Abstract:
A method and apparatus for expanding a free end of a tube by use of a fluted spinning tool. The fluted spinning tool of the present invention, when rotated at a predetermined speed into the free end of the tube, produces a combination of force, rotation, and heat which results in uniform expansion of the free end of the tube. Further, the fluted spinning tool of the present invention allows for the rapid and efficient production of expanded tube parts, such parts being evenly formed with minimal bias on the expanded free ends of the tubes.

Description:
FIELD OF THE INVENTION 
   The invention relates generally to the field of expanding tubular material and, more particularly, to a method and apparatus for expanding the outside diameter (O.D.) of an end of a malleable thin walled tube. 
   DESCRIPTION OF THE RELATED ART 
   It can be appreciated that conventional tube expansion processes have been in use with a variety of tubular material applications for many years. A number of the conventional tube expansion processes involve the use of tube expander rollers which are skewed relative to the longitudinal axis of the tube so that the rollers are pulled into the tube as the tube expander rollers rotate. One problem with such conventional tube expanders is that the expanding rollers have a tendency to extrude the tube metal during tube expansion toward the front and rear of the tube as a result of changes in tube wall thickness which occur during the expanding or rolling operation. Other conventional tube expansion methods involve the use of a standard blunt-ended punch type tube expander which is inserted into a tube end with sufficient force to cause expansion of the tube end. Problems encountered with this type of tube expansion method include the following: inconsistently formed parts, weak parts, breakage of parts during the expansion process due to improper alignment of the tube in the tube expansion apparatus, and limits on the degree of expansion which can be achieved. 
   Therefore, there is a need for a method for a cost-efficient and reliable tube expansion that address at least some of the problems associated with conventional methods particularly in the area of air conditioning liquid return line system manufacturing. In this area, a number of small copper tubes, each tube usually having a 3/16 inch O.D., are used to form liquid return lines in air conditioning coil systems. The end of each 3/16 inch O.D. copper liquid return line or tube is inserted into a standard end of a receiving tube, the standard end of such receiving tube being sized to receive a ⅜ inch O.D. tube. A tight joint must somehow be formed between the two tube ends. Conventional methods for forming such a joint between the two tube ends typically involves manually crimping the larger tube end so as to brace the smaller 3/16 inch O.D. tube end against the inner walls of the larger O.D. tube end. Such conventional methods require significant labor and time, lead to inefficiency, result in increased production costs, and often result in a poorly formed joint between the two tubes. 
   The tube expansion process, therefore, requires a method and apparatus which can facilitate the rapid and efficient expansion of a tube end so that the expanded tube end can form a tight joint when inserted into another tube end having a slightly larger O.D. Such a method would eliminate the need for manually crimping the larger O.D. tube end and result in the production of strong, evenly formed expanded tube ends. Further, a tube expansion method and apparatus is needed which can overcome the adverse effects often associated with the combination of force, rotation, and heat required in order to accelerate expansion of the O.D. of a tube end. 
   SUMMARY OF THE INVENTION 
   An embodiment of the present invention provides a method for expanding the O.D. of an end of a tube. The method of the present invention comprises inserting a fluted spinning tool, while rotating the fluted spinning tool at a predetermined speed, into a free end of a tube substantially along a central longitudinal axis of the tube, such that the fluted spinning tool contacts and rubs against the inner walls of the free end. Friction caused by contact between the fluted spinning tool and the inner walls of the free end of the tube generates heat the heat causes a rise in temperature and is believed to assist in expansion of the tube end. In one embodiment, the tube is formed from copper. An embodiment of the invention provides that the tube is aligned by means of a tube alignment member in which the tube is abutted perpendicularly against a tube stop member, thereby securing the tube in a predetermined axial and radial position. The tube alignment member preferably has an optical switch which detects whether the tube is properly aligned within the tube alignment member. In one embodiment, the tube is secured by means of a tube clamp member, the tube clamp member preferably having an optical switch which detects whether the tube is properly aligned within the tube clamp member. 
   Another embodiment of the present disclosure provides a fluted spinning tool having helical flutes. The helical flutes of the fluted spinning tool are preferably oriented in the form of a helix, preferably a right-handed helix, and most preferably a 30° right-handed helix. In one embodiment, the helical flutes are grooved into the tube expanding member of the fluted spinning tool at a depth of about 0.065 inches with a rake angle from about 10° to about 12°. The fluted spinning tool is preferably rotated in a direction opposite the twist or helix of the helical flutes. In an embodiment of the invention, the predetermined speed for rotating the fluted spinning tool is between about 4500 rpm and about 9000 rpm, most preferably between about 6000 rpm and about 8000 rpm. In one preferred embodiment, the fluted spinning tool is formed from INCONEL 718. In alternate embodiments, the fluted spinning tool may be formed from sub-micron grade carbide or any other suitable carbide material known to a person of ordinary skill in the art. 
   In another embodiment of the invention, the fluted spinning tool for expanding the O.D. of an end of a tube is comprised of a conical point which inserts or presses into the free end of a tube, a neck which is continuous with the conical point, a tube expanding member continuous with the neck and having helical flutes, and a shank which is continuous with the tube expanding member and which is received into the chuck of a drill head. In another embodiment, the tube expanding member comprises approximately ⅔ of the fluted spinning tool and the diameter of the conical point is less than ½ the diameter of the tube expanding member. In another embodiment, the helical flutes are positioned on the tube expanding member in at least four locations at 90° increments. The helical flutes of the fluted spinning tool are preferably oriented in the form of a 30° right-handed helix. In a preferred embodiment, the helical flutes are grooved into the fluted spinning tool at a depth of about 0.065 inches with a rake angle from about 10° to about 12°. The fluted spinning tool of the present disclosure is preferably rotated in a direction opposite the orientation of the helical flutes. In a preferred embodiment, the fluted spinning tool disclosed herein expands the free end of a tube from a 3/16 inch O.D. to a ⅜ inch O.D. However, in alternate embodiments, the fluted spinning tool may be used to expand tubes of various initial O.D. dimensions to certain expanded O.D. dimensions as needed for particular tube expansion applications. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a perspective view of a tube clamp member, tube alignment member, and the fluted spinning tool mounted to a drill head; 
       FIG. 2  is a side view of a fluted spinning tool having a conical point, neck, tube expanding member, helical flutes grooved into the tube expanding member, and a shank; 
       FIG. 3  is a perspective view of blocks for aligning a tube, jaws for clamping a tube clamp and a fluted spinning tool mounted on a retracted drill head; 
       FIG. 4  is a perspective view of the a fluted spinning tool mounted on a retracted drill head and an unexpanded tube on a tube support block, with the tube being passed through the open first jaw and second jaw of the tube clamp member, towards a large alignment block and a small alignment block of a tube alignment member, shown in an open position; 
       FIG. 5  is a perspective view of a fluted spinning tool mounted to a retracted drill head, as well as an unexpanded tube positioned on a tube support block, passing through an open tube clamp member, and engaged by a closed tube alignment member; 
       FIG. 6  is a perspective view of a fluted spinning tool inserted into the free end of a tube, with the tube being secured between closed jaws of a tube clamp member and with alignment blocks of the tube alignment member shown apart, in the open position; 
       FIG. 7  is a perspective view of a fluted spinning tool fully inserted into a free end of a tube, showing expansion of the free end, with the tube being secured between the closed jaws of the tube clamp member and with the alignment blocks of a tube alignment member shown apart, in the open position; 
       FIG. 8  is a perspective view of the drill head and the fluted spinning tool being retracted subsequent to expansion of the free end of the tube, with the tube remaining secured between closed jaws of the tube clamp member and with alignment blocks of the tube alignment member shown apart, in the open position; 
       FIG. 9  is a perspective view of the apparatus depicting the first jaw and second jaw of the tube clamp member in the open position allowing release of the tube subsequent to expansion of the free end of the tube by the fluted spinning tool, the small alignment block and large alignment block of the tube alignment member being shown in the open position, the tube being supported by the tube support block, and the fluted spinning tool being shown as mounted on the retracted drill head; and 
       FIG. 10  is a perspective view of the apparatus depicting the tube having been removed from between the open first jaw and second jaw of the tube clamp member, the small alignment block and the large alignment block of the tube alignment member being shown as being brought together in the closed position, and the fluted spinning tool being shown as being mounted on a retracted drill head. 
   

   DETAILED DESCRIPTION 
   In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without such specific details. In other instances, well-known elements have been illustrated in schematic or block diagram form in order not to obscure the present invention in unnecessary detail. The accompanying drawings disclose various embodiments of the tube expansion method and apparatus of the present disclosure wherein like reference numerals have been applied to like elements. Corresponding numerals and symbols in the different figures refer to corresponding parts unless otherwise indicated. Alternate embodiments of the apparatus and method are illustrated in the various figures. 
   In  FIG. 1  and  FIG. 3 , the apparatus as used in connection with the method of the present invention is seen in its entirety and is generally referred to by reference number  10 . In this embodiment of the tube expansion method disclosed herein, alignment of tube  11  (not shown in  FIGS. 1 and 3 ) is performed in order to minimize any bias of the free end of the tube  11  which may occur during the tube expansion process. 
   Referring to  FIG. 4  and  FIG. 5 , alignment of tube  11  in a predetermined orientation is achieved by placement of tube  11  on tube support block  13  and passing tube  11  through tube guide  12  of a fixture referred to as tube clamp member  14  until forward progress of the tube  11  is impeded by tube stop member  18  of tube alignment member  16 . At such point, tube  11  is abutted perpendicularly against tube stop member  18 , thereby securing tube  11  in a predetermined axial and radial position. Tube stop member  18  is formed when small alignment block  20  and large alignment block  22  of tube alignment member  16  are held together in a closed position by operation of pneumatic cylinders  24  (only one of which is shown in  FIGS. 4 and 5 ). 
   Referring to  FIG. 1  proper alignment of tube  11  is detected by optical switches, of any suitable type known in the art, located in both tube clamp member  14  and in optical switch housing  15  of tube alignment member  16 . The optical switches function by preventing apparatus  10  from operating unless proper alignment of tube  11  within both tube clamp member  14  and tube alignment member  16  is detected. Once the optical switches detect that tube  11  is aligned properly, operation of apparatus  10  is triggered. (For clarity, optical switch housing  15  is not shown in  FIGS. 2–10 ). 
   As shown in  FIG. 6 , first jaw  28  and second jaw  30  tube clamp member  14  are brought together or closed automatically, thereby securing tube  11  in a properly aligned position. First jaw  28  and second jaw  30  of tube clamp member  14  are mounted to jaw plate  32  which is secured to clamp block  34 , the clamp block  34  being movably mounted on table base  35 . Tube clamp member  14 , like tube alignment member  16 , is operated by any suitable pneumatic means known in the art. After tube clamp member  14  has moved into a closed position, small alignment block  20  and large alignment block  22  of tube alignment member  16  then move apart or open automatically in order to allow space for insertion of fluted spinning tool  36  into the free end of tube  11  to be expanded. 
   As can be seen in  FIG. 6  and  FIG. 7 , once small alignment block  20  and large alignment block  22  of tube alignment member  16  have moved apart, then drill head  38  automatically extends horizontally, via extension of concentric cylinders of decreasing diameter  40 ,  40 ′,  40 ″, and  40 ′″ toward tube alignment member  16 . Shank  42  of fluted spinning tool  36 , provided in the preferred embodiment of the invention, is mounted in chuck  50  of drill head  38 . The extension of drill head  38  occurs by pneumatic means of the type commonly used in conjunction with self-feeding drill heads or spindles as known in the art. It should be understood that any suitable type of self-feeding drill head or spindle known in the art may be used for performing the spinning operation of fluted spinning tool  36  and that drill head  38  shown in  FIG. 1  is shown merely for illustrative purposes. In a preferred embodiment, fluted spinning tool  36  is preferably rotated by drill head  38  at a predetermined speed of between about 4500 rpm and about 9000 rpm, most preferably between about 6000 rpm and about 8000 rpm. Such rotation of fluted spinning tool  36  may be accomplished by any number of known pneumatic or electric drill motors having chucks sized to fit shank  42 . Fluted spinning tool  36 , rotating at the predetermined speed, is thereby inserted or pressed into the free end of tube  11  by extension of drill head  38  in order to expand the free end of tube  11 . 
   As shown in  FIG. 8 , once the free end of tube  11  has expanded, then drill head  38  retracts automatically via the aforementioned pneumatic means. It can be seen in  FIG. 9  that, after retraction of drill head  38 , the first jaw  28  and second jaw  30  of tube clamp member  14  move apart or open automatically by pneumatic means known in the art, thereby releasing tube  11  and leaving only tube support block  13  as support for tube  11 . As shown in  FIG. 10 , once tube  11  is removed from apparatus  10 , small alignment block  20  and large alignment block  22  of tube alignment member  16  close automatically to form tube stop member  18  in preparation for the next operation cycle. 
   As can clearly be seen in  FIG. 2  and  FIG. 3 , tube expanding member  46  of fluted spinning tool  36  is provided with conical point  44  and neck  48  integrally formed therewith or fixedly secured thereto. In one embodiment, conical point  44  is continuous with neck  48 , the neck  48  being centrally located with regard to conical point  44  and situated between conical point  44  and tube expanding member  46 . Tube expanding member  46  is continuous with neck  48  and with shank  42 , shank  42  being received into chuck  50  of self-feeding drill head  38 . Referring to  FIG. 2 , which depicts one embodiment of the invention, conical point  44  has a taper of 15° with a 0.010 inch diameter and a tolerance of ±0.01 at apex  55  of conical point  44 . Base  56  of conical point  44  has a diameter of 0.100 with a tolerance of +0.000 and −0.004. Tube expanding member  46  has a length of 0.875 inches with a tolerance of ±0.005 and a taper of 20° from neck  48  to the 0.332 inch major diameter of tube expanding member  46  which has a tolerance of ±0.001. Shank  42  has a diameter of 0.375 inches and a length of at least about 1.0 inches. The distance between apex  55  of conical point  44  and the beginning of shank  42  is 1.125 inches with a tolerance of ±0.020. 
   As can be seen in  FIG. 2 , a plurality of helical flutes  52  are positioned on tube expanding member  46  of fluted spinning tool  36  at 90° increments in at least four locations on tube expanding member  46 . Helical flutes  52  are cut or grooved into tube expanding member  46  at an angle of about 30° as a right-handed helix and have a depth of about 0.065 inches deep and a rake angle of between about 10° and about 12°. Helical flutes  52  are positioned so as to engage the sidewalls of the tube during rotation of tube expanding member  46  and exert radial and longitudinal force on the inner walls of tube  11 , preferably expanding the O.D. of tube  11  from a 3/16 inch O.D. to a ⅜ inch O.D. It is believed helical flutes  52  function by minimizing the amount of contact between tube  11  and fluted spinning tool  36 , thereby preventing fluted spinning tool  36  from acting as a heat sink which, in turn, would slow the heating and expansion of the free end of tube  11 . Helical flutes  52  located on fluted spinning tool  36 , therefore, provide for accelerated expansion of the free end of tube  11 . Further, it is believed that helical flutes  52  of fluted spinning tool  36  help maintain the integrity of the inner walls of tube  11  by allowing for a consistent inner wall thickness to be achieved during expansion of the tube  11 . 
   It will further be understood from the foregoing description that various modifications and changes may be in the preferred embodiment of the present invention without departing from its true spirit. This description is intended for purposes of illustration only and should not be construed in a limiting sense. The scope of this invention should be limited only by the language of the following claims.