US3707029A

US3707029A - Superimposed modular construction of vaporizable patterns

Info

Publication number: US3707029A
Application number: US75538A
Authority: US
Inventors: John T Parsons
Original assignee: Individual
Current assignee: HIGH PERFORMANCE MACHINE Inc A CORP OF MI
Priority date: 1970-09-25
Filing date: 1970-09-25
Publication date: 1972-12-26
Anticipated expiration: 1989-12-26
Also published as: CA941131A

Abstract

Vaporizable patterns of substantial depth and/or complexity are carved in modules by tape-controlled milling machines. The modules have abutting edge surfaces into which oversize bisymmetrical dovetail splines of the same material are inserted. A standard depth for the modules is the working length of rotating cutter tools. The partial elasticity of the material makes assembly possible and gives the joint bend resistance to exclude foundry sand.

Description

United States Patent Parsons [451 Dec. 26, 1972 [54] SUPERIMPOSED MODULAR CONSTRUCTION OF VAPORIZABLE PATTERNS [72] Inventor: John T. Parsons, 205 Wellington,

Traverse City, Mich. 49684 22 Filed: Sept. 25, 1970 211 App]. No.: 75,538

Related U.S. Application pm [63] Continuation-in-part of Ser. Nos, 867,980, Oct. 20, 1969, Pat. No. 3,635,124, and Ser. No. 874,930,

Nov. 7, 1969, Pat. NO. 3,625,280.

[52] US. Cl. ..29/407, 29/451, 29/525,

[51] Int. Cl. ....B23q 17/00, 823p 11/02, 1323p 19/02 [58] Field of Search ..29/406, 446, 164, 407, 451,

[56] References Cited UNITED STATES PATENTS 7 1,814,678 7/1931 Ferguson ..29/446 3,172,932 3/1965 Heyden' ..29/446 3,269,424 8/1966 Fisher ..29/446 Primary Examiner-Thomas H. Eager Attorney-Jerome A. Gross 571 ABSTRACT Vaporizable patterns of substantial depth and/or complexity are carved in modules by tape-controlled milling machines. The modules have abutting edge surfaces into which oversize bi-symmetrical dovetail splines of the same material are inserted. A standard depth for the modules is the working length of rotating cutter tools. The partial elasticity of the material makes assembly possible and gives the joint bend resistance to exclude foundry sand.

6 Claims, 4 Drawing Figures SUPERIMPOSED MODULAR CONSTRUCTION OF VAPORIZABLE PATTERNS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending applications entitled Use of Tape-Controlled Milling Machines to Carve Combustible Casting Patterns, Ser. No. 867,980, filed Oct. 20, 1969, Pat. No. 3,635,124, and Self-Aligned Multi-part Combustible Casting Pattern and Method of Making Same, Ser. No. 874,930, filed Nov. 7, 1969, U.S. Pat. No. 3,625,280; and to the extent of the disclosure of common subject matter, priority is claimed as of the filing dates of said applications.

BACKGROUND OF THE INVENTION This invention relates to methods of forming vaporizable patterns by machine carving, especially using programmed machine tools. It is particularly applicable to making patterns whose total depth exceeds the working length of rotating cutters available for machining, and to constructing hollow patterns which could not be machined in a single piece.

vaporizable patterns have been used in foundries for the formation of metal castings for a number of years. In one conventional practice, shown in US. Pat. to Shroyer, No. 2,830,343, foundry sand is packed about such patterns and about a pouring gate leading thereto and the molten metal is cast without removing the pattern. The heat of the metal vaporizes the pattern material as the 'molten metal descends from the gate to and through the pattern form, replacing the pattern material with metal.

Conventionally such patterns are formed by building up segments cut from blocks or slabs of low density polystyrene, using procedures similar to those used in the making of wood patterns. The several pieces are assembled usually by gluing, and fillets of wax are wiped into the joints. This method of assembly is disadvantageous, especially when the pattern is hollow and box-like. The glued joint may separate under the forces of packing sand, either failing completely or admitting sand particles into the joint. Further, since glue and wax do not vaporize completely at the same low temperature as the polystyrene, these too may form inclusions in the casting.

The general purpose of the present invention is to provide a method of assembling modules of machinecarved vaporizable patterns. Other purposes include machine carving of combustible patterns of greater depth and complexity than would otherwise be feasible. Further purposes will beapparent from the detailed disclosure hereof.

SUMMARY OF THE INVENTION The present invention is advantageously used in carving and assembling those vaporizable patterns whose depth exceeds the available working length of rotating cutters of a machine tool, and also those whose complex form makes necessary their carving in modules. In the preferred form of invention, I first establish a standard depth to whichmodules of the pattern may be carved, which depth is no greater than the working length of the rotating cutters. I divide the overall form of the pattern into a plurality of modules whose depth equals or is no greater than this standard depth. Using square cut slabs of expanded vaporizable material whose depth equals this standard depth, inserted into the machine tool so that the cutter axis will be aligned in the direction of the depth, I carve each module, and provide square cut mating surfaces. I then machine undercut grooves in the mating surfaces, in alignment with corresponding grooves vof adjacent modules. After masking the mating surfaces including the grooves, I spray the exposed surfaces with a ceramic material. Then removing the masking, I press fit, into I BRIEF DESCRIPTION OF THE DRAWINGS I FIG. 1 is a fragmentary perspective view showing the carving of a lower module of a multi-part vaporizable pattern according to the method of the present invention.

FIG. 2 is an exploded perspective view showing steps in the assembly of the lower pattern module of FIG. 1,

an intermediate module, and an upper module similarly carved.

FIG. 3 is an enlarged fragmentary view taken along line 3-3 of FIG. 2, also showing a groove cutter removed upwardly.

FIG. 4 isan enlarged fragmentary sectional view taken along line 4-4 of FIG. 2 and showing a typical section of a pattern wall joint, in which the dashed lines show a grooved lower wall of the intermediate module of FIG. 2 when assembly is completed.

DESCRIPTION OF THE PREFERRED EMBODIMENT In this embodiment, I illustrate and describe procedures for carving a polystyrene pattern whose total depth is three times the standardized depth d of large carving cutters of a milling machine, such as the rotatable cutter generally designated b. To achieve a pattern of this total depth requires three modules of depth d; these include a lower module generally designated 10, an intermediate module generally designated 11 and an upp r module generally designated 12. As shown in FIG. 2, the depth of each module equals the depth d of the cutter b. Each of the modules 10, l1 and 12 is carved from a square cut slab of vaporizable pattern material, preferably expanded polystyrene whose density is in a range between 1 and 1% pounds per square foot. Such material is partially elastic and hence well adapted for assembly in the manner hereinafter set forth. Use of slabs whose upper and lower surfaces are square cut to define the precise depth d simplifies carving and assures precise abutting fit on assembly of the modules.

In carrying out the present process the first step is to carve the

individual modules

10, 11 and 12. Only the right end of each module is illustrated. Using the rotating milling cutter b, the entire outer surface 14 of the lower module is carved to desired contour around its entire periphery, preferably using a tape controlled milling machine in the manner taught by my said copending application Ser. No. 867,980, US. Pat. No. 3,635,124 entitled Use of Tape Controlled Milling Machines to Carve Combustible Casting Patterns; and its entire inner surface 15, including the fillets and cutout illustrated, is carved by the same procedure. Similarly the entire outer surfaces 16 and inner surfaces 17 of the intermediate module 11 are carved, the milling machine being so programmed as to bring about precise alignment of its vertical wall portions with those of the lower module 10. Likewise the upper module 12 is carved to provide vertical walls with aligned outer surfaces 18 and inner surfaces 19, as well as an inner top wall 20. I

Where the total pattern depth is not an even multiple of the standard depth d of the rotating cutters b, programming of the milling machine may be facilitated by utilizing such standard depth for all but one of the pattern modules, but this may not be feasible, for example, where internal portions of the pattern are so complex as to require carving in separate pieces of lesser depth. In this event, their upper and lower wall edge surfaces will be square cut horizontally.

On assembly the adjacent square cut edge surfaces of the

pattern modules

10, 11 and 12 are to abut and mate. Thus, the top edge surface 21 of the lower module 10 will be presented abuttingly against the lower edge 22 of the intermediate module 11, and its upper edge 23 will similarly abut the lower edge surface 24 of the upper module 12.

In order to complete each module and mate these abutting surfaces, aligned grooves are cut into them. Three such grooves, each generally designated 25, are shown in FIG. 1 cut into the upper surface 23 of the lower module 10. A groove cutterf, shown in'FlG. 3, has radial cutting blades g which are flat along their undersurfaces taper narrowingly upwards. To cut .the grooves 25 the cutter f is forced downwardly,-as it rotates, ata point between the ends of the desired length k of the groove, forming a cylindrical groove portion 26, shown in cross-section in FIG. 3, whose diameter equals that of the greatest diameter of the tapering cutter f. The cutter is then moved longitudinally in both directions within the wall in which the groove is to be cut, forming an undercut groove or dovetail 25 whose bottom surface 27 is equal in width to the greatest diameter of the cutter f and whose walls taper inwardly, according to the conformation of the cutter blades g, to a lesser top groove width 28.

By the length k of the groove 25 is meant the length due to longitudinal, movement of the shaft of the cutter f, without taking account of semi-circular rounded end portions 29 which are unavoidably left, due to the radius of the cutter f.

, The undercut grooves 25 in the mating surface 21 of the lower module 10 may be located at positions convenient for joining, taking into consideration wall thickness available in the module 10 and in the undersurface of mating portions of the intermediate module 1 l, in which similar grooves 30 are cut in precise alignment. Likewise, similar undercut grooves generally designated 31 are cut in the upper mating surface 23 of the intermediate module 1 l, and corresponding aligned grooves 32 are cut in the lower mating surface 24 of the upper module 12, all as shown in FIG. 2.

In the use of expanded polystyrene patterns in sand molds, it is conventional to spray coat their outer surfaces with a ceramic coating. With any modular construction of patterns, a problem is presented how to exclude such coating from the mating surfaces 21, 22, 23, and 24 or in the

grooves

25, 30, 32; ceramic material in these places would form inclusions in the casting when the pattern material was vaporized by molten metal.

With the present construction, this problem is readily solved. Ordinary masking tape 34 is utilized to cover these surfaces and the grooves therein, prior to spraying such ceramic coating. Once spray coated, the masking tape 34 is peeled off, as shown in F IG. 2.

Assembly splines generally designated 35 shown in FIGS. 2 and 4, previously formed and cut to the length k, are then press fitted into the grooves 25 in one of each pair of mating surfaces; F IG. 2 shows two of them in the grooves 25 of the surface 21 of the lower module 10. The assembly splines 35 are formed of the same partially elastic low density vaporizable material as the

pattern modules

10, 11 and 12. They may be formed initially as a long strip of double dovetailed cross-section, as seen in the explodedperspective FIG. 2, and then cut to the length k. Considering the cross-section, its width at its mid-height corresponds generally to the top groove width 28; it tapers to broader top and bottom edges whose width may substantially equal the bottom width 27 of a groove 25. The partial elasticity of the material permits press fitting the splines 35 into the grooves 25 without maintaining precise tolerances.

' Since the preferred expanded polystyrene plastic material is also subject to partial permanent set when compressed, this may be compensated for by using splines 35 which are slightly oversize and whose top and bottom edges may be rounded to facilitate press fitting. 7

Patterns made in modules and assembled in accordance with the present invention must have adequate strength and bend resistance as to assure against the entrance of sand particles into the joints when foundry sand is packed against them. Where the pattern walls are relatively slender compared with their height, it may be necessary to provide long continuous grooves 25 and splines 35 therein to lock the mating wall portions together over the entire lengths of the mating surfaces. In the present invention this'offers no difficulty; strips of spline material are cut to whatever length the grooves k have been carved.

Several advantages of the present construction are worthy of special mention. The

modules

10, 11 and 12, being of a standard depth or less, are readily handled during shipment to the foundry. Prior to shipment, they may be masked and sprayed; as the ceramic coating hardens, it strengthens the vaporizable material. Then,

after shipment to the foundry, the masking is removed and the spline insertion and assembly operations may be performed. In contrast to the possible alternative of assembly of pattern modules by tongue and groove construction, there are here no projecting tongue portions which might break in handling and would be difficult to mask off prior to spraying. These advantages make the present construction uniquely valuable wherever patterns are made in modules and assembled at the foundry. I

In case of patterns which, like the pattern as illustrated, are deep, box-like, or both, the sand may bev packed about the lower module before its masking tape 34 is removed; and the spline insertion and assembly may thus progress one module at a time, as the sand is packed, successively about each. This permits the construction, integrally, of castings which might not be easily made by any prior known process.

In certain patterns, the location of hubs bosses and other complicating features may require zig-zag or irregular mating surfaces of portions of the modules. Carving the pattern form by first dividing it into irregular modules whose boundaries permit the machine carving of such bosses and hubs, and then assembling the pattern as taught herein, permits casting complex forms to substantially final configuration, so that only a minimum of subsequent machining is required.

I claim:

I. A method of constructing multi-part vaporizable patterns, consisting of the steps of carving from vaporizable partially elastic pattern material a first and a second pattern module with mating surfaces adapted to abut each other,

cutting in the mating surfaces of each module a lengthwise under-cut groove spaced to align with a corresponding groove in the mating surface of the other module,

press fitting, into the groove of one module, one half of an oversize bi-symmetrical spline of the same material and having such form as will engage within the undercut of said groove,

press fitting the groove of the other pattern module over the other half of the dovetail spline projecting from said mating surface,

whereby the partial elasticity of the material will hold the mating surfaces in abutment in a sealed bendresistantjoint.

2. A method of constructing hollow patterns for castings, consisting of the steps of v carving out the interior portion of a solid slab of vaporizable pattern material to leave an outer wall terminating in a square cut mating surface, thereby to provide a first pattern module,

carving from the same material a second pattern module including an aligned wall terminating in a square cut mating surface adapted to abut the mating surface of the first module,

cutting in the mating surfaces of each module an undercut groove spaced to align with a corresponding groove in the mating surface of the other module, and

press fitting, into the groove of one module, one

dovetail side of an oversize bi-symmetrical spline of the same material,

whereby the partial elasticity of the material will hold the mating surfaces in a sealed bend-resistant joint.

3. A method of machine carving and assembling vaporizable patterns whose depth exceeds the available working length of rotating cutters of a machine tool, comprising the steps of I establishing a standard depth to which modules of such pattern may be carved, which depth is no greater than such working length of the rotating cutters,

dividing the overall form of the pattern into a plurality of modules whose depth equals or is no greater than said standard depth, carving square cut slabs of expanded, partially elastic, vaporizable pattern material of such standard depth to form such pattern modules by rotating such cutters on axes aligned in the direction of said depth, and providing square cut mating surfaces on adjacent modules, machining undercut grooves in said mating surfaces in alignment with the corresponding grooves in the mating surfaces of adjacent modules, press fitting, into the grooves in one module, one dovetail side of an oversize bi-symmetrical spline of the same partially elastic material, and press fitting the groove-of a second module elastically over said other dovetail side of the spline, whereby the partial elasticity of the material will hold the mating surfaces in a sealed bend-resistant joint. 4. The method as defined in claim 3, together with the intermediate steps, performed after carving the modules and machining their grooves, of masking said grooved mating surfaces, spraying a ceramic coating on the unmasked surfaces, and then removing the masking, all prior to the defined press fitting steps. 5. A method of machine carving and assembling vaporizable patterns whose depth exceeds the available working length of rotating cutters of a machine tool, comprising the steps of establishing a standard depth to which modules of such pattern may be carved, which depth is no greater than such working length of the rotating cutters, dividing the overall form of the pattern into a plurality of modules whose depth equals or is no greater than said standard depth, carving square cut slabs of expanded, partially elastic, vaporizable polystyrene pattern material of such standard depth to form'such pattern modules by rotating such cutters on axes aligned in the direction of said depth, and providing square cut mating surfaces on the modules to be mated to eachother, machining grooves in said mating surfaces in alignment with the corresponding grooves in the mating surfaces of the adjacent modules, masking said grooved mating surfaces, applying a pattern coating onto the pattern modules about the surface portions so masked, removing the masking, press fitting, into the grooves in one module, one half of an oversize bi-symmetrical spline of the same partially elastic material, and press fitting thegroove of a second module elastically onto said other half of the spline until the mating surfaces abut each other, whereby the uncoated mating surfaces will be held sealed in a bend-resistant joint. 6. A method of machine carving and assembling vaporizable patterns comprising the steps of dividing the overall form of the pattern into a plurality of modules,

removing the masking, press fitting, into the groovesin one module, one portion of an oversize spline of the same partially elastic material, and press fitting the groove of a second module elastically onto said other half of the spline until the mating surfaces abut each other, whereby the uncoated mating surfaces will be held sealed in a bend-resistant joint.

* 10K IIK

Claims

1. A method of constructing multi-part vaporizable patterns, consisting of the steps of carving from vaporizable partially elastic pattern material a first and a second pattern module with mating surfaces adapted to abut each other, cutting in the mating surfaces of each module a lengthwise under-cut groove spaced to align with a corresponding groove in the mating surface of the other module, press fitting, into the groove of one module, one half of an oversize bi-symmetrical spline of the same material and having such form as will engage within the undercut of said groove, press fitting the groove of the other pattern module over the other half of tHe dovetail spline projecting from said mating surface, whereby the partial elasticity of the material will hold the mating surfaces in abutment in a sealed bend-resistant joint.

2. A method of constructing hollow patterns for castings, consisting of the steps of carving out the interior portion of a solid slab of vaporizable pattern material to leave an outer wall terminating in a square cut mating surface, thereby to provide a first pattern module, carving from the same material a second pattern module including an aligned wall terminating in a square cut mating surface adapted to abut the mating surface of the first module, cutting in the mating surfaces of each module an undercut groove spaced to align with a corresponding groove in the mating surface of the other module, and press fitting, into the groove of one module, one dovetail side of an oversize bi-symmetrical spline of the same material, whereby the partial elasticity of the material will hold the mating surfaces in a sealed bend-resistant joint.

3. A method of machine carving and assembling vaporizable patterns whose depth exceeds the available working length of rotating cutters of a machine tool, comprising the steps of establishing a standard depth to which modules of such pattern may be carved, which depth is no greater than such working length of the rotating cutters, dividing the overall form of the pattern into a plurality of modules whose depth equals or is no greater than said standard depth, carving square cut slabs of expanded, partially elastic, vaporizable pattern material of such standard depth to form such pattern modules by rotating such cutters on axes aligned in the direction of said depth, and providing square cut mating surfaces on adjacent modules, machining undercut grooves in said mating surfaces in alignment with the corresponding grooves in the mating surfaces of adjacent modules, press fitting, into the grooves in one module, one dovetail side of an oversize bi-symmetrical spline of the same partially elastic material, and press fitting the groove of a second module elastically over said other dovetail side of the spline, whereby the partial elasticity of the material will hold the mating surfaces in a sealed bend-resistant joint.

4. The method as defined in claim 3, together with the intermediate steps, performed after carving the modules and machining their grooves, of masking said grooved mating surfaces, spraying a ceramic coating on the unmasked surfaces, and then removing the masking, all prior to the defined press fitting steps.

5. A method of machine carving and assembling vaporizable patterns whose depth exceeds the available working length of rotating cutters of a machine tool, comprising the steps of establishing a standard depth to which modules of such pattern may be carved, which depth is no greater than such working length of the rotating cutters, dividing the overall form of the pattern into a plurality of modules whose depth equals or is no greater than said standard depth, carving square cut slabs of expanded, partially elastic, vaporizable polystyrene pattern material of such standard depth to form such pattern modules by rotating such cutters on axes aligned in the direction of said depth, and providing square cut mating surfaces on the modules to be mated to each other, machining grooves in said mating surfaces in alignment with the corresponding grooves in the mating surfaces of the adjacent modules, masking said grooved mating surfaces, applying a pattern coating onto the pattern modules about the surface portions so masked, removing the masking, press fitting, into the grooves in one module, one half of an oversize bi-symmetrical spline of the same partially elastic material, and press fitting the groove of a second module elastically onto said other half of the spline until the mating surfaces abut each other, whereby the Uncoated mating surfaces will be held sealed in a bend-resistant joint.

6. A method of machine carving and assembling vaporizable patterns comprising the steps of dividing the overall form of the pattern into a plurality of modules, carving expanded, partially elastic, vaporizable polystyrene pattern material to form such pattern modules, and providing square cut mating surfaces on the modules, to be mated to each other, machining grooves in said mating surfaces in alignment with the corresponding grooves in the mating surfaces of the adjacent modules, masking said grooved mating surfaces, applying a pattern coating onto the pattern modules about the surface portions so masked, removing the masking, press fitting, into the grooves in one module, one portion of an oversize spline of the same partially elastic material, and press fitting the groove of a second module elastically onto said other half of the spline until the mating surfaces abut each other, whereby the uncoated mating surfaces will be held sealed in a bend-resistant joint.