US3216072A - Die casting method and apparatus - Google Patents

Description

Nov. 9, 1965 A. F. BAUER 3,216,072

DIE CASTING METHOD AND APPARATUS Filed Dec. 15, 1961 3 Sheets-Sheet l INVENTOR. ALFRED F. BAUER ATTORNEYS Nov. 9, 1965 A. F. BAUER DIE CASTING METHOD AND APPARATUS 3 Sheets-Sheet 2 Filed Dec. 13, 1961 INVENTOR. ALFRED F. BAUER BY 2 ATTORNEYS Nov. 9, 1965 A. F. BAUER 3,216,072

DIE CASTING METHOD AND APPARATUS Filed Dec. 15. 1961 3 Sheets-Sheet 3 'llll 2 5/ 1 IN VEN TOR.

ALFRED F. BAUER F 1757. 4%? g v AIIQRNELS V.

United States Patent Jersey Filed Dec. 13, 1961, Ser- No. 159,025 6 Claims. (Cl. 22 167) This invention relates to a die casting method and apparatus for producing complicated die cast parts in which a core having a multiplicity of separable parts is required.

In die casting parts which have undercuts, or holes so disposed or shaped that they cannot be cored by the conventional method employing a movable or stationary core in the die, it has been an accepted practice to make a portion of the die cavity in the form of a core having a multiplicity of separable loose pieces. The so-called collapsible core is assembled outside of the machine and is inserted into the die as a unit. After the shot is made the core is ejected with the casting and its parts are removed in a particular sequence, leaving the casting with the desired undercut, openings, etc. The present practice relating to the use of collapsible cores and loose core pieces is described in the publication Die Casting by H. H. Doehler, McGraw-Hill, 1951. The disadvantages of the collapsible core system are noted in the publication and their use is discouraged if it is possible to make the part in any other manner. However, I have found that all of the disadvantages of collapsible cores can be overcome and that this technique can be made a simple and very valuable aid in die casting if the core pieces are assembled in the usual manner and are then coated with a surrounding temporary body of sufiicient thickness to hold the parts together as a unit prior to inserting the assembly in the die and the coating is such that it remains with the casting upon removal of the core pieces.

One of the presently accepted problems in the use of collapsible cores is that metal from the casting enters as flash between the elements of the core. This undesired flash metal in many instances will make it very diflicult to separate the core parts from each other and form the casting after the part is ejected and further, trimming and finishing of the casting are made more diflicult due to the additional flash lines and scams on the casting. By the use of the present invention, all flash lines of the cast metal between the parts of a collapsible core are eliminated, and the injected metal comes in contact only with a continuous surface represented by the exterior of the coating. The coating is applied outside of the die casting machine by an appropriate device such as a metallizing gun and the applied coating, being under almost zero pressure, has little tendency to enter the parting line between the assembled parts of the collapsible core. Thus only a very small ridge, a few thousandths of an inch high, appears in the casting to show the line of demarcation between the core parts after they are removed from the finished piece.

It has also been found that collapsible cores have a relatively short life because they are worn and eroded by the chemical and thermal action and the high pressure of the casting metal. Thus even though the parts which make up the core fit very well and very closely when the core is new, a few hundred casting cycles may be sufficient to so erode and distort the parts that replacement becomes necessary. By protecting the core parts from physical deterioration, the present invention provides a means for greatly increasing the life expectancy of the parts of a collapsible core.

It is sometimes diflicult to hold the various parts that make up a collapsible core in place during the casting operation, and for this purpose the parts are ordinarily provided with elaborate and precise dovetail joints by which they are interrelated, and are so interfitted with each other and with the remainder of the die that no substantial movement Will take place when the shot is made. Since the molten metal is put into the die with great rapidity and the casting pressure is normally from 6000 p.s.i. to 10,000 p.s.i. it is not unusual to find that shifting of the collapsible core parts relative to each other has taken place. This hifting need be only a few thousandths of an inch to cause the part to be defective in many instances; The present invention makes it possible to anchor the core parts together as a complete and selfsustaining unit which can be related to the remainder of the die elements with the same precision that would be expected from a single die insert. The parts of the core are so closely fitted and held that almost no flash enters between them in areas where no coating has been applied, and the division line, while visible in the completed casting, has a width and height of only one or two thousandths of an inch.

The primary object of the present invention, therefore, is to provide a method and apparatus for die casting relatively complicated parts by which a plurality of separable die pieces are temporarily related into a single, protected core body for insertion into a die casting die.

Another object of the invention is to provide a method and apparatus for die casting relatively complicated parts by which a plurality of separable die pieces are temporarily related by means of a protective coating of metal which is transplanted by the casting operation from the die pieces to the castings so that the die pieces are easily withdrawn from the casting.

Another object of the invention is to provide a method and means for protecting and thus extending the life of the several parts of a collapsible die casting core.

Other objects and advantages of the invention will become apparent from the following detailed description of a preferred form thereof, reference being had to the accompanying drawings, in which: 7

FIG. 1 is an exploded top plan view of the parts included in a typical collapsible die casting core;

FIG. 2 is an exploded perspective view of the parts shown in FIG. 1;

FIG. 3 is a perspective view of the parts shown in FIG. 2 in assembled relation;

FIG. 4 is a perspective view of the core parts after coating;

FIGS. 5 and 6 are cross-sectional views of a completed casting indicating the removal sequence of the core parts;

FIG. 7 is a somewhat diagrammatic longitudinal sectional view showing the relationship between the core parts and other die elements for making a casting; and

FIG. 8 is a section on line 88 of FIG. 7.

The drawings illustrate an apparatus for casting acylinder for an internal combustion engine, and also illustrate the manner in which the method of the present invention may be carried out.

A collapsible core is shown in top plan View in FIG. 1 and in perspective in FIG. 2, in each instance with the parts that will constitute the core in a disassembled condition. A central, major core body 10 is provided, the base of which is shaped to be received in an ejector die part. The manner of fixing the collapsible core in the die may be the same as is now known in the art. Usually this comprises a means to locate the core in a particular position in the die as well as some means to aflix it against lateral displacement.

The main core body 10 is provided with shoulders 12 on which the side pieces are supported, the side pieces being designated 14, 15 and 16. Suitable temporary locating devices such as pins 17 project from the shoulders 12 and are received in holes 18 in the base of the respective side core pieces. The side core pieces may be made long or short, at the selection of the designer. In the form shown the side core pieces 14 and 16 include projections 20 which extend in a direction normal to the axis of the main core piece 10 (which will be the central axis of a resulting casting). These projections will cooperate with stationary die cores 22 and 23 (FIG. 7) to form intake passages for the engine cylinder in the resulting casting. Were it not for the collapsible core technique these passages would have to be formed by side cores entering at right angles to the axis of the die and leaving openings which would then be covered or closed in a subsequent operation.

The remaining side core 15, in the example shown, carries lateral projections 25 which will form exhaust ports by cooperating with a stationary core piece 26 (FIG. 8). The stationary core pieces 22, 23 and 26 project from the ejector half of the die in a known manner.

The collapsible core so far described dilfers from a conventional collapsible core for making the same part largely in that it substitutes the simple locating dowel pins 17 for a much more elaborate dove-tailing system which would ordinarily be used to attach the side pieces 14, 15 and 16 to the main or center core part 10. Thus the complexity and expense of machining these joints are eliminated. The core is smooth on its exterior surface in accordance with known die making practice.

The center core part 10 in the form shown is provided with a boss 90 which will form a recess in the top of the cylinder casting, and may be of any desired top configuration.

Referring now to FIGS. 1, 2, 3 and 4, the core pieces so far described are shown first in separated relationship in FIGS. 1 and 2 and in assembled relationship in FIG. 3. When the pieces are put together as shown in FIG. 3, they are then coated as shown in FIG. 4. The coating (designated applied to the assembly is preferably a metallic coating having properties which are of special utility in the resulting casting, although in accordance with the present invention the coating may be of the same com position as the metal which will ultimately be cast around it in which case the coating performs only the functions of retaining the collapsible core elements in assembled relationship and protecting them against deteriorating during the casting cycle.

In the casting that has been selected for purposes of explaining the present invention, a cylinder for an internal combustion engine, it is desirable that the protective coating 35 be of a metal which will form a highly wear resistant interior surface for that portion of the cylinder swept by the engine piston. It is known that iron alloys are satisfactory for this purpose. Therefore, one coating which may be applied to carry out the present invention may consist of an iron alloy deposited by a metallizing gun which will result in a mixture of the iron alloy and iron oxide. If the coating as applied by making several passes of the metallizing gun axially of the assembled core parts while the core parts are rotated in an appropriate fixture, it will be found that a desirable stratification occurs and that the grain structure of the coating is elongated in the axial direction. If desired, the coating may be made thicker at one end of the cylinder than the other to impart a physical reinforcement thereto, or it may be varied in composition from end to end to be more refractory in the combustion chamber end of the cylinder, and more retentive of oil in the lower or crankcase end.

One very distinct advantage flows from the use of the applied coating in the particular casting shown which has not heretofore been possible of attainment. In a two-stroke cycle internal combustion engine cylinder cast from light metal alloys, it has been found that deterioration occurs at the port areas because of the corrosive and erosive efi'ects of the gases flowing into and out of the cylinder. The damage is especially severe at the exhaust ports. By extending the coating 35 over the projections 25 around which the metal is cast to form the engine exhaust ports, the resulting casting will have a liner on the walls of the ports which effectively resists deterioration over the life of the engine.

The coating 35 may be applied also by dipping the assembled core parts, or by brushing a suitable material in place. These techniques are applicable where the coating material is capable of suspension in a liquid to form a workable slip. The applied slip may then be fired or cured to form a body which will not wash off during the casting step and which will protect the core parts from the casting metal. Regardless of the method of application of the coating material, whether it be brushing, spraying or dipping, the application pressure is almost zero and the coating material is not forced between the elements of the collapsible core. The penetration will depend, of course, on the fits between parts, greater penetration occurring if the parts are loosely fitted than if they are closed. Penetration will also depend on the degree that the coating material wets the core pieces and thus to some extent on the surface characteristics of the core elements themselves. It is desirable, therefore, that the core elements be assembled with rather close tolerances so that the joints between them are not wide.

It is desirable that the exposed surface of the coating 35 be somewhat rough, irregular and porous so that it will adhere to the casting and will be transplanted from the core as taught in my copending application Serial No. -8l=1,6l1, filed May 7, 1959, now U.S. Patent No. 3,083- 424. Thus the coating has a greater degree of adhesion to the casting than to the smooth core pieces on which it was initially formed or deposited.

As previously noted the thickness of the coating 35 may be varied. The lower limit of thickness depends only on two factors; first, the coating must be thick enough to hold the assembled core parts together in cooperation with the remaining support elements such as the dowel pins 17; and secondly, it must be thick enough to resist the washing effect of the molten metal entering the die during the casting operation.

After the assembled core parts 10, 14, 15 and 16 are coated as shown in FIG. 4 the coated core is put into the die and the shot is made. The core is then ejected with the casting. The coating 35 will have become adhered to the casting and will have transplanted from the core, as taught in my said copending application Serial No. 811,611. The center core part 10 is removed first, which separates the dowelled connection between this element and the side parts 14, 15 and 16, which can then be taken out sequentially as indicated in FIGS. 5 and 6 of the drawings.

At this time the casting is ready for trimming in the usual manner and, in addition will be finished by opening up the intake and exhaust ports. This operation requires only that the web of coating material which was formed over the exposed lateral face of the projections 25 be broken away where it spans the ports which is accomplished without difficulty.

Castings made in accordance with the present invention show that the coating material enters between the parts of the core for only a few thousandths of an inch, leaving small ridges or raised lines in the casting. These ridges are readily honed out of an engine cylinder but may, of course, be left unfinished in some castings where their presence is unimportant as in a valve body, for example. The presence of the coating material assures that none of the casting metal can enter as flash into the spaces between the core parts while flash causes rapid deterioration in many collapsible cores. Further, the coating material prolongs the life of the core parts by preventing direct contact between the casting metal and the core parts.

While the present invention has been described in conjunction with the manufacture of an engine cylinder, and with a specific form and composition of the coating, it should be expressly understood that the description is for purposes of illustration only, and is not a limitation on the scope of the invention as defined in the appended claims.

What I claim is:

1. A method of die casting comprising assembling a plurality of separable and re-usable core parts, applying a thin coating comprising a mixture of metal and metal oxides over selected areas of the assembly of core parts including at least some of the joining lines between the core parts said coating having a thickness at least suflicient to hold said core parts in assembled relation prior to insertion into a die and to maintain its integrity during a subsequent casting operation, inserting the coated assembly as a unitary core piece into a die casting die with the coated surface exposed to the die cavity, casting metal into the die cavity under high pressure to cause the casting metal to bond to the coating with a bond strength higher than the strength of the adhering force between the coating and the assembly of core parts, ejecting the casting, and finally removing the core parts leaving the coating material adhered to the casting.

2. A method in accordance with claim 1 in which said metallic coat is applied by spraying.

3. A method in accordance with claim 1 in which said metal and metal oxides have a higher melting point than the casting metal.

4. Core apparatus for making high pressure die casting comprising, the combination of a plurality of separable and re-usable core elements which when related define at least a part of a die cavity, and an integral, continuous protective metallic coat surrounding said separable core elements and covering at least the majority of all lines of separation therebetween, said coat being interposed between said core elements and the remainder of the die cavity for contact with molten metal to be injected into said die cavity and said coating having an exposed surface of such rough, irregular and porous nature as to be removed from said core element and adhered to the die casting upon completion of casting and withdrawal of said core elements.

5. Core apparatus in accordance with claim 4 in which at least one of said core elements includes a lateral protrusion for forming an off-set in a casting, and said coating covers said protrusion.

6. Apparatus for making a composite high pressure die casting with a lining having special utility therein comprising, an assembled plurality of separable core elements including a major element and at least one minor element, one of said core elements having a laterally extending projection which cooperates with other die portions to form an off-set opening, means to temporarily fasten said minor elements on said major element, said elements when assembled forming a portion of a die cavity, an integral continuous mechanically applied metallic coating covering at least the major portion of the line of separation between said major and minor core elements and covering said lateral projection, said coating being interposed between said core elements and said die cavity and being of such nature as to prevent the entry of molten metal as flash between said core elements in the covered area, said coating presenting a relatively rough surface to said die cavity whereby the coating interlocks with and mechanically bonds to the casting upon removal of said core elements, said coating thus acting to cover the interior of at least the oil-set portion of the casting.

References Cited by the Examiner UNITED STATES PATENTS 1,195,303 8/16 Weiss 1845 1,348,982 8/20 Coates 22173 1,561,287 11/25 Stern 22-192 2,903,375 9/59 Peras 22216.S X 3,083,424 4/63 Bauer 22203 FOREIGN PATENTS 1,248,693 11/60 France.

841,891 7/60 Great Britain.

873,012 7/ 61 Great Britain.

OTHER REFERENCES Die Casting, Doehler, H. H., 1951, M=cGraw-Hill Book Co., Inc., p. 169.

Bonding Cast Iron to Aluminum Casting, Light Metal Age, October 1959, page 17.

Aluminum Bonded by Diecasting Process, Steel, Nov. 30, 1959, pages 98-100.

Transplant Coated Aluminum Cylinder Bores, Bauer, A. F., 369C., 1961 Summer Meeting, Society of Automotive Engineers, Inc., 485 Lexington Ave., N.Y.

I SPENCER OVERHOLSER, Primary Examiner.

MARCUS U. LYONS, ROBERT F. WHITE, MICHAEL V. BRINDISI, Examiners.

Claims (2)

1. A METHOD OF DIE CASTING COMPRISING ASSEMBLING A PLURALITY OF SEPARABLE AND RE-UNSABLE CORE PARTS, APPLYING A THIN COATING COMPRISING A MIXTURE OF METAL AND METAL OXIDES OVER SELECTED AREAS OF THE ASSEMBLY OF CORE PARTS INCLUDING AT LEAST SOME OF THE JOINING LINES BETWEEN THE CORE PARTS SAID COATING HAVING A THICKNESS AT LEAST SUFFICIENT TO HOLD SAID CORE PARTS IN ASSEMBLED RELATION PRIOR TO INSERTION INTO A DIE AND TO MAINTAIN ITS INTEGRITY DURING A SUBSEQUENT CASTING OPERATION, INSERTING THE COATED ASSEMBLY AS A UNITARY CORE PIECE INTO A DIE CASTING DIE WITH THE COATED SURFACE EXPOSED TO THE DIE CAVITY, CASTING METAL INTO THE DIE CAVITY UNDER HIGH PRESSURE TO CAUSE THE CASTING METAL TO BOND TO THE COATING WITH A BOND STRENGTH HIGHER THAN THE STRENGTH OF THE ADHERING FORCE BETWEEN THE COATING AND THE ASSEMBLY OF CORE PARTS, EJECTING THE CASTING, AND FINALLY REMOVING THE CORE PARTS LEAVING THE COATING MATERIAL ADHERED TO THE CASTING.

4. CORE APPARATUS FOR MAKING HIGH PRESSURE DIE CASTING COMPRISING, THE COMBINATION OF A PLURALITY OF SEPARAABLE AND RE-USABLE CORE ELEMENTS WHICH WHEN RELATED DEFINE AT LEAST A PART OF DIE CAVITY, AND AN INTEGRAL, CONTINUOUS PROTECTIVE METALLIC COAT SURROUNDING SAID SEPARABLE CORE ELEMENTS AND COVERING AT LEAST THE MAJORITY OF AL TIMES OF SEPARATION THEREBETWEEN, SAID COAT BEING INTERPOSED BETWEEN SAID CORE ELEMENTS AND THE REMAINDER OF THE DIE CAVITY FOR CONTACT WITH MOLTEN METAL TO BE INJECTED INTO SAID DIE CAVITY AND SAID COATING HAVIN AN EXPOSED SURFACE OF SUCH ROUGH, IRREGULAR AND POROUS NATURE AS TO BE REMOVED FROM SAID CORE ELEMENT AND ADHERED TO THE DIE CASTING FROM COMPLETION OF CASTING AND WITHDRAWAL OF SAID CORE ELEMENTS.

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