US2611475A - Cup drawing apparatus - Google Patents

Description

23, 1952 R. E. sLATl-:R

CUP DRAWING APPARATUS Filed oct. '7, 1948 o 0 Ac D u 0 0 0 o 0 5 2 3 w M 0 0 d 6 9 0 0 0 0 0 0 0 M l INVENTOR. /PA YMoA/ 5 SLA 727? A rra/wf Ys Patented Sept. 23, 1952 CUP DRAWING APPARATUS Raymond E. Slater, New Rochelle, N. Y., assignor to Remington Arms Company, Inc., Bridgeport,

Conn., a corporation of Delaware Applicationoctober 7, 1948, Serial No. 53,298

This invention `relates to apparatus for Vthe forming of cup-like articles of manufacture and has particular reference to a punch and die set arranged to form such articles by a drawing op' eration and to simultaneously trim the mouth portion thereof to prescribed dimensions.

This application is a continuation-in-part of my copending application Serial Number 598,083, filed June 7,1945, entitled Die, and now abandoned.

It is an object of my invention to provide a die in which a cup'may be drawn by a draw punch to a desired depth and wall thickness, and wherein the metal at themouth edge vof the drawn cup, which has usually been trimmed off in a subsequent operation,'is removed in the die at a predetermined fracture point, the resultant cup having a predetermined height dimension and a substantially smooth trimmed edge.

In theusual cup drawing die the entrance to the land of the die is defined by a generatrix at a relatively small angle with the axis of the die land and is of substantial depth, so that as the wall of the cup is drawn the metal in the entrance portion of the die for a considerable `distance above the die land assumes the cross-sectional shape .of the space between the entrance portion and the punch, being gradually reduced and drawn through the land and producing at the upper edge of the cup an irregular edge which is later removed in a suitable trimming or cutoff machine. It has also'been a relatively common practice tol use with dies ofthis type a punch having a shoulder closely fitting the die land which shears or. pinches oii the upper portion of the cup as the shoulderpasses into the land of the die. With such close fitting tools there is always a tendency for apart of the edge of the cup to be extruded into the small clearance between punch shoulder'and die, with the result that the edge of the trimmed cup will be surmounted with a numberof paper thin ypinnacles or weblike protuberances. If these pinnaclesare permitted to remain on a shot shell cup they may be turned into the paper body ,on linal assembly, causing frequent cutoifs on flringas a result of the localized weakness of the body. The avoidance of cutofs has required that pinch-off work for shot shells be tumbled in sawdust to break off the pinnacles, and the rough handling incident tol the tumbling operation has resulted in the appearance of a multitude of new defects of one sort or another.

It is proposed in the present invention to provide a die having an entrance portion which is Claims. (Cl. 205-7) 2 deiined by -a generatrix` at a relatively largeangle with the axis of the die land, so that it does not outwardly co-nne the metal, and which therefore permits the formation by iianging means on the punch of a flange at the mouth edge of the drawn cup, and it is further proposed according to the invention to utilize this nange formation for the purpose of trimming the drawn cup at a predetermined point in the drawing operation.

In the drawing of tubes or cups, if the metal being drawn is at any time so treated that the forces imposed thereon exceed the strength'of the metal a break will occur, and this canhappen in either of two ways. A fracture .can be started in the metal and the forces drawing the metal relied upon to complete the break, orthe thickness of the metal can be so reduced that, presuming a relatively constant drawngfo-rce, the ultimate tensile strength of the Wall of the tube is exceeded and the break occurs. If this breaking can be predetermined as to occurrence and location, a result'simlarto va cutoff occurs, the tube or cup can be drawn to a desired length, and surplus metal scrapped'by breaking it of and discarding. In the drawing operation, the resistance to the movement of the draw punch is developed against the face of the entry by the metal which has not as yet been sizedto the diameter oi the die land, and as the forceof the punch is, to a large degree, exerted through the nose of the punch the metal passing the die land is under considerable tension. It is proposed in the inventionto provide means whereby at a pre'- determined point inthe movement of the .punch the now' of metal through the'die land is sharply restricted by the shoulder on the punch, so that this restricted metal must thereupon carry the full tensile load of the piece being drawn and, as a result, is stressed beyond its ultimate tensile strength.

It is further proposed to so shape the shoulder on the punch and the corner of the die land as to provide symmetrical opposed notches contiguous to the stressed metal, with the result that a combination of tensile forces, directly from the pull of drawing, and secondarily from the notch effect, produce a fracture in the metal, causing the flange formed at the upper end of the tube to .be separated as a scrap ring,.the fracture line of the drawn piece being ata predetermined point and constituting a substantially smooth trimmed edge. Since such a fracture is analogous to that which occurs when a notched tensile test specimen is fractured, the necking down which follows the exceeding of the elastic limit will con 3 tribute materially to the production of a smooth outwardly and inwardly beveled edge.

The exact nature of the invention as well as other objects and advantages thereof will more clearly appear from consideration of the following specification referring to the attached drawing, in which:

Fig. l is a vertical sectional view showing a punch engaged with a cup which is in the process of being drawn in a die of the preferred form. The relative wall thickness of the cup is exaggerated for clarity in illustration. Fig. 2 is a similar view at a later point in the drawing cycle where the shoulder on the punch has commenced to cooperate with the die corner to reduce the cross section of the cup.

Fig. 3 is a similar View after the cup has been fractured from the scrap ring along the line defined by the reduction in thickness.

Fig. 4 is an enlarged, partial vertical sectional view illustrating the shape of the edge of the cup and of the scrap ring in the zone of the fracture.

Fig. 5 is a graphical diagram on which punch shoulder angle is plotted against die entrance angle. The closed figure surrounds an area within which work of uniformly high quality is produced with a compressive reduction of the cup wall thickness at the cutoff line of only 75% of the total wall thickness.

Fig. 6 is a similar figure showing the conditions at a reduction of only 62.5%, and

Fig. 7 is a similar figure showing conditions when the cup wall isreduced only 50% prior to fracturing.

Referring to the drawing, it will be seen that the first three figures illustrate successive steps in the drawing and trimming of a cup-shaped workpiece I0. In accordance with the usual drawing procedure, the workpiece I has been, in a previous step, positioned in alignment with the draw punch Il which, upon descending, enters into the workpiece and forces it into the draw die l2. The forces acting on the punch Il are transmitted through the nose of the punch to the bottom of the workpiece l0 and serve in the usual manner to draw out the side walls thereof, increasing the height of the cup and sizing the walls thereof to match the space between the nose portion I3 of the punch and the land I4 of the die. As the resistance to the drawing of the workpiece is developed against the conical entrance l of the die, it follows that the side Walls of the workpiece are under a heavy tensile load. As the punch descends, the gripping action of the die entrance is enhanced by the action of the shoulder I6 on the punch which acts to flare the mouth of the workpiece into a ange engaging a greater area of the die entrance cone than would otherwise be the case. This is the condition illustrated in Fig. 1 with the flanged mouth Illa of the workpiece securely gripped in the die entrance and high tensile loads imposed on the wall of the workpiece.

As shown in Fig. 2, the continued advance of the punch causes the shoulder thereon to approach the corner between the die land and the conical entrance portion of the die, with the result that a sharply defined annular zone of reduced thickness will be formed in the workpiece wall. This zone will be at its minimum thickness when the shoulder is in opposition to the corner of the die land, and at this time the flange Ia of the workpiece will be most securely held. It is therefore inevitable that the continued application of tension to the workpiece will result in the development of a fracture in the notched wall in exactly the same manner as a notched tensile test specimen fractures in a testing machine. This condition is illustrated in Fig. 3, and in Fig. 4 an enlarged cross section shows the typical necking-down and fracture of a notched tension fracture.

The magnitude and rate of development of the forces involved are, to a large extent, dependent upon the clearance between punch and die and yon the relative angles of the die entrance throat and the shoulder of the punch. Since both die entrance throat and punch shoulder can be most conveniently formed as conical surfaces concentric with the axis of the die land, it is convenient to define the angles involved by reference to the axis of the die land or the axis of the punch. For example, in the following discussion, a die throat which is of frusto-conical shape and is defined by an included angle of could be generated by a line which makes an angle of 45 with the axis of the die land and will be spoken of as a 45 die. The same practice will be followed in regard to the shoulder on the punch.

In an extensive study of the mechanism involved in single operation draw and cutoff work, it has been found that, when the extremely close clearances characteristic of the prior art are maintained between a punch shoulder and the die land, the major considerations are found in maintaining the close clearance and sharpness of the punch shoulder necessary to cut through the Wall of the workpiece or to exert a shearing or pinching action thereon. The punches employed have been uniformly provided with a 90 or square, sharp shoulder and die entrance angles have varied from curved throats tangent to the die land to frusto-conical surfaces generated by a line making a fairly low angle with the axis of the die land. Applicant has found that die entrance angles materially greater than 42 are not useful with any range of clearances or with any shape of punch shoulder since the resistance to drawing of the cup wall is so great that the punch will tear the bottom out of the cup or pull the wall apart at some indefinite point determined by slight irregularities in metal composition or condition. Similarly, applicant has found that die entrance angles lower than 17, when used with punches having little or no clearance in the die land, invariably result in the characteristic edge contour of the prior pinch-olf practice. The trimmed edge is characterized by a multiplicity of small webs and pinnacles extruded from the severed edges by the high radial pressures involved. With such dies, tools having medium or large clearance fail to cut off at all. Within the operative range of clearances any damage to the sharp corner of the punch quickly results in an unacceptable product.

Within a range of die entrance angles between about 17 and 42, applicant has found that even when the clearance between punch shoulder corner and die land corner is equal to 25% of the thickness of the cup wall, as distinguished from a shearing or pinch-off clearance, uniformly excellent work may be obtained throughout almost the entire range when the punch shoulder angle is varied from substantally 15 to substantially 60. This condition is illustrated in Fig. 4. As might be expected, the critical nature of die throat and punch shoulder angles becomes increasingly apparent when attempts are made to operate with greater clearances between punch shoulder corner and die land corner. Figs. 6 and acume 7 illustrate the conditions which prevail when the web oftheworkpiece in thenotched zone was respectively 37.5% and 50% of the thickness of' the cup wall in the region below the fracturev line. Although thel same carefully controlled tests were not carried out to determine the absolute limit ofv clearance which may be employed, instances arev known in which excellent `cutois were obtainedwhen the minimum thickness ofthe reduced zone approached two-thirds the thickness of the cup wall. The necessary condition appears to be one in which punch shoulder and die entrance throat are substantially parallel `frusto conical surfaces, each being dened by a line generatrlx making an angle with the axis of the die land within arange between 17 and 42V with the optimum angles for both punch and die being near or slightly below 30.

The importance of starting initially with a fairly high clearance will be better appreciated with the realization that it is extremely difficult to keep punches and dies in absolute alignment Aand that no press feeding device is infallible. In

production operations concentricity of the workpiece is to a considerable degree dependent upon the self-centering action of the workpiece 'encountering the die throat and centering the punch either by slight flexing of the punch shank or shifting of the press head upon its guide-ways. If the feeding device should fail, punch and die may then make direct contact which, in the case of a close clearance, square shouldered punch, may, and usually does, result in deformation of the punch shoulder edge with the subsequent production of draw components having a burr at this point. The greater the clearances the less liability to tool contact due to misalignment, and when the punch shoulder and die entrance are formed on mating angles the damage from direct contact of tools will often be avoided and always minimized.

A further important advantage of the use of the optimum tool design will be found in the greater wear which may be obtained from such tools. Starting with a matching punch and die of the optimum angles and with a clearance which is a minimum consistent with the avoidance of direct tool contact, as noted above, the tools may be run until the diameters of the cup are no longer acceptable without failure to produce good cutois and accurate sizing as to length of the cup wall. In fact, the eiects of wear on the punch shoulder and on the corner of the die land are, to a considerable extent, self-compensating for the eiective angles tend to change together and to maintain their parallel relationship. Thus, the zone of minimum thickness remains sharply defined and at substantially the same distance from the nose of the punch producing a substantially constant height of cup. In actual production use tools produced in accordance with this invention have a working life many times greater than the low clearance, square punch shouldered tools employed for pinch-off or shear cutoi work.

The preceding discussion is intended to be illustrative only of certain preferred embodiments of my invention and is not intended to serve as a limitation thereon to any greater extent than set forth in the claims appended hereto.

I claim:

1. Apparatus for the forming and trimming of metallic cups comprising a draw die having a die land and a frusto-conical entrance throat having a least diameter substantially equal to 6. the inside diameter ofthe die land and leading thereinto, 'saldi irusto-cori-ical throat being defined bya line generatrix'forming an angle with theaxi'sy ofthe die land of between 17 and 42; and a draw punch cooperating with said die having' a generally cylindrical nose portion constructedl andv arranged to engage a cupped workpiece and to draw same through the die land, said punch being formed at` the upper end oi? said nose portion with a diametrically enlarged shoulder, the radial clearance between the major diameter of said'shoulder and the die land beingmore than one-'fourth of and less than one-half ofthe radial clearance betweenvthe nose portion of the punch and the die land.

2. Apparatus for the 'forming and trimming of metallic cups comprising a draw die having a die land and a "frusto-conical entrance throat having 'a least diameter substantially equal to the inside diameter ofthe die land and leading thereinto, said frusto-ccnical throat being defined by a line generatrix forming an angle with theaxis of the die land of between 17 and 42; anda draw punch cooperating with said die having a generally cylindrical nose portion constructed'and arranged to engage a cupped workpiece and yto draw same through the die land, said punch being formed at the upper end of said nose portion'withA an upwardly and outwardly enlarged frusto-conical shoulder the radial clearance between the major diameter of said shoulder and the die land being more than one-fourth of and less than one-half of the radial clearance between the nose portion of the punch and the die land.

3. Apparatus for draw forming metallic cupshaped workpieces and trimming such workpieces to a predetermined height comprising a draw die having a die land of generally cylindrical form and substantially the diameter of the finished workpiece, and a die entrance throat of substantially frustro-conical shape having a least diameter substantially equal to the inside diameter of said die land and leading thereinto, said throat being defined by a line generatrix making an angle with the axis of the die land of between 17 and 42; and a draw punch cooperating with said die and having a generally cylindrical nose portion of substantially the diameter of the inside of the iinished workpiece and of substantially the same length as the depth of said finished workpiece, said nose portion terminating in an enlarged frusto-conical shoulder defined by a line generatrix making an angle with the axis of the punch of between 17 and 42 with the axis of the die land, the radial clearance between the major diameter 0f said shoulder and the die land being equal to or more than one-fourth of and less than one-half of the radial clearance between the nose portion of the punch and the die land.

4. Apparatus for draw forming metallic cupshaped workpieces and trimming such workpieces to a predetermined height comprising a draw die having a die land of generally cylindrical form and substantially the diameter of the finished workpiece, and a die entrance throat of substantially frustro-conical shape having a least diameter substantially equal to the inside diameter of said die land and leading into said land, said throat being defined by a line generatrix making an angle with the axisof the die land of between 17 and 42; and a draw punch cooperating with said die and having a generally cylindrical nose portion of substantially the diameter of the inside of the finished workpiece and of substantially the same length as the -depth of said nished workpiece, said nose portion terminating in an enlarged frustro-conical shoulder dened by a generatrix which intersects the axis of the punch at substantially the same angle as the angle between the line generating said die throat and the axis of the die land, whereby said frusto-conical shoulder and said frustoconical die throat will bel dened by ysubstantially parallel surfaces, vthe radial' clearance between the major diameter of said shoulder and the die land being betWeen-one-fcurth and one-half of the radial clearance between the nose portion of the punch and the die land.

5. Apparatus for draw forming metallic cupshaped workpieces and trimming such workpieces to a predetermined height comprising a draw die having a die land of generally cylindrical form and substantially the diameter of the finished 20 workpiece, and a die entrance throat of Substantially frusto-conical shape having a least diameter substantially equal tc the inside diameter of said die land and-leading into said land, said throat being dened by a line generatrix making an angle with the axis of-the die land of between 23 and 32; and a draw punch cooperating with said die and having a generally cylindrical nose portion ofl substantially the 8 diameter of the inside of the finished workpiece and of substantially the same length as the depth of said iinished workpiece, said nose portion terminating in an enlarged frusto-conical shoulder dened by a generatrix which intersects the axis of the punch at substantially the same angle as the angle between the line generating said die throat and the axis of the die land, whereby said frusto-conical shoulder and said frusto-conical die throat will be dened by substantially parallel surfaces, the radial clearance between the major diameter of said shoulder and the die land being between one-fourth and one-half of the radial clearance between the nose portion of the punch and the die land.

v RAYMOND E. SLATER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS' Number Name Date 1,617,491 Mallory Feb. 15, 1927 1,638,995 Hodge Aug. 16, 1927 1,753,258 Zerk Apr. 8, 1930 1,968,563 Lofgren July 31, 1934 2,300,353 Eberhardt Oct. 27, 1942 2,419,862 Wales Apr. 29,I 194,7,

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