US2256338A - Method of forming mold patterns - Google Patents

Description

equally spaced and parallel sections Patented Sept. 16, 1941 PATENT OFFICE 2,256,338 METHOD. OF FORMING MOLD PATTERNS Joseph B. Brennan, Cleveland, Ohio No Drawing. Application Serial No.

1 Claim.

This invention relates to the art of casting metals, and more particularly to an improved method of making patterns, templets and the like, to be used in making molds for castings.

As is well known, patterns are employed to 5 shape the mold into which molten metal is cast, in making the casting. Since the metal will shrink upon cooling, it is necessary that the pattern and mold be made sufliciently larger than the finished casting to compensate for such shrinkage.

The usual practice in the production of a casting, begins with the preparation of a drawing which is made to the scale of the finished casting. From this drawing, the pattern-maker will build a facsimile or pattern which is used to shape the mold for the casting. The patternmaker, in building the pattern, must allow for the shrinkage of the cast metal which will vary between one-eighth and one-quarter inch per foot, according to the kind of metal which is being used in making the casting. The patternmaker, in laying out the pattern, is not able to take the dimensions of the pattern directly from the drawing of the casting, but must resort to a shrink rule or calculate the amount of shrinkage that will take place in order to build the pattern to the desired size. Diflicult and time-consuming operations which require the service of skilled workers are thus encountered.

In the case of large castings or castings of an extremely irregular contourwhich cannot readily be made from a single piece of material, the pattern is usually made of sections of wood or metal, and the finished pattern is completed by piecing such sections together. Another common way of building patterns for such castings, is to make a series of drawings corresponding to of the casting, and form templets corresponding to such sections. These templets are then used to form a skeleton-like reproduction of the casting which may be filled in to form the finished pattern in a manner well known in the art. The accurate building of a pattern from sections pieced together is rendered difficult due to the fact that an error in the size of one of the sections will usually result in such error being transmitted to an adjacent section.

Castings which require the accurate reproducion of an irregular contour, such as a surface having a small radius of curvature, are almost impossible to reproduce in the form of a pattern which will accurately take into account the shrinkage that will take place in such surface. 55

December 16, 1940, 870,375

For example, where the dimensions of the material forming such surface are in odd fractions of an inch, an extremely small and unmeasurable fraction of an inch must be added to compensate for the shrinkage which will take place. In such cases, the pattern-makers usually make such surfaces considerably over-size in order to be certain that the casting will not be undersize with respect to such surfaces.

time-consuming grinding and machining operations.

. One of the principal objects of this invention is to provide an improved method of laying out a pattern to pattern size on the material from which the pattern is to be made, which will eliminate the human errors normally encountered in laying out such pattern by the use of a shrink rule, or by the employment of mental calculations.

A further object is to provide an improved method of forming a mold pattern in which the shape of the pattern is photographically reproduced to pattern size on the material from which the pattern is to be made.

A further object is to provide an improved method of forming a mold pattern in which a drawing to finished-scale is photographically reproduced to pattern size on the material from which the pattern is made.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described, and particularly pointed out in the claim, the following description setting forth in detail certain illus trative embodiments of the invention, these being indicative however, of but a few of the various ways in which the principle of the invention may be employed.

The method of this invention is particularly adapted for use in connection with patterns which are made up from sections in the nature of templets, and in which the templets are formed by laying out the desired contour of the section on the plate, and then cutting away the material lying without the confines of the contour as laid out.

In carrying out the method of this invention, a drawing of the casting is made to finished scale size in accordance with a conventional practice. The drawing is then photographically reproduced to pattern size on the surface of the material from which the pattern is to be made. In reproducing the drawing to pattern size on the surface of the material from which the pattern is to be made, the surface of such material is first sensitized to receive a photographic reproduction by the application to such surface of a light-sensitive substance, which substance may be of any kind now commonly employed in the photographic art. Since many types of apparatus are available for reproducing a drawing on such a sensitized surface, it is not believed necessary to specifically refer to the construction or operation of such apparatus, any suitable apparatus capable of enlarging the drawing accurately, a sufficient percentage to compensate for a predetermined shrinkage being employable for the purposes of carrying out themethod of this invention.

In the preferred practice of this invention, it is desirable that the drawing to be reproduced be made to full scale of the finished casting, and an enlarged reproduction of such drawing is then photographically transmitted to the surface of the material from which the pattern is to be made, the enlargement being sufficient to compensate for the shrinkage which will take place upon cooling of the casting metal. However, it will be understood that the invention is. applicable to any case, wherein the original drawing is made to a scale other than a full scale size, the photographic reproduction apparatus being availed of in such case to compensate, for example, those cases wherein the original drawing is made to one-half or one-quarter size.

To reproduce the casting or finished product to pattern size on the material from which the pattern is to be made, it will be first necessary to make a negative of the original drawing. The negative which is thus made may be either of the same size as the original drawing or may be enlarged to pattern size or an amount sufficient to compensate for the shrinkage which will take place upon cooling of the molten casting metal. Whether or not the negative is or is not enlarged will be dependent upon the particular step in the reproducing of the drawing to pattern size on the material from which the pattern is being made in which the enlarging of the original drawing takes place. If the negative is made to the same size as the original drawing, it will be necessary to employ the photographic enlarging apparatus in reproducing the drawing on the sensitized surface. If the photographic enlarging apparatus is employed in making the negative of the drawing, then it will only be necessary to reproduce such negative on the sensitized surface by the conventional photographic methods of preparing a positive print from a negative print. If desired, the enlarged negative may be formed directly upon the sensitized surface, and in such case, if the mold pattern section is in the form of a flat templet, the step of actually reproducing a negative print prior to transmittal to the sensitized surface will be eliminated. The preferred practice, for most cases, will be'to employ the photographic enlarging step in the preparation of the negative.

Regardless of the step in which the photographic enlarging operation takes place, the apparatus by which such enlargement is made will be found to employ a. lens which must be adjusted relatively to the surface of the drawing and to the surface on which the negative is to be formed in order that the object and image focal distances will be proper to secure the desired enlargement. It is contemplated that the parts by which such adjustments are made be promade.

vided with suitable scales and indicia setting corresponding to the material to be worked with. There would be thus different settings for the different metals to be worked with, and it would be merely necessary for the operator to move such parts to the setting for cast iron to secure the desired adjustment if cast iron is the material from which the casting is to be made; and likewise, there would be provided similar adjustments for copper, steel, bronze, and other metals.

In this way, it is possible to produce the mold pattern to exact pattern size without the employment of a shrink rule or mental calculations. If the metal worked with has a shrinkage of /4 inch per foot, the photographic enlargement can be made to add V to the size of every part regardless how small, such reproduction being virtually impossible where a shrink rule is employed.

Although the preferred practice has been described for the case wherein the drawing is reproduced directly upon the surface of the material from which the section is to be made, it will be understood that this invention is intended to have a field of use wherein the nature of the casting is such as to prevent such direct reproduction. In such case, the original drawing need not be directly reproduced to pattern size on the material by photographic methods, and there need be formed only a photographic enlargement or print of the drawing. The pattern maker will then make the pattern in the usual manner and obtain his measurements directly from the enlarged print through the use of dividers or calipers.

In those cases where it is desired to construct an unusually strong pattern from steel templets formed in accordance with the principles of this invention and arranged at spaced intervals to form the skeleton of the pattern, the templets may be bolted or welded together to form a rigid framework. Such framework may then be filled in to complete the pattern with plaster or other suitable molding materials, such as certain well known pheno-formaldehyde compounds which set at room temperatures. -In connection with the material from which the templets are made,

it will be understood that plywood or any other material capable of taking a sensitized photographic plate may be employed.

Where metallic templets are employed, it will be apparent that the process of this invention permits the use of etching as a means of securing a clean delineation of the contour of the drawing transferred to such plate. If the metal from which the templet is formed is sufiiciently thin, the etching may be employed to remove the excess material surrounding the templet in place of other cutting operations.

The process of this invention provides important advantages in the construction of large castings, such as dies. In such case, patterns can be made to /8 or A size from which a miniature model of the die, or other casting, may be The model may then be tried out to see how the metal will flow in a press, if the model be a die, and to observe other characteristics which it is often important to know before constructing a full size die which may weigh many tons. Any correction needed may then be made in the pattern or model of reduced size. Thereafter the model or pattern can be cut up into sections and photographs of such sections can be employed in the construction of the full size model. In such case, the photographs would be enlarged to full size plus any allowance desired for shrinkage.

In those instances, wherein reference is made to a drawing in this application, it will be understood that the dimensions of such drawing do not take into consideration the shrinkage which will take place upon cooling of the cast metal. It will also be understood that where the term photographically reproducing such drawing to pattern size" is employed, there is meant a reproduction which has been mechanically changed by the photographic reproducing apparatus to compen sate for the metal shrinkage.

From the foregoing, it will be apparent that the method of this invention enables the production of a pattern which will accurately compensate tor the shrinkage of the cast metal regardiess of any irregularities or odd shape in the suriace oi the finished casting. By this method, the expensive grinding and finishing operations heretofore employed and necessary to finish the casting to size are thereby substantially eliminated.

Other modes oi applying the principle oi-the invention may be employed, change being made as regards the details described, provided the features stated in the following claim, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

In the method or forming a mold pattern, the

steps which comprise preparing a drawing in accordance with the exact dimensions of the 11mished casting, phctographically reproducing and enlarging said drawing an amount suiiicient to compensate for the shrinkage of the metal to be employed in making the casting, and employlng said photographic enlargement to secure the dimensions of the pattern.

JOSEPH B. BRENNAN.