US 3732614 A
Tubular shells are made from pre-cut blanks of basically flat sheet stock by placing the blanks in an indexed position, clamping the blanks tangentially against a forming arbor, and then forcing shaped jaws having an end configuration complementary to the outer periphery of the arbor against the unclamped portions of the blank to progressively bend the blank and wrap the same about the arbor, in a manner which brings the ends of the blank together closely adjacent one another but at least slightly spaced apart. The space between the ends of the blank are then secured together by welding, in a manner which deposits welding material in the space between the ends of the blank, thereby producing a circumferentially continuous tubular wall. The secured blank is then forced endwise off the arbor and over a sizing plate which accurately sizes the interior of the tubular shell. The blanks are pre-cut by use of a shearing die which simultaneously coins the sheared end and bends the same slightly to promote precise circularity when the end extremities are welded together.
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Description (OCR text may contain errors)
ilnite States atent 11 1 outell  METHOD FOR MAKING MOTOR SHELLS AND THE LIKE  Inventor: Henry E. Boutell, Norton Shores,
731 Assignee: EMF, 111e, Muskegon, Mich. 221 Filed: Sept. 10,1970  AppLNo; 71,185
1 1 3,732,614 1 1 May 15, 1973 Primary Examiner-J. Spencer Overholser Assistant ExaminerRichard Bernard Lazarus Att0rney Price, Heneveld, Huizenga & Cooper  ABSTRACT Tubular shells are made from pre-cut blanks of basically flat sheet stock by placing the blanks in an indexed position, clamping the blanks tangentially against a forming arbor, and then forcing shaped jaws having an end configuration complementary to the outer periphery of the arbor against the unclamped portions of the blank to progressively bend the blank and wrap the same about the arbor, in a manner which brings the ends of the blank together closely adjacent one another but at least slightly spaced apart. The space between the ends of the blank are then secured together by welding, in a manner which deposits welding material in the space between the ends of the blank, thereby producing a circumferentially continuous tubular wall. The secured blank is then forced endwise off the arbor and over a sizing plate which accurately sizes the interior of the tubular shell. The blanks are pre-cut by use of a shearing die which simultaneously coins the sheared end and bends the same slightly to promote precise circularity when the end extremities are welded together.
12 Claims, 9 Drawing Figures PATENTEDHAYI 51913 3732,61 1
SHEET 1 [IF 4 FNBA W PATENTEDHAY 1 W5 3.732.614
SHEET 20F 4 PATENTED MAY 1 5191s sum 3 BF 4 N I WIJ NW C a I) INVENTOR 4/19/25 A. 50072944. V BY W FIG. 5
METHOD FOR MAKING MOTOR SHELLS AND THE LIKE BACKGROUND OF THE INVENTION This invention relates to the manufacture of tubular shells, and particularly tubular sheet metal motor casings or shells, from basically falt sheet stock which is normally pre-cut to the desired size prior to the forming and securing operations which produce the finished tube.
In the past, tubular shells for housing the various component parts of electrical motors have been made by one or the other of two predominating methods. According to one of these methods, flat pre-cut blanks are subjected to a series of discrete and separate stamping operations in which the bland would first be preformed, i.e., stamped into a very wide U-shaped configuration, it would then be U-formed, meaning that it was again stamped at least one or more times to progressively bring its U-shaped configuration more toward circularity although always maintaining the basic U" shape. Ultimately, the stamped piece would be placed in a closing die, normally comprising a pair of semicircularly-recessed die members which are clamped about the outside of the stamped blank to draw the same into tubular configuration, whereupon the end extremities of the blank would be welded together. According to the other prevalent process, the metal blanks are, after having been cut to size, rolled in a series of cylindrical rollers which give the blank a curving U-shaped configuration, following which a clamping die is used to draw the piece into a closed tubular shape, so that the ends can be welded.
It is well known that both of the processes just mentioned inherently produce shells which do not have accurate circularity, which taper along their length, which have an angular roof or ridge at the point where the ends are brought together, and most importantly, which have widely varying inside diameters. As will be understood, the latter defect is quite apparently inherent in these processes, since the use of an externally-disposed clamping die necessarily sizes the exterior of the resulting tubular member and leaves its internal diameter to chance, depending upon random tolerance variations in the thickness of the particular piece of sheet stock involved. Furthermore, in almost all cases the ends of the blank are brought into direct abutting contact, and for this reason the same are welded by the tungsten inert gas process, which is one of fusion, in which no weld material is added. This process calls for very precise alignment and positioning, and in the processes under discussion such precision is frequently absent, thereby producing defective welds. Additionally, the butt or junction of the ends of the blank normally are found to roof", i.e., the endmost extremities of the blank remain substantially linear and unbent, and come together at a broad obtuse angle, forming a wide U rather than a continuous circular shape, as is desired.
The foregoing defects in current practices for manufacturing motor shells has caused considerable concern and difficulty in the past. One of the most important such difficulties arises from the fact that the field laminations for the motors are pressed into place within the shell and, where accurate circularity is not maintained in the shell itself, the field is distorted when so pressed into place. This causes variations in the air gap between the field and the rotor, and thus causes defective motor operation, including speed irregularities, loss of power, greater current consumption and, consequently, over heating. Nonetheless, as stated, the aforementioned two processes are basically those which have been followed for many years in the motor industry, and these persist even at the present time. The problems created by these processes involve more than the end product itself (i.e., the motor), since the forming and welding steps are carried out at different places and, necessarily, at different points in time. Therefore, the various partially-formed configurations must be stored between operations, at least for a brief time, and this requires the use of great amounts of floor space, since the various types of U-shaped partially-formed blanks of course require many times the storage space that flat pre-cut sheets require. Thus, the prevalent processes necessitate a significant and continuing waste of space, time, and effort, as well as producing basically inferior parts.
SUMMARY OF INVENTION The present invention obviates the difficulties associated with and inherent in the prevalent processes, since it produces tubular motor shells or the like having very accurate internal dimensions regardless of the tolerance variations existing in the stock which is used, and the tubular shells produced have extremely accurate circularity at all points, with very little taper. Furthermore, and of considerable significance, the present invention eliminates the space requirements for storage of partially-formed parts which has been such an inseparable adjunct of the prevalent processes.
Thus, briefly stated, the major objectives of the invention are to provide a method and an apparatus for forming tubular motor shells and the like from basically flat stock in a single, continuous operation formed at a single location and during a single brief, continuous time interval, thereby requiring storage facilities only for pre-formed flat blanks and for finished tubular shells which can be immediately packed for shipment. Further important objectives are the production of tubular motor shells having extremely accurate internal dimensions and precise circularity with little or no discernible taper, for accurate and effective motor manufacture.
The foregoing major objectives of the invention, together with other objectives and advantages equally a part thereof, will be more readily understood upon reading the following specification and in view of the drawings, referred to specifically hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary end elevational view of the apparatus of the invention;
FIG. 2 is an enlarged, fragmentary perspective view showing certain details of the apparatus;
FIG. 3 is a further enlarged fragmentary perspective view showing other details of the apparatus;
FIG. 4 is an enlarged, fragmentary, frontal perspective view illustrating portions of the apparatus during the process of forming a tubular shell;
FIG. f is an enlarged fragmentary front elevational view showing the apparatus at a further point in the process from that shown in FIG. 4;
FIG. 6 is an enlarged, fragmentary frontal perspective view showing the apparatus at the end of the process;
FIG. 7 is a fragmentary, enlarged frontal perspective view illustrating the means for ejecting finished parts;
FIG. 8 is an enlarged, fragmentary perspective view illustrating the preferred means for cutting and preforming the sheet metal blanks; and
FIG. 9 is a further enlarged, fragmentary end elevational view showing the preferred die of FIG. 8 in operation.
DESCRIPTION OF A PREFERRED EMBODIMENT Referring first to FIG. 1, it may be seen that the apparatus 10 of the invention generally comprises a support or bed portion 12, a forming arbor 14 disposed above the bed and mounted upon an arbor support 16 carried on the bed, as well as lateral frame portions 18 and 20, each of which carries a pivotally-mounted jaw element 22, 24, respectively. Each of the jaw elements is pivotally connected to the ram or piston 25 and 27 of power cylinders 26 and 28, respectively, which are preferably hydraulic units. As will be understood, the support or bed 12 may be supported above floor level by any suitable structure, and portions of the bed may be used to anchor the rearward extremities of the power cylinders 26 and 28. The upright lateral frames 18 and must be rigid supports and must therefore be suitably interconnected and or braced, although it is not regarded as necessary to specifically show such extraneous structure. The arbor 14 is supported by its base 16 in cantilever fashion, projecting endwise forwardly across the bed 12, and a movable front support 17 is provided for restraining the ended end of the arbor when the same is under load, to be described hereinafter. The bed 12 carries indexing means 30, which may comprise widely flanged shoulder bolts or the like, against which a sheet of the stock may be positioned at the start of a forming cycle.
As illustrated generally in the various figures, the forward end extremities of the jaw elements 22 and 24 are concave in shape, having a curvature which is complementary to the exterior periphery of the arbor 14. The overall structure of the jaw elements which are basically identical, is best illustrated in FIGS. 2 and 6. As illustrated, each such element carries a pair of spaced rearwardly-projecting bosses 32,34 which define apertures through which passes a heavy pin 35. A yoke 36 mounted on the end of the power cylinder ram is pivotally carried on pin 35, as is the lower extremity of a heavy support link 38, the upper end of which is pivotally supported on the lateral frame portions 18 and 20, at each side of the apparatus. From this arrangement, it will be appreciated that with forward movement of the power cylinder rams, the link 38 will pivot about its upper support point, thereby moving the jaws 22 and 24 along a rising arcuate path of movement. It has been found helpful to provide counter balance means 40, illustrated herein as a counterweight, attached to each of the jaws above its pivot point on pin 35, so as to maintain the jaws in an upwardly-pivoted orientation, helping to assure that the lower lip of each jaw will extend forwardly and more nearly align vertically with the upper lip of the jaw, for purposes described hereinafter.
To limit the allowable forward travel of each hydraulic cylinder ram, a chain 42 may be attached between a suitable fixed point on the cylinder (or the bed) and to the ram. As illustrated in FIG. 6, this limit of jaw travel is held to closely approach, but not cover, the closely-adjacent end extremities of a piece of stock 44 tightly wrapped about the arbor in the concluding phase of the process. A wire-welding tip 46 is supported in place above the adjacent end extremities of the stock, between the upper edges of the jaws 22 and 24 in their closed position, for automated welding of such end extremities. Although it is important to the invention to use a welder of the type which deposits welding material, rather than a fusion-type welder, the specific welding apparatus and its supporting structure is not particularly critical, and will not be discussed in detail herein. It may be stated, however, that the supporting structure for the welder head should provide for a range of accurate vertical and horizontal adjustments, for proper positioning. Also, the welding tip or head should be mounted for automated forward and rearward reciprocation, as by a motorized carriage or on a power cylinder ram, so that the welding process may take place automatically upon a predetermined signal produced when the jaws are fully closed with respect to the arbor.
Carried on the table 12 beneath the arbor 14 is a third shaped jaw element 48 (FIG. 3) which is mounted between a pair of upright guides 50 for vertical movement. Spaced apertures in jaw 48 provide for passage therethrough a pair of pins 52, which may move upwardly generally radially of the arbor 14 to pin or clamp a formed blank of the sheet stock against the arbor at the beginning of a cycle of operation. As will be understood, the pins 52 may be interconnected beneath the bed 12 and operate by a power cylinder independently of the third jaw 48, which also should be operated by an appropriate power cylinder or the like. It is important to note that the pins 52 may move vertically independently of jaw 48, which has a concave upper face whose curvature is complementary to that of the arbor, in the same manner as the end extremities of jaws 22 and 24, discussed above.
FIG. 3 also shows the nature of the movable arbor support 17, which is pivotally mounted between a pair of support blocks 19 which are rigidly secured to the bed 12. As stated above, the arbor 14 extends cantilevered over the bed 12 and over the third jaw 48 and the pinning means 52, and the movable arbor support 17 braces and supports the free or projected end of the arbor during the operation of the apparatus. For this purpose, the end extremity of the arbor may have a circular recess 15, and the movable support 17 may have a cylindrical projection 17a which fits into recess 15 when the support 17 is pivoted upwardly into place. A rotatable lock or latch member 54 is provided to retain the movable support 17 in its upwardly-pivoted position, although this can be accomplished in many different ways. It is desirable to preclude operation of the apparatus when the support 17 is in a downward position, and this may readily be accomplished by mounting a pushbutton contact switch 56 (FIG. 4) in the plane of rotation of support 17, so that the switch will be tripped by the weight of support 17 when the latter is pivoted into its lowered position.
As stated above in connection with FIG. 6, the free ends of the stock 44 are welded together while the stock blank is tightly wrapped about the arbor 14; hence, upon completion of the welding step and subsequent retraction of the jaw elements 22, 24, and 48, as
well as retraction of the pins 52 and lowering of arbor support 17, the completed tubular shell may be removed from the arbor. This is accomplished by an ejector or pusher structure 60 illustrated in FIG. 7 and comprising a pair of arcuate pusher elements 62 and 64 positioned in circumferentially flanking orientation about the outer periphery of the arbor I4 and mounted upon reciprocable pusher rods 66, which may be operated by appropriate power cylinder means or the like (not shown). As will be apparent, forward reciprocation of the pusher or ejector means 60 will push the completed tubular shell forwardly and off the projecting end of the arbor, to remove the shell therefrom.
Such ejection is actually a duplicate operation in accordance with the invention, inasmuch as a precision sizing plate 70 is secured to the outermost end of the arbor. Therefore when the completed tubular shell is pushed off the free end of the arbor it is at the same time accurately sized internally by the plate 70. In this connection, it is to be noted that the sizing plate '70 should have a precise predetermined shape and size to obtain the desired internal diameter of the completed shell, whereas the arbor 14 should be somewhat smaller in circumference (on the order of perhaps 0.008 to perhaps 0.010 inches smaller), although of course being co-axially mounted with respect to the sizing plate. Furthermore, the blanks of sheeted stock 44 should be cut so that, even considering random tolerance variations, the longest such blank likely to be encountered is at least slightly shorter than the circumference of the arbor, so that even upon complete closure of the shaped jaw elements and consequent wrapping of the blank about the arbor, at least a slight gap will exist between the end extremities of the blank. This will be mentioned in more detail subsequently, but it is to be noted here that by this approach the tolerance variations which will inevitably occur in the length of the pre-cut blanks are effectively nullified, since the metal-adding welding technique used herein can readily till any of the varying gaps at the ends of the wrapped blank which will occur with normal tolerance variations in the sheet metal involved. Thus, the resulting completed tubular shell will always have the same internal diameter, which is of the essence for such a product, even though the size and thickness of the sheet metal blanks involved may vary in a normal manner. By sizing the completed shells in the aforementioned manner, no additional time or effort is required, inasmuch as the sizing occurs simultaneously with ejection of the completed shell from the arbor. Furthermore, during the sizing of the completed shell, the weld is in effect destructively tested, since defective welds will separate under the expanding forces which occur during sizing.
The overall operation of the present apparatus, characterizing the inventive method provided herein, has for the most part already been described. Briefly, the pre-cut blanks are indexed in position beneath the arbor upon the bed 12, by contact against the indexing pins or bolts 30. At the start of the cycle, the pusher means 60 is fully retracted away from the free end of the arbor, as are the three shaped jaws and the pin means 52. The movable arbor support 17 may be lowered to provide access for loading a sheet metal blank, and after such loading the movable support is pivoted upwardly into position, where it is latched by the member 54.
Next the pinning means 52 move upwardly against the center part of the blank of stock, moving the entire blank upwardly and pinning the same rigidly against the bottom of the arbor. Immediately thereafter, the third shaped jaw 48 moves upwardly against the blank of stock, immediately bending the same about the bottom curvature of the arbor (see FIG. 4). Thereafter, the jaw elements 22 and 24 are forced inwardly toward the arbor and the stock, with the upper lip or edge of each such jaw making first contact with the diverging portions of the stock which are not yet clamped against the arbor (FIG. 4). Upon further inward movement of the jaw elements (FIG. 5), the rotation of the jawsuspending links 38 continuously raises the jaws as they travel inwardly, thus bringing both upper and lower lips of each jaw against the stock and wrapping the stock about the arbor. When the lower lip of each jaw has forced the stock against the arbor, the jaws may pivot about their pins 35 and against their counterbalances 40, thus continuing the wrapping procedure, until finally, with the jaws fully extended (FIG. 6), the blank of stock is completely wrapped tightly above the arbor in a rigid and positive manner. Thereafter, the welding head is actuated and travels outwardly along the seam between the ends of the blank, securing the latter together and completing the tubular shell. Following this, the shell is ejected and sized, in the manner noted above. In this operation, the beneficial effect of the pinning means 52 is noteworthy, inasmuch as this preliminary step rigidly holds the blank of stock tangentially against the arbor, precluding any accidental shifting or like movement during subsequent phases of the forming process. As will be understood, all of the steps in the foregoing process may readily be controlled automatically by a sequentially-operating electric circuit, which may utilize limit switches or the like to ensure the completion of each step prior to initiation of the next succeeding step.
As stated above, the present invention also embraces a preferred method of pre-forming the blanks of sheet stock from which the tubular shells are made. This is illustrated in FIGS. 8 and 9. In FIG. 8, the lower half of a cut-off and pierce die is shown, by which blanks 44 of the sheet stock are cut to proper length from an longated strip of the stock which has been pre-cut for width. In addition to merely cutting the blanks 44 to proper length and punching desired holes in each blank, however, the die means in accordance with the invention also coins both the trailing and leading edge extremities 44a and 44b, respectively, of the blanks, bending the edge extremities downwardly along a predetermined edge width and at a predetermined curvature. This is an important feature, since it precludes the aforementioned roof effect at the junction of the edges of a piece of stock when the same are welded together to form the completed tubular shell, described hereinabove. Thus, in accordance with the invention, the lower die portion 60 includes a fixed shearing block 82 which is rigidly mounted on the lower die plate 01 (FIGS. 8 and 9), as well as a movable shearing block 84 which is mounted on the lower die plate upon compression springs 86. Similiarly, a matching upper die plate carries a spring-loaded movable shearing block 92, mounted on springs 96, positioned in direct vertical alignment with the fixed block 82 of the lower die, and also carries a fixed shearing block 94 mounted in direct vertical alignment with the movable block 84 of the lower die.
In the operation of the die means just described, the advancing strip of stock passes beneath a guide plate 88 (FIG. 8) carried on the lower die plate 81 and is automatically indexed for length (by means of a conventional nature not specifically described), such that the desired point at which cutting should occur becomes automatically positioned upon each cycle of operation in direct alignment with the junction of shearing blocks 82 and 84, which also is the line of junction between blocks 92 and 94. At this point, the upper die undergoes a sudden and forceful downward movement, whereupon the springs 86 and 96 are compressed, with the upper block 92 tightly gripping the sheet stock, and with the upper block 94 moving downwardly, thereby forcing block 84 downwardly against the pressure of springs 86. As illustrated in FIG. 9, the adjoining edges of the lower blocks 82 and 84 are relieved or reduced in thickness along a radius of curvature approximating that of the arbor 14. The upper blocks 92 and 94 have a complementary configuration at their adjoining edges. Therefore, upon the downward movement of the upper die portion just mentioned, the sheet of stock is first bent downwardly into a crease-like configuration, and immediately thereafter the fixed upper shear block 94 will cut the stock along the line of demarcation between block 94 and blocks 82 and 92. Due to the very nature of the die, the aforementioned bending must take place prior to shearing; therefore, the edges of the sheared stock are not cut at right angles to the main plane of the stock, but are instead at a slight acute angle with respect thereto. This is also a useful feature, since when a given blank of the stock is subsequently wrapped about the forming arbor, the free ends of the blank will define an outwardly-widening V-shaped configuration, which is ideal for the metal-adding welding process already mentioned. In this connection, it is to be noted that, as mentioned above, the length of the blanks of stock 44 cut by the die means is controlled such that there will always be a slight gap between the ends when the blanks are wrapped about the forming arbor 14, to insure that the inside diameter of the completed tubular shell will always be accurate. It is this slight spacing which the welding process fills in accordance with the invention, and not necessarily the entire depth of the V-shaped separation just described, although this too will normally be substantially filled, and even somewhat rounded-over on the outside circumference of the completed shell.
in accordance with the invention as described and defined herein, a number of terms are used which should be understood in a descriptive or qualitative sense, and not necessarily in a strict and absolute sense. Thus, while the completed blanks may be said to be basically flat, they need not be strictly flat or planar, and may certainly have at least a minimal amount of curvature if desired, including of course the preformed edge extremities 44a and 44b, which may be said to be deformed toward one another, i.e., in the same general direction. The term clamping, applied to the operation of the pins 52, means basically that the blank is held or pinned rigidly against the forming arbor, and is not meant to imply either that the blank is or is not necessarily then bent or deformed against the shape of the arbor as an incident to the clamping. Also, while the blank is said to be wrapped about the arbor, the
amount of actual bending of the sheet material is something which may vary from application to application, as is the fact that the bending may be characterized either by elastic or plastic deformation, depending upon the character of the material involved. The jaw elements are said to have shaped end extremities, and this should be understood as meaning that the jaws have a characteristic shaping at their end which is related to the shape of the arbor and to the desired shape of the finished product.
It is entirely conceivable that upon examining the foregoing disclosure, those skilled in the art may devise embodiments of the concepts involved which differ somewhat from the particular embodiments shown and described herein, or may make various changes in structural details to the embodiments which have been described in detail. Consequently, all such changed embodiments or variations in structure as utilized the concepts of the invention and clearly incorporate the spirit thereof are to be considered as being within the scope of the claims appended herebelow, unless these claims by their language specifically state otherwise.
The embodiments of the invention in which an exclusive property is claimed are defined as follows:
1. A method of making tubular shells from basically flat sheet-form stock, comprising the steps: fixing the position of at least two sides of a generally rectangular basically flat piece of such stock in a predetermined orientation relative to and spaced from a forming arbor which has an outer configuration corresponding essentially to the desired inner configuration for the finished shell; maintaining said piece of stock in such fixed orientation while moving the piece into initial contact with the arbor, and clamping the piece of stock against said arbor; forcing portions of said piece which are not yet clamped against and in contact with said arbor progressively against the latter, to wrap all such portions around said arbor and hold the same tightly in circumferential contact therewith; and connecting the free ends of the wrapped piece together by filling a space existing therebetween, thereby forming a tubular shell having a substantially continuous circumferential wall.
2. The method of claim 1, including the steps of ejecting the tubular shell endwise off said arbor and forcing the shell over a sizing instrument.
3. The method of claim 2, wherein said shell is forced over said instrument during said ejecting.
4. The method of claim 1, wherein said portions of said piece are forced against and wrapped around said arbor by forcing at least one shaped jaw element against such portions.
5. The method of claim 1, wherein the central part of said piece is first clamped against said arbor and each portion between the clamped part and the respective free ends of the piece arethen wrapped around said arbor.
6. The method of claim 5, wherein each of said portions is wrapped around said arbor by forcing a shaped jaw against each.
7. The method of claim 6, wherein said jaws are first forced against and make contact with their respective portions adjacent the clamped part and then moved along such portions toward their end extremities.
8. The method of claim 1, wherein said piece of stock is pre-formed prior to being clamped against said arbor by bending the end edge extremities of said piece.
9. The method of claim 1, wherein said piece of stock is clamped against the arbor by maintaining the latter in fixed position and using a movable clamping member to move said piece of stock generally radially of and toward said arbor to pinch the stock against the same.
10. The method of claim 1, wherein said piece of stock is clamped against said arbor by use of clamping means moved generally radially of and toward said arbor to pinch the stock therebetween, and wherein during such clamping step a shaped jaw member is forced against such stock at the point of clamping to bend the stock against the periphery of the arbor at such point.
11. A method of making tubular shells from basically flat sheet-form stock, comprising the steps: pinching a basically flat piece of such stock securely against a forming arbor which has an outer configuration corresponding essentially to the desired inner configuration for the finished shell, while maintaining the basically flat configuration of said piece of stock prior to and at the initial contact thereof with said arbor, and by use of a single line of force directed radially at the axis of said arbor and generally orthogonally of said basically flat piece of stock to bring the same into initial contact with the arbor and pinch the stock tightly against the latter; forcing portions of said piece of stock which are not yet pinched against and in contact with said arbor toward and against the latter, to wrap all such portions I around said arbor and hold the same tightly in circumferential contact therewith; and connecting the free ends of the wrapped piece together by filling a space existing therebetween, thereby forming a tubular shell having a substantially continuous circumferential wall.
12. A method of making tubular shells from basically flat sheet-form stock, comprising the steps: clamping a predetermined part of a basically flat piece of such stock securely against a forming arbor which has an outer configuration corresponding essentially to the desired inner configuration for the finished shell; then moving at least one shaping jaw against portions of the piece of stock which are not yet clamped against the arbor but which are located generally adjacent those portions already clamped against the latter, to thereby force such adjacent unclamped portions against the arher; and then moving the shaping jaw circumferentially around the arbor while continuing to force the jaw against other portions of the piece of stock to thereby wrap the remaining unclamped portions thereof around and tightly against the arbor; holding the wrapped piece of stock tightly in circumferential contact with the arbor; and connecting the free ends of the wrapped piece of stock together by filling any space existing therebetween, thereby forming a tubular shell having a substantially continuous circumferential wall.
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