US3483723A

US3483723A - Process for the deep drawing of mainly cylindrical hollow objects from blanks and blank holder and drawing ring for carrying out the said process

Info

Publication number: US3483723A
Application number: US675691A
Authority: US
Inventors: Arie Verkaik; Leonardus Bouwer
Original assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Current assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Priority date: 1966-10-31
Filing date: 1967-10-16
Publication date: 1969-12-16
Anticipated expiration: 1986-12-16
Also published as: GB1195278A; BE705873A; DE1602521C3; SE326421B; DE1602521B2; DE1602521A1; NL6615372A

Description

Dec. 16. ERK ETAL 3,483,723

PROCESS FOR THE DEEP DRAWING OF MAINLY CYLINDRICAL HOLLOW OBJECTS FROM BLANKS AND BLANK HOLDER AND DRAWING RING FOR CARRYING OUT THE SAID PROCESS Filed Oct. 16, 1967 United States Patent 3,483,723 PROCESS FOR THE DEEP DRAWING OF MAIN- LY CYLINDRICAL HOLLOW OBJECTS FROM BLANKS AND BLANK HOLDER AND DRAW- ING RING FOR CARRYING OUT THE SAID PROCESS Arie Verkailr, Rotterdam, and Leonardus Bouwer, De'ft, Netherlands, assignors to Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk Onderzoek ten behoeve van Nijverheid, Handel en Verkeer, a corporation of the Netherlands Filed Oct. 16, 1967, Ser. No. 675,691 Claims priority, application Netherlands, Oct. 31, 1966, 6615372 Int. Cl. B21d 22/26 US. Cl. 72350 9 Claims ABSTRACT OF THE DISCLOSURE A process for the deep drawing of mainly cylindrical objects from blanks, in which additional bending loads according to a predetermined pattern are applied to the blank in order to provide the separation of the blank into zones which are substantially exempt from deformation in tangential direction and zones which are subjected to a considerable deformation in tangential direction, as a result of which process cutting losses due to corners of the blank or to textures in the blank material are compensated, and a drawing ring provided with protruding arms in the shape of a starfish and a blank holder provided with cams protruding f om a base surface to fit this shape, the flanks of the said arms and of the said cams being adapted to apply additional bending loads to a blank and to separate zones supported by the arms and being substantially exempt from deformation in tangential direction from zones subjected to a considerable deformation in tangential direction.

When deep drawing mainly cylindrical hollow objects, round blanks, which have been obtained from a plate or band through punching, are usually started from. By arranging the blanks in the plate or the band according to a predetermined pattern, the least possible punching loss is aimed at because the material which is left over between the blanks is reduced to waste after the punching. After the blanks have been punched they are conveyed towards the deep drawing tools and drawn into hollow objects.

These deep drawing tools comprise a drawing ring and a drawing punch, which can be moved right into and through the rounded bore of the drawing ring, to which is usually added an annular blank holder, which is pressed by a constant or a variable force round about the drawing punch on to the blank, which is supported by the drawing ring. The pressing starts before the drawing punch has been set in motion and may continue until the object has been drawn and driven into the bore of the drawing ring.

When deep drawing, stresses of various nature will already occur in the blank outside the diameter of the bore of the drawing ring. If a round blank is started from, the stresses are in the first instance equal on all the places over the whole of the circumference on a defi ite radius and the most desired situation is for the whole to continue on a rotationally symmetrical course. Usually, this is no longer the case as soon as deformation begins to occur.

The blank holder has to take care that an even deformation and displacement of the material of the blank is achieved and that wrinkling is suppressed.

When the compressive force is constant, the blank 3,483,723 Patented Dec. 16, 1969 holder will exert an axial compressive stress which will in general be parallel to the centre line of the tools and this means that the specific axial compressive stress, when the compressive force is constant, will increase as the blank gradually disappears into the bore.

When the compressive force is not constant, the specific axial compressive stress may be kept constant or may be controlled according to a definite program during the whole process. The course of the compressive force may be controlled in accordance with the requirements of the material of the blank. However, many other factors are to be taken into account, such as the centric situation of the round blank with respect to the die, clearance, reinforcement during deformation, speed of deformation, friction and lubrication.

The motion of the drawing punch gives rise to radial drawing stresses in the blank, which stresses are dependent on the circumference of the circle on which they occur and which must lie within certain determined limits. If the drawing stress comes to exceed the local strength, the blank may tear apart, but if the stress is too little, no displacement will follow and the aim of taking the material to the bore is not reached.

Because in the beginning the blank has a much larger diameter than the bore in the drawing ring, a tangential compressive stress will begin to make itself felt as a result of the radial drawing stress, which tangential stress makes the circumference smaller but also takes care that in that region upsetting takes place in the blank and the blank becomes thicker and may Wrinkle.

This wrinkling must be prevented by the blank holder and the axial compressive stress exerted by it.

Thus far, all the stresses and deformations could be rotationally symmetrical, if it were not that the material was hardly ever isotropical, but may have certain preferred directions. As a result of this, there will always be formed an irregular stress distribution with irregular deformations, so that a drawn cylindrical object will always show a wavy edge with two or more so-called ears, where the drawn cylinder mantle is considerably higher than in the intermediate places. In order to obtain an object without a wavy rim, a cutting treatment is necessary, entailing a second loss of material which depends on the size of the ears. 7

If a material with a pronounced texture, i.e. with clearly preferred directions, is started from, the said ears often are the cause of great losses and it is one of the objects of the invention to overcome these difliculties. In order to become more familiar with the idea of texture we would explain that a material with a texture herein is understood to mean a material, in which the yielding properties in various directions, chiefly at right angles to one another, may differ considerably. With sheet and band material this will result in objects in which ears develop usually at about forty-five degrees to the rolling direction, but the angle may also decrease to thirty degrees, in which case six ears may form instead of four. A few experiments will quickly determine the nature of the material.

Another object of the invention is to obtain a further saving, by starting the production of cylindrical objects not from round blanks, but from blanks having more or less straight edges and preferably having a square or rectangular shape. Punching is then superfluous and the plates/ sheets or bands are cut so as to form these blanks. In this manner it is possible to eliminate the normal punching losses and to dismiss of the whole of the punching treatment together with its tools.

If, in the most favourable case, the angular blanks have been cut out of a plate/sheet or band having a pronounced texture in such a manner that car formation 3 takes place on those parts of the blank, which are situated between the corner points, a great advantage may be attained, but even if the texture is less pronounced considerable advantage may be reached as to the consumption of material and as to processing.

In order to realize a complete or part implementation of the above-described advantages, the present invention provides a process in which a round or a nonround and preferably a square or rectangular blank is subjected by the co-operating blank holder and drawing ring to additional tangential bending loads, which are distributed over the circumferences of circles according to a predetermined pattern, and which largely separate zones having substantially no deformation in tangential direction from zones having a considerable deformation in tangential direction and consequentially also in radial direction.

According to this process, the breaking in upon the theoretical rotationally symmetrical stress course is deliberately aimed at and this course is replaced by a stress distribution, in which the stress and deformation course inherent to the material of the blank is compensated by external means to form a practical deformation pattern of high efficiency of the material required for the production of the object.

In carrying out the process according to the invention, use is made of a drawing ring, which is profiled in the shape of a starfish preferably with four arms, and a blank holder, which is correspondingly profiled with due observance of the clearance required for the thickness of the blank to be processed.

For this purpose, the blank holder according to the present invention may be provided with a number of cams, the height of the active surface of the said cams above the base surface of the blank holder decreasing from the periphery towards the centre line of the holder, and with flanks which extend from the periphery towards the centre line up to a diameter which is larger than the diameter at which the rounding of the bore of the drawing ring begins, the drawing ring being provided with a number of supporting arms corresponding to the number of the cams of the blank holder, the upper surfaces of the said supporting arms corresponding to the base surface of the blank holder and the flanks of the said arms corresponding to the flanks of the cams, whilst the sectors of the drawing ring which lie between adjoining arms have been recessed at most as deeply as the height of the cams above the base surface of the blank holder on the selfsame diameter.

Preferably, the corresponding flanks of the cams and of the arms run parallel to each other and to the centre line of the blank holder and the drawing ring and they extend up to the circumferences of circles having diameters on which the upper surfaces of the arms merge into the rounding of the bore of the drawing ring.

The flanks of the cams preferably run straight up to the lowest point and the flanks of adjoining arms that are turned towards each other are connected by bent surfaces near the lowest point.

For a satisfactory operation it is desirable that the junctions of the flanks and the upper surfaces of the cams and of the arms should be provided with roundings, which decrease from the periphery towards the centre line.

Preferably, the upper surfaces of the arms are shaped in a flat plane and the active surfaces of the cams form part of a conical mantle. In that case, the base surface on which the cams are supported, is also a flat plane and the surface of the sectors maybe part of a conical.

The arms of the drawing ring need not necessarily form a fixed part of the drawing ring, but may be exchangeable, either as complete stars or as separate arms. In the latter case, it is possible to adjust the angles between the arms to the material to be used. Naturally, the same holds good for the cams on the blank holder, provided cams and arms correspond with each other.

The arms and the cams may also be exchang d for dit- .4 ferent ones, the flanks of which run a different course with respect to the main direction of the arms. Generally speaking, it will be possible to use exchangeable cams and arms with testing tools, but for the tools used for production a construction with fixed arms and cams is to be preferred.

The invention will hereinafter be elucidated with reference to the accompanying drawing of a blank on which diverse zones are indicated and of an embodiment of a lank holder and a drawing ring according to the invention.

FIGURE 1 shows a square blank 1, in which various zones A, B and C are indicated.

FIGURE 2 shows a perspective view of the blank holder seen from below.

FIGURE 3 shows a perspective view of the drawing ring 3 belonging to the blank holder 2 seen from above.

It is clear that, when a square blank 1 is placed between a generally known flat bank holder and drawing ring, this blank will be drawn by a round punch to form a substantially cylindrical hollow object, the mantle of which shows tips which derive from the corners of the blank. When an object is drawn on this blank holder and drawing ring from a round blank having the diameter of the dotted circle drawn within the square, this object will not show the tips of the previous object, but it will show ears which are due to the texture present in the blank. In order to obtain a flawless object, the upper edge of the mantle should in both cases be cut, the tips causing a greater loss than the ears. However, the loss of the tips had already been incurred when the round blank was punched from the square, so that about the same amount of material is lost in both cases.

With a square blank 1 according to FIGURE 1, which is drawn to form a cylindrical hollow object, the zones A and B are to be distinguished. Zone A runs from an encircled central part C towards a corner point and zone B towards the middle of a side. The material from the zone A, which broadens towards the central part C, should only flow in radial direction, whilst the material of the zone B should be compressed in tangential direction, so that the radial stream is increased. In the example of FIGURE 1, a zone A covers about sixty degrees of the circumference of the central part C and the zone B covers about thirty degrees. Generally speaking, the diameter of the central part C is somewhat larger than the diameter of the bore of a drawing ring increased by the roundings towards the drawing bore and there about /3 of the blank surface.

In order to get as high as possible a wall for the cylindrical object, it is desirable that the surfaces of the zone should be proportional to their arcs of the central part i.e. in this case zone A should be about twice as large as zone B.

However, the proportion between the zones A and B and the direction of the separating lines is dependent on the blank material and the proportions between the surface of the blank, the thickness of the material and the diameter of the die.

In order to reach the desired aim, it is attempted to avoid the occurrence of compressive stresses in the zone A and to prevent a radial extension as much as possible.

This may be achieved by compensating the compressive stresses in a tangential direction, so that a tangential drawing stress remains and extension in radial direction is pre vented.

In zone B on the other hand, a considerably higher than normal compressive stress must be excited, because here a large radial extension is indeed necessary.

Therefore according to this invention, the blank is subjected to additional bending loads, which are distributed over the circumferences of circles according to a predetermined pattern, which loads separate the zones A mainly without deformation in tangential direction from the zones B with large deformation in tangential direction and consequentially also in radial direction. The points on the various circle circumferences, at which this bending load should be applied, are indicated on the blank 1 by the separating lines between the zones A and B. The bending load is applied by having the zones A flow between a blank holder and a drawing ring in their own plane under a medium compressive force and by bending the zones B from the plane of the blank over certain edges of the tools before and during drawing. Because these edges do not run radially, but according to the separating lines A and B, a tangential drawing stress is produced during drawing in the zone A, which gets broader towards the centre line, whilst in the zones B, which are compressed by the edges in a direction perpendicular to the said edges, a tangential compressive stress arises, which considerably compresses the material in a tangential direction and in this way brings about an extra extension in radial direction.

The course of the tangential width of the zone A is a measure for the compensation of the tangential stresses and is related to the texture, the size and the thickness of the blank and the diameter of the punch with which the object is drawn. When the surface of the central part C is small with respect to the blank, the separation lines of a zone A can almost run parallel to each other, but when the central part C is large, the tapering of a zone A should be much greater. In this case a zone B is compressed to a considerably larger extent and the deflecting should be more forceful, if the separation of the two zones is to remain etfective at deformation.

The tools that will be described in the following by way of embodiment may be used in carrying out the process of the invention.

According to FIGURE 2, a blank holder 2 is provided with a flat base surface 4 round about an aperture 5, through which may move a drawing punch not shown in the drawing. On the base surface 4 are provided four cams 6, the active surfaces 7 of which form part of a cone mantle having a top, which is situated on the centre line of the blank holder within the aperture 5. The height of the cams 6 above the base surface 4 decreases regularly from the periphery to within a little distance from the aperture 5.

Between the cams 6 channels 8 have been formed, which broaden towards the aperture 5, and the principal directions of which stand under angles of ninety degrees, and which are defined by the base surface 4 on the one hand and by the erect flanks 9 of the cams on the other hand. The flanks of the cam 6 are at right angles to the base surface 4 and run along a straight line to end in a point. They are rounded ofl towards the active surface 7 and the radius of curvature 10 increases from the point towards the periphery.

According to FIGURE 3, a drawing ring 3 belonging to the blank holder 2 is provided with a conical mantle surface 11 and a bore 12, which is larger than the aperture 5. The top of the conical mantle is situated on the centre line of the bore 12 but above the said bore. The top angle of the cone corresponds to the top angle of the active surfaces 7 of the blank holder 2. Four carrier arms 13 protrude above the surface 11 as the arms of a starfish, the upper surfaces 14 of the said arms being at right angles to the centre line of the bore 12.

The main directions of the arms 13 correspond to the main directions of the channels 8 and consequentially here also form angles of ninety degrees.

The upper surfaces 14 extend as far as to the circle circumference 15, where the rounding-off towards the bore 12 begins.

The carrier arms 13 have flanks 16, the height of which increases with respect to the intermediate sectors of the cone surface 11 from the vicinity of the circle circumference 15 as far as to the periphery and they are parallel to the centre line of the bore 12, consequentially they are at right angles to the upper surfaces 14.

The junctions between the flanks 16 and the upper surfaces 14 are provided with roundings, the radii of curvature 17 of which increase towards the periphery. The arms 13 have a size which corresponds to that of the channels 8, but they are narrower by at least twice the thickness of the blank to be treated. For this reason, the flanks 16 of adjoining arms, which flanks run along a straight line, are interconnected by curves 18 and do not taper into points as the flanks of the cams 6 do.

On equal diameters, the arms protrude less far above the intermediate sectors of the cone surface 11 than the cams 6 protrude above the base surface 4 of the blank holder 2, because the compressive force of the blank holder on these parts should be greater than between the arms 13 and the channels 8.

Under certain circumstances it may be recommendable to have a base surface 4 not of plane but of conical construction, the upper surface 14 then being flat or also conical. it is, for instance, necessary that the vertical distance between base surface and upper surface should decrease from the periphery towards the centre line, in order that, when the drawing is started, the specific axial pressure near the periphery shall be greater than in those parts of the blank which are situated nearer to the centre line.

The flanks need not always be plane surfaces or parallel to the centre line of the blank holder and drawing ring, but they may be bent or they may form an angle with them, in such a way that the arms 13 get broader from the upper surface 14, for instance, towards the surface 11 and that the channels 8 get narrower from the active surface 7 towards the base surface 4. The minimum width of the cleft between the flanks of the cams and those of the arms is equal to the thickness of the blank, but will generally be larger, because the extra stresses caused by the tangential bending load, should indeed be sufficient to compensate the tangential stresses in the desired mannet and to separate the zones, but not so great as to have the passage offer such a great resistance when drawing, that the strength of the blank is locally exceeded with the result that it is torn apart. It is for this reason that the radii of

curvature

10 and 17 decrease together with the flanks towards the centre line, because otherwise excessive concentrations of stress could arise at the locations of the points of the flanks 9 on the cams 6 and near the curvatures 18 at the ends of the flanks 16.

Therefore, the shape of a blank holder and a drawing ring depends as to detail on the flowing properties of the blank material and the relations between the blank surface, the blank thickness and the die diameter.

A blank holder and a drawing ring according to the above-described embodiment of the invention may be operated as follows.

A square blank cut from a sheet with feeble texture is laid with its corners on the arms 13. The cams 6 of the blank holder press the zones B through towards the cone surface 11, whilst the zones A are jammed between the base surface 4 and the upper surfaces 14. Thus, a higher axial pressure arises in the zones B than in the zones A and the tangential bending stress is realized by the junctions of the surfaces with the flanks on the separation lines between the zones. When the drawing punch comes down and the drawing towards the bore 12 is started, the blank is gradually diminished. Owing to this, the zones A of the blank are not compressed tangentially by the broadening of the arms towards the centre line, but they are stretched a little and flow regularly towards the roundingotf circle 15, whilst the zones B, which have been pressed through by the cams 6, are just very strongly compressed in tangential direction between the flanks of adjoining arms which are directed towards each other. This mighty compression might give rise to wrinkles, if it were not that the specific axial stress in that location is greater and that the naturally possible wrinkles are drawn away over the rounded-off edges of the erect flanks in radial direction. The cylindrical hollow object which is finally formed in many cases still has four erect wall tips, deriving from the original square form of the blank, but the lower parts in between, which derive from the straight sides of the blank, are shaped and pulled up in such a way that it is possible to cut an object with a smooth edge, which is higher by about 30% than that of an object normally obtained from a blank of the same dimensions without applying the present invention. The object obtained according to the process of the present invention has a height which is about equal to the height of an object cut from a blank of considerably larger area.

The wall of an object normally drawn from a blank measuring 66 x 66 mm. has a height of about 40 mm. at the tips and a minimum height of about 21 mm. Consequentially, the object, after its edge has been trimmed, has a maximum height of 21 mm. If the object is normally drawn from a round 66 mm. blank, there is a punching loss of with respect to the square which is lower if the round blanks are cut from a sheet in a staggered way, for instance in a coordination as equilateral triangles. Irrespective of the costs of the punching tools, the punching loss equals the cutting loss of the tips after drawing.

However, if from a blank of 66 X 66 mm. an object according to the invention is drawn, the wall is 40 mm. high at the tips but the minimum height amounts to 29 mm., so that the object is about 30% higher than without the application of the invention, the punching tools being superfluous. An object with such a height of 29 mm. can only be obtained by starting from a round or square blank of 74 to 75 mm. with a normal punching or cutting loss of 20%, if the present invention is not applied. The overall saving in material alone amounts already to 66 with respect to 74 mm. or about 20%.

In the foregoing it was assumed that the blank material had a feeble texture. However, if this is not the case, and the material has, as a result for instance of rolling, a strong tendency to ear formation, there are two possibilities. With a rolling texture, four ears are usually formed at forty-five degrees to the rolling direction, whilst for other materials six ears are not impossible.

If round blanks are started from and it is known to be possible for the blanks to be placed on deep drawing tools in an oriented way, the invention offers the possibility of positioning the blank on the drawing ring in such a manner that the ear formation shows to full advantage. This may be achieved by having the main direction of the arms 13 and the direction of the ears coincide. As a matter of fact, in this case the material situated in the zone between the ears must be specially stretched in radial direction in order to be able to join smoothly in the flow. The even flow is obtained by compressing the said zones in tangential direction by the application of the additional bending load. The process according to the invention is then carried out in such a manner that the points at which the bending load is applied to the various circle circumferences, are situated on lines, which at most are parallel to the direction according to which the ears would form. Preferably, the flanks 16 of the arm 13 then no longer diverge towards the centre line, but they run parallel to each other per arm just as the flanks 9, which limit a channel 8. If there is a possibility of ears forming, which form angles different from those of forty-five degrees with the rolling direction, the arms and channels should naturally be provided below these angles, and when six ears are present they may form angles of 30, 90 and 30 degrees respectively with the rolling direction. By applying this process, the possibility is obtained of saving material on the diameter, but a punching loss for the production of round blanks remains unavoidable.

If unround and preferably square or rectangular blanks are started from made from a material with ear formation, the punching loss thus having been reduced or eliminated by the continuous straight or broken cutting lines, the invention may also be applied. In this case, ear formation is used in a different way from that described above, by having the ear formation occur in those places. where an extra extension is necessary. These are the places where the distance to the central part of the blank is smallest, i.e. opposite the straight or nearly straight edges of the blank. Then only the normal flow in radial direction will occur in the direction of the diagonals which connect opposite corners whilst the yielding opposite the edges is composed from the yielding due to ear formation and the radial extension deriving from the tangential compression caused by the additional tangential bending load. In this case the points, at which this load is applied, are preferably situated on lines, which at most are parallel to the diagonals, so that the zones A of the blank do not increase as do tangential width towards the centre line.

If the ear formation is not symmetrical per ear, it is possible all the same to make use of the invention, if the flanks of arms and cams are not positioned symmetrically with respect to the main direction. In the case of laboratory tools being provided with exchangeable cams and arms, the proper shape for the production of a definite object from a definite material may be determined prior to its being manufactured. It is then possible to start from a rectangular almost square blank instead of from a square one, which has no influence on the cutting of blanks from sheet or band, but may indeed contribute towards the saving of material,

When working up textured sheet there may be a complication when ear formation does not occur lengthwise or transversely in the plate/sheet, but, as is usual, under forty-five degrees. In that case the angular blanks should be cut from the sheet according to oblique lines, for instance also under forty-five degrees, which will cause cutting losses at the edges of the sheet. If, however, the blanks are small as compared with the sheet, this loss is more than compensated by the advantages of the process according to the invention. When the blanks are larger. oblique cutting may entail greater losses, but then the refinement of the use of the ear formation is neglected and cutting is after all effected along a straight or broken line mainly parallel to the edge of the sheet.

It is a matter of course that, as in this specification cylindrical objects made from square or rectangular blanks have been dealt with, the application of the tangential bending load for the separation of certain zones of the blank, when manufacturing hollow objects with rounded rectangular or square or elliptical or even different transverse cross-sections, fall within the scope of the present invention.

What is claimed is:

1. A blank holder and a drawing ring forming a cooperating set for deep drawing; said blank holder comprising a base surface provided with an aperture through which a drawing punch is moved, a plurality of cams provided on said surface, the height of said cams above said base surface and the width of the cams parallel to said base surface decreasing from the periphery of the blank holder towards the aperture, said cams forming a plurality of channels between adjacent cams and extending from the periphery of the blank holder towards said aperture; and a drawing ring counter pro filed to mate with the base surface of the blank holder with clearanct necessary for the blank to be processed, said drawing ring comprising a surface provided with an aperture through which a drawing punch is moved and .a plurality of raised arms registrable with the channels of said blank holder, the height of said arms above the surface of said drawing ring decreasing from the periphery of the drawing ring to the aperture therein.

2. A blank holder and drawing ring according to claim 1 wherein each of the arms on said drawing ring includes two sides, the adjacent sides of adjacent arms being interconnected at the lowermost point of said arms adjacent the aperture of said drawing ring.

3. A blank holder and drawing ring according to claim 2 wherein the edges of each of said arms formed along the junction of the side and upper surface of each arm is rounded, the radius of curvature of the rounded edges decreasing from the periphery towards the aperture.

4. A blank holder and drawing ring as claimed in claim 1 wherein said blank holder is provided with four cams forming four channels spaced at nominally 90 from one another around the blank holder, and wherein said drawing ring has four arms likewise spaced around the drawing ring.

5. In a method of deep drawing an object in which a blank is subjected to an axial compressive force between a holding blank and a drawing ring, and wherein the blank is drawn through an aperture in said drawing ring, the improvement wherein a minimum amount of the drawn material is wasted by the formation of wavy edges on the drawn object which comprises providing a cooperating blank holder and drawing ring, said blank holder having a base surface provided with an aperture through which a drawing punch is moved, a plurality of cams provided on said surface, the height of said cams above said base surface and the width of the cams parallel to said base surface decreasing from the periphery of the blank holder towards the aperture, said cams forming a plurality of channels between adjacent cams and extending from the periphery of the blank holder towards said aperture, and a drawing ring counter profiled to mate with the base surface of the blank holder with the clearance necessary for the blank to be processed, said drawing ring comprising a surface provided with an aperture through which a drawing punch is moved and a plurality of. raised arms registrable with the channels of said blank holder, the height of said arms above the surface of said drawing ring decreasing from the periphery of the drawing ring to the aperture therein, deep drawing a material between said blank holder and drawing ring whereby zones of the material drawn over said arms are substantially free from deformation in a direction tangential to said axial force, and zones of the material drawn over said cams are subjected to considerable tangential deformation and consequently to deformation in a radical direction.

6. A method according to claim 5 wherein said blank is round.

7. A method according to claim 6 wherein the material forming said blank is oriented such that upon deep drawing ears are formed in a known direction related to the orientation and wherein the blank is positioned between the drawing ring and blank holder such that zones of the material which would form the ears are located adjacent the arms on the drawing ring to minimize formation of said ears.

8. A method according to claim 5 wherein said blank is square.

9. A method according to claim 3 wherein the zones of material forming the corners of said square blank are located adjacent the arms on the drawing ring to minimize the formation of wavy edges.

References Cited UNITED STATES PATENTS 15,513 8/1856 Gomme et a1. 72350 598,800 2/1898 Meyer 72-350 1,915,164 6/1933 Orem et al. ll3120 2,681,630 6/1954 Hempel 72350 FOREIGN PATENTS 647,274 10/ 1964 Belgium.

3? 414 10/1885 Germany.

RICHARD J. HERBST, Primary Examiner