US2729894A - Plastic die model and method of making same - Google Patents

Description

Jan. 10, 1956 H. v, ANDREWS 2,729,894

PLASTIC DIE MODEL. AND METHOD OF' MAKING SAME Filed Aug. 6, 1952 INVENTOR. HERBERT V. AND/ems United States Patent O PLASTIC DIE MODEL AND METHOD OF MAKING SAME Herbert V. Andrews, Wayne, Mich.

Application August 6, 1952, Serial No. 302,966

6 Claims. (Cl. 33-174) The present invention relates to a plastic die model and the method of making the same.

It is conventional practice to use an expensive grade of wood when forming die models for items such as automobile panels, doors and the like. There are many disadvantages in using wooden die models, but to date this has been the best method developed. Among the disadvantages of the wooden die models are the excessive Weight and the failure of the model to retain close dimensions. The failure to retain the desired dimensions is due to warping of the wood, and changing in the dimensions due to changes in atmospheric temperature and humidity.

Therefore, it is `a-principal object of the present invention to provide a die model which will retain close dimensions within extremely limited tolerances and which is light in weight.

It is another object of the present invention to provide such a die model which is sturdy in construction and which may be economically constructed.

It is a further object of the present invention to provide a method for forming a plastic die model which is simple and eilicient and involves a minimum number of positive steps.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

In the drawings:

Figure 1 is a top View of a rectangular die model using the construction of the present invention,

Figure 2 is an enlarged fragmentary View of a portion of the die model of Figure l showing the internal cell structure,

Figure 3 is an enlarged fragmentary section taken along the line 3-3 in the direction of the arrows, Figure 1 Figures 4 and 5 show alternate configurations of the cell structure which may be used in place of the hexagonal cells shown in Figs. 1-3,

Figure 6 is a perspective View of a plastic die model of an automobile door formed according to the present invention with the contour templates in position, and

Figure 7 is a perspective view of the initial set up of the cell structure of the die model of Figure 6.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Referring to the drawings a rectangular shaped die model is indicated generally at 10 in Figure 1. The model is formed of complementary sheets of polyester impregnated fiberglass cloth such as the sheets 12 and 14 which are aixed together to form hexagonal shaped cells 16.

i barrel.

These cells are preferably about live inches across. Smaller hexagonal filler cells 18, also formed of polyester im; pregnated fiberglass, are then disposed at the top and bottom of each of the primary cells 1.6 and extend a short distance into the said primary cell. These filler cells i8 are preferably approximately one-half inch across. The hollow center 20 of each primary cell ld is iilled with a phenolic foam resin. The foam resin extends to within of the top of each ller cell 1S adjacent the model face, and a surface plastic 22 extends l/e down into each filler cell 18 and AG above the primary cells 16. The primary cell and filler cell construction holds the die model surface plastic stable and breaks up structural strains which may develop when the surface plastic is setting. The foam core of the model renders the model light and easy to handle.

The model is constructed according to the following method. Strips of polyester impregnated berglass cloth are passed between a steam heated barrel having half hexagon impressions and a runner having half hexagon teeth thereon which mate with the impressions in the As the polyester impregnated fiberglass cloth passes through the device it is formed into a sheet of half hexagon impressions such as the strip 12 or i4 and is dry and ready for use when it emerges. Both the large primary hexagonal cell strips and the smaller filler cell strips are formed in this manner. The large primary cells 16 are formed by securing the large five inch strips together. The ller cells l are formed by securing the small sheets of 1/2 hexagonal fiberglass together.

ln constructing a plastic die model of an automobile door 23, for example, a full size door template 24 is placed flat on a steel table 26. Two large angle plates 2li are then placed at and against the bottom edge of the door template 24. A strip of the five inch impressed polyester impregnated fiberglass of the desired length is then placed on edge within the template and it is shimmed and clamped on the angle plates 1/8 inside of the edge of the template. Additional sheets of the 5 fiberglass are then placed in position and sealed one to the other to complete a nest or honeycomb Bti of 5 primary cells 16. The honeycomb Btl is then removed as a unit from the te1nplate and the ends and sides are sanded or ground to a size which is /s short of the inside edge ofthe template.` The sides of the honeycomb are wrapped with impregnated polyester fiberglass cloth binding and a nish coating 32 of polyester plastic is added around the model to exceed 1A" for later shaping. A preliminary base line is then established and female templates Sli are placed down into the honeycomb for approximately every 5 inches of model surface. After the templates 34 are worked in g'fbelow the normal surface with a disc sander or the like, the templates are removed.

The honeycomb structure 39 is set firmly on the waxed steel table 26 and a clay lillet is run around the honeycomb to seal it to the table. Strips of the one-half inch polyester impregnated fiberglass cloth of the desired length are then inserted into each primary cell 16 and are lowered to the table surface to form the bottom filler cells 18. A phenolic plastic foam resin is then poured into'each primary cell 16 and is allowed to foam or rise. Any such resin is suitable so long as it is relatively shrinkfree after curing and will be stable to close dimensions, such as JAMOO inch. The Kish phenolic foam resin has been found satisfactory. During such foaming, additional strips of the one-half inch liberg'lass cloth are placed into each primary cell at the top thereof. The phenolic resin rises through the cells 18 formed by the latter one-half inch strips and is scraped even with the top of the honeycomb. The foam plastic is allowed to set for a period from four to ve hours and then the model is removed from the table and baked in a suitable oven at approximately 250 F. until dry. Y

Next the model is taken back to the steel table 26 and turned over on its face. The back is cleanedl thoroughly and: a thin coat of polyester plastic is painted on. Immediately thereafter a sheet of polyester impregnated fiberglass cloth is laid over the back area. The back area is allowed to dry and then the edges are cleared and locating pads 36 formed of laminated impregnated fiberglass cloth are positioned on the back of the model. Thepads are secured to the model with cadmium coated screws which will not rust or corrode. The model is then turned over so that the locating pads are flat on the table 26. The face of the model'is then cleared of foam plastic with a sander or other suitable means so that each indi'- vdual one-half inch filler cell has a depression 1/16. deep. These depressions permit the surface plastic which is later poured to enter each filler cell and break up any strain which might develop in the surface plastic. Next a six inch piece of polyester impregnated tape is wrapped around the model to hold the surface plastic on the face of the model as the surface plastic is poured. The model is then cleaned with air and a face surface of polyester plastic is poured to extend at least IAQ above the honeycomb and down into the 1/16 depressions in the filler cells 18. Any of numerous polyesters are suitable. The surface plastic must be relatively shrink-free after curing and should hold a close dimension such as t1/10,000 inch. Triallyl cyanurate is an example of such a polyester.

. The female face templates 34 are then set up again and pressed into the surface plastic until they are positioned properly. After all the templates are properly positioned, the model is allowed to set until the surface plastic is hard. The face templates 34 are then removed and the outlining door template 24 is placed on the back of the model. The model is. then shaped all around by machine to the exact outline of the door template. The template is then removed and the surface of the modelv is worked until the impressions in the plastic caused by the templates are removed. The model is then cleaned with air and finished.

The same principles may be applied to the method of female duplication wherein a female is made from a male model, theV primary cells and lter cells being formed atop the male model to the desired contour and then being lled with foam resin and coated with surface plastic as explained previously.

The word honeycomb is used herein to describe a unitary group of cells, and it is to be understood that the cells may have shapes other than hexagonal.

From the foregoing, it will be seen that I have provided a simple and lightweight die model which is dimensionally stable and which is relatively free of internal stresses and strains. The method for forming such die models is novel and eflicient and comprises a small number of simple and positive steps.

Having thus described my invention, I claim:

l. A close dimension plastic die model comprising a unitary outer honeycomb structure formed of a plurality of substantially vertical primary cells of plastic impregnated brous material, a plurality of groups of smaller substantially vertical plastic ller cells, one group disposed within each of said primary cells, said groups of ller cells being formed separate from said primary cell structure and each group of filler cells being engaged at its outer boundaries with the adjacent primary cell so that said primary cell is a wall surrounding said group of iiller cells, said filler cells being formed of a stable material of high compressive strength and extending substantially to the top level of theprimary cell, a Vcore of light weight, stable plastic having high compressive strength disposed within said primary and filler cells and extending short of the top of said filler cells, and a layer of low shrinkage surface plastic which will remain stable over a relatively large range of temperal tures extending over and above the face of said honeycomb structure and into the primary cells and llercells to the core in said filler cells, said primary and tiller cell structure relieving internal stresses and strains and adding to the strength of said die model.

2. A close dimension plastic die model comprising a unitary outer honeycomb structure formed of a plurality of substantially Vertical primary cells of plastic impregnated glass liber material, a plurality of groups of smaller substantially vertical ller cells of plastic impregnated glass ber material, one group disposed within each of said primary cells, said groups of ller cells being formed separate from said primary cell structure and each group of filler cells being engaged at its outer boundaries with the adjacent primary cell so that said primary cell is a wall surrounding said group of ller cells, said ller cells extending substantially to the top level of the primary cell, a core of light weight stable foam plastic disposed within said primary and filler cells and extending short or" the top of said iiller cells, and a layer of low shrinkage surface plastic which will remainstable over a relatively large range of temperatures extending over and' above the face oi' said` honeycomb structure and. into the primary cellsv and filler cells tothe core in said filler cells, said primary and tiller cell structure relieving internal stresses and strains and adding to the strength of said die model.

3. A close dimension plastic die model comprising a unitary outer honeycomb structure formed of a plurality of substantially vertical primary cells of plastic impregnatecl fibrous material, a plurality of groups of smaller substantially vertical short-length filler cells, one groupA of said filler cells being disposed at the bottom of eachy of said primary cells and one group of said filler cells being disposed at the top of each of said primary cells, said shortdength filler cells leaving an open central pcrtion in each of said primary cells, a core of light weight, stable plastic having high compressive strength disposed within said primary and ller cells and extending entirely throughout the bottom liller cells and the central portion of the primary cell but extending short of the top of the top filler cells, and a layer of low shrinkage surface plastic which will remain stable overa relatively large range of temperatures extending over and above the face of said honeycomb structure and into the primary cells and top filler cellsto the core in said iil'ler cells, said primary and ller cell structure relieving internal stresses and strains and adding to the strength of said die model.

4. The method of forming a close dimension die model comprising the steps of forming a honeycomb structure of substantially vertical primary cells of plastic impregnated tibrous material, shaping the honeycomb structure of primary cells to the desired contour, sealing the sides of the honeycomb structure with plastic tape, inserting a group of separate substantially vertical plastic ller cells within each of the primary cells so that each groupv of iiller cells contacts the adjacent primary cell at the side boundaries of said groups, applying a light weight plastic of high compressive strength withinsaid tiller cells to form a core, sealing the bottom of the die model with plastic, aiiixing a casing around the sides of said model so that it will extend above the top face of the honeycomb structure, applying a stable, low-shrinkage Surfaceplastic to the top face of the honeycomb structure so that said surface plastic extends within each filler cell and above the face of said honeycomb structure, removing the cas,- ing, and finishing the surface plastic to the proper dimensions. Y

5. The method of forming a close-dimension, plastic die model comprising the steps of aixing together complemental strips of plastic impregnated fibrousy material to form a unitary honeycomb of substantially vertical primary cells, shaping the honeycomb structure of primary cells to the desired contour, sealing the `sides `of the, honeycomb structure with plastic tape, forming a plurality of separate honeycomb structures of smaller substantially vertical ller cells by atixing together complemental strips ot' plastic impregnated fibrous material, inserting a honeycomb structure of filler cells into each of the primary cell-s so that the side boundaries of said ller cells contact the sides of the primary cell and the tops of said filler cells are even with the top of the primary cell, applying a light-weight plastic of high compressive strength within said filler cells to form a core, sealing the bottom of the die model with plastic, afxing a casing around the sides of said model so that it will extend above the top face of the primary honeycomb structure, applying a stable, low-shrinkage surface plastic to the top face of the primary honeycomb structure so that said surface plastic extends within each filler cell and above the face of said primary honeycomb structure, removing the casing, and finishing the surface plastic to the proper dimensions.

6. The method of forming a plastic die model comprising the steps of aixing together complemental strips of plastic impregnated fibrous material to form a unitary honeycomb of substantially vertical primary cells, shaping the honeycomb structure of primary cells to the desired contour, sealing the sides of the honeycomb structure with plastic tape and applying a iinish coating of stable, low-shrinkage surface plastic to said plastic tape, forming a plurality of groups of smaller substantially vertical filler cells of short depth by afxing together complemental strips of plastic impregnated fibrous material, inserting one such group of liller cells in each primary cell at the bottom thereof so that the side boundaries of said filler cells contact the sides of the primary cell, pouring a stable foam plastic of high compressive strength into said primary cells, inserting another group of short depth filler cells into the top of each primary cell so that the filler cells and primary cell are level at their tops, thus leaving the central portion of said primary cell unoccupied by filler cell-s, sealing the bottom of the die model with plastic, cleaning 'the foam plastic out of each top filler cell to the depth of approximately 1/13 inch, aixing a casing around the sides of said model so that it will extend above the top face of the primary honeycomb structure, applying a stable, low-shrinkage surface plastic into the filler cells to extend approximately 1/16 inch therein and 1A@ inch above the face of the honeycomb of primary cells, removing the casing, and finishing the surface plastic to the proper dimensions.

References Cited in the le of this patent UNITED STATES PATENTS 1,942,989 Thomson Ian. 9, 1934 2,371,047 Groehn Mar. 6, 1945 2,420,359 Dasher May 13, 1947 2,447,620 Singleton Aug. 24, 1948 2,477,852 Bacon Aug. 2, 1949 2,622,999 Faussuer Dec. 23, 1952 2,625,748 Renaud Ian. 20, 1953 2,632,622 Kish Mar. 31, 1953

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