OA11911A

OA11911A - Apparatus and method for forming a pipe with increased wall-thickness at its ends.

Info

Publication number: OA11911A
Application number: OA00100091A
Authority: OA
Inventors: Donald P Sahlem
Original assignee: Wyman Gordon Co
Priority date: 1998-10-09
Filing date: 1999-10-08
Publication date: 2006-04-10
Also published as: CZ20011246A3; ATE239562T1; DE69907711D1; CA2346705A1; AU1108600A; EP1121209A1; EP1121209B1; BR9914346A; NO20011682D0; CN1326387A; NO20011682L; JP2002527241A; MXPA01003613A

Abstract

Apparatus for and method of extruding a metal pipe having a uniform inner diameter, and forward and rearward end sections (62, 66) which are thicker than the middle section (64) of the pipe. A metal billet (54) having a bore (56) is inserted into an open ended cylindrical bore of a stationary container (12). The billet (54) is moved axially within the bore of the container (12) by a press (13) which includes a pressing surface (38, 39) and a mandrel (44) extending forwardly from the pressing surface through the bore of toward the billet (54). The mandrel (44) has a cylindrical large diameter rearward portion (48), a cylindrical small diameter middle portion (50) and a forwardly and outwardly tapering forward portion (52). Metal from the billet (54) is forced through the small diameter bore of a two part removable first die (20) around the middle portion (50) of the mandrel (44) by moving the press forwardly for a first distance to form a preliminary forward end section (62) of pipe. The press is moved forwardly for a second distance for forcing metal from the billet through the bore of the first die (51) around the rearward portion (48) of the mandrel for extruding the middle section (64) of pipe and causing the preliminary forward end section (62) of pipe to pass over the tapered forward portion (52) of the mandrel to form the forward end section (62) of pipe. The press is moved forwardly for a third distance for forcing metal from the billet through the relatively large bore of a second die (53) around the rearward portion (48) of the mandrel to form the rearward end section (66) of pipe.

Description

(1) 119 1 1

TECHN1CAL F1ELD

The présent invention is directed to pipe manufacture, especially forming a fluidconveying pipe known in the trade as a "double ended upset pipe". Such a pipe has aforward, or "pin" end section, an elongated middle section and a rearward, or "box" endsection. The inner diameters of ail three sections of the pipe are the same. The outerdiameters of the forward and rearward end sections of the pipe are substantially greater thanthe outer diameter of the middle section of pipe. Therefore, the thickness of the middlesection of the pipe is substantially thinner than either of the forward and rearward endsections of the pipe.

BACKGROUND OF THE INVENTION

The présent invention is directed to an apparatus for forming a fluid conveying pipeknown in the trade as a "double ended upset pipe". Such a pipe has a forward, or "pin" endsection, an elongated middle section and a rearward, or "box" end section. The innerdiameters of ail three sections of the pipe are the same. The outer diameters of the forwardand rearward end sections of the pipe are substantially greater than the outer diameter of themiddle section of pipe. Therefore, the thickness of the middle section of the pipe issubstantially thinner than either of the forward and rearward end sections of the pipe. Theextra thickness of the forward and rearward end section of the pipe is machined and/orthreaded to enable the forward, or "pin" end of a first pipe to be coupled to the rearward or"box" end of a second pipe.

In the past, metallic double ended upset pipes hâve been formed by extruding themiddle and end sections of the pipe separately and welding the forward and rearward endsections to opposite ends of the middle section. Since the welded areas represent potentiallyw.eak areas of the pipe, each section of the pipe is made thicker than that which wouldnormally be needed. This procedure is time consuming and expensive. The extra thicknesswhich requires extra material also adds a material cost to the pipe. The added weight of thepipe adds still further costs in shipping and handling. (2) 119 11

Many métal extrusion devices and methods hâve been developed for extruding a pipefrom a billet with the use of a press, a die, and a mandrel. However, there is no knownapparatus or System for extruding an intégral pipe having a uniform inside diameter in whichthe opposite end sections of the pipe hâve an outside diameter greater than the outside 5 diameter of the middle section of the pipe. These and other difficulties experienced with theprior art pipe extruding devices or methods hâve been obviated by the présent invention.

It is, therefore, a principal object of the invention to provide an apparatus forextruding a pipe from a métal billet for producing an integrally formed pipe having a constantor uniform inside diameter and a middle section which has a smaller outside diameter than 10 the outside diameter of each of the opposite end section of the pipe. A further object of the invention is the provision of an apparatus for extruding a pipefrom a métal billet as described above in a single continuons extrusion operation.

Another object of the présent invention is the provision of a method of extruding apipe from a métal billet in which the pipe has uniform inside diameter and a middle section 15 having a smaller outside diameter than the outside diameter of the opposite end sections ofthe pipe. A still further object of the invention is the provision of a method of extruding froma métal billet a pipe as defined above in a single continuous process.

Still another object of the invention is the provision of having an outside non-uniform20 configuration mandrel for use in a métal extrusion machine for extruding from a métal billeta pipe having a uniform inside diameter and a middle section which has a smaller outside diameter than the outside diameter of the opposite end sections of the pipe.

Another object of the invention is the provision of an apparatus for extruding a pipefrom a métal billet wherein the middle section of the pipe has a smaller outside diameter thani the outside diameter of each of the opposite end sections of the pipe and one end section ofthe pipe has a smaller inner diameter that the inner diameter of the middle section and opposite end section of the pipe.

With these and other objects in view, as will be apparent to those skilled in the art.the invention résides in the combination of parts set forth in the spécification and covered bythe daims appended hereto. (3) 119 11 BR1EF SUMMARY OF THE INVENTIONApparatus for and method of extruding a métal pipe having a substantially uniform inner diameter. The forward and rearward end sections of the pipe are thicker than the middlesection of the pipe. A heated métal billet having a cylindrical longitudinal bore is insertedinto the rear opening of a cylindrical bore of a stationary container. A two-part removableinner die is located witbin the bore of the container adjacent the forward end of the containerand an outer die is located outside of the container adjacent the front end of the container.The inner die has a relatively small diameter cylindrical bore. The outer die has a relativelylarge diameter cylindrical bore. The billet is moved along a central longitudinal axis withinthe bore of the container by a press which includes a circular forward pressing surface anda mandrel extending forwardly from the pressing surface toward the billet. The mandrel hasa cylindrical relatively large diameter rearward portion, a cylindrical relatively small diametermiddle portion and a frusto conical forward portion which tapers outwardly in the forwarddirection from the diameter of the middle portion to the diameter of the forward portion.Métal from the billet is forced through the bore of the inner die around the small diameterportion of the mandrel by moving the press forwardly for a first distance for extruding apreliminary forward end section of pipe. The press is moved forwardly for a second distancefor forcing métal from the billet through the bore of the inner die around the large diameterrearward portion of the mandrel for extruding the middle section of pipe and causing diepreliminary forward end section of pipe to pass over the tapered forward portion of diemandrel. This causes the preliminary forward end section of pipe to be expanded transverselyof its central longitudinal axis to an inner diameter which is equal to the inner diameter ofthe middle section and a wall tfaickness which is greater than the wall thickness of the middlesection of pipe. The inner die is removed from die container and die press is movedforwardly for a third distance fch* forcing métal from the billet through die bore of the outerdie around the rearward portion of the mandrel to extrade the rearward end section of pipehaving an inner diameter which is equal to the inner diameter of the middle section of pipeand a wall thickness which is greater than the wall thickness of the middle section of pipe. (4) 119 11

BRIEF DESCRIPTION OF THE DRAWINGS

The character of the invention, however, may be best understood by référencé to oneof its structural forms, as illustrated by the accompanied drawings, in which: FIG. 1 is a longitudinal cross-sectional view of the primary functional components ofthe extruding apparatus of the présent invention for forming a double ended upset pipe; FIG. 2 is a side elevational view of the mandrel portion of the apparatus; FIG. 3 is an end view of a two-pait die which also forms a portion of the apparatus; FIGS. 4-12 are operational views illustrating the formation of the forward and middlesections of the pipe; FIGS. 13-18 are operational views showing the formation of the rearward section ofthe pipe; FIGS. 19a, 19b, 19c, and 19d are vertical cross-sectional views which may be joinedtogether along the common Unes A-A, B-B, and C-C and showing the overall extrudingapparatus of the présent invention; and FIG. 20 is a view similar to FIG. 10 and showing a modified mandrel.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIGS. 19a, 19b, 19c, and 19d, the pipe extruding apparatus of theprésent invention is generally indicated by the référencé 10. Apparatus 10 conquises arearward machine base 72, and a forward machine base 72 connected to the rearward machinebase by four connecting rods 74. A press, generally indicated by the référencé numéral 13,is mounted on the pipe extruding apparatus 10 between the machine bases 70 and 72 forlongitudinal movement along central longitudinal axis 18.

Press 13 includes a crosshead 78 located between the machine base 70 and 72. Apiston 75 is connected to the rearward side of the crosshead 78 through a horizontal connecter79. Piston 75 is slidably mounted within a single acting hydraulic cylinder 77 which is fixedto the rearward machine base 72. Cylinder 77 is connected to a high pressure hydraulicsource, not shown, through hydraulic line 73. Crosshead 78 is supported on a pair oflongitudinal ways 81 and guided on the connecting rails 74 for longitudinal forward andrearward movement along the longitudinal axis 18. Crosshead 78 has a horizontal bore 65which is coaxial with longitudinal axis 18. A double acting hydraulic cylinder 81 is fixed to (5) 119 11 the hydraulic cylinder 77 through a structural support 82. A piston, generally indicated bythe reference numéral 85, includes a piston head 89 slidably mounted within the cylinder 81and a piston rod 93 extending from the cylinder 81 and fixed to the upper end of thecrosshead 78. Cylinder 81 is connected to a high pressure hydraulic source, not shown,through hydraulic lines 76. Actuation of cylinder 77 causes the piston 75 and the crosshead78 to move forwardly toward the forward machine base 70. The relatively large size of thecylinder 77 provides the large forces required to force a billet through the die structure to bedescribed at the forward end of the extrader. The crosshead 78 and the piston 75 are movedrearwardly to their starting positions by actuating the cylinder 81 so that the head 89 is movedrearwardly within the cylinder 81. Press 13 also includes a cylindrical housing or stem 36that is fixed to the forward side of crosshead 78 and extends forwardly along the longitudinalaxis 18. A double acting hydraulic cylinder 69 is fixed to the rearward side of crosshead 78and connected to the high pressure hydraulic source through hydraulic lines 68.

Stem 36 has a chamber 40 and a forward end 47 which contains a forward opening49 to the chamber 40. A pressing ring 38 is located at the forward opening 49 of the housing36 and contains a cylindrical bore 42 and a circular forward pressing surface 39. A mandrel44 is located within the chamber 40 and bas a rearward end 45 configured to be coupled tothe forward end of a driving rod 46. A bushing 59 is fastened to the forward end of thedriving rod 46 with a clearance fit within the stem 36. This helps to support the driving rod46 and maintains the mandrel 44 on center. The rearward end of the driving rod 46 iscoupled to a piston 71 which is slidably mounted within the cylinder 69. The cylinder 69enables the mandrel 44 to be selectively moved forwardly and rearwardly along thelongitudinal axis 18 relative to the stem 36. The mandrel 44 is coaxial about the centrallongitudinal axis 18. The mandrel 44 has a cylindrical rearward portion 48, a redoceddiameter cylindrical middle portion 50, and a frasto conical forward portion 52 which tapersoutwardly from the reduced diameter middle portion 50 to the forward end of the mandrel.The extreme forward end of the mandrel 44 bas the same diameter as that of the rearwardportion 48. The mandrel 44 extends freely through the bore 42 of the pressing ring 38. Thepressing ring 38 is not attached to the stem 36 and is supported on the mandrel 44. (6) 119 11 A housing or container 12 is supported on the forward machine base 70. The housing12 is fixed to a pair of oppositely extruding connecting arms 80. Connecting arms 80 arefixed to the rearwardly extending ends 85 of a pair of pistons, generally indicated by thereference numéral 84. The forward ends of pistons 84 are slidably mounted within doubleacting hydraulic cylinders 88 which are connected to the high pressure hydraulic sourcethrough hydraulic Unes 90. The hydraulic cylinders 88 are fixed to the forward machine base70. The housing 12 contains a cylindrical tube or liner 14 having a circular bore 16 whichis coaxial with the longitudinal axis 18. The bore 16 has a circular rear opening 15 and acircular front opening 17. Referring also to FIGS. 1 and 3, a cylindrical inner die 20 islocated within the bore 16 adjacent the front opening 17 of the bore. The inner die 20 isdivided transversely along the line 21 to form two separable halves 20a and 20b. An outerdie assembly, generally indicated by the reference numéral 23, is located outside of the frontopening 17 of the bore 16. The outer die assembly 23 includes a die holder 24 which hasa bore 37, a rearward end 41, and a forward end 43. An outer die 26 is located within diebore 37 at the rearward end 41 of the die holder 24. A back plate 30 is located at theforward end 43 of the die holder 24. The outer die 26 has a circular bore 28. The backplate 30 has a circular bore 32. The diameter of the bore 32 is slightly larger than thediameter of the bore 28. The bore 22 of the inner die 20 has a smaller diameter than diediameter of the bore 28.

The pipe which is to be fonned by the extruding apparatus 10 of the présent inventionis formed from a cylindrical billet 54 that has a cylindrical longitudinal bore 56. The sizeof the billet 54 is such that there is a specified amount of clearance between the outer surfaceof the billet relative to the inner surface of the liner 14 which defines the bore 16. Thediameter of the bore 56 of billet 54 has a specified clearance relative to the outer diameterof the portions 48 and 52 of the mandrel. The stem 36 of the press 13 moves along the axis18 and appUes ali of the forward force of the press 13 to the billet 54.

The outer die assembly 23 is located within a retaining ring 92 which is located at therearward end of a removable housing or outer die carrier 98. Die carrier 98 is located withina horizontal chamber 100 in the forward machine base 70. Chamber 100 has a rear opening103 and a forward opening 99. Carrier 98 has a central horizontal bore 97 that has a forwardopening 86 and a rearward opening 87. The rearward portion of the bore 97 has a (7) Π9 î 1 counterbore 96 which contains the retaining ring 92 and outer die assembly 23. A retainingplate 94 is located at the forward end of the counterbore portion of the bore 97. Retainingplate 94 has a bore 91 which has a larger diameter than the bore 32 of the back plate 30.

The outer die carrier 98 is maintained at the rearward end of the chamber 100 by areleasable stop mechanism, generally indicated by the référencé numéral 102. Stopmechanism 102 includes a pair of oppositely facing gates 104 slidably mounted withintransverse bores 101 which intersect the chamber 100. Each gâte 104 is connected to one endof a piston 108. The opposite end of each piston 108 is slidably mounted within a hydrauliccylinder 110. Each hydraulic cylinder 110 is fixed to the forward machine base 70. thehydraulic cylinders 110 can be controlled for selectively moving the gates 104 between anactive position, as shown in FIG. 19d, in which the gates 104 are located within the chamber100 to an inactive position in which the gates 104 are outside of the chamber 100. When thegates 104 are in their active positions, they block any forward movement of the outer diecarrier 98 and maintain the outer die assembly 23 against the forward end of the container12 and the inner die 20. When the gates 104 are in their inactive positions, the outer diecarrier 98 can be removed from the chamber 100 through the front opening 99. A guide tube 95 is fixed to the forward side of the retaining plate 94. Guide tube 45is coaxial with the longitudinal axis 18 and extends forwardly through the front opening 99.A table 112 is fixed to the guide tube 95 and extends below the tube 95. A plurality of guiderollers 114 are located on the upper surface of the table 112.

Having described the details of the pipe forming apparatus of the présent invention,a double ended upset pipe blank is formed in accordance with the following description.

Referring to FIG. 1, the mandrel 44 is shown retracted into the stem 36 to enable thebillet 54 to be positioned between the mandrel 44 and the opening 15 of the chamber 16.The billet 54 is then loaded into the bore 16 of the container 12. Once the billet 54 has beenIoaded into the bore 16, as shown in FIG. 4, the cylinder 69 is actuated to force the driver46 forwardly relative to the crosshead 78 and stem 36. The mandrel 44 is thereby extendedforwardly by the driver 46, relative to the stem 36, so that the rearward portion 48 of themandrel is at the forward end of the stem 36 and within the bore 42 of the pressing ring 38.At this point, the mandrel 44 is maintained in a fixed position relative to the ring 38. Thecylinder 77 is actuated to move the press 13, comprising crosshead 78, stem 36, mandrel 44, (8) 119 11 and pressing ring 38, forwardly as a single unit. The press 13 is moved forwardly, as shownin FIG. 5, along the longitudinal axis 18 so that the mandrel 44 extends through the bore 56of the billet 54, through the bore 22 of die inner die 20, through the bore 28 of the outer die26 and through the bore 32 of the back plate 30. The stem 36 also enters the bore 16, asshown in FIG. 5. The pressing ring 38 is shown in FIG. 5 abutting the rearward end of thebillet 54 just prior to applying a forward compressing force to the billet. Λ preferred variation of this first step is to actuate cylinder 69 to push the mandrel44 through the bore 56 of the billet 54 while the billet is supported on a moveable carnage.The cylinder 77 is actuated to move the press 13 toward the container 12, thereby carryingthe mandrel 44 and the billet 54 into the bore 16 of the container to the position shown inFIG. 5.

The billet is forced against the rearward end of the inner die 20 by additional forwardmovement of the press 13. A small forward movement of the press 13 squeezes the billet54 and forces métal from the billet to completely fill the space between the inner surface ofthe liner 14 and the billet. Métal at the forward end of the billet 54 is also forced inwaidtytoward the reduced diameter middle portion 48 of the mandrel 44 as shown in FIG. 6 to forman inward bulge or "upset" 60 of material. At this point, the forward force of the stem 36has squeezed the billet 54. The billet is thereby reduced slightly in length aad thecorresponding volume of the billet is diverted to the gap between the liner 14 and the billet54 and to the gap between the mandrel and the billet to form the "upset" 60. The locationof the intersection between the reduced diameter middle portion 50 of the mandrel andrearward portion 48 of the mandrel, relative to the inner die 20, déterminés the length of thepreliminary forward or "pin" section 62 of the pipe, as shown in FIG. 7.

Continuons squeeâng of the billet 54 by the forward movement of stem 36 for a fîrstdistance forces métal from the billet through a first ring-shaped opening or gap 51 betweenthe inner surface of the inner die 20 and the reduced diameter middle portion 50 of tbemandrel to form the cylindrical preliminary forward end section 62 of the pipe, as shown inFIG. 7. Preliminary forward end section 62 will eventually become the "pin" or forward endsection of the pipe. The middle section 64 and the forward section 67 of the pipe are formedby moving the press 13 forwardly for a second distance. At this point, the cylindrical largediameter rear portion 48 of the mandrel reaches the rearward portion of the inner die 20. (9) 119 11

When the rearward portion 48 of the mandrel enters the bore 22 of the inner die 20, as shownin FIG. 8, a second ring shaped opening 53 is formed between the inner surface of the innerdie 20 and the rearward portion 50 of the mandrel. The inner diameter of the second ring-shaped opening 53 is greater than the inner diameter of the first opening 51. This also meansthat the second ring-shaped opening 53 is narrower than the first ring shaped opening 51.Métal from billet 54 is, therefore, forced through the opening or gap 53 by the forwardpressure of the stem 36 as a tubular extrusion having a thinner wall thickness. This beginsthe formation of a cylindrical middle section 64 of the pipe. At the same time, thepreliminary forward end section 62 of the pipe reaches the tapered forward portion 52 of themandrel, as shown in FIG. 8, and begins to expand transversely of the axis 18. Since thecross section of the billet 54 is much larger than the cross section of the finished pipe, theextruded pipe is several times longer than the billet. The length of the extruded pipe isdetermined by the ratio of the cross sectional area of the billet to the cross sectional area ofthe pipe (or extrusion ratio). For example, fôr an extrusion ratio of 12 to 1, for every inchthat the press 13 advances, 12 inches of extruded pipe will be formed. This élongation at thepoint of extrusion causes the extruded pipe to stide over the outside diameter of the mandrel44, since the mandrel is maintained in a fixed relationship to the housing or stem 36. FIG. 9 shows further squeezing of the billet 54 and the lengthening of the middlesection 64 of the pipe and continued flaring of the preliminary forward end section 62 of thepipe as it is forced over the tapered forward end portion 52 of the mandrel 44. FIGS. 10 and 11 show the completion of the expansion process for the forward endsection of the pipe. As the forward end of the preliminary forward end section 62 of the pipepasses the forward end of the tapered forward portion 52 of the mandrel, it becomescylindrical, as shown in FIG. 10. Also, the inside diameter of the expanded forward endsection 62 is the same as the inside diameter of the middle section 64. The preliminaryforward end section 62 of the pipe is shown fully expanded in FIG. 11, thereby completingthe formation of the forward, or "pin", end section of the pipe and is identified by thereference numéral 67.

As the stem 36 continues to advance forwardly, the length of the middle section 64of the pipe gradually lengthens until the required length of pipe has been extruded as shownin FIG. 12. After the middle section 64 of the pipe has been formed, the cylinder 77 is (10) 119 11 deactivated and the cylinders 81 and 85 are activated simultaneously to move the stem 36 andthe container 12 rearwardly. The billet 54 and the partially extruded pipe also moverearwardly with the container 12, as shown in FIG. 13. This créâtes a small gap betweenthe container 12 and the die holder 24 and éliminâtes the forward pressure on the die carrier98. The cylinders 110 are then actuated to remove gates 104 from the chamber 100 and theremovable die carrier 98 is moved forwardly to create a gap 57 between the die holder 24and the container 12, as shown in FIG. 14. Gap 57 is wider than the inner 20. The cylinder81 is deactivated and the cylinder 77 is again activated to move the stem 36 forwardly. Thisforces the inner die forwardly out of the container 12 and into the space 57, as shown in FIG. 15. When the inner die 20 clears the front opening 17 of the bore 16, the two halves of theinner die 20 separate and fall away from the middle section 64 of the pipe, as shown in FIG. 16. The housing 98 is moved rearwardly and the stem 36 and container 12 are movedforwardly to the rear opening 103 of the chamber 100 so that the die holder 24 abuts theforward surface of the container 12, as shown in FIG. 17. The cylinders 110 are actuatedto retum to the gates 104 to the chamber 100 in front of the die carrier 98.

The remaining portion of the billet 54 is used to form the rearward or "box" sectionof the pipe.

The cylinder TJ is actuated to move the press 13 and the stem 36 forwardly a thirddistance. The space between the rearward portion 48 of die mandrel and the inner surfaceof the bore 28 defines a third ring-shaped opening or gap 55. Forward movement of thepress 13 for die third distance forces métal from the billet 54 through the third ring-shapedopening or gap 55. The bore 28 of the outer die 26 has a larger diameter than the bore 22of die inner die 20 so that die thickness of the ring-shaped opening or gap 55 is greater thanthe thickness of the second ring-shaped opening or gap 53. Therefore, the métal from thebillet 54 which is forced through the third opening 55 fonns the relatively thicker rearwardend section 66 of the pipe, as shown in FIG. 18. The outer diameter of the rearward endsection 66 is substantially greater than the outer diameter of the middle section 64 of the pipe.At this point, the extrusion of the pipe is complète. A small unextruded portion of the billet54 remains after the full desired length of the pipe has been extruded. The unextrudedportion is identified by the référencé numéral 68 in FIG. 18. The unextruded portion 68 canbe removed from the pipe at the extrader by actuating the cylinder 69 to move the mandrel (Π) 119 11 rearwardly out of the extruded pipe and by actuating the cylinder 88 to move the container12 rearwardly. The rearward movement of the container 12 pushes the unextruded portion68 of the billet out of bore 16 where it can be sawed front the end of the pipe. Preferably,the extruded pipe, including the unextruded portion 68 is moved a short distance rearwardto facilitate removal of the unextruded portion 68. The extruded pipe is removed byactuating the cylinders 110 to move the gates 104 fo their inactive positions out of thechamber 100. The die housing 98 is removed from the chamber 100 through the frontopening 99. This enables the extruded pipe to be moved frorn the chamber 100 through thefront opening 99. The unextruded portion 68 can be removed frorn the rearward end of theextruded pipe by any desired means, i.e., shearing, sawing, grinding, torching, laser cutting,etc. The extruded pipe is then removed frorn the chamber 100. The extruded pipe is a blankpipe form for subséquent finishing. The ends of the pipe are threaded and machined in aconventional manner to form a finished pipe.

Referring to FIG. 20, a modified mandrel, generally indicated by the référencénuméral 44% is shown within the container 12 at the expansion step of the forward endsection of the pipe. The mandrel 44' has a cylindrical rearward portion 48', a reduceddiameter cylindrical portion 50' and a frusto conical portion 52* which tapers outwardly frornthe reduced diameter middle portion 50' to the forward end of the mandrel. The mandrel 44'is identical to the mandrel 44 with respect to the rearward and middle portions of themandrel. However, the mandrel 44' difïers frorn the mandrel 44 with respect to the frustoconical forward portion of the mandrel. The outer diameter of the extreme forward end ofthe mandrel 44' is greater than the outer diameter of the middle portion 50' and less than theouter diameter of the rearward portion 48'. As the forward end of the preliminary forwardend section 62 of the pipe passes the forward end of the tapered portion 52' of the mandrel44', section 62 becomes cylindrical, as shown in FIG. 20. However, the inside diameter ofthe expanded forward end section 62 is less than the inside diameter of the middle section 64of the pipe.

The invention having been thus described, what is claimed as new and desired tosecure by Letters Patent is:

Claims

(12) 119 1 1 What is claimed:

1. An apparatus for extruding a métal pipe having a substantially uniform innerdiameter, said pipe having a forward end section, a rearward end section and a middle sectionhaving an outer diameter which is substantially smaller than die outer diameter of each oi saidforward and rearward sections, said apparatus comprising: (a) a machine brame; (b) a container supported on the machine frame, said container having a centrallongitudinal axis and a longitudinal cylindrical first bore coaxial with saidcentral longitudinal axis for receiving a cylindrical métal billet having alongitudinal cylindrical bore, said container having a front opening to said firstbore and a rear opening to said first bore; (c) a cylindrical inner die having a cylindrical second bore coaxial with said firstbore, said inner die having an outer diameter equal to the diameter of said firstbore, said second bore having a diameter which is smaller than the diameterof said first bore, said inner die being divided longitudinally into twosubstantially equal half portions, said inner die being movable through saidfront opening along said central longitudinal axis between an inner positionwithin said first bore adjacent said front opening to an outer position outsideof said first bore; (d) an outer die assembly located forward of said container and having alongitudinal cylindrical third bore which is coaxial with said first and secondbores and which has a largo* diameter than said second bore, one of said outerdie assembly and said container being movable along said central longitudinal (13) 119 1 1 axis between an active position wherein said container and said outer dieassembly abut at said front opening and an inactive position wherein said outerdie assembly and said container are spaced sufficiently to enable said inner dieto be moved to said outer position for removal from said apparatus; (e) a press located rearward of said container and movable along said centrallongitudinal axis toward and away from said container, said press having acircular forward pressing surface facing the rear opening of said container anda mandrel extending forwardly from said pressing surface toward said rearopening, said pressing surface and said mandrel being coaxial with said firstbore, said pressing surface having substantially the same outer diameter as the inner diameter of said first bore with sufficient clearance to enable said pressing surface to move longitudinally within said first bore, said mandrelhaving a cylindrical rearward portion whîch has a smaller outer diameter thanthe inner diameter of said second bore, a cylindrical middle portion which hasa smaller outer diameter than the outer diameter of said rearward portion, anda frusto-conical forward portion which extends forwardly from said middleportion from an outer diameter equal to the outer diameter of said middleportion to an outer diameter substantially equal to the outer diameter of saidrearward portion; and (f) an actuator for moving one of said outer die assembly and said containeralong said longitudinal axis relative to the other of said outer die assembly and said container. (14) 119 11
2. An apparatus as recited in daim 1, wherein the longitudinal length of eachsection of said mandrel, relative to the longitudinal length of said inner die and a spécifiebillet length being such that said middle portion is within said second bore when said billetis pushed forwardly into engagement with said inner die by said press and said press ispushed forwardly along said central longitudinal axis a first distance to a point that saidrearward portion is at the rearward end of said second bore for forcing métal from said billetthrough said second bore around said middle portion for extruding a preliminary forward endsection of said pipe having an outside diameter which is equal to the diameter of said secondbore and an inside diameter which is equal to the diameter of said middle portion, theforward movement of said press along said central longitudinal axis for a second distance,while said rearward portion is within said second bore, causing métal from said billet; to beforced through said second bore around the rearward portion of said mandrel to extrade themiddle section of said pipe having an outer diameter which is equal to the inner diameter ofsaid second bore and an inner diameter which is equal to the outer diameter of said rearwardportion, the forward movement of said press for said second distance also causing thepreliminary forward end section of said pipe to pass ovar the forward portion of said mandrelso that said preliminary forward end section is expanded transversely of said centrallongitudinal axis to form the forward end section of said pipe having an inner diameter whichis equal to the outer diameter of the rearward portion of said mandrel and a thickness whichis greater than the thickness of the middle section of said pipe, the forward movement of saidpress along said central longitudinal axis for a thîrd distance, after removal of said inner diefrom said apparatus and while said outer die assembly in said active position, causing métalfrom said billet to be forced through said thîrd bore around the rearward portion of said (15) 119 1 1 mandrel to extrade the rearward section of saîd pipe having an inner diameter which is equalto the outer diameter of said rearward portion and an outer diameter which is equal to the inner diameter of said third bore.
3. An apparatus as recited in claim 1, wherein said outer die assembly comprises: (a) a die holder having a fourth bore, said die holder having a rearward end anda forward end; (b) an outer die located in said fourth bore at the rearward end of said outer dieholder and containing said third bore; and (c) a stop member located in said fourth bore at the forward end of said dieholder, said stop member having a cylindrical fifth bore having a diameterwhich is larger than the diameter of said fourth bore.
4. An apparatus as recited in claim 1, wherein said mandrel bas a rearward endand said press comprises: (a) a housing having a chamber for containing said mandrel and a forward endhaving a opening to said chamber; (b) a pressing ring located at the forward end of said housing at said forwardopening, said pressing ring including said forward pressing surface and acylindrical bore having an inner diameter which is substantially equal to theouter diameter of the rearward portion of said mandrel; and (c) a driver operatively connected to the rearward end of said mandrel for movingsaid mandrel along said central longitudinal axis between a rearward (16) 119 11 •ar withdrawn position in which said rearward portion is within said chamber anda forward extended position in which the rearward portion of said mandrel inwithin the bore of said pressing ring and the remainder of said mandrel i$forward of said pressing ring.
5. An apparatus as recited in claim 1, wherein said apparatus further comprisesan actuator for moving said one of said outer die assembly and said container along saidcentral longitudinal axis relative to the other of said outer die assembly and said container.
6. An apparatus as recited in claim S, wherein said actuator is a fluid actuatorcomprising: (a) a cylinder fixed to said machine frame; and (b) a piston slidable within said cylinder and having a rearward end extendingrearwardly of said cylinder and operatively connected to said container.
7. An apparatus as recited in claim 6, wherein there is a first one of said fluidactuator on one side of said central longitudinal axis and a second one of said fluid actuatorat an opposite side of said central longitudinal axis and said container îs fixed to the pistons of said first and second fluid actuators.
8. An apparatus as recited in claim 1, wherein said outer die assembly comprises: (a) a carrier having a central bore coaxial with said central longitudinal axis, said central bore having a forward opening and a rearward opening; (17) 119 11 (b) a die holder wîthin said central bore at the forward opening of said centralbore, said die holder having a cylindrical fourth bore, a rearward end and a forward end; and (c) an outer die located in said fourth bore at the rearward end of said outer dieassembly and containing said third bore; and a stop member located in saidfourth bore at the forward end of said holder, said stop member having acylindrical fifth bore having a diameter winch is larger than the diameter of said fourth bore.
9. An apparatus as recited in claim 8, wherein said outer die assembly furthercomprises a retaining ring in said central bore and surrounding said die holder.
10. An apparatus as recited in claim 9, wherein said outer die assembly furthercomprises a retaining plate within said central bore and forward of said die holder, saidretaining plate having a cylindrical bore which is coaxial with said central longitudinal axisand having a diameter which is larger than the diameter of said fifth bore and smaller than the diameter of said fourth bore.
11. An apparatus as recited in claim 10, wherein said outer die assembly furthercomprises a guide tube fixed to said retaining plate and extending forwardly through theforward opening of said central bore, said guide tube having an inner diameter is at least aslarge as the inner diameter of the bore of said retaining plate/ (18) 119 11
12. An apparatus as recited in claim I, wherein said machine trame has a chamberwhich has a rear opening and a iront opening, said outer die assembly being Iocated withinsaid chamber for longitudinal movement along said central longitudinal axis, said apparatusfurther comprising a releasable stop mechanism for releasably maintaining said outer dieassembly within said chamber in functional contact with said inner die.
13. An apparatus as recited in claim 12, wherein said machine frame has atransverse bore extending transversdy of said central longitudinal axis and intersecting saidchamber, said releasable stop mechanism comprising a gâte slidabîy mounted within saidtransverse bore between an active position in which at Ieast a portion of said gâte is withinsaid chamber and an inactive position in which said gâte is outside of said chamber.
14. An apparatus as recited in claim 13, wherein said releasable stop mechanismfurther comprises an actuator for selectiveîy moving said gâte to said active and inactivepositions.
15. An apparatus as recited in claim 14, wherein said actuator is a fluid actuator.
16. An apparatus as recited in claim 1, wherein said apparatus further comprisesa guide table forward of said outer die assembly for supporting and guiding said pipe as saidpipe is extruded. (19) 119 1 1
17. An apparatus as recited in claim 16, wherein saîd guide table has upwardlyextending rollers for supporting saîd extruded pipe.
18. An apparatus as recited in claim 17, wherein saîd apparatus further comprisesa guide tube extending from saîd outer die assembly to saîd guide table for guiding saidextruded pipe from said outer die assembly to said guide table.
19. A mandrel for use in a métal extruding machine for extruding a métal pipehaving a uniform inner diameter of a first dimension, a forward end section, a rearward endsection, and a middle section between said forward and rearward end sections, said middlesection having an outer diameter of a second dimension and each of said rearward andforward end sections having an outer diameter of which is greater than said seconddimension, said mandrel comprising: (a) a cylindrical rearward portion having an outer diameter equal to said firstdimension; (b) a cylindrical middle portion having an outer diameter substantially less thanthe outer diameter of said rearward portion; and (c) a forward portion which has a frusto-conical outer surface extending forwardlyfrom said middle portion from an outer diameter equal to the outer diameterof said middle portion to an outer diameter equal to the outer diameter of saidrearward portion. (20) 119 1 1
20. A method of extruding a cylindrical métal pipe having a constant innerdiameter, said pipe having a forward end section, a rearward end section and a middle sectionhaving an outer diameter which is substantially smalier than the outer diameter of each of saidforward and rearward sections, said method comprising: (a) positioning a cylindrical métal billet having a cylindrical longitudinal borewithin a cylindrical first bore of a container by inserting said billet through arear opening to said first bore, said first bore having a central longitudinalaxis, said container having a front opening to said first bore and containing aninner die within said first bore adjacent said front opening and an outer dieoutside of said container adjacent said front opening, said inner die having acylindrical second bore which bas a smalier diameter than the diameter of saidfirst bore, said outer die having a tfaird bore which has a diameter which isless than the diameter of said first bore and greater than the diameter of saidsecond bore, each of said inner and outer dies sdectively being movable alongsaid central longitudinal axis, said inner die comprising two separable halfportions; (b) positioning a press along said central longitudinal axis, said press having acircular forward pressing surface facing said container and a mandrelextending forwardly from said pressing surface toward said container, saidpressing surface and said mandrel being coaxial with said first bore, saidpressing surface having substantially the same outer diameter as the innerdiameter of said first bore with sufficient clearance to enable said pressingsurface to move longitudinally within said first bore, said mandrel having a (21) '119 1 1 cylindrical rearward portion which has a smaller diameter than said secondbore, a cylindrical middle portion which has a smaller diameter than saidrearward portion, and a frusto conical forward portion which extendsforwardly from the diameter of said middle portion from a diameter equal tosaid middle portion to a diameter equal to the diameter of said rearwardportion; (c) moving said press forwardly along said central longitudinal axis so that saidmandrel extends through the bore of said billet and said middle portion lieswithin said second bore to form a first ring-shaped opening and the junctureof said middle portion and said rearward portion is spaced rearward of saidinner die when said forward pressing surface first engages said billet to pushsaid billet against said inner die; (d) moving said press forwardly a first distance along said central longitudinal axisto a point that the juncture of said middle portion and said rearward portionis at the rearward end of said second bore for forcing métal from said billetthrough said first ring-shaped opening to extrade a preliminary forward endsection of pipe having an outer diameter which is equal to the inner diameterof said second bore and an inner diameter which is equal to the outer diameterof said middle portion; (e) moving said press forwardly along said central longitudinal axis a seconddistance wîth said rearward portion within said second bore to form a secondring-shaped opening for forcing métal from said billet through said secondring-shaped opening to extrade the middle section of said pipe having an outer (22) 119 11 diameter which is equal to the inner diameter of said second bore and an innerdiameter which is equal to the diameter of said rearward portion and causingthe preliminary forward end section of pipe to pass over the forward portionof said mandrel during forward movement of said press for said seconddistance so that the preliminary forward end section of said pipe is expandedtransversely of said central longitudinal axis to an inner diameter which isequal to the inner diameter of the middle section of said pipe and an outerdiameter which is greater than the outer diameter of the middle section of saidpipe; (f) moving one of said outer die and said container along said central longitudinalaxis so that said outer die is spaced from said stationary container a distanceat least equal to the longitudinal Iength of said inner die; (g) removing said inner die from said first bore through said front openîng so thatsaid inner die is forward of said container; (h) removing the half portions of said inner die from said pipe and mandrel; (î) moving one of said outer die and said container rearwardly along said centrallongitudinal axis so that said outer die is in engagement with said containerand said rearward is within said third circular bore to form a third ring-shapedopening; (j) moving said press forwardly along said central longitudinal axis for a thirddistance for forcing métal from said billet through said third ring-shaped (23) 119 1 1 opening to extrade the rearward section of said pipe having an inner diameterwhich is equal to the outer diameter of said rearward portion and an outerdiameter which is equal to the inner diameter of said third bore; and (k) removing said extruded pipe from said mandrel.
21. A method of extruding a métal pipe as recited in claim 20, wherein saidextruded pipe is removed from said mandrel by moving said mandrel rearwardly along saidcentral longitudinal axis until said mandrel is rearward of said extruded pipe.
22. A method of extrading a métal pipe as recited in claim 20, wherein saidcontainer is moved rearwardly along said central longitudinal axis relative to said outer dieand said mandrel at step (f) of claim 20 for forcing said inner die out of said first bore.
23. A method of extruding a métal pipe as recited in claim 20, wherein anunextraded portion of said billet remains within said first bore after the forward movementof said mandrel for said third distance and said method comprises the following additionalsteps: (a) moving said mandrel rearwardly along said central longitudinal axis until saidmandrel is rearward of said extruded pipe; (b) moving one of said outer die and said container forwardly along said centrallongitudinal axis so that said outer die is spaced from said container; and (c) removing the unextraded portion of said billet from the rearward end sectionof said extruded pipe. (24) 1 19 1 1
24. A method of extruding a métal pipe as reeited in claim 23, wherein saidcontainer is moved rearwardly along said central longitudinal axis relative to said outer dieand said mandrel at step (b) of claim 23 for forcing the unextruded portion of said billet from said first bore.
25. A method of extruding a cylindrical métal pipe having a uniform innerdiameter of a first dimension, a forward end section, a rearward end section, and a middlesection between said forward and rearward end sections, said middle section having an outerdiameter of a second dimension and each of said rearward and forward end sections havingan outer diameter which is greater than said second dimension, said method comprising thefollowing steps: (a) pressing a cylindrical métal billet within a cylindrical bore of acontainerthrough a first ring shaped opening having an inner diameter which is less thansaid first dimension and an miter diameter which is equal to said seconddimension to extrade a preliminary forward end section of said pipe having aninner diameter which is less than said first dimension; (b) pressing said métal billet within said bore through a second ring shapedopening having an inner diameter which is equal to said first dimension andan outer diameter which is equal to said second dimension to extrude themiddle section of said pipe; (c) moving said preliminary forward end section of pipe over a mandrel which hasa frusto-conical outer surface shaped for expanding the preliminary forwardend section of said pipe to form the forward end section of said pipe having (25) 119 11 an inner diameter equal to said first dimension and an outer diameter whichis greater than said second dimension; and (d) pressing said métal billet within said bore through a third ring shaped openinghaving an inner diameter which is equal to said first dimension and an outerdiameter which is greater than said third dimension to extrade the rearwardend section of said pipe.
26. An apparatus for extruding a métal pipe having a forward end section, arearward end section and a middle section having an outer diameter which is substantiallysmaller than the outer diameter of each of said forward and rearward sections, said forwardend section having an inner diameter which is smaller than the inner diameter of each of saidrearward end section and said middle section, said apparatus comprising: (a) a machine frame; (b) a container supported on the machine frame, said container having a centrallongitudinal axis and a longitudinal cylindrical first bore coaxial with saidcentral longitudinal axis for receiving a cylindrical métal billet having alongitudinal cylindrical bore, said container having a front opening to said firstbore and a rear opening to said first bore; (c) a cylindrical inner die having a cylindrical second bore coaxial with said firstbore, said inner die having an outer diameter equal to the diameter of said firstbore, said second bore having a diameter which is smaller than the diameterof said first bore, said inner die being divided longitudinally into twosubstantially equal half portions, said inner die being movable through said (26) 119 1 1 front opening along said central longitudinal axis between an inner positionwithin said first bore adjacent said front opening to an outer position outsideof said first bore; (d) an outer die assembly located forward of said container and having alongitudinal cylindrical third bore which is coaxial with said first and secondbores and which has a larger diameter than said second bore, one of said outerdie assembly and said container being movable along said central longitudinalaxis between an active position wherein said container and said outer dieassembly abut at said front opening and an inactive position wherein said outerdie assembly and said container are spaced suffîciently to enable said inner dieto be moved to said outer position for removal from said apparatus; (e) a press located rearward of said container and movable along said centrallongitudinal axis toward and away from said container, said press having acircular forward pressing surface facîng the rear opening of said container anda mandrel extending forwardly from said pressing surface toward said rearopening, said pressing surface and said mandrel being coaxial with said firstbore, said pressing surface having substantially the same outer diameter as theinner diameter of said first bore with suffîcient clearance to enable saidpressing surface to move longitudinally within said first bore, said mandrelhaving a cylindrical rearward portion which has a smaller outer diameter thanthe inner diameter of said second bore, a cylindrical middle portion which hasa smaller outer diameter titan the outer diameter of said rearward portion, anda frusto-conical forward portion which extends forwardly from said middle (27) 119 7 1 portion from an outer diameter equal to the outer diameter of said middleportion to an outer diameter larger than the outer diameter of said middleportion and smaller than the outer diameter of said rearward portion; and (f) an actuator for moving one of said outer die assembly and said containeralong said longitudinal axis relative to the other of said outer die assembly and said container.
27. A mandrel for use in a métal extruding machine for extruding a métal pipehaving a uniform inner diameter of a fîrst dimension, a forward end section, a rearward endsection, and a middle section between said forward and rearward end sections, said middlesection having an inner diameter of a fîrst dimension and an outer diameter of a seconddimension, each of said rearward and forward end sections having an outer diameter whichis greater than said second dimension, said forward section having an inner diameter winchis less than said fîrst dimension, said mandrel comprising: (a) a cylindrical rearward portion having an outer diameter equal to said fîrstdimension; (b) a cylindrical middle portion having an outer diameter substantialîy less thanthe outer diameter of said rearward portion; and (c) a forward portion which has a frusto-conical outer surface extending forwardîyfrom said middle portion from an outer diameter equal to the outer diameterof said middle portion to an outer diameter which is less than said fîrstdimension and greater than the outer diameter of said middle portion. (28) 119 11
28. A method of extruding a cylindrical métal pipe having a forward end section,a rearward end section and a middle section having an outer diameter which is substantiallysmaller than the outer diameter of each of said forward and rearward sections, said forwardend section having an inner diameter which is smaller than the inner diameter of each of saidrearward end section and said middle section, said method comprising: (a) positioning a cylindrical métal billet having a cylindrical longitudinal borewithin a cylindrical first bore of a container by inserting said billet through arear opening to said fîrst bore, said fîrst bore having a central longitudinalaxis, said container having a front opening to said fîrst bore and containing aninner die within said fîrst bore adjacent said front opening and an outer dieoutside of said container adjacent said front opening, said inner die having acylindrical second bore which has a smaller diameter than the diameter of saidfirst bore, said outer die having a third bore which has a diameter which isless than the diameter of said fîrst bore and greater than the diameter of saidsecond bore, each of said inner and outer dies selectively being movable alongsaid central longitudinal axis, said inner die comprising two separable halfportions; (b) positioning a press along said central longitudinal axis, said press having acircular forward pressing surface facing said container and a mandrelextending forwardly from said pressing surface toward said container, saidpressing surface and said mandrel being coaxial with said fîrst bore, saidpressing surface having substantially the same outer diameter as the innerdiameter of said fîrst bore with sufficient clearance to enable said pressing (29) 119 11 surface to move longitudinally within said first bore, said mandrel having acyiindrical rearward portion which has a smaller outer diameter than the innerdiameter of said second bore, a cyiindrical middle portion which has a smallerdiameter than said rearward portion, and a frusto conical forward portionwhich extends forwardly from said middle portion front an outer diameterequal to the outer diameter of said middle portion h) a diameter which is largerthan the outer diameter of said middle portion and smaller than the àasa&terof said rearward portion; (c) moving said press forwardly along said central longitudinal axis so that saidmandrel extends through the bore of said billet and said middle portion lieswithin said second bore to form a first ring-shaped opening and the junctureof said middle portion and said rearward portion is spaced rearward of saidinner die when said forward pressing surface first engages said billet to pushsaid billet against said inner die; (d) moving said press forwardly a first distance along said central longitudinal axisto a point that the juncture of said middle portion and said rearward portionis at the rearward end of said second bore for forcing métal from said billetthrough said first ring-shaped opening to extrade a preliminary forward endsection of pipe having an outer diameter which is equal to the inner diameterof said second bore and an inner diameter which is equal to the outer diameterof said middle portion; (e) moving said press forwardly along said central longitudinal axis a seconddistance with said rearward portion within said second bore to form a second (30) 1 »9 ), « ring-shaped opening for forcing métal from said billet through said secondring-shaped opening to extrade the middle section of said pipe having an outerdiameter which is equal to the inner diameter of said second bore and an innerdiameter which is equal to the diameter of said rearward portion and causingthe preliminary forward end section of pipe to pass over the forward portionof said mandrel during forward movement of said press for said seconddistance so that the preliminary forward end section of said pipe is expandedtransversely of said central longitudinal axis to an inner diameter which is lessthan the inner diameter of the middle section of said pipe and an outerdiameter which is greater than the outer diameter of the middle section of saidpipe; (f) moving one of said outer die and said container along said central longitudinalaxis so that said outer die is spaced from said stationary container a distanceat least equal to the longitudinal leagth of said inner die; (g) removing said inner die from said first bore through said front opening so thatsaid inner die is forward of said container; (h) removing the half portions of said inner die from said pipe and mandrel; (i) moving one of said outer die and said container rearwardly along said centrallongitudinal axis so that said outer die is in engagement with said containerand said rearward is within said third circular bore to form a third ring-shapedopening; (j) moving said press forwardly along said central longitudinal axis for a thirddistance for forcing métal from said billet through said third ring-shaped (31) J 19 1 1 opening to extrade the rearward section of said pipe having an inner diameterwhich is equal to the outer diameter of said rearward portion and an outèrdiameter which is equal to the inner diameter of said third bore; and (k) removing said extraded pipe front said mandrel.
29. A method of extruding a métal pipe as recited in claim 28, wherein saidextraded pipe is removed from said mandrel by moving said mandrel rearwardly along saidcentral longitudinal axis until said mandrel is rearward of said extraded pipe.
30. A method of extrading a métal pipe as recited in claim 28, wherein saidcontainer is moved rearwardly along said central longitudinal axis relative to said outer dieand said mandrel at step (f) of claim 20 for forcing said inner die out of said first bore.
31. A method of extrading a métal pipe as recited in claim 28, wherein anunextruded portion of said billet remains within said first bore after the forward movementof said mandrel for said third distance and said method comprises the following additionalsteps: (a) moving said mandrel rearwardly along said central longitudinal axis until saidmandrel is rearward of said extraded pipe; (b) moving one of said outer die and said container forwardly along said centrallongitudinal axis so that said outer die is spaced from said container; and (c) removing the unextruded portion of said billet from the rearward end sectionof said extraded pipe. (32) 119 11
32. A method of extruding a métal pipe as recited in ciaim 31, wherein saidcontainer is moved rearwardïy along said central longitudinal axis relative to said outer dieand said mandrei at step (b) of ciaim 23 for forcing the unextruded portion of said billet from said first bore.
33. A method of extruding a cylindrical métal pipe having a forward end section,a rearward end section, and a middle section between said forward and rearward end sections,said middle section having an inner diameter of a first dimension and an outer diameter ofa second dimension, said rearward end section having an inner diameter of said firstdimension and an outer diameter greater than said second dimension, said forward end sectionhaving an outer diameter which is greater than said second dimension and an inner diameterof a third dimension which is less than said first dimension, said method comprising thefollowing steps: (a) pressing a cylindrical métal billet within a cylindrical bore of a containerthrough a first ring shaped opening having an inner diameter which is less thansaid third dimension and an outer diameter which is equal to said seconddimension to extrade a preliminary forward end section of said pipe having aninner diameter which is less than said third dimension; (b) pressing said métal billet within said bore through a second ring shapedopening having an inner diameter which is equal to said first dimension andan outer diameter which is equal to said second dimension to extrade themiddle section of said pipe; 1 (33) 119 11 (c) moving said preliminary forward end section of pipe over a mandrel which hasa frusto-conical outer surface shaped for expanding the prehminaiy forwardend section of said pipe to form the forward end section of said pipe havingan inner diameter equal to said third dimension and an outer diameter whichis greater than said second dimension; and (d) pressing said métal billet within said bore through a third ring shaped openinghaving an inner diameter which is greater than said first dimension and anouter diameter which is greater than said second dimension to extrade therearward end section of said pipe.