US3160130A

US3160130A - Forming method and means

Info

Publication number: US3160130A
Application number: US86188A
Authority: US
Inventors: Frank J Pesak
Original assignee: North American Aviation Corp
Current assignee: North American Aviation Corp
Priority date: 1961-01-31
Filing date: 1961-01-31
Publication date: 1964-12-08
Anticipated expiration: 1981-12-08

Description

Dec. 8, 1964 F. J. PESAK 3,150,130

FORMING METHOD AND MEANS Filed Jan. 31, 1961 4 Sheets-Sheet l INVENTOR.

FRANK J. PESAK ATTORN EY Dec. 8, 1964 F. J. PESAK 3,160,130

FORMING METHOD AND MEANS Filed Jan. 51, 1961 4 Sheets-Sheet a FRANK J. PESAK X W w ATTORNEY Dec. 8, 1964 F. J. PESAK 3,160,130

FORMING METHOD AND MEANS Filed Jan. 51, 1961 4 Sheets-Sheet 4 2- 1- I m 1 l 13% R m N\ o N 4 a: o

a] g N qo o --N a I "H g 1 m N N N r r N N N no 2 g u. 3

l0 3 &

,3 N N INVENTOR.

FRANK J. PESAK m -xx ATTORN EY RESERVOIR United States Patent 3,16%,139 FURMING METHOD AND MEANS Frank .F. Pena-k, Encino, (Kalli, assignor to North American Aviation, Inc. Filed Jan. 31, 1961, Ser. No. 86,188 12 Claims. (Cl. 1l344) This invention concerns method and apparatus for forming various objects of diverse shapes and materials starting initially from an elongate workpiece or blank of generally tubular form. More particularly, this inven tion contemplates improved method and apparatus for fabricating a hollow article from a tubular blank or specimen of deformable material by deforming the material progressively starting at or near one end of the blank and proceeding along its length, and by closely controlling the amount, the rate, and the location of deformation of such material by the application of forces thereon.

The invention disclosed herein is applicable to the fabrication of any article which can be formed by expansion of a generally tubular blank by the application of fluid pressure within the same. In addition, the forming process may utilize one or more dies having workfaces corresponding to the desired final shape of the article, whether symmetrical or not, and regardless of variations in the shape or cross-sectior1al area of such article throughout its length. The method disclosed herein, as applied to the fabrication of articles from metallic tubular blanks avoids ballooning or excessive elongation of metal in localized areas during deformation of the blank by confining the tube within a sleeve which surrounds the outer surface thereof and which is gradually withdrawn while a hollow mandrel within the tubular blank supports the inner wall surface thereof and permits the application of hydraulic pressure to expand the blank into any one of various complex or intricate shapes determined by the workface contours of a surrounding die cavity. The outer sleeve surrounding the tubular blank restricts and otherwise limits the expansion of the blank which would otherwise occur due to the outward force of hydraulic pressure from within its tubular walls. As the stated sleeve is withdrawn from the die, force is simultaneously applied radially from within the tubular blank and axially against the end thereof, the effect of which is to cause deformation of the workpiece progressively along that portion which is not restrained by the stated sleeve.

One result of the method disclosed herein as referred to above is that an increase in diameter up to one hundred percent greater than the initial diameter of the tubular .blank may be achieved with little or no change in wall thickness of the workpiece. In contrast to this, conventional methods for expanding tubular blanks into finished articles of bulbous form are successful only in the case of very small diametral expansion ratios, the precise value of which depends upon the initial length of the lank considered with the starting wd final diameters of the workpiece before and after formation of the finished article. Specifically, the amount which a workpiece of any given metal or alloy in tube or cylindrical form may be successfully expanded by conventional tube forming devices without resulting in rupture of the workpiece is partly dependent upon the length of the workpiece over which the expansion occurs. For example, a ten percent increase in diameter of a tubular workpiece of short length may be achieved with relative ease by applying fluid pressure within the workpiece suificient to force the sides radially outward in all directions an equal amount, whereas the same diametral ratio of expansion could not be accomplished by the stated method in a workpiece of relatively great length. In the longer workpiece, application of force from within the tube in an amount sufiicient to exceed the yield strength of the material therein will "ice result in ballooning or local expansion of the workpiece at some relatively small area along its length, followed by rupture of the workpiece material at the stated area if the application of radially outward force is continued. Between the two stated extremes there lies a particular value of length for any given workpiece size, material, condition and expansion ratio which may be termed the critical length, at which expansion under the stated conditions may occur without rupture, and which if exceeded will result in localized and uncontrollable ballooning followed by rupture. For example, uniform expansion of a tubular blank of aluminum to a diameter in excess of five percent by conventional means when the critical length is exceeded has been found to result in rupture of the material even with superior uniformity of material composition, thickness and surface smoothness in the blank before the forming operation is begun.

Accordingly, it is a principal object of the instant invention to provide improved apparatus for forming tubular blanks into articles of diverse shapes having larger area at one or more cross-sections therethrough than the stated blank.

It is a further object in the instant case to provide method and apparatus for expanding tubular blanks into various shapes having non-uniform cross-sectional size by pressure applied outwardly from within the tube walls.

It is another object of the invention disclosed herein to provide method and apparatus permitting expansion of tubular blanks to form articles having length greater than critical length and cross-sectional sizes substantially in excess of the cross-sectional size of such blanks.

It is also an object of the invention disclosed herein to provide method and apparatus as set forth in these objects permitting greater versatility in the selection of sizes and shapes of finished articles formed from tubular blanks characterized by the absence of significant change in wall thickness of the starting blank compared with the finished article.

it is a further object of the invention disclosed herein to provide method and apparatus as referred to in the above objects including means for forming articles from tubular blanks concerning winch greater relative length of the blanks and of the articles may be achieved than with devices of the same class known to the prior art.

It is a further object of the invention in this case to provide apparatus for achieving the various objects set forth above by means not requiring the use of dies, molds or the like.

Other objects and advantages will become apparent upon a close reading of the following detailed description of an illustrative embodiment of the inventive concept, reference being had to the accompanying drawings, wherein:

FIGURE 1 shows in side elevation and partly in section, a general view of apparatus incorporating the inven tive concept disclosed herein,

FIGURE 2 shows an enlarged sectional view, partly broken away, of a portion of the apparatus of FIGURE 1,

FIGURE 3 shows a cross-sectional view corresponding generally to FIGURE 2 but with a different shape of die workface, and incorporating microswitch means for con trolling the operation of the apparatus of FIGURES 13, inclusive.

FIGURE 4 shows a view substantially identical with FIGURE 3 except for the mieroswitch actuating means in a different operating condition than that shown in FIG- URE 3, and

FIGURE 5 shows a general schematic view of the elec trical and hydraulic systems suitable for use with the apparatus of FIGURES 1-4, inclusive.

With reference to the drawings described above and particularly to FIGURES 1 and 2, a tube forming device incorporating the inventive concept disclosed herein is generally designated by reference numeral 1 and principally comprises a die portion 16 and a ram portion 12. While die portion may be omitted in "the case of dieless forming as discussed below, the apparatus of FIGURE 1 shows an embodiment of the inventive concept as applied to die forming. Die portion 10 mainly comprises a pair of

separable die elements

14 and 16 which may be formed from suitable strong and lightweight material such as plastic. Die

elements

14 and 16 are containedwi hin a two part high strength casing 18 having flanges 29 whereby the casing elements may be securely held in operative relationship by appropriate means such as holding bolts 22.

Separable die elements

14 and 16 are shaped to define a cavity 24 formed by workface 26, the contours of which coincide with the desired final exterior shape of the articles to be formed therein. The ends of cavity 24 are designated by reference numerals 28 and 39, which may be relatively far apart as shown by the illustrative examples of FIGURES 1 and 2. The stated example also involves a non-uniform variation in the diameter of the cavity 24 as shown by comparison of

diameters

32 and 34 representing the diameters of two illustrative cross-sections through the stated cavity.

The material from which a finished article may be formed is initially a hollow elongate shell such as tubular blank or workpiece 36, one end of which is capped or otherwise closed by appropriate means such as plug 33 while the other end remains open. In a manner subsequently described, tubular blank 36 may be deformed so that the initial or starting diameter of the blank as indicated by reference numeral 49 may be expanded or otherwise enlarged as indicated by reference numeral 42. Thus, a portion of tubular blank 36 is deformed such as indicated by numeral 44 progressively along an unrestricted portion of the workpiece upon the application of force thereto.

The amount, the rate, and the location of such progressive deformation is controlled by restricting means including wall supporting means in the form of outer sleeve 46 surrounding tubular blank 36 and in close proximity or 7 bearing contact with the workpiece walls about a portion thereof so that no outward deformation or increase in cross-sectional size of the blank can occur in that portion contacting outer sleeve 46. Force means for applying force axially upon workpiece 36 are provided in the form of an inner sleeve 48 situated within outer sleeve 46 and slidable with respect thereto. Inner sleeve 48 is slightly recessed so that it is not in contact with outer sleeve 46 except at end portion 56 of inner sleeve 43, where annular projection 52 is formed as shown by FIGURE 2. Conventional sealing means are provided in the form of annular groove and O ring means 54 for sealing contact between annular projection 52 and the inner surface of outer sleeve 46. An edge 56 of annular projection 52 on inner sleeve 48 abuts the end of tubular blank 36 opposite from the closed end thereof.

A hollow mandrel 53 is further provided within inner sleeve 48, by means of which fluid flowing through conduit means 60 may be conducted to the space enclosed by tubular blank 36 during the forming operation. Mandrel 58 is characterized by a recessed portion 62 of lesser diameter than tubular blank 36, and by a bearing portion 64 at the distal end of mandrel S8 of slightly larger diameter than recessed portion 62. Bearing portion 64 is sized to provide a sliding fit with the inner surface of tubular blank 36. Passage means 66 communicating between conduit means 60 and recessed portion 62 of mandrel 58 permits fluid under pressure within the conduit to apply force outwardly upon the walls of tubular blank 36 from within the same, thus avoiding column failure of the blank upon the application of axial loads to the ends thereof as described in greater detail below.

With specific reference to FIGURE 1, moving means for causing movement of sleeve 46 may be seen to include a conventional flange coupling or joint 68 by means of which outer sleeve 46 is secured to an hydraulic cylinder 76 at one end thereof. At the endof cylinder '70 opposite from sleeve 46, the cylinder is closed by a plate element 73 and is affixed by means of a flange coupling 72 to another hydraulic cylinder 74 containing a stationary piston '76. Piston rod '78 affixed to piston '76 extends through a rod seal 86 and terminates in ball end 82 contained within a recess 84 in a stationary end wall 86 and retained therein by plate retention means 88 affixed to wall 86 by suitable means such as bolts 94

Fluid connections

92 and 94 are provided at either end of cylinder 74 so that, upon pressurization of either side of stationary piston 76, cylinder 74 and elements connected thereto will be laterally moved to the left or right as seen in FIGURE 1.

Lateral movement of cylinder 7 4 in the manner referred to above is accompanied by corresponding movement of cylinder 70 and mandrel 58 attached thereto. Independently movable with respect to cylinder "id is a piston d6 contained therein, through the center of which mandrel 58 extends. Piston d6 thus constitutes part of the force means for applying axial force to workpiece 36 as referred to above. Independent relative movement of piston 96 with respect to cylinder 70 may be caused by pressurization of cylinder 76 on either side of piston 96 through appropriate fluid connections 98 and 101 Pressurization within tubular blank 36 may be caused independently and regardless of the pressure conditions in cylinders '70 or 74. Separate conduit means 60 is provided within mandrel 58 and communicates in turn through passage 102 to external fluid connection 104 at the peripheral edge of flange assembly '72.

Reaction forces due to pressurization of cylinders 70 and '74 and applied by connecting rod '78 to stationary end wall 86 are opposed by stationary wall 106 through tension beams 108, 110 and 112, while vertical support for the hydraulic components of ram portion 12 is provided by a plurality of resilient support elements such as selfcentering

hydraulic cylinders

114, 116 and 113 connecting lugs 12% to each of the stated tension beams. It will be understood that other resilient means such as springs may be used in place of

cylinders

114, 116 and 118. Casing elements 18 enclosing die means 14 and 16 are affixed to wall 106 by appropriate means such as

bolts

122 and 124 shown in FIGURES 1 and 2.

Referring now to FIGURE 3, tube forming means corresponding generally to that shown in FIGURES 1 and 2 and discussed above may be seen with the exception of the shape of cavity 124 formed by work-face 126. Moreover, the structure shown by FIGURE 3 includes control means affecting the forming operation as discussed in detail below.

While the total distance between

cavity extremities

128 and 130 shown in FIGURE 3, and between extremities 23 and 36 shown, for example, by FIGURE 2, are in both cases substantially greater than the largest crosssectional diameter of the respective cavities, the cavity shapes in each case may be seen to differ considerably. Thus, cavity 124 forms a plurality of connecting bulbous or bellows shaped contours adjoining a bore 132. Otherwise, the structure of FIGURE 3 corresponds with that shown and described above in connection with FIGURES 1 and 2. Thus, outer sleeve 146 surrounds a tubular blank 136 in which inner sleeve 148 is operatively engaged with abutting edge 156 against the distal end of the tubular blank, while mandrel 158 having central conduit means 160 therein contacts the inner surface of the workpiece.

In addition to the structure referred to above, outer sleeve 146 is provided with a collar 209 slidable with respect thereto and normally projecting slightly beyond the distal end of the outer sleeve under the biasing force of spring 208 in the manner shown by FIGURE 3. Collar 2% is provided with a contact screw 202 adjustably 55 mounted on a radially projecting lug 204 and aligned with a microswitch 206 in operative relationship therewith. Microswitch 2% is connected in circuit with electrical controls described more particularly in connection with FIGURE 5 below.

As seen from the general schematic view of FIGURE 5 showing an illustrative system adapted for use with the devices of FIGURES 1 to 4, a source of pressure is provided in suitable form such as pump Zltl having its outlet connected with conventional pressure modulating means such as accumulator 212. The outlet from accumulator 212 is divided into two

lines

214 and 216 connected to

valves

218 and 220, respectively. Valve 212i is a three-way valve connected to

lines

222 and 224 communicating with cylinders 76 and 74, respectively. The ends of cylinders 7t and 74 opposite from the connections of

lines

222 and 224 thereto, respectively, are connected to valve 22d by means of lines 226 and 223. In the position shown, valve 218 connects pressure source 210 through line 214% to fluid connection 100 of cylinder 7% and to fluid connection 94 of cylinder '74, while valve 22% connects the side of each cylinder opposite from the stated fluid connections to a common drain line 2% communicating with reservoir 248.

While many different conventional items may be used to perform the various functions required for operation of the tube forming device disclosed herein, the structural details in connection with valve 21%, for example, will serve to illustrate appropriate functional characteristics of the stated control elements without limiting the control system of FIGURE 5 to the precise structural details used to illustrate the same. Thus, valve 213 is shown as being provided with arms 232 and 234 by means of which opposing moments of force may be applied to valve 218 by link 236 and resilient element 242, respectively connected to the stated arms. Movement of link 235 may be caused by suitable means such as a solenoid 238 electrically connected in circuit with microswitch 2% and battery or other power source sea.

It may further be seen from FIGURE 5 that fluid pressure from source 210 is connected through

lines

216 and 244 with an additional valve 245 which also communicates through line 246 to reservoir 248.

Operation The apparatus disclosed herein may be used in forming a tremendous variety of diverse articles, and operation of the apparatus may vary slightly depending upon the shape of the finished article, the desired final wall thickness or dimensional accuracy of the article, and the nature or properties of the material in the workpiece. Among the possible variations in operation, for example, hot forming liquids may be conducted through conduit 68 to apply fluid pressure for expanding the article when deformation of the workpiece material will be facilitated thereby. Moreover, the application of forces to a workpiece may be controlled in their sequence or intensity and coordinated with movement of

sleeves

46 and 48 so that deformation of the workpiece may be accomplished according to a predetermined schedule without the use of dies. In addition, beneficial results may be had in forming some articles by the apparatus of FIGURE 1 except omitting bearing portion 64- of mandrel 58. However, operation of the apparatus as shown in FIGURE 1, for example, will be explained in connection with the use of all the elements shown therein, including dies 14 and 16.

The first step in operating the tube forming apparatus shown by FIGURE 1 requires positioning of a tubular blank or workpiece within cavity 24 with the tube end nearest die cavity inner extremity 28 plugged or otherwise closed as mentioned above. In the position referred to, outer sleeve 45, which is sized according to the requirements of each particular forming problem or size of workpiece, is fitted thereover so that substantially all of workpiece 36 is contained within outer sleeve 46 and cir- 5. cumferentially restricted thereby, while a portion of the workpiece extending beyond the distal end of sleeve 46 remains exposed. Before the forming operation is begun, valve 227 in line 226 may be closed to prevent passage of fluid in either diretcion through the stated line and valve 218 may be positioned to connect

lines

222 and 224 with drain line 2349. Thereafter, valve 220 may be positioned to connect

linesc

226 and 228 to pressure line 216 whereby pressure will be applied at fluid connection 92 of cylinder 74, resulting in the application of force against plate element 73 to move sleeve 46 toward the left to position the same with respect to the workpiece substantially as shown in FIGURE 1. With the components of tube forming device 1 positioned in the required relationship at the beginning of the tube forming operation, edge 56 of annular projection 52 on inner sleeve 48 contacts the end of the tubular workpiece opposite from the closed end thereof and is in abutting relationship therewith.

With the various stated elements of device 1 in the starting relationship described above, the tube forming operation may be initiated by opening valve 227 and

positioning valves

218 and 220 in the manner shown by FIGURE 5. In this position, fluid pressure will be applied in cylinders 7t) and '74 in a direction resulting in the application of force to move cylinder 74 toward the right as shown in FIGURE 1 while piston 76 contained therein remains stationary. Movement of cylinder 7 4 in the stated manner results in simultaneous corresponding movement of sleeve 46 and mandrel as structurally connected thereto. Simultaneously with the application of pressure through fluid connection Q4 on cylinder 74, pressure is also applied through line 222 to fluid connection 1% on cylinder 70. The application of fluid through connection in the stated manner causes the application of force on piston tending to move the piston toward the left as shown in FIGURE 1. During the application of fluid pressure through

fluid connections

94 and 1% as described above, independently operable valve 245 may be positioned as shown by FIGURE 5 to cause fluid flow through connection ltld and passage 1&2 to conduit 60 within hollow mandrel 53, resulting in the application of force radially outward against the walls of tubular workpiece 36.

Referring to FIGURE 2, it may be seen that the application of fluid pressure through conduit 60 if sufficiently great may cause deformation of the walls of tubular blank 36 to expand the same. The amount and location of such deformation is limited by workface 26 forming cavity 24 and further by outer sleeve 46. Thus, before expansion occurs, outward deformation of the walls of workpiece 36 in the portion surrounded by sleeve 46 is prevented or otherwise restricted by circumferential contact with outer sleeve 46, whereas after expansion occurs in an amount suflicient for the walls of workpiece 36 to contact workface 26 of cavity 24, further deformation is prevented by the stated Workface surfaces. In consequence of the stated restriction effects, portion 44 of workpiece 36 shown in FIGURE 2 is an area of local deformation which moves progressively and in a plurality of separate adjoining increments along the entire length of cavity 24 as sleeve 46 is withdrawn.

Due to the structural relationship of parts in the apparatus disclosed herein and the functional results obtained therefrom as discussed above, it will be understood that the application of pressure through fluid connection 94 to cylinder 74 to withdraw sleeve 46 during the forming operation is accompanied by the application of pressure through fluid connection 1% of cylinder 70 applying force to piston 96, and that the force thus applied to piston 96 is transmitted through inner sleeve 48 and abutting edge 56 to workpiece 36. As detailed below, the stated force applied by abutting edge 56 is used to cause movement of the tubular workpiece longitudinally toward the left as shown in FIGURE 2.

The effect of the forces applied to workpiece 36 as a result of the operations described above causes deformation of the workpiece material to form an article having an external shape coinciding with the contours of workface 2,6. The stated deformation begins with the simultaneous ap lication of force due to fluid pressure within workpiece 36 and endwise by projecting edge 56 causing movement of workpiece material toward the left as shown in FIGURE 2, for example. Thus, excessive local deformation of the workpiece material due to expansion of the workpiece diameter is avoided by reason of the continuous addition of such material by movement of inner sleeve 48 toward the left in FIGURE 2. Simultaneous with the application of radial force due to fluid pressure within workpiece 3d and endwise force on the workpiece material due to leftward movement of inner sleeve 48, outer sleeve 46 is gradually withdrawn so that deformation of the workpiece material occurs only in the portion thereof which is nearest the distal end of the outer sleeve. Thus, deformation is localized and occurs only in a narrow increment along the workpiece length, the number and size of such increments depending upon the movement of sleeve 45.

The amount of force required in each case and the rate of movement of each stated element acting on workpiece 36 may be varied to produce the best results depending upon the factors involved in each particular forming problem. For example, the force sutlicient to expand the diameter of workpiece 3d obviously depends upon that required to exceed the yield strength of the workpiece material. Similarly, variations in the rate of'moven'i nt of the movable parts discussed above may occur within a wide range depending on the Shape of workr'ace as as well as the extent of dimensional change involved in the comparison of initial and final workpiece sizes. For example, orifices 25 and 252 are shown as a possible means for controlling the relative response of cylinders Ill and '74 according to a desired relationship between their respective movements.

' In any case, it is of utmost importance in practicing the inventive apparatus and method disclosed herein that outer sleeve 46 is initially positioned in close proximity to the walls of workpiece 36 and prevents the application of fluid pressure within the workpiece from deforming that portion of the workpiece wln'ch may contact the sleeve. Similarly, it is of further and equally crucial importance that deformation of the workpiece material occurs in a controlled and localized area progressively throughout substantially the entire length of the workpiece, starting at or near the closed end thereof and thereafter moving toward the distal or open end of the workpiece during carefully coordinated movement of

sleeves

46, 48, mandrel 58, and simultaneous application of pressure in a predetermined amount through conduit 69. From the description of structure and operation of the same as discussed above, it will be understood that the action of outer sleeve 46 in FIGURE 2, for example, during coordinated movement of inner sleeve 4% provides control of the amount and rate of deformation occuring at any moment of time during the tube forming operation. Thus, local deformation of the workpiece material occurs only when or as permitted by movement of the apparatus parts which apply force to the workpiece as detailed herein, and cannot occur at unpredictable or uncontrolled times and locations such as characteristic of conventional devices for expansion forming of large articles from tubular blanks. Even during dieless forming as referred to above, the location and amount of deformation can be accurately controlled by coordinated movements of a plug-type mandrel having a closed tip and otherwise similar to mandrel 58 but axially movable with respect to outer sleeve 45.

While various controls or programming devices for coordinating or controlling the forces applied on workpiece 36 and the amount or rate of mandrel and sleeve movements discussed above will occur to those skilled in the art, the scope of the teachings herein is not limited by the selection of any particular controls or regulating devices. Accordingly, use of microswitch 2% and associated structure is disclosed'herein as merely illustrative of one type of control. From the description set forth above relating to collar Zilli shown in FIGURE 3, for example, it may be seen that the deforming portion 44 of workpiece 136 has a characteristic curvature, the precise contours of which depend upon the amount of deformation in the stated material which occurs while outer sleeve 146 remains in any given position. When pressure is continuously applied radially outward against the walls of tubular workpiece 136, the characteristic shape of deforming portion .44 causes the workpiece material to contact the edge of collar 200 as shown by FIGURE 4, after which continued pressure applied in the stated manner causes movement of deforming portion 44 to move collar 2% toward the right as viewed in FIGURES 3 and4 whereby contact screw ZilZ causes actuation of microswitch 2%. Actuation of microswitch 2% may cause momentary positioning of valves 213 to apply pressure from source are to cylinders 7i? and 74. Upon application of pressure to cylinder 74 outer sleeve 146 will move toward the right as viewed in FIGURE 3 by amount depending upon the pressure applied within cylinder 74 and the period of time during which it is applied. Movement of outer sleeve 146 and collar 2% mounted thereon toward the right will separate collar 2% y from deforming portion 4a of workpiece 136, permitting spring 2% to move collar Ziltl toward the left with respect to outer sleeve 14%, thus releasing microswitch 2636 and dcenergizing solenoid 233. When solenoid 238 is deenergized, return spring 242 may alter the position of valve 218 to close the same and prevent the application of pressure to cylinders 7th and '74. Thus, outer sleeve 146 may remain in the position with respect to workpiece 136 which it had at the time that spring 242 causes valve 218 to close, and to maintain substantially the same position until further deformation of workpiece material causes movement of collar 2M? and again actuates microswitch 206. In the stated manner, automatic and progressive forming of an article within cavity 24 may occur in gradual stages proceeding from one end to the other of the stated cavity.

In addition to the cavity shapes shown by FIGURES 1-4, the inventive concept disclosed herein is useful in fabricating objects of many different types, materials and shapes, including arcuate or curved tubular ducts and the like. Moreover, many shapes may be achieved by programming the amount or rate of movement of sleeves 46, 4t; and pressures applied through conduit 60 even without the use of

die elements

14 and 16 or other workface element, according to the process referred to in the art as dieless forming. However, when dies are used in the novel process herein disclosed, it is characteristic of the tube forming process taught herein that the workpiece material as it expands to the utmost limit permitted by workface 26 in cavity 24 of FIGURE 1, for example, will guide or control the direction of sleeves 46 and 43 and the movable parts of device 1 associated therewith. In order to provide freedom of directional movement of that portion of tubular workpiece 36 contained within outer sleeve 46, together with the sleeve itself and associated parts, ram portion 12 is mounted on ball end con nection 82. at one extremity and supported by resilient means 134, 116 and 118 near the other extremity as described above. Moreover, the end of cavity 24 into which

sleeves

46 and 48 initially project may be oversized as in the case of bore 132 shown in FIGURE 3, to permit a limited range of directional movement of the stated sleeves and associated parts with respect to stationary die portion it). This movement permits the deformation of the workpiece, as affected by the contours of workface 26, to vary the position of

sleeves

46, 48, mandrel 58, and other parts supported by

resilient means

114, 116,

and 118 continuously if necessary throughout the forming operation.

The tube forming method and apparatus taught herein avoids the extremely severe limitations associated with conventional tube forming techniques well known to those skilled in the art. For example, the formation of an article in the final shape corresponding to cavity 24 shown in FIGURE 2 starting with a metallic tubular blank of the relative size shown by the stated figure using conventional method and apparatus could only result in excessive local elongation of the workpiece material in an unpredictable area followed inevitably by rupture of the same long before the final diameter of the finished part could be achieved. Thus, if radial force were applied from within the tubular blank by hydraulic pressure without the action of outer sleeve 46 in FIGURE 2, for example, expansion of the workpiece would not be uniform throughout each increment of its length, but the amount and rate of expansion would vary with each variation in unit strength and wall thickness at each increment. If the material thickness were not absolutely uniform and constant, the relative weakness of the workpiece at the locations of least wall thickness would result in local expansion at such locations in excess of that occurring elsewhere throughout the workpiece. In view of the normal practical manufacturing tolerances involved in industry, minute variations in wall thickness occurring in the average initial workpiece or tubular blank are sufficient to render expansion-forming of articles of greater than critical length totally impractical from an economic and design standpoint. Small or relatively short objects such as door knobs, for example, are commonly formed within die cavities by the application of hydraulic force from within and longitudinal force applied by mechanical means to the end of the tubular blank, but the stated technique is unworkable in the fabrication of larger objects having significantly greater length than that which characterizes door knobs and the like.

In contrast to the limitations of conventional tube forming techniques as referred to above, the invention disclosed herein provides several advantages and results not achieved previously in the art, and has been successfully used in forming objects 36 inches long, but could be used for objects of even greater length. The optimum choice of fabrication method based upon considerations such as weight, reliability and cost is provided by the teachings contained herein. Thus, for example, ducting, bellows members, elongate tanks or other fluid containing elements may be fabricated in the manner described above to provide one-piece, accurately formed parts of complex shape and uniform wall thickness throughout the finished part having final diameters as much as one hundred percent greater than the initial diameter of the tubular blank from which the part is formed. The cost of fabrication usin' the teachings set forth above are considerably less than those involved in the fabrication of similar parts by conventional methods. For example, one orthodox approach in the fabrication of large, relatively thin-walled components of complex shape is to fabricate the part from individual sections which are separately formed and thereafter welded together along a plurality of seams. In addition to avoiding the increased cost of various joining methods incident to fabrication of a part in two or more separate pieces, the tube forming method and apparatus disclosed herein reduces tooling costs by the use of plastic material in separable die elements M and 16, or in eliminating the necessity for dies if the desired final shape of the article permits dieless forming of the same. Where dies are used such as shown at 14 and 16 in performing the process taught herein, they are subjected only to compression and are not required to possess high strength properties or surface hardness such as characteristics of forging dies, for example, since die

elements

14 and 16 do not deform the workpiece material but merely limit or otherwise restrain the amount of deformation occurring by reason of the forces applied mechanically and hydraulically as described above.

While the particular structural details set forth above and in the drawings are fully capable of attaining the objects and providing the advantages herein stated, the structure thus disclosed is merely illustrative and could be varied or modified to produce the same result without departing from the scope of the inventive concept as defined in the appended claims.

I claim:

1. In apparatus for forming a hollow article by expansion forming of a generally elongate hollow rigid blank of deformable material; die means including a die cavity of generally elongate shape, at one extremity of which said blank is adapted to be supported by said die means while the remainder of said blank is unsupported by said die means within said cavity, the length of said die cavity being substantially in excess of the critical length for said material with respect to the amount of said expansion, fluid pressure means for filling the interior of said blank with fluid under pressure whereby outwardly direct force is applied within said blank to expand the same, restricting means circumferentially contacting a portion of the outer surface of said blank whereby expansion of said portion is initially prevented during application of said outward force, moving means for moving said restricting means relative to said blank during application of said force whereby the material in said portion is gradually exposed and thereby permitted to expand, said expansion occurring progressively by successive deformation of said material in a plurality of increments as each increment of said surface is exposed by movement of said restricting means by said moving means, and force means for applying force axially to displace said portion simultaneously with movement of said restricting means and in a direction opposite to said movement.

2. The method of forming a hollow article from a rigid shell blank having an open end and a closed end, said method comprising: positioning wall supporting means in close juxtaposition with a first portion of the exterior surface of said blank while a second portion thereof is exposed, applying outwardly directed force to the interior surface of said blank, simultaneously applying axially directed force on the open end of said blank to displace said first portion thereof along a generally linear path, and during the application of said forces, moving said wall supporting means with respect to said blank in a direction opposite to the direction of said displacement to gradually expose said first portion whereby deformation of said blank occurs progressively starting with said second portion and continuing by progressive increments along the length of said blank as said first portion is exposed by said movement of said wall supporting means.

3. The method of forming a hollow article from an elongate rigid tubular shell blank having an open end and a closed end, including: placing said blank in a die with said closed end rigidly supported by said die and the remaining length of said blank unsupported by said die, positioning a mandrel within said blank and axially aligned therewith, extending a sleeve over a portion of said unsupported length of said blank with said sleeve in axial alignment therewith and in slidable contact with the outer surface of said blank, filling said blank with fluid under sufficient pressure to deform the walls thereof, thereafter retracting said sleeve thereby permitting said blank to deform progressively proceeding incrementally along the length of said blank as said sleeve is retracted during the application of said fluid pressure, and applying axial force to displace said portion in a direction opposite to the movement of said sleeve during retraction thereof, said displacement occurring simultaneously with said movement and operatively coordinated therewith.

4. In apparatus for forming a hollow article from an elongate shell blank of deformable metallic material; fluid pressure means for filling the interior of said blank with fluid under pressure whereby outwardly directed l l a force is applied to the wails of said blank to deform the same, restricting means positioned in close proximity to a portion of said Walls exteriorly thereof whereby deformation of said portion is initially prevented during application of said outward force, moving means for moving said restricting means relative to said blank during application of said force whereby the material in said portion is gradually exposed and thereby permitted to deform, said deformation occurring progressively and coincidentally with the movement of said restricting means by said moving means, and force means for applying force axially to displace said portion simultaneously with movement of said restricting means and in a direction opposite to said movement, said restricting means including an elongate hollow member adapted to surround said portion in sliding contact with the walls of said blank, said blank being cylindrical with one end closed and the other end opened, said elongate hollow member being an outer sleeve having complete circumferential contact with said portion and sized to provide a sliding fit therewith, said force means including an inner sleeve concentrically located Within said outer sleeve and axially movable with respect thereto, said inner sleeve having an annular projection adapted to contact said open end of said blank in abutting relationship therewith.

5. The apparatus set forth in claim 4 above in which said fluid pressure means includes a hollow mandrel having conduit means therein through which said fluid may be flowed into the interior of said blank to fill the same.

6. The apparatus set forth in claim 5 above in which said mandrel has a lesser diameter than the interior surface of said walls whereby fluid pressure holds said Walls against internal collapse.

7. The apparatus set forth in claim 6 above including in addition thereto, a workface for limiting the amount of expansion of said walls whereby the shape of said article is made to coincide with the contours of said workface.

8. In apparatus for forming a hollow article from an elongate shell blank of deformable metallic material; fluid pressure means for filling the interior of said blank with fluid under pressure whereby outwardly directed force is applied to the walls of said blank to deform the same, restricting means positioned in close proximity to a portion of said walls exteriorly thereof whereby defor-.

mation of said portion is initially prevented during application of said outward force, moving means for moving said restricting means relative to said. blank during application of said force whereby the material in said portion is gradually exposed and thereby permitted to deform, said deformation occurring progressively and coincidentally with the movement of said restricting means by said moving means, force means for applying force axially to displace said portion simultaneously with movement of said restricting means and in a direction opposite to said movement, and a Workface adapted to limit the amount of deformation of said walls whereby the shape of said article is made to coincide withthe contours of said workface, said blank being initially cylindrical, said restricting means including an outer sleeve in sliding contact with said portion of said blank, and said force means including an inner sleeve concentrically located within said outer sleeve.

9. The apparatus set forth in claim 8 above, including in addition thereto, control means for coordinating said movements of said restricting means and said force means according to a predetermined schedule to vary the shape of said article produced by said deformation.

10. In apparatus for forming a hollow article from an elongate shell blank of deformable metallic material; fiuid pressure means for filling the interior of said blank with fluid under pressure whereby outwardly directed force is applied to the walls of said blank to deform the same, restricting means positioned in close proximity to a portion of said walls exteriorly thereof'whereby deformation of said portion is initially prevented during application of said outward force, moving means for moving said restricting means relative to said blank during application of said force whereby the material in said portion is gradually exposed and thereby permitted to deform, said deformation occurring progressively and coincidentally with the movement of said restricting means by said moving means, force means for applying force axially to displace said portion simultaneously with movement of said restricting means and in a direction opposite to said movements, said restricting means including a sleeve in which said workpiece slidably fits with the external surface of said portion in contact with the internal surface of said sleeve while the remaining portion of said workpiece projects beyond the distal end of said sleeve, and said apparatus further includes control means for coordinating said movement of said restricting means and said displacement of said force means according to a predetermined schedule to vary the shape of said article produced by said deformation, die means including a die containing a cavity with a bore communicating said cavity with the external die surface, said sleeve being adapted to project into said cavity through said bore, said sleeve being universally mounted to permit angular variations in the position of said sleeve with respect to said die during said deformation, and said bore being larger in cross-sectional area than said sleeve to permit said variations.

11. The structure set forth in claim 10 above in which said moving means includes hydraulic force means comprising a cylinder for moving said sleeve upon the application of said hydraulic pressure within said cylinder, a source of fluid pressure, and connecting means between said cylinder and said source, said force means including an abutting member adapted to contact the open end of said blank, a hydraulic piston operatively associated with said abutting member whereby axial force is applied to said workpiece upon the application of fluid pressure to said piston, and connecting means between said piston and said source adapted to apply pressure to said piston.

12. The apparatus set forth in claim 11 above in which said control means includes a movable element slidably mounted on said sleeve, a microswitch mounted on said sleeve and operatively associated with said movable element whereby intermittent movement of said movable References Cited in the file of this patent UNITED STATES PATENTS 2,288,454- Hobson June 30, 1942

Claims

1. IN APPARATUS FOR FORMING A HOLLOW ARTICLE BY EXPANSION FORMING OF A GENERALLY ELONGATE HOLLOW RIGID BLANK OF DEFORMABLE MATERIAL; DIE MEANS INCLUDING A DIE CAVITY OF GENERALLY ELONGATE SHAPE, AT ONE EXTREMITY OF WHICH SAID BLANK IS ADAPTED TO BE SUPPORTED BY SAID DIE MEANS WHILE THE REMAINDER OF SAID BLANK IS UNSUPPORTED BY SAID DIE MEANS WITHIN SAID CAVITY, THE LENGTH OF SAID DIE CAVITY BEING SUBSTANTIALLY IN EXCESS OF THE CRITICAL LENGTH FOR SAID MATERIAL WITH RESPECT TO THE AMOUNT OF SAID EXPANSION, FLUID PRESSURE MEANS FOR FILLING THE INTERIOR OF SAID BLANK WITH FLUID UNDER PRESSURE WHEREBY OUTWARDLY DIRECT FORCE IS APPLIED WITHIN SAID BLANK TO EXPAND THE SAME, RESTRICTING MEANS CIRCUMFERENTIALLY CONTACTING A PORTION OF THE OUTER SURFACE OF SAID BLANK WHEREBY EXPANSION OF SAID PORTION IS INITIALLY PREVENTED DURING APPLICATION OF SAID OUTWARD FORCE, MOVING MEANS FOR MOVING SAID RESTRICTING MEANS RELATIVE TO SAID BLANK DURING APPLICATION OF SAID FORCE WHEREBY THE MATERIAL IN SAID PORTION IS GRADUALLY EXPOSED AND THEREBY PERMITTED TO EXPAND, SAID EXPANSION OCCURING PROGRESSIVELY BY SUCCESSIVE DEFORMATION OF SAID MATERIAL IS A PLURALITY OF INCREMENTS AS EACH INCREMENT OF SAID SURFACE IS EXPOSED BY MOVEMENT OF SAID RESTRICTING MEANS BY SAID MOVING MEANS, AND FORCE MEANS FOR APPLYING FORCE AXIALLY TO DISPLACE SAID PORTION SIMULTANEOUSLY WITH MOVEMENT OF SAID RESTRICTING MEANS AND IN A DIRECTION OPPOSITE TO SAID MOVEMENT.