US3270383A

US3270383A - Method of die casting

Info

Publication number: US3270383A
Application number: US289903A
Authority: US
Inventors: Harry D Hall; David C Salatin; Don R Sutherland; Clayton J Trible
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1963-06-24
Filing date: 1963-06-24
Publication date: 1966-09-06
Anticipated expiration: 1983-09-06

Description

Sept. 6, 1966 H. D. HALL ETAL 3,270,383

METHOD oF DIE CASTING Filed June 24, 1963 2 Sheets-Sheet l WVENTORS A TIURNEV/ Sept-6, 1966 H. D. HALL ErAL METHOD 0F DIE CASTING 2 Sheets-Sheet 2 Filed June 24, 1963 United States Patent O 3,270,383 METHOD F DIE CASTING Harry D. Hall, Birmingham, David C. Salatin, Royal Oak, Don R. Sutherland, Mount Clemens, and Clayton J. Trible, Berkley, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed .lune 24, 1963, Ser. No. 289,903 Claims. (Cl. 22-200) This invention relates to die casting and more particularly to a process -for making improved die castings and to apparatus for carrying out the process.

Conventional die casting procedures involve injecting molten metal into a die cavity at a relatively high pressure in order of 10,000 pounds per square inch by means of a piston-like ram. Typically, the molten metal is forced through a restrictive sprue passage to cause the metal to enter the die cavity in particulate for-m and at a high velocity to facilitate filling of the die cavity. The molten vmetal therefore enters the die cavity in a highly turbulent state and the high pressure of the injection is relied on to compress the molten metal in the die cavity to obtain reasonably dense castings. Die casting procedures of this type may be of the hot-chamber type, as is typically used in zinc die casting, in which the injection mechanism or gooseneck is submerged in a mass of molten metal or of the cold-chamber type, typically used in aluminum or magnesium casting, in which the injection mechanism is maintained in an atmospheric environment. The principal advantage in the above high pressure type of die casting is in the speed with which the castings are made since only a few seconds are involved in the entire procedure of injecting the molten metal-into the die cavity, solidification of the casting, and its removal from the die. The principal disadvantage of this high pressure type die casting is that since as above indicated the metal is injected into the dies under high pressures rand generally through a res-tricted sprue opening the metal enters the 'die cavity in a highly turbulent condition with the result that the castings tend to be porous and unsuitable for many purposes. Thus, for example, castings made by the above-)mentioned high pressure die casting are suitable for automotive body hardware, ornamental parts, and the like. However, due to the inherent porosity of such castings, they are generally unsuitable for making cylinder blocks, cylinder heads, pump housings, and the like.

Another well-known type of die casting generally referred to as low pressure casting involves mounting the dies over Van enclose-d pot of molten metal, providing a tube or stalk which extends 'from a point within the molten metal to the sprue of the die, and subjecting the molten metal to a superimposed pressure differential in the order of a few pounds per square inch whereby the molten metal is forced slowly up into the stalk and thence into the die cavity under essen-tially non-turbulent conditions. The principal advantage in this type of die casting is that a more dense casting is formed. The principal disadvantage resides in the fact that a typical casting cycle req-uires a considerable amount of time since the molten metal is injected into the die cavity slowly and slow solidification is provided to prevent premature solidification of the casting in the cavity.

It is the principal object of this invention to provide an improved die casting process whereby highly improved, dense castings are made 4at a relatively high speed and whereby the advantages of prior :art procedures are realized and the disadvantages are eliminated. Another object of this invention is -to provide apparatus 4for carrying out this process These and other objects are carried out by apparatus ,27(l,383v Patented Sept. 6, 1966 ice generally of the cold-chamber type having a novel cornbination of machine elements including an enlarged gate of suicient volume to permit non-turbulent passage of the molten metal therethrough into the die cavity, a coldcharnber type shot sleeve, a duplex shot plunger operable within the shot sleeve consisting of a relatively small diameter plunger reciprocally operable within a larger diameter plunger of substantially the same 'diameter las the shot sleeve, wherein the tip of the smaller plunger is adapted to be positioned substantially at the tip of the larger plunger in a first position thereof and to extend to a longitudinal position substantially beyond the tip of the larger plunger in a second position thereof, and hydraulic and control means for operating the two plungers as a unit when the plungers are in said first position and for operating the smaller plunger independently of the larger one to obtain said second position.

The process includes the steps of admitting a measured charge of molten metal into the shot sleeve, operating the duplex plunger as a unit to move the molten metal non-turbulently into the die cavity in the form of a solid front, maintaining a relatively high compacting pressure on the molten metal by means of the duplex unit until a realtively thin shell of molten metal has solidified adjacent the walls of the `die cavity, the gating, and the duplex plunger tip to prevent further application of compacting pressure and thereafter actuating the smaller plunger independently of the larger one whereby its tip breaks through the solidified metal shell adjacent the tip orf the smaller plunger to thereby subject the molten core portion of the metal in the die cavity to continued high pressure and continued filling until'the metal has solidified.

Preferably, means are provided whereby the actuation of the smaller plunger is in response to the pressure built up against the larger plunger due to the aforementioned solidified metal shell having been formed adjacent the plunger and shot sleeve walls thereby preventing the larger plunger from subjecting the molten metal in the die cavity -to further compression and whereby the solidilication of the casting is not permitted to progress to a point which would involve solidification of the core portion of the casting or to a point which would make it difficult for the smaller plunger to break through the solidified shell.

Other objects and advantages will be apparent from the following detailed description of the invention, reference being had to the -accompanying drawings of which:

FIGURE 1 is a fragmentary cross-sectional view of die casting apparatus embodying this invention showing the dies and injection mechanism in a position just as the die cavity is filled with molten metal.

FIGURE 2 is a fragmentary cross-sectional view of the die cavity and plunger tip portion of the apparatus at an intermediate stage of the process of this invention just prior to the actuation of the smaller plunger.

FIGURE 3 is a fragmentary cross-sectional view similar to that of FIGURE 1 but after the actuation of the smaller plunger.

FIGURE 4 is a view of the apparatus shown in FIG- URE l together with hydraulic and electrical control apparatus shown in schematic form.

Referring now to the drawings and particularly to FIGURE 1, it will be observed that there is included in the fragmentary illustration of the die casting machine a cover die 10 and an injector die 12 defining a die cavity 14 therebetween. The die member 10 is supported on the face of a stationary platen 16 by suitable bolts (not shown) which in turn is mounted on a base plate (not shown).

The stationary platen 16 also supports one end of each of four longitudinally extending tie bars 18, the opposite end of each of the tie bars being supported by a suitable upright stationary plate (not shown).

The movable ejector die 12 is supported on the movable platen 20` mounted on the tie rods 18 for longitudinal movement thereon. The movable platen 2() is movable reciprocally along the tie rods 18 between die open and closed positions by means of a toggle device 21 as is well known in the art.

In the space within the movable die 12, there is provided an ejecting mechanism comprising a head plate 22 and a plurality of ejecting pins 24. rThe ejecting pins 24 are each secured at one end of the head plate 22 and are slidably received in suitable bores formed in the ejector die 12. A plunger 26 has its forward end secured to the head plate 22 of the ejecting mechanism and extends rearwardly through an axially aligned bore in the die 12 and the movable platen 20. A bushing 28 having sealing rings 30 is provided to prevent leakage through the movable platen about the plunger 26. When the movable platen 20 is retracted and closely approaches the limits of its rearward movement, the plunger 26 is adapted to engage a stop (not shown) whereby its rearward movement is terminated. The continued movement of the platen to its rearward limit thereafter results in relative movement between the platen 20 and the plunger 26 and between the ejector pins 24 and the movable die 12, the front ends of the pins being urged outwardly from the face of the die to dislodge the casting formed in the cavity.

Extending snugly through the aligned bores in the platen 16 and the cover die 10` is a shot sleeve 32 having a vertical extending opening 34 therein for admitting a charge of the molten metal into the shot sleeve in any well-known manner. An important aspect of the invention resides in the provision of a wide gating 36 extending from the end of the shot sleeve 32 into the die cavity proper 14. As will hereinafter more fully be described, the gating 36 is of sutiicient volume so that the molten metalmay be moved into the die cavity 14 without significant turbulence. As may be seen from the drawing, the gating 36 may be initially of the same dimensions as the shot sleeve to avoid turbulence as the molten metal changes from horizontal to vertical flow into the die cavity.

Another important aspect of the invention resides in a duplex plunger indicated generally as 38 which consists of a relatively larger outer plunger 40 snugly and reciprocally received in the shot sleeve 32 and a relatively small plunger 42 reciprocally received within a longitudinal bore of the larger plunger 40' centrally thereof. The larger plunger 40 is slidably supported on a plurality of tie rods 44, each bolted 'at one end thereof to the station ary planten 16, 'by means of the flange 45 integrally attached to the plunger 40. To the opposite ends of the tie rods 44, there is bolted a hydraulic cylinder 46 including a piston stop 47 attached to the end thereof and having a piston 48 reciprocally positioned therein. The piston 48 is attached to` a connecting rod 50 which is slidably mounted on the tie rods 44 by means of the integral ange 52. .The flange 52 is connected to the flange 45 of the plunger 40` by means of the cylinder 54 welded thereto whereby the piston 48 is connected to the plunger 40 by means of the connecting rod 50, the

flanges

45 and 52, and the cylinder 54. The

anges

45 and 52 have aligned bores 4therein which receive the bushings 56 and are welded thereto. These in turn slidably receive the tie rods 44. The cylinder 54 also forms a hydraulic cylinder including the piston stop 55 attached to the rod 50, which contains a piston 58 attached to the smaller plunger piston 42.

It will thus be observed that reciprocal motion of the piston 48 is operable to move the smaller or inner plunger 42 and the larger or outer plunger 40 as a unit. On the other hand, the reciprocal motion of the piston 58 is operative to reciprocate the inner plunger 42 independently of the motion of `the outer plunger 40. As will be hereinafter described, hydraulic and control means are provided for moving the outer plunger 40 Aand the inner plunger 42 in a predetermined sequence in accordance to the requirements of the process of this invention.

Referring to FIGURE 4 an example of suitable hydraulic mechanism for practicing the process of this invention includes a gear pump 62 having an input line 64 connected to an oil sump 66 and an output line 68 connected to a relief valve 69 discharging to the sump; to an accumulator 70; to a first line 72 connected to the portion of the cylinder 46 -outwardly of the piston 48 through a flow control valve 73, a two-way solenoid operated valve 76, the hydraulic line 79 and the hydraulic line 84; and to a second line 78 connected to the portion of the cylinder 46 outwardly -of the piston 48 through the flow control valve 80,' the solenoid operated four-way valve 82 and the lines 77 and 84. The line 78 is also connected to that portion of the cylinder 46 inwardly of the piston 48 through the ilow control valve 80, the four-way solenoid operated valve 82 and the line 83. The outlet 68 of the gear pump 62 is also connected to a third line 86 which connects with the portion of the cylinder 54 outwardly of the piston 58 through the fourway solenoid operated valve 88 and the reducing valve 98. The line 86 is also connected to the portion of the cylinder 54 inwardly of the piston S8 through the lfourway valve 88 and the line 89. The portion of the cylinder 46 inward -of the piston 48 is also connected to the oil sump 66 through the line 83, the four-way valve 82, and the line 81. 'I'he portion of the cylinder 46 outward of the piston 48 is also connected to the oil sump through line 84, the four-way valve 82 and the line 81. Similarly, the` portion of the cylinder 54 inw-ard of the piston 58 is connected to the oil sump 66 by means of the line 89, the four-way valve 88, and the line 87; and the portion of the cylinder 54 outwardly of the piston 58 is connected fto the sump 66 through the line 92, the four-way valve 88 and the line 87. The lcharacter and operation of the electrical components for operating the hydraulic apparatus will be apparent from FIGURE 4 and the detailed description' of the operation of the mechanism to -be made hereinafter.

The process of this invention stated generally in terms of FIGURES l, 2, and 3 involves rst returning the duplex plunger 38 to a cycle commencement position in which the plunger 40 is withdrawn sulciently from the shot sleeve to expose the inlet 34. When operated as a unit the tips of each of the plungers are substantially aligned to form a composite tip of more or less conventional shape. A measure charge of the molten metal is poured into the shot sleeve which is suicient to lill the die cavity 14 as well as the enlarged gating portion 36 when the plunger 38 reaches the end of its stroke. Hydraulic fluid is then caused to enter the hydraulic cylinder 46 on the side thereof outward of the piston 48 whereby the duplex plunger 38 including the outer plunger 40 and the inner plunger 42 moves as a unit forward toward the die cavity to nonturbulently move the molten metal into the die cavity 14. The volume of the gating 36 and the speed of the duplex plunger is such as to provide a lineal velocity through the gate not in excess of about 50 feet per second, i.e., a nonturbulent flow, whereby a solid front of the metal moves into and fills the cavity. Just before the die cavity 14 is filled with molten metal, additional hydraulic pressure is ,applied outwardly of the piston 48 where'by a squeeze in the neighborhood of 5,00()-l0,000 pounds per square inch is applied to the metal in the die cavity 14. The molten metal begins immediately to solidify in the die cavity and the gating adjacent the metal walls of the die. After the lapse of a short period of time in the vicinity of a fraction of a second, a relatively thin layer of the molten metal 124 is formed adjacent the metal walls of the die within the die cavity 14 as well as the gating 36 and over the tip .of the duplex plunger as shown in FIGURE 2. The formation of this metal shell prevents the further application of pressure by the duplex plunger tip on the molten metal sin-ce this metal shell creates an annular barrier 126 about the periphery of the duplex plunger tip. This condition is evidenced by a marked increase in the hydraulic pressure developed in the cylinder 46 outwardly of the piston 48. Electrical and hydraulic control mechanism is provided to cause this increase in pressure to then admit hydraulic pressure into the cylinder 54 outwardly of the smaller piston 58 whereby the smaller inner plunger 42 is caused to move forward and break through the shell 124 as shown in FIGURE 3 and whereby the core or internal molten portions of the casting is subjected to continued pressure 4on the order of 10,000 pounds per square inch to further feed molten metal into the die cavity to compensate for shrinkage until the molten metal has solidified, and thereby produce a high quality dense casting. After the metal has solidified, the hydraulic pressure outwardly of the smaller piston 58 is relieved and hydraulic pressure is applied to the cylinder 54 inwardly of the piston 58 whereby the smaller plunger 42 is withdrawn from the casting. The dies are then opened and the continued pressure of the duplex plunger upon the solidified gating biscuit forces the latter from the cover die 10. Thereafter the pressure in the cylinder 46 outwardly of the piston 48 is relieved and hydraulic pressure is applied inwardly of the piston 48 whereby the entire duplex plunger is withdrawn from the shot sleeve so as to expose the inlet 34 preparatory to another casting cycle. Withdrawal of the smaller plunger 42 prior to the withdrawal of the larger plunger 40 is essential to efficiently eject the casting.

It will be apparent that the process described has a number of important advantages. As described above, the molten metal is moved into the die cavity slowly and non-turbulently in the form of a substantially solid front so that atmospheric air in the die cavity is expelled through the die vents ahead of the rising front of molten metal thus minimizi-ng casting porosity due to air entrapment. The slow progressive filling of the die cavity operates to seal the die vents and the die parting line crevices at low pressure and thus hashing (liquid metal escaping from the die cavity through the parting line and vents) is minimized. Thus, the process is particularly advantageous in producing castings with dies which are somewhat deteriorated lat the parting lines. Further, the solid shell 124 is formed substantially at lower pressures and the shell functions to contain the molten metal within the shell when the high pressure is applied by the nal squeeze of the larger plunger and the smaller plunger thus reducing the necessary die clamping force by as much as 50%. Moreover, the high pressures applied by the smaller plunger causes the shell 124 to lie up snugly against the casting cavity to obtain improved casting dimensions. A very important aspect of the process is that the inner portions of the casting are subject to continued pressure until complete solidication has been substantially completed whereby shrinkage and porosity of the casting is minimized.

The process described may be advantageously practiced using the hydraulic and electrical apparatus shown in FIGURE 4. At the commencement of a casting cycle, the dies and 12 have been closed by actuation of the toggle mechanism 21 operated by the usual hydraulic means and the duplex plunger 38 has Ibeen moved outwardly so that the plunger exposes the shot sleeve opening 34. The shot sleeve is then charged with molten metal. At this time, t-he operator moves the switch 96 to the plunger forward position shown in FIGURE 4. In this position of the switch the contact 118 is open whereby the large plunger return 4solenoid 119 of the four-way double solenoid valve 82 is deenergized whereby the portion of the cylinder 46 inwardly of the piston 48 is open to the oil sump 66 through the hydraulic lines 83 and 81. The contact 102 thereof is closed to prepare the circuit of the solenoid 106 of the two-way valve 76. The contact 94 thereof is closed and is operative to energize the forward motion solenoid 98 of the four-way valve 82 to open the portion of the cylinder 46 outwardly of the piston 48 to hydraulic pressure from the gear pump 62 through the hydraulic line 78, the flow control valve 80, and the lines 77 and 84. The closure of the contact 94 also energizes the timer 99 to close the normally open contacts 101 and 103 by means of the coil 100 and as will be seen is necessary at a subsequent stage of the cycle to return the smaller plunger 42 from its forward position.

Actuation of the solenoid 98 causes hydraulic pressure to be admitted into the cylinder 46 through the lines 77 and 84 whereby the duplex plunger moves relatively slowly into the shot sleeve as a unit moving the molten metal Iahead of its non-turbulently and with a solid front. The flow of hydraulic fluid is controlled by the ow control valve to insure a solid till flow Velocity of about 50 lineal feet per second Or less. As the duplex plungers nears the end of its stroke, it closes the limit switch 104 by the action -of the cam 105 attached to the flange 52 acting on the switch arm 107. The actuation of the limit switch 104 energizes the solenoid 106 of the two-way valve 76 whereby the valve opens and additional hydraulic fluid with the aid of the accumulator 70 is m-oved into the cylinder 76 outwardly of the piston 48 through the lines 72, 79, and 84. This increases the speed of the duplex plunger at the very end -of its stroke and subjects the metal in the cavity to an increased filling velocity. Since the gating is now submerged, the solid front fill is not disturbed by this increased velocity and the resulting higher pressure.

When the pressure in the cylinder 46 outwardly of the piston 84 builds up to pre-set relatively higher pressure due to the die cavity having been lled and the molten metal therein having been compressed, the pressure switch 108, which is exposed to the pressure in the outward portion of the cylinder 46 through the Iline 85, is closed whereby the timer 110, including the coil 112 and the contact 113, is energized to close the contact 113. When the timer times out, which involves va time delay in the neighborhood of a fraction of a second, sucient to allow the solidification of the layer 124 and 126, the timer energizes the solenoid 114 of the four-way valve 88 through the timer 99 which as described above had been closed when the timer 99 was energized. As a consequence, the portion of the cylinder 54 outward of the piston 58 is subjected to hydraulic pressure through the pressure `reducing valve 90, the line 92, the valve 88 .and the line 86 and the smaller plunger 42 is caused to move forward and break through the solidied shell 124 as shown in FIGURE 3 to subject the molten material to continued pressure and to cause the shell to lie up snugly against the cavity walls and to compensate for metal shrinkage.

A short time before the dies 10 and 12 are to be opened, the timer 99 times out thereby de-energizing the solenoid 114 and energizing the solenoid 116 of the four-way valve 88. This causes the hydraulic pressure outwardly of the piston 58 to be relieved through the lines 92 and 87 and for hydraulic pressure to be applied inwardly of the piston 58 through the lines 86 and 89. As a result, the plunger 42 is caused to be withdrawn from the solidified casting biscuit and returned to its original position las shown in FIGURE 4. Thereafter, other mechanism is actuated (not shown) to open the dies and effect ejection of the casting by the action of the ejector pins 24 associated with the bar 22 and plunger 26 in a well-known manner. While the dies are being opened, however, continued pressure applied by the duplex plunger forces the casting biscuit 127 (FIGURE 3) from the cover die.

After the dies are .fully open, the operatormoves the switch 96 to a return position. As a consequence, the contact 94 is opened de-en-er-gizing the solenoid 98 and the timer 99. As a result, the hydraulic pressure outwardly of the large hydraulic piston 48 is relieved. The contact 102 is opened de-energizing the solenoid 106 and the contact 118 is closed energizing the return solenoid 119 whereby hyd-raulic pressu-re is applied inwardly of the piston 48 through the lines '78 and 83 to return the duplex piston to its original position. The return of the piston 48 to its original position causes `the limit switch 10d to open whereby the cycle is completed.

It will be understood that the control mechanism described above to illustr-ate the invention is a simplified version of control apparatus which may be used. However, it will be obvious to those skilled in the art that it is desirable to integrate the operation of the apparatus described with the control of the ope-ration of the entire die casting apparatus and to install additional control and safety features.

Although the invention has been described in terms of a specific embodiment, it will be understood that various modications may be made within the scope of the invention.

We claim:

1. The method of die casting comprising the steps of moving by means of a plunger a molten metal mass into the cavity of die casting dies through a substantially nonrestricted passa-ge at a velocity such that ya substantially solid front of the molten metal enters the die cavity, maintaining pressure on the molten metal by means of said plunger until substantially only a layer of the metal has solidified 4adjacent the said die cavity and passage walls to arrest the further application of pressure on the molten portions of the meal mass by said plunger, and then forcing a second plunger through said layer and into the molten interior portion of the metal mass to maintain pressure on the molten portions of the mass until it has solidified.

2. The method of die casting comprising the steps of moving a mass of molten metal into the cavity of die casting dies through a substantially non-restricted passage by means of a plunger comprising a larger plunger having a smaller plunger reciprocal therein at a velocity such that a substantially solid front of the molten metal enters the die cavity, maintaining pressure on the molten metal by means of said plunger until substantially only a layer of the metal has solidified adjacent the die cavity and said passage walls to arrest the further application of pressure on the molten portions of the metal mass, and then forcing said smaller plunger through said layer into the molten interior portion of the metal mass to maintain pressure on said interior molten portion until it has solidified.

3. The method of die casting comprising the steps of moving by means of a first hydraulic means operated plunger a molten metal mass into the cavity of die casting dies through a substantially non-resistricted passage by a velocity such that a substantially solid front of the molten metal enters the die cavity, maintaining pressure on the molten metal by means of said plunger until substantially `only a layer of the metal has solidified adjacent said die cavity and passage walls to arrest the further application of pressure on the molten portions of the metal mass by said plunger, and then forcing a second plunger operated by a second hydraulic means in response to the pressure build-up in said first hydraulic means due to the formation of said layer into the molten interior portions of the metal mass to maintain pressure on the molten portions of the mass until it has solidified.

4. The method of die casting comprising the steps of moving a mass of molten metal into the cavity of die casting dies through a substantially non-restricted passage by means of a plunger comprising a larger plunger having a smaller plunger reciprocal therein and .adapted to form a portion of the tip of the larger plunger when in a first position and to extend substantially beyond the tip of the larger plunger when in a second position at a velocity such that a substantially solid front of the molten metal enters the die cavity, maintaining pressure on the molten metal by means of said plunger until substantially only a layer of the metal has solidified adjacent the die cavity and said passage walls to arrest the further application of pressure on the molten portions of the metal mass, and then forcing said smaller plunger through said layer to said second position and into the molten interior portion of the metal mass to maintain pressure on said interior molten portion until it has solidified.

5. The method of die casting comprising the steps of moving by means of a plunger a molten metal mass into the die cavity of die Casting dies through a substantially non-restricted passage in the form of a substantially solid front, said molten metal filling the die cavity progressively and filling and freezing in the vents and parting line crevices at it fills the die cavity, then applying a relatively high pressure by means of said plunger substantially .at the time the die cavity is filled, maintaining said relatively high pressure on the molten metal by means of said plunger until a layer of molten metal has formed adjacent the passage walls to arrest the application of continued pressure on Ithe molten interior portions of the metal mass by said plunger, and then forcing a second plunger into the molten interior of said mass to maintain pressure on the molten portions of the mass and continued .feed of the die cavity until complete solidification has occurred.

6. The method of die casting comprising the steps of moving at a relatively low velocity by means of a plunger a molten metal mass into the die cavity of die .casting dies through a substantially non-restricted passage lin the form of a solid front, said molten metal `at said low velocity filling the die cavity progressively :and filling and freezing in the vents and parting line crevices as it fills the die cavity, then increasing the velocity of said plunger substantially at the time the die cavity is filled to subject the molten metal to a relatively high pressure, maintaining said relatively high pressure on the molten metal by mea-ns of said plunger until a layer of molten metal has formed adjacent the passage walls to arrest the further application of continued pressure on the outer portions of the molten mass by said plunger and then forcing a second plunger into the molten interior of said mass to maintain pressure on the molten portions of the mass and continued feed of the die -cavity until complete solidification has taken place.

7. The method of claim l wherein said second plunger is withdrawn from the casting before the dies are opened and pressure is maintained on the solidified casting by said plunger after Ithe dies are opened to force the portion of the casting within said passage therefrom as the dies are opened.

8. The method of claim 2 wherein the smaller plunger is withdrawn from the casting before the dies are opened and pressure is maintained on the solidied casting by said larger plunger after Ithe dies are opened to force the portions of the casting within said passage therefrom as the dies .are opened.

9. The method of die casting comprising the steps of moving a mass of molten metal into the die cavity of die casting dies through a substantially non-restricted passage by means of .a plunger comprising a `first larger plunger having a smaller plunger reciprocal therein ,and adapted to form a portion of the tip of the larger plunger when in a first position and to extend substantially beyond -the tip of the larger plunger when in a second position,

said molten metal filling the die cavity progressively and filling and freezing in the vents and parting line crevices as it fills the die cavity, then increasing the velocity of said larger plunger while said smaller plunger is in said first position to impose a relatively high pressure on the molten metal and to insure complete filling of the cavity substantially at the time the die cavity is filled, maintaining said relatively high pressure on the molten metal by means of said plungers until a layer of solidified metal has formed adjacent said passage walls to arrest the application of continued pressure on the molten metal portions of the metal mass, and then moving said .smaller plunger to said second position thereby forcing said smaller plunger into the molten interior of said mass to maintain continued pressure on the molten portions of the mass and continued feed of the die cavity until solidification 'has occurred.

10. The method of die casting comprising the steps of moving a mass of molten metal into a die cavity of die casting dies through substantially non-restricted pas-sage by means of a plunger comprising a first larger plunger -operated by hydraulic means having a smaller plunger operated by a second hydraulic means reciprocal therein and adapted to form a portion of the tip of the langer plunger when in a rst position and to extend substantially Ibeyond `the tip of the larger plunger when in a second position, said molten metal filling the die cavity progressively and flling and freezing in the vents and the parting line crevices as it llsthe die cavity, then increasing the velocity of said larger plunger While said smaller plunger is in said rst position Ito impose the relatively high pressure on the molten metal and to insure complete filling of the cavity substantially at the time the die cavity is -lled, maintaining said relatively high pressure on the molten metal by means of said plunger until a layer of molten metal has formed adjacent said passage walls to arrest the application of continued pressure on the molten metal portions of the metal mass, and then moving said smaller plunger in response to the pressure build-up in said rst hydraulic means due t0 the formation of said layer to said second position thereby forcing said smaller plunger by said second hydraulic means into the molten interior of said mass to maintain continued pressure on the molten portions of said mass and continued feed of the die cavity until solidication has occurred.

References Cited by the Examiner UNITED STATES PATENTS 2,581,550 1/1952 Misfeldt 18-30 FOREIGN PATENTS 126,544 1/ 1948 Australia.

J. SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0 D 3, 270,383 September 6, 1966 Harry D. Hall et al.

It :Ls hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 5l, for "planten" read platen column 6, line 16, for "plungers" read plunger line 3l, for "up to" read up to a column 7, line 28, for "meal" read metal line 5l, for "non-resistrcted" read nonrestrcted Column 8, line 13, for "at" read as Signed and sealed this 22nd day of August l96'7 (SEAL Atst:

ERNEST W. SWIDER EDWARD I. BRENNER Attest'mg Officer Commissioner of Patents

Claims

1. THE METHOD OF DIE CASTING COMPRISING THE STEPS OF MOVING THE MEANS OF A PLUNGER A MOLTEN METAL MASS INTO THE CAVITY OF DIE CASTING DIES THROUGH A SUBSTANTIALLY NONRESTRICTED PASSAGE AT A VELOCITY SUCH THAT A SUBSTANTIALLY SOLID FRONT OF THE MOLTEN METAL ENTERS THE DIE CAVITY, MAINTAINING PRESSURE ON THE MOLTEN METAL BY MEANS OF SAID PLUNGER UNTIL SUBSTANTIALLY ONLY A LAYER OF THE METAL HAS SOLIDIFIED ADJACENT THE SAID DIE CAVITY AND PASSAGE WALLS TO ARREST THE FURTHER APPLICATION OF PRESSURE ON THE MOLTEN PORTIONS OF THE METAL MASS BY SAID PLUNGER, AND