US2971556A

US2971556A - Cold tube bending and sizing

Info

Publication number: US2971556A
Application number: US852462A
Authority: US
Inventors: David E Armstrong; Thomas J J Dunn; Walter H Stulen; Gerald P Roeser
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-11-12
Filing date: 1959-11-12
Publication date: 1961-02-14
Anticipated expiration: 1978-02-14

Description

Feb. 14, 1961 D. E. ARMSTRONG EFAL 2,971,556

- cow TUBE BENDING AND SIZING Filed Nov. 12, 1959 2 Sheets-Sheet 1 IN VE N TOES David E Bmflrorg ORNE Y Feb. 14, 1961 D. E. ARMSTRONG EIAL 2,971,556

cow TUBE BENDING AND SIZING Filed Nov. 12, 1959 2 Shets-Sheet 2 CflMPRESS/ON 121/?50 T/ON 1 l8 TENS/0N H3724.

D/AE C Tl ON 4 7' GAP 0,? l/NSUPPORTED AREA INVENTORS 56 David E. Elmira/2g 2 Tlwmas JJ Damn -59 WaZZer 1i: ZZ4Z'6H/ I go 1. BUGS e1 ATTORNEY United States PatefitO COLD TUBE BENDING AND SIZING David 'E. Armstrong, Cherry Lane, Doylestown, Pm; Thomas J. J. Dunn, 9809 Burwood St., Philadelphia County, Pa.; Walter H. Stulen, 17 Hamilton Drive E., North Caldwell, NJ.; and Gerald 'P. Bucks County, Pa.

Filed Nov. 12, 1959, Ser. No. 852,462

20 Claims. (Cl. 153-32) The present invention relates generally to a method and apparatus for simultaneously cold-forming and cold sizing of openended metal tubular material to its final shape in a shaping die under opposing forces within the leading edge and against the trailing edge of the tubular workpiece and is specifically adapted for the manufacture of open-ended tubular fittings of metals from open-ended metal blanks which are diflicult to cold-form and coldsize in the shaping die by reason of the hardness of the metal or by reason of the seizing and galling characteristics of the metal against the die under cold-forming conditions.

Roeser, Lahaska,

ing'causes upsetting of the hard metal.

Patented Feb. 14, 1961 2 by the flow of metal in the tube blank during cold-form- By use of a. freely floating lead guiding member within the workpiece the fiow of metal is such that upon completion of the formed 90 L the opposite side of the blank has been flowed forwardly to be square with the leading bevel of the tubular blank. If the metal flow is restricted by shouldering at the leading edge, then the upsetting of the hard metal which occurs results in the production of wrinkles, thickened areas and unduly thinned areas in the-finished fitting which cannot be removed while maintaining the desired dimensional tolerances of the formed product. 1

The prior art recognizes that wrinkling readily occurs during cold-forming of hard metals having relatively high tensile strength in the order of about 70,000 p.s.i. 'It is not practical to try to iron out in hard metals, such as stainless steel, wrinkles which are caused by upsetting of the metal. Once the hard metal has been upset and wrinkled, the metal cannot readily be thereafter mechanically smoothed to size in the cold and cannot be smoothed in heated condition without completely altering the structure of the metal. It is the microstructure of the metal which alfects the metallurgical characteristics and the physical properties of the metal and heating alters this structure.

The present invention is an improvement over the method disclosed in Patent No. 2,907,102 to two of the inventors herein.

The apparatus of the present invention differs mainly from that in Patent No. 2,907,102 in respect to the utilization of'a multiple part mandrel formed of elastomeric material, said multiple part mandrel having end-retaining sections formed of homogeneous hard elastomer and a middle section of soft homogeneous elastomer. The hard elastomer end sections of the multiple part mandrel have a critical modulus of elasticity within a relatively narrow range, and further have a limited range of hardness to provide a brake-shoe type of frictional engage-j ment of the retaining end sections in direct contact with the inner walls of the open-ended tubular stock whereby extrusion of the soft middle section is prevented under the extremely high pressures which are developed within the tube during forming and sizing. These end sections are further characterized by a good elastic memory to permit these frictional engaging end sections to quickly recover and return to their original shape for easy removal from the finished tubular product and be reused in the multiple mandrel assembly for mass production.

' The method and apparatus of the present invention enable the rapid production of uniformly formed and sized product from tubular stock of hard metals and metals which are subjected to seizing and galling as illustratively shown in Tables A nad B below, with practically no waste of the metal.

The art has long recognized the distinction between the cold-forming of hard metals of the type as shown in Tables A and B below and the relative ease of coldforming of metals which are soft and have good lubricity, such as, for example, copper, copper base alloys, zinc and zinc base alloys. In the case of the soft metals or metals of good lubricity, cold-forming operations are carried out prior to a separate sizing.

Wrinkling and buckling occur with the hard-or seizing metals in the region of the smallest radius during forming to a 45, 90 orl80 L which. is readily ironed out steps to make the metal malleable andductile.

Thus, a cold-forming operation carried out for hard metals readily wrinkles the hard metal and it is necessary thereafter to iron outthe wrinkles by processes involving heating. The ironing process suggested in the prior art requires a series of heating and mechanical working Ironing which must therefore-be carried out'at high tempera? tures defeatsthe entire purpose of the present invention which is expressly designed to carry out a forming and sizing operation in the cold.

The present invention provides a freely floating leading element which acts entirely within the tubular blank and which first transmits counter-thrust locking pressure to the multiple part mandrel to cause the self-locking multiple part mandrel to come into brake-shoe locking engagement under the counter thrust, pressurizing during the sizing operation for soft metals but which cannot be carried out for hard metals.

- It isa-necessary requirement of the present invention that the leading edge of the hard tubular blank metalwhich is beveled at the start of cold-forming dare not be restrained by shouldering or spherical capping where- TABLE A Metals exhibiting high seizing and .galling' characteristics against hardened steel die surfaces Zirconium and zirconium alloys Titanium and titanium alloys Stainless steel Carbon steel Cobalt and cobalt alloys Aluminum and aluminum base alloys TABLE B Metals, alloys and related metallic mixtures of high hardness hitherto not capable of being cold-formed into standard fixtures without wrinkling, upselting and fracturing Tantalum and tantalum alloys Titanium and titanium alloys Tungsten and hard tungsten alloys Molybdenum and hard molybdenum alloys Cobalt and cobalt alloys-Hz'astelloy B, Hastelloy C Cobalt-alumina Cermets containing up to 40% of cobalt;

or cobalt alloy and.6 A1 0 Cermets Harder metals listed under Table A above, when cold-. formed in accordance with the invention require the application of a pushing force for cold forming, this pushing force bearing against the trailing edge of the workpiece and the trailing hard end of the multiple part mandrel of about 1000-1500 pounds.

Softer metals such aslisted under Table B above require lower pushing forces for cold-forming. For exam ple with an aluminum workpiece, the push force may be as low as about 500-600 pounds for /24" diameter tubular stock.

The manufacturing methods of the invention accomplishes simultaneous cold-forming and sizing of fittings. which meets standard specifications of the type used .for stainless steel fittings. These standard specifications widely used at the present time for hard metals include:

(0) M88. Standard Practice SP-43-1956 for Stainless Steel Butt-Welding Fittings, developed and approved by the Manufacturers Standardization Society of the. Valve: and Fittings Association, New York 17, NY. (originallyapproved Oct. 1950).

(b) ASA No. B3619 Specification'for Austenitic Stainless Steel Pipe, American Society of Mechanical Engineers, 29 West 39th Street, New York city.

Rapid. forming operations can be carried out by copper tube. bending apparatus as taught inv United States patent to Arbogast; No; 2,701,002 granted February 1,

1 955; Arbogastspush ram element for forcing the tu-' buiar blank through the die, supports the trailing edge of theblank while the supporting headpiece engaging the die, thisArbogast apparatus is unable to cold-form seizing metals of the type'which are listed in Table A above or to cold-form hard metals of the type which are listed in Table B without wrinkles.

Cold-forming andsizing of the hard metals and seizing metals are carried out in accordance with-the invention by employing a multiple part mandrel of elastomeric material which is constructed as a self-contained unit to come into frictional-engagement at its ends, wholly within the interior of the tube blank, tomaintainthe mandrel in fixed frictional or brake-shoe type of engagement wholly within the tubular blank throughout the entire coldforming and cold-sizing operation. 3

Thus it is a feature of the invention to eliminate entirely the supporting engagement. of the metal lead piece of Arbogast with the leading. edge of the tubular workpiece, and to rely upon the multiple part elastomer mandrel under pressure from thejfiexible force transmitting linkage delivering hydraulic counter thrust for sealing the: mandrel during the coldsforming and cold-sizing operation.

The invention includes an improved flexible forcetransmitting linkage for transmitting the opposing hydraulic force to the multiple. part: elastomer mandrel while the tubular workpiece: with themandrel inserted therein is being formed in the.die. by theforWard thrust of the hydraulic ram.

nected interfitting ball and socket hat-shaped members which are driven by the counter thrust hydraulic ram. At the head of the new linkage is a guiding lead member which is placed entirely within the workpiece for engaging the front face of the multiple part elastomer mandrel.

- The novel, lead guiding member of the invention is a free-floating metal part in counter thrust engagement for actuating the self-locking multiple part mandrel. guiding member is constructed to be freely movable within the tubular blank before bending and yet can be fulcrumed during cold-forming to direct the metal flow. The lead member freely enters into the tubular blank under action of the opposing counter thrust force during the preliminary pressurizing operation and induces locking of the leading edge of the multiple part mandrel by its pressure action. The lead member is constructed with a spherical face at its outer edge which subsequently contacts the bent portion of larger radius of the cold-formed tube. The spherical face acts as a fulcrum during the cold-forming operation directing the flow of metal at the inner tube wall of the maximum radius and helps to tilt the lead member around the curved portion of the die cavity. This spherical face permits a sliding action and obviates metal thinning in the tubular region of larger radius which ordinarily occurs under tensile forces during forming. The freely floating lead member is also constructed with a flat or planar face at its inner edge with relation to the bent portion of smaller tubular radius to direct metal flow within thisportion of the tube wall as it thickens during the cold-forming operation.

During the initital pressurizing operation, the selfsealing multiple part mandrel within the blank is anchored. at the forward end of the tubular blank by the pressurizing force transmitted exclusively by the internally located free-floating lead member. As a result;

of, the forward movement of the workpiece, which is urged into cold-formed condition by the forward push ram, the flow of metal in the thickened inner radius is directed around the curve of the die by the tilting of the lead guiding member during forming. This action is car ried out as a result of the flat contact of the planar surfaceto the inner radius of the tubular work while the spherical sliding surface at the outer radius of the bent tube fulcrums the metal flowing action by lever movement about the center pivot of the lead member which moves,v along the axis of the tubular blank.

The invention also provides a new flexible force transmitting linkage comprising an assembly of unconnected,

interfitting ball and hat shapedmembers for transmitting counter thrust hydraulic forces to the lead member within the workpiece and thus, to the front face of the multiple part mandrel. during simultaneous cold-forming and cold-sizing of the tubular workpiece in the die.

An object of the invention is to provide a new free floating lead member functioning entirely within the work, and mechanically engaging the front face of the multiple part mandrel to maintain itself and the mandrel within the workpiece throughout the cold-forming and cold-sizing. operation under opposing forces within the die- A further object of the invention is to provide an improved linkage for the free floating lead member uniquely adapted tonegotiatc the sharp angle of bending.

A further object of the invention is to provide a linkage for the free floating lead member which is constructed to provide longer service life of this member.

A further object of the invention is to provide a new multiple part elastomer mandrel for insertion into-the tubular work' whichis self-locking under pressure action by internally directed counter forces.

' The multiple part mandrel, uniquely constructed for cold-forming of hard metal tubular stock, is characterized by self-sealing ends operative under pressure to pre- This. new linkage comprises an assembly ofunconvent extrusion. of the soft middle part. The mandrel,

This

while exerting uniform internal pressure on the inner walls of the tubular stocks, controls the flow of the metal, preventing upsetting of the metal and prevents wrinkling during the bending and sizing operation.

A further object of the invention is to provide a new multiple part elastomer mandrel formed of materials hav-' ing superior physical properties of resistance to abrasion, elastic memory, toughness, compressibility, and frictional engagement for the interior wall of the tubular workpiece to thereby provide a long lasting mandrel capable of long repeated use in production.

A further object of the invention is to provide a new coaction of the multiple part mandrel of the invention in' combination with the new flexible force transmitting slidably movable within the die. This combination is adapted to pressurize and lock the multiple part elastomer mandrel solely by counter thrust pressure.

It is a characteristic of the multiple part elastomer mandrel of the invention that the form of the mandrel need not be tapered at its leading edge. It is preferred that the ends of the mandrel be squared off for alignrnent with, the force transmitting members at the forward and rearward positions of the oppositely directed bydraulic thrust members. It is surprising that the hard end sections containing the soft middle unit are able to completely withstand the tearing and abrasive forces due to the interior irregularities of the workpiece which cause destruction of the unitary rubber mandrel of the type as used in the Arbogast Patent No. 2,701,002 during very rapid forming operations under high pressure.

The non-tapered multiple part mandrel is assembled in accordance with the invention from separate mating sections of hard elastomeric end pressure sealing members and a soft elastomeric middle section. These sections are merely dropped into the workpiece. The forming operation can be carried out in an ordinary hardened steel die. The thinning which ordinarily occurs at the larger radius of the bend is substantially obviated with the mandrel of the invention and the thickening which ordinarily occurs in the region of smaller radius is confined to a very small segment of the are.

For example, using the multiple part self-contained pressure sealing mandrel in the apparatus of the invention for the shaping of 2" tube blanks of stainless steel into full 90 Us, and with a wall thickness for the tube blank of 0.109 inch, it has been found that an increase in wall thickness of 37 /z% based on the initial thickness occurs in the region of smallest radius. At the same time the thinning in the corresponding region of greatest radius which is due to tensile forces is at most about 5-10% of the original thickness of the tubular blank. Thus, the flow of metal is adequate to prevent thinning of the metal at the outside portion of the bend by maintaining the permissible wall gauge requirement of the accepted industry standard referred to above.

It is an important characteristic .of the multiple part mandrel of the present'invention in. comparison with the mandrel of the patent to two of the present inventors, Patent No. 2,907,102, that the multiple part mandrel may be used again and again without being mangled, cut, and' eroded by surface irregularities and without cracking due to repeated compression and elastic recovery in continuous production. H

ofthemandrel ofthe invention which are preferably formed-of a vinyl chloride resin plastisol baked at elevated The softer, readily compressible middle section of the multiple part mandrel is formed preferably of soft natural rubber, synthetic compounded rubber, or polysulfide rubber which is adjusted in known manner by'formulation to a hardness value varying from about a Shore Hardness Rating to about 5 to 60 on the Shore A scale and which has a modulus of elasticity which is less that 54 the value of the hard end sections.

The service life of the softmiddle section when made of natural rubber in terms of number of stainless steel fittings made is from about 2000-4000 pieces depend ing upon the skill of the operator. The service life of polysulfide rubber is about 1000 to 2000 pieces.

In contrast, the use of a single or unitary mandrel, whether made of natural rubber, synthetic rubber such as neoprene, 'butadiene-styrene polymer, etc., or vinyl e. V ,For, example, the service. life of the hardzendsections resin plastisol, etc., as disclosed by the prior Patent No. 2,907,102 there is achieved a service life of only about 3 fittings in the hands of an unskilled operator. This can be improved to 10 fittings in the hands of a skilled operator atfer which the mandrel has completely deteriorated.

It has been found that the modulus of elasticity of the hard mandrel end members of elastomer material must decrease in proportion to the ratio of cross sectional area taken at the external diameter of the tube to the wall thickness.

ticity of elastomer end pieces is required. For example,

with /2" to 4" pipe a suitable range of E will lie between 10,000 to about 20,000 p.s.i.

Limits for the modulus of elasticity of the mandrel end pieces in relation to tube cross-sectional area (O.D.) are listed in Table C below, the data given for stainless steel pipe.

TABLE C Pipe size: E (p.s.i.) /2" to 1" inclusive 15,000-25,000 Above 1" to 2" inclusive 10,000-20,000 Above 2" to 3" inclusive 5,000-10,000 Above 3" 300-5,000

In smaller sizes of standard tubing, wall thickness in proportion to cross-sectional area increases and the tendency for the soft middle section to extrude also increases. For this reason the preferred E values for thicker tubes of smaller diameter is close to 20,000 p.s.i.

Corresponding Shore Durometer D values for these pipe sizes are shown in Table D.

At Durometer D hardness above the end piece tends to fracture.

'Preferred materials for vinyl resin plastisol which is best due to its excellent elastic memory, urethane rubber, cast epoxy resin, and other elastometer materials such as hard rubber either natural or synthetic. These other elastomer rubbers may be formulated to provide the necessary propertieswithin the specified limits for hardness and modulus-of elasticity. Other and further objects of the present-invention will appear from the more detailed description set forth below, it being understood that such more detailed description is given by way of illustration and explanation;

Thus, with a small ratio of cross sectional area to wall thickness a higher modulus of elas-' the mandrel end pieces include.

7. only and not by way of limitation, sinceva-rious changes. therein may be made by those skilled in the ,art without. departing from the scope. and spirit of the present invention.

In connection with the more detailed description, there is shown in the drawings,jin

Fig. 1 is a fragmentary elevationalview of an appara tus embodying our invention:andadaptedfor useiimprac ticing our method with parts being-broken awayandu-im section to illustrate structural details.

Fig. 2 is a fragmentary view-ofgone of the diernem= bers with a work blankand the'forming mechanism in an initial positionwith parts sectioned and .brokenaway. for convenience; in illustration.

Fig. 3 is a fragmentaryview: with one-of'the diemembers removed, illustrating the apparatus in. fully actuated position in which position-the tubular blank has. been formed to angled shape;

Fig. 4 is a fragmentary viewpartly in section along line 44v of Fig. 2showing-rone'type'of link whichmay be used for connecting the inner metalt guiding member to. the hat-shaped leading elementengageable withthe flex ible hat-shaped elements in theforce transmitting assembly. 1

Fig. 5 is a side elevational 'view partly in section illustrating a modified form' of ball'and'socket joint- Fig. 6 is a vertical sectional view on line 6-6 of Fig. 5.. v Fig. 7 is a diagram for purposes of mathematical analysis, illustrating the physical forces and factors afiecting the forming of hardmetals. I

Fig. 8 is a diagram showing, for purposes of mathematical-analysis, the elastic and plastic propertiesof the. tube material;

Fig. 9 is a diagrammatic showing for purposes of mathematical analysis.

Figs. 10:: andlOb are diagrammatic showings of shear deformation aifectingbuckling and wrinkling.

Figs. 11a and 11b are diagrammatic showingsof factors affecting buckling and wrinkling.

Fig. 12 is a diagrammatic view illustrating the-forces exerted at the leading edge 'ofthe work for the purpose of demonstrating internal brake-shoe frictional forcesagainst the inner surface of the workpiece and counter thrust pressurizing forces parallel to'the longitudinal surface of the workpiece.

Figs. 13 and 14 illustrate in diagrammatic fashion by side viewandbottom view, respectively, a special form of beveled and tapered tubular workpiece which allows a distribution of, forces within the. die with no waste of workpiece material.

Fig. 15 is a side elevational view partly in section illustrating a modified form of ball and socket joint.

Fig. 16 is a vertical sectional view on line 16-46 of Fig. 15.

Referring now to Figs. 1-3, inclusive, a tubular Workpiece 18 is shown inserted within the entrance portion of a die cavity 15 formed by a pair of hinged dies, lower die member 13 and upper die member 14, these die membersbeing connected by pins 17 and. supported by lower support 11 and upper support 12, which with the hydraulic mechanism are hired to the main frame of the press (not shown).

Within the-tubular workpiece 18 thereis inserted the multiple part elastomer mandrel of the invention. The mandrel as shown in Figs. 2 and 3 comprises hard elastomer end sections 22a and 22b, one of which is in force bearing relation to the forward push ram 19 and the other 225 in force bearing-relation to-counter-thrust ram 23. The other hard mandrel end section 22b is brought into frictional locking engagement against theinterior wall of the tubular workpiece at the forward or leading end of-the workpiece as a result of the application of a pressurizing force by the counter-thrust ram 23 acting through the flexible force transmitting meansand the internal prcssurizing, and aligning lead piece.

The middle sections 22' and 22" of the multiplepart elastomer mandrel are each soft in comparison with the hard end sections-22a and 22b and. are distinguished from these hard end sections'by performing thefunction-of a fluid under pressure whentheentire mandrel is confined within the workpiece and the workpiece and mandrel are subjected to'high pressures.

Each tubular workpiece 18 cold-formed and cold-sized, in accordance with-the invention is forced through: die cavity 15-and curved die cavity 16under the simultaneous application of pressure. by forward push ram 19 and counter-thrustram 23 actuated by a hydraulic force from cylinder 25.

The forward and rearward movement of push ram 19 is controlled by the hydraulic mechanism shownin Fig. 1' of applicants Patent No. 2,907,102 and this mechanism forms no part of the present invention.

With the ram'19'fully retracted and the four-wayxvalve. in port closing position rotated about 45 from the position shown in' Fig. 1 in" Patent. No. 2,907,102, the pump unit is energizedfor'flow of hydraulic fluid through a relief valve, a check valve and by. the line into the righthand and of the cylinder 36 associated with ram 19. Fluid pressure is developed aginst the piston which moves to the left in cylinder to build up pressure on the multiple part mandrel- The: pressure build-up on the multiple mandrel occurs by. reasonv of the movement of aligning member 27' against the multiple part mandrel 18, and

particularly against the leading'hardened end section: 22b

of the mandrel.

Thus, with shoulder20 of the push ram 19 coming into force bearing relationship at bearing surface 21 against the trailing end face ofthe'hard end-section 22a of the mandrel (see Fig:- 2), the multiple part mandrel is brought to an initial-pressurized condition. To initially pressurize the multiple mandrel the required movement is small, of the order of Arof an inch (see Fig. 2 for initial pressurizing). When this pressure attains a predetermined value, of the order of SOO-GOO pOunds-per" square inch, the four-way'valve of Fig. 1, Patent No. 2,907,102, is moved to a position to admit fluid pressure from pump by way of associated'lines to'the upper end of the cylinder associated with ram'19 to applyagainst the piston a forming pressure of the order of about 550-l,500 pounds'per square inch. Since the forming pressure of push ramI19 exceeds that of' the mandrel pressure of counter=thrust ram 23, there willbe movement of the tube workpiece :8 auto the forming position of the die cavity 16 at the The pressure applied by the pistons to the push ram 19 and counter-thrust ram 23 may now be simultaneously increased and equalized in order to raise the pressure on the multiple part mandrel and upon the formed tubular workpiece 1-8. The pressure applied to the piston for the push ram 19 is increased'by raising the setting on the relief valve from 500-600 pounds per square inch to about 1,500 pounds per square inch. By suitably adjusting the settings of these relief valves any desired differential of pressure may be applied to the tube workpiece depending uponthe'materials of the workpiece and anydesired final finishing or sizing pressure may likewise be established (see Fig. 3 for cold-forming). It will be understood that particular pressures will be selected. on the basis of the hardness and seizing properties of the metal material and the wall thickness of the tube work; piece.

Each of the elastomer'mandrel sections,- the soft cen-. tral-section 22", the adjaceutmiddle sections 22'and the hardened sections have a form approximating the in ternal form. of the-tubular blank to be slidably movable within the workpiece for -easy= removal after forming: About inch clearance is convenient. Each of thes'e sections is characterized by good-elasticrecovery'to'peF mit repeated' reuse; Eaclr' of the sections is" tough to" 9 withstand repeated abrasion in cold-forming andcoldsizing. Each of the sections is homogeneous and reinforcing agents may be used to impart toughness. Sponge rubber cannot be used because of its tendency to tear after one cold-forming operation, particularly due to abrasive forces caused by surface irregularities of the interior of the tubular workpiece; hence it is preferred that the mandrel sections be non-porous.

Radial expansion of hardened end sections 22a and 22b locks the entire mandrel within the tubular workpiece by brake-shoe engagement against the internal surface of the workpiece under the opposing pressurizing forces. This radial expansion prevents extrusion of the soft elastomer sections 22' and 22" shown for the five- 22b against the internal surface of the tubular workpiece during pressurizing and cold-forming operations is based solely upon the frictional forces between the radially expanded end sections and the material of the tubular workpiece. The middle sections move relative to the 10 engagement with the guiding element" 50 and the hat shaped member 60. The ball and

socket connections

54, 59 and 61, Figs. 5, 6,: l5 and 16, are preferred {to-the cross-link. connection 24 of Fig. 4 since these. are longer lasting and providemore uniform action in their directing action for metal flow under cold-forming by the free floating leading member 27. The guiding member 56 in the embodiments shown in each of these Figs. 5, 6, and 16 is fitted with spherical end 54 to ball socket 59 in the leading element. A similar hall and socket close fit is provided by the other end of the rod terminating in spherical ball portion 54 which 'fits in the spherical counterbore 61 of the hat-shaped member 60. The spherical dome of the hat extends'from the annular edge of bat member 60 to engage the annular socket or counterbore of an adjacent hat-shaped member31 in the assembly as shown in Figs. 2 and 3. In Figs. 5 and 6 snap rings 62 and split washers 63 lock the ball ends 54 of the connecting rod in place in the socket 59-of the lead internal surface of the workpiece during pressurizing and forming operations but the end sections are substantially fixed.

The counter-thrust pressure applied against the leading hard end section 22b of the multiple part mandrel is transmitted through the flexible assembly of unconnected hat-shaped members 31 which are located in the bend channel portion 16 of the shaping die as shown in Figs. 1-3.

A novel lead element is interposed between the flexible assembly of hat-shaped members 31 and the mandrel hard end section 22b, this element comprising a metal flow guiding element 27 which is located wholly within the tubular workpiece 18 as shown in Fig. 2 and adjacent the leading tapered edge thereof, this guiding element 27 being linked to a hat-shaped member 31 by a connecting rod 28. One surface of the guiding element 27 is planar or flat for directing metal flow along the minimum radius of bend in the die. The opposite surface of the guiding element 27 is spherical to contact the area of maximum radius of bend in the die. The spherical face acts as a fulcrum during the cold-forming operation directing the flow of metal at the inner tube wall of the maximum radius and helps to tilt the lead member around the curved portion of the die cavity.

The connecting rod 28 shown in Fig. 4 is one species 1 guiding element 27 lies wholly within the workpiece 18.

The length of the connecting rod 28 is equal to the radius of the die cavity 16 at the bend. If this length is substantially less than the radius, the pin would jam and the workpiece .would jam at the bend-16in the die.

cavity. If the rod lengths were substantially larger than v this radius, the rodwouldsnapwhen the work and mandrel move under cold-working pressure around the bend.

Two types of leading element which 'are' preferred are shown in Figs. 5 and '6 and Figs. 15 and 16. In each of these types the connecting rod 52 is in ball and socket guiding element 50 and hat member 60, respectively. In Figs. 15 and 16 set

screws

71, 72, 73 and 74 in

bores

75, 76, 77 and 78 perform the function of the snap rings and washers. The embodiment of Figs. 15 and 16 is preferred to that of Figs. 5; and 6, the set screws providing longer service life than the-rings.

By lubricating the forming surfaces and using a metal dissimilar from that of the tube workpiece, the friction developed during-the formingis decreased. diiferen; tial of pressure of the order of 0 1,500 p.s.i. is adeg quate for the bending of tube workpiece formed-9fv the hardest of metals to the desired dimensions of curvature.

The usual lubricating compounds utilizedfor dieswill be found suitable for cold-forming the harder and seizing metals. Preferred lubricants include 'Houghton Draw Oil No. 3105, chlorinated rubber solid film lubricant (up to 40-50% chlorine) and carnauba wax emulsion lubricant. Such lubricants as molybdenum ,disulfide; linseed oil, white lead, linseed oil oil-white lead graphite, and lard oil are not satisfactory since they give rise to seizing and galling in the die. V

Each tubular workpiece is open-ended and of a beveled length to keep to a minimum the loss of material in the final finishing operation. The end of the tube workpiece 18 engaged by the pressure member 19 does not require any finishing operation-since the end surface thereof is maintained essentially flat and square by the engagement thereof with the shoulder 17a. At the leading end of the tube workpiece 18 only a small amount of metal need generally be removed to bring it to its final dimension of a flat and square surface.

Generally, the tubular workpiece is beveled at one end and square at the other end in order to permit cold: forming and cold-sizing without loss of material. The

- bevel is such that the flow of the material of the workpiece along the shorter dimension brings the metal to a substantially square edge after forming.

In Figs. 13 and 14 there is shown a preferred beveled tubular workpiece in which the shorter length moves forward during the cold-forming operation.

In order to distribute the pressure on the front end of the tubular blank as it passes the die split, a fiat spot is ground on the tube as shown in these figures. This flat spot 2 prevents excessive pressure on the front end 4 of the tubular blank of Figs. is an -14;

The following example illustrates the bending of stain less steel tubing 304 in accordance with the invention and brings out' thejphysi cal -relationship of'IiiiSlYfdfej restraining force,'"reaction"force and friction force for bending ,of' hard, metals. i Eff-$113;

Reference is made to Figs 7-14 for the diagrammatic representation of the mathematical factors. I

Mathematical. analysis (a) PROBLEM 'The problem illustrated inthis-exam le is 'tdlfomr a straight'tube into a 90 L. The equations developed herein are applicableitoany' size and the example given below applies to-a stainless tube of the following dimensions:

'd =2.'37'5'ii1..

NOMENCLATURE P=push force in pounds P =restraining force in pounds Pg reacti-on force at outside'turn-in pounds F5=friction force caused by reaction force P in pounds F friction force causedby tube expansion (this is in addition to F p=coefiicient of friction t=initialwall thickness'of tube r': outside radius of tube in inches R;=-in side radius of bend in-inches- R =mean radius of bendin inches R =outsideradius of bend in inchesp=mandrel pressure in p.s.i. rg=inside radius of tube v =angle between P3 and P E=rnodulus of elasticity of 'tube material in p.s.i. M=moment required to bend tube in inch-pounds A =inside area of tube in square inches Si=ultiinate tensile strength of material in p.s.i. S=ultimate compressive strength of material in p.s.-i. S =tensile yield strength of material in p.s.i. fi -compressive yield strength of material in p.s.i. E;=fricti0n caused by burst pressure on push side-pounds ii -friction caused by burst pressure on restraint side S=in'side surface area oftube in square inches 7=Poissons ratio v (0) EFFECT OF INTERNAL AND EXTERNAL PRESSURE Withthe tubefree in the die, the burst stress and radial expansion may'be readily computed by standard formulae from the internal pressure.

In this example:

. et'cris' larger than the die cavity. The flow pressure of stainless" steel 304 is about equal to the ultimate tensile strength or may be about 20% higher; Thus, the greatest pressure will occur when the flow pressure causes a circumferential compressive yield and flow which u hen l..134.='0.0034 (or about0007" interferenceonthe diameter) Accordingly a preferred fit in the-"die is a-clearanceof Arr-about .001. V i

1.2 The corresponding pressure is:

,OO0 .l'09 p 1.134 =8 640 p.s.i.

To this pressure is added the internal mandrel pressure at an interference of 0.007 on diameter or greater then The external friction is then equal to:-

F'= SX/1-(8640+P)=Su(8640+%) (4) In this example:

S =6 6-sq. in. A =3.65sq. in. .=.20 (bad lubrication) =.05 (good lubrication) A solid film lubricant, chlorinated paraflin (50% chlorine) was used with u=0.05.

(d) VALUES OF F ARE NOW SHOWN ASA FUNCTION OF LUBRICATION Pressure, p.s.i.

Qr=.20)Bad-lubricati0n 121,200 147,000 166,800 (p=.05) Good lubrication 31,800 36,800 41,700

A value of p=2500 p.s.i. may be taken to be typical and the force F=735200 ,u.

(e) MOMENT TOBEND'TUBE Reference is made to Fig. 8. For a first approximation it maybe assumed that the tube material is an ideal elastic-plastic material with no work hardening property. Also, it may be'assumed that the yield point in tension is the same as that in compression and that all strains are sufiiciently large to be in the plastic range. On this basis the moment resisting the bending may be readily computed as follows. for a thin-wall tube:

P =P ,(sin (H- cos 6.) P ==P (cos 0-;rsin 0) 2M R. 0 I E'TiI SK Squaring'the first two equations and adding Since is not likely to be greaterthanOJS then P3EVPO2+P12 1 W e can get an approximate solution by noting-that .the resulting moment is 'Since P ranges from 8,000 to 20,000 pounds the Wrinkling and buckling Reference is made to Figs. a and 10b.

' Wrinkles are caused by buckling of the tubes where the compressive stresses exceed the local column strength. Along the side AA the compressive stresses are the highest. Buckling will occur if these stresses are too high and the internal pressure of the rubber is not sufficient. From this source, the wrinkles are to be expected to be at right angles to the axis of the tube. This is shown in Fig. 10b. However, due to the lesser compression (or even tension) along BB compared to the'high compression along AA, there is a shear type of deformation as shown by the exaggerated sketch in Figs. 11a and llb. This shear deformation causes compressive stresses that are at 45 to the axis of the tube and cause a buckling'that is in the direction as shown in Fig. 11b.

' From the foregoing it is seen that there are two sources of the buckling forces. tial compressive stresses that are introduced from pinching the tube in the die from an oversize tube. Furthermore, the main axial compressive stresses are in creased from the frictional forces from an oversize tubel .There is one method of preventing local bucklingand this is by employing suflicient internal pressure. Of course, the condition leading to buckling may be-greatIy alleviatedby maintaining very low frictional forces: (by proper lubricant and having smooth surfaces ondie and tube). 1

An estimate of the required internal pressure is made by taking a one inch square surface of the tube and. assuming the axial force corresponding to the compressive yield of the material. The compressive force is equal to:

. cx Y If there isa local eccentricity or bow of 0.005 inch,

For y =100,000 and t=0.109, this moment is 54 .5 in. lbs.

' :In upsetting practice, the free length of a bar should not exceed about 3 /2 diameters to prevent buckling. This length is'about 0.4 inch of plate. The laterally in duced moment is I x pa 4000 p.s.i,

A third cause is the circumferen- 5 '14 The force F; to give this is P =1r/4 2.08?=13,800 lbs.

Equation 12 gives the friction developed when the inter- 5 ference is greater than about 0.007 inch. Very high push forces are needed to overcome this friction which developed when the leading edge of the tubular workpiece made of hard metal negotiates the curve in the die cavity, Although the push force may be loweredsomewhat by suitable lubricants, high values of push force are still needed due to friction, particularly when the lubrication is inadequate. If P is the force on the end of the tube (excluding the rubber pressure) the compressivestress in the metal is of the push stress 8 Since r is roughly equal to r,-,, then stress s=l/t,u(8640+'p)' (15) Typical values are t 1.=. =0.05 to'0.20 I p=l500 mm Y 7 stress s=1,000,000 L Then if the coeflicient of friction exceeds about 0.09, compressive yield or upset occurs! when the force is first applied.

From the present example it is seen'that an initial interference fit will cause a large increase in the push load. This increase under bad lubrication can easily be as high as 60 tons. However, even when the lubrication is fairly good, a heavy interference will cause buckling of the tube because of upsetting. No frictional forces (other than that at the reaction P will exist'if the tube is about 0.002 inch to 0.003 inch loose in the die.

M andrel pressure The-corresponding end force is 1 P= A,=ss00 3. s.- 2-1,20010s. 3

It can therefore be seen that the pushforce s'hould not bear too heavily on the mandrel or excessive burst will occur on the tube, to cause metal upset.

v Loss of rubber pressure p V There is a loss of rubber pressure due tofi'iction peg tween the unlubricated rubber and the tube. See-Fig. 12,

This is calculated as follows; e A dp=21rnpndx The limiting Example:

r =l.08 x= V V 3.56 p =4000 p.S.i. p=4000 1470 540 '='0.3

P 400 X e-- x This shows that the rubber pressure drops rapidly with distance. .If there is a poor fit between shoulder 20 and the hard trailing end 22a, soft rubber from 22' may eXtrude rearwardly' into the gap or unsupported area shown in Fig". 12'. p

The 2 inch tube of this example is pressurized under 7 a force of 500 pounds and cold worked into a 90 L by The steps of Example I were carried out with Hastelloy B tubing, 2 inch pipe size, under forming pressure of 1,600 pounds and mandrel locking pressure of 500' pounds.

A perfect 90 L was made.

EXAMPLE III The steps of Example I were carried out with aluminum tubing, 2 inch pipe size, under forming pressure of 600 pounds and mandrel locking pressureof 500 pounds.

A perfect 90 L was made.

EXAMPLE IV The steps of Example I- were carried out with titanium tubing,f2 inch pipe size, under forming pressure of 1600 pounds and mandrel locking pressure of 500 pounds.

A perfect 90 L was made.

EXAMPLE V The steps of Example I were carried outwith zirconium tubing, 2 inch pipe size, under forming pressure of 1600 pounds and mandrel locking pressure of 500 pounds.

A perfect 90 L was made.

Modifications of this invention not described herein will-become apparent to those skilled in the art; Therefore,= it is intended that the matter contained in the foregoingdescription and the accompanying drawings be interpretedas illustrative and not limitative, the scope of the invention being defined in the appended claims.

In each of the foregoing examples a'five part mandrel was used as shown in Figs. 2 and 3, the center part 22" of the multiple part mandrel. being Thiokolrubber filled with zinc sulfide and being softest, the intermediate adjacent section's-22"being natural rubber which is harder than the Thiokol rubber and the hard end sections being vinyl chloride plastisolin a ratio of 68/32 vinyl chloride resin totricresyl phosphate plasticizer, baked at 400 F.

to shore hardnes's'o'f" 65 D. Other plasticizers, for'example dibutyl phthalate and dibutylfsebacate may be used to attain preferred short Dhardness values of 55-75 and the modulus of elasticity values indicated 'lfer'e'inbeforeand the formulation proportions maybe adjusted for lower hardness values, e.g; 12-55 with elasticity'values from about 300 to 25,000 p.s.i.

We claim:

l. A method of simultaneously cold-forming and coldsizing open-ended tubular workpiece to its final shape without upsetting the 'material and wo'rkpiece in a shaping die comprising inserting a removably expansible multiple part elastomer! mandrel having the same cross-sectional external shape as the intemal cross-sectional shape of said workpiece and being easily slidable into and through said workpiece, said multiple part mandrel comprising end sections having a modulus of elasticity lying between about 300 to 25,000 pounds per square inch, a hardness value on the Shore Durometer" D scale of between about 12 and 75 and good elastic recovery and a middle section of soft elastomer having good elastic recovery, applying a pressurizing force within said workpiece against the front face of said mandrel while pushing against the other end of the workpiece to thereby expand the end sections at the front face, and locking the mandrel in position for cold-forming, applying a cold-forming force against the trailing edge of said workpiece whilemaintaininng; the

pressurizing force against the front face of said mandrel to force said workpiece through said die thereby coldforming and cold-sizing said workpiece.

2. A method as claimed in claim 1 wherein said workpiece is formed of a hard material which is flowed by a guiding member forwardly of the leading edge of said mandrel to thicken said material uniformly at the inner internalv radius of bend of the formed final shape.

3. A method as claimed in claim 2 wherein said uniform flow of the thickened material is carried out, by application of a flat guiding surface to the inner thickened portion of the formed tube and wherein said flat guiding surface is fulcrumed at the bend from a fulcrum which is opposite to the thickened section, said uniform thickening taking place under the action'of the pushing force and the pressurizing force against said mandrel. o

4. A method as claimed in claim 2- wherein said tubular workpiece is beveled to provide a shorter workpiece length at the inner radius of forming-and a longer workpiece edge atthe outer radius of forming, said longer edge becoming shorter under the application of pushing and tensile forces during cold-forming to be square at the leading edge of the workpiece with the shorter edge in the cold-formed workpiece.

5. A method as claimed in'claim 4 wherein-said mandrel is pressurized by counter-thrust forces within said workpiece acting on the front face of said mandrel by force transmitting and aligning means, the center of said force transmitting and aligning means being on the axis of said workpiece.

6. A method as claimed incl'aim 5 wherein-the'center of said force transmitting and aligning means for said counter-thrust pressurizing. force for said mandrel is in alignment with both the'forward edge of said shorter beveled length and the forward edge-of said longer beveled length of the workpiece before cold-forming.

7. A methodas' claimed in claim 6.wherein'said-tubular workpiece is flat at its longestedge'to provide a hat tapered spade section at the outer'portion'of the longest cdgeato provide more uniform distribution of forces on the workpiece. within the die;

8. A method as claimed in claim 6 wherein said counter-thrust pressurizingiforce is about 500-600 p0u'nds andsaid pushing: force is about 600 :to about 1500 pounds;

9.: A method-as claimed in claim 8 whereinsaidworkpiece is lubricated with a chlorinated hydrocarbon solid film lubricant, said counter-thrust pressurizing force being about 500 pounds. and said pushing -fo'rceiwhich is larger than said counter-thrust force being; about 600 pounds to cold-form a workpiecemade of aluminum.

10. A method as claimed in claim 8 wherein said workpiece is lubricated with a chlorinated hydrocarbon solid film lubricant, said counter-thrust pressurizing force beingabout" 500 pounds a and said pushing force which is larger than said counter-thrust force being 'at' least about 1500 pounds to'cold-form a workpiecemade of stainless steel.

11. Apparatus for simultaneously cold-forming and cold-sizing an open ended tubular workpiece to its final shape without upsetting the material of the workpiece in a shaping die comprising a removably expansible mul- 17 tiple part elastomer mandrel having the same cross-sectional external shape as the internal cross-sectional shape of said workpiece and being easily slidable into and through said workpiece, said multiple part mandrel comprising end sections having a modulus of elasticity lying between about 300 to 25,000 pounds per square inch, a hardness value on the Shore Durometer D scale of between about 12 and 75 and good elastic recovery and a middle section of soft elastomer having good elastic recovery, said mandrel being locked in frictionally fixed position within the workpiece under the pressurizing action of a force applied within the workpiece against the front face of the mandrel and a greater cold-working force applied against the trailing edge of the workpiece and mandrel.

12. Apparatus as claimed in claim 11 wherein said multiple part mandrel comprises end sections of hard polyvinyl chloride plastisol and a middle section of soft elastic rubber.

13. Apparatus as claimed in claim 11 wherein said multiple part mandrel comprises end sections of hard polyvinyl chloride plastisol and a middle section of soft elastic polysulfide rubber.

14. Apparatus as claimed in claim 11 wherein said multiple part mandrel comprises five parts, there being two end sections of hard polyvinyl chloride plastisol, in termediate sections of soft elastic rubber and a center section of soft elastic polysuliide rubber, said centrally located polysulfide rubber being softer than said intermediate sections of rubber.

15. Apparatus for simultaneously cold-forming and cold-sizing an open ended tubular workpiece to its final shape in a shaping die under opposing forces acting within the leading edge and against the trailing edge of said workpiece comprising a removably expansible multiple part elastomer mandrel having the same cross-sectional external shape as the internal cross-sectional shape of said workpiece and being easily slidable into and through said workpiece said multiple part mandrel comprising end sections having a modulus of elasticity lying between about 300 to 25,000 pounds per square inch, a hardness value on the Shore Durometer D scale of between about 12 and 75 and good elastic recovery and a middle section of soft elastomer having good elastic recovery, in combination with pressurizing and aligning means delivering a counter-thrust force to the front face of said mandrel within said workpiece while pushing said workpiece and mandrel at the trailing edges of both, said mandrel being locked in frictionally fixed position within the workpiece by the brake shoe action of the end sections under the pressurizing section of the force applied through said pressurizing and aligning means within said workpiece against the forward end section of said mandrel.

16. An apparatus for cold-forming and cold-sizing as claimed in claim 15 wherein said pressurizing and aligning means contain flexible force transmitting means adapted to deliver a pressurizing counter-thrust to a flexible mandrel within the tubular workpiece, said force transmitting means comprising an assembly of a plurality of unconnected identical hat-shaped members, each of said hat-shaped members being constructed of an annular base defining a socket in said base, said annular base slidably fitting within the die cavity, and a socket engaging spherical dome portion opposite said base adapted to fit into and bearingly engage the socket of the adjacent member during forced passage of said unconnected assembly through the bend of the die while cold-forming and cold-sizing.

17. Apparatus as claimed in claim 15 wherein a guiding member for metal flow is provided in advance of said mandrel, said member having a fiat metal flow guiding surface adapted to direct the metal flow during coldforming against the inner thickened portion of the formed workpiece in advance of said mandrel and wherein said directing surface is fulcrumed at the bend of the die from a fulcrum opposite the thickened portion, said guiding for said thickened portion taking place under the ac tion of the pushing force and the pressurizing force against said mandrel.

18. Apparatus as claimed in claim 17 wherein said fulcrumed opposite portion of said guiding member is spherically shaped and said guiding member is linked to said pressurizing and aligning means by a ball and socket.

19. Apparatus as claimed in claim 18 wherein said ball and socket includes a connecting rod whose length is shorter than the shortest radius of bend of the work piece.

20. Apparatus as claimed in claim 11 wherein said tubular workpiece is formed of a metal which exhibits seizing and galling characteristics against steel and wherein the internal forming surfaces of said die are made of hardened steel.

References Cited in the file of this patent UNITED STATES PATENTS 1,978,452 Fladin Oct. 30, 1934 1,993,361 Cornell Mar. 5, 1935 2,701,002 Arbogast Feb. 1, 1955