US2528577A - Metal drawing stripper - Google Patents

Description

Nov. 7, 1950 R. T. CATLIN ET AL 2,

METAL DRAWING STRIPPER Filed May 5, 1949 4 Sheets-Sheet 1 INVENTOR. GEORGE E. ECKS TE/N BY ROBERT T. 6A7'L/N ATTORN E Nov. 7, 1950 R. 'r. CATLIN E L 2,528,577

METAL DRAWING STRIPPER Filed May 5, 1949 I 4 Sheets-Sheet 2 IN VEN TOR. GEORGE E. ECKS TE/N BY ROBERT T. CA 71 //v ATTORNEYS Nov. 7, 1950 R. T. CATLlN ET METAL DRAWING STRIPPER Filed May 5, 1949 4 Sheets-Sheet 5 INVENTOR. GEORGE R. ECKS TE/N YROBERT 72 CA TL/N Nov. 7, 1950 R. T. CATLIN ETAL 2,528,577

METAL DRAWING STRIPPER.

Filed May 5, 1949 4 Sheets-Sheet 4 IN VEN TOR. GEO/76E R. [TC/(STEIN BY ROBERT T. CA 7'L/N AM Zia 3 w.

Arrow/5mg Patented Nov. 7, v 1950 stein, Milford, Cnn., assignors to Remington Arms Company, Inc., Bridgeport, Conn.,-a; cor

poration of Delaware ApplicationMay 5, 1949,. Serial No. 91,432-

9 Claims.

This invention relates to apparatus for drawing thin tubular articles, such as cartridge cases and detonator shells, and. more particularly to means for stripping such drawn components from a draw punch after the punch and com.- ponent have passed through a draw die.

Previous studies of this problem have resulted in various adaptations of the segmental ring stripper held in engagement with the punch and workpiece by an encircling or garter spring. Examples of such designs are shown in Patents Nos. 2,327,936, 2,345,857, and 2,369,260. Strippers of this type require an appreciable amount of space in the bottom of the die holder and, as shown in the patents, are not well adapted to retaining control of the drawn component until it has passed entirely beneath the bottom face of the die holder. In certain types of machines it is desirable to be able to transfer a drawn component into a transfer meansfor shifting the component to a succeeding draw or other operation. Such a transfer is facilitatedif the stripper extends below the bottom face of the die block which cannot be done with the garter spring strippers. A

Other disadvantages of the garter spring stripper have been the fact that they are completely disabled by broken springs, that as a result of scrap between the segments, ragged edge cups and other irregularities, they do not Further objects are the provision of a simple one-piece design of the stripping element and a design which can be adapted to any stripping problem regardless of the size of the drawpiece involved.

It is contemplated that these objects can'be best accomplished by the provision of a member comprising a spring flange and a plurality of individual low inertia collet-like fingers each of which is formed as an integral extension from the spring flange. Such a stripper may be'supported" in the bottom of the. draw die with. the passage through the fingers in'alignment with the die. opening.

the die block beneath In use, the .drawn component passesv through the fingers springing them outwardly and they closejupon" the shank of the punch. As, the pun'chiis retracted, the fingers act, as com-pressi'on struts between the mouth, of the drawpiece and the lower fa'ceof thedraw die or stripper support. .Since a componentof the stripping force acts to hold the endot the finger in engagement with the punch shank, there can be no. slippage. Since the individually movable collet' fingers have low inertia, they will respond quickly and may ,beused at very high. press speeds. Y Y

The exact nature of the inventionas. welljas other/objects-and advantages. thereof will be- ,come apparent from consideration of the following specification. referring to the attached drawings-in which:

Figure, 1 is a vertical sectional view through a die set including our. improved stripper, the

,partsbeing shown in, the, position in which a drawn component is entering the stripper.

v Figure 21 is a similar .viewflshowing the. parts in the position they occupy while the punch is returning and. the fingers are stripping the component from the punch.

Q Figure 3' is a partial elevational View of the stripper. g p

.jFig'ure 4jis a .top plan View of the stripper.

:iFlg'ure is a. vertical sectional view similar to ,Fi'gure1,2,"showing a modifiedxstripper andsupport thereforadapted; to beused as a replacement for strippersofithe type shown in the three patents above referred to.

, Referringi to; the drawings by characters of reference; it may be seen that Figures 1 and 2 illustrate: a I die setup which, except. for the stripper, 'is" of the conventional form used for deep drawing tubular articles. This arrangement comprises a die, cup I, fixedly mounted v v on. the bed' of a draw press and arranged to re- :ceive, and toretain by means of the retainer plate 2,. a die stack comprising a pocket die 3, adraw'die '4. draw die support ring 5, and stripper of thinning and elongating the sidewall of the drawpiece, and the stripper 6. As the punch is returned to its upper position, it is the function of the stripper to remove the now tightly fitting drawpiece from the punch.

Referring particularly to Figures 3 and 4, it may be seen that the stripper 6 is of unitary construction and comprises an annular plate-like portion 9 which may be provided with a rim I of greater thickness. The plate-like portion 9 is separated into generally radial segments II by slots 12 which may terminate in holes l3 of any convenient shape and of a size such as to define between adjacent holes a portion [4 of the segment adapted to act as a spring for the entire segment. Depending from the inner edge of the segments H are the stripper fingers l5, each of which is an integral extension of one of the'segments ll separated from its neighbors by continuations of the slots [2. As may readily be seen from the drawings, the fingers I5, considered as a group, define a collet which is spring-urged to a minimum diameter by the spring action of the portions M of the segments ll Preferably, the fingers [5 are of materially heavier crosssection than the segments II and, hence, comparatively stiff. Internally, the collet presents a frusto-conical shape of such dimensions that a drawpiece impaled on the draw punch will force the fingers to open to permit their passage. Ex-

;ternally, the collet may ,alsapresent a similar frusto-conical shape and should preferably be solidly backed with adequate clearance by some such construction as the frusto-conical wall I 6 formedrin the bottom of ,the diecup I. This clearance should be so determined as to permit adequate opening of the collet for passage of the punch and any normal drawpiece while preventing the over-expansion and possible finger breakage which might otherwise result from the passage of an upside-down cup or'of scrap or other fragments forced through the die with or ahead of a normal drawpiece. Preferably, the arrangement should be such that upon maximum expansion, simultaneous contact is established at corner I! as well as on the conical surface I6.

It will be noted that the flange 9 of the stripper is received in the die cup I with an appreciable amount of diametrical clearance which permits a lateral shifting and self-alignment of the stripper with the entering drawpiece. The

freedom of the stripper forsuch self-alignment is preserved, in spite of the thrust exerted ion-the draw dies by supporting the dies through the medium of pins l8 passingthrough the'holes l 3 of the annular flange and acting as compression struts between the bottomof the die cup and the lower draw die. Conveniently, these pins l8 may be maintained intheir position by engagement in the die support ring .5 having an axial hole 20 of less diameter than the entrance to the conical portion of the stripper. The maximum permis-' sibledimension of the hole 20 is determinable by considering a condition in which the stripper is displaced as a result of its floating movement to a maximum extent in one direction and the die support. ring similarly displaced. in a diametrically opposite direction. .Under this extreme condition the hole 20,must be small enough .to

drawpiet s as w,

lized in a draw press for caliber .22 cartridge cups having an outside diameter of substantially .224

they pass through the stripper, the land 2| on each stripper finger should preferably be lapped to a radius of curvature substantially the same as that of the drawpieces and the edge of each finger should be well rounded. To insure that the stripper fingers will fit snugly on the punch shank vand strip positively, the normal or unstressed inside diameter of the stripper lands should be slightly less than that of the punch shank. For an illustration, we may consider a stripper utiand radius of curvature seem at first contradictory, it is believed that a brief description of the .preferred method of manufacture will make it apparent that these conditions can be met with steel suitable for the manufacture of spring collets by conventional turning techniques in the form of a suitably dimensioned tube of somewhat greater length than the fingers and having an annular flange integral with one end. The annular flange may then be drilled at spaced intervals to separate the segment and to provide a run-out for the cutoff wheel or narrow milling cutter used to form the slots 12. Preferably, the slots will be started from near the end of the tubular section and the cuts are, m'ade toward the holes 13. If an end of the tubular portion is left Without slotting, this provides a support to prevent distortion of the fingers during heat treatment and the 'end'may be later severed by a suitable cutofl wheel. Before heat treatment,

the web of the'flange should be polished free of may include oil quenching from 1450 F. followed bya 30-minute draw at 450. F. This treatmenton, one typical, collet steel yields a spring structure havinga Rockwell C hardness between 58 and 60 and has been tested for over 10,000,000 cycles of extreme flexing without failure due to fatigue or other causes.

After heat treatment and cutofi to square the end of the fingers at the right length, the stripper will be found to have substantially the desired form except that the stripper lands will define a circle .208 inch in inside diameter. Obviously, this radius of curvature is such that when a .224 inch drawpiece is forced therethrough the contact with the drawpiece will be confined substantially to the edges of the fingers with resultant production of scratches which deface theproduct and may act as stress raisers to promote body splits. This situation can be corrected by introducing a .224. inch lap and.continuing the lapping of the lands of the fingers until the lap just begins to contact .at the center of each finger. With the lapremoved, the point at the center of the land of each finger will fall on an inscribed circle of .208 inch while the radius of curvature of each finger will be the same as that of a drawpiece.224 inch in diameter. As a further precaution against scratches, the edges of each finger may be well rounded by P ssi g a r bon of polishing paper through adjacent.sl'ots and working it back and forth by successively pulling on opposite ends.

so reducing the unit pressure thereon as to preclude the possibility of scratching. As the drawpiece passes beyond the fingers they spring inwardly, attempting to resume their normal inside diameter and close upon the shank of the punch. As the punch is retracted, the mouth of the drawpiece comes into engagement with the square end of one or more of the stripper fingers and the stripper is lifted with the punch until the upper face of the web comes into solid engagement with the lower face of the guard ring and all vertical play is taken out of the die stack. The stripper fingers then act as compression struts between the mouth of the drawpiece and the solidly supported die support ring with a positive stripping action and with no strain on the spring segments of the flange. Since cups sel dom draw without some scalloping or other mouth irregularity, the independence of the fingers and the rigidity of each individual finger which permits any one or more to strip the workpiece without distorting the other segments is of great signficance in regard to stripper life.

Other significant contributions to stripper life are the result of backing up the fingers with a suitable outside support to prevent over-expansion and, in the presence of a die support ring or other means, overlapping the entry face to prevent a distorted or upside-clown drawpiece from contacting the upper face of the stripper. The full floating mounting'of the stripper is also an important factor in stripper life inthat it assures correct alignment and equalization of stressesfcr each operation.

It will be noted that the stripper fingers extend below the bottom face of the die cup and are therefore well adapted to use with a transfer type mechanism in which the drawpiece is inserted into a transfer carrier as a function of the advancing movement of the draw punch after passing through the die stack. 7

Figure 5 shows a modified form of our invention adapted to use as a replacement unit in certain existing presses. Since this construction will be fairly obvious from consideration of the foregoing, the description will be brief. As in the case of the modification previously discussed, the assembly illustrated comprises a die cup 25 having mounted therein by means of a retainer plate 25, a pocket die 21, a draw die 28, stripper 29, and stripper support ring 30. This form is well adapted for use with short stroke punch presses as a result of the comparatively small vertical dimension of the stripper assembly. In this case the support ring 3 3 provides the exterior support against over-expansion of the fingers and the guarding of the upper face is provided by the draw die 28. The amount by which the diameter of the stripper cone at the entry face exceeds that of the die land should be determined by a realistic appraisal of the conditions which may exist with a maximum tolerance diameter die cup, a minimum tolerance diameter'die, and with die and stripper displaced toa maximum extent in diametrically opposite directions. Under such extreme conditions, thedie should still'protect the upper face or the stripper flange. As in the case previously discussed, the die stack is supported from thebottom of the die cup by pins 3i passing through holes 32 in the stripper flange. The stripper should have sufficient lateral freedomtopermitself-aligmnent with the drawpiece under 'themost extreme condition of-press misalignment which may be encountered.

Although two specif c. forms of the invention have been illustrated in detail and some specific dimensions have been discussed, we do not consider that our invention is limited to these specific embodiments. Accordingly, reference may be had to the appended claims for the limitations properly applying to our invention.

We claim:

1. In drawing apparatus including a reciprocating punch, stripper means for removing a drawn component from said punch comprising a spring collet supported in axial alignment with said punch and having a normal inside diameter not greater than the diameter of said punch, said spring collet comprising a plurality of separate substantially rigid fingers, and a spring and supporting flange surrounding said fingers and including radially extending portions, each formed integrally with and extending radially outward from each of said fingers.

2. Stripper means as described in claim 1, said flange having a continuous outer rim and being separated into a plurality of segments extending radially inward from said continuous rim to said integral fingers.

3. In drawing apparatus including a draw die and an advancing and retracting punch, stripper means for removing a drawn component from said punch during retraction thereof comprising an annular, platelike member of spring material supported substantially coaxially with said punch, said member being radially divided into a plurality of segments each integrally united to the member adjacent the outer circumference thereof and each separated from its adjacent segments at the inner circumference of said member, and a substantially rigid finger integral with each segment and extending from the inner edge thereof in the direction of advancing movement of the punch, said fingers defining an inwardly tapering spring collet adapted to spring open to permit the punch and drawn component to pass therethrough as the punch is advancing and to close upon said punch after the drawn component has passed.

4. Stripper means as defined in claim 3, the free end of each of said fingers being formed to define a surface substantially normal to the axis of movement of said punch.

5. Stripper means as defined in claim 4, said annular member being supported at its outer circumference with limited freedom for lateral movement whereby said collet may align itself axially with said punch.

6. Stripper means as defined in claim 5, said collet being supported with limited freedom for axial movement with said punch to facilitate flexing of said annular member and a fixedly positioned stop abutment member overlying the inner circumference of said member from which said fingers extend.

7. Stripper means as defined in claim 6, and guard means circumferentially surrounding said spring fingers in slightly spaced relation thereto with the lower face of the draw die to support same without impeding limited lateral and axial movement of the said annular member.

ROBERT T. CATLIN. GEORGE R. ECKSTEIN.

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

UNITED STATES PATENTS Name Date Newell Apr. 4, 1944 Number

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