US2492131A

US2492131A - Shaping die

Info

Publication number: US2492131A
Application number: US585842A
Authority: US
Inventors: Lewis E Burger; Jennings B Skinner
Original assignee: Solar Aircraft Co
Current assignee: Solar Aircraft Co
Priority date: 1944-02-23
Filing date: 1945-03-31
Publication date: 1949-12-27
Anticipated expiration: 1966-12-27

Description

Dec. 27, 1949 E, BURGER r 2,492,131

SHAPIN'G DIE Original Filed Feb. 23, 1944 2 Sheets-Sheet 1 INVENTORS. LEW/s E. fil/EGEE, :Zs-AW/A/Gs 5- SKIN/Vile,

Arron/95v Dec, 27, 1949 LE. BURGER ETAL SHAPING DIE 2 Sheets-Sheet 2 Original Filed Feb. 23, 1944 INVE Patented Dec. 27, 1949 STATES ATENT OFFICE SHAPING DIE fornia Original application February 23, 1944, Serial No. 523,516. Divided and this application March 31, 1945, Serial No. 585,842

3 Claims.

This invention relates to the die stamping art in which metal sheets are stretched and bent into desired shapes by pressing or striking them between dies, and more particularly to that phase of the art in which a plurality of sets of dies of successively greater depth are required to produce the desired shape.

This application is a division of our copending application Serial No. 523,516, filed February 23, 1944, and entitled Method of making preliminary shaping die, which issued as Patent No. 2,383,706 on August 28, 1945.

An object is to provide preliminary dies of superior shape in that they so prepare the sheet metal for the final dies that the latter can produce deep and abrupt slopes wihout breaking or excessively thinning or wrinkling the metal.

Heretoiore, when a stamping or drawing operation of more than one stage was necessary in order to produce a satisfactory deep or abrupt slope in a work sheet, it was the practice to have the dies used in the preliminary stages made manually by highly skilled pattern makers who produced them largely by the process of trial and error and with the expenditure of a great deal of time.

In accordance with the present invention, We provide a routine procedure for preparing preliminary dies from finish dies, greatly reducing the amount of time and skill required and yielding dies more uniformly satisfactory than those formerly made by highly skilled pattern makers.

The present invention is based on the principle that the preliminary drawing or stamping operations should so shape the sheet that the final operation is largely a bending operation, involving relatively little stretching or compression of the sheet. Hence, we make the preliminary dies with substantially the same absolute area as the final die but having less depth so that the projected area is greater. This result is obtained by using as a pattern for making the preliminary die a substantially non-stretchable, flexible sheet that has been first shaped in the finish die and then flattened out by bending to reduce its depth, A suitable material for such a sheet is wax reinforced by fabric in such a way as to prevent it from stretching or shrinking, while ermitting it to bend.

A full understanding of the invention may be had from the following detailed description with reference to the drawing of a specific procedure in accordance with the invention.

In the drawing:

Fig. 1 is a perspective View of a pattern for a finish die;

Fig. 2 is a cross section of the pattern of Fig. 1 taken in the plane 11-11 and showing a wax pattern 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 Fig. 1;

Fig. 4 is a cross section of the wax pattern sheet as it appears when removed from the pattern of Fig. 2;

Fig. 5 is a cross section of the pattern sheet after it has been partially flattened out, the section being taken in the position corresponding to the line V-V of Fig. 3;

Fig. 6 is a cross section showing the pattern sheet of Fig. 5 supported and reinforced with plaster;

Fig. '7 is a cross section showing the reinforced pattern sheet of Fig. 6 inverted and mounted in a box ready for casting the plaster pattern of Fig. 3; and

Fig. 8 is an enlarged detail cross section of a portion of the pattern sheet.

Referring first to Figs. 1 and 2, there is shown a plaster pattern l0 for making a female finish die for use in a drop hammer or the like for shaping sheet metal. In accordance with well known procedure, the die may be cast in a sand mold, which mold was first formed from the pattern ll]. Insofar as the present invention is concerned, either the pattern Ii! or the finish die formed therefrom can be employed since both are of identical shape. It is usually most convenient to employ the plaster pattern Hi.

It is to be understood that in the stamping press or drop hammer, a male die or punch is employed and that the sheet metal to be shaped is pressed or struck between the male and female dies. However, it is customary to make the male die or punch from the female die, and hence, it is suificient in connection with the present invention to disclose the method of preparing the pattern for only the female die, the latter being hereinafter referred to as the die.

There is shown in 3, a plaster pattern H for forming the preliminary die which is used to shape the sheet metal before it is placed in the finish die corresponding to the pattern ill of Fig. 1. It will be observed that the pattern H of Fig. 3 bears little resemblance to the pattern ll) of Fig. 1, yet the shape of pattern I! is inherently such as to prepare the sheet metal for stamping in the finish die so that it can take the form of the finish die without breaking and without thinning or wrinkling excessively. The reason for this is that the total surface of the pattern i I is substantially the same as that of Fig. 1, the depth of pattern ll being substantially less and the projected area correspondingly greater. Pattern II is obtained in accordance with the present invention by the following procedure:

First there is formed in the finish pattern H] a thin pattern sheet 52 of wax reinforced with cheesecloth. This is done by first painting the surface of the plaster pattern 9 with a thin paint of modeling clay, liquid soap and water to prevent the pattern sheet 52 from sticking to the plaster. Before this paint has dried, a first sheet 53 (Fig. 8)

of cheesecloth is placed on the pattern ill and pressed into intimate contact with the surface thereof, the cheesecloth being sufiiciently yieldable to permit such shaping.

Next, the cheesecloth i3 is coated ith a suitable wax It by applying it on top the cheeseq cloth H3 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. The wax congeals as soon as it applied to the cheesecloth by virtue of conduction of heat therefrom into the plaster pattern, and by repeated applications of the molten wax wi brush, the layer it of wax is built up to a depth of approximately of an inch.

Next, a second sheet of cheesecloth i5 is pressed into the wax it while the latter is relatively soft, this second sheet l5 being laid on the bias with respect to sheet it; that with its threads runhim; at approximately 45 with respect to the threads of cloth l3. Thereafter, a thin coat 16 of wax is brushed on to the cloth l5, thereby completing the pattern sheet l2 as shown in Fig. 2.

After it has cooled a little more and becomes fairly stiff, the pattern sheet if? is removed from the pattern if! by gradually pulling it away therefrom with the hands. It comes away quite readily because of the thin coat of modeling clay, liquid soap and water that was placed on the plaster pattern before the pattern sheet was formed. As removed from the pattern iii, the pattern sheet l2 appears as shown in Fig. 4, having the shape of the finish pattern ill. It is then flattened out into the shape shown in Fig. 5, this flattening operation being performed by pulling he pattern sheet apart with force applied at juxtaposed points on the edge thereof accompanied by slight force applied to the under side of 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 procedure illustrated in Figs. 6 and 7.

Referring to Fig. 6, the pattern i2 is first suping substantially the same ported at relatively closely spaced points on its under surface by means of clay bolsters I! extending upwardly from a supporting table or base [8, after which a thick layer l9 of plaster of Paris is applied to the upper surface of the pattern sheet, this layer [9 being formed by applying plaster in relatively stiff condition with a trowel, or with the hands.

After the plaster backing H! has set, the assembly of the pattern sheet 12 and the backing I 9 is removed from the clay bolsters i1, inverted and supported on clay bolsters 20 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 willbe 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 simpleand 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 intermediate 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 thenusing it to make themold for casting 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 makers 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, a preliminary shaping die for partially forming and preparing sheets for further shaping with a second die having substantial curvature in all directions, said preliminary shaping die having a general configuration similar to the second die, and having substantially the same absolute surface area throughout as the second die, but having less depth and a correspondingly greater projected area than the second die.

2. In the art of sheet stamping and drawing, a preliminary shaping die for partially forming and preparing sheets for further shaping with a. second die having substantial curvature in all planes intersecting the working surface of the die, said preliminary shaping die having the same general configuration as the second die, and havabsolute surface area throughout as the second die, but having less depth and a correspondingly greater projected area than the second. (lie, and having its steepest surfaces substantially less steep than the corresponding surfaces of the second die.

3. In the art of sheet stamping and drawing,

a series of dies for successively shaping a Work sheet in which all the dies have the same general configuration and are irregularly double curved and asymmetrical as to curvature and have the same absolute surface area, but in which one of the early stage dies has less depth and a corresponriingly greater projected area than the next later stage die, and in which the steepest surfaces of said early stage die are substantially less steep than the corresponding surfaces of said later stage die.

LEWIS E. BURGER.

JENNINGS B. SKINNER.

REFERENCES SITE?) The following references are of record in the file of this patent:

5 UNITED STATES PATENTS Number Name Date 173,954 Hoeltge Feb. 22, 1876 1,375,305 Maisel Apr. 19, 1921 1,909,930 De Bidder May 23, 1933 1,932,318 O-estnaes Nov. 27, 1934 2,181,020 Le Jeune Nov. 21, 1939 2,295,852 Le Jeune Sept. 15, 1942 2,383,706 Burger Aug. 28, 1945 2,422,325 Wheelon June 17, 1947 FOREIGN PATENTS Number Country Date 1,301 Great Britain 1887 225,710 Great Britain 1924 OTHER Die Design and Diernaking Practice, sec. ed. 1941, pub. by The Industrial Press, N. Y.