CA1190024A - Method and apparatus for squeeze casting pistons with wear resistant inserts - Google Patents
Method and apparatus for squeeze casting pistons with wear resistant insertsInfo
- Publication number
- CA1190024A CA1190024A CA000393999A CA393999A CA1190024A CA 1190024 A CA1190024 A CA 1190024A CA 000393999 A CA000393999 A CA 000393999A CA 393999 A CA393999 A CA 393999A CA 1190024 A CA1190024 A CA 1190024A
- Authority
- CA
- Canada
- Prior art keywords
- die cavity
- ring
- alloy
- wear resistant
- lightweight
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D19/00—Casting in, on, or around objects which form part of the product
- B22D19/0009—Cylinders, pistons
- B22D19/0027—Cylinders, pistons pistons
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
Abstract
Abstract of the Disclosure The pistons are cast in a die cavity which is shaped in conformity to the exterior surface of the pistons. An annular ring of wear resistant austenitic iron material is dipped in molten aluminum to preheat and coat it. The annular ring is disposed in the die cavity. A predetermined amount of molten aluminum alloy is poured into the die cavity over the ring. The die cavity is closed by a punch which applies a force to the aluminum alloy as it solidifies. The pressure of the punch presses the aluminum alloy into firm and continuous contact with the ring and the inner surface of the die cavity. The pouring is facilitated by a pouring disc placed in the top of the die cavity to distribute the molten alloy.
The pouring disc has a central portion with a plurality of apertures arranged around its periphery.
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The pouring disc has a central portion with a plurality of apertures arranged around its periphery.
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Description
~900zg BACKGROUND OF THE INVENTION
This invention relates to the art of castin~ composite articlesO It is particularly appllcable to castLng improved lightweight pistons and will be described ~ith plrticular referencQ
thereto. It will be appreciated, however9 that the ln~ention also finds application in casting other composite articles, partlcularly those which include wear resistant lnserts.
Aluminum alloys and othe]r lightweight materials are advantageously used in the manufacture of plstons. One method of casting aluminum and other alLoys is known as squeeze castingO In squeeze casting1 a female die cavity is fashioned i~ the shape to be castO The die is open at the top to allow a molten alloy to be poured into the dle cavity. The die is closed by a top punch ~hich is inserted into the upper opening of the die cavity. The punch ex-.
erts a pressure on the molten metal which continuously forces thealloy against the walls of the dle cavity as it solidifies. The top punrh enters the die cavity further with shrlnkage. An article cast by the squee~e casting technique has good conformity to the die cav-ity surface, has a fine microstructure, and rela~i~ely little or no porosity.
Aluminum and many other light~eight alloys tend to wear quickly~ This lack of wear resls~ance makes aluminum and other lightweight alloy pistons undesirable for heavy-duty engines such as are found in large trucks, large far~ vehicles, and off the highway equipment. To improve the wear resistance of aluminum and other lightweight pistons, it has been suggested that a ring of wear re-sisted material be inserted around the plston. Examples of such composite plston structures are illustrated in U~S. Patent No.
4,008,051, issued February 15, 1977 to T. M~ Cadle~ U.S. Patent No.
3,533,329, issued October 13, 1970 to E. Galli, U.S. Patent No.
This invention relates to the art of castin~ composite articlesO It is particularly appllcable to castLng improved lightweight pistons and will be described ~ith plrticular referencQ
thereto. It will be appreciated, however9 that the ln~ention also finds application in casting other composite articles, partlcularly those which include wear resistant lnserts.
Aluminum alloys and othe]r lightweight materials are advantageously used in the manufacture of plstons. One method of casting aluminum and other alLoys is known as squeeze castingO In squeeze casting1 a female die cavity is fashioned i~ the shape to be castO The die is open at the top to allow a molten alloy to be poured into the dle cavity. The die is closed by a top punch ~hich is inserted into the upper opening of the die cavity. The punch ex-.
erts a pressure on the molten metal which continuously forces thealloy against the walls of the dle cavity as it solidifies. The top punrh enters the die cavity further with shrlnkage. An article cast by the squee~e casting technique has good conformity to the die cav-ity surface, has a fine microstructure, and rela~i~ely little or no porosity.
Aluminum and many other light~eight alloys tend to wear quickly~ This lack of wear resls~ance makes aluminum and other lightweight alloy pistons undesirable for heavy-duty engines such as are found in large trucks, large far~ vehicles, and off the highway equipment. To improve the wear resistance of aluminum and other lightweight pistons, it has been suggested that a ring of wear re-sisted material be inserted around the plston. Examples of such composite plston structures are illustrated in U~S. Patent No.
4,008,051, issued February 15, 1977 to T. M~ Cadle~ U.S. Patent No.
3,533,329, issued October 13, 1970 to E. Galli, U.S. Patent No.
2,956,8469 issued October 18, 1960 to W. E. McCullough, and U.SO
Patent No. 2,550,879, issued May 1, 1951 to C. E~ Stevens, Jr~
These composite pistons are cast in a permanent mold which has runners, ga~es, or risers for introducing molten metal in~o the mold . '?V~
cavity at the proper places and rates. To allow for shrinkage, as much as 40~ extra alloy is poured lnto the mold, runners, gates, and risersO When the ~etal solidlfies~ the two or more parts of the permanent mold are opened and the plston is removed. Varlous machining steps are needed to cut off the excess metal, ad~ust the plston dimenslons for shrinkage, and prepare it for preclae flnish machining. The piston tends to be weakened by porosity and a coarse microstr~cture, both of which are attributable to shrinkage from the die walls durlng solidificatlomO
The wear resistant insert ring, commonly an iron alloy, and the aluminum piston body ha~e diffe~ent physical properties. For e~-ample, the iron alloy's speciflc gravity is generally 2 to 3 tlmes that of the aluminum alloy9 the iron alloy~s thermal expanæion coefficient is generally 1 to 1 1/2 times that of the aluminu~
alloyD the iron alloy's thermal conductivity is generally less than half that of the aluminum alloy. These different physical pro perties cause residual stresses in the composite pisto~s.
To resist these stresses, it is essential that a strong bond be formed between the wear resistant ring and the aluminum alloy. In it9 normal life cycle, a composite piston is sub~ect to the shocks and vibrations of innumerable firing cycles as well as numerous heating and cooling cycles from starting and stopping the engine.
~en a minute crack or bonding failure between the wear resistant ring and the aluminum alloy can propagate quickly under these adverse conditlons. The propagation of cracks is accelerated by the formation of a brittle aluminum-iron intermetallic compound or the formation of o~ides at the interface. The propagation of cracks can cause pieces of pistons to break loose resulting in catastrophic en-gine damage.
Although composite articles ha~e been squeeze cast or molded ~n the past9 note U.S. Patent No. 3>792~726, issued February 19, 1974 to Sakai et al., U.S. Patent No. 2,157,453, issued May 9, 1939 t~
Jaeger, V.S. Patent No. 1,950,356, issued March 6, 1934 to DeBats~
and Japanese Patent 9557, issued July 4, 1961 to Iwamura et al.
~Chemical ~bstracts 14862(h), 1962)~ squee7e casting of pistons has not, heretofore, been successful. This may be attributable to the difficulty in achieving adequate bonding, particularly to the lower side of the wear resistant ring. This may also be attributable to the additional internal stresses from flexing of the wear resistant ring under the forces from the top punch.
One of the principal problems in composite piston casting techniques is achieving a strong, fracture resistant bond between the wear resistant ring and the aluminum or other lightweight alloy.
Yet another problem with casting composite pistons has been the number of machining steps and other labor processes required to finish the cast product.
The present invention contemplates a new and improved method and apparatus for casting composite articles, particularly pistons9 which overcomes the above-referenced problems and others. Yet it provides a composite piston in which the unlike metal alloys are strongly bonded, which is crack and fatigue resistant, and which is finished with fewer machining steps.
t The invention relates to a method of casting a lightweight f 20 piston with a wear resistant insert.
In accordance with one aspect of the invention there is provided a method of casting a lightweight piston with a wear resistant insert comprising: preheating a ring of wear resistant material; causing the preheated ring to be disposed in a die ~` cavity; pouring a predetermined amount of` a molten lightweight alloy into the die cavity through a plurality of paths which are disposed adjacent the outer die surface; closing the mold cavity with a punch which is recieved in the die cavity; and applying a force with the punch which tends to compress the lightweight alloy in the die cavity, wherein the lightweight alloy is pressed in continuing contact with the ring and the die cavity as the alloy solidifies.
In this manner the lightweight alloy is pressed into firm and continuous contact with the ring and the die cavity even as the alloy shri.nks during solidification.
In accordance with another aspect of the present invention, there is provided a mold assembly for casting a lightweight piston which has a wear resi.stant insert.
In particular there is provided a mold assembly for casting a lightwei.ght piston with a wear resistant insert comprising: a female di.e having a die cavity with a sub-stantially cylindrical outer die surface; support means forsupporting the wear resistant insert, the supporting means being a ledge extending around the outer die surface and being connected with the cylindrical outer die surface; a movable pouring disc which is selectively disposed in an upper portion of the die cavity, the pouring disc having a plurality of passages arranged circumferentially around its perimeter and disposed generally above said ledge, whereby molten metal which is poured on the pouring disc flows through the passages and into the die cavity adjacent its 2~ outer die surface flows over the wear resistant insert which is supported on the ledge; and a punch which is mounted for selectively entering the upper portion of the die cavity after removal of the pouring disc.
- 3a -A principal advantage of the present invention is that it produces a cornposite piston of a lightweight alloy with a wear resistant insert in which the bond between the lightweight alloy and the insert is strong and durable.
Another advantage of the present invention is that it rninimizes machining steps, labor, and manufacturing time by casting a composite piston which is in close conformity to the shape of the final piston product.
The invention may take physical form in certain parts and arrangements of parts~ a preferred embodiment of which is illustrated in the accompanying drawings. The drawings are only for purposes of illustrating the preferred embodiments of the invention and are not to be construed as limiting it.
Figure 1 is a cross-sectional view of a die cavity in which a wear resistant insert ring and a pouring disc are disposed in accordance with the present invention;
Figure 2 is a cross-sectional illustration of the die cavity of Figure 1 during the pouring of a molten lightweight alloy into the die cavity;
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~ oo;~
Figure 3 is a cross-sectional illustration of the die cavity of Eigu;es 1 and 2 after pourlng in which ~n upper opening of the die cavity is closed by a top punch for exerting pressure on the solidifylng alloy;
Plgure 4 is a cross~sectional illustration of the die cav~ty of ~igures 1-3 after the lightweight alloy has solldified;
Figure 5 is a top plan view of the wear res:Lstant insert rlng illustrated in Figures 1-4;
Figure 6 is a cross~sectional view through se~tion line 6-6 of Figure 5, Figure 7 is a top plan view of the pouring disc illustrated ln ~igures 1 and 2; and Flgure 8 is a perspective view in partial section of a com posite piston manufactured in accordance with the present lnven~
tion~
DESCRIPTION 0~ THE PR~FERRED EMBODIMENTS
A mold assembly is illustrated in Figures 1-4 for castlng com-posite pistons of a lightwelght alloy wlth a wear reslstant insert as illustrated in Figure 8. The mold assembly includes a two-piece femala die 10 which has a die cavity 12. The die cavity is shaped ~n conformity to the piston or other structure to be cast~ The die cavity 12 includes an outer die surface 14 whlch is configured ~o conform to the exterior of the pistonO The outer die surface 14 ~s smooth and polished to minimize machining steps to finish the cast piston. The outer die surface 14 extends peripherally around the die cavlty along a circular path. In the center of the die cavity 12, a core 16 is disposed for defining a hollow interior to the piston. Toward the top of the die cavity is a supporting ~eans 18 for supporting a wear reslstant insert 20. In the preferred ~m-bodi~ent, the supporting means 18 is a peripheral ledge or land which extends around the outer die su;face 140 Above the peripheral ledge or supporting ~eans 18, the outer die surface 14 has an en-larged upper portion 22. This enables the insert 20 to be placed into the upper portion ~2 of the die cavity 12 through an upper horizontal openlng 24. The upper portlon 22 has a cross section :
~1900~g whlch conformg the periphery of the insert 20.
The insert 20 comprises an annular rlng 30 which is shown in greater detail in Flgure 5. ~he annular ring 30 ls fashioned of a wear resistant materlal that has e~panslon and contractlon pro-pertles which are similar to the expanslon and contrac~ion pro-perties of the lightweight alloy from which the piston is to be cast. In the preferred embodiment, the wear resistant material is an austenitic alloy of iron, nickel, chromiuml and copper, par-tLcularly advantageous i9 the alloy sold by Thomas Foundries, Inc.
of Birmingham9 Alabama under the trademark NI-RESIST . The annular ring has a peripheral edge 32 whlcll conforms with the exterior dia-meter of ~he piston to be castO In the preferred embodiment, the diameter of the peripheral edge 32 is slightly larger than the Pinished piston to allow the exterior surface to be machined to close tolerances. Extending outward from the peripheral edge 32 1 at least one pro~ection. In the preferred embodiment, the a~ leas~
one projection is a plurality of tabs 34 whicll are dimensioned to be received snugly within the upper portion 22 of the die cav:lty and rest on supporting means 18. The diameter of the periphera1 edge 32 of the annular ring is dimensioned to be substantially the same or slightly smaller than the diameter of the outer die surface 14. As illustrated ln Figure 6~ each of the tabs 34 is sufficien~ly thin that it is frangible under the pressures norntally associated with squeeze casting. Alternatively) the at least one projection may be a continuous frangible flange whlch extends peripherally along the perlpheral edge 32. As yet another alternative9 the tabs 34 may be substantially the same thickness as the annular rt~g 30.
To cast a composite piston~ the wear resistant annular ring 30 is cleaned, preheated, and coated with a thln coating 40 of ductile metal. The thlckness of the coating 40 is exaggerated in Flgures 1 and 8 for eas~ of illustration. The coatlng of ductile metal form~
a stress absorbing buffer betwèen the annular ring 30 and the lightweight alloy. In the preferred embodiment~ the annular ring immersed Ln a bath of pure aluminum or aluminuDt alloy which ls heated to within 200 F. of the temperature at which the lightweight ., .
~ æ~
~lloy is to be cast. The duration whlch the annular ring 30 isimmersed in the aluminum i8 kep~ to a mlni~um to miniml~e the formation of brittl~ aluminum-lron lntermetalltc compounds~ After the annular ring 30 is preheated and coated with the ductile metal, it is plaeed on supporting mean~ 18 in ~he die cavityO
A pouring disc 50 is placed ln the upper opening of the cavity.
The pouring disc 50 is a means for distributing the melted lightweight alloy into the die cavity during pouring. Particularly~
it distributes the poured melted alloy such that it flow~ evenly over the insert 20. This inhibits the formation of oxides at the interface and aæsists in retaining the insert near the temperature of the ~olten alloy during the pouring operation.
With cont~nued reference to Flgure 1 and further reference to Figure 7, the pouring disc 50 ls dimensioned to be received in the upper portion 22 of the die cavity. The pouring disc has a central portion 52 which in con~unction with part of the upper portion 22 of the die cavity forms a temporary reservoir for receiving and holding the molten llghtweight alloy. The depth of the temporary reservoir determines the pressure head of the molten alloy hence the flow rate into the d~e cavity.
Arranged peripherally around the pouring disc 50 are a plurality of passages for channeling the molten alloy into the mold cavity around its periphery. In the preferred embodiment, th2 plurality of passages is formed by a plurality of circular apertures 54 arranged around the perimeter of the pouring disc.
Alternatively9 the passages may include a plurallty of radial slots around the periphery, a screen or mesh around the periphery, an annular gap between the disc and the die cavity, or the like.
Connected with the pouring disc 50 are a plurality of means 56 for supporting and centerlng its central portion 52 in the upper portion of the die cavityO Projecting upward from the central portion 52 of the pouring disc is a chimney 58 for allowing air within the die cavity to escape as molten lightweight alloy is poured in without aerating or agitating the mol~en alloyO The chimney 58 i9 a tubular pro~ec~ion of sufficient length to extend .
.~, above tlle molten alloy in the ~emporary reservolr.
Wi~h particular refere~ce to Figure 2, before the preheate~
lnsert 20 cools, a predetermined amount of molten llghtwe:Lght alloy, denoted by reference nu~eral 607 iS poured from a furnace or cruc-ible 62 GntO the pouring disc 50. From the temporary reservolr, the ~olten alloy passes through the apertures 54 around the perimeter of the pouring dlsc and impinges upon the insert 20. The molten alloy flows over and around the insert lnto the lower portion3 of the dle cavity. ~en the predetermlned amount of molten alloy has been introduced into the dle cavity, the pouring disc 50 is removed. The flow of the molten alloy partially dissolves the thin aluminum coat-:Lng 40 making it even thinner.
With particular reference to Figure 3, the upper opening of the die ca~ity is closed by a top punch 70 preferably wlth an annular pro~ection 72 for forming a combustion bowl in the top of the pl~ton. The top punch 70 is dimensioned to conform with the cross section of the upper por~lon 22 of the die cavity within very close tolerances to prohibit the ~olten alloy from passing between the punch and the outer die surfaceO Top punch 70 is caused by a hydraulic cylinder ~not shown) to exert several tons of pressure on the lightweight alloy in the die cavity. As the molten alloy solidifies, it contracts. The top punch continues to press the alloy firmly and continuously agalnst the surfaces of the die cav~
ity, tha punch, and the insert as the lightweight alloy solidifi~sO
The contraction of the lightweight alloy during solidif~cation allows the top punch 70 to advance into the die cav~ty by a cor-responding amount. It has been found that the pressure from the top punch tends to deflect the annular ring which causes interual stresses after solidificatlonO This deElection is alleviated with the annular ring construction of Figures 5 and 6 because the tabs 34 space the peripheral edge 32 of the ring a sufflcient distance from the outer die surface 14 that the lightweight alloy flows between the ring and the die surface.
With particular reference to Flgure 4, the deflection is fur~her reduced by the fracture of the frangible ~abs 34 . .
Under the pressure exerted by the top punch 70, the tabs 34 breakallowin~ the ann~llar ring 30 to shift downward in the die cavlty wlth the contraction during solidification.
After the lightweight alloy Eolidifies, the top punch i8 withdrawn, the die cavlty opened, and the composite piston removed.
The composlte piston is finished by a machining operation. Because the exterior surface conforms very cloæely to the outer surface of the punch and the die, very little machining is required. The top surface of the piston conforms to the surface of the punch with suf-ficlent accuracy that, as a rule, no further machining ~8 required to finish the top surfaceO The exterior surface of the piston i8 ~achined to remove the severed tabs 34 and the excess material from the increased diameter of the upper portion 22 of the die cavity.
The machining may further be used to give tlle piston a circular cross section with very precise dimensional tolerances. With re-ference to ~igure 8, the machining operation further includes cut-ting a plurality of grooves into the piston to receive piston rings~
A top piston ring groove 82 is machined in the annular ring 30.
Additional piston ring grooves 84 and 86 are also machined in the piston 80. A wrist pin 88 connects the piston 80 with a rod 900 The invention has been described with reference to the pre-ferred embodiment. Obviously, modifications and alterations will occur to others upon readin8 and understanding this specification.
It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
- .
:
. ' _g_ : ,, ..
Patent No. 2,550,879, issued May 1, 1951 to C. E~ Stevens, Jr~
These composite pistons are cast in a permanent mold which has runners, ga~es, or risers for introducing molten metal in~o the mold . '?V~
cavity at the proper places and rates. To allow for shrinkage, as much as 40~ extra alloy is poured lnto the mold, runners, gates, and risersO When the ~etal solidlfies~ the two or more parts of the permanent mold are opened and the plston is removed. Varlous machining steps are needed to cut off the excess metal, ad~ust the plston dimenslons for shrinkage, and prepare it for preclae flnish machining. The piston tends to be weakened by porosity and a coarse microstr~cture, both of which are attributable to shrinkage from the die walls durlng solidificatlomO
The wear resistant insert ring, commonly an iron alloy, and the aluminum piston body ha~e diffe~ent physical properties. For e~-ample, the iron alloy's speciflc gravity is generally 2 to 3 tlmes that of the aluminum alloy9 the iron alloy~s thermal expanæion coefficient is generally 1 to 1 1/2 times that of the aluminu~
alloyD the iron alloy's thermal conductivity is generally less than half that of the aluminum alloy. These different physical pro perties cause residual stresses in the composite pisto~s.
To resist these stresses, it is essential that a strong bond be formed between the wear resistant ring and the aluminum alloy. In it9 normal life cycle, a composite piston is sub~ect to the shocks and vibrations of innumerable firing cycles as well as numerous heating and cooling cycles from starting and stopping the engine.
~en a minute crack or bonding failure between the wear resistant ring and the aluminum alloy can propagate quickly under these adverse conditlons. The propagation of cracks is accelerated by the formation of a brittle aluminum-iron intermetallic compound or the formation of o~ides at the interface. The propagation of cracks can cause pieces of pistons to break loose resulting in catastrophic en-gine damage.
Although composite articles ha~e been squeeze cast or molded ~n the past9 note U.S. Patent No. 3>792~726, issued February 19, 1974 to Sakai et al., U.S. Patent No. 2,157,453, issued May 9, 1939 t~
Jaeger, V.S. Patent No. 1,950,356, issued March 6, 1934 to DeBats~
and Japanese Patent 9557, issued July 4, 1961 to Iwamura et al.
~Chemical ~bstracts 14862(h), 1962)~ squee7e casting of pistons has not, heretofore, been successful. This may be attributable to the difficulty in achieving adequate bonding, particularly to the lower side of the wear resistant ring. This may also be attributable to the additional internal stresses from flexing of the wear resistant ring under the forces from the top punch.
One of the principal problems in composite piston casting techniques is achieving a strong, fracture resistant bond between the wear resistant ring and the aluminum or other lightweight alloy.
Yet another problem with casting composite pistons has been the number of machining steps and other labor processes required to finish the cast product.
The present invention contemplates a new and improved method and apparatus for casting composite articles, particularly pistons9 which overcomes the above-referenced problems and others. Yet it provides a composite piston in which the unlike metal alloys are strongly bonded, which is crack and fatigue resistant, and which is finished with fewer machining steps.
t The invention relates to a method of casting a lightweight f 20 piston with a wear resistant insert.
In accordance with one aspect of the invention there is provided a method of casting a lightweight piston with a wear resistant insert comprising: preheating a ring of wear resistant material; causing the preheated ring to be disposed in a die ~` cavity; pouring a predetermined amount of` a molten lightweight alloy into the die cavity through a plurality of paths which are disposed adjacent the outer die surface; closing the mold cavity with a punch which is recieved in the die cavity; and applying a force with the punch which tends to compress the lightweight alloy in the die cavity, wherein the lightweight alloy is pressed in continuing contact with the ring and the die cavity as the alloy solidifies.
In this manner the lightweight alloy is pressed into firm and continuous contact with the ring and the die cavity even as the alloy shri.nks during solidification.
In accordance with another aspect of the present invention, there is provided a mold assembly for casting a lightweight piston which has a wear resi.stant insert.
In particular there is provided a mold assembly for casting a lightwei.ght piston with a wear resistant insert comprising: a female di.e having a die cavity with a sub-stantially cylindrical outer die surface; support means forsupporting the wear resistant insert, the supporting means being a ledge extending around the outer die surface and being connected with the cylindrical outer die surface; a movable pouring disc which is selectively disposed in an upper portion of the die cavity, the pouring disc having a plurality of passages arranged circumferentially around its perimeter and disposed generally above said ledge, whereby molten metal which is poured on the pouring disc flows through the passages and into the die cavity adjacent its 2~ outer die surface flows over the wear resistant insert which is supported on the ledge; and a punch which is mounted for selectively entering the upper portion of the die cavity after removal of the pouring disc.
- 3a -A principal advantage of the present invention is that it produces a cornposite piston of a lightweight alloy with a wear resistant insert in which the bond between the lightweight alloy and the insert is strong and durable.
Another advantage of the present invention is that it rninimizes machining steps, labor, and manufacturing time by casting a composite piston which is in close conformity to the shape of the final piston product.
The invention may take physical form in certain parts and arrangements of parts~ a preferred embodiment of which is illustrated in the accompanying drawings. The drawings are only for purposes of illustrating the preferred embodiments of the invention and are not to be construed as limiting it.
Figure 1 is a cross-sectional view of a die cavity in which a wear resistant insert ring and a pouring disc are disposed in accordance with the present invention;
Figure 2 is a cross-sectional illustration of the die cavity of Figure 1 during the pouring of a molten lightweight alloy into the die cavity;
..~
~ oo;~
Figure 3 is a cross-sectional illustration of the die cavity of Eigu;es 1 and 2 after pourlng in which ~n upper opening of the die cavity is closed by a top punch for exerting pressure on the solidifylng alloy;
Plgure 4 is a cross~sectional illustration of the die cav~ty of ~igures 1-3 after the lightweight alloy has solldified;
Figure 5 is a top plan view of the wear res:Lstant insert rlng illustrated in Figures 1-4;
Figure 6 is a cross~sectional view through se~tion line 6-6 of Figure 5, Figure 7 is a top plan view of the pouring disc illustrated ln ~igures 1 and 2; and Flgure 8 is a perspective view in partial section of a com posite piston manufactured in accordance with the present lnven~
tion~
DESCRIPTION 0~ THE PR~FERRED EMBODIMENTS
A mold assembly is illustrated in Figures 1-4 for castlng com-posite pistons of a lightwelght alloy wlth a wear reslstant insert as illustrated in Figure 8. The mold assembly includes a two-piece femala die 10 which has a die cavity 12. The die cavity is shaped ~n conformity to the piston or other structure to be cast~ The die cavity 12 includes an outer die surface 14 whlch is configured ~o conform to the exterior of the pistonO The outer die surface 14 ~s smooth and polished to minimize machining steps to finish the cast piston. The outer die surface 14 extends peripherally around the die cavlty along a circular path. In the center of the die cavity 12, a core 16 is disposed for defining a hollow interior to the piston. Toward the top of the die cavity is a supporting ~eans 18 for supporting a wear reslstant insert 20. In the preferred ~m-bodi~ent, the supporting means 18 is a peripheral ledge or land which extends around the outer die su;face 140 Above the peripheral ledge or supporting ~eans 18, the outer die surface 14 has an en-larged upper portion 22. This enables the insert 20 to be placed into the upper portion ~2 of the die cavity 12 through an upper horizontal openlng 24. The upper portlon 22 has a cross section :
~1900~g whlch conformg the periphery of the insert 20.
The insert 20 comprises an annular rlng 30 which is shown in greater detail in Flgure 5. ~he annular ring 30 ls fashioned of a wear resistant materlal that has e~panslon and contractlon pro-pertles which are similar to the expanslon and contrac~ion pro-perties of the lightweight alloy from which the piston is to be cast. In the preferred embodiment, the wear resistant material is an austenitic alloy of iron, nickel, chromiuml and copper, par-tLcularly advantageous i9 the alloy sold by Thomas Foundries, Inc.
of Birmingham9 Alabama under the trademark NI-RESIST . The annular ring has a peripheral edge 32 whlcll conforms with the exterior dia-meter of ~he piston to be castO In the preferred embodiment, the diameter of the peripheral edge 32 is slightly larger than the Pinished piston to allow the exterior surface to be machined to close tolerances. Extending outward from the peripheral edge 32 1 at least one pro~ection. In the preferred embodiment, the a~ leas~
one projection is a plurality of tabs 34 whicll are dimensioned to be received snugly within the upper portion 22 of the die cav:lty and rest on supporting means 18. The diameter of the periphera1 edge 32 of the annular ring is dimensioned to be substantially the same or slightly smaller than the diameter of the outer die surface 14. As illustrated ln Figure 6~ each of the tabs 34 is sufficien~ly thin that it is frangible under the pressures norntally associated with squeeze casting. Alternatively) the at least one projection may be a continuous frangible flange whlch extends peripherally along the perlpheral edge 32. As yet another alternative9 the tabs 34 may be substantially the same thickness as the annular rt~g 30.
To cast a composite piston~ the wear resistant annular ring 30 is cleaned, preheated, and coated with a thln coating 40 of ductile metal. The thlckness of the coating 40 is exaggerated in Flgures 1 and 8 for eas~ of illustration. The coatlng of ductile metal form~
a stress absorbing buffer betwèen the annular ring 30 and the lightweight alloy. In the preferred embodiment~ the annular ring immersed Ln a bath of pure aluminum or aluminuDt alloy which ls heated to within 200 F. of the temperature at which the lightweight ., .
~ æ~
~lloy is to be cast. The duration whlch the annular ring 30 isimmersed in the aluminum i8 kep~ to a mlni~um to miniml~e the formation of brittl~ aluminum-lron lntermetalltc compounds~ After the annular ring 30 is preheated and coated with the ductile metal, it is plaeed on supporting mean~ 18 in ~he die cavityO
A pouring disc 50 is placed ln the upper opening of the cavity.
The pouring disc 50 is a means for distributing the melted lightweight alloy into the die cavity during pouring. Particularly~
it distributes the poured melted alloy such that it flow~ evenly over the insert 20. This inhibits the formation of oxides at the interface and aæsists in retaining the insert near the temperature of the ~olten alloy during the pouring operation.
With cont~nued reference to Flgure 1 and further reference to Figure 7, the pouring disc 50 ls dimensioned to be received in the upper portion 22 of the die cavity. The pouring disc has a central portion 52 which in con~unction with part of the upper portion 22 of the die cavity forms a temporary reservoir for receiving and holding the molten llghtweight alloy. The depth of the temporary reservoir determines the pressure head of the molten alloy hence the flow rate into the d~e cavity.
Arranged peripherally around the pouring disc 50 are a plurality of passages for channeling the molten alloy into the mold cavity around its periphery. In the preferred embodiment, th2 plurality of passages is formed by a plurality of circular apertures 54 arranged around the perimeter of the pouring disc.
Alternatively9 the passages may include a plurallty of radial slots around the periphery, a screen or mesh around the periphery, an annular gap between the disc and the die cavity, or the like.
Connected with the pouring disc 50 are a plurality of means 56 for supporting and centerlng its central portion 52 in the upper portion of the die cavityO Projecting upward from the central portion 52 of the pouring disc is a chimney 58 for allowing air within the die cavity to escape as molten lightweight alloy is poured in without aerating or agitating the mol~en alloyO The chimney 58 i9 a tubular pro~ec~ion of sufficient length to extend .
.~, above tlle molten alloy in the ~emporary reservolr.
Wi~h particular refere~ce to Figure 2, before the preheate~
lnsert 20 cools, a predetermined amount of molten llghtwe:Lght alloy, denoted by reference nu~eral 607 iS poured from a furnace or cruc-ible 62 GntO the pouring disc 50. From the temporary reservolr, the ~olten alloy passes through the apertures 54 around the perimeter of the pouring dlsc and impinges upon the insert 20. The molten alloy flows over and around the insert lnto the lower portion3 of the dle cavity. ~en the predetermlned amount of molten alloy has been introduced into the dle cavity, the pouring disc 50 is removed. The flow of the molten alloy partially dissolves the thin aluminum coat-:Lng 40 making it even thinner.
With particular reference to Figure 3, the upper opening of the die ca~ity is closed by a top punch 70 preferably wlth an annular pro~ection 72 for forming a combustion bowl in the top of the pl~ton. The top punch 70 is dimensioned to conform with the cross section of the upper por~lon 22 of the die cavity within very close tolerances to prohibit the ~olten alloy from passing between the punch and the outer die surfaceO Top punch 70 is caused by a hydraulic cylinder ~not shown) to exert several tons of pressure on the lightweight alloy in the die cavity. As the molten alloy solidifies, it contracts. The top punch continues to press the alloy firmly and continuously agalnst the surfaces of the die cav~
ity, tha punch, and the insert as the lightweight alloy solidifi~sO
The contraction of the lightweight alloy during solidif~cation allows the top punch 70 to advance into the die cav~ty by a cor-responding amount. It has been found that the pressure from the top punch tends to deflect the annular ring which causes interual stresses after solidificatlonO This deElection is alleviated with the annular ring construction of Figures 5 and 6 because the tabs 34 space the peripheral edge 32 of the ring a sufflcient distance from the outer die surface 14 that the lightweight alloy flows between the ring and the die surface.
With particular reference to Flgure 4, the deflection is fur~her reduced by the fracture of the frangible ~abs 34 . .
Under the pressure exerted by the top punch 70, the tabs 34 breakallowin~ the ann~llar ring 30 to shift downward in the die cavlty wlth the contraction during solidification.
After the lightweight alloy Eolidifies, the top punch i8 withdrawn, the die cavlty opened, and the composite piston removed.
The composlte piston is finished by a machining operation. Because the exterior surface conforms very cloæely to the outer surface of the punch and the die, very little machining is required. The top surface of the piston conforms to the surface of the punch with suf-ficlent accuracy that, as a rule, no further machining ~8 required to finish the top surfaceO The exterior surface of the piston i8 ~achined to remove the severed tabs 34 and the excess material from the increased diameter of the upper portion 22 of the die cavity.
The machining may further be used to give tlle piston a circular cross section with very precise dimensional tolerances. With re-ference to ~igure 8, the machining operation further includes cut-ting a plurality of grooves into the piston to receive piston rings~
A top piston ring groove 82 is machined in the annular ring 30.
Additional piston ring grooves 84 and 86 are also machined in the piston 80. A wrist pin 88 connects the piston 80 with a rod 900 The invention has been described with reference to the pre-ferred embodiment. Obviously, modifications and alterations will occur to others upon readin8 and understanding this specification.
It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
- .
:
. ' _g_ : ,, ..
Claims (8)
1. A method of casting a lightweight piston with a wear resistant insert comprising:
preheating a ring of wear resistant material;
causing the preheated ring to be disposed in a die cavity;
pouring a predetermined amount of a molten lightweight alloy into the die cavity through a plurality of paths which are disposed adjacent the outer die surface;
closing the mold cavity with a punch which is received in the die cavity; and applying a force with the punch which tends to com-press the lightweight alloy in the die cavity, whereby the lightweight alloy is pressed in continuing contact with the ring and the die cavity as the alloy solidifies.
preheating a ring of wear resistant material;
causing the preheated ring to be disposed in a die cavity;
pouring a predetermined amount of a molten lightweight alloy into the die cavity through a plurality of paths which are disposed adjacent the outer die surface;
closing the mold cavity with a punch which is received in the die cavity; and applying a force with the punch which tends to com-press the lightweight alloy in the die cavity, whereby the lightweight alloy is pressed in continuing contact with the ring and the die cavity as the alloy solidifies.
2. A method as set forth in claim 1, wherein the ring is preheated to a temperature within 200°F. of the temperature at which the molten lightweight alloy is poured into the die cavity.
3. A method as set forth in claim 1, wherein the step of preheating the ring includes immersing the ring in a bath of molten ductile metal, whereby a layer of ductile metal is cast between the ring and the lightweight alloy to absorb stresses.
4. A method as set forth in claim 2, wherein the step of preheating the ring includes immersing the ring in a bath of molten ductile metal, whereby a layer of ductile metal is cast between the ring and the lightweight alloy to absorb stresses.
5. A method as set forth in claim 3, wherein the ring is an austenitic iron alloy.
6. A method as set forth in claim 5, wherein the light-weight alloy is an aluminum alloy.
7. A method as set forth in claim 6, wherein the molten metal is aluminum or an aluminum alloy.
8. A mold assembly for casting a lightweight piston with a wear resistant insert comprising:
a female die having a die cavity with a substantially cylindrical outer die surface;
supporting means for supporting the wear resistant insert, the supporting means being a ledge extending around the outer die surface and being connected with the cylindrical outer die surface;
a movable pouring disc which is selectively disposed in an upper portion of the die cavity, the pouring disc having a plurality of passages arranged circumferentially around its peri-meter and disposed generally above said ledge, whereby molten metal which is poured on the pouring disc flows through the passages and into the die cavity adjacent its outer die surface flows over the wear resistant insert which is supported on the ledge; and a punch which is mounted for selectively entering the upper portion of the die cavity after removal of the pouring disc.
a female die having a die cavity with a substantially cylindrical outer die surface;
supporting means for supporting the wear resistant insert, the supporting means being a ledge extending around the outer die surface and being connected with the cylindrical outer die surface;
a movable pouring disc which is selectively disposed in an upper portion of the die cavity, the pouring disc having a plurality of passages arranged circumferentially around its peri-meter and disposed generally above said ledge, whereby molten metal which is poured on the pouring disc flows through the passages and into the die cavity adjacent its outer die surface flows over the wear resistant insert which is supported on the ledge; and a punch which is mounted for selectively entering the upper portion of the die cavity after removal of the pouring disc.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US22483681A | 1981-01-13 | 1981-01-13 | |
| US22482081A | 1981-01-13 | 1981-01-13 | |
| US06/224,820 | 1981-01-13 | ||
| US06/224,836 | 1981-01-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1190024A true CA1190024A (en) | 1985-07-09 |
Family
ID=26919035
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000393999A Expired CA1190024A (en) | 1981-01-13 | 1982-01-12 | Method and apparatus for squeeze casting pistons with wear resistant inserts |
Country Status (8)
| Country | Link |
|---|---|
| AU (1) | AU7900381A (en) |
| BR (1) | BR8200140A (en) |
| CA (1) | CA1190024A (en) |
| DE (1) | DE3200641A1 (en) |
| GB (1) | GB2090780B (en) |
| IN (1) | IN155115B (en) |
| IT (1) | IT1147564B (en) |
| MX (1) | MX159185A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3370512D1 (en) * | 1982-12-31 | 1987-04-30 | Ae Plc | Squeeze casting of pistons |
| GB2135222B (en) * | 1983-02-04 | 1987-11-11 | Ae Plc | The reinforcement of pistons of aluminium or aluminium alloys |
| GB8413800D0 (en) * | 1984-05-30 | 1984-07-04 | Ae Plc | Manufacture of pistons |
| JP2908297B2 (en) * | 1995-11-24 | 1999-06-21 | イズミ工業株式会社 | Piston casting method |
| DE19701085A1 (en) * | 1997-01-15 | 1998-07-16 | Kolbenschmidt Ag | Casting engine piston using support ring |
| US5979298A (en) * | 1997-05-08 | 1999-11-09 | Zellner Pistons, Llc | Cooling gallery for pistons |
| JP3928336B2 (en) * | 1999-09-21 | 2007-06-13 | 株式会社豊田自動織機 | Manufacturing method of piston for compressor |
| EP1094219B1 (en) * | 1999-09-21 | 2004-11-24 | Kabushiki Kaisha Toyota Jidoshokki | Swash plate compressor piston with pore-free die-casted head |
| JP2001090654A (en) * | 1999-09-21 | 2001-04-03 | Toyota Autom Loom Works Ltd | Manufacture of body member of piston for swash plate type compressor |
| DE102014216517A1 (en) * | 2014-08-20 | 2016-02-25 | Mahle International Gmbh | Casting tool and method of manufacturing a piston for an internal combustion engine |
-
1981
- 1981-12-08 IN IN1398/CAL/81A patent/IN155115B/en unknown
- 1981-12-16 GB GB8137975A patent/GB2090780B/en not_active Expired
- 1981-12-24 AU AU79003/81A patent/AU7900381A/en not_active Abandoned
-
1982
- 1982-01-11 IT IT47529/82A patent/IT1147564B/en active
- 1982-01-12 CA CA000393999A patent/CA1190024A/en not_active Expired
- 1982-01-12 BR BR8200140A patent/BR8200140A/en unknown
- 1982-01-12 DE DE19823200641 patent/DE3200641A1/en not_active Withdrawn
- 1982-01-13 MX MX190951A patent/MX159185A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| GB2090780A (en) | 1982-07-21 |
| GB2090780B (en) | 1985-03-06 |
| IN155115B (en) | 1985-01-05 |
| DE3200641A1 (en) | 1982-08-12 |
| MX159185A (en) | 1989-04-28 |
| BR8200140A (en) | 1982-11-03 |
| IT1147564B (en) | 1986-11-19 |
| IT8247529A0 (en) | 1982-01-11 |
| AU7900381A (en) | 1982-07-22 |
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| MKEX | Expiry |