Patent Publication Number: US-7210325-B2

Title: Tube thread forming apparatus and method

Description:
BACKGROUND OF INVENTION  
   The present invention relates to an apparatus and method for forming threads in a tube. 
   There are tubes employed in various applications where the tubes require a very limited number of relatively course (partial) threads on one end. For example, a fuel filler tube that extends from a vehicle fuel tank to an opening in the side of the vehicle will have threads at one end for securing a mating part thereto. It may be desirable for the mating part to only need, for example, one quarter or one half turn to be fully engaged with the tube. The threads, then, may each extend only part of the way around the circumference of the tube. In such tubes, a metal forming operation is employed to form these partial threads rather than cutting threads into the tube, as may be the case with tubes that have a full set of threads on their ends. 
   In the past, such tubes with these partial threads may have been roll formed, or have the threads formed in a six-segment die actuated by a large press. But these processes have drawbacks, including, for example, a limited ability to adapt to changes in tube outside diameters, and a limited ability to detect an out of tolerance part before or during the thread forming process. Still other forming processes mate one side of the tube with a die and apply pressure via a second die being pressed from the opposite side. But such asymmetrical processes do not always produce the desired result. Since these partial threads are not necessarily formed all of the way around the tube, there is not equal pressure all of the way around, so the tube may tend to deform to an oval shape at the location of the threads. 
   Thus, it is desirable to form partial threads on a tube while overcoming the drawbacks of the prior art. 
   SUMMARY OF INVENTION  
   In its embodiments, the present invention contemplates a partial thread forming apparatus for forming partial threads on a tube. The apparatus may comprise a base having a first arm and a second arm spaced from the first arm, and a prime motive apparatus fixed relative to the base and having a controllable shaft extending therefrom. The apparatus may also include a thread forming assembly located generally between the first arm and the second arm. The thread forming assembly may include a first end plate connected to and movable by the controllable shaft, a second end plate affixed to the second arm, an internal die located between the first and second end plates and sized to be insertable within the tube, a first external die mounted to the first end plate and having a first flange with a first forming surface extending toward the internal die, a second external die mounted to the second end plate and having a second flange with a second forming surface extending toward the internal die, a first stripper piece elastically coupled to the first end plate and including a first securing surface extending adjacent to the first forming surface and adapted to support the tube, and a second stripper piece elastically coupled to the second end plate and including a second securing surface extending adjacent to the second forming surface and adapted to support the tube. 
   An embodiment of the present invention also contemplates a partial thread forming apparatus for forming partial threads on a tube, with the apparatus including a base having a first arm and a second arm spaced from the first arm, and a prime motive apparatus fixed relative to the base and having a controllable shaft extending therefrom. The partial thread forming apparatus may also include a thread forming assembly located generally between the first arm and the second arm and including a first end plate connected to and movable by the controllable shaft; a second end plate affixed to the second arm; an internal die located between the first and second end plates and sized to be insertable within the tube, with the internal die including a first half and a separate second half; a mandrel located between the first half and the second half and adapted to be operable to move the first and second halves in opposed directions into contact with the tube; a first external die mounted to the first end plate and having a flange extending toward the internal die; a second external die mounted to the second end plate and having a flange extending toward the internal die; a first stripper piece coupled to the first end plate and including a first securing surface adapted to support the tube; and a second stripper piece coupled to the second end plate and including a second securing surface adapted to support the tube. 
   An embodiment of the present invention additionally contemplates a method of forming partial threads in a tube having an inner surface and an outer surface, the method comprising the steps of: locating a portion of the tube around an internal die having a first half and an opposed separate second half and partial teeth forming recesses located thereon; moving the first half and the second half apart and into contact with the inner surface of the portion of the tube; engaging the outer surface of the portion of the tube with support surfaces of a pair of opposed stripper pieces; engaging the outer surface of the portion of the tube, with a first and a second forming surface of a respective first and opposed second external die, adjacent to the corresponding support surfaces of the pair of stripper pieces to thereby form partial threads in the tube; and releasing the tube from the first and second external dies, the pair of stripper pieces and the internal die. 
   An advantage of an embodiment of the present invention is that equal force is applied to opposite sides of the tube in order to improve the result of the forming operation. 
   A further advantage of an embodiment of the present invention is that the tendency of the tube to deform to an oval during the thread forming operation is significantly reduced. 
   An additional advantage of an embodiment of the present invention is that some out of tolerance parameters can be detected just prior to the thread forming operation and prevent the operation if tolerance is out of a desired range. Moreover, out of tolerance parameters may be detected during the forming operation, allowing such tubes to be rejected if unsatisfactory. 
   Another advantage of an embodiment of the present invention is that different size tubes, which have small differences in diameter, can have partial threads formed thereon by this apparatus and method. 

   
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a side elevation view of the tube thread forming apparatus in accordance with an embodiment of the present invention. 
       FIG. 2  is a perspective view of the thread forming apparatus of  FIG. 1 . 
       FIG. 3  is a perspective view similar to  FIG. 2 , but illustrating a mandrel in its actuated position. 
       FIG. 4  is a perspective view of a pair of external dies in accordance with an embodiment of the present invention. 
       FIG. 5  is a perspective view of the thread forming apparatus with a tube mounted thereon, with the apparatus in is open, disengaged position, in accordance with an embodiment of the present invention. 
       FIG. 6  is a perspective view similar to  FIG. 5 , but illustrating the apparatus in its closed, engaged position. 
       FIG. 7  is a side elevation view of the thread forming apparatus with a tube mounted thereon, with the apparatus in its closed, engaged position, in accordance with an embodiment of the present invention. 
       FIG. 8  is a flow chart illustrating a tube thread forming method in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION  
     FIGS. 1–7  illustrate a tube thread forming apparatus, indicated generally at  20 . The apparatus  20  includes a base  22  upon which a main support structure  24  is securely mounted. The main support structure includes a first arm  26  and a second arm  28  that form a cradle  30 , within which is mounted a forming assembly  32 . 
   A pneumatic assembly  33  is mounted to the first arm  26  and extends from one end of the support structure  24 . The pneumatic assembly  33  includes a pneumatic cylinder  34  and a shaft  36  in engagement with the forming assembly  32 . The connections and operation of the pneumatic assembly  33  are known to those skilled in the art and so will not be discussed further herein. While the pneumatic assembly  33  is illustrated as the prime motive apparatus, other suitable apparatuses may be employed instead, if so desired. For example, a hydraulic, mechanical or electromechanical driver (not shown) may be employed for controlling the motion of the shaft  36 . 
   A tube support tool  38  mounts to the base  22  adjacent to the cradle  30  and is employed to provide for the initial locating and support of a tube  40  (only illustrated in  FIGS. 5–7 ) upon which the forming operation will be performed. The tube  40  illustrated in  FIGS. 5–7  is specifically employed as a fuel filler tube that extends from a vehicle fuel tank to an opening in the side of the vehicle. Although, this forming apparatus and process may be employed to form partial threads in other similar types of tubes, if so desired. 
   The forming assembly  32  includes a pair of internal die sections  44  extending through a hole in a support plate  46 . The internal die sections  44  are shaped so that the outer surface of each extends around somewhat less than a full semi-cylinder, and sized so that, when the two are held together, the generally cylindrical shape that is formed is smaller than the inside diameter of the funnel portion (fuel filler neck portion)  48  of the tube  40 . A spring (not shown) or other type of suitable mechanism biases the two internal die sections  44  into surface contact with one another. In this way, the funnel portion  48  can be easily slipped onto the internal die sections  44 . In addition, each internal die section  44  also includes a recess  50 , around a portion of its outer surface, that is configured to receive and shape tube material during the partial thread forming operation. 
   A central mandrel  52  (shown in  FIG. 3 ) is located generally under and between the internal die sections  44 , with a tapered upper end  54 . The mandrel  52  is supported and can be moved up and down relative to the internal die sections  44  by a conventional linear drive mechanism (not shown). Accordingly, after a tube  40  is located over the internal die sections  44 , the mandrel  52  is driven upward, which forces the two internal die sections  44  apart and into contact with the inner surface of the tube  40 . This centers the tube  40  about the internal die sections  44  and holds the outer surfaces of the internal die sections  44  in surface contact with the tube  40 . The support plate  46 , internal die sections  44  and mandrel  52  can move relative to the other parts of this assembly by being mounted on top of and slidable relative to a central base  47 . The central base  47  is secured to the main base. A biasing mechanism, such as a spring (not shown) and stop (not shown) locates these elements in their initial positions prior to the start of each thread forming operation. 
   Extending across either end of the forming assembly  32  are a first end plate  58  and second end plate  60 . The first end plate is fixed to and movable by the shaft  36  of the pneumatic assembly  33 , while the second end plate  60  is fixed to the second arm  28 . The second end plate  60  is shown as being separate from the second arm  28 , however, with the second end plate  60  being stationary relative to the second arm  28 , it could be formed integral thereto, if so desired. Guide tubes  59  are mounted to the first end plate  58  and telescopically received through passages in the second end plate  60 . The guide tubes  59  maintain the orientation of the first end plate  58  relative to the second end plate  60  as the first end plate  58  is driven toward the second  60  by the shaft  36 . 
   Mounted to and extending outward from each end plate  58 ,  60  is a respective one of a pair of external die sections (halves)  64 . Each die section  64  has a main flange  65  that includes a generally semi-cylindrical surface  66  with a thread forming flange  68  extending therefrom. The surfaces  66  and thread forming flanges  68  cooperates with the corresponding recesses  50  on the outer surface of the internal die sections  44  in order to form the partial threads  70  on the tube  40 . 
   The forming assembly  32  also includes a pair of stripper pieces (external alignment clamps)  56 , each engaging one of the first and second end plates  58 ,  60 . Each stripper piece  56  engages its respective end plate  58 ,  60  via support shafts  62  and springs  63 . Each support shaft  62  can telescope slightly relative to its corresponding end plate  58 ,  60 , and helps support and maintain the proper orientation of its corresponding stripper piece  56 . The stripper pieces  56  are biased away from the end plates  58 ,  60  by the springs  63 . These springs  63  may be gas springs (such as nitrogen gas) or may be more conventional mechanical springs. The stripper pieces  56  also each include concave, generally semi-cylindrical surfaces  72  for making contact with and supporting the outer surface of the tube  40 . The stripper pieces  56  each have a slot  74  extending therethrough, with the slots  74  being aligned with the surfaces  72 . The main flanges  65  of the external die sections  64  extend through these slots  74 . 
   The forming assembly  32  may also optionally include sensors (not shown) that may measure tube outside diameter, pressure and/or contact height during thread forming operations. Since pressure and distance measuring sensors are known to those skilled in the art, they will not be discussed further herein. 
     FIG. 8  illustrates a process of forming partial threads on a tube that may be employed by the apparatus  20 , as discussed above relative to  FIGS. 1–7 . The process begins by locating the tube  40  on the support plate  46  and tube support  38 , with the funnel portion  48  generally centered over the internal die sections  44 , step  102 . The mandrel  52  is actuated, moving it up between the internal die sections  44 , which forces the internal die sections  44  into engagement with the inner surface of the tube  40 , step  104 . 
   The pneumatic assembly  33  is activated, which causes the cylinder shaft  36  to push against the first end plate  58 . As the first end plate  58  moves, it pushes the corresponding external die section  64  and stripper piece  56 , as well as the support plate  46 , internal die sections  44  and mandrel  52 , along with it. This movement eventually causes the semi-cylindrical surfaces  72  to engage the outer surface of the tube  40 , step  106 . 
   At this point in the process, optional steps relating to detecting out of tolerance parts may be performed. For example, a sensor (not shown) may be employed to detect the spacing between the stripper pieces  56 , which corresponds to the outer diameter of the tube  40 , step  108 . If the outer diameter is out of an acceptable range, step  110 , then the tube may be rejected, step  114 . Of course, if so desired, other types of known sensors may be employed to measure other parameters for determining if the tube is acceptable. 
   As the pneumatic assembly  33  causes the first end plate  58  to continue moving, the springs  63  will allow the stripper pieces  56  to remain securely against and support the outside of the tube  40  without deforming or crushing the tube  40 . Due to the stripper pieces  56 , the tube  40  will remain seated on the support plate  46  in its proper position and orientation while the partial threads  70  are formed, and they also support the tube  40  around its periphery so that it will not deform into an oval shape during the partial thread forming process. The continued movement of the first end plate  58  will also cause the external die sections  64  to fully engage the tube  40 , with the thread flanges  68  deforming tube material into the recesses  50  of the internal die sections  44 , thereby forming the partial threads  70 , step  112 . Preferably this motion at the end of the stroke (i.e. the portion of the stroke that actually produces deformation in the tube  40 ) is a relatively high speed, low force motion. 
   At this point in the process, additional optional steps relating to detecting out of tolerance parts may be performed. For example, sensors (not shown) may be employed to detect the pressure and/or contact height between the external die sections  64  and the outer surface of the tube  40 , step  116 . If any of the measured parameters are out of an acceptable range, step  118 , then the tube may be rejected, step  114 . Such measured parameters may, for example, indicate that a particular tube has too thick or too thin of material, or that any lubricant employed is too thin. 
   After thread forming is complete, the pneumatic assembly  33  then retracts the shaft  36 , and thus the first end plate  58 . The external die section  64  and stripper piece  56  attached to the first end plate  58  will, of course, retract with the first end plate  58 . Also, since the support plate  46 , internal die sections  44 , and mandrel  52  are biased away from the second end plate  60 , they will move the tube  40  away from the stripper piece  56  and external die section  64  that are attached to the second end plate  60 . Retraction of the mandrel  52  will free the tube  40  from the thread forming apparatus  20 , and it can now be easily removed therefrom, step  120 . 
   While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.