US3868986A

US3868986A - Pattern alignment means for use with lost foam molding process

Info

Publication number: US3868986A
Application number: US430972A
Authority: US
Inventors: Ralph A Olsen
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1974-01-04
Filing date: 1974-01-04
Publication date: 1975-03-04
Anticipated expiration: 1992-03-04
Also published as: CA1045780A

Abstract

An apparatus and method is disclosed for casting parts by the cavityless molding method. A plurality of complex or difficult cored consumable patterns are stabilized on a heat resistant frame. Means is employed to prevent the transfer of heat between the molten charge (subplanting the patterns) and the stabilizing frame. The assembly is installed in a semifilled flask or empty flask; fluidizing means is employed when a partly sand-filled flask is used and a deep pouring spout is used for an empty flask.

Description

United States Patent [191 Olsen 1 1 Mar. 4, 1975 PATTERN ALIGNMENT MEANS FOR USE WITH LOST FOAM MOLDING PROCESS Ralph A. Olsen, Grosse Pointe Woods, Mich.

Assignee: Ford Motor Company, Dearborn,

Mich.

Filed: Jan. 4, 1974 Appl. No.: 430,972

Inventor:

US. Cl 164/7, 108/107, 164/34, 164/244. 164/246, 211/134, 248/239 Int. Cl. B22c 7/02, B22c 15/22 Field of Search 164/7, 34, 244, 246, 350, 164/385; 211/134; 108/107, 109; 248/239 References Cited UNITED STATES PATENTS 3/1968 Snelling 164/34 6/1971 Krzyanowski 164/34 FOREIGN PATENTS OR APPLICATIONS 249,475 7/l9l2 Germany 211/134 Primary ExaminerRobert D. Baldwin Attorney, Agent, or Firm-Joseph W. Malleck; Keith L. Zerschling [57] ABSTRACT An apparatus and method is disclosed for casting parts by the cavityless molding method. A plurality of complex or difficult cored consumable patterns are stabilized on a heat resistant frame. Means is employed to prevent the transfer of heat between the molten charge (subplanting the patterns) and the stabilizing frame. The assembly is installed in a semifilled flask or empty flask; fluidizing means is employed when a partly sand-filled flask is used and a deep pouring spout is used for an empty flask.

12 Claims, 4 Drawing Figures PATTERN ALIGNMENT MEANS FOR USE WITH LOST FOAM MOLDING PROCESS BACKGROUND OF THE INVENTION Cavityless molding performed with consumable patterns have several distinct advantages, the chief of which is that the shape to be cast may take any configuration. Molding, itself, comprises ramming the sand or other suitable molding material around the pattern, without regard to a parting line or pattern draft. This allows for a considerable decrease in the cost of molding, particularly for parts where a single casting is required from a given pattern.

Typically, the expendable pattern may be made from an expanded plastic material, such as expanded polystyrene beads or polyethylene which, as is well known, is porous because it contains air voids in the expanded condition. The material is light weight, economical and easy to form into any desired shape. This pattern material is capable of being volatilized or burned, particularly in the absence of oxygen without appreciable residue remaining. The method of casting conventionally employed by those skilled in the art, is to utilize the molten charge for combusting and destroying the pattern. Molten metal poured into a mold containing a polystyrene pattern consumes the pattern, fills the resultant cavity with molten metal, which later solidifies, leaving a casting having the exact contour of the original pattern.

This mode of casting has worked admirably well for parts which are relatively open and can be freely filled with sand during flask filling operations. That is to say, success has been achieved to date only with patterns that, when set within a flask, permit dry unbonded sand to be easily introduced and which will occupy all voids within and without the patterns. However, when a multiple number of castings are attempted to be cast within a single flask and particularly from a common sprue, the feasibility of sand filling is considerably reduced. In addition, when the parts to be cast are not necessarily of a simple type, but have small openings leading to cored parts which will not lend themselves to free sand filling, the concept of cavityless casting is hampered. One suggestion, according to this invention to overcome these problems, is to separately pre-fill the polystyrene patterns with loose unbonded sand and close the polystyrene pattern in some fashion to assure the retention of the closed parts. These relatively heavy filled parts must be stabilized in some manner during overall flask filling. Proper alignment of parts relative to each other, as well as to the placement of sprues and risers, is extremely important if efficiency in the casting process is to be maintained.

Accordingly, there is a need for a method which will allow complex and intricate polystyrene patterns to be used in' multiple numbers within a single flask and which method lends itself to a high speed molding operation; the method may work with conventional sand filling mechanisms, such as sand slingers or deep pouring spouts.

SUMMARY OF THE INVENTION The primary object of this invention is to provide a method and apparatus which will permit the casting of a plurality of complex parts (or simple parts having small openings) within a single flask requiring precise alignment with appropriate sprues and risers, the

LII

method employing cavityless casting whereby the pattern is consumed by contact with molten metal.

Still another object of this invention is to provide an apparatus for stabilizing a plurality of polystyrene patterns within a single flask; the patterns have removable means for connecting to a stabilizing apparatus and have means to prevent deterioration of the stabilizing apparatus during the metal pouring operation.

Yet still another object of the invention is to provide a stabilizing apparatus and accompanying method for coordinating a plurality of polystyrene consumable patterns in a single flask which will prevent damage and distortion of the patterns during handling and filling operations associated with cavityless molding techniques.

SUMMARY OF THE DRAWINGS FIG. 1 is an overall elevational view of a mechanism upon which one or more flasks may be mounted for appropriate sand compacting and filling;

FIG. 2 is an enlarged sectional view of a portion of FIG. 1 showing the arrangement of the pattern stabilizing means within the flask;

FIG. 3 is a greatly enlarged perspective view of the stabilizing means and consumable patterns mounted thereon; and

FIG. 4 is a highly enlarged exploded view ofa portion of the pattern and stabilizing means of FIG. 3.

DETAILED DESCRIPTION One of the key problems to be overcome by this invention is to permit the use of a multiple number of relatively complex shaped or narrowly cored consumable patterns to be used in a high production casting line.

The use of consumable patterns is relatively well known in the art. This known technique has had its greatest demonstrated feasibility in connection with open parts which will fill relatively easy with sand during flask filling. However, when a number of relatively complex parts are utilized or where openings in the outer configuration will not fill easily with sand, special measures must be undertaken particularly with respect to the necessity for special alignment and stabilization. Parts such as manifold intakes or heaters for cooling systems, hub-type rotors or disc brake castings, all are of complex configuration which will not fill easily with sand. Simple parts having small cored openings may comprise exhaust manifolds, water pumps, unusually designed hollow section crank shafts, transmission oil pumps and disc brake calipers.

To overcome these problems, consumable patterns are hung on a fixture which cooperates with air fluidization of mold sand or with special sand pouring spouts to facilitate proper flask filling. Consumable patterns 10 are provided with at least one preformed consumable ear ll typically extending outwardly from one side wall 12 of the pattern 10. Preferably, at least three of such ears 11 extend outwardly in equi-circumferentially spaced arrangement about the side wall of the pattern to lay in a common plane. Each of the ears is provided with an opening 13 to receive stabilizing means 14, the latter being re-useable in subsequent cycles of the casting method. Each of the ears is provided with an annular groove 5 or recess at the juncture with The stabilizing means 14 comprises a rigid stabilizing frame 15, which is preferably constructed of tubular heat resistant steel. The frame has an annular base 15a adapted to seat in asecure position on a horizontal wall of the molding flask. The frame has uprights 15b along at least two sides thereof which connect with an upper annular ring 150. At spaced elevations along the uprights, fingers 16 extend inwardly toward the inner region of the frame wherein the patterns are hung. Each finger has an upright pin 17 at its inner extremity effecof the pattern.

Means 18 is provided to prevent the transfer of heat between the molten charge (displacing the pattern 10) and the supporting or stabilizing frame 14. To this end, one mode may comprise the use of an annular ceramic insert 19 which is preformed into the polystyrene ear; the insert may have a central opening 20 commensurate in size and shape to receive one of the pins 17 of said stabilizing frame. An annular groove 21 in the side wall 19a of the insert assures a good interlock with the ear.

Another mode may comprise the use of a narrow gauge in the connection between the ear and frame; an extremely narrow or wire-like restriction can be provided in pin 17 as a substitute for the separating ceramic insert 19. Accordingly when the molten charge is applied, the narrow gauge of the supporting finger prevents undue transfer of heat therealong and can be easily replaced with low cost replacement for a subsequent molding operation.

A preferred method mode would comprise:

A. Prepare a skeleton stabilizing frame effective to be seated on a horizontal plane within a molding flask; the frame should have a plurality of fingers extending inwardly of the frame to support a body in spaced vertical orientation,

B. Prepare consumable foam-type patterns having configurations not easily filled internally with sand and may have cored parts. Each pattern should be prepared with a plurality of ears extending outwardly in circumferentially spaced arrangement about the side walls of said patterns so as to mate with the fingers of said frame and be supported in a stabilizing .manner,

C. Prepare a consumable common sprue effective to be combusted without residue by a molten charge and risers for said consumable patterns,

D. Insert said supported stabilized patterns into a flask having sufficient space about the frame to introduce sand to the bottom thereof; fluidize the sand by air pressure to assist in placement of the assembly of patterns, compact the introduced sand by vacuum or vibration,

E. Introduce molten metal to said sprue and patterns to displace same and form a solidified casting having ears as defined by said patterns, and

F. Strip the patterns from said sand and remove said frame therefrom for reuse of said sand. Re-install said frame work with a new set of patterns in a similar flask devoid of sand. Tap the ears of said castings for being stripped therefrom.

The consumable pattern is adapted to be displaced in a mold by the poured casting charge; it is converted substantially in its entirety to a gaseous state and permitted to escape from the mold through suitable vent provisions. To this end, any suitable material which is '10 tive to extend through the opening 13 in a mating ear readily combustible substantially without residue upon subjection to a molten casting charge can be used as pattern material. It should be sufficiently rigid to safely withstand the stresses induced by the customary ramming of molding sand thereagainst. A suitable material for these purposes is an expanded polystyrene. It has been found that polystyrene is well adapted for the intended purposes if it is expanded to a density substantially but not more than 2 lbs./ft. If this material has substantially greater density, it will not readily burn away on subjection to a molten casting charge. On the other hand there is a limit to the expansion of this material in order to be suitable for forms of this type, for if the density becomes too low, it may lack adequate strength to withstand ordinary molding pressures and other stresses, at least in parts, to spoil a mold. It is comparatively easy to make a form of this material for the production of a casting of most any configuration. For the sake of illustration, the pattern is shown as a simple block having a plurality of ears extending from a continuous side wall thereof, the ears being circumferentially spaced thereabout.

A typical preferred apparatus useful in carrying out step (D) of the preferred method is illustrated in FIGS. 1 and 2. A carousel 30 is employed having a turn table 31 or disc mounted at its center upon a tubular support 32 which in turn is stabilized on a base plate 33. A plurality of sand flasks 34 (for example, as many as eight) may be carried at various stations about the periphery of the turn table. Each of the flasks 34 is mounted on a pair of trunnions 35 at spaced locations along the turn table, the trunnions permitting the flask to be tilted for emptying of sand upon completion of the casting mode. To enable the carousel to be automated, an electric motor- 36 and transmission 38 may be employed to drive the main bearing ring 37 of the turn table; another electric motor 39 may be employed to rotate the flasks about their trunnions 34, the drive being through chains 40.

Each of the flasks 34 may be of one piece or nonseparable construction in which the mold is destroyed upon removal of the cast object and the pattern is destroyed during the casting process. Each flask is preferably provided with an air permeable wall 41 over at least the floor of the flask interior, space, the air permeable plate or wall being preferably formed of a sintered metal (such as iron). The permeable wall divides the interior of the flask into a casting chamber 42 and a gas plenum chamber 43, the latter selectively communicating by way of suitable ducts 44 with a suction source at one side and selectively communicating with a source 45 of fluid under pressure from the opposite side thereof. The communications may be respectively provided by the inlet duct 46 passing through the right hand trunnion and the communication of suction provided by a conduit 44 having a high velocity jet 44 connected to a source of pressure in the interior of the support 32 of the carousel. The interior of the support may act as a compressed air storage tank or accumulator fed by a pump 50.

In operation, the emptied upwardly oriented flask is halted at a first station of the carousel. Sand (molding medium) of the dry unbonded type is introduced in a predetermined quantity to the interior of the flask. This may be preferably accomplished by use of a deep penetrating pouring spout which would effectively fill chamber 42 in a manner as water would fill a vessel. While sand is being introduced, air is fed through passage 46 from source 45 to the chambers 43 which will effectively fluidize sand in chamber 42 thereby enabling the frame 14 and patterns to be inserted into the flask. The fluidization of the sand is carried such that the motion of the particles is slightly turbulant and yet no substantial tendency to drive the particles out of the mold is maintained. Because of the fluidization of the molding medium, the patterns and frame can be easily seated in the molding chamber 42 without noticeable resistance.

The carousel may then be indexed to the next position where the compressed air is interrupted and vibrators 47 are set in motion to compact the sand mass around the pattern. An air impermeable membrane 48 such as aluminum foil or polyester film is placed across the top of the sand body in the flask and may have an aperture for a casting funnel. The carousel is then indexed to a third position where suction is applied through the passage 44 and thus a differential pressure is applied between the membrane 48 and the floor 41 of the sand body. Suction may be created by use of a high velocity jet 49 in conduit 44. The pouring of molten metal can be carried out at the third station and as the molten metal is introduced to the mold, the pattern is destroyed and the mold cavity is filled. Gas evolved by the destruction of the porous polystyrene pattern may be drawn off through the sand mass under suction. The carousel is indexed to a fourth station where the casting is permitted to cool, solidify. Upon advance of the carousel to a fifth station, the cast body may be removed from the sand mass. In this station, the compressed air may be again supplied to the chamber 42 beneath the floor 41 to fluidize and loosen the sand to enable the cast bodies and frame to be drawn outward without effort. Finally, the carousel may be indexed to a sixth position where the flask is tilted and the sand medium is withdrawn.

1 claim:

1. Pattern apparatus for use in making multiple castings from a single pouring through a common sprue in a body of sand, the apparatus comprising:

a. a plurality of consumable foam type patterns which are combustible substantially without residue on subjection to a molten casting charge, each of said patterns having at least one ear effective to serve as a stabilizer,

b. a rigid stabilizing frame supported against movement, said frame having at least one extending finger for each of said patterns, each finger providing a support upon which said ear of one of said patterns may be journalled,

c. independent sprue means for conducting a molten metallic charge to said combustible patterns for consummation, and

d. means to prevent consummation of said frame during introduction of said molten charge.

2. The apparatus as in claim 1, in which said means to prevent consummation of said frame comprises a ceramic annular insert carried by said consumable foam pattern in the ear thereof, said insert having a central opening of a size effective to fit snugly about the finger of said stabilizing frame.

3. The apparatus as in claim 1, in which said means to prevent consummation of said stabilizing frame comprises a narrow or wire-like restriction in said finger so that the molten charge coming in contact therewith is ineffective to transmit damageable heat content to the remainder of said stabilizing frame.

4. The apparatus as in claim 1, in which the patterns each have at least three ears extending away from said pattern in a horizontal plane and spaced apart about said pattern to provide a secure horizontal support for said pattern, said stabilizing frame having a finger for each of said ears effective to secure said ears in said predetermined horizontal plane.

5. The apparatus as in claim 4, in which the horizontal planes for each of said patterns are spaced apart generally equally with the patterns generally vertically aligned.

6. The apparatus as in claim 1, in which said ears have an annular recess at the joint between said principal pattern and the ear whereby upon casting, the solidified casting ear may be easily severed by impact.

7. The apparatus as in claim 1, in which said frame is formed of tubular heat-resistant steel, and said ear having a ceramic insert disposed to surround said finger for preventing transfer of heat therebetween.

8. A method for fabricating a plurality of castings from a single pouring through a common sprue in a body of sand, the method comprising:

a. preparing a skeleton stabilizing frame effective to be easily inserted into a fluidized sand medium, said frame having a plurality of fingers extending inwardly thereof in a number of common planes generally equally spaced apart,

b. preparing a plurality of consumable foam patterns of the type which is combustible substantially without residue on subjection to a molten casting charge, each said pattern being provided with a plurality of foam ears extending generally away from said pattern to lay in one of said horizontal planes defined by the fingers of said frame, said patterns being joined together by a consumable sprue effective to be combusted without residue by said molten charge for defining a channel to feed said patterns,

c. filling said flask with a body of dry, loose unbonded sand, said sand being introduced to said flask by means effective to fluidly locate said sand progressively from the bottom upwardly through said flask,

d. pouring molten metal into said consumable sprue and pattern for combusting said foam material to occupy the void left by said foam,

e. stripping said patterns from said frame and fingers and from said sand, and then breaking off said cast ears from said casting, and

f. re-installing said frame in a stripped peating steps b through e.

9. The method as in claim 8, in which said patterns are aligned and supported on said frame prior to assembly of said frame within said flask whereby damage due to handling of said patterns is prevented as well as distortion while packing with sand.

10. The method as in claim 8, in which a pouring spout is utilized to direct filling sand first to the lower most regions of said flask.

11. The method as in claim 8, in which air pressure is utilized to fluidize said sand while installing said frame and attached patterns in said flask.

12. The method as in claim 11, in which vacuum is utilized to compact said fluidized sand after the patterns are installed in the flask.

flask and re-

Claims

1. Pattern apparatus for use in making multiple castings from a single pouring through a common sprue in a body of sand, the apparatus comprising: a. a plurality of consumable foam type patterns which are combustible substantially without residue on subjection to a molten casting charge, each of said patterns having at least one ear effective to serve as a stabilizer, b. a rigid stabilizing frame supported against movement, said frame having at least one extending finger for each of said patterns, each finger providing a support upon which said ear of one of said patterns may be journalled, c. independent sprue means for conducting a molten metallic charge to said combustible patterns for consummation, and d. means to prevent consummation of said frame during introduction of said molten charge.

8. A method for fabricating a plurality of castings from a single pouring through a common sprue in a body of sand, the method comprising: a. preparing a skeleton stabilizing frame effective to be easily inserted into a fluidized sand medium, said frame having a plurality of fingers extending inwardly thereof in a number of common planes generally equally spaced apart, b. preparing a plurality of consumable foam patterns of the type which is combustible substantially without residue on subjection to a molten casting charge, each said pattern being provided with a plurality of foam ears extending generally away from said pattern to lay in one of said horizontal planes defined by the fingers of said frame, said patterns being joined together by a consumable sprue effective to be combusted without residue by said molten charge for defining a channel to feed said patterns, c. filling said flask with a body of dry, loose unbonded sand, said sand being iNtroduced to said flask by means effective to fluidly locate said sand progressively from the bottom upwardly through said flask, d. pouring molten metal into said consumable sprue and pattern for combusting said foam material to occupy the void left by said foam, e. stripping said patterns from said frame and fingers and from said sand, and then breaking off said cast ears from said casting, and f. re-installing said frame in a stripped flask and repeating steps b through e.