US2383706A - Method of making preliminary shaping dies - Google Patents

Description

Aug. 28, 1945. L. E. BURGER ETAL 2,383,706

METHOD OF MAKING PRELIMINARY SHAPING DIES Filed Febyzs, 1944 2 Sheets-Sheet 1 INVENTOR. Aswxa E. BURGER JEN/wuss .B. d'k/NNER n-rronlvav 1945- L. E. BURGER ETAL I 2,383,706

METHOD OF MAKING PRELIMINARY SHAPING DIES I Filed Feb. 23, 1944 2 Sheets-Sheet 2 Arron/45v Patented Aug. 2a, 1945 Mn'rnon or MAKING rimmmuaar snarnvo pms Lewis E. Burger, La Mesa, and Jennings B. Skinner, San Diego, Calif asslgnors to Solar Aircraft Company, San Diego, Calli'., a corporation of California 1 Application February 23, 1944, Serial No. 523,516

oi-the art in 6 Claims. (Ci. 76-107) -This invention relates to the die stamping art in which metal sheetsare stretched and bent .into desired shapesby pressing or striking them between dies,: and more particularly to that phase which a plurality of sets of dies of successively greater depth are required to produce the desired shape. n

An object of the invention is to simplify the construction of dies for use in the preliminary In the drawings:

Fig. l is a perspective view of a pattern for a finish die; A Fig. 2 is a cross section of the pattern of Fig. 1 taken in the plane IT-II and showing a wax pattem sheet formed therein;

Fig. 3 is a perspective view of a pattern for a preliminary stage die made in' accordance with the. present invention from the finish pattern of stages of a multi-stage drawing or stamping oper- '10 Fig. 1; ation. v Fig. 4 is a cross section of the wax pattern Another object is to reduce the amount of skill sheet as it appea wh n r v r h P required to produce effective preliminary dies. m f 181 2;

Another object is to provide preliminary dies Fls. 51s a cross section of the pattern sheet "or superior shape. in that they so prepare the after it has been part lly flattened out. the sec-- sheet metal for the final dies that the latter can i n being taken in t e osi io c rr spon in produce deep and abrupt slopes without breaking t0 the line V-V of Fig. 3; or excessively thinning or wrinkling the metal. Fig. 6 is a cross section showing the p n -Heretofore, wheria stamping or drawing oper- Sheet 0! 8- Supported n r inf rced with ation of more than one stage was necessary in p order to produce. a satisfactory deep or abrupt Fig. 7 is a cross section showing the reinforced slope in a work sheet, it was the practice to have Pattern Sheet of a 6 n te ndmounted in the dies used in the prellminarystages made a D ready casting the pl r pa rn 01 manually by highly skilled pattern makers who n produced them largely by the process of trial and -r j' oil ign fieg ga sridsgggflross section of a a 3 32 w expenditure of a eIna-m; de 1 Referringfirst to Figs. 1 and 2, there is shown In accordance with-the present invention, we a Plaster p n for m kin a female finish provide a routine procedure for preparing predie for use ina drop hammer or the like for liminai-y dies from finish dies, greatly reducing Shaping Sheet m l- In accordance with well the amount of time and skill required and yieldknown procedure. t e di may be cast in a sand ing dies more uniformly satisfactory than those -m01d. which mold was firs f m f m the p i'ormerly made by highly skilled pattern makers. tern l0. insofar as the present invention is con- I The present invention is based on the prin- 35 rn d, either the pattern ll or the finish die ciple that the preliminary drawing or stamping formed therefrom can be employed since both are operations. .should soshape the sheet that the of identical shape. It is usually most convenfinal operation is largely .a bending operation, ient to employ the plaster pattern It. involving. relatively little stretching or compres- It is to be understood that in the stamping press '-sion of. the sheet. Hence, we make the prelim- 40 or drop hammer, amale die or punch isemployed inary ,dies with substantially the same absolute and'that the sheet metal to be shaped is pressed areae-as-the ilnal die but having less depth so or struck between the male and female dies. that the projected area is greater. This result However, it is customary to make the male die is obtainedeby-using as a pattern i'ormaking the or punch from the female die, and hence, it is preliminary die a substantially non-stretchable, sufli'cient in connection with the present invenfiextble. sheet that has been-first shaped in the tion to disclose the method. or preparing the patflllishidie and then flattened ou y i g tern for only the femaledie, the. latter being reduce its depth. A suitable material for such hereinafter referred to as the.die." asheet is waxreinforced by fabric in such a Ther is shown in Fig. 3 a, plaster pattern ll way as to prevent it from stretching or shrinki 5 for forming the preliminary die which is used to while permitting it to bend. shape the sheet metal before it is placed in the "A full understanding of the inven i n m y be finish ,die corresponding to the pattern ill of had from the following detailed description wit .Fig. 1. It will be observed that the pattern ll of reference to the-drawings of a specific procedure Fig. 3 beats little resemblance to-the pattern ill in accordance with the invention.

of Fig. 1, yet the shape of pattern II is inherently such as to prepare the sheet metal (or stamping in the finish die so that it can take the form of the finish die without breamng and without thinning or wrinkling excessively. The reason for this is that the total surface of the pattern H is substantially the same as that of Fig. 1, the depth of pattern H being substantially less and the projected area correspondinglyv greater. Pattern ii is obtained in accordance with the present invention by the following procedure:

First there is formed in the finish pattern id a thin pattern sheet I: of wax reinforced with cheesecloth. This is done by first painting the surface of the plaster pattern I! witha thin paint of modeling clay, liquid soap and water to prevent the pattern sheet I! from sticking to the plaster. Before this paint has dried, a first sheet 13 (Fig. 8) of cheesecloth is placed on the pattern IB and pressed into intimate contact with the surface thereof, the cheesecloth being sumciently yielda-ble to permit such shaping.

Next, the cheesecloth It is coated with a suit able wax It by applying it on top of the cheesecloth 13 in melted condition with a brush. At the same time the cheesecloth is again forced into all the corners of the pattern with the brush. This wax congeals as soon as it is applied to the cheesecloth by virtue of conduction of heat therefrom into the plaster pattern, and by repeated applications of the molten wax with the brush, the layer it oi wax is built up to a depth of approximately a; of an inch.

Next, a second sheet of cheesecloth i is pressed into the wax Id while the latter is relatively soft, this second sheet id being laid on the bias with respect to sheet 53; that is, with its threads running at approximately 45 with respect to the threads of cloth i3. Thereafter, a final thin coat it of wax is brushed on 'to the cloth 16, thereby completing the pattern sheet i2 as shown in Fig. 2.

After it has cooled a little more and becomes fairly stiff, the pattern sheet i2 is removed from the pattern l9 by gradually pulling it away therefrom with the hands. It comes away quite readily because of the thin coat of modelin clay, liquid soap and water that was placed on the plaster pattern before the pattern sheet was formed. As removed from the pattern id, the pattern sheet I2 appears as shown in Fig. 4, having the shape of the finish pattern lb. It is then flattened out into the shape shown in Fig. 5. this flattening operation being performed by pulling the pattern sheet apart with force appliedat juxtaposed points on the edge thereof accompanied by slight force applied to the under side oi the intermediate portion with the hands. This operation changes the shape of the pattern sheet without appreciably changing its area because the two sheets of cheesecloth laid on the bias with respect to each other largely prevent stretching of the pattern. Such stretching could not be avoided if the pattern sheet were made of wax alone without any fabric reinforcement.

After the pattern sheet has been flattened as shown in Fig. 5, it is used to cast the preliminary stage plaster pattern shown in Fig. 3 by the procedures illustrated in Figs. 6 and 7.

Referring to Fig. 6, the pattern I: is first supported at. relatively closely spaced points on its under surface by means of clay bolsters i1 ex tending upwardly from a supporting table or base l8, after which a thick layer IQ of plaster of Paris is appliedto the upper surface of the pattern sheet, this layer I9 being formed by applying plaster in relatively still condition with a trowel, or with the hands. 7

After the plaster backing 19 has set, the assembly of the pattern sheet 12 and the backing i9 is removed from the clay bolsters i'I, inverted and supported on clay bolsters 28 extending upwardly from a base 2| as shown in Fig. 7. Thereafter, side walls 22 of wood or other suitable material are constructed around the plaster backed pattern sheet to form therewith a mold into which liquid plaster of Paris can be poured. When this plaster of Paris has solidified and has been removed from the mold, it constitutes the preliminary pattern of Fig. 3.

It will be observed from the procedure described that the invention provides a routine process for developing patterns for preliminary dies from patterns of finish dies, requiring very little special skill. Furthermore, the procedure is relatively simple and does not require much time,

In some cases, it is necessary to employ more than one preliminary die to bring the sheet metal into the final desired form by successive stages.

each involving a relatively small change in shape from the next preceding stage. Hence, in some instances, it may be desirable to form an intermediate stage pattern from the final pattern and then form a first stage pattern from the intermte stage pattern. Under such conditions, the intermediate stage pattern can be prepared as described, after which a first stage pattern can be prepared from the same wax pattern by further flattening it and increasing its projected area and then using it to make the mold for easting the first stage pattern.

Although various waxes may be employed in forming the pattern sheet i2, a composition that has been found suitable in practice consists of a mixture of from one-half to two-thirds beeswax with the balance a pattern. maker's wax such as "Master sheet wax made by Kindt-Collins Co.

of Cleveland, Ohio. If overheated, the wax may become too hard, under which condition it may be softened with the addition of a small amount of turpentine.

Various departures from the exact procedure described may be made, while still obtaining the advantages of the invention, and the latter is therefore limited only to the extent set forth in the appended claims.

We claim:

1. In the art of sheet stamping and drawing, the method of preparing a preliminary shaping die from a later stage die, said method comprising the steps of: first, forming in said later stage die a flexible, substantially non-stretchable and non-compressible sheet pattern; second, removing said sheet pattern from said later stage die and partially flattening it to reduce its depth and increase its projected area withoutmaterially changing its absolute area; and third, using said flattened sheet pattern as a mold to reproduce its shape in the preliminary shaping die to be prepared.

2. In the art of sheet stamping and drawing, the method of prepar g a ina y s pin die from a later stage die, said method comprising the steps of: pressing against said later stage die a sheet of readily deformable fibrous material and coating it with plastic wax and permitting the wax to congeal; second, removing said sheet of deformable material coated with wax from said later stage die and partially flattening it to reduce its depth and increase its projected area without materially changing its absolute area; and third, using said partially flattened sheet as a mold to reproduce its shape in the preliminary shaping die to be prepared.

3. In the art of sheet stamping and drawing, the method of preparing a preliminary shaping die from a later stage die, said method comprising the steps of: first, placing against said later stage die a first sheet of textile material; second, coating said sheet with heated plastic wax; three, pressing a second sheet of textile material on to said wax while the latter is still soft with the threads of said second sheet of textile material extending diagonally with respect to the threads flexible, plastic material reinforced with sheet textile material,

5. Th method described in claim 1 in which said sheet pattern consists of a layer of wax reinforced with a plurality of sheets of textile material laid on the bias with respect to each other.

6. In the art of sheet stamping and drawing the method of preparing a plurality of preliminary shaping dies of successively greater depth from a later stage die, said method comprising the steps of: first, forming in said later stage die a flexible substantially non-stretchable and noncompressible sheet pattern; said sheet pattern from said later stage die and partially flattening it to reduce its depth and increase its projected area without'materially changing its absolute area; third, using said partially flattened sheet pattern as a mold to reproduce its shape in an intermediate stage shaping die to be prepared; fourth, further flattening said sheet pattern to further reduce its depth and increase its projected area withoutv materially changing its absolute area; and fifth, using said further flattened sheet pattern as a mold to reproduce its shape in the first stage die to be prepared.

LEWIS E.- BURGER. JENNINGS B. SKINNER.

second, removing

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