US 3701270 A
A method of drawing tubing using a conventional draw bench and a die assembly having a die ring in the form of a peripherally grooved nylon spool held in a case defining a pressure chamber around the spool. A tube to be drawn is telescoped onto a shaped mandrel and inserted in the die, and the chamber is filled with fluid under substantially constant pressure that is maintained by a relief valve or an accumulator, while the tube is drawn through the die, the pressure being sufficient to collapse the tubing initially around the mandrel and then to iron the tubing smoothly onto the mandrel during drawing.
Claims available in
Description (OCR text may contain errors)
United States Patent Matthews [451 *Oct, 31, 1972 1541 9 METHOD OF DRAWING METAL TUBES  Inventor: Raymond A. Matthews, 2332 Via Anacapa, Palos Verdes Estates, Calif. 90274 [*1 Notice: The portion of the term of this patent subsequent to March 16, 1988, has been disclaimed.
 Filed: Dec. 3, 1970  Appl.No.: 94,755
Related US. Application Data  Division of Ser. No. 760,823, Sept. 19, 1968,
Pat. No. 3,570,297.
 U.S.Cl. ......72/57, 72/276, 72/468  Int. Cl. ..B21c 3/06  Field of Search ..72/57,468,276, 283
 Y References Cited UNITED STATES PATENTS 3,570,297 3/1971 Matthews ..72/276 2,218,904 10/1940 Burd ..29/235 2,052,448 8/1936 Colaert ..29/235 4 ea 52 E- V-;'. 50 4 5/ 252,423 l/l882 Buckingham ..72/276 2,294,138 8/1942 Strock ..72/274 2,597,623 5/1952 Dies ..72/57 2,927,372 3/1960 Powell ..72/84 2,960,142 11/1960 Cimochoski ..72/59 3,134,832 5/1964 Smith ..72/468 3,243,985 4/1966 Green ..72/468 3,327,513 6/1967 Hinshaw ..72/274 Primary Examiner-Richard J. Herbst Attorney-Fulwider, Patton, Rieber, Lee & Utecht  ABSTRACT A method of drawing tubing using a conventional draw bench and a die assembly having a die ring in the form of a peripherally grooved nylon spool held in a case defining a pressure chamber around the spool. A tube to be drawn is telescoped onto a shaped mandrel and inserted in the die, and the chamber is filled with fluid under substantially constant pressure that is maintained by a relief valve or an accumulator, while the tube is drawn through the die, the pressure being sufficient to collapse the tubing initially around the mandrel and then to iron the tubing smoothly onto the mandrel during drawing.
9 Claims, 14 Drawing Figures METHOD OF DRAWING NETAL TUBES CROSS-REFERENCE TO RELATED APPLICATION 19, 1968, entitled DIE AND METHOD OF DRAW- ING METAL TUBES.
BACKGROUND OF THE INVENTION This invention relates generally to the drawing of sections of metal tubing through die assemblies to change the cross-section of the tubing, and has particular reference to a method and die assembly primarily intended for the drawing of metallic tube sections from a substantially uniform starting diameter to a tapered finished form.
In the past, the tapering of metal tubing for verious articles, ranging from relatively small items such as golf club shafts to larger items such as lamp posts, has been a slow, expensive and often complicated operation requiring special machinery and sometimes involving compromises such as the progressive stepping of the tube diameter, the welding of a longitudinal seam to form sheet material into tapered tubes, or the use of socalled sacrificial dies which are usable usually for only one tapering operation, or at most a few, before being discarded or reshaped for further use. Spinning or rolling of tapered tubes is another approach that has been satisfactory for some purposes, but this type of operation requires extremely expensive machinery and produces a tube that may have circumferential imperfections or faults likely to fracture under bending stresses.
An early approach to the tapering of metal tubing used expansible, soft metal die rings which were capable of stretching as a tube and tapered mandrel were forced through the ring, so that the ring expanded progressively while collapsing the tube around the mandrel to a taper conforming to the taper of the man drel. An example of this approach is US. Pat. No. 252,423. A more recent adaptation of this approach is shown in US. Pat. No. 3,327,513 in which an expansible drawing ring, composed of special metal, is used to collapse tubing onto a tapered mandrel. The die ring in this patent is said to be usable for tapering more than one tube before work-hardening of the special metal renders it incapable of proper expansion and contractron.
The aforementioned co-pending application is directed to a die assembly and a method of drawing tubing with such a die assembly, while this application pertains to a method of drawing tubing with such a die assembly to eliminate the need for a tube-pointing operation preparatory to drawing of a tube. As is well known in the art, the term pointing refers to the usual reduction in size of the end of the tube to permit it to be inserted through a drawing die and gripped by a chuck for pulling the tube through the die.
SUMMARY OF THE INVENTION The primary object of the present invention is to provide an improved method for drawing ductile metal tubing, and particularly for tapering tubing, with a variable orifice die that is capable of tapering a large number of workpieces, and in which the need for pointing of a tube preparatory to the drawing operation is eliminated, with the savings in time and cost resulting from elimination of the preliminary pointing operation.
More particularly, the invention contemplates the provision of a tapered guide extension in generally coaxial relation with one end of a tube to be drawn, and the use of this extension to expand a variable-orifice die of the type in said aforementioned application as the die is passed along theguide extension and onto the end of the tube, which typically is telescoped onto a mandrel to which the guide extension is attached. Then the die is contracted around the tube to collapse the latter around the mandrel, and the tube and the mandrel are drawn together through the die while the latter is backed by pressure sufficient to collapse the tube along the full length of the mandrel. Other objects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary side elevational view of a tube-drawing apparatus including a die assembly for practicing the present invention, parts of the apparatus being broken away andsome parts being shown in cross-section for clarity of illustration, and a conventional pointed tube being shown.
FIG. 2 is a fragmentary side elevation generally similar to part of FIG. 1 showing the entire length of a tube to be drawn, and partly broken away and shown in cross-section.
FIG. 3 is an enlarged fragmentary cross-sectional view of the die assembly as shown in FIGS. 1 and 2.
FIG. 4 is an enlarged fragmentary cross-sectional view of parts shown in FIG. 2 with the parts moved to the position indicated by the line 44 of FIG. 2, and illustrating a condition of the die ring that is believed to occur in use.
FIG. 5 is a view similar to FIG. 4 with the parts moved to the position indicated by the line 55 of FIG. 2.
FIG. 6 is an enlarged break-away side elevation of a representative mandrel.
FIG. 7 is an enlarged break-away side elevation of a representative section of conventional pointed tubing to be tapered, the tube section being shown partly in cross-section.
FIG. 8 is a break-away side elevation of the tube section after tapering and finishing operations.
FIG. 9 is a view similar to FIG. 2, and primarily in cross-section, showing the die assembly in condition for beginning of the tapering of a tube section from the larger end toward the smaller end, and including a guide extension in accordance with the present invention.
FIG. 10 is a view similar to FIG. 9 illustrating an intermediate position and condition of the die assembly in the tapering of the tube section in accordance with the invention.
FIG. 11 is a view similar to part of FIG. 10 but showing the condition of the die assembly near the end of the tapering operation.
- FIG. 12 is a cross-sectional view taken in perpendicular transverse plane through a modified form of the die assembly having special bracing elements.
FIG. 13 is a cross-section taken substantially along the line 1313 of FIG. 12.
FIG. 14 is an enlarged perspective view of one of the bracing elements.
DETAILED DESCRIPTION Shown in FIGS. 18 of the drawings for purposes of illustration is a die assembly mounted on a post 11 upstanding from a conventional horizontal draw bench 12 with a section 13 of tubing telescoped onto a tapered mandrel 14 ready to be drawn. In the conventional fashion, one end portion 15 of this tube section is pointed" to a reduced diameter so as to extend loosely through a die ring 17 in the die assembly and into a horizontal bore 18 in the post, where it is gripped in a chuck 19 on the end of a rod 20 connected at 21 to the reciprocating piston rod 22 of a horizontal hydraulic cylinder 23.
The cylinder 23 is pivotally anchored at 24 on the left-hand portion of the bench 12 so that admission of fluid under pressure to the right end portion of the cylinder through a supply line 25 shifts the piston rod 22 to the left to draw the chuck 19 to the left and pull the tube 13 through the die ring 17. A second fluid line 27 is connected to the left end of the cylinder to effect the return stroke of the piston rod. It should be understood that this drawbench arrangement is merely representative of varioustypes of conventional benches that are well known in the art, and that the construction of the bench is not part of the present invention.
During the forward stroke of the piston rod 22, to the left as viewed in the drawings, the tube 13 and mandrel 14 are pulled together through the die assembly 10, which herein is held stationary in a recess 28 in the right side of the post 11. Thus, the tube is sized and shaped by the orifice of the die ring 17 around the mandrel inside the tube.
The die ring 17 for use in practicing the invention is composed of relatively hard and tough, non-metallic plastic material capable of expanding and contracting repeatedly in annular form withing a substantial range without rupturing or hardening, and has a central through-passage (see FIG. 3) including a land 29 between the ends of the passage and, a bell 30 flaring from the land toward the entry end. A substantially constant compressive force is uniformly distributed around a radially yieldable annulus 31 of plastic material having the land on its inside surface, and the die ring as a whole is rigidly supported within the die assembly 10 against axial yielding under the drawing force exerted by the cylinder 23.
With this arrangement, it has been found that relatively hard plastics have the capability of crushing ductile metal tubing against a mandrel when backing pressure commensurate with the tubing strength is applied to the outside of the yieldable annulus 31, and also can withstand the axial forces tending to extrude the land area out of the die as the tubing is drawn through. Thus, the crushing compressive force is applied along the full length of the tube to taper the latter on the mandrel, without any destructive effect on the ring. In addition, it is believed that the special configuration of the bell 30 and the varying thickness of the annulus adjacent the land result in a novel buckling or rolling action of the annulus to cause the effective land area to move axially within the die ring while maintaining approximately the same land width, thereby preventing an increase in frictional resistance to movement of the tube as the tube diameter increases. In any event, this die assembly has the demonstrated ability to taper ductile tubing sections of different thickness and compositions effectively over prolonged periods of production use.
The preferred embodiment of the die ring 17 is in the form of a nylon spool having axially spaced, annular flanges or heads 32 (see FIGS. 3-5) at the ends of the spool, separated by a peripheral groove 33 formed with a curved bottom surface 34 (FIG. 3), the groove preferably being generally centered axially of the spool. The through-passage constituting the variable orifice of the die extends axially through the spool with the bell 30 in the right end portion of the passage and a relief 35 in the left end portion, the bell and the relief herein being virtually identical and flaring arcuately in both directions away from the central land 29.
While it is not necessarily intended to limit the invention to such arcuate flaring, it is believed that the curvature of the bell, coupled with the curvature of the bottom surface 34 of the groove 33, enhances the operation of the die ring 17 by producing the progressive rolling action of the land, as previously mentioned and illustrated in FIGS. 4 and 5. Although the land 29 initially is a circular line Where the bell 30 and relief 35 merge with a smooth curvature, as indicated in FIG. 3, and may flatten somewhat against the tube when backing pressure sufficient to collapse the tube 13 around the mandrel 14 is exerted in the groove 33, the progressive increase in the diameters of the mandrel and the tube in the die, during drawing, results in engagement of the tube with the die ring a progressively increasing distance to the right from the original line. Instead of merely flattening out between the original line and the moving point of engagement, however, the central portion of the ring appears to buckle outwardly away from the tube, as permitted by the space in the groove 33, to maintain a relatively narrow land in engagement with the tube, and thereby maintain a substantially constant working force on the tube.
To achieve this result, the yieldable annulus 31 has been designed with the narrowest section backing the original land and the thickness increasing gradually to the right from this section toward the entry end of the passage. It will be seen that this is achieved by centering the curvature of the bottom surface 34 of the groove 33 on the arcuate inner surface of the bell 30 and the yieldable annulus, both centers lying generally in a plane perpendicular to the axis of the ring and the groove being narrower than the annulus. The result is the rolling, travelling action of the land which remains relatively narrow while the central portion of the passage wall lifts itself out of rubbing engagement with the portion of the tube that already has been tapered, as shown in FIGS. 4 and 5.
The preferred means for applying uniform backing force to the flexible annulus 31 is fluid pressure. For this purpose, and also to provide rigid axial support for the ring 17 as a whole, the die assembly 10 includes a case encircling the ring and cooperating with the groove 33 to define a sealed chamber encircling the annulus to confine fluid under pressure, from a suitable source such as a pump (not shown), around the annulus.
Herein, the case comprises a cylindrical body 37 of the same length as the spool and having an inside diameter sized to receive the spool heads 32 with a tight fit, and a pair of circular end rings 38 secured by bolts 39 to the ends of the case body and formed with center holes 40 larger than the diameter of any part that is to pass through the die assembly. For optimum sealing, the spool may be made somewhat oversized and compressed within the case by the clamping action of the bolts.
As shown in FIGS. 1-5, a supply line 41 from the pressure source opens into the case and into the groove chamber 33 therein through a fitting 42 screwed into an inlet port 43 in the body 37 in axial alignment with the groove 33. The backing pressure produced in the chamber is controlled during tapering from the smaller end toward the larger end by means of a pressure relief valve 44 (FIG. 1) for draining fluid from the chamber as the outward buckling and expansion of the yieldable annulus 31 tends to increase the pressure. Thus, the pressure is maintained substantially constant, automatically as an incident to the changes in the volume of the chamber.
With the foregoing arrangement, a tube-drawing operation may be started by placing a conventional mandrel 14, as shown most clearly in FIG. 6, inside a pointed tube 13 of the type shown in FIG. 7, the sizes of the mandrel and tube being correlated so that the larger end of the mandrel fits closely in the unpointed end of the tube with a stem 45 on the smaller end of the mandrel disposed within the pointed portion of the tube. Then the pointed portion is inserted through the die ring 17, as shown in FIGS. 1 and 2, and is gripped in the chuck 19, ready to be drawn, with the smaller end portion of the mandrel within the land 29.
Until this time, the pressure within the chamber 33 should be relieved for free insertion of the tube 13 in the relaxed die ring 17. Then the die assembly is pumped up" to contract the land 29 against the tube with sufficient pressure to collapse the tube firmly against the mandrel 14. It should be noted that it is possible to apply pressure sufficient to clamp the tube against the mandrel so tightly that the drawing force on the tube will exceed the tensile strength of the tube. If this happens, a tube can be torn apart. Accordingly, the pressure applied should be limited to that which is sufficient to collapse the tube and to continue such collapsing as the tube is drawn.
The appropriate pressure, of course, will vary with the thickness and composition of the tubing. For example, for relatively thin-walled aluminum tube, such as 606l-T6, 0.060 of an inch thick, being tapered from one inch to one-half inch, a pressure on the order of 5,000 psi in the die assembly has been sufficient, while a thicker-walled tube composed of steel may require pressure on the order of 20,000 25,000 psi, or higher. Experience with a particular type of tubing quickly indicates the suitable pressure range.
After the die assembly 10 has been pumped up, the draw cylinder 23 is actuated to pull the tube 13 and the mandrel 14 as a unit through the die'ring 17. Since the pressure is sufficient to collapse the tube, all of the tube wall is cammed and guided into the bell 30 of the die ring with a smooth, rolling action as shown at 47 in FIG. 4, and is ironed out onto the mandrel by the ring.
As the diameter of the tapered portion of the tube grows, the minimum diameter of the die passage must grow correspondingly, and the original land area buckles outwardly away from the tube, as shown at 48 in FIG. 4, while the effective land progresses along the bell toward the entry end of the passage. Consequently, the actual area or band of tight, pressing engagement between the die ring and the tube remains relatively narrow.
This action continues as the die ring 17 moves relative to the tube 13 and the larger ends of the tube and the'mandrel 14 approach the die ring, the conditions of the parts near the end of the drawing stroke being shown in FIG. 5 wherein it will be seen that the land has progressed to a point along the curvature of the bell where the diameter of the passage is approximately the same as the diameter of the larger end of the tube. During further movement of the tube from this position, the die ring smooths the free end of the tube onto the mandrel and then slides off the latter. It should be noted that the die ring will remain substantially in the expanded condition until the pressure in the chamber is changed to return the ring to its original condition.
When the drawing operation has been completed, the pointed end portion 15 of the tube 13 is trimmed off to form a completed tube 13a, shown in FIG. 8, having the desired taper according to the taper of the mandrel used. Circumferential distribution of any minor defects that may have been present in the original tube blank has been avoided, and the tapered wall has the same thickness as the wall of the original blank. In the production drawing of a series of identical tubes, the die ring now is returned to is original condition by changing the pressure in the chamber, and the die as sembly 10 is ready for another draw.
In accordance with the primary aspect of the present invention, and as illustrated in FIGS. 9-11, a tapered guide section 49 is fixed to one end of the tube 13 in generally coaxial relation therewith, preferably by fastening the guide section to one end of the mandrel 14, and the die is expanded from its normal, contracted form (FIG. 9) to a size large enough to pass from the guide section over the tube by passing the die along the guide section and then off the guide section and onto the tube. To this end, the guide section is tapered from a smaller end sized to fit into the die orifice when the die is contracted, to a larger end at least as large as the initial size of the tube, and is fixed at the larger end to one end of the tube as a coaxial extension thereof, and herein also is fixed to the mandrel as an extension of the mandrel.
As shown in FIGS. 9 and 10, the guide extension 49 is a generally conical piece with a coaxial stem 50 connected to its smaller end to be gripped by a chuck, and with a coaxial counterbore 51 forming a seat in its larger end for receiving the larger end of the mandrel 14 with a clearance fit. A threaded stud 52 holds the two securely together, and the end of the tube 13 is clamped snugly in the clearance between the mandrel and the extension.
Starting with the die ring 17 in its contracted form, it is expanded to slightly larger than the size of the tube 13 on the mandrel 14, simply and quickly, by drawing the extension 49 through the ring until the land of the ring passes the right-hand end of the extension. This preliminary operation causes the yieldable annulus 31 to buckle outwardly, just as before, as shown at 31a in FIG. 10, into the proper condition for engagement with the tubing. Then, after application of sufficient pressure to collapse the tube around the mandrel, the drawing operation proceeds as before. Of course, the yieldable annulus now is contracted progressively around the tube and the mandrel, by the backup pressure in the groove chamber 33, and the land area travels progressively away from the entry end of the die passage as the diameter of the work decreases, returning substantially to the normal, contracted condition as the smaller end of the mandrel is drawn through the ring, as shown in FIG. 1 1. To maintain the backing pressure substantially constant, a conventional accumulator 53 (FIG. 9) may be used to supply additional fluid to the chamber at the selected pressure.
The primary advantage of this method of operation is the elimination of the need for a tube-pointing operation preparatory to drawing. By using the guide extension 49 to expand the ring 17 prior to contraction, the
deformation of the ring is kept within the same range of movement that is experienced in the method described in connection with FIGS. 1-5.
When the die assembly 10 is to be used in relatively heavy drawing operations, the die ring 17 will,of course, be designed for higher backing pressures and with correspondingly thicker wall sections in the yieldable annulus 31. More rigid plastic materials also may be used for example, with fiber reinforcement of the type used in the material sold as Nylafil. In addition to sustaining the higher backing pressures, the die ring must withstand the greater axial forces tending to pull the land area through the die with the tube.
For greater axial strength under such loads, the die assembly .10 also may be modified, in the manner shown in FIGS. 12-14, with a plurality of radially moveable, axially rigid braces 54 distributed around the die ring 17. Herein, these braces are sheet metal fingers shown most clearly in FIG. 14 as being U- shaped transverse cross-section and being pivoted at their outer ends on pins 55 spanning the sidewalls of a groove 57 in the body. 37a of the case. The fingers preferably are urged counterclockwise (FIG. 12) about the pivot pins 55 by suitable spring means (not shown) which hold the free ends yieldably under light spring pressure against the bottom wall 34 of the groove 33 around the die ring and in close-fitting relation with the adjacent walls of the heads 32 on the spool.
Thus, the radially free ends of the fingers 54 are positioned close to the yieldable annulus 31 to resist axial deformation of the land, throughout the operation, while being movable radially so as to avoid interference with proper radial yielding of the die ring 17. In all other important respects, the construction and operation of the modified die assembly are the same as those previously described.
It has been stated that hard nylon is a suitable material for use in the die ring, and that reinforced nylon such as that sold as Nylafil has even higher ultimate yield strength for resisting failure under the forces to which the ring is subjected, these forces being the fluid pressure introduced into the die assembly, the overall axial force tending to pull the ring out of the case and, most importantly, the axial extruding force to which the land area is subjected as a tube is drawn through the ring. Thus, the key characteristics of the die material are the ability to expand and contract repeatedly through the range necessary for a particular drawing operation, and sufficient hardness and strength or toughness to transmit the backing pressure to the tubing without failing axially as the tubing is drawn.
Along with these characteristics, the die material should have a low coefficient of friction to minimize the drag and heat accompanying the drawing operation. With a nylon die, simple bar soap has been used as a satisfactory lubricant, whereas many conventional drawing operations are believed to require complex and sophisticated lubricant mixtures.
Specifically, the material sold as Bunting Cadco is a preferred hard nylon for the die ring. It is believed that Delrin also will be satisfactory, and that there are various other plastic materials with the proper physical characteristics for the present invention. In view of the teachings herein, particular materials will suggest themselves to those skilled in the plastics art.
From the foregoing, it will be evident that the present invention provides both an improved dieassembly 10 and a novel tube-drawing method using an expansible and contractible die ring 17, backed by uniformly distrubuted pressure, to collapse a tube 13 around a mandrel 14 into a desired form as the tube and mandrel are moved endwise through the die ring, the backing pressure being maintained substantially constant throughout the draw. In addition, the die ring is expanded by moving it along a tapered extension in front of the mandrel in order to eliminate the need for, and the cost of, a pointing operation prior to the drawing operation.
It will also be apparent that, while a particular form of the invention has been illustrated and described, various modifications may be made without departing from the spirit and scope of the invention. Moreover, while the die assembly 10 is intended primarily for the tapering of tubing on mandrels, its usefulness is not necessarily so restricted.
I claim as my invention:
1. The method of tapering'ductile metal tubes on a tapered mandrel with an expansible plastic die ring having an orifice of predetermined size normally larger than the smaller end of said mandrel and smaller than the larger end, said method comprising the steps of:
positioning a first tube on the mandrel in close fitting relation with said larger end;
placing a reversely tapered extension on said larger end beyond said tube;
guiding said ring along said reversely tapered extension to enlarge said orifice to a size large enough to move onto said tube around said larger end and moving the die ring from the extension onto the tube;
applying backing pressure around said ring sufficient to contract the latter around the tube and collapse the tube around said mandrel;
and maintaining said pressure substantially constant while moving said tube and said mandrel together through said ring to contract the ring and collapse the length of said tube around the mandrel.
2. The method as defined in claim 1 in which said backing pressure is applied by confining fluid under preselected pressure around said ring, and adding fluid at said pressure as the ring contracts.
3. The method of tapering a ductile metal tube of preselected initial size on a tapered mandrel with an expansible plastic die ring having an orifice of predetermined size smaller than the tube, said method comprising the steps of:
providing a mandrel having the taper desired for the tube; positioning on the larger end of the mandrel a reversely tapered guide extension having a smaller end sized for entry into the die ring when the orifice thereof is said predetermined size, and having a larger end at the larger end of the mandrel and at least as large as said preselected initial size; positioning the tube on the mandrel; guiding the die ring onto the guide extension and along the latter toward the mandrel to enlarge the orifice to a size at least as large as said initial size;
moving the die ring in the enlarged condition onto the portion of the tube around the larger end of the mandrel; applying backing pressure uniformly around the die ring sufficient to contract the latter around the tube and collapse the tube against the mandrel;
and moving the tube and the mandrel relative to the die ring to pass the latter along the tube while maintaining sufficient backing pressure to collapse the tube around the mandrel.
4. The method as defined in claim 3 in which said orifice is enlarged by said guide extension to a size larger than said initial size of the tube, to pass freely onto the tube.
5. The method as defined in claim 3 in which the tube is clamped between the mandrel and the extension and is drawn through the die ring by drawing force applied to the extension.
6. The method as defined in claim 3 in which said backing pressure is applied by confining fluid under pressure in a chamber around the die ring defined in part by a peripheral groove around the die ring, and adding fluid under pressure to the chamber as the ring contracts during movement of the tube and mandrel through the ring.
7. The method of tapering a ductile metal tube on a tapered mandrel with an expansible plastic die ring having an orifice of predetermined size smaller than the tube, said method comprising the steps of:
positioning the tube on the mandrel in close fitting relation with the larger end of the mandrel;
placing a tapered guide section at one end of the mandrel beyond the tube with the guide section increasing in size toward the mandrel from a size capable of fitting into said orifice to a size at least as large as the tube diameter;
guiding said die ring along said guide section to enlarge the orifice to a size large enough to move onto the tube, and moving the die ring from the guide section onto the tube;
applying backing force around the ring sufficient to contract the latter around the tube and collapse the tube against the mandrel;
and moving the tube and the mandrel through the ring while maintaining sufficient backing force to coll seth tube 0 dth an rel. 8. The? inethgd of d r awiiig of til ucti le metal tube of preselected initial size to a smaller size with an expansible plastic die ring having an orifice of predetermined size smaller than said initial size, said method including the steps of:
providing a tapered guide extension having a smaller end sized for entry into the die ring when the orifice thereof is said predetermined size, and a larger end at least as large as the initial size of the tube;
fixing the guide extension to one end of the tube in outwardly projecting, generally coaxial relation therewith, and with the larger end at said one end of the tube;
guiding the die ring along the guide extension toward the tube to enlarge the orifice to a size at least as large as said initial size;
moving the die ring from the guide extension onto the tube;
applying backing force around the die ring sufficient to contract the latter and collapse the tube;
and moving the tube through the die ring while controlling the backing force to draw the tube to said smaller size.
9. The method as defined in claim 8 including the step of positioning the tube on a shaped mandrel prior to fixing the tube to the guide extension, the tube and the mandrel being drawn together through the die ring to shape the tube to the shape of the mandrel.