Patent Publication Number: US-6990841-B2

Title: Method and apparatus for lean spin forming transition portions having various shapes

Description:
FIELD OF THE INVENTION 
   The present invention relates to an apparatus and method for spin forming a workpiece. More specifically, the invention relates to a multiple step reduction forming pass, multiple cycle apparatus and method of spin forming a workpiece having a formed axis that is non-coaxial with the non-processed axis of the workpiece. 
   BACKGROUND OF THE INVENTION 
   Many processes are available for manufacturing a tubular workpiece having a circular, oval or otherwise hollow cross section with a transition portion, where the formed portion is non-coaxial with a non-processed portion of a workpiece. Applications for these components include catalytic converter housings used in automotive exhaust systems. Geometries such a substantially curved or “snorkel” shape may improve flow characteristics. In the prior art, these components were usually made from several pieces, such as a pair of clam shells or a tubular section and formed end pieces joined by non-sophisticated techniques, such as resistance, TIG or MIG welding. However, welding these components together is not desirable because of durability concerns. 
   Other known processes for forming a transition portion on a work piece include forming techniques. One such technique is a ram forming process. However, ram forming has limitations regarding diameter reduction ratios. Another known process is spin forming, one example of an apparatus for spin forming is shown in  FIGS. 1–4 . A spin forming apparatus  1  of the prior art includes a plurality of rollers  3  supported by a rotatable carrier  2 . Each roller  3  has a tapered face  4 . The rollers  3  reduce the original diameter  12  of workpiece  6  to a reduced diameter  8 . A mandrel  5  provides internal support to the workpiece  6  during a spin forming operation. Although the prior art spin forming apparatus disclosed in  FIGS. 1–4  is effective for creating a transition portion on a workpiece, there are a number of shortcomings associated with the apparatus  1 . 
   One shortcoming of apparatus  1  is the reduction ratio, the ratio of the original diameter to the reduced diameter, that can be achieved. Exceeding the reduction ratio limitation will collapse the reduced portion of the workpiece, resulting in scrap. The amount of reduction available for apparatus  1  is limited by the reduction ratio. 
   Another limitation inherent in apparatus  1  is multiple machines are required to achieve a desired reduction in diameter if multiple passes are required for additional reduction in diameter beyond the limitations of the reduction ratio for apparatus  1 . Accordingly, the workpiece must be transferred from one machine to another machine that has rollers that are arranged in a smaller diameter to further reduce the diameter of a portion of a workpiece. The workpiece continues to be transferred to another machine having a smaller diameter yet, until the desired diameter is achieved. As a result, additional machines, or stations, are required as well as additional floor space. Furthermore, a significant amount of time is required to reduce a portion of the workpiece. 
   Other spin forming machines have rollers that are inwardly adjustable to permit multiple passes on a work piece by a single machine. This solution may eliminate the need for multiple machines to reduce the diameter of a single workpiece; however, these machines still have limitations in the reduction ratio for a single forming pass. Therefore, several passes are required to achieve a desired reduction in diameter of a workpiece. For example, 21 passes are typically required to reduce a portion of a workpiece from a 4 inch diameter to a 2 inch diameter. Although spin forming machines that have inwardly adjustable rollers respond to the concerns of floor space usage and multiple stations, these spin forming machines are still not efficient enough. 
   Referring now to  FIG. 5 , an improved spin forming apparatus  9  according to the prior art is shown. The apparatus  9  includes a plurality of rollers  11  operatively supported by a rotatably supported carrier  10 . Each of the rollers  11  is radially and axially offset from the other rollers  11 . The axial and radial offset of the rollers  11  allows the apparatus  9  to make multiple reductions in a single forming pass, resulting in a superior reduction ratio for a work piece. As workpiece  6  and rollers  11  are engaged, the one of the rollers  11  furthest from the carrier  10  will contact the workpiece  6  first. As the rollers  11  and workpiece  6  are further engaged, the next one of the rollers  11  closest to the carrier  10  will contact the workpiece  6 , further reducing the workpiece  6 . This process continues until the workpiece  6  and rollers  11  are completely engaged. Apparatus  9  provides a favorable reduction ratio and an improved forming time, however, multiple stations are still required, as apparatus  9  is limited by the number of rollers that may be mounted on the carrier  10 . As an example, four stations would be required to reduce a workpiece from a 4 inch diameter to a 2 inch diameter by employing apparatus  9 . Furthermore, apparatus  9  cannot create a substantially curved or snorkel shaped formed portion. 
   Therefore, there exists a need for a spin forming machine and process that has an improved efficiency and that can create a formed portion that has a formed axis that is non-coaxial with the axis of the non-processed portion of a workpiece and that does not require multiple stations. Furthermore, there is a need for an improved machine that can create a substantially curved or snorkel shaped formed portion. 
   Thus, it is desirable to provide a method and apparatus for spin forming a workpiece that can create a formed portion that has a formed axis that is non-coaxial with the axis of the non-processed portion of a workpiece and that has an improved efficiency while capable of completing a forming operation on a single machine and that can form a variety of transition portion shapes. 
   SUMMARY OF THE INVENTION 
   An apparatus for spin forming a portion of a workpiece where the formed portion has a formed axis that is non-coaxial with the non-processed axis of the workpiece comprises a carrier rotatable about a spin axis. At least a first roller and a second roller are operatively supported on the carrier. The first roller is radially and axially offset from the second roller. The first and second rollers are radially movable toward and away from the spin axis. A rotational drive mechanism spins the carrier about a spin axis. A radial drive mechanism radially translates the first roller and the second roller toward and away from the spin axis to position the rollers for a forming pass. A fixture is provided for constraining the workpiece. A pivoting mechanism rotates either the carrier or workpiece about a pivot point from a first angular position to a second angular position during a forming operation to create a formed axis that is non-coaxial with the non-processed axis of the workpiece. An axial drive mechanism reciprocates one of either the first and second rollers or the workpiece along a spin axis to sequentially engage the first roller and then the second roller the workpiece where the first roller and the second roller sequentially reduce the diameter of portion of the workpiece during a forming pass. The pivoting mechanism may cause either the carrier or workpiece to pivot at least once. The pivoting mechanism may cause either the carrier or workpiece to pivot between forming passes. The pivoting may pivot within a plane containing the spin axis. An actuator may be pivotally attached to the fixture for pivoting the workpiece. The actuator may be a linear positioner. 
   A programmable controller may be operatively coupled to the radial drive mechanism, the pivoting mechanism and the axial drive mechanism to govern the forming operation. The formed axis may be non-linear. Furthermore, the pivot point may be fixed relative to the workpiece. 
   A method of spin forming a portion of a workpiece where the formed portion has a formed axis that is non-coaxial with the non-processed axis of the workpiece comprises spinning at least a first roller and the second roller about a spin axis where the first roller is radially and axially offset from the second roller. The first roller and second roller are commanded to translate radially to position the rollers for a forming pass. One of the rollers or workpiece is rotated about a pivot point from a first angular position to a second angular position during a forming operation. A forming pass is commanded to cause one of the rollers or workpiece to travel along the spin axis to engage the first roller and then the second roller to a first end of the workpiece to sequentially reduce the diameter of a portion of the workpiece to create a formed portion having a formed axis that is non-coaxial with the non-processed axis of the workpiece. The formed axis may be nonlinear. One of the rollers or workpiece is rotated about a pivot point more than once during a forming operation. The rollers or workpiece may be rotated about a pivot point prior to a subsequent forming pass. The rollers or workpiece may be rotated about a pivot point within a plane containing the spin axis. The rotation of the rollers or workpiece may be controlled to form a substantially curved formed portion. 
   Further objects, features and advantages of the present invention will become apparent to those skilled in the art from analysis of the following written description, the accompanying drawings and the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an illustration of a prior art spin forming apparatus; 
       FIG. 2  is an illustration of the prior art spin forming apparatus in  FIG. 1 , further revealing the rollers fully engaged on a workpiece; 
       FIG. 3  is a cross sectional view of a portion of a workpiece to be formed prior to engaging the rollers of the prior art spin forming apparatus in  FIG. 1 ; 
       FIG. 4  is a cross sectional view of a portion of a workpiece formed by the rollers of the prior art spin forming apparatus in  FIG. 1 ; 
       FIG. 5  is another prior art spin forming apparatus, revealing a plurality of rollers having different axial positions and radial positions; 
       FIG. 6  is a side view of a first embodiment of the spin forming apparatus according to the principles of the present invention, having a portion thereof sectioned; 
       FIG. 7  is a side view of a second embodiment of the spin forming apparatus according to the principles of the present invention, having a portion thereof sectioned; 
       FIG. 8  is a side view of another embodiment of the spin forming apparatus according to the principles of the present invention; 
       FIG. 9  is a front view of the spin forming apparatus of  FIG. 8 ; 
       FIG. 10  is an enlarged partial perspective view of the spin forming apparatus of  FIG. 8 ; 
       FIGS. 11   a  through  11   d  are plan and side views of another embodiment of the present invention, further including a fixture and device for pivoting the workpiece, showing the workpiece before and after forming; 
       FIG. 12  is another embodiment of the present invention, disclosing two carriers and two sets of rollers for forming both ends of the workpiece. 
       FIG. 13  is an illustration of a workpiece formed by the present invention, with examples of possible formed portions on each end of the workpiece and axes therefore. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With initial reference to  FIG. 6 , a side view of a first embodiment of a spin forming apparatus  20  according to the principles of the present invention is shown. The apparatus  20  comprises a rotational drive mechanism  100 , which in the present embodiment, includes a drive shaft  104  that is rotatably supported in a case  95  by two pairs of bearing elements  101 ,  102 . The case  95  is slidably supported on a machine base  89 . A motor  110  for driving the shaft  104  is fixedly mounted to the case  95 . In the preferred embodiment, the motor  110  is an electric motor, however those skilled in the art will immediately recognize that any rotary actuator may be substituted for an electric motor. Power from the motor  110  is transferred from a pulley  115  secured to an output shaft of the motor  110  through a drive belt  116  to a pulley  117  secured to the drive shaft  104 . Drive shaft  104  is coupled to a carrier  50  that is rotatable about a spin axis  25 . Although a belt and pulley drive system is disclosed, any suitable substitute may be employed, including, but not limited to, a chain driven system or shaft driven system. 
   When the rotational drive mechanism  100  receives a command to spin the carrier  50  about the spin axis  25 , the motor  110  spins pulley  115 , causing drive belt  116  to spin pulley  117 . Pulley  117  spins the drive shaft  104  and carrier  50 . 
   Carrier  50  includes a carrier housing  53  and a faceplate  52  At least a first roller  21  and second roller  22  are operatively supported on the carrier  50  by bearing blocks  41  and  42  through shafts  31  and  32 , respectively. Roller  21  is axially offset from roller  22  by a distance n. Roller  21  is also radially offset from roller  22 . In the present embodiment, roller  21  is disposed at a first axial position and roller  22  is disposed at a second axial position, where the first axial position is further from the faceplate  52  than the second axial position. Roller  21  is disposed at a first radial position and roller  22  is disposed at a second radial position, where the first radial position is further from the spin axis  25  than the second radial position. In the preferred embodiment, the rollers  21 ,  22  are axially and radially offset by 1 mm. However, those skilled in the art will immediately recognize that factors such as heating the workpiece, the workpiece material, and feed rate, among others, will affect the optimal offset. Although two rollers are disclosed in the present embodiment, those skilled in the art will immediately recognize that three or more rollers may be employed by the spin forming apparatus  20  of the present invention. As the rotational drive mechanism  100  rotates the carrier  50 , the rollers  21 ,  22  spin about the spin axis  25 . 
   The rollers  21 ,  22  are radially movable toward and away from the spin axis  25  by a radial drive mechanism  60 . Radial drive mechanism  60  includes an actuator  80  fixedly mounted to the case  95 . In the preferred embodiment, actuator  80  is a programmable linear actuator; however, those skilled in the art will immediately recognize that any suitable substitute may be employed. The actuator  80  controls the position of a rod  81 , which extends therefrom. The rod  81  is fixedly attached to a lever  82  at a first end. The second end of lever  82  cooperates with a yoke  72 . The yoke  72  is fixedly attached to a hollow shaft  71 . 
   Drive shaft  104  extends through, and rotates relative to, hollow shaft  71 . Hollow shaft  71  has an inner diameter that is sufficient to provide a clearance condition with drive shaft  104 . Hollow shaft  71  has a toothed portion  63  on the outside of the shaft. A pair of gears  61 ,  65  are rotatably supported by the carrier housing  53  and mesh with the toothed portion  63  of hollow shaft  71 . Bearing blocks  41  and  42  have racks  62  and  66  and also mesh with gears  61 ,  65 , respectively. The faceplate  52  has a plurality of radially extending channels  51  to guide bearing blocks  41 ,  42 . In the present embodiment, the faceplate  52  has two channels  51 , with each channel dedicated to a bearing block. In the preferred embodiment, the bearing block and channel combination is an L-gib slide. 
   When the radial drive mechanism  60  receives a command to radially translate the rollers  21 ,  22  toward or away from the spin axis  25 , actuator  80  extends or retracts the rod  81 , which causes the hollow shaft  71  to axially translate accordingly. When the rod  81  extends away from the case  95 , the hollow shaft  71  translates away from the case  95 , causing the toothed portion  63  of hollow shaft  71  to rotate gears  61 ,  65  clockwise and counterclockwise, respectively. The rotation of gears  61 ,  65  that are meshed with the racks  62 ,  66  causes the bearing blocks  41 ,  42  and rollers  21 ,  22  to translate radially outward. 
   Alternatively, when the actuator  80  translates the rod  81  toward the case  95 , the toothed portion  63  of the hollow shaft  71  causes the gears  61 ,  65  to rotate counterclockwise and clockwise, respectively, translating the bearing blocks  41 ,  42  and rollers  21 ,  22  radially inward. 
   Drive shaft  104  extends through and rotates relative to hollow shaft  71 , which permits the shaft  71  to radially position the rollers  21 ,  22  while the carrier  50  is spinning. In the present embodiment, the radial drive mechanism  60  is referred to as an external actuation device, as the location of the hollow shaft  71 , as the means for actuating the rollers, is located external to the drive shaft  104 . 
   An axial drive mechanism  90  includes an actuator  91  fixedly secured to the machine base  89 . A rod  92  extends from the actuator  91  and connects to the case  95  via a connector  93 . The case  95  is translatable with respect to the machine base  89  along the spin axis  25 . When the apparatus  20  requires the rollers  21 ,  22  to move along the spin axis  25 , actuator  91  extends or retracts rod  92  to translate the case  95  and rollers  21 ,  22 . 
   The axial drive mechanism  90  reciprocates the rollers  21 ,  22  along the spin axis  25  to sequentially engage roller  21  and then roller  22  to the workpiece  15 . Alternatively, the axial drive mechanism  90  may be employed to reciprocate the workpiece  15  instead of the rollers  21 ,  22 . 
   Apparatus  20  may include a controller (not shown) that is coupled to the apparatus  20  to provide control signals for spin forming a workpiece  15 . As such, a controller may be coupled to the rotational drive mechanism  100 , axial drive mechanism  90  and radial drive mechanism  60 . 
   The present invention creates a formed portion  17  by spin forming a portion  16  (shown in phantom) of the workpiece  15 . The spin forming operation begins by providing a workpiece  15  to the apparatus  20  and is complete when a portion to be formed  16  of the workpiece  15  is reduced to the desired diameter. Although a formed portion  17 , as shown, is substantially conical, other shapes may be formed by the apparatus and method of the present invention, including a substantially cylindrical formed portion. The apparatus  20  of the present invention may create a formed portion  17  of a workpiece  15  during a forming operation on a single apparatus  20 . 
   In the preferred embodiment, the rotational drive mechanism  100  is constantly spinning the carrier  50  about a spin axis  25  during the forming operation. The forming operation is more efficient if the carrier  50  is spinning continuously rather than stopping and starting. The time to complete a forming operation is thus reduced by providing a radial drive mechanism  60  that adjusts the rollers  21 ,  22  while the carrier  50  is spinning. Before the axial drive mechanism  90  sequentially engages the rollers  21 ,  22  to the workpiece  15 , the radial drive mechanism  60  is commanded to radially position the rollers  21 ,  22  for a forming pass. In the preferred embodiment, the rollers  21 ,  22  are translated in unison. A forming pass begins when the rollers  21 ,  22  contact the workpiece  15 . The forming pass is complete when the rollers  21 ,  22  reach the desired location on the workpiece  15 . 
   Prior to a first forming pass, radial drive mechanism  60  positions the first roller  21  to a first radial distance and the second roller  22  to a second radial distance, relative to the spin axis  25 . The first radial distance is greater than the second radial distance. The axial drive mechanism  90  then translates the rollers  21 ,  22  or workpiece  15  from a first axial position to a second axial position, relative to the workpiece  15 , to complete a forming pass. As the axial drive mechanism  90  translates the rollers  21 ,  22  along the spin axis  25 , the diameter of the workpiece  15  is sequentially reduced until the rollers  21 ,  22  reach a desired location on the workpiece  15 . 
   The axial drive mechanism  90  then translates the rollers  21 ,  22  or workpiece  15  to a first axial position. After the first forming pass, the radial drive mechanism  60  radially translates the first roller  21  from a first radial distance to a third radial distance, relative to the spin axis  25 , where the first radial distance is greater than the third radial distance and the second roller  22  from a second radial distance to fourth radial distance, relative to the spin axis  25 , where the second radial distance is greater than the fourth radial distance. 
   When a forming pass is complete, the radial drive mechanism  60  may translate the rollers  21 ,  22  away from the spin axis  25  to provide clearance between the rollers  21 ,  22  and workpiece  15  before the axial drive mechanism positions the rollers  21 ,  22  for a subsequent pass. The axial drive mechanism  90  reciprocates either the rollers  21 ,  22  or the workpiece  15  along the spin axis  25  by sequentially engaging roller  21  and then roller  22  to the workpiece and then retracting the rollers  21 ,  22  from the workpiece  15 . Roller  21  and roller  22  sequentially reduce the diameter of a portion of the workpiece  15  during a forming pass. The axial drive mechanism  90  causes the first roller  21  to engage the workpiece  15  to reduce the diameter of the workpiece  15  from a first diameter to a second diameter and then engages the second roller  22  to the workpiece  15  to reduce the diameter of the workpiece from a second diameter to a third diameter. By sequentially reducing the workpiece  15 , a higher reduction ratio is achieved. Thus, the present invention may reduce the diameter of a portion  16  of the workpiece  15  to achieve a desired diameter with a minimum number of passes. 
   The present invention has an improved reduction ratio over spin forming apparatus of the prior art. Each roller  21 ,  22  may be disposed to optimize the forming operation by maximizing the amount of reduction without causing the workpiece  15  to collapse. Furthermore, additional rollers may be operatively supported on carrier  50 . As the number of rollers is increased, a higher reduction ratio may be achieved. It should be intuitive that if the radial offset among the rollers  21 ,  22  is constant, the amount of reduction possible in a single forming pass is a function of the number of rollers. In the preferred embodiment, the radial drive mechanism  60  translates rollers  21 ,  22  an equivalent radial distance. 
   Prior to a subsequent forming pass, the radial drive mechanism  60  positions the rollers  21 ,  22  to permit the rollers  21 ,  22  to further reduce the workpiece  15  when the axial drive mechanism  90  engages the rollers  21 ,  22  to the workpiece  15 . The axial drive mechanism  90  continues to reciprocate the rollers  21 ,  22  or workpiece  15  while the radial drive mechanism  60  radially translates the rollers  21 ,  22  inwardly between forming passes until a desired reduction in diameter is achieved. 
   The axial drive mechanism  90  reciprocates the rollers  21 ,  22  or workpiece  15  to execute a plurality of forming passes. After completing a forming pass, the axial drive mechanism  90  positions the rollers  21 ,  22  to prepare for the next forming pass or to provide clearance for the workpiece  15  to be removed from the apparatus  20 . The radial drive mechanism  60  may be controlled to translate the rollers  21 ,  22  inwardly in calculated steps. For example, the rollers  21 ,  22  may be radially translated in a very small increment to perform a finishing pass on the workpiece  15 . 
   In operation, the present invention for spin forming a portion  16  of a workpiece  15  spins at least the first roller  21  and second roller  22  about the spin axis  25  where the first roller  21  is radially and axially offset the second roller  22 . The first roller  21  and second roller  22  are commanded to translate radially to position the rollers  21 ,  22  for a forming pass. A forming pass is then commanded, wherein one of either the rollers  21 ,  22  or workpiece  15  travel along the spin axis  25  to engage the first roller  21  and then the second roller  22  to the workpiece  15  to sequentially reduce the diameter of a portion of the workpiece to create a formed portion  17 . If an end portion is being process, then the rollers  21 ,  22  may engage an end of the workpiece  15 . The diameter of a portion  16  of the workpiece  15  is sequentially reduced until a desired diameter is achieved, permitting a portion of the workpiece to be reduced from an original diameter to a final diameter on a single apparatus. A plurality of forming passes may be commanded to sequentially reduce the diameter of the portion  16  of the workpiece  15  during a forming operation. 
   The apparatus  20  executes a plurality of cycles during a forming operation. Each cycle begins with the axial drive mechanism  90  positioning the rollers  21 ,  22  at a first axial position, relative to the workpiece  15 , and the radial drive mechanism  60  radially positioning the rollers  21 ,  22 , relative to the spin axis  25 , for a forming pass. The axial drive mechanism then engages the first roller  21  and then the second roller  22  to the workpiece  15 , causing the rollers  21 ,  22  to travel along the workpiece, sequentially reducing the diameter, until the forming pass is complete. The axial drive mechanism then retracts the rollers  21 ,  22 , causing the rollers  21 ,  22  to move along the spin axis  25  in the opposite direction to prepare for the next cycle or to remove the workpiece  15 . 
   Referring now to  FIG.7 , a side view of a second embodiment of a spin forming apparatus  120  according to the principles of the present invention is shown. A rotational drive mechanism  200  comprises a drive shaft  204  rotatably supported in a housing block or case  195  by a first pair of bearing elements  201  and a second pair of bearing elements  202 . The case  195  is slidably supported on a machine base  189 . A motor  210  is fixedly mounted to the case  195 . A pulley  215  is operatively coupled to an output shaft rotatably driven by the motor  210 . Pulley  215  drives a belt  216  that rotates a pulley  217 . Pulley  217  is operatively coupled to drive shaft  204 . Also attached to drive shaft  204  is a carrier  150 . Carrier  150  includes a carrier housing  153  and faceplate  152 . The faceplate  152  has at least two radially extending channels  151 . 
   A radial drive mechanism  160  includes an actuator  180  fixedly secured to machine base  189 . A rod  172  extending from actuator  180  is coupled to a shaft  174  by a connector  173 . The shaft  174  extends through the hollow drive shaft  204 . A yoke  171  is fixedly secured to the shaft  174 . A pair of levers  181 ,  182  are pivotally attached to carrier  150  by pins  183 ,  184 . A first bearing block  141  and second bearing block  142  are each disposed in one of the radially extending channels  151 . A first roller  121  and second roller  122  are operatively supported on the carrier  150  by shafts  131 ,  132  extending from bearing blocks  141 , 142 , respectively. The first roller  121  is radially and axially offset from the second roller  122 . The rollers  121 ,  122  are radially movable toward away from the spin axis  25 . The levers  181 ,  182  engage bearing blocks  141  and  142 . When the actuator  180  retracts the shaft  174 , levers  181 ,  182  cause the bearing blocks  141 , 142  and the attached rollers  121 ,  122  to translate radially inward. 
   Hollow drive shaft  204  rotates with respect to shaft  174  which permits the radial drive mechanism  160  to translate the rollers  121 ,  122  while the rollers  121 ,  122  are spinning. In the present embodiment, the radial drive mechanism  160  is referred to as an internal actuation device, as shaft  174  is internal to hollow drive shaft  204 . Furthermore, shaft  174  may retract, extend or move along with hollow drive shaft  204 . 
   An axial drive mechanism  190  includes an actuator  191  that is fixedly secured to machine base  189 . A rod  192  extends from actuator  191  and is coupled to the slidably supported case  195  by a connector  193 . 
   Referring now to  FIG. 8 , a side view of another embodiment of the spin forming apparatus  120  according to the principles of the present invention includes actuator  180  fixedly secured to the case  195 . The case  195  is slidably disposed on the machine base  189 , guided by ways  196 . In the present embodiment three rollers  121 ,  122 ,  123  are operatively supported by the carrier  150 . 
   Referring now to  FIG. 9 , a front view of the spin forming apparatus  120  of  FIG. 8  reveals the carrier  150  in greater detail. The bearing blocks  141 ,  142 ,  143  are slidably supported within the channels  151  disposed in carrier  150 . 
   Referring now also to  FIG. 10 , an enlarged partial perspective view of the spin forming apparatus  120  of  FIG. 8  more clearly reveals the mounting scheme for the rollers  121 ,  122 ,  123 . Rollers  121 ,  122 ,  123  are each fixedly secured to bearing blocks  141 ,  142 ,  143 , respectively. Each of the bearing blocks  141 ,  142 ,  143  radially translate within one of the plurality of radially extending channels  151 . 
   Referring now also to  FIG. 12 , another embodiment of a spin forming apparatus  420  according to the principles of the present invention is shown. Apparatus  420  comprises a first carrier  450  and second carrier  550 . First carrier  450  has a plurality of rollers  421 ,  422 ,  423  operatively supported thereon and second carrier  550  has a plurality of rollers  521 ,  522 ,  523  operatively supported thereon. Each of the rollers  421 ,  422 ,  423  is radially and axially offset from the other rollers. For example, roller  421  is disposed the greatest axial distance of the three rollers from the face of the carrier  450 . Roller  421  is also disposed at the furthest radial distance from the spin axis  425 . Roller  422  is disposed the next furthest axial distance from the face of the carrier  450  and is disposed the next furthest radial distance from the spin axis  425 . Roller  423  is disposed at the shortest axial distance to the face of the carrier  450  and the shortest radial distance to the spin axis  425 . Rollers  521 ,  522 ,  523  are arranged in a like manner. 
   A fixture  470  is provided to constrain workpiece  415 . An axial drive mechanism may reciprocate one of the carriers  450 ,  550  or workpiece  415  along the spin axis. The carriers  450 ,  550  may cause the rollers  421 ,  422 ,  423 , and rollers  521 ,  522 ,  523  to engage the workpiece  415  simultaneously or alternately. Alternatively, the axial drive mechanism may cause the workpiece to shuttle between the rollers  421 ,  422 , 423  and rollers  521 ,  522 ,  523 . Accordingly, the present embodiment of apparatus  420  may process both ends of the workpiece at the same time or during the same forming operation. 
   Referring now to  FIGS. 11   a  through  11   d , plan and side views of another embodiment of a spin forming apparatus  220  according to the principles of the present invention is shown. A carrier  250  is rotatable about a spin axis  225 , having a plurality of rollers  221 ,  222 ,  223  operatively supported thereon. Each roller is radially and axially offset from the other rollers. The rollers  221 ,  222 ,  223  are radially movable toward and away from the spin axis  225 . 
   The spin forming apparatus  220  in the present embodiment comprises a pivoting mechanism  260  for rotating a workpiece  315  about a pivot point  230 . It is within the scope of the present invention that the pivoting mechanism  260  may rotate carrier  250  instead of or in conjunction with the workpiece  315 . 
   Referring now also to  FIG. 13 , an illustration of the workpiece  315  formed by the exemplary embodiment of the present invention reveals example formed portions and axes thereof on each end of the workpiece  315 . Workpiece  315  has a non-processed portion  316  and a non-processed axis  321 . At a first end of workpiece  315  is a substantially curved first processed portion  317  having a non-linear formed axis  318 . At a second end of workpiece  315  is a substantially oblique processed portion  319  having a linear formed axis  320 . Each formed axis  318 ,  320  is non-coaxial with the non-processed axis  321 . 
     FIG. 11   a  is a plan view of the apparatus  220 , revealing an unprocessed workpiece  315  constrained by a fixture  270 . The fixture  270  is shown oriented at first angular position where the axis  321  of the unprocessed workpiece  315  is aligned with the spin axis  225 . In the present embodiment, the pivoting mechanism  260  includes an actuator  240  pivotally attached to a fixture  270  for rotating the fixture  270  about the pivot point  230 . In the preferred embodiment, the actuator  240  is a programmable actuator. During a forming operation, the pivoting mechanism  260  positions the workpiece  315  as required by rotating the workpiece  315  about the pivot point  230  to create a formed axis that is non-coaxial with the axis of the non-processed portion  316  of a workpiece  315 . 
     FIG. 11   b  is a side view of the apparatus  220 , with the unprocessed workpiece  315  secured in the fixture  270 . The fixture  270  is pivotally mounted on the base  232  and rotates about a pivot point  230 . A pivot pin  231  is provided within the base  232  to locate the fixture  270  for rotation about the pivot point  230 . Although a pin  231  is shown, any suitable substitute known in the art may be employed to permit relative rotation about a pivot point including shafts, bearings, bushings and the like. In the present embodiment, the pivot point  230  is fixed relative to the workpiece  315 ; however, it is within the scope of the present invention that the relative location of the pivot point may be movable. 
     FIG. 11   c  is a plan view of the apparatus  220 , revealing a processed workpiece  315  constrained by a fixture  270 . The fixture  270  is shown oriented at a final angular position where the axis  321  of the unprocessed portion of the workpiece  315  is positioned at an oblique angle relative to the spin axis  225 . The processed end of the workpiece  315  has a substantially curved or “snorkel” shape, which enhances flow characteristics. 
     FIG. 11   d  is a side view of the apparatus  220 , with the processed workpiece  315  secured in the fixture  270 , shown oriented at a final angular position. In operation, the pivoting mechanism  260  rotates either the carrier  250  or workpiece  315  about the pivot point  230 , from a first angler position to a second angular position, during a forming operation to create a formed axis  318  that is non-coaxial with the non-processed axis  321  of the workpiece  315 . The pivoting mechanism  260  may cause the carrier  250  or the workpiece  315  to rotate several times during a forming operation, preferably between forming passes. In the preferred embodiment, a programmable controller (not shown) is operatively coupled to the radial drive mechanism, the pivoting mechanism  260  and the radial drive mechanism to govern the forming operation. In the present embodiment, the carrier  250  or workpiece  315  pivot within a plane containing the spin axis  225 . 
   The instant embodiment of the spin forming apparatus  220  of present invention spin forms a portion of the workpiece  315  where the formed portions  317 ,  319  have formed axes  318 ,  320  respectively, that are non-coaxial with the axis  321  of a non-processed portion  316  of the workpiece  315 . The workpiece  315  is formed by spinning at the rollers  221 ,  222 ,  223  about the spin axis  225 , where each roller  221 ,  222 ,  223  is radially and axially offset from the others. The rollers  221 ,  222 ,  223  are commanded to translate radially toward and away from the spin axis to position the rollers  221 ,  222 ,  223  for forming pass. The rollers  221 ,  222 ,  223  or workpiece  315  are rotated about a pivot point  230  from a first angular position to second angular position during forming operation. A forming pass is commanded where either the rollers  221 ,  222 ,  223  or workpiece  315  travel along the spin axis  225  to engage the first roller  221  and then the second roller  222  and then lastly the third roller  223  to the workpiece  315  to sequentially reduce the diameter of portion  317  of the workpiece  315  to create a formed portion  317  having a formed axis  318  that is non-coaxial with a non-processed axis  321  of the workpiece  315 . 
   Formed portion  317  is referenced for exemplary purposes, however it should be understood that formed portion  317  represents a generic formed portion having a formed axis that is non-coaxial with the non-processed axis of the workpiece  315  and is not to be interpreted as limiting in any way. Quite the contrary, various shapes may be formed by the process and apparatus of the instant embodiment of the present invention. The angular position of the workpiece  315  or rollers  221 ,  222 ,  223  may change more than once during a forming operation. In the preferred embodiment, one of the rollers  221 ,  222 ,  223  or workpiece  315  is rotated about a pivot point  230  prior to a subsequent forming pass. In the present embodiment, one of the rollers  221 ,  222 ,  223  or workpiece  315  is rotated about the pivot point within a plane containing the spin axis  225 . The pivoting of the rollers  221 ,  222 ,  223  or workpiece  315  may be controlled to form a substantially curved portion. To form a substantially curved portion, the rollers  221 ,  222 ,  223  or workpiece  315  is rotated about a pivot point  230  to multiple angular positions during a forming operation. 
   The foregoing discussion discloses and describes the preferred structure and control system for the present invention. However, one skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined in the following claims.