Abstract:
Apparatus and method for forming a plurality of elongate members into a helical bundle in which a pair of bending die assemblies are mounted on a moveable carriage, the moveable carriage itself being supported by a frame. The bending dies each have a plurality of grooved rollers that engage the sides of the tubes to apply a bending force while allowing the tubes to move longitudinally through the die assemblies. The die assemblies can be rotated independent of each other or in unison by means of stepper motors. A collet, attached to the frame, holds the ends of the tubes during the bending operation.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to methods and devices used for forming elongate wire, rod, tubing and the like into shapes, in particular forming wire or tubing into helical shapes. 
     As disclosed in U.S. patent application Ser. No. 13/864,018, the contents of which are incorporated herein by reference, a heat exchanger in which the heat exchanger tubes are formed into helical tube bundles has significant advantages over straight-tube heat exchangers in terms of durability, size and thermal efficiency. 
     Apparatus and methods for forming a single rod of wire or tube into a helical shape are well known. U.S. Pat. No. 4,402,205 to Yakovlev et al. discloses various methods for forming helical springs by winding a resilient rod around a rotating mandrel. U.S. Pat. No. 4,606,209 to Eisinger discloses a disk roller mechanism for forming a wire into a helical shape in which the wire is drawn through a plurality of staggered disk-shaped forming rollers while the wire is also being rotated about its own axis. Although the prior art discloses numerous methods of forming a single wire into a helix, or multiple thin strands into wire rope, the prior art does not disclose a method and apparatus for simultaneously forming a plurality of tubes into a helical bundle. 
     SUMMARY OF THE INVENTION 
     The present invention comprises an apparatus and method for forming a plurality of rigid or semi-rigid elongate members, for example a plurality of stainless steel tubes, into a helical bundle. According to an illustrative embodiment, a pair of bending die assemblies are mounted on a moveable carriage, the moveable carriage itself being supported by a frame. The bending dies each have a plurality of grooved rollers that engage the sides of the tubes to apply a bending force while allowing the tubes to move longitudinally through the die assemblies. The die assemblies can be rotated independent of each other or in unison by means of stepper motors. A collet, attached to the frame, holds the ends of the tubes during the bending operation. 
     With the tubes firmly held by the collet, the first bending die assembly is rotated about the axis of the tube bundle until the lead angle of the helix is established, taking into account the elastic recovery of the tubes. Thereafter, both bending die assemblies are rotated in unison as the carriage is advanced along the axis of the tube bundle. The pitch (helical angle) of the tube bundle can be varied by varying the spacing of the bending die assemblies, the angular orientation between the two bending die assemblies and/or by varying the speed of advancement of the carriage relative to the rotation of the die assemblies. The helical radius of the tube bundle can be adjusted by altering the depth of the grooved rollers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements and, in which: 
         FIG. 1  is a front perspective view of a bending apparatus incorporating features of the present invention; 
         FIG. 2  is an exploded perspective view of a portion of the bending apparatus of  FIG. 1 ; 
         FIG. 3  is a cross sectional view of a bending die used in the bending apparatus of  FIG. 1 ; 
         FIG. 4  is a side view of the bending die of  FIG. 3 ; 
         FIG. 5  is a perspective view of the bending die of  FIG. 3 ; 
         FIG. 6  is a perspective view of an alignment die used in the bending apparatus of  FIG. 1 ; 
         FIG. 7  is a front view of the alignment die of  FIG. 6 ; 
         FIG. 8  is a side view of the alignment die of  FIG. 6 ; 
         FIG. 9  is a cross-sectional view of the alignment die of  FIG. 6 ; 
         FIG. 10  is an enlarged perspective view of a portion of the bending apparatus of  FIG. 1 ; 
         FIG. 11  is a side view of the bending apparatus of  FIG. 1  in an initial position; and 
         FIG. 12  is a side view of the bending apparatus of  FIG. 1  in a final position. 
     
    
    
     DETAILED DESCRIPTION 
     The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and detailed description are not intended to limit the invention to the particular form disclosed, but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention. 
     With reference to the figures and in particular  FIGS. 1-2 , apparatus  10  comprises a front bending die assembly  12  and a rear bending die assembly  14 . With further reference to  FIGS. 3-5 , rear bending die assembly  14  comprises a die mounting plate  16  which supports a plurality of bearing blocks  18  arranged in a circular array about helical axis  20 . In the illustrative embodiment, there are three bearing blocks bolted to die mounting plate  16  for forming a helical bundle of three cylindrical tubes having the same diameter, however, it is not intended that the invention be limited to forming bundles of any particular number of elongate members, that the elongate members be tubes, that the elongate members be cylindrical, or if cylindrical that they be of the same diameter. 
     Each of bearing blocks  18  has a central bore  22  which supports a ball bearing  24  retained in central bore  22  by a snap ring  26 . A bending die comprising a grooved roller  28  is disposed in central bore  22  supported at one end by ball bearing  24  and the other end by a needle roller bearing  30 . A die retaining screw  32  secures grooved roller  28  to bearing block  18 . Collectively the grooved rollers  28  form guideways that exert a lateral force for bending tubes  42  while allowing tubes  42  to pass through bending die assembly  14 . Although the illustrative embodiment discloses grooved rollers supported by ball bearings and needle roller bearings, other art-recognized equivalents may be substituted without departing from the scope of the invention, for example a non-roller supported forming die may be used, provided sufficient lubrication is applied to prevent galling of the surfaces of the tubes being formed. Accordingly, it is not intended that the invention be limited to the particular method of supporting the bending dies disclosed in the illustrative embodiment. 
     As can be determined from an inspection of  FIG. 3  the axis  34  of central bore  22  is offset from a radial line  38  extending outward from helical axis  20  by a distance  40  so that the lateral force applied by grooved roller  28  to the tubes  42  is primarily a side load reacted by roller bearing  30  with little or no axial load on ball bearing  24 . The profile of grooved portion  44 , the offset distance  40 , and the depth “D” of grooved rollers  28  may be adjusted to accommodate tube bundles of varying dimensions and the orientation of bearing blocks  18  can be reversed for producing helical bundles of right hand or left hand twist. As can also be determined from an inspection of  FIG. 3 , the grooved portion  44  of grooved roller  28  comprises a semicircular groove having a radius equal to or slightly smaller than the radius of the tubes  42  being formed in the apparatus  10 , as is customary in rotary draw bending applications. The center of curvature of the grooved portions  44  therefore form an equilateral triangle  46  having side substantially equal to 2R+t where R is the radius of the tubes being formed and “t” is the spacing between the tubes. Die mounting plate  16  further comprises a plurality of mounting holes  48  to enable die mounting plate to be attached to the axle flange  50  as more fully described hereinafter. Front bending die assembly  12  is substantially identical in construction and therefore will not be discussed in detail herein. 
     With additional reference to  FIGS. 6-9 , apparatus  10  further includes an alignment die  56 . Alignment die  56  comprises a solid body  60  having three lobes  62 ,  64  and  66  each of which includes an aperture  68 ,  70 ,  72 . Apertures  68 ,  70 ,  72  each have an axle  74 ,  76 ,  78  which supports a roller  80 ,  82 ,  84 . Rollers  80 ,  82 ,  84  each comprise a pair of semicircular cutouts  86 ,  88  separated by a central flange  90 . The semicircular cutouts  86 ,  88  together with the central flange  90  of rollers  80 ,  82 ,  84  collectively form a tri-lobed guideway  92  that engages the lateral sides of the tubes  42  to constrain tubes  42  into a bundle while allowing the tubes to pass through alignment die  56 . Alignment die further includes mounting holes  94 ,  96 ,  98  for mounting alignment die  56  to front axle flange  100 . 
     With additional reference to  FIG. 10 , rear axle flange  50  is attached to rear drive gear  102  by means of an axle  52  passing through rear wall  104  of carriage assembly  106 . Rear drive gear  102  is driven by a stepper motor  108  through a gear train consisting of rear primary gear  110 , and rear primary pinion gear (not shown) which engages rear drive gear  102 . Front axle flange  100  is similarly attached to front drive gear  112  by means of an axle  116  passing through front wall  114  of carriage assembly  106 . Front drive gear  112  is driven by a stepper motor  118  through a gear train consisting of front primary gear (not shown), and front primary pinion gear  120  which engages front drive gear  112 . Carriage assembly  106  is supported by rails  122 ,  124  and is driven along the rails by means of a conventional gear-reduction stepper motor  126  and lead screw  128 . 
     With further reference to  FIGS. 11-12 , in operation, alignment die  56 , front bending die assembly  12  and a rear bending die assembly  14  are oriented so that tubes  42  may be fed through alignment die  56 , front bending die assembly  12  and a rear bending die assembly  14  and secured by collet with lead-in die assembly  130  to the frame  132  of apparatus  10 . Collet and lead-in die assembly  130  is specially constructed with three recesses for securing the tubes necessary to form a preferred three-tube bundle. Once tubes  42  are secured, a software program running on a general purpose computer (not shown) engages stepper motor  118  to rotate front bending die assembly  12  and alignment die  56  a predetermined amount to establish the helical angle (pitch) of the helical tube bundle taking into account the elastic recovery of the tubes. Once the initial helical angle is established, stepper motor  108  is engaged to rotate rear bending die assembly  14  in unison with front bending die assembly  12  so that the angular orientation between rear bending die assembly  14  and front bending die assembly  12  remains constant. Simultaneously, drive motor  126  engages to drive lead screw  128  which moves carriage assembly  106  along longitudinal axis  134  of apparatus  10  supported by rails  122 ,  124  until the carriage reaches its final position as shown in  FIG. 12 . 
     Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the invention. For example, although in the illustrative embodiment, the angular orientation between rear bending die assembly and front bending die assembly remain constant the angular orientation between rear bending die assembly  14  and front bending die assembly  12  can be varied, and the rotational velocity of the bending die assemblies relative to the speed of the carriage imparted by lead screw  128  can be varied if a variable pitch helical tube bundle is desired. Accordingly, it is intended that the invention should be limited only to the extent required by the appended claims and the rules and principles of applicable law. Additionally, as used herein, references to direction such as “up” or “down” are intend to be exemplary and are not considered as limiting the invention and, unless otherwise specifically defined, the terms “generally,” “substantially,” or “approximately” when used with mathematical concepts or measurements mean within ±10 degrees of angle or within 10 percent of the measurement, whichever is greater, and as used herein, a step of “providing” a structural element recited in a method claim means and includes obtaining, fabricating, purchasing, acquiring or otherwise gaining access to the structural element for performing the steps of the method.