US3494169A - Deep drawing method and apparatus - Google Patents

Description

Feb. 1-0, 1970 w. T. SAUNDERS 3,494,169 A DEEP DRAWINGMETHOD AND APEARA'I'US V Filed Jan. 21, 1966 2 Sheets-Sheet 1 gm gig) 5325 m R AZT RiNG,30 35 Rlms I FIX-E2? DIE A 3 i i Z y P mNERRmms P P H04 FIGS H a Q Q A A E Q 32 36 30 32 as so 32 as INVENFOR WILLIAM T. SAUNDERS ATTORNEW Feb. 10, 1970 w, T. SAUNDERS 3,494,169

DEEP DRAWING METHOD AND APPARATUS Filed Jan. 21, 1966 2 Sheets-Sheet 2 FIG? - mvmon WILLIAM T. SAUNDERS B ysw ATTORNEYS .United States Patent 3,494,169 DEEP DRAWING METHOD AND APPARATUS William T. Saunders, Weirton, W. Va., assignor to National Steel Corporation, a corporation of Delaware Filed Jan. 21, 1966, Ser. No. 522,312

Int. Cl. BZld 22/22 US. Cl. 72350 11 Claims ABSTRACT OF THE DISCLOSURE This invention is concerned with cold drawing methods and apparatus for forming container bodies from sheet metal.

In cold drawing of sheet metal, a flat blank is placed between a die cavity and a movable punch and the metal is formed into the desired shape by moving the punch into the die cavity. Edges of the die cavity and punch are sufiiciently rounded to prevent cutting of the metal and the spacing between the die cavity and the punch is sufiicient to allow for the .full thickness gauge of the sheet metal blank so-that substantially no reduction in thickness of themetal takes place in the drawing operation. q

However during drawing the. metal is subjected to stresses tending to deform the metal other than desired. For example, the peripheral dimensions of a sheet metal blank are reduced during a drawing operation. This places the metal under compression in a peripheral direction. At the same time, the drawing action tends to stretch the metal in a radial direction. The peripheral compression tends to buckle the metal forming wrinkles and the radial tension tends to tear the metal. In a shallow draw these stresses can be held within strength limits of the metal being drawn. But, where the depth of draw requires the periphery of a blank to be decreased about twenty-five percent, or more, the prior art had no economically practicable solution to these stress problems. With soft metals, buckling or stretching of the metal was accepted. With steel, several drawing steps were required, often coupled with heat treatment or other special steps to avoid tearing of the metal.

The present invention makes possible a deep-drawing operation where the peripheral outline of the blank can be decreased forty percent and more in a single stroke without formation of wrinkles and without tearing of the metal. In addition a uniform-thickness-sidewall container body can be drawn because the metal is under substantially uniform pressure throughout the single stroke. The invention is applicable to conventional temper (TU) steel, full hard steel plate such as that proposed for container sidewalls, tinplated or other metallic plated steel, and softer metals such as aluminum and copper.

The accompanying drawings will be referred to for a more detailed and specific description of the invention, including other unique features and advantages. In these drawings:

FIG. 1 is a cross sectional schematic view of die structure at the start of a drawing operation,

FIG. 2 is a cross sectional schematic View of the die structure of FIG. 1 at an intermediate stage in a drawing operation,

FIG. 3 is a schematic cross sectional view of die structure embodying the invention at the start of a drawing stroke,

FIGS. 4 through 6 are schematic, cross sectional partial views of the die structure of FIG. 3 at intermediate stages of a drawing stroke, and

FIG. 7 is a schematic diagram partially in cross section of apparatus embodying the invention.

In FIGURES 1 and 2 a sheet metal blank 12 is drawn over a fixed die 14 using movable punch 16. Fixed die 14 has a cylindrical shape and movable punch 16 is tubular. The movable punch 16 is moved into overlapping coaxial relationship with fixed die 14 and the metal at peripheral portion 18 of metal blank 12 is drawn down the sides of the die 14.

Metal blank 12 is gripped between movable punch 16 and pressure pad 20 which is tubular in configuration and is coaxial and overlapping with fixed die 14. Great force is needed to initiate a draw and, to avoid formation of wrinkles, edges of the metal blank must be held with a force matching that of the drawing force. Pressure pad 20 is used for this purpose and the upward pressure of pad 20 will prevent wrinkling of the metal during a shallow draw.

It will be noted in FIGURE 2 that the area of the metal blank 22 between movable punch 16 and pressure pad 20 decreases as the blank is drawn. The high pressures required for the draw are more concentrated as the area of metal between the movable punch and the pressure pad decreases and tearing of the metal will result if a deep draw is attempted. Also the metal has a tendency to stretch unevenly under these high pressures causing earing of the cup, that is, the open edge of the article formed will be uneven and its sidewall will have varying lengths at differing points about the open edge periphery. When back pressures are relieved in order to avoid tearing the metal or reduce the earing problem, wrinkling of the metal around the sidewall of the cup will be encountered during a deep draw.

The present invention permits deep-drawing in a single stroke, provides for substantially uniform pressures on the metal during the draw to avoid earing of the metal, and at the same time prevents wrinkling without tearing of the metal. For this purpose a plurality of pressure rings are used which successively contact the metal blank being drawn to prevent wrinkling of the metal during the drawing stroke and, after contact with the metal blank, each of the pressure rings opposes the pressure of the movable punch to help equalize the pressure on the diminishing area of the metal blank being drawn.

The starting position for the single-stroke drawing operation of the present invention is shown in FIGURE 3. Circular metal blank 24 is positioned over a cylindrical fixed die 26 and gripped at its outer periphery between movable punch 28 and outer ring 30. The pressure on outer ring 30 is parallel to the longitudinal axis of fixed die 26 and exerts a force opposite to the direction of movement of movable punch 28.

Referring to FIGURE 4, as the movable punch 28 starts downwardly the diameter of sheet metal blank 24 is decreased. After start of the stroke, and before the peripheral portion of sheet metal blank 24 loses contact with outer ring 30, middle ring 32 comes into contact with the sheet metal blank. It will be noted that middle ring 32 independently exerts a force similar in direction to that of outer ring 30'. Also, as shown in FIG. 3, that its upward movement is determined by flange surface 34 between middle ring 32 and inner ring 36. Similarly, flange surface 35 determines the upward movement of outer most ring 30. Flange surfaces 34, 35, and

flange surface 38 between inner ring 36 and fixed die 26, serve as interconnecting means to determine the initial positioning of the other ring 30, middle ring 32 and inner ring 36. Initial contact of middle ring 32 with the sheet metal blank 24 is selected so as to prevent wrinkling of the sheet metal blank and to maintain a continuous substantially uniform back pressure on the blank.

As movable punch 28 continues downwardly in its stroke the sheet metal blank terminates contact with outer ring 30. Before loss of contact however, pressure on the metal blank is spread over a greater area by the contact with the middle ring 32. After termination of Contact of sheet metal blank 24 with outer ring 30, the ring moves into contact with movable punch 28 and the upward force exerted by outer ring 30 opposes the downward pressure of movable punch 28. This reduces the pressure on the reduced-area peripheral portion of sheet metal between movable punch 28 and middle ring 32 and helps equalize the pressure of the sheet metal blank during the drawing stroke.

As shown in FIGURE 5, sheet metal blank 24 has been drawn so that a peripheral portion is in contact with middle ring 32. Inner ring 36 has come into contact with the sheet metal blank to prevent wrinkling of the metal and distribute the pressure exerted by punch 29 as the blank is drawn. Outer ring 30 opposes the downward force exerted by punch 28.

In FIGURE 6, the peripheral portion of blank 24 is being drawn between inner ring 36 and movable punch 28. Outer ring 30 and middle ring 32 exert a force in opposition to the downward pressure of movable punch 28.

The number of pressure rings, the spacing of the rings along the longitudinal axis of the die structure, and the individual force exerted by the rings are selected to make the pressure on the metal substantially uniform as the blank is drawn and thereby produce a uniform thickness sidewall. In general the deeper the draw, the greater the number of rings to be used. Also, the blank contact area of the several rings can be varied to help maintain uniform pressure on the metal.

The basic principles of the invention have been described in relation to a cylindrical die and movable punch of tubular configuration. However, those skilled in the art will readily visualize the application of these principles to other configurations and to drawing structure in which a closed-end cylindrical punch draws the sheet metal by being moved into coaxial relationship with a hollow die cavity. In the latter embodiment, the pressure rings are mounted in coaxial relationship with the cylindrical punch and spaced along its longitudinal axis. The pressure rings move with the cylindrical punch and help take up draw pressure and prevent wrinkling of the metal as the diameter of the blank decreases. As in the illustrated embodiment, the outermost pressure ring will contact the peripheral portion of the sheet metal blank first and the innermost ring will contact the blank last.

With either the tubular punch or closed-end cylindrical punch embodiments, the automatically functioning features of the invention which prevent wrinkling or tearing of the metal come into play independently without resort to a coordinated-movement physical linkage between the movable punch member and the rings to control pressure on the metal. These features of the invention permit drawing of a sheet metal blank to form a container body or cup shaped article without substantially changing the gauge of the metal. While some stretching of metal is practically inevitable in a drawing operation it is emphasized that the teachings of the present invention do not rely on stretching of metal to form the desired shape.

Assembled apparatus for single-stroke cutting and drawing of a sheet metal blank is shown schematically in FIG. 7. Drive means 44, which can be conventional, drives punch 46. On the downward stroke of punch 46 sheet metal 48 is blanked by cutting edges 52 and 54. The cut blank isthen gripped between punch 46 and pressure ring 56 as the punch moves into coaxial relationship with fixed die 58. Pressure ring 56 is supported by a plurality of pins such as pins 60 and 62 on thrust pad 64. Spring 66 is supported between the thrust pad 64 and washer 68. Stem 70 is threaded at 72 and nut 74 fixes the position of washer 68. The force exerted by spring 66 on pressure ring 56 can be varied by adjusting the position of nut 74 along the stem 70'.

As the blank is drawn, contact is made with inner ring 76. This ring is supported by a plurality of pins such as pins 78 and 80 which rest on thrust pad 82. Spring 84 acts between thrust pad 82 and washer 86. Nut 88 fixes the position of washer 86 and can be used to adjust the force exerted by spring 84.

The pin support structures are used in the embodiment of FIG. 7 to give access to the adjustment nuts. Cylindrical supports with access holes to adjustment nuts could be used as well.

Other yieldable compression means can be substituted for the springs shown in FIGURE 7 and shock absorber rubber pads can be used at the thrust pads and washers. While the spring action is preferred for simplified automatic functioning it is understood that pneumatic or hydraulic compression means could readily be used.

It is to be understood that the springs shown in FIG. 7 are for purposes of illustration only and are not neces sarily in true size relationship. The size of the springs and length of stroke of individual rings are selected based on the depth of draw and the material being drawn. With the present disclosure of the principles of the invention, selection of spring sizes or other compression means, the number of rings, blank contact area of individual rings, and the stroke of individual rings will be within the purview of one skilled in the art. It is also to be understood that other ring support arrangements, than shown in FIG. 7 which avoid physical connection between the rings and the movable punch, can be resorted to without departing from the scope of the invention as covered by the appended claims.

What is claimed is:

1. Apparatus for forming a sheet metal blank into a container body by a single-stroke deep-drawing operation compnsmg die means including a die cavity, punch means, and

means for moving the punch means into coaxial relationship with the die cavity to form a container body having an endwall and sidewall from a sheet metal blank, and

a plurality of coaxial pressure rings positioned to successively grip an outer peripheral portion of the sheet metal blank as the sheet metal blank is formed, each pressure ring being yieldably mounted and having means for independently exerting a force opposite in direction to movement of the punch means during a drawing stroke, the plurality of pressure rings including at least an outer ring and an inner ring arranged to contact the sheet metal blank around its entire periphery with the outer ring contacting the sheet metal blank prior to contact by the inner ring during a drawing stroke.

2. Apparatus for cold forming a sheet metal blank of predetermined thickness gauge into a container body with a wrinkle-free sidewall of substantially uniform thickness by a single-stroke deep-drawing operation comprising an elongated fixed die over which the sheet metal blank is to be formed, the fixed die having an endwall surface and a sidewall surface spaced from the longitudinal axis of the fixed die,

movable punch means having a tubular configuration with internal dimensions permitting the punch to be moved into overlapping coaxial relationship with the fixed die with spacing between the sidewall of the fixed die and the movable punch means being at least as great as sheet metal thickness gauge,

a plurality of pressure rings including an outer ring and an inner ring positioned in overlapping and coaxial relationship with each other and fixed die,

yieldable pressure means acting on the pressure rings tending to force the pressure rings along a path parallel to the longitudinal axis of the fixed die in a direction opposite to the direction of movement of the movable punch means when the movable punch means is being moved into overlapping relationship with the fixed die, and

interlocking means for initial positioning of the pressure rings in spaced relationship along the longitudinal axis of the fixed die so that the outer ring contacts the sheet metal blank prior to contact by the inner ring as the movable punch means is moved into overlapping coaxial relationship with the fixed die to form the container body.

3. The apparatus of claim 2 in which the fixed die has a cylindrical configuration and the sheet metal blank has a circular configuration.

4. The apparatus of claim 2 in which the plurality of pressure rings are spring mounted to exert a force opposite to the direction of movement of the movable punch.

5. The apparatus of claim 2 further including blanking means for cutting the sheet metal blank as part of the single stroke operation prior to drawing of the sheet metal blank.

6. Method of forming a sheet metal blank into a container body by a single-stroke, deep-drawing operation comprising the steps of positioning a sheet metal blank between a die cavity and a movable punch means,

driving the movable punch means under predetermined pressure into the die cavity to shape the sheet metal blank into a container body having an endwall surface and a sidewall surface, and during shaping of the sheet metal blank,

gripping a portion of the sheet metal blank about its entire periphery with an individual pressure ring selected from a plurality of pressure rings yieldablymounted to independently exert a force against the sheet metal blank in a direction parallel to direction of movement of the punch means, the plurality of pressure rings including at least an outer ring and an inner ring in coaxial relationship and positioned to successively contact the sheet metal blank as the movable punch means is driven into the die cavity with the outer pressure ring contacting the sheet metal blank prior to contact by the inner pressure ring.

7. In forming a container body from a sheet metal blank by single-stroke deep-drawing of the sheet metal blank by moving a tubular punch into overlapping coaxial relationship with an elongated fixed die, a method for providing substantially uniform sidewall draw and preventing buckling of sidewall metal of the container body during drawing comprising the steps of providing a plurality of pressure rings of tubular configuration and positioned in overlapping coaxial relationship with each other and the elongated fixed die, the plurality of pressure rings including at least an outer pressure ring and an inner pressure ring,

yieldably forcing the pressure rings in a direction opposite to the'direction of movement of the tubular punch during a drawing stroke,

positioning the rings initially in spaced relationship longitudinally of the elongated fixed die to contact the sheet metal blank at diifering times during a drawing stroke, with the outer pressure ring contacting the sheet metal blank prior to contact by the mner pressure ring,

gripping the sheet metal blank between the tubular punch and the outer ring, and

driving the tubular punch with predetermined force into overlapping relationship with the fixed die so as to form the sidewall of the container body, with a portion of the sheet metal blank around its entire periphery coming into successive contact with individual pressure rings starting with the outer pressure ring, with each next adjacent inner pressure ring contacting the sheet metal blank before release by each next adjacent outer pressure ring in order to apply continuous pressure on the sheet metal blank during drawing to prevent buckling of the blank and with each pressure ring opposing the force of the movable punch after releasing the sheet metal blank.

8. In forming a container body by deepdrawing sheet metal over an elongated fixed die in a single stroke with a tubular punch which is moved into overlapping coaxial relationship with the fixed die, a method for providing uniform sidewall draw and preventing buckling of sidewall metal comprising the steps of providing a plurality of pressure rings including an outer ring and an inner ring in coaxial and overlapping relationship with each other and the fixed die, each pressure ring being yieldably mounted to exert a force in a direction parallel to the longitudinal axis of the fixed die and opposite to the direction of movement of the tubular punch when being moved into coaxial relationship with the fixed die, the plurality of pressure rings being positioned initially along the longitudinal axis of the fixed die so that the outer pressure ring contacts the sheet metal prior to contact by the inner ring during movement of the tubular punch into coaxial relationship with the fixed die and driving the tubular punch under predetermined pressure into overlapping relationship with the fixed die to form a container body.

9. The method of claim 8 further including the step of cutting a blank of predetermined peripheral dimension from the sheet metal during the single stroke of the tubular punch and prior to drawing of the sheet metal.

10. The method of claim 9 in which the peripheral dimension of the sheet metal blank is reduced in excess of twenty-five percent by the single drawing stroke of the tubular punch.

11. The method of claim 10 in which the sheet metal blank comprises steel.

References Cited UNITED STATES PATENTS Re. 20,009 6/ 1936 Hothersall 72-351 1,453,652 5/1923 Auble et al. 72349 1,550,387 8/1925 Nilson et a1 72349 1,675,910 7/ 1928 Riker 72347 1,967,245 7/ 1934 Hothersall 7235 1 2,591,061 4/1952 Gaudreau 72351 3,203,218 8/1965 Bolt et al 72349 FOREIGN PATENTS 280,900 5/ 1952 Switzerland.

CHARLES W. LANHAM, Primary Examiner E. M. COMBS, Assistant Examiner

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