BACKGROUND OF THE INVENTION 
     This invention relates generally to seat frames and more specifically to the joining of a headrest guide tube to a tubular seat frame such as for automotive application. 
     FIELD OF THE INVENTION 
     One method of providing support for the seat back of an automotive seat is to provide a frame of metal tubing which runs generally contiguous to the perimeter of the seat. As automotive seats require headrests for passenger safety, provision is required to secure the headrest to the seat frame. 
     One manner of mounting a headrest is to provide the headrest with two generally parallel downwardly depending mounting posts which are slidable relative to corresponding guide tubes mounted to the seat frame. The headrest guide tubes generally receive an insert which may be a polymeric sleeve to provide smooth motion. A detent means may also be provided which acts between the headrest guide tube and the headrest mounting posts to maintain position of the headrest at a desired height. 
     Traditionally the headrest guide tubes were secured to the seat frame tube by welding. This proved undesirable principally because of the difficulty in assuring close dimensional tolerances and good alignment in any cost effective mass production process. 
     More recently, as evidenced by U.S. Pat. No. 5,759,499 to Dudash and U.S. Pat. No. 6,035,516 to Petersen securement of a headrest guide tube to a seat frame tube by forming beads on the headrest guide tube has been introduced. The securement generally involves forming a web by flattening the seat frame tube and punching a hole through the web in the seat frame tube to receive the headrest guide tube. A first radially outwardly extending bead is formed on the tube and the beaded tube is inserted into the hole using the bead to position the headrest guide tube. A second bead is then formed on the headrest guide tube on the opposite side of the flattened seat frame tube to capture the seat frame tube between the two beads. 
     A significant drawback to the above beading method is the loss in rigidity associated both with flattening of the seat frame tube and the loss of metal removed in punching a hole of significant diameter relative to the amount of material present in the seat frame tube. In an effort to recover some of the lost rigidity Petersen teaches forming upstanding flanges on either side of the flattened area. Nevertheless, the amount of rigidity provided by the flanges is not significant compared to the rigidity of the seat frame tube before punching. 
     Another drawback to the process of the foregoing patents is the possibility of the headrest guide tube rotating relative to the seat frame tube. This is undesirable as the positional relationship between the headrest guide tube and the seat frame tube should be maintained in order to maintain orientation of the detent means. 
     It is an object of the present invention to provide a method whereby a headrest guide tube opening may be formed in a seat tube with only minimal removal of metal from the seat frame tube. 
     SUMMARY OF THE INVENTION 
     A method of forming a transversely extending passage through a tubular seat frame for receiving a headrest guide tube comprises the steps of: 
     forming first and second diametrically opposed axially aligned openings through said tubing; 
     (ii) flowing metal from around said first opening through said tube and through said second opening while expanding said first opening to form at least part of an inner wall of said passage; 
     (iii) flowing metal from around said second opening outwardly from said tube while expanding said second opening to form an outer wall of said passage extending about said inner wall. 
     A method of securing a headrest guide tube to a tubular seat frame member of ductile metal comprises the steps of: 
     (i) forming first and second diametrically opposed axially aligned openings through said tubular member; 
     (ii) flowing metal from around said first opening through said tubular seat frame member and through said second opening while expanding said first opening to initiate a passage extending through said tubular member; 
     (iii) flowing metal from around said second opening outwardly from said tubular seat frame member while expanding said second opening to receive said metal from around said first opening and form an upstanding wall about said passage, said passage having an entrance adjacent said tubular seat frame member and an exit distal said tubular seat frame member; 
     (iv) inserting said guide tube through said passage; 
     (v) deforming said guide tube to form a first detent on said guide tube for limiting displacement of said guide tube in a first direction into said entrance; and 
     (vi) forming a second detent by deforming at least one of said upstanding wall and said guide tube to, in conjunction with said first detent, fixedly secure said guide tube to said tubular seat frame member. 
     The forming of the first and second diametrically opposed axially aligned openings may be carried out by punching. A first detent may be a first bead. 
     The second detent may be a second bead on the guide tube or alternatively, formed by clenching the upstanding wall about the guide tube. 
     A portion of the upstanding wall may be caused to flow into the guide tube to secure the guide tube against rotational movement relative to the seat frame. 
     A recess may be formed in the guide tube prior to clenching to receive the portion of the upstanding wall. 
     The flowing of metal from around the first and second openings may be achieved by placing the tubing in an extruding die-set with a core of the die-set aligned with the first hole and a cavity of the die-set aligned with the second hole. The core may then be urged toward the cavity to cause metal surrounding the first and second holes to flow into the cavity while simultaneously enlarging the first and second holes to form the guide tube passage. 
     A tubular seat frame member is provided which has a run of ductile metal tubing with at least two headrest guide tube mounting passages extending transversely therethrough. Each of the mounting passages may have an upstanding wall encircling the passage and extending outwardly from one side of the tubular seat frame member. The passage may have a first end proximal the run of tubing and a second end distal the run of tubing. 
     The upstanding wall may further have nested inner and outer wall members extending respectively from opposite sides of the tubular seat frame member. 
     The tubular seat frame member may include a respective headrest guide tube extending through each of the passages. Each of the guide tubes may be secured to the seat frame by first locating means at the first end and second locating means at the second end. 
     The first and second locating means may be respective beads formed in the guide tube. 
     The first locating means may be a bead formed in the tube and the second locating means may be a clenching of upstanding wall about the headrest guide tube. 
     The headrest guide tube and the runs of tubing may have inter-engaging projections and recesses formed therein to restrain the guide tube from rotation relative to the run of tubing. 
     The run of tubing may have a flattened region in the vicinity of the passage. 
    
    
     DESCRIPTION OF DRAWINGS 
     Preferred embodiments of the present invention are described below with reference to the accompanying illustrations in which: 
     FIG. 1 is a partially cut-away schematic representation of a punch for forming a hole in a seat frame tube in an open configuration; 
     FIG. 2 is a view corresponding to FIG. 1 but illustrating the punch in a closed configuration; 
     FIG. 3 is a partially cut-away schematic view of an extruding die-set in an open configuration and illustrating a punched seat frame tube prior to extrusion; 
     FIG. 4 is a view corresponding to FIG. 3 but illustrating the die-set in a closed configuration; 
     FIG. 5 is a partially cut-away schematic view of beading die in an open configuration illustrating a headrest guide tube inserted through an extruded opening in a seat frame tube; 
     FIG. 6 is a view corresponding to FIG. 5 but showing the die in a closed configuration and the formation of a first bead; 
     FIG. 7 is a partially cut-away schematic view of a clenching die-set in an open configuration; 
     FIG. 8 is a view corresponding to FIG. 7 of the clenching die-set in a closed configuration; 
     FIG. 9 is a perspective view of a headrest guide tube secured to a tubular seat frame member by a combination of clenching and beading; 
     FIG. 10 is a perspective view corresponding to FIG. 9 but illustrating two headrest guide tubes in a longer run of seat frame tubing; 
     FIG. 11 is a perspective view of a pair of headrest guide tubes secured to a tubular seat frame member. 
     FIG. 12 is a front elevation of two headrest guide tubes secured to a section of seat frame tubing; 
     FIG. 13 is a perspective view corresponding to FIG. 10 but illustrating a longer run of tubing; and, 
     FIG. 14 is an end elevation of a headrest guide tube inserted through a tubular seat frame. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a punch set having an upper member  100 , a lower member  102  and a punch  104  in an open configuration. FIG. 1 further illustrates a “length” or “run” of ductile metal tubing  50  placed between the upper member  100  and lower member  102 . 
     FIG. 2 illustrates the forming of first and second diametrically opposed axially aligned openings  52  and  54  respectively in the tubing  50 . This is accomplished by bringing the upper member  100  and lower member  102  toward the tubing  50  and passing the punch  104  through the tubing  50  and into a mating receptacle  106  in the lower member  102 . The first opening  52  and second opening  103  are labeled in FIG.  3 . 
     The shape of the tubing  50  in the region of the first and second holes,  52  and  54  respectively, will depend on the configuration of the upper member  100 , the lower member  102  and how closely these members are brought together. The arrangement illustrated in FIGS. 1 and 2 provides a flattened region  58  about the openings  52  and  54 . Other arrangements may provide walls about the flattened area  58  which may provide additional rigidity. 
     After the “punching” operation the tubing  50  is transferred to an extruding die-set as schematically illustrated in FIGS. 3 and 4. The extruding die-set has a core  200  and a cavity  202  which is aligned with the core. The punched tubing  50  is placed between the core  200  and the cavity  202  with the first and second openings,  52  and  54  respectively, aligned therewith. The extruding die-set is moved from an open configuration as illustrated in FIG. 3 to a closed configuration as illustrated in FIG. 4 by passing the core  200  through the openings  52  and  54  and into the cavity  202 . This has the effect of flowing metal from about the first opening  52  through the second opening  54  while also enlarging the first opening  52  and the second opening  54 . 
     The extrusion process also forms a passage  60  extending through the tubing with an upstanding wall  62  extending thereabout. The upstanding wall  62  has an inner wall  64  defined at least in part by metal surrounding the first opening  52  and an outer wall  66  formed from metal surround the second opening  54 . The passage  60  has two ends which for the sake of convenience are herein referred to as an entrance  68  adjacent the tubing  50  and an exit  70  distal the tubing  50 . 
     The extrusion process forms the passage  60  without removing a significant amount of metal in contrast with earlier processes. Instead, the passage  60  is formed by causing metal that would otherwise be removed, to flow into the wall  62  which defines the passage  60 . Accordingly, rather than being removed, the metal surrounding the first opening  52  and second opening  54  is relocated and therefore available to provide torsional rigidity to the resultant structure. 
     FIGS. 5 through 8 illustrate the mounting of a headrest guide tube  80  to the tubing  50  which may be a tubular seat frame member. As illustrated in FIG. 5, the guide tube  80  may be inserted into the passage  60  as a “blank” tube (i.e. having generally straight sides free of projections). The guide tube  80  is placed over a mandrel  300  which extends through a second forming member  310 . The mandrel  300  has a shoulder  302  which extends radially outwardly to limit the distance the guide tube  80  may be slid therealong. The mandrel  300  resists inward collapse of the guide tube  80  during forming and thereby maintains alignment and a minimum diameter of the inside of the guide tube  80 . 
     The second forming member  310  is configured to closely receive the guide tube  80  and the wall  62  about the passage  60  through the tubing  50 . In a first position illustrated in FIGS. 5 and 6, the mandrel  300  is positioned relative to the second forming member  310  to abut against the tubing  50  about the wall  62  and provide support thereabout. 
     A first forming member  320  is next lowered over the guide tube  80  and mandrel  300 . The first forming member has a receptacle  322  for receiving the mandrel  300  and the guide tube  80 . The receptacle  322  has a shoulder  324  for abutting against the end of the guide tube  80  and limiting its travel into the receptacle  322 . Continued movement of the first forming member  320  toward the tubing  50  as supported by the second forming member  310  will cause deformation of the guide tube  80  in a radially outward direction in the space between the first forming member  320  and the tubing  50 . As a result, a bead  82  forms adjacent the entrance  68  of the passage  60  through the tubing  50 . 
     It will be appreciated that the bead  82  may be pre-formed on the guide tube  80  before insertion into the passage  60 . It is however believed that forming the bead  82  while the guide tube  80  is in the passage  60  will cause better conformity between the profile of the bead  82  and the passage  60 . 
     The bead  82  acts as a first detent on the guide tube to limit displacement of the guide tube in a first direction, namely into the entrance  68 . 
     FIGS. 7 and 8 illustrate the final forming steps. As illustrated in FIG. 7, the first forming member  310  is moved away from the tubing  50  and the mandrel  300  is slid upwardly as illustrated relative to the first forming member  310  to extend further therefrom. This exposes a portion  84  of the guide tube  80 . 
     The second forming member  310  and the mandrel  300  are next urged toward the first forming member  320  which is now supporting the bead  82 . This causes some of the exposed portion  84  of the guide tube  80  to deform radially outwardly into the wall  62  of the passage  60  as shown at reference  86 . The second forming member  310  restrains the wall  62  from expanding radially outwardly. This forming operation is referred to as “clenching” and is one manner in which a second detent may be formed to, in combination with the first detent (the bead  82 ) fixedly secure the guide tube  80  into the tubing  50  which comprises the tubular seat frame member. 
     Alternatively the second forming member  310  may be configured to form a second bead adjacent the exit  70  of the passage  60 . This may be accomplished by transferring the guide tube  80  and tubing  50  assembly after the first beading operation to a further forming member similar to the first member  320  and forming a bead in much the same way as with the first bead  82 . 
     FIGS. 9 through 14 illustrate finished assemblies with a headrest guide tube  80  mounted to a tubular seat frame member of metal tubing  50 . A notch  90  is illustrated in some of the guide tubes  80  which would have to be correctly oriented to receive the detent means or to align the insert (not shown) associated with the headrest guide posts (not shown) to be inserted therein. 
     The above description is intended in an illustrative rather than a restrictive sense. Variations may be apparent to persons skilled in metal forming and such structures without departing from the spirit and scope of the invention which is defined by the claims set out below.
A tubular seat frame member is provided which has a run of ductile metal tubing with at least two headrest guide tube mounting passages formed therein and extending transversely there through. Each of the mounting passages has an upstanding wall encircling the mounting passage and extending outwardly from one side of the tubular seat frame member. Each upstanding wall is formed from an integral with the run of ductile metal tubing. Each of the mounting passages has a first end proximal the run of tubing and a second end distal the run of tubing.