylinder 88, filling cylinder 90, and slide valve 92. The hydraulic cylinder 82, plunger 84, and shot sleeve 80 are coaxial and vertically oriented with the upper end opening 94 of the shot sleeve in fluid communication with the cavity of the die. As with the embodiment of Fig. 3, filling cylinder 90 is situated with its axis angularly offset to the shot sleeve axis and spaced apart from the shot sleeve axis where the axes cross. Filling cylinder 90 overlaps and partially intersects the shot sleeve 86 such that the internal bores of both are in fluid communication through a filling opening or hole 96. Fig. 6 further illustrates an alternative means for introducing molten metal into the filling cylinder which eliminates the need for ladling and seals the filling system from the atmosphere. The axis of the filling cylinder 90 is tilted upwardly toward a reservoir 98 of molten metal. The lower extent of the reservoir 98 is formed with an opening 100 which leads to a downwardly sloping passage 102. The lower end of the passage 102 is connected to the upper end opening 104 of the filling cylinder 90. Thus, when slide valve 92 is withdrawn, molten metal flows by gravity from the reservoir 98 down the passage 102, into the filling cylinder, through filling hole 96 and into the shot sleeve 86. The molten metal fills the shot sleeve by rising until it is at the same surface level as the molten metal in the reservoir 98. Once the shot sleeve is filled, hydraulic cylinder 88 extends the slide valve 92 to seal off the filling hole 96. Slide valve 92 is formed with a recess (not shown) similarly to the recess 70 shown in Fig. 5a to allow the plunger 84 to pass the filling hole 96 without interference. Thus, it may be seen that the invention is easily adaptable to convert a conventional die cast apparatus to squeeze cast apparatus in which relatively high pressures are developed in the injected molten metal. Conventional intensification systems may be used with the invention. Existing shot stroke adjustment is used to adjust shot size. The invention is suitable for casting steel, aluminium and magnesium, as well as other metallic and nonmetallic materials. The movements of the plunger and the slide valve keep the pouring paths clear.

Claims: A die casting apparatus comprising a die (10) having a die cavity (19); a shot sleeve (50;86) having an axial internal bore in fluid communication with the die cavity and a filling hole (60;96)in fluid communication with the internal bore, a plunger (26;84) disposed in the internal bore of the shot sleeve for reciprocating axial movement therein, and a filling cylinder (52;90) having an axial internal bore disposed with its axis angularly offset with respect to the axis of the shot sleeve (20;86) such that both of the said internal bores are in overlapping fluid communication with each other through the said filling hole (60;96), the filling cylinder further having an opening (68;104) for the introduction of molten material into the internal bore of said filling cylinder, characterised in that the axes of the shot sleeve and filling cylinder are spaced from one another, and by a slide valve means (66;92) disposed in the internal bore of the filling cylinder for reciprocating axial movement therein between a first position in which the filling hole (60;96) is open to allow molten material to flow from the internal bore of the filling cylinder through the filling hole into the internal bore of the shot sleeve and a second position in which the slide valve overlyingly seals the filling hole during axial movement of the plunger. A die casting apparatus according to claim 1 wherein the shot sleeve (20) is disposed axially horizontally. A die casting apparatus according to claim 2 wherein the filling cylinder (52) is disposed axially perpendicularly to the axis of the shot sleeve (50). A die casting apparatus according to claim 1 wherein the filling cylinder (90) is disposed axially sloping such that molten material introduced into the said opening (104) flows downwardly through the internal bore of said filling cylinder, through the filling hole (96), and into the internal bore of the shot sleeve (86). A die casting apparatus according to claim 4 wherein the shot sleeve (86) is disposed axially vertically. A die casting apparatus according to claim 4 or claim 5 further comprising a reservoir (98) for molten material and a passage (102) interconnecting the reservoir and the opening (96) of the filling cylinder, whereby molten material flows by gravity from the reservoir through the passage and the opening. A die casting apparatus according to any of claims 1 to 6 wherein the slide valve (66;92) is formed with a recess (70) having a shape complementary to the shape of the internal bore of the shot sleeve. A die casting apparatus according to any of claims 1 to 7 wherein the internal bore of the shot sleeve (50;86) is connected at one end to the die cavity (19) and the filling hole (60;96) is adjacent the other end of the internal bore. A method for closed shot die casting comprising providing a shot sleeve (50;86) having an axial internal bore in fluid communication with the cavity (19) of a die (10); providing a filling cylinder (52;80) axially angularly offset to the shot sleeve and overlapping the shot sleeve, the filling cylinder having an internal bore partially intersecting the internal bore of the shot sleeve in fluid communication therewith through a filling hole (60;96); introducing molten material into the filling cylinder; allowing the molten material to flow from the filling cylinder through the filling hole into the internal bore of the shot sleeve and advancing a plunger (26;84) within the internal bore of the shot sleeve past the filling hole to inject the molten material into the cavity of the die; characterised by allowing the molten material to completely fill the internal bore of the shot sleeve with molten material; and advancing a slide valve (66;92) within the internal bore of the filling cylinder to overlyingly seal the filling hole. An apparatus for injecting a shot of molten material into the cavity of a die, the apparatus comprising: a shot sleeve (50;68) defining an elongated shot bore, a shot plunger (26;84) reciprocable within the shot bore, and a filling cylinder (59;90) having an elongated filling bore with its axis angularly offset with respect to the axis of the shot bore, said shot bore and said filling bore intersecting one another so as to be in fluid communication with one another at a filling hole (60;96), the filling cylinder having an opening (68;104) for the introduction of molten material into the shot bore, characterised by a slide valve (66;92) reciprocable within the filling bore, the slide valve being operable between a filling position permitting molten metal to flow from the filling bore to the shot bore and a shot position where it overlyingly seals the filling hole and prohibits molten metal from flowing from the filling bore to the shot bore. An apparatus according to claim 10 in which the slide valve defines a recess (70) aligned with the shot bore when the slide valve is in the shot position and dimensioned to permit the shot plunger to pass therethrough. An apparatus as claimed in claim 10 or claim 11 in which the plunger (26;84) is disposed in the shot bore for reciprocating axial movement therein; the filling hole (60;96) being formed where the shot bore and filling bore intersect one another such that their internal bores are in fluid communication with each other through the filling hole, and such that molten material in the filling cylinder may pass through the filling hole into the shot sleeve and completely fill the shot sleeve, the slide valve (66;92) being disposed in the internal bore of the filling cylinder for reciprocating axial movement therein between the filling position in which the filling hole is open to allow molten material to flow from the internal bore of the filling cylinder through the filling hole into the internal bore of the shot sleeve to completely fill the shot sleeve, and the shot position in which the slide valve is disposed at and overlies the filling hole and prevents molten material from flowing between the filling bore of the filling cylinder and the shot bore of the shot sleeve through the filling hole. An apparatus as claimed in any one of claims 1 to 8 or claims 10 to 12 in which a central extent of the internal filling bore overlaps the shot sleeve (50;68).

Inventors: SHIMMELL DENNIS S, SHIMMELL, DENNIS S.
Applicants: NELSON METAL PROD CORP, NELSON METAL PRODUCTS CORPORATION
Application year: 1992
Main classification: B22D17
IPC codes: B22D17