US2930483A - Cold shaping of steel - Google Patents

Description

March 29, 1960 B. KAUL 2,930,483

COLD SHAPING OF STEEL Filed May 24, 1951 s Sheets-Sheet 1 ulna:

MI I W 6/ INVENTOR.

BEA! A7904 Arrox/vzrs March 29, 1960 B. KAUL 2,930,483

COLD SHAPING OF STEEL Filed May 24, 1951 3 Sheets-Sheet 3 INVENTOR. az/v x4 04 This invention relates to cold shaping of steel and more particularly .to the cold shaping of a ,steelblank to form a tubular article having one or more radially enlarged portions ion the outer surface thereof.

In the manufacture of tubular articles there often arises the necessity ofproviding on the outer surface of the article one or more radially enlarged portions, or bourrelettes .as they are sometimes referred to. When these bourrelettes are formed integrally with the article, they are 7 usually formed ,by casting or by forging, depending on the nature of the workpiece and the method of forming the tubular article. ;-Where the conditions of useof the article impose relatively high strength requirements, the

material used for forming the tubular article is usually an and hardness without heat treatment by controlling-the extent to whichvarious portions of the blank from which the article is formed are cold worked.

More specifically, the invention contemplates ,a procedure for cold extrusion of steel wherein the metal is permitted to how in a more or less unconfined manner within a range of elongation permitted by .the yield strength of the steel. When steel is permitted to flow freely not onlyare the pressures required for-coldshaping substantially reduced but ofequal importance is thefact that the extent to which the metal is hardened by cold working is substantially reduced. This latter factisextremely important in any process of-cold extrusion or cold shaping of steel because, when the steel has been cold I 2, 9 30,t83 Patented Mar. 29, 196% Fig. '2 is a diagrammatic sectional view of the die arrangement employed in carrying out the first step of my pro s 1 .Fig. 3 is a diagrammatic sectional view of the die arrangement employed in the second step of my process Whichcomprises the first rearwardextrusion operation.

Figs. 4 and 5 are diagrammatic views illustrating the die arrangement employed for the second and third rearward extrusion operations, respectively.

,Fig. 6 is a diagrammatic view showing the. die arrangement employed in the forward extrusion operation of my process which follows the rearward extrusion operation shown in Pig. 5. v

Fig. 7 is a diagrammatic view showing the die ment for expanding the bourrelette.

Fig. v8 is .a diagrammatic view similar to Fig. v6 and showing a modified die arrangement.

Fig. 9 is a diagrammatic view of the die arrangement for expanding the bourrelette on the blank formed by the operation illustrated in Fig. 8.

Fig. 10 is a view similar to Fig. 6 showing a further arrange- .modified die arrangement for producing a plurality of bourrelettes on the surface of the article.

Fig. '11 is a diagrammatic view of the die arrangement for expanding the bourrelettes on the blank formed by the operation illustrated in Fig. 110,

, alloy steel and the workpiece, when cast or forged, is nsubjected to one or more :heat treatments to obtain the to the other.

,Figs. 12 and 13 are sectional views showing the shape ofthe blanks utilized in the operationsillustrated in Figs. 8 and 10, respectively.

The drawings illustrate a method .and apparatus for cold shaping a steel blank to form a closed bottom tubular container. It will become apparent as the description proceeds that the invention is not limited'to the extrusion of closed bottom containers but is equally adapted for producing tubular articles which are open from one end The method and apparatus is .described with reference to .a closed bottom container only for the purposes of illustration, and itiwill be readily appreciated that manydifferent forms of-tubular articles can be produced by the method and apparatus described herein.

The starting blank in my process of cold extrusion comprises a cylindrical piece of steel, designated 9 in the the .blank may have any cross section desired such as square, rectangular, hexagonal, etc.

worked to substantially its yieldpoint, further cold work-- 5 truding tubular metal articles and forming bourrelettes on the outer surface of the article to develop a desired, substantially uniform hardness throughout the article by controlling the extent of cold working the various portions of the article. In my method of cold extrusion, after a particular sectionof the article has been brought down to its final size, this particular section has been cold worked to the extent necessary to bring the hardness and strength up to the desired value; and it is not thereafter cold worked to any great extent. Likewise, the sections of the article which are to be subsequently cold worked are maintained in a soft flowable condition so that in most instances little or no annealing is necessary before subjecting these sections to further cold working operations for the purpose of bringing them down to their final size and shape.

in the drawings:

Fig. 1 is a view in side elevation of a metal blank cut from steel bar stock as received from the ,mill which is used as a starting blank in my cold extrusion process.

Steel .bar stock as received from the mill is not always of accurate dimension. It maybe slightly out-of-round andthe diameter thereof may vary slightly. These variations must be eliminated in the first step to control the accuracy of later steps of my new procedure because, for

regularities in later operations employed for cold shaping the .blank into the final article.

Thesteel employed in my process of cold shaping need not be of a high quality. An ordinarycarbon steel with the carbon ranging up to (40% is satisfactory. The carbon or other alloycontentof the steel selected will-depend upon thesize and shape of the finished article, the use to which the article is put and the amount of cold shaping required to transform the steel blank intothe'finished :article. The hardness obtainable by cold working varies in accordance with the carbon or other alloy content of the steel but, on the other hand, the amount of cold work which is permissible before the yield strength of the steel is reached generally varies inyerselywith the amount of alloys contained in the steel. Therefore, although a particular high quality analysis of steel is not required in my process, a steel should be selected which will meet the cold working and strength requirements of the finally shaped article. 7

In order to size the blank 9,the blank is first subjected to the coining operation illustrated in Fig. 2. The blank is placed within a die 10 having a cavity 11 which has a tapered portion 12 connected with a reduced tapered portion 13 by an angular shoulder 14. The punch 15 is cylindrical in shape and is provided with a shallow nose 16 which has a fiat lower face 17, rounded corners and conical side walls 18. The diameter of nose 16 is less than the diameter of punch 15. The upper end of cavity 11 is cylindrical and has a close fit with punch 15. The die cavity 11 is dimensioned such that, when the blank '9 is inserted in die 10, it assumes the position illustrated by dotted lines in Fig. 2 wherein the lower end of the blank is supported on the angular shoulder 14 of the die. When the punch is driven downwardly on blank 9, nose 16 forms a depression 20 at the central portion of the top face of blank 9 and the downward pressure applied to the blank by reason of punch 15 causes the'blank to assume the position and shape indicated by solid lines in Fig. 2.

In carrying out the sizing operation illustrated in Fig. 2 the side walls of blank 9 are compressed by the punch 15 to fill the accurately sized tapered die cavities 12 and 13 and the blank is slightly elongated as illustrated. This sizing operation removes all out-of-roundness that may have been present-in the bar stock from which the blank 9 was cut and provides perfect roundness for all portions of the blank. The blank thus sized, generally indicated as 21, has a reduced tapered portion 22 and a larger tapered portion 23 connected with the portion 22 by an angular shoulder 24. The bottom wall of blank 21 is unsupported during the downward movement of punch 15.

Since the portions 22, 23 and 24 of blank 21 taper outwardly from the lower to the upper end of the blank,'it will be observed that the blank can be readily ejected from the die 10 by means of the knock-out member 26.

Since the punch nose 16 is perfectly centered with respect to the die cavity 11, the depression 20 formed in the top face of the blank is perfectly centered with respect to the side walls of the blank 21, thereby forming a centering means for the punch used in the next operation so that the cup-shaper blank to be formed thereby will have walls of uniform thickness. tofore encountered in the cold extrusion of steel has been the inability to obtain perfect concentricity and uniform wall thickness in the finished article. If a punch used in an extrusion operation does not or is not permitted to cavity portion 32. When the blank 21 is inserted in cavity 29 it drops to the position indicated in dotted lines in Fig. 3 with the bottom face 25 of the blank seated upon the knockout member 35 which is slidably arranged in a cylindrical bore 36 at the lower end of the die. There is associated with die 28 a punch 37 having a cylindrical nose portion 38 which is arranged to seat within the recess 20 of blank 21. Nose 38 has a flat bottom face 39 connected with the side walls of the punch by a rounded corner portion 40 which is tangent to bottom face 39 but not tangent to the cylindrical side walls of the punch, as is explained with greater particularity in my co-pending application Serial No. 161,760, filed May 13, 1950, now Patent No. 2,748,932.

When punch 37 moves downwardly in cavity 29 from thejposition illustrated in broken lines to that shown in solid lines, the flat bottom face 39 of the punch engages the depression 20 and causes the metal around depression 20 to fiow radially outwardly beneath the flat bottom face 39 of the punch and upwardly around the corner 40. Since corner 40 is not tangent to the side walls of the punch, the metal beneath the bottom face flows outwardly and upwardly around corner 40 out of contact with the side walls of the punch. There is no friction between the side walls of the punch and the blank being formed. The clearance between the punch and the side walls of the cavity 41 formed thereby shown exaggerated in Fig. 3. The metal in the lowermost part of portion 22 of the blank is merely subjected to pressure and not subjected to appreciable cold working. The blank 27 is thereby 5 provided with side wall 42 together with a relatively heavy bottom wall 43 defining cavity 41.

The metal immediately below cavity 41 and in the 7 anneal the blank at this point prior to further cold working.

For instance, I have found that when the blank 9 is cut from hot-rolled bar stock having the composition of A.I.S.I. C-lO l2, the cold working operation illustrated in Fig. 3 produces a hardness on some surfaces of blank 27 as high as 98' to 102 Rockwell B.

Since the subsequent cold forming operations would inthe extrusion process. When any surface of an extruded One of the difiiculties herecenter exactly, the punch may be crowded to one side or' the other and may break; or in the absence of breakage, non-uniform wall thicknesses may result, which in turn may produce non-uniform hardness in the walls of the finished article at any section.

Since the coining operation illustrated in Fig. 2 is performed by permtting the metal in the portion 23 of the blank to expand slightly under compression without appreciable friction, the portion 23 of the blank retains substantially the same softness as the starting blank 9 except at the depression 20 which is only slightly cold worked. The metal at the portions Hand 24 is compressed and caused to flow axially slightly and the metal in these portions is therefore cold worked to a slight extent.

After theblank 9 has been shaped into the accurately sized blank 21, it is ready for cold shaping into the extrusion blank indicated generally at 27. To deform blank 21 into the shape of blank 27, the die arrangement illustrated in Fig. 3 is employed. This arrangement includes a die 28 having a cavity 29 shaped to receive blank 21. Cavity 29 has a reduced upwardly and outwardly tapered portion 30 and an upwardly and outwardly extending shoulder 31 which connects the portion 30 with a tapered part approaches a hardness of about 102 Rockwell B, the part must be softened by heat treatment before further extrusion can be performed without rupture of the Work piece. A normalizing or an annealing treatment at 'about 1450" F. reduces the hardness of blank 27 to about 64 or 65 Rockwell B.

'lower end of which has a reduced upwardly and outwardly tapered portion 46 which is connected with an upper enlarged upwardly and outwardlytapering portion 47 by .a tapered shoulder 48. When the blank 27 is dropped into cavity 45, it assumes the position indicated by dotted lines with the bottom face of the blank supported by the knock-out member 50. A punch 51 is arranged to be moved downwardly into the cavity 41. The shank of punch 51 has a nice fit with the walls of cavity 41 and the nose 52 of the punch has a relatively flat bottom face 53 which is connected with the side walls of the punch by an arcuate, outwardly and upwardly tapering corner portion 54.

When the punch 51 is moved downwardly from the position indicated by broken lines to that indicated by full lines in Fig. 4, that is, to a point wherein the fiat bottom face 53 ofthe nose 52 is substantially at the level of of blank 27 is displaced radially outwardly beneath the flat face 53 and upwardly around the arcuate corner direction.

portion54 to produce the .blank 55 having .side walls 56 and a bottom wall 57 which define a cavity 58. fIhe arcuate corner portion 54 on punch '51 produces an annular inwardly extending shoulder portion 59 at the .lower 'end of cavity 58. During the rearward extrusion operation illustrated in Fig. 4, .the metal in the side wall 42 of blank 27 is cold worked to a slight extent and the bottom wall 43' is merely subjected to compression. The blank 55 .is then subjected to the .final rearward extrusion operation illustrated in Fig. 5. In this operation the blank is inserted in a die .60 having a cylindrical cavity 61 which is reduced as at 62 to accommodate Zthe side wall portion .56 of blank 55 and which is further areduced as at angular shoulder 63 to provide, at the lower.end of the cavity, a portion 64 which accommodates shoulder 91.

ames a ing extrusion shoulder .83.:on .d ie;8i) and .the bottom wall of the blank is disposed at a-level,.below the cavity portion 84. Punch 82,.has acylindrical portion 86 which .slidably engages the cylindrical cavity 81 and a shank I portion 87 which is connected with the cylindrical portion; 86 by .a rounded corner 88. At the lower end of shank 87 the punch is provided with a semi-spherical nose 90 connected with the shank 87 by .an arcuate Shank 87 has a diameter which corresponds generallywiththe diameter of cavity -.76 .above shoulder 68 of blank 75 and nose 90 has a diameter corresponding generally with .the diameter of cavity 76 belowzshoulder 68. Punch 82 is dimensioned in length the bottom wall portion.57 of blank 55. The portion 62 of cavity 61.tapers slightly outwardly in an upwardly The punch 69 has a cylindrical portion 65 which has a sliding fit 'in cavity '61. At the lower end jof cylindrical portion 65, the punch is provided with a concentric shank .66 provided with asemi-spherical nose portion 67 which is of smaller diameter than shank 66. .The nose portion 67 is connected with shank 66 by an arcuate shoulderportion 68. .The diameter of shank 66 ..corresponds with the diameterof the cavity 58 adjacent the upper. end of blank55. When the blank 55 is inserted .in die 60, it assumes the position indicated by dotted .lines with the annular ;.shoulder 70 of blank 55 which ,is

formed bythe-shoulder 48 on die 44 resting upon shoulder =63 and with the bottom face of the blank seated upon the knock-out :member 71;at the :lower end of the die :.cavity. It will be observed that blank 55 substantially completely fills the cavity of die 66 and that the lower .end f the blank cavity -58'is substantially at the level .ofsshoulder 63. 1,

.As ,thepnnch 69 moves downwardlyitrom the position indicated in broken lines to that indicated by solid lines in Fig. 5, the metalinthe bottom wall ,57 flows outwardly sand upwardly around the punch and is extruded between the nose 67 of punch 63 and annularrshoulder 63. The .metal in the .side wall 56 of blank 55 moves upwardly .in the-portion 62 of cavity 61. vAs the nose .67 moves downwardly past the shoulder 63on .die .60, it will be observed that the shoulder 70 on blank 55 moves up wardly in cavity portion 62 outof'contact withshoulder .63. It will be noted that since the cavity portion 62 .tapersinwardly from top to bottom, the metal is extruded upwardly free of friction with the walls of cavity portion 62. The elimination of friction atthis point materially reduces the pressure required for extrusion. The blank 75 thus formed has a cavity 76 which corresponds .in shape and size withtheshank-66 of punch 69 and the nose 67 thereof. .Cavity 76 has a shoulder 74 which corresponds in contour with shoulder 68 on punch 69. The metal in the side wall 77 ofblank 75 above shoulder 70 has substantially the same hardness as the side wall portion 56 of blank 55, whereas, the metalin the insert :sidewall portion 78, that is, the inwardly offset side wall portion below shoulder 70, has been subjected to considerable cold work and is stressed to a point approaching the yield strength of the material.

The blank 75 produced by the operation illustrated in Fig. 5 "comprises the forward extrusion blank, and the :subsequent forward extrusionoperationis performed with the apparatus illustrated in Fig. 6 wherein the die bilhas --a cylindrical cavity 81v inwhich a punch 82 is slidably artranged. Cavity 81: is provided with an inwardlyextending,

.such that, when the rounded corner.88 on the punch moves downwardly into engageemnt with the upper end of the side wall 77 of blank 75, nose 90-of the punch-is spaced upwardly and does-not bottom on the bottom wall of cavity 76.

When the punch :821is ,forced downwardly from the position shown in dotted lines to that indicated in solid 7 lines in Fig. v6, the extrusion shoulder 88 on the punch exerts a compressive torce'on the upper end of the wall portion 77 of blank and themetal in the wall portion 77 and the upper portion of wall 78 flows downwardly and is extruded around extrusion shoulder 83 and through I the'clearance between the nose 90; and the side Wall of the cavity portion 84. The metal flow isindicated by the arrows 92. This portion of the extrusion operation position where the shoulder-91is horizontally aligned with the bottomregion of extrusion shoulder 83, the wall portion 73.is-.extruded t o ataperedshape as'indicated It willsbe'observed that, as-theshoulder 91 -moves downwardly past shoulder 83 {and through extrusion cavity 84, the extrusion orifice is gradually reduced in size due to the enlargement of thepunch at this point and the downward inward taper of. cavity 84 and the side walls 94' of the extruded blank 95 above the tapered .shoulder portion 96 are thinned down to the thickness desired in the finished tubulararticle. In this operation the metal in the side walls77of blank 75 ,is'cold worked to the degree desired to obtain the-strength and hardness required of the finished-article. It will be appreciated, of

course, that the dimensions iof the annealed blank .27 are calcaulated such that the extrusion operations illustrated in Figs. 4, 5 and 6 will subject the blank -to the cold working necessary to produce thelhardness in the side walls 94 desiredof the finished tubular article and a hard- .ness in the side wa1li97 below arcuate shoulder 96 just I slightly below that desired in the finished article. ,The

metal in the outwardly flared upper end 98 of, blank 75, however, remains relatively soft.

The taperedwall portions -97 -areproduced in the blank I )5 to provide for the formation of an enlargement or a bourrelette on theouter surface of the article adjacent the. lower end thereof. This enlargement is produced by the apparatus ;illustrated*in;F ig. 7 wherein a die 100 is provided with a cylindrical cavity 101' having a diameter corresponding to the outer diameter ofthe enlargement "desi edonthe article. A punchltiz is arranged to move downwardly into and centrally of cavity. 101. vPunch 392. has arshank 103 of slightly less diameter than the cavity in blank 95 ab0ve shoulder 96, and an inwardly tapering nose 1M thecross section of whichis greater than that of the cavity in blank 95 below shoulder '96.,

As the punch 102 moves downwardly into the blank 95, the nose 1% engages shoulder 96 and the metal in the wall portion 97 is, displaced outwardly until it comes in contactwith the side wall of cylindrical cavity 101. A portion of theexcess'metal' in' the tapering-side wall portion 97 is therefore displaced outwardly beyondthe shown in Figs. 2 through 5.

, outer surface of the side wall portion 94 to produce the desired enlargement'105 on the completely extruded blank 106. This operation produces only slight cold working of the metal in the side wall portion 97 so that the hardness of the finished blank is substantially uniform throughout and .is' developed solely by controlled col working of the metal in the successive blanks.

The upper flared end 98 of the blank may'begnosed [inwardly and machined in accordance with the shape desired of the final article. The nosing operation is one of cold forming and increases thehardnessof that section to approximately the hardness. of the remainder of the blank. A final stress relieving treatment at about 750 F. is optional depending on the end product. The

desired yield strength can be obtained entirely by cold working if the analysis of the steel is such that the ultimate strength is not exceeded by such cold working.

In the operations illustrated in Figs. 2 through 7 it will be noted that the excess metal'on the inside of the blank for forming the bourrelette 105 is provided by extruding the blank such that the side wall of the blank in the vicinity of the desired bourrelette gradually tapers inwardly toward the bottom 'of the blank. This excess metal shown in Fig. 12 may be utilized in the forward extrusion' operation. The blank, generally designated 11!), has a side wall111 fashioned with an extrusion shoulder 112 on the outer surface thereof and with a rather sharp shoulder 113 on the inner surface thereof which connects the upper enlarged bore portion 114 with the reduced lower bore portion 115. Blanks 110 may be formed in a manner and with apparatus similar to that The blanks 75 and 110 are shaped similarly with respect to their exterior surfaces. The principal diiference between these blanks lies in the differently shaped shoulders within the bore of the blanks. In blank 75 shoulder 74 forms a gradual ta'per in bore 76, whereas, in blank 110 the bore diameter changes abruptly at shoulder 113.

Blank 110 is forwardly extruded in the apparatus illustrated in Fig. 8 which includes a die 116 which is of the same design as die'80 shown in Fig. 6. Die 116 has an upperenlarged bore 117 and a lower reduced bore 118 which are connected by the extrusion shoulder 120. The punch 121 is somewhat similar to punch 86 except that the shank 122 and the nose 123 are connected by a rather sharp corner portion 124. When blank 11% is inserted within the cavity 117 of die 116, it assumes the dotted line position shown in Fig. 8 wherein the shoulder 112 seats upon extrusion shoulder 120 on the die. When the punch 121 is driven downwardly from the dotted to the full line position, the shoulder 124 on the punch engages the shoulder 113 on the blank and the rounded corner portion 125 at the upper end of the punch shank 122 engages the wupper end of the blank. As the punch moves downwardly, the metal in theside wall 111 is extruded through the orifice formed bythe nose 123 of the punch and the reduced bore 118 on the die just below shoulder 120. It will be noted that this extrusion orifice is of substantially uniform cross section until the shoulder 124 moves downwardly past shoulder 121 then the extrusion orifice is' abruptly reduced in cross section due to the enlargement of shank 122. The forwardly extruded blank 126 is therefore fashioned with a side wall having a thick portion 127 at the lower end of the blank and a thinner portion 128 at the upper end of the blank. Blank 126 has a substantially cylindrical outer surface and the side wall- portions 127 and 128 are connected by a shoulder 129 on the inner surface of'the blank.

In order to form a bourrelette on the outer surface of blank 126, the apparatus illustrated in Fig. 9 is employed. This apparatus includes a two-part die 130 having an upper section 131 and a lower section 132 assembled together with abutting fiat faces 133 and 134. Die section 131 has a cavity 135 which is shaped to snugly receive the lower end of blank 126. Cavity 135 has a depth corresponding to the spacing desired between thebourrelette to be formed on the blank and the lower end of the 1 blank. Die section 132 has a bore 136 which corre- 130 has a cylindrical shank 141 having a diameter corresponding to'the diameter of the bore of blank 126 above shoulder 129 and 'a reduced nose portion 142 having a diameter corresponding to the diameter of the bore of blank 126 below shoulder 129. Shank 141 and nose 142 are connected by a rounded shoulder 143. When blank 126 is inserted in die 130 and punch 140 is driven upwardly into the blank from the dotted to the solid line position, shoulder 143 on punch 140 engages shoulder 129 on blank 126; and as the punch is driven upwardly, the metal in the side wall portion 127 is displaced outwardly by the shoulder 143 into the cavity formed by counterbore 137 to form the bourrelette 144. By reason of the counterbore 137, it will be observed that the bourrelette 144 has more sharply defined corners than the bourrelette 105 which is formed by the operation illustrated in Fig. 7.

one bourrelette on the surface of a tubular article.

In some instances it may be desired to form more than The procedure for forming a plurality of bourrelettes spaced axially along the tubular article is shown in Figs. 10 and ll; andthe blank employed is illustrated in Fig. 13. The

blank 150 has an external shape similar to blanks 110 and 75. The bore 151 of blank 150, however, comprises three portions of different diameter, an upper enlarged portion 152, an intermediate portion 153 and a smaller portion 154. The portions 152 and 153 are connected by a rather abrupt shoulder 155 and the portions 153 and 154 are connected by a similar shoulder 156. This bore formation in blank 150 provides the blank witha side wall having a thin'portion 157 at the upper end 164 is similar to punch 121 (Fig. 8) except that the shank of the punch is formed with three sections 165, 166 and 167 of progressively decreasing cross section which correspond respectively with the bore portions 152, 153 and 154 of blank 158. Section 165 connects with section 166 by means of a rather sharply rounded corner portion 168 and'the portion 166 connects with the portion 167 by means of a rather sharply rounded corner portion 169. The sections 165,. 166 and 167 aredimensioned such as to interfit with the corresponding portions of the blank as illustrated in dotted lines in Fig.10. The portion 167, however, is shorter than the depth of bore portion 154 so that the lower endof thc punchatiitdoes not bottom at the lower end of the-blank 150.

When blank 150 is inserted withindie 160,:it assumes the position illustrated in broken lines :in Fig.10 wherein the external shoulder 170 on blank 150 seats dhe g extrusion shoulder 163 of the die.-- When the punch is driven downwardly from the position shown tin ghroken :lines to that shown in full lines, shoulder .1694on3the punch engages shoulder 156 on .the blank, shoulder 168 engages shoulder 155, and the rounded corner portion 171at the upper-end of .the punch engages the upper end of ,theiblank 150. .As the punchm'ovesdownwardly; the

.metal-in the .thick wall portion 158 above shoulder 170 v on the blank is extruded through the orifice formed by shoulder I63 and .the shank portion .167 of the punch. This extrusion orifice is substantially uniform until the punch moves downwardly to a position wherein the shoulder 163 where the extrusion orifice is then abruptly reduced by the shank portion 165 and the tapered shoulder 184 is extruded. The extrudedblank 175 is thereby provided with a relatively thick wall portion 176 at the lower end thereof, a thin wall portion 177 adjacent the upper end thereof, and a wall portion 178 of intermediate thickness between portions 176 and 177.

The bourrelettes are formed on the outer surface of blank 175 by the apparatus illustrated in Fig. 11, which apparatus includes a two-part-die 180 having an upper section 181 and a lower section 182 provided with flat abutting faces 183 and 184, respectively. Section 181 is provided with a downwardly opening cavity 185 which is shaped to receive the bottom or closed end of blank 175. Section 182 is formed with a bore 186 having a diameter to snugly receive the cylindrical'side wall portion of blank 175. At its upper end bore 186 is counterbored as at 187 and 188 to provide two enlargements at the upper end of bore 186 which are connected by a relatively sharp annular shoulder 190. Shoulder 190 is located such that the vertical distance between shoulder 190 and the upper end of cavity 185, when the sections 181 and 182 are assembled as shown, corresponds.gen-' with the upper internal shoulder 194 on blank 175 when -;ness desired in dhezfinal article. The wall-portions .178

grand 1 76..-are-c old worked a .lesser extentlso that-:thecold forming operation illustrated in Fig. 11 slightly increases the hardnessat the wall portions 176 and -178=to thereby produce hycold -.working a .hardness which is substantially iuniform throughout the axial extentof the article.

, It will thus be seen that I have provided armethod 'of extent in an unconfined manner and wherein the :extent of cold working of the metal is controlled in the various steps to produce iazsubstantially uniform desired hardness in the finished work piecesolely by reason of cold work- I ,ing. Wherever possible, such as in the operations illusitra'tedin'Figs. 3, 4"and'5, the 'die and punch are designed fto reduce friction *withthe work piece to a "minimum. The reduction or elimination of friction is highly dcsir- I "able, since it reduces the pressures requiredfor 'cold forming the metal. When the metal is permitted to flow without substantial friction between the work piece and the walls of the die and punch, the metal flows freely and the extent to which it is cold worked is thereby reduced. This elimination or reduction in friction reduces and, in some instances, entirely eliminates the necessity for softening the blank between cold forming operations by a normalizing treatment.

I claim:

1. The method of cold forming a solid steel blank into a tubular article having a circumferentially-enlarged porportion of the blank, confining said side fiow of the metal to a' diameter larger than the diameter of the original blank, stopping said punching force in a plane spaced above the zone of lower side wall confinement to form a cup-shaped blank having side walls provided with an annular inwardly extending shoulder on the outer surface thereof in the region of the bottom wall of the blank, applying apunching force to the upper face of said bottom wall over a central area of smaller extent than the upper face of the bottom wall, continuing the application of said last mentioned punching force into the zone of the blank is inserted in the die 180 as illustrated in Fig.

11. When the die parts 181 and 182 are assembled as shown, the fiat face 183 of section 181 overhangs counterbore 187 to form an annular shoulder 195.

Punch 195 has a shank 197 having a diameter corre sponding to the internal diameter of the upper end of blank 175 and a reduced nose portion 198 having a diameter corresponding with the internal diameter of the lower end of blank 175' Shank 197 and nose 198 are connected by a rounded corner portion 199. When blank 175 is inserted in die 18%) and punch 196 is driven upwardly from the position shown in dotted lines to that shown in solid lines, the rounded corner portion 199 on the punch engages shoulder 194 and displaces the metal in wall portion 178 radially outwardly into the cavity portion 188, and as the punch progresses upwardly, the corner 199 engages shoulder 191 and displaces a portion of the metal in wall portion 176 radially outwardly into the said lower side wall confinement whereby to reduce the thickness of the central portion of said bottom wall and simultaneously form an inwardly projecting annular shoulder within said cup-shaped blank, laterally confining the inwardly offset side wall portion of the cup-shaped.

blank adjacent said outer annular shoulder and applying endwise pressure to the upper end of the blank side wall to reduce the external dimension of the upper expanded portion of the blank, thereby forming a cup-shaped work piece having an inner annular shoulder, and thereafter displacing at least a portion of the metal below said inner annuar shoulder outwardly beyond the outer surface of .the side wall above said inner annular shoulder to form an enlargement around the outer surface of the work dimension of said portion of lower side wall confinement is substantially greater than the thickness of the side walls of the-cup-shaped blank. a v

4. The method called for in claim 1 whereinthe application of said second mentioned punching force is stopped at a zone substantially below said outer'annular shoulder.

5. The method called for in claim 1 wherein said second mentioned punching force is applied to the upper face of said bottom wall so as to form a second annular inwardly projecting shoulder around the inside of the' cup-shaped blank below said-first mentioned inner annular shoulder.

'6. The method called for in claim Swherein at least a portion of the metal below both of said inner annular shoulders is displaced outwardly beyond the outer surface of the side walls of the cup-shaped work piece; the portion of the metal below said second mentioned inner References Cited in the file of this patent UNITED STATES PATENTS 268,011 Goehler Nov. 23, 382 756,368 Hurdle ,Apr. S, 1904 1,412,194 Penfield Apr. 11,1922

Franklyn et al. -..,Mar. 17,1936

. 12 2,140,775 Talbot-Crosbie et al. Dec. 20, 1938 2,228,301 1 Ditzel etal.' Ian. 14, 1941 2,248,755 Hathorn' July 8,1941 2,340,784 Westin et al. Feb. 1, 1944 2,344,803 -Criley Mar. 21, 1944 2,358,892 Upton Sept 26, 1944 1 2,368,980 Frothinghamuuz .2 Feb; 6, 1945 2,483,376 Temple Sept. 27, 1949 T FOREIGN PATENTS j 6,612 Great Britain AD. 1909 469,550 Great Britain July 27, 1937 627,697 Great Britain Aug. 15,. 1949 Germany May 8, 1942 OTHER REFERENCES Cold Shaping of SteeLJuly 1, 1947, Hientz Mfg. ct, Phila., Pa., TS. 225, H4, pp. 66-69 etc. 7

Iron Age Magazine, Aug. 4, 1949, pp. 90-105. I

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