US3065511A

US3065511A - Method of making a pattern for a die

Info

Publication number: US3065511A
Application number: US853049A
Authority: US
Inventors: Ammon M Leitzel
Original assignee: Pacific Pulp Molding Co
Current assignee: Pacific Pulp Molding Co
Priority date: 1959-11-16
Filing date: 1959-11-16
Publication date: 1962-11-27
Anticipated expiration: 1979-11-27

Description

INVENTOR.

2 Sheets-Sheet 1 A. M. LEITZEL METHOD OF MAKING A PATTERN FOR A DIE AMMO/V /l LE/TZEL Fig. 2-

Buc/r/vom, Chew/70m 8 B/ore Nov. 27, 1962 Filed NOV. 16, 1959 Fig. 3

ATTORNEYS Nov. 27, 1962 A. M. LEITZEL 3,065,511

METHOD OF MAKING A PATTERN FOR A DIE Filed Nov. 16, 1959 2 Sheets-Sheet 2 l t I ,0 9a INVENTOR.

AMMa/v M LE/TZEL 1 BY i Buck/70m, Chea/ham 8 Elana A T TORNE YS "formed in 'a mold drag.

United States Patent Ofilice 3365511 Patented Nov. 27, 1962 3,665,511 METHOD OF MAKING A PATTERN FQR A DEE Ammon M. Leitzel, Portland, Greg, assignor to Pacific Pulp Molding (30., Portland, Greg, a corporation of Washington Filed Nov. 16, N59, Ser. No. 853,049 Claims. (Cl. 22-195) This invention relates to a method of making cast metal mating die members and more particularly to a method of making patterns for casting such die members.

The method of the present invention has particular utility in making suction die members and mating compression die members employed in suction die pulp molding operations. Both of such die members, in general, have contoured die surfaces. The contoured surface of the suction die member is during use covered with one or more thicknesses of woven wire screen also contoured to fit such surface and the die surface of the mating compression die member is correspondingly contoured to provide room between such members for the screens and also for a layer of pulp of desired thickness. Such layer of pulp is formed upon the outer surface of the screens by dipping the suction die member into a slurry of pulp and applying a vacuum through a plurality of suction apertures through the suction die member. The layer of pulp is thereafter compressed between the suction die member and the compression die member.

In accordance with the present invention, a pattern for one of the die members having a contoured die surface is first formed and then a sheet of thermoplastic material is heated and forced into contact with the contoured surface of the pattern. Such sheet has a thickness approximately equal to the desired distance between such die members when such members are used to compress a molded pulp article. The sheet is allowed to cool while in contact with the pattern and is then employed to form a pattern for the mating die member. For a mating die member which is to be operated at the same temperature as the one die member referred to above, the edges of such sheet are held against movement during cooling of the sheet so as to prevent shrinkage thereof. For a mating die member operated at a higher temperature than such one die member, the sheet can be allowed to shrink during cooling to compensate for expansion of such mating die due to heating to such higher temperature.

The present invention also includes a novel series of steps for casting the pattern for the one die member referred to above. By such series of steps, a complete pattern for such die member is produced from a simple basic pattern having a preferred contoured surface which is the reverse and of greater size than that of the contoured surface of the complete pattern. Such series of steps involves forming a mold core from such first pattern and then installing such core in the lower portion of a sand mold The upper portion of such sand mold is then formed in a mold cope by contact with such core. The core is thereafter modified and the upper portion of the mold spaced from the lower portion to provide a mold cavity for casting the complete pattern.

It is therefore an object of the present invention to provide an improved method of making cast mating die members.

Another object of the invention is to provide an improved method of making patterns for casting mating die members. a i

Another object of the invention is to provide a method of making a pattern for casting a die member having a contoured die surface mating with the contoured surface of a first die member, in which method a sheet of thermoplastic material is heated and formed to fit the contoured surface of such first die member and then employed to form a pattern for the die member having such mating contoured surface.

A further object of the invention is to provide a method of casting a pattern for a die member having a contoured surface in which method a basic pattern having a contoured surface is employed to form a mold core, and such mold core is employed to produce a contoured surface on a mold member, the core being thereafter modified to provide a modified mold cavity for casting a complete pattern for such die member.

Other objects and advantages of the present invention will appear in the following description thereof in connection with the attached drawing of which:

FIG. 1 is a cross section through a basic casting pattern having a contoured surface thereon;

FIG. 2 is a cross section through a core forming device showing how a mold core is formed from the pattern of FIG. 1;

FIG. 3 is a cross section through a sand mold showing the core of FIG. 2 mounted in the lower portion of a sand mold in a mold drag and an upper portion of a sand mold formed therefrom in a mold cope;

FIG. 4 is a view similar to FIG. 3, showing the core of H68. 2 and 3 after being modified and showing the upper portion of the mold spaced from the lower portion thereof to provide a mold cavity;

FIG. 5 is a cross section through a complete pattern for a suction die member, which pattern has been cast in the mold of FIG. 4;

FIG. 6 is a cross section through a vacuum device employing the pattern of FIG. 5 and showing a sheet of thermoplastic material which is to be formed on a surface of such pattern in preparation for making a pattern for a compression die;

FIG. 7 is a cross section through the pattern and thermoplastic sheet of FIG. 6 after such sheet has been formed on such pattern and also showing a device for casting a plaster pattern on such sheet;

FIG. 8 is a cross section through a device for forming a mold core on the plaster pattern of FIG. 7;

FIG. 9 is a cross section through a mold showing the core of FIG. 8 installed in the lower portion of a sand mold formed in a mold drag and showing a supplemental pattern member positioned in a mold cope;

FIG. 10 is a view similar to FIG. 9 showing the upper portion of a sand mold formed on the core and supple mental pattern member of FIG. 9 with such upper portion of the mold spaced from the lower portion of the mold to provide a mold cavity;

FIG. 11 is a cross section through a compression die member cast in the mold cavity of FIG. 10 after such die member has been machined and secured to a die support member;

FIG. 12 is a cross section through a suction die member cast directly from the pattern of FIG. 5 by conventional casting procedures after such die member has been machined and secured to a die support member;

FIG. 13 is a View similar to FIG. 6, showing a modified device;

FIG. 14 is a view similar to FIG. 7, showing a device in which a modified plaster pattern can be cast;

FIG. 15 shows acomplete plaster pattern for a modified compression die member;

FIG. 16 shows a modified compression die member cast from the pattern of FIG. 15 by conventional casting procedures; and

FIG. 17 shows a modified suction die member also cast directly from the pattern of FIG. 5 by conventional casting procedures after such die member has been macln'ned and secured to a die member support.

Referring more particularly to the drawing, a basic pattern 20 is shown in cross section in FIG. 1. Such patfor modifying the core 40 to form the core 40.

tern may be of wood or other suitable material and has a contoured surface 22. In the example selected, the surface 22 corresponds to the reverse of a desired contoured surface 24 of a pulp molding suction die member 26 shown in FIG. 12, except that the surface 22 of FIG. 1 is greater in size to provide for two successive shrinkages due to casting metal, such as aluminum, in sand molds. The surface 22 may be of substantial area and may, for example, be contoured in a manner providing for forming molded pulp trays of the type disclosed in my copending application Serial No. 746,817 filed Iuly 7, 1958. Thus the surface '22 may have a plurality of spaced dome shaped projections 28 corresponding to cup shaped pockets 30 in the die member 26 of FIG. 12. Such dome shaped projections of FIG. 1 are separated from each other by grooves 32 corresponding to ridges 34 of the die member of FIG. 12, the grooves 32 being laterally separated between laterally spaced dome shaped projections 28 of FIG. 1 by minor projections 36 extending between longitudinally spaced dome shaped projections 28.

As shown in FIG. 2, the pattern 20 may be placed in a suitable frame providing a wall 38 around the edges of such pattern. A sand core 45 may be formed in contact with the surface 22. Such sand core has a contoured surface 42 which is the reverse of the surface 22 and which corresponds to the desired surface '24 of the suction die of FIG. 12 except that it is greater in size. As shown in FIG. 3, the core 40 may be positioned in a sand mold formed in a drag 44 so as to have the surface 42 thereof at the parting line between the lower portion of a sand mold in the drag 44 and the upper portion of a sand mold in a cope 46. The upper portion of the sand mold is formed in the cope 46 in contact with the core 46 so as to have a contoured surface 22 thereon, which is the same as the surface 22 of the basic pattern 25.

As shown in FIG. 4, the core 45 of FIGS. 2 and 3 may be modifiedto provide va modified core 40' after the core 40 has been employed to form the surface 22 on the upper portion of the sand mold in the cope 46. For example, depressions 48 may be formed in the lowermost portions of the pockets in the surface 42 of FIGS. 2 and 3 to provide a modified contoured surface 42'. Such depressions 48 correspond to support posts 50 on the suction die 26 of FIG. 12. It will be apparent that the upper portion of the sand mold in the cope 46 must be removed from the lower portion of the mold in the drag 44 to provide access It will be further apparent that the core 41 of FIG. 3 can be modified by removing material from such core to form the depressions 48. When the upper portion of the mold in the cope 46 is replaced, it is held in vertically spaced position with respect to the lower portion of the mold in the drag 44 by a spacing frame providing walls 52 surrounding the edges of the core 40" to provide a mold space '54 in which a metal pattern 56 for a suction die member I end of the form shown in FIG. can be cast. The spacing frame 52 has a thickness providing a suitable thickness of the pattern 56 which will provide a desired thickness of the suction die member 26 of FIG. 12 to be cast in the mold casting.

-It will be apparent that known or suitable foundry procedures may be employed in the actual fabrication of the sand core 40 and the sand molds in the cope 46 and drag 44. It will also be apparent that the mold of FIG. 4 will be provided with suitable inlet ports for molten metal and vents for escape of air and gas in accordance with known or suitable foundry practice. A suitable metal for casting the pattern 56 is aluminum but other metals can be employed.

The pattern of FIG. 5 corresponds in all essential details to the suction molding die member 26 shown in FIG. 12, except that it is greater in size to provide for shrinkage during casting of such suction die member. That is to say, the pattern 56 of FIG. 5 has a contoured *surface158 which is the reverse of the contoured surface 22 of the pattern 20 of FIG. 1, except that it is smaller because of shrinkage during casting of the pattern 56. The suction die member 26 of FIG. 12 may be cast by any known or suitable foundry procedures employing the pattern 56 of FIG. 5. Shrinkage will also take place during such casting so that the pattern 22 of FIG. 1 must have a surface 22 which is sufiiciently greater in size than the surface 24 of the suction die member of FIG. 12 to provide for two separate shrinkages. The cast suction die member 26 is shown in FIG. 12 after it has been machined and secured to a die member support plate 59.

At least two patterns 56 such as shown in FIG. 5 will usually be cast. One will be employed as a pattern for casting suction die members such as the suction die member 26 of FIG. 12. The other will be modified by having suction apertures 60 and 62 drilled therein as shown in FIG. 6 to provide a modified pattern 64 employed in the process of making a mold for a compression die member. Such modified pattern 64 may be mounted so as to form the top wall of a vacuum chamber 66. A sheet 68 of thermoplastic material having its edges secured in a supporting frame 70 is warmed to a softening temperature in any suitable manner, for example, in an oven or by being exposed to infra red lamps, and then is placed in contact with the contoured surface 58 of the modified pattern 64. A vacuum is then produced in the chamber 66 by withdrawing air through a vacuum connection 72. The heated thermoplastic sheet is pulled into intimate contact with the surface 58 and is allowed to cool in contact therewith while the vacuum is maintained in the chamber 66. The

pattern 64 has right angular edges at 74 and the frame 68 is depressed around the chamber so that the edges of the sheet are hooked over the edges 74. This prevents shrinkage of the sheet during cooling to provide a formed sheet 68' shown in FIG. 7 after the sheet has been cut from the frame 70. This procedure is employed in casing a compression die member which will be employed at the same temperature as the suction die member 26 of FIG. 12.

The sheet 68 is selected to have a thickness which corresponds to the desired distance or space between the suction and'compression die members when such die members are employed to compress a formed layer of pulp. Such distance must be suflicient to accommodate the wire screens conventionally employed to cover the suction die member of the mating dies in such an operation as well as the layer of pulp on such screens. Such screens may be of the general type shown in my copending application Serial No. 832,790 filed August 10, 1959.

The contoured surface 76 of the sheet 68' of FIG. 7 thus corresponds to the desired contoured surface 78 of a compression die member, such as the compression die member 80 of FIG. 11, except for being greater in size to provide for shrinkage during casting of the die memher 80. Since the material of the sheet 68 stretches thinner at the positions of greatest stretching, small shims 82 of foraminous material may be employed in the pockets provided by the contouredsurface 58 of the pattern 64 of FIG. 6 so as to compensate for such thinning of the sheet of material.

As shown in FIG. 7, the pattern 64 and sheet 68' supported thereon may be employed to make a plaster pattern 84 by employing a frame providing a wall 86 and casting such plaster pattern in contact with the sheet 68'. As shown in FIG. 8, such plaster pattern 84 may then be employed to make a sand core 88 in a manner similar to that described with reference to FIG. 2, such core having a contoured surface 90. The sand core 88, as indicated in FIG. 9, may be positioned in the lower portion of a sand mold in a drag 92 with its contoured surface at the upper surface of the lower mold portion. In the example selected a supplemental pattern 94 in the form of a rectangular flanged rim member is positioned above the core 88 and the upper portion of a sand mold formed in a cope 95 in contact with such pattern and the core 88. The only purpose of supplemental pattern 94 is to cast a flange on the compression die member which is to be cast in the mold. Such flange is used in holding the die member during machining andis removed in the latter stages of such machining.

The final mold is shown in FIG. after the upper portion of the mold has been formed and the supplemental pattern 94 removed. Also the upper portion of the mold has been supported in spaced relation above the lower portion of the mold in the drag 92 by a spacer ring 96 surrounding the edges of the core 88 so as to provide a mold cavity 98. A compression die member of a suitable metal such as aluminum can be cast in the resulting mold and it will be understood that the mold will be provided with suitable inlet ports and vents.

The resulting cast compression die member 80 is shown in FIG. 11 after it has been machined and secured to a die member support 100. Such compression die has a contoured surface 102 which is the reverse of the contoured surface 24 of the suction die member of FIG. 12 and is of a shape such that for one relative position of the two die members when such die members are at the same temperature, the contoured surfaces thereof are spaced from each other in directions measured perpendicularly to the contoured surfaces a constant distance equal to the combined thicknesses of woven wire screens covering the contoured surface 24 of the suction die member 26 and of a layer of pulp upon such screens.

In use the suction die member 26 will form one wall of a vacuum and pressure chamber and will have a large number of small holes (not shown) drilled therethrough so that a vacuum can be employed to produce such layer of pulp and so that air pressure can be employed to assist in removing a resulting molded pulp article from the suction die member. Similarly, the compression die member 80 will form a wall of another similar chamber and will have a lesser number of small holes drilled therethrough to enable a vacuum to be employed to assist in removing such molded pulp article from the suction die member and to enable air pressure to be employed to discharge the molded pulp article from the compression die member. The compression die member 80 is employed to compress the layer of pulp upon the screens on the suction die member 26 to form the molded pulp article and such compression operation is carried out while both die members are at very nearly the same temperature.

An alternative procedure may be employed in making a compression die member which is used to compress a layer of pulp while the compression die member is at a temperature substantially above the temperature of the cooperating suction die. Another sheet 104 of thermoplastic material is shown in FIG. 13 as having its edges secured in a frame 70. Such sheet is heated and positioned upon a modified pattern 64 which may be the same as the pattern 64 of FIG. 6. Such pattern 64 forms the upper wall of a vacuum chamber 106 which may be the same as the vacuum chamber 66 of FIG. 6, except that its edge walls 108 are thicker and extend up around 'the edges of the pattern 64 and are provided with inclined surfaces 110 which mask the corners 74 of the pattern. As described with reference to FIG. 6, a vacuum is produced in the chamber 106 by withdrawing air through the pipe 72 to draw the sheet 104 into intimate contact with the contoured surface 58.

Instead of hooking the sheet 104 over the corners of the pattern, the sheet is cut from the frame 70 and allowed to shrink during cooling while held on the pattern 'by the vacuum. The inclined surfaces 110 enable such shrinkage. The resulting formed and cooled sheet 104' is removed from the pattern 64 and as shown in FIG. 14, is placed on a support 112 and employed to cast a plaster pattern 114 employing a frame providing a surrounding wall 86 in the same manner as the plaster pattern 84 of FIG. 7 is cast.

The resulting plaster pattern 114 may be positioned within a supplemental pattern 116 to provide a complete pattern, such as shown in FIG. 15, for a compression die member. A metal compression die member 118 shown in FIG. 16 may then be cast by employing the pattern of FIG. 15 in any known or suitable foundry procedure. The die member 118 may be employed with another suction die member 26 shown in FIG. 17, which sucton die member may be the same as the suction die member 26 of FIG. 12. and may have a contoured surface 24. The compression die member 118 of FIG. 16 may also have a contoured surface 120 which, when the die member 118 is heated, is the reverse of and corresponds to the contoured surface 24- of the suction die member 26 in the same manner that the contoured surface 10-2 of the compression die member of FIG. 11 corresponds to the contoured surface 24. That is to say, the shrinkage of the sheet 104 of thermoplastic material of FIGS. 13 and 14 compensates for the expansion of the compression die member when such die member is heated, and the result is that the contoured surface of the die member 118 when such die member is heated is substantially identical with the contoured surface 102 of the compression die member 80 of FIG. 11 when the die member 80 is at approximately room temperature.

As a specific example sheets of polystyrene .125 inch thick have been found suitable for both the

sheets

68 and 104 of FIGS. 6 and 13, respectively. Such sheets provide the correct spacing between the suction and compression die members and have the correct shrinkage for compensating for the heating of a compression die member 118 of FIG. 16 made of brass to a temperature of approximately 700 F. Other metals may be employed for the heated compression die and, in general, sheets of other thermoplastic materials having approximately the correct shrinkage can be found for making a pattern for casting such die member.

It will be apparent that the contoured surfaces of the various die members may be varied in shape, for example, the number and size of the pockets 30 on the suction die members 26 and the corresponding projections on the compression die members 80 and 120 of FIGS. 11 and 16, respectively, may likewise be varied. For die members having the same overall lateral and longitudinal dimensions, the same supplemental patterns 94 and 116 of FIGS. 9 and 15, respectively, may be employed with a plurality of different types of cores 88 or plaster patterns 114.

I claim:

1. The method of making a second pattern having a contoured surface from a first pattern having a contoured surface to provide for casting first and second die members having contoured die surfaces, mating in substantially constant spaced relationship With each other, which method comprises, heating to a softening temperature a sheet of thermoplastic material having a thickness approximately equal to the desired space between said surfaces of said die members, positioning the resulting heated sheet over said surface of said first pattern while subjecting the opposite surfaces of said sheet to a fluid pressure differential forcing one surface of said sheet against said surface of said first pattern, cooling said sheet while on said surface of said first pattern to provide a formed sheet having its other surface corresponding to the desired contoured die surface of said second die member except for any shrinkage in casting said second die member, and forming said second pattern from said other surface of said formed sheet.

2. The method of making a second pattern having a contoured surface from a first pattern having a contoured surface to provide for casting first and second die members having contoured die surfaces mating in substantially constant spaced relationship with each other when said die members are at the same temperature, which method comprises, heating to a softening temperature a sheet of thermoplastic material having a thickness approximately equal to the desired space between said surfaces of said die members, positioning the resulting heated sheet over said surface of said first pattern while subjecting the opposite surfaces of said sheet to a fluid pressure difierential forcing one surface of said sheet against said surface of said first pattern, cooling said sheet while on said surface of said first' pattern, holding the edges of said sheet during said cooling to provide a formed sheet having its other surface corresponding to the desired contoured die surface of said second die member except for any shrinkage in casting said second die member, and forming said second pattern from said other surface of said formed sheet.

3. The method of making a second pattern having a contoured surface from a first pattern having a contoured surface to provide for casting first and second die members having contoured die surfaces mating in substantially constant spaced relationship with each other when said second die member is at an elevated temperature relative to said first die member, which method comprises, heating to a softening temperature a sheet of thermoplastic material having a thickness approximately equal to the desired space between said surfaces of said die members, positioning the resulting heated sheet over said surface of said first pattern while subjecting the opposite surfaces of said sheet to a fluid pressure differential forcing one surface of said sheet against said surface of said first pattern, cooling said sheet while on said surface of said first pattern, releasing the edges of said sheet to enable shrinkage of said sheet to provide a formed sheet having its other surface corresponding to the desired contoured die surface of said second die member except for any shrinkage in casting said second die member, and forming said second pattern from said other surface of said formed sheet.

4. The method of making first and second cast die members having contoured die surfaces mating in substantially constant spaced relationship with each other, which method comprises, making said first member by forming a pattern having a contoured surface corresponding to the desired contoured surface of said first member and of a size providing for shrinkage during casting of said first member, making a mold for said first member from said pattern, casting said first member in said mold, and making said second member by heating to a softening temperature a sheet of thermoplastic material having a thickness approximately equal to the desired space between the mating contoured surfaces of said members, positioning the resulting heated sheet over said contoured surface of said pattern While subjecting the opposite surfaces of said sheet to a fluid pressure differential forcing one surface of said sheet against said contoured surface of said pattern, cooling said sheet while on the last mentioned surface to provide a formed sheet having its other surface corresponding to the desired contoured surface of said second member except for any shrinkage in casting said second die member, forming a second pattern from said other surface of said sheet, making a second mold for said second member from said second pattern, and casting said second member in said second mold.

5. The method of making first and second cast die members having contoured die surfaces mating in substantially constant spaced relationship with each other when said die members are at the same temperature, which method comprises, making said first member by forming a pattern having a contoured surface corresponding to the desired surface of said first member and of a size providing for shrinkage during casting of said one member, making a mold for said first member from said pattern, casting said first member in said mold, and making said second member by heating to a softening temperature a sheet of thermoplastic material having a thickness approximately equal to the desired distance between the contoured surfaces of said members, positioning the resulting heated sheetinover saidv contoured surface of said pattern while subjecting the opposite surfaces of said sheet to a fluid pressure. differential forcing one surface of said sheet against said contoured surface of said pattern, cooling said sheet While on the last mentioned surface, holding the edges of said sheet during said cooling to prevent shrinkage thereof toprovide a formed sheet having its other surface corresponding to the desired contoured surface-of said second member except for any shrinkage in casting said second die member, forming a second pattern from said other surface of said sheet, making a second mold for said second member from said second pattern, and casting said second member in said second mold.

6. The method of making first and second cast die members having contoured die surfaces mating with each other in substantially constant spaced relationship when one of said members is at an elevated temperature relative to the other, which method comprises, making said first member by forming a pattern having a contoured surface corresponding to the desired surface of said first member and of a siZe providing for shrinkage during casting of said first member, making a mold for said first member from said pattern, casting said first member in said mold, and making said second .memberby heating to a softening temperature a sheet of thermoplastic material having a thickness approximately equal to the desired distance between the contoured surfaces of said members, positioning the resulting heated sheet over said contoured surface of said pattern 'while subjecting the opposite surfaces of said sheet to a fluid pressure differential forcing one surface of said sheet against said contoured surface of said pattern, cooling said sheet while on the last mentioned surface to shrink said sheet and provide a formed sheet having its other surface corresponding to the desired contoured surface of said second member except for any shrinkage in casting said second die member, forming a second pattern from said other surface of said sheet, making a second mold for said second member'from said second pattern, and casting said second member in said second mold.

7. The method of making a pattern for casting a second die member having contoured die surface mating in substantially constant spaced relationship with a contoured surface on a first die member, which method comprises, heating to a softening temperature a sheet of thermoplastic material having a thickness approximately equal to the desired distance between the contoured surfaces of said die members, positioning the resulting heated sheet over the corresponding contoured surface of a pattern for said first die member while subjecting the opposite surfaces of said sheet to a fluid pressure differential forcing one surface of said sheet against said contoured surface of said pattern for said-first die member, securing the edges of said sheet to the edges of said first pattern to prevent shrinkage of said sheet and cooling said sheet while on the last mentioned surface to provide a formed sheet having its other surface corresponding to the desired contoured surface of said second die member except for any shrinkage in casting said second die member, and forming a pattern for said second die member from said other surface of said sheet.

8. The method of making a pattern for casting a second die member having contoured die surface mating in substantially constant spaced relationship with a contoured surface on a first die member, which method comprises, heating to a softening temperature a sheet of thermoplastic material having a thickness approximately equal to the desired distance between the contoured surfaces of said die members, stretching the resulting heated sheet over the corresponding contoured surface of a pattern for said first die member while subjecting the opposite surfaces of said sheet to a fluid pressure differential forcing one surface of said sheet against said contoured surface of said pattern for said first die member, cooling said sheet while on the last mentioned surface, releasing the edges of said sheet to enable said sheet to shrink during said cooling to provide a formed sheet having its other surface corresponding to the desired contoured surface of said second die member except for any shrinkage in casting said second die member, and forming a pattern for said second die member from said other surface of said sheet.

9. The method of making patterns for casting die members having contoured die surfaces mating in substantially constant spaced relationship with each other, which method comprises, making a pattern member having a contoured pattern surface which is the reverse of the contoured surface of one of said die members and of a size providing for a double shrink in subsequent casting operations, forming a mold core having the reverse of said pattern surface by contact with said pattern surface, positioning said core in a lower mold portion with said reverse pattern surface exposed, forming an upper mold portion in contact with said core, thereafter supporting said upper mold portion in spaced relation to said lower mold portion to provide a mold cavity, casting a first die member pattern having a contoured surface in said mold cavity, heating to a softening temperature a sheet of thermoplastic material having a thickness approximately equal to the desired distance between the contoured surfaces of said die members, positioning the resulting heated sheet over the said contoured surface of said first die member pattern, subjecting the opposite surfaces of said sheet to a fluid pressure differential forcing one surface of said sheet against said surface of said first die member pattern, cooling said sheet While on the last mentioned surface to provide a formed sheet having its other surface corresponding to the desired contoured surface of a second die member except for any shrinkage in casting said second die member, and forming a pattern for said second die member from said other surface of said sheet.

10. The method of making patterns for casting die members having contoured die surfaces mating in substantially constant spaced relationship with each other which comprises making a pattern member having a contoured pattern surface which is the reverse of the contoured surface of one of said die members and of a size providing for a double shrink in subsequent casting operations, forming a mold core having the reverse of said pattern surface by contact with said pattern surface, positioning said core in a lower mold portion with said reverse pattern surface exposed, forming an upper mold portion in contact with said core, removing said upper mold portion from said lower mold portion and removing material from said core to modify the exposed surface of said core to a desired shape, thereafter supporting said upper mold portion in spaced relation to said lower mold portion to provide a mold cavity, casting a first die member pattern in said mold cavity, heating to a softening temperature a sheet of thermoplastic material having a thickness approximately equal to the desired distance between the contoured surfaces of said die menibers, positioning the resulting heated sheet over the said contoured surface of said first die member pattern, subjecting the opposite surfaces of said sheet to a fluid pressure differential forcing one surface of said sheet against said surface of said first die member pattern, cooling said sheet while on the last mentioned surface to provide a formed sheet having its other surface corresponding to the desired contoured surface of a second die member except for any shrinkage in casting said second die member, and forming a pattern for said second die member from said other surface of said sheet.

References Cited in the file of this patent UNITED STATES PATENTS 1,480,644 Vogan Jan. 15, 1924 1,489,726 Wood Apr. 8, 1924 2,261,181 Rempel Nov. 4, 1941 2,348,086 Miller May 2, 1944 2,396,195 Pattison Mar. 5,1946 2,420,756 Miller May 20, 1947 2,694,227 Fordyce et al Nov. 16, 1954 2,706,309 Lampman Apr. 19, 1955 2,846,742 Wagner Aug. 12, 1958 OTHER REFERENCES British Plastics, vol. 31, No. 12, December 1958, pp. 518521.

Steel, February 11, 1957, pp. 108-409.

Modern Castings, May 1956, pp. 72-75.