US3373585A - Sheet metal shaping apparatus and method - Google Patents

Description

March 19, 1968 T. D. REYNOLDS 3,373,585

SHEET METAL SHAPING APPARATUS AND METHOD Filed Sept. 21, 1964 2 Sheets-Sheet l March 19, 1968 T. D. REYNOLDS 3,373,585

SHEET METAL SHAPING APPARATUS AND METHOD Filed Sept. 21, 1964 2 SheetsSneet 2 3,373,585 SHEET METAL SHAPING APPARATUS AND METHOD Thomas D. Reynolds, Winston-Salem, N.C., assiguor to R. J. Reynolds Tobacco Company, Winston-Salem, N.C., a corporation of New Jersey Filed Sept. 21, 1964, Ser. No. 397,766 9 Claims. (Cl. 7257) ABSTRACT OF THE DISCLOSURE A process and apparatus for drawing a sheet metal blank, the process comprising positioning the blank across a die cavity, forcing the blank into the cavity while holding the cavity surrounding portions thereof against the die with sufiicient force to only partially restrain the lateral movement of these portions of the blank into the cavity, and thereafter forcing the blank further into the cavity while holding the cavity-surrounding portions thereof with a force sutficient to substantially completely restrain the lateral movement of these portions. The apparatus comprises a first member including a die having a cavity and a second member including a blank holder and a punch. The forward end of the punch is sized to fit partially into the die cavity and spring means extends between the punch and the blank holder. Means is provided for applying a fluid pressure between the forward end of the punch and the blank to force the partially deformed blank further into the cavity.

This invention relates to a sheet metal shaping apparatus and method and more particularly to an improved apparatus and method wherein a sheet metal blank is forced into and assumes the shape of a die cavity.

Heretofore the drawing of sheet metal has been accomplished either by a punch and die arrangement or by means of an arrangement wherein the blank is driven into the die cavity under fluid pressure. The punch and die method of drawing commonly results in the stretching or drawing of the sheet in such a manner that the drawn product not only becomes thinner and harder than the blank from which it was formed but the stretching or drawing tends to take place non-uniformly over the structure. This varied amount of stretching in the drawn product tends to become accentuated as the punch and dies deteriorate with wear. In addition, there are a limited number of shapes which can be produced with the punch and die technique. The dies involved are expensive, and lubricating oils which are necessary to the process quite often have to be removed at the end of the process.

Air forming is one means for avoiding some of these difiiculties; however, even in the air forming processes which have been practiced to-date, work hardening is often non-uniform and localized. In general, the air forming processes prior to this invention appear to have been limited to rather shallow draws, unless interstage annealing was employed in the process.

It is therefore one object of this invention to provide an economical and improved process and apparatus for drawing sheet metal.

It is an additional object of this invention to provide an improved process for drawing sheet metal wherein the drawn product will be more uniform in its strength and appearance.

It is still a further object of this invention to provide a process for forming sheet material which will permit the product to be formed in one operation and will eliminate the necessity for intermediate annealing stages.

It is still another object of this invention to provide a process for drawing sheet metal blanks which will provide a uniformly good product without danger of scratch- .ing or rupturing during forming, thus resulting in subcompanying drawings.

The process for forming sheet material in accordance with this invention is a two-step forming process. After the sheet metal blank has been positioned across the die having a cavity of suitable shape, the initial forming step of the process takes place. In this initial forming step the blank is forced partially into the die cavity, while at the same time the portions of the blank which surround the cavity are held against the corresponding cavity-surrounding portions of the die with a force which is sufficient only to partially restrain the lateral movement of these blank portions into the die cavity during this initial forming step.

Thereafter the second forming step takes place which consists of further deforming the blank by forcing it further into the cavity while at the same time holding the surrounding cavity portions of the blank against the die with a force which is of higher magnitude than the first force and is sufiicient to substantially completely restrain the lateral movement of these blank portions into the cavity during this further deforming step.

It will be noted that in the first step of the process the material surrounding the die cavity is permitted a limited movement into the die cavity, whereas during the second step the cavity-surrounding material is substantially pre vented from further moving into the die.

The preferred apparatus for drawing the sheet metal blanks comprises a pair of members which are adapted to accommodate the blank therebetween. One of the members includes a die having a cavity of the desired shape. The other member includes an apertured blank holder for engaging and holding the portions of the sheet metal blank against the portions of the die surrounding the die cavity. The second member further includes a punch which has a forward end adapted to enter and force the blank partially into the die cavity. This punch is disposed within the aperture of the blank holder, and either the punch on the one hand or the blank holder and die on the other hand is relatively movable from a retracted position in which the forward end of the punch is withdrawn from the die cavity and an extended position wherein the forward end of the punch is disposed forwardly of the blank holder and partially within the cavity of the die.

Spring means acting between the blank holder and punch resiliently urge the punch toward its retracted position, and the punch may be moved relative to the blank holder to its extended position against the resistance of this spring means. While the punch is being so moved to its extended position, relative to the blank holder, the peripheral portions of the blank will be held against the die by the blank holder acting under the influence of the spring means, and when the punch has reached its fully extended position, portions of the punch Will firmly engage portions of the blank holder so that additional pressure on the punch will result in a corresponding increase of the pressure on the blank holder and a corresponding increased gripping of the peripheral portions of the blank. Thus the initial forming is done by the punch moving into the die cavity while the edges of the blank are lightly restrained against lateral movement. Means is provided for completing the draw by fluid pressure forcing the blank the remaining way into the die, and during this finishing step the peripheral edges of the blank are firmly held against movement.

With reference to the drawings:

FIGURE 1 is a side elevation View of an apparatus constructed in accordance with this invention;

FIGURE 2 is a sectional elevation view showing the blank positioned over the die cavity and held in place by the blank holder under the influence of the spring means preliminary to the initial forming step;

FIGURE 3 shows the position of the punch relative to the blank holder and the die after the initial forming operation has been completed;

FIGURE 4 shows the portions of the apparatus and the formed blank after the second and final forming operation has been completed;

FIGURE 5 is a sectional elevation view showmg a modified form of apparatus with the blank positioned in preparation for the first forming operation;

FIGURE 6 is a sectional elevation view of the apparatus of FIGURE 5 showing the position of the blank after the first forming operation; and

FIGURE 7 is a sectional elevation view of the apparatus of FIGURE 5 showing the formed blank after the second and final forming operation.

With further reference to the drawings and particularly to FIGURE 1, the apparatus 10 is adapted to draw a flat sheet metal blank 11 into a hollow shell or dish of desired size and shape. This apparatus includes a two-part forming assembly 12 and means such as a hydraulic press 14 for applying a mechanical force to the parts of the assembly 12. The illustrated press 14 includes a first platen 16, a second platen 18 and means such as a hydraulic cylinder 19 and piston 20 for moving platens 16 and 18 relatively toward and away from each other.

Hydraulic pressure to the cylinder 19 is supplied. through lines 21 and 22, and a suitable hydraulic pressure gauge 24 may be provided to inform the operator of the level of pressure or force being exerted by the press upon the forming assembly 12.

The forming assembly 12 consists of two parts or members, and the details of one embodiment of this assembly are best illustrated in FIGURES 2 through 4. The first part of the forming assembly comprises a die having a cavity 32 of the desired configuration. Suitable air vents 34 extend through the die and communicate with the cavity 32, and circumjacent the cavity 32, the die 30 has a laterally extending surface 36.

The second part of the forming assembly overlies the die 30 and includes an apertured and preferably annular blank holder or holding ring 38, the central aperture 38a of which is approximately the same size as the opening into the cavity 32 of the die. A punch 40 is disposed for movement relative to the blank holder within the aperture 38a of the blank holder between a retracted position, as illustrated in FIGURE 2, and an extended position, as illustrated in FIGURES 3 and 4.

It will be noted that when in its extended position, the forward end 40a of the punch protrudes downwardly from the bottom surface of the blank holder 38, and this protruding forward end thus extends partially into the cavity 32 of the underlying die. As will be later described, this extension of the forward end of the punch provides the deformation of the blank during the first part of the drawing operation.

Resilient means such as springs 42 and 44 extend between the blank holder 38 and a shouldered portion 4% of the punch 40, and thus the punch and blank holder are urged to their relative positions illustrated in FIGURES 1 and 2 wherein the punch is considered to be retracted. Thus, as the punch 40 is moved relative to the blank holder from its retracted position, as illustrated in FIG- 4 URE 2, to its extended position, as illustrated in FIG-- URES 3 and 4, the blank 11 will be held against the surface 36 of the die only by the resilient downward force exerted by the springs 42 and 44.

The resilient strength of the springs 42 and 44 is such that these springs will exert a sufficient force on the blank holder to efiectively but only partially restrain the peripheral portions of the blank from slipping laterally inwardly toward the die cavity 32 during the initial forming stage as the punch moves relative to the blank holder to its extended position. The effect of this limited and controlled slipping during the initial forming stage is to moderately work harden the portion of the vertical wall of the partially drawn shell.

Extending to and through the forward end 40a of the punch is a conduit 46 for conveying fluid under pressure to the top surface of the blank. The fluid is preferably air and the pressure may be obtained by means of a suitable compressor 48 such as schematically illustrated in FIGURE 1. The air pressure may be indicated by a suitable pressure gauge 49 on the conduit 46.

During the second stage of the drawing operation, air under pressure in conveyed through conduit 46 to the top surface of the partially formed blank, as illustrated in FIGURE 3, and this air pressure forces the shell the remainder of the way into the die cavity 32 to the position illustrated in FIGURE 4.

During the initial forming stage of the draw, which with the apparatus of FIGURES 2 through 4 is a punch and die forming stage, the blank holder 38 is totally dependent for its holding power upon the resilient strength of the springs 42 and 44. During the second forming stage of the draw, however, the holding power of the blank holder 38 is not dependent upon the springs, but rather is dependent upon the external force applied to the punch and die, as by the press 14, to force the punch and die together. This force is sufficient to insure that the blank is held with sutficient firmness between the blank holder 38 and the surface 36 of the die to substantially completly restrain further lateral movement of the peripheral portions of the blank into the cavity during the second forming stage of the draw.

The second or final air forming operation results in a product which has a more uniform thickness and hardness than products achieved with previously employed processes and apparatus.

In the operation of the apparatus of FIGURES 2 through 4, the blank 11 is positioned beneath the punch and blank holder portion of the forming assembly 12 so that it overlies the die and completely covers the die cavity 32. The force is exerted by the press 14 on the parts of the assembly 12 to press these parts together and, upon the exertion of this force, the blank holder 38 will engage and hold those portions of the blank which surround the cavity 32 against the top surface 36 of the underlying die. This force will be dependent upon the compressive resilience of the springs 42 and 44 as the punch 40 moves downwardly relative to the blank holder 38 toward its extended position. During its downward movement relative I to the blank holder the punch forces the blank downwardly and partially into the cavity 32 of the die until the position illustrated in FIGURE 3 is reached. At this point the shouldered portion 40b of punch 40 firmly engages the blank holder 38 and further pressure exerted on the punch and die by the press 14 results in an increased squeezing action on the peripheral portions of the blank between the blank holder 38 and the cavity-surrounding surface 36 of the die. This pressure will be sufiicient to hold these portions of the blank against further lateral movement into the cavity as the blank is deformed by the application of air pressure through the conduit 46 to the top surface of the partially formed blank.

A forming apparatus of modified form is illustrated in FIGURES 5 through 7. In this apparatus the operation is a two-stage air draw rather than a first-stage punch and die operation and second stage air draw as was the case in the previous embodiment. In the apparatus of FIG URES 5 through 7 a die 50 is employed having a cavity 52 with communicating air vents 54, this die being substantially identical in all respects to the die 30 of the previously described embodiment. Instead of employing a punch and blank holder, however, the apparatus of FIG- URES 5 through 7 employs a cover plate 56 which also serves as a blank holder. This cover plate has a fluid conduit 58 leading to the forward face thereof. The cover plate 56 never enters the cavity 52 of the die, but instead merely overlies the die 50 and die cavity 52. An external force may be applied to the die and cover plate by the press 14 illustrated in FIGURE 1.

In the operation of the apparatus of FIGURES 5 through 7, the blank 11 is inserted between the die 50 and the cover plate 56, and the die and cover plate are forced together by the press 14 under a first force which is sufficient to only partially restrain the lateral inward movement of the peripheral portions of the blank during the initial forming stage. With this apparatus the initial forming is done by air applied under pressure through the conduit 58, and the initial holding force on the cover plate and die is exerted until the air forces the blank partially into the die cavity 52, as illustrated in FIGURE 6. Thereafter the pressure on the holding plate 56 and die 50 is increased so that the peripheral portions of the partially formed blank will be gripped between these members with sufficient force to substantially completely resist any further lateral movement of the peripheral portions of the blank as the partially formed blank is forced by air pressure the remainder of the way into the die cavity 52 to the position illustrated in FIGURE 7.

It may be seen that with each of the two illustrated forming assembly embodiments the peripheral portions of the blank 11 are only partially restrained from lateral movement toward the die cavity during the initial forming stage of the draw, and during the second and final stage of the draw the pressure on these peripheral portions is increased so that their lateral movement toward the die cavity is substantially completely restrained.

The apparatus of FIGURES 2 through 4 has the advantage of not requiring the application of two pressures in the squeezing of the punch and die together. The lower holding force on the peripheral portions of the blank during the initial forming stage is accomplished automatical ly by the resilience of the springs 42 and 44.

The apparatus of FIGURES 5 through 7 has the advantage of not requiring a punch, a separate holding ring, or springs for accomplishing the initial holding force. Nevertheless, the apparatus of FIGURES 5 through 7 does require the application of force by the press in two stages.

During the first stage of operation with both types of apparatus, the initial holding force on the peripheral portions of the blank may, for example, be on the order of 100 pounds per square inch. In the case of the embodiment illustrated in FIGURES 2 through 4, this initial holding force is accomplished by the springs 42 and 44, whereas in the case of the apparatus of FIGURES 5 through 7 this holding force is accomplished by the pressure of the lower platen 18 against the die 50. During the second stage of the drawing operation the holding force on the peripheral portions of the blank may be increased substantially to perhaps 200 pounds per square inch or to double that of the initially applied pressure. The holding pressures will, of course, vary according to the properties of the material and the forming pressures employed.

For a thin aluminum sheet of 3 to 5 mils in thickness, the initial air forming with the apparatus of FIGURES 5 through 7 may be accomplished under a pressure of, for example, 45 pounds per square inch. The air pressure employed to form the blank in the second or final forming step of the draw with each of the embodiments illustrated in the case of the aforementioned thin aluminum sheet may, for example, be on the order of pounds per square inch. These pressures will, of course, vary according to the thinness and physical properties of the material being formed, and according to the size, shape and depth of the cavity into which the material is to be formed.

The vents 34 in the embodiment of FIGS. 1-4, and the vents 54 in the embodiment of FIGS. 5-7 are provided to permit the ready egress of air from the die cavity as the blank is formed downwardly into the cavity. However, it may be desirable to use these or similar vents to facilitate the application of at least a partial vacuum to the die cavity below the blank 11, to assist the positive forming pressure applied through conduits 46 and 58 to the top of the blank.

It may be seen with the foregoing invention deeper draws can be accomplished without producing wrinkles in the sheet and these draws may be done on equipment which is of simplified construction and in a manner which is quite economical. The formed product will be more uniformly hardened and have a more uniform thinness and appearance than products produced by previously employed processes and apparatuses. This invention eliminates the need for special lubricants or expensive intermediate annealing steps, and the product may be formed completely in one operation.

Further modifications of this invention will be apparent to those skilled in the art and it is desired, therefore, that my invention be limited only by the showing of the prior art and the scope of the appended claims.

I claim:

1. A process for drawing a sheet metal blank which comprises positioning the blank across a die having a cavity, initially deforming the blank by forcing it into the cavity while simultaneously holding the cavity-surrounding portions thereof against the die with a first force sufiicient only to partially restrain the lateral movement of these blank portions into the cavity during the initial deforming step, and thereafter further deforming the blank by forcing it farther into the cavity while holding the cavity-surrounding portions against the die with a second force sufficient to substantially completely restrain the lateral movement of these blank portions into the cavity during said further deforming step.

2. A process for drawing a sheet metal blank which comprises positioning the blank across a die cavity, forcing the blank partially into the die cavity while the portions of the blank surrounding the die cavity are gripped to permit controlled slipping of these portions into the cavity as the blank is deformed, whereby the peripheral portions of the blank within the cavity may be work hardened, and thereafter forcing the blank farther into the cavity while the portions of the sheet surrounding the cavity are gripped tightly to prevent movement of these portions into the cavity, whereby the remaining portions of the blank within the cavity may be work hardened.

3. A process for drawing a sheet metal blank which comprises positioning the blank across a die having a cavity, initially deforming the blank by forcing it partially into the cavity while simultaneously holding the cavitysurrounding portions thereof against the die with a first force sufficient only to partially restrain the lateral movement of these blank portions into the cavity during the initial deforming step, and thereafter further deforming the blank by applying fluid pressure to the top surface thereof sufficient to force it farther into the cavity while at the same time holding the cavity-surrounding portions of the blank against the die with a second force sufficient to substantially completely restrain the lateral movement of these blank portions into the cavity during said further deforming step.

4. A process for drawing a sheet metal blank which comprises positioning the sheet metal blank across a die having a cavity, initially deforming the blank by causing fluid pressure between the bottom of the die cavity and the blank to be less than the fluid pressure on the opposite side of the blank, while simultaneously holding the cavity-surrounding portions of the blank with a first force sufiicient only to partially restrain the lateral movement of these portions into the cavity during the initial deforming step, and thereafter further deforming the blank by increasing the differential in fluid pressure on the opposite sides of said blank to force the blank farther into the cavity while simultaneously holding the cavity-surrounding portions of the blank with a second force sufficient to substantially completely restrain the lateral movement of these blank portions into the cavity during said further deforming step.

5. The process recited in claim 4 wherein the cavitysurrounding portions of the blank are held against the corresponding portions of the die, and the force exerted upon these portions during the initial deforming step is substantially less than that exerted upon these portions during said further deforming step.

6. The process according to claim 5, wherein the holding force on the cavity-surrounding portions of the blank during the initial deforming step is on the order of about one half that of the force exerted on these portions during said further deforming step.

'7. An apparatus for drawing a sheet metal blank, said apparatus comprising a pair of members adapted to accommodate the blank therebetween, one of said members including a die having a cavity, the other of said members including a blank holder for engaging and holding portions of the blank against portions of the die circumjacent said cavity, a punch having a forward end sized to fit partially into said die cavity, said punch being disposed for movement relative to said blank holder between a retracted position in which said forward end is withdrawn from said die cavity and an extended position in which portions of said punch firmly engage said blank holder and the forward end of said punch is extended from said blank holder and only partially into said die cavity, spring means extending between said punch and said blank holder and effective to urge said punch toward its retracted position, whereby as said punch is moved to its extended position the blank will be partially forced into said cavity while said blank holder engages and holds the peripheral portions of the blank against the die circumjaceut the cavity only under the influence of said spring means and means for forcing the blank farther into said die cavity after said punch has firmly engaged the blank holder to substantially increase the holding force against the peripheral portions of the blank.

8. An apparatus for drawing a sheet metal blank, said apparatus comprising a pair of members adapted to accommodate the sheet metal blank there-between, one of said members including a die having a vented cavity, and the other of said members including an apertured blank holder for engaging and holding portions of the blank against portions of the die surrounding said cavity, a punch having a forward end sized to fit into said die cavity and conduit means for conducting fluid under pressure to said forward end, said punch being disposed for movement within the aperture of said blank holder between a retracted position in which said forward end is withdrawn from said die cavity and an extended position in which portions of said punch firmly engage said blank holder and the forward end of said punch is extended from said blank holder and partially into said die cavity, and spring means extending between said blank holder and said punch and urging said punch to its retracted position, whereby as said punch is moved to its extended position the blank will be partially forced into said cavity while said blank holder engages and holds the peripheral portion of the blank against the die circumjacent the cavity only under the influence of said spring means.

9. An apparatus for drawing a sheet metal blank, said apparatus comprising a pair of members adapted to accommodate the sheet metal blank therebetween, one of said members including a die having a vented cavity, and the other of said members including an apertured blank holder for engaging and holding portions of the blank against portions of the die surrounding said cavity, a punch having a forward end size to fit into said die cavity and conduit means for conducting fluid under pressure to said forward end, said punch being disposed for movement within the aperture of said blank holder between a retracted position in which said forward end is withdrawn from said die cavity and an extended position in which portion of said punch firmly engage said blank holder and the forward end of said punch is extended from said blank holder and partially into said die cavity, and spring means extending between said blank holder and said punch and urging said punch to its retracted position, whereby as said punch is moved to its extended position the blank will be partially forced into said cavity while said blank holder engages and holds the peripheral portion of the blank against the die circumjacent the cavity only under the influence of said spring means, and power means for exerting a force on said punch greater than that required to move it to its extended position, whereby after the partial forming of said blank by said punch the holding force on the peripheral portions of the blank may be increased preparatory to forcing said blank farther into the cavity under fluid pressure.

References Cited UNITED STATES PATENTS 562,309 6/ 1896 Leavenworth 7260 873,297 12/ 1907 Chillingworth 72--348 1,270,933 7/1918 Elsener 113-120 1,711,445 4/ 1929 Burvenick 113-120 1,837,720 12/1931 Lucf et al. 72--348 FOREIGN PATENTS 915,327 7/ 1954 Germany.

RICHARD J. HERBST, Primary Examiner.

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