US3068539A - High pressure permanent molding - Google Patents

Description

Dec. 18,1962 R` E. wlLcoxoN HIGH PRESSURE PERMANENT MOLDIRG Filed Aug. 4, 1960 INVENToR. Qa/,oh E #Vf/casco ATTYS` Dlec. 18, 1962 n. :-:.w1|.coxoN 3,068,539

HIGH PRESSURE PERMANENT Momma IN VEN TOR.

,Qa/,olv E14/Wears ATTYS.

Dec. 18, 1962 Filed Aug. 4, 1960 R. E.WILCOXON HIGH PRESSURE PERMANENT MOLDING 4 Sheets-Sheet 5 ATTvs.

II'VVENTOR. PV//caxon Dec. 18, 1962 R. E. wxLcoxoN HIGH PRESSURE PERMANENT MOLDING 4 Sheets-Sheet 4 Filed Aug. 4, 1960 humm INVENToR. Qa/,o E.' M/f/coxon y ATTYS.

ite rates 3,663,539 HIGH PRESS E PERMANENT MOLDING Ralph E. Wiicoxon, Cleveland, hio, assigner to Thompson Ramo Wooldridge Ine., Cleveland Gillo, a corporation of Shin Filed Ang. d, 195i?, Ser. No. 46,695 12 Claims. (Cl. 22-93) This invention relates to the manufacturing of pistons and more particularly to improved methods and means for high pressure molding of internal combustion engine pistons from molen metal involving iiiling of a die cavity therewith, followed by the insertion of a plunger in the metal to form a core, and controlling of the flow of metal under pressure, thereby producing a piston requiring no inside inish.

In accordance with this invention, lightweight metals, such as aluminum and aluminum alloys, may be heated to above their melting points and poured into a split die mold. A sealing collar is then wedge iitted on a complementarily tapered rim of the split die mold. The collar and mold rim define therebetween a chamber for receiving the molten metal overilow from the die cavity lwhich communicates with the die cavity through a narrow, restricted passage for restricting metal iow and to hold the pressure in the die cavity.

The plunger type core has a snug sliding fit in the collar and, as the core is urged into the molten metal pool, the excess metal flows into the overow chamber.

The molten metal is poured into the die cavity in a quantity in excess of that required for molding of the piston. The stationary base of the die assembly includes an ejector housing which forms the base of the die cavity. When the molten metal has cooled suiiiciently, the movable core assembly is retracted, and a pneumatically or hydraulically operated piston assembly moves the ejector housing which pivots the split dies and pushes out the newly formed piston casting.

A feature of this invention resides in the provision of a spring-biased collar carried by the movable core platen which positively pre-seats on the rim of the split d-ie means securing the die means before the molding pressures are applied to the collar and die assembly by the core. A further feature of the present invention resides in passaging of the split dies in communication with the die cavity in a location where the wrist pin bores are to be formed in the casting being molded and the positioning of movable members in the die passages which, in a first retracted position, define sump or reservoirs for molten metal and which may be movable to an extended position into the die cavity thereby forcing the metal from the reservoirs into the die cavity -to compensate for volume loss due to cooling caused shrinkage. It has been my ex erience that metal injected from a reservoir to cornpensate for cooling caused shrinkage in the die cavity produces a weaker grain structure in the area where the metal is injected, apparently because of the dil-'ference in cooling rates and times of the metal initially solidifying in the die cavity and the metal subsequently injected. Additionally the grain crystalline growths of the metals are different which appears to cause a weaker interstitial bond between the aforementioned initial and injected metals. This phenomenon is visible to the naked eye as is hereinafter more fully explained.

By injecting the metal in the area from which the wrist pin bores are to be drilled or otherwise removed, I effectively eliminate substantially all of the weakly bonded injected metal from the formed piston. The above arrangement eliminates the heretofore required gates, riser formation, related molding components and, in addition,

n 3,068,539 EQ@ Patented Dec. 1s, 1962 reduces the metal setting time within a fraction of tha heretofore required in the prior art.

It is, therefore, a general object of the present invention to provide improved pistons.

Another object of the present invention is to provide a method of molding pistons under high pressure conditions.

A still further object of the present invention is to provide a method of making molded aluminum pistons.

A still further object of the present invention is to provide a method of manufacturing internal combustion engine type pistons by filling the die cavity of molding apparatus with molten metal followed by the insertion of a core into the metal in the cavity to form the interior of the piston and thereafter controlling the liow of metal under pressure.

It is yet another object of the present invention to provide high pressure molding apparatus for the manufacture of components of irregular contour.

A still further object of the present invention is to provide apparatus requiring a minimum number of parts for high pressure molding of molten metal.

Yet another object of the-present invention is to provide pistons molded under high pressure conditions requiring a minimum of nishing and of tine' grain and high structural strength.

A still further object of the present invention is to provide apparatus for high pressure molding of pistons'which is simple and compact in construction and eicient and high speed in operation.

These and other features, objects and advantages of the present invention will become more apparent upon a careful consideration of the following detailed description, when considered in conjunction with the accompanying drawing illustrating .a preferred embodiment of the present invention, wherein like reference characters and numerals refer to like or corresponding parts throughout the several views. i

On the drawings:

FIGURE l is a front elevational view of molding apparatus according to this invention.

FIGURE 2 is a fragmentary view in cross-section of the apparatus of FIGURE 1.

FIGURE 3 is a view taken along lines III-III of FIGURE l.

FIGURE 4 is a fragmentary view in cross-section illustrating the excess metal plungers in the retracted position.

FIGURE 5 is a fragmentary view in partial cross-section illustrating the excess metal plungers in extended position. l

FIGURE 6 is a fragmentary plan view of a formed piston illustrating the injection area of the weakened bond between the initial and compensating metal.

FIGURE 7 is a fragmentary view in cross-section of the plunger injected metal, and v FIGURE 8 is a view in cross-section of a piston formedy in accordance with the present invention.

As shown on the drawing: Briefly stated, apparatus for piston manufacture illustrated in FIGURE l may include a base support membery 11 carrying a die assembly base l2, having secured thereto an ejector assembly base I3 which has pivotally mounted thereto a pair of ejector actuator arms 13a and 13b which are adapted to be moved by contact with an ejector housing I4 operatively responsive to a pneumatic or hydraulic piston assembly 14a. Removably held by a plurality of restraining members 15 is a generally rectangularly shaped split die comprising die members 16 and die member 16', each of which is secured to the ejectorY arms 13a and 13b respectively, by llanges 15a and each .of which is pro-vided with `a raised annular ange or rim 16a.

A movable platen 18 seats a plurality of springs i9 in a sleeve .2b. Springs 19 urge a movable collar 21 from Contact with the sleeve 2t? and surround a movable collar support means 2in. Collar 21 has a peripheral harige complementary' to the rims 16a of the split dies for holding the dies securely together and'for cooperating with the die members to deiine an overflow chamber for receiving molten metal from the die cavity. Movably carried by the platen 1S is a die core assembly 17a dimensioned to the desired internat conguration of the piston to be formed.

The platen 18 is movably carried by a shaft 22 which is actuated by a pneumatic or hydraulic piston assembly 23 of conventional construction. A stationary platen 24 may support the piston assembly 23 and may serve as a support for a plurality of guide members 25 for the movable platen 18 and the core assembly 17a.

Referring particularly to FIGURE 2, wherein the core assembly 17a is shown in the retracted position, each of the ejector follower arms 13a and 13b is provided with a pivot 13e and 13d, respectively, each of which is journaled in a pair of raised bearing members 26 and 27 secured to the ejector assembly base 13, as by bolts 28 and 29 respectively. The ejector y'assembly base 13 is recessed as at 30 and 31 to permit a wider pivot arc for members 13a and 13b (FIGURE 2 and 3) during operation.

Centrally located within the base 13 is a bore, indicated by the numeral 32, which is provided with a tapered shoulder 32a and a counterbore 33 for receiving the ejector 14 and for providing a shoulder 34 for Vthe peripheral annular flange 3 5 of the ejector 14.

Similarly, each of the T shaped pivotable arms ma and 13b is inwardly tapered from the top surface thereof, as shown in FIGURE 2 to prevent binding vthereof with theejector 14 during the ejection operation.

As more clearly appears in FIGURE 3 the split die members 1 6 and 16 are rectangular in shape and when assembled define a die core receiving cavity. The split die members 16 and 16 are held in position by a plurality of bracket members carried by the actuator arms i3d and 13b and ythe die anges 15a secured thereto.

The core guides may, if desired, pass through the hase member 12 and be secured in the base member 11.

As appears in FIGURES 2 and 5, the ejector assembly may b e provided with means for cooling the split die members thereby reducing the time required to solidify the molten metal. For this purpose, the ejector 14 may be provided with an inlet conduit 37 for introducing the cooling medium into an internal passage 38 which communicates with an annular passage 39 in the upper portion of the ejector which provides the base for the split die means. The annular passage 39 in the ejector head 14h communicates with a similar internal outlet passage and port (not shown) for discharge of the coolant medium from the ejector.

The two die members 16 and 16' define therebetween the molten metal die well or cavity 48, and which, for purposesof the example hereof, is cylindrical in contiguration.

As aforementioned, the upper core portion as appears in FIGURE l includes a stationary platen 24 which may carry the core piston assembly 23 and may serve as support means for the guides 25 of the core carrying movable platen 13. Guides 25 may be secured at the lower end in the support member l2 and to the stationary platen 24 at the upper ends .in threaded engagement therewith as by nuts 47 and 48a.

As appears in FIGURE l, the movable platen 18 has secured thereto or formed integral therewith an upper boss 49 which is adapted to secure the piston rod 22 of the core piston assembly 23 to the platen 18. Secured as by bolts Si) to the under side of the movable platen 18 is the peripherally hanged sleeve 20.

Inwardly of the flange 51, the sleeve or ring 2@ is bored to receive the plurality of movable threaded members 21a adapted to retain and support the collar 21. Adjacent the collar 21, the ring Zit is provided with a plurality of annularly spaced bores 52 to receive the springs 19 which urge the collar from contact with the ring 20. Each of the springs 19 seats against the shoulder provided by the complementary counterbore 52a in the ring 2E? and is bottomed against the collar Zi. Each of the pin receiving bores are also counterbored, as indicated by the numeral '52!7, adjacent the movable platen 18 to permit movement of pins 21a and contact between the opposed faces S3 and 54 of the ring and collar during the molding operati-on, as clearly appears in FGURE 5, The heads 2lb of the pins 2id prevent unlimited movement of the pins.

The core head 17a is prevented from rotating by a key 59, as appears in FIGURE 7, and is removably secured to the ring 2t) as by bolts (not shown) inserted through slots 69 formed in the ring 20.

Centrally located in the core head 27a is a stepped passage defining a cooling medium inlet 62 communicating with a passage of smaller diameter 63 which is opened at the botom end to permit circulation of a cooling medium in the fluid passage 64 which comunicates with the uid outlet passage 65. The passage conduit 63 is supported by a plug 66 which prevents the uid ow from circulation passage 614 into inlet passage 62. Inlet passage 62 cornmunicates with an inlet 66a which may be adapted to receive the fluid inlet conduit 67 which passes through a bore 69 provided in the ring 2t). Similarly, outlet 65 is adapted 'to receive conduit 70 which passes through a similar bore 7i in the ring Zit. Thus a circulation system is provided for the core assembly 17a which cooperates with the circulation system provided in the ejector 14 to reduce the time required to set the molten metal being formed in the die cavity '48.

The collar 21 carried by the bolts 21a is provided with an annular channel 73 inwardly of the periphery thereof and has complementarily tapered surfaces for engagement with the rims 16a of the split die members 16 and i6', thereby locking the die members. Thus, the rim 16a and the groove '73 of the collar 21 cooperate, as appears in FIGURES 4 and 5, to define a chamber 75 which receives the overflow of molten metal from the die cavity 43 through an annular passage 76 of restricted height defined by the internal ange 77 of the collar 21 and the opposed top surface 7S of the split die members. The peripheral liange 79 of the collar 21 and the rim 16a of the dies i6 and 16 cooperate to prevent extrusion of molten metal across the parting line to the exterior of the apparatus.

The core, of course, is shaped to dene the inside diameter of the particular component to be molded in the apparatus above described, and, for purposes of illustration, is shown shaped to deiine the interior of an internal combustion engine piston.

Each of the split die members 16 and 16' has a passage 49 communicating with the interior of the die cavity adapted to -receive retractable and extendable plunger members 41 and L32, respectively, generally shaped preferably to the dimension of the wrist pins. The plunger members d and l452 are reciprocably responsive to conventional piston assemblies 43 and 44, respectively, which are mounted on a pair of brackets and i6 secured to the pivotable ejector actuator arms 13a and tb as by bolts 47a.

In operation, molten metal teta may be poured into the die cavity and the plunger arms #Si and E retracted to the position shown, thereby defining the sump or reservoir chambers it communicating with the die cavity.

The platen i8 is moved downwardly carrying with it the core 17a for insertion thereof in the molten metal in the die cavity 4% The spring-biased collar 21 seats on the rim 16a of the split die members and holds them securely together while cooperating therewith to define the overflow chamber communicating with the die cavity through the narrow annular passage 76 before articleforming pressure is applied by the core 17a in the die cavity.

A coolant is introduced through conduit 37 of the ejector assembly 14, and a coolant is also introduced into the core 17a through conduit 67 for circulation and discharge through conduit 70.

ln the second stage of operation, with the collar 21 urged downwardly by the springs 19 in engagement with the rim 16a before the plunger core 17a is fully positioned in the die cavity, the upper platen 18 continues in its downward movement against the fo-rces exerted by the springs 19 until contact is made between the opposed faces S3 of the ring 2G' and 54. of the collar 21, as appears in FlG- URE 4. The pins 21a will have been moved to their uppermost position in the -recesses 52a (FIGURE 4) when contact between the collar and ring 2d is made. Similarly, with the core 17a moving into the pool of molten metal 48a, the displaced metal will flow into the reservoirs 4t) and through the narrow restricted passage 76 into the overiiow chamber 75. As aforesaid, the ejector head 14a serves as a base or bottom for the die cavity.

The coolant circulation systems in both the core and ejector reduce the metal setting temperature within a range from about 350 P. to about 450 F., if water is the cooling medium.

After the metal has partially set, the plungers 41 and 42 are moved inwardly by activation of the piston assemblies 43 and 44 forcing the molten rnetal from the reservoirs 49 into the die cavity to compensate for the shrinkage of the molten metal which takes place as the metal solidies. Movement of the plungers 41 and 42 in compensating for metal loss in the die cavity due to shrinkage does not cause displacement of the metal through the narrow, restricted passage 76 leading to the overiiow chamber since the plungers are not moved until the metal in the restricted passage '76 has frozen or solidified before the plungers 41 and l2 are extended.

As an example of the material to be molded, a high silicon content aluminum alloy (MS 143) preferably formed of the following general composition was heated to a pouring temperature of approximately l220 F.:

impurities, such as the following may also be included in the alloy:

Percent iron l Zinc O 5 A preferred specific alloy forming the pistons in accordance with the practice of this invention include the elements of the general composition set forth above as well as the impurities.

Heretofore, it was necessary to permit a chill time from 2 to 10 minutes in order to permit setting of the molten metal before the formed piston was removed from the die cavity. By my method, the time required for setting is reduced to from about l0 to about 30 seconds, depending upon the alloy involved and other physical and metallurgical properties desired, since a colder die is used and since pressure forces are employed to control flow.

For the example above given, the core 17a was constructed of high temperature die steel material sold by the Crucible Steel Company under the trade name NU- DLE-V which is a hot-work, chromium-vanadium steel. The die members 16 and 16' of the above example were constructed of a low alloy sold by the Wheelock-Lovejoy Company under the trade name HY-TEN-B-3X which is a ferrous alloy of nickel and chromium.

In the third stage of the operation, the plungers 41 and Cil 42 may be extended into the die cavity to form the wrist pin bores, as appears in FIGURE 5.

Next, after an appropriate setting time, preferably within the range of from about 10 seconds to about'30 seconds, has elapsed, the piston assembly 23 is actuated to retract the core 17a from the die cavity. As the core is being initially withdrawn from the die cavity, the springs 19 maintain the collar 21 firmly seated on the die rim 16a thereby maintaining the split dies in the locked position until the bolts or pins 21a contact the bottom of the recesses 52a and carry the collar upwardly from contact with the rim 16a of die members 16 and 16. Thus, the die members are securely locked together before pressure is applied in the die cavity and remain locked by the collar until pressure is removed from the `die cavity.

The plunger piston assembly 43 and 44 are then actuated to retract the plungers 41 and 42 from the die mold cavity into the passages in the split die members. Circulation of the coolants in the ejector assembly and the core 17a is terminated and thereafter the ejector piston assembly 14a actuated to move the piston head 44h upwardly in contact with the ejector 14. The ejector head 14h will continue its upward movement whereby the ejector 14 is unseated and the ejector flange 35 engages the ejector actuator arms 13a and 13b and pivots the arms upwardly. The split die members 16 and 16 are therefore opened and the molded formed piston is now ready for removal from the apparatus.

The molded piston 85 is easily removed from the ejector 14.

The flash 85a of the molded piston is quite thin near the inner periphery thereof and may be easily removed. The end surfaces Sib of the sleeve portion of the piston is substantially uniformly fiat requiring a minimum of finishing in this area. No finishing is required on the inside ofthe piston, and the close tolerance permitted by the molding method described above facilitates external finishing of the piston. Thus sound pistons are obtained in less time, thereby increasing production rates, and, because of the reduced chill time required, a finer grain piston is obtained having greater structural strength than was heretofore considered obtainable Without additional treatment of the piston. In addition, grain refiners, such as titanium, boron, etc., are not required as alloy additives. Moreover, in the molding operation, closer tolerances may be obtained than were heretofore possible with the permanent die type apparatus which must be coated to prevent attack on the dies in the high temperature, slow cooling methods.

If desired, conventional toggle arrangements may be employed to maintain the core in the die cavity. For this purpose, the toggle cleats may be pivotally secured to the upper stationary platen Z4 and to the movable platen 13.

'As appears in FIGURE 6, the effects of different cooling and solidifying rates is readily apparent visually. The bores 87 in the formed piston from which the plunger was extracted is surrounded by a discolored area, the limits of which, for purposes of illustration, are indicated by the numeral 8S and the size of which depends upon such factors as plunger pressure and the amount of metal being forced into the die cavities to compensate for cooling caused shrinkage. The dotted line 89 indicates the outer limits of the area from which the wrist pin bore will be drilled, the size of which depends upon such factors as the ultimate use of the pisto-n.

FGURE 8 illustrates in cross-section the piston after the final finishing and wrist pin bore milling operation. Thus, it will be appreciated that, by positioning the plungers to force the shrinkage compensating metal into the die cavity in a location where the wrist pin bores are to be drilled, I provide an improved piston having the same structural strength and grain refinement throughout.

For the aluminum piston of the above example, the flash is merely broken olf, the piston then subjected to accesso ai heat treatment-for. atperiod of from about lhours at about 400 F. and theri airl quenched,y After this treatment, the piston was lready for the machining and milling operations.

Itwill, therefore, be appreciated that withithe high pressuremolding apparatus and methods of the present invention, I provide means for the elimination or" gates and riserformations, reduce the time required to set the molded piston, and obtain a pistonV of higher quality than was heretofore obtained without the necessity of addi'- tional alloy elements or fabricating steps and treatments.

Although minor modifications might be suggested by those skilled in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon, all such embodiments as reasonably and properly come within the scope of my contribution to the art.

I claim as my invention:

l. Apparatus for high pressure permanent molding of articles from molten metal comprising: die means defining alcore-receiving die cavity; a movable die core-carrying platen; means normally biasing a separate collar movably carried by said 'platen from contact therewith, said biased collar being vadapted to contact saiddie means and remain in contact therewith when said core is being inserted cr retracted from said cavity for' applying molding presssure on molten metal in Vsaid cavity; said contacting collar and said die means cooperating to define therebetween a molten metal overflow chamber communicating with said die cavity through a narrow, restricted'passage; said platen being movable to a second position in pressure contact with said' collar to insert the core in the die cavity for applying article-forming molding pressure on molten metal therein whereby excess metal flows` from said cavity into said overow chamber; at least one compensating passage communicating with said die cavity and formed in a side of said die means, means for forcing molten metal into said die cavity through said passage formed in said die means to compensate for metal volume loss dueto cooling caused shrinkage; and ejectormeans forgu'nsea'ting a formed article in said cavity.

2 Apparatus for high pressure permanent molding of' articles from molten metal comprising: split die means defining a core-receiving die cavity; a movable die core carrying platen; means normally biasing a separate collar movably carried by said platen from contact therewith,

said biased collar being adapted to lock said die vmeansV and remain in locking contact therewith when said core is being inserted or retracted from said cavity, said collar and said die means when in contact cooperating to deline therebetween a molten metal oven-liow chamber communicating with said die cavity through aV narrow restricted passage, said platen being movable to a second position in pressure contact with said collar to insert the core in the die cavity for applying article-forming molding pressure on molten metal therein whereby excess metal ows from said cavity into said ove'row chamber; at least one compensating passage communicating with said die cavity and formed in a side of said die means, means for forcing molten metal through said passage in said die means into said die cavity to thereby compensate for metal volume loss due to cooling caused shrinkage; and ejector means for parting said split die means and for unseating a formed article in said cavity.

3. Apparatus for high pressure permanent molding of articles from molten metal comprising: a stationary base member; split die means on said base member defining a core-receiving die cavity therebetween; a'movable die core-carrying platen disposed to position a die core in said cavity; a separate collar movably carried by said platen normally biased from contact` with said platen, said biased collar being adapted to Contact with split die means when said platen is in a first position before said core is fully inserted or retracted from said die cavity for applying molding pressure therein, said collar and said split die means cooperating to define a metal 8 overiiow chamber communicating-with said die cavity through a narrow, restricted passage therebetween; 'said platen being adapted to move to asecond position against the force ofthe collar biasing means to thereby contact said collar and position said core in said die cavity for applying article-forming molding pressure on molten metal therein whereby excess metal flows into said overr flow chamber through said restricted passage; at least one:

compensating passage communicating with said die cavity and formed in a side of said die means, piston actuatedl plunger means for forcing molten metal from said pas 7 sage in saiddie means into said die cavity to thereby' compensate for metal volume loss due to shrinkage; anl

ejector assembly for separating said split die means and for unseating a formed article in said die cavity, and.

said ejector assembly forming the base of said die cavity.`

4. Apparatus for high pressure permanent molding of articles from molten metal comprising: a stationary base member; split die means carried by said base member defining a core-receiving die cavity therebetween; a mov-v able die core-carrying platen disposed to position a die core in said cavity; a separate collar movably carried by said platen normally biased from contact with said platen, said biased collar being adapted to contact and lock said split die means defining said die cavity when said platen Ais moved to a rst position before said core is fully inserted in or retracted from said die cavity for applying article-molding pressure on molten metal therein, said collar and said split die means cooperating to define a metal overliow'chamber communicating with', said die cavity through a narrow, restricted passage'therebetween, said platen being adapted to move to a second position against the collar biasing means to thereby contact said collar and position said core kin said die cavity forapplying article-forming molding pressure on molten metal therein whereby excess metal flows into said overflow chamber through said'restricted passage; a pair of compensating passages formed in the side of said die means andi communicating with said die cavity, each of said passages'being adapted to receive a piston actuated plunger for forcing molten metal from the passage into said die cavity to thereby compensate for metal volume loss due to shrinkage; and a die cavity base-defining ejector assembly for unseating a formed article in the die cavity.

5. Ap''pai-"attrsV for aV high pressure permanent molding of articles from molten metal comprising: spit die means defining a core-receiving die cavity; a reciprocal platen carrying a die core; spring means normally biasing a separate collar movably carried by said platen from contact therewith, said collar being adapted to lock said die means and remain in locking contact therewith when said core is being inserted or retracted from said cavity for applying molding pressure on molten metal in said cavity, said contacting collar and said die means cooperating'to deline therebetween a molten metal overflow chamber communicating with said die cavity through a narrow, restricted passage, said platen being movable to a second position in pressure contact with said collar to position the core in the die cavity for applying articleforming molding pressure on molten metal therein wherebyexcess metal is displaced from said die cavity into said overflow chamber; a pair of compensating passages formed in the sides of said spit die means and in communication with said die cavity for receiving metal displaced when said core is inserted in the die cavity, and means for forcing displaced metal from said passages into said die cavity to compensate for cooling caused shrinkage; ejector means for opening said split die means and for unseating a formed article in said cavity including a housing deiining die cavity base and a pair ot' pivotable members supporting said housing operatively responsive to movement of said housing to separate said split die means; and means for moving said ejector assembly to pivot said ejector assembly arms and to separate said split die means when said core is retracted from said cavity; means fer cooling said cavity.

6. Apparatus for high pressure permanent molding of piston assemblies from molten metal comprising: die means defining a core-receiving die cavity; reciprocable die core carrying means; a separate collar movably carried by said core carrying means normally biased from contact therewith, said biased collar being adapted t contact said die means and remain in contact therewith when said core is being inserted or retracted from said cavity and to cooperate with said die means to deiine therebetween a molten metal overow chamber communicating with said die cavity through a narrow, restricted passage; said core carrying means being reciprocably movable to a second position in pressure contact with` said collar to insert the core in the die cavity for applying piston-forming pressure to molten metal therein whereby excess metal flows from said cavity into said overflow chamber; at least one compensating passage communicating with said die cavity and formed in a side of said die means at the Wrist pin aXis of said piston assembly, and means for forcing molten metal, displaced from said die cavity by said core into said compensation from said compensating passage into said cavity to compensate for metal volume loss due to cooling-caused shrinkage; and ejector means for unseating a formed piston in said cavity.

7. Apparatus for high pressure permanent molding of articles from molten metal comprising: split die means dening a die cavity and having a pair of compensating passages formed in the sides thereof for receiving metal displaced from said die cavity by a core inserted in the die cavity for applying article-forming pressure to molten metal therein, and means including a movable member in each passage adapted to force said displaced molten metal from said passage into said die cavity to compensate for metal volume loss due to cooling-caused shrinkage in the die cavity.

8. Apparatus for high pressure permanent molding of articles from molten metal comprising: a die cavity defined by a pair of split die members, said die cavity being adapted to receive a core, a compensating passage formed in the side of each of said split die members for receiving metal displaced from said die cavity by said core when inserted into said cavity for applying article- `forming pressure on molten metal therein, and means including a movable member in each of said passages for forcing said displaced molten metal fromI the passage into the die cavity to compensate for metal volume loss due to cooling-caused shrinkage.

9. Apparatus adapted for high pressure permanent molding of articles comprising: die means defining a pressurizable die cavity for receiving a core adapted to apply article-forming pressure on molten metal in said die cavity, at least one passage formed in a side wall of the die means and directly communicating with the die cavity for receiving molten metal from said die cavity displaced by said core, and a movable member disposed in said passage for forcing said displaced molten metal into the die cavity to compensate for metal volume lost due t0 cooling-caused shrinkage in the die cavity.

l0. Apparatus adapted for high pressure permanent molding comprising: split die means defining a pressurizable die cavity, at lesat one passage formed in a side wall of the die means and in direct communication with the die cavity for receiving molten metal displaced by a core inserted in the cavity for applying articleforming pressure on molten metal therein, and a movable member disposed in the passage for forcing said displaced molten metal from the passage into the die cavity to compensate for metal volume loss due to cooling-caused shrinkage.

l1. Apparatus for high pressure permanent molding of articles comprising: split die means defining a pressurizable die cavity, a plurality of passages formed in a side of each split die means and in direct communication with the die cavity for receiving molten metal displaced by a core inserted in the pressurizable die cavity for applying article-forming pressure to molten metal in the die cavity, and a movable member disposed in each passage for forcing displaced molten metal from the passage into tne die cavity to compensate for metal volume loss due to cooling-caused shrinkage.

12. Apparatus for high pressure molding comprising: split die means defining a pressurizable die cavity, a pair of diametrically opposed passages formed in a side of the die means and in direct communication with the die cavity for receiving molten metal displaced from the die cavity by a core inserted therein for applying articleforming pressure to molten metal in the cavity, and a movable member disposed in each passage for forcing said displaced molten metal into the die cavity to thereby compensate for metal volume loss due to cooling-caused shrinkage.

References Cited in the file of this patent UNITED STATES PATENTS 1,961,942 Pack June 5, 1934 1,997,074 Novotny Apr. 9, 1935 2,253,822 Sundback Aug. 26, 1941 2,415,395 Ulrich Feb. 4, 1947 2,582,260 Kutik Jan. 15, 1952 2,804,666 Saives Sept. 3, 1957

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