Abstract:
A welding system for heat welding a component to the contact surface workpiece is provided with a carriage and a component holding positioning unit and workpiece melting unit. The component holding unit and workpiece melting unit each include a respective hooked-shaped holding arm assembly and an associated support assembly used to secure and movably mount the holding arm assembly and an associated support assembly used to secure and movably mounted the holding arm assembly to the carriage. A heating or welding unit is mounted towards a distal end of the holding arm assembly, and which is operable to melt the contact surface when moved thereagainst. The component holding unit is provided with a component holder operable to fixedly grasp or release the selected component in its mounting to the workpiece. The carriage is provided for rotatable movement relative to a rotation axis to selectively move the component holding unit and workpiece melting units between melt operations position, wherein the heating or welding unit is brought into contact with the workpiece and activated to soften or partially melt the contact surface in advance of the component being moved thereagainst; and a fixture placement position, where the component holder moves the component into juxtaposition with the softened contact surface to cool and fuse with the workpiece.

Description:
SCOPE OF THE INVENTION 
       [0001]    The present invention relates to a welding system for use in securing a component to a workpiece, and more preferably a welding system which is adapted to join components and workpieces made of thermoplastic or other heat fusible materials. 
       BACKGROUND OF THE INVENTION 
       [0002]    Various hot plate welding apparatus are known for fusing together heat weldable components and workpieces. Typically such devices incorporate a hot plate which by thermal contact melts part of the component and/or the workpiece to a partially melted or tacky state. After such partial melting, the component and workpiece are moved into physical contact and cooled, fusing together and forming the finished article. 
         [0003]    Frequently such hot plate welders are used in the final production of blow molded thermoplastic products, such as plastic gas tanks and fluid containers as are used in automobiles or as brake, antifreeze and/or washer fluid reservoirs. Conventional hot plate welding systems typically incorporate a movable hot plate which is brought into bearing contact against the outer bottom, side or top wall (hereinafter collectively referred to as the sidewall) of a formed or molded workpiece to effect the partial melting of a contact surface to which a selected component is to be joined. Following the initial melting, the hot plate is then moved to a remote location, and the selected component, such as a plastic seal plug, filler neck, bracket, vent nipple, blow pin, or the like, is then moved against the contact surface to form the completed product. 
         [0004]    While conventional hot plate welding systems have been successfully applied for many different applications, automotive fuel tanks manufactured from HDPE (High Density Polyethylene) have proved to be especially challenging. Low fuel vapor permeation requirements necessitate that the container wall be formed using multiple layers of plastic materials. An EVOH layer, which provides permeation reduction, is typically sandwiched between an inner and outer HDPE layer which are necessary for advantageous physical properties of the fuel tank. Additional layers are typically required so that the EVOH layer can properly bond to the HDPE layers. Ideally, to manufacture an end product with the lowest possible fuel vapor permeation the container wall formed in this fashion should not be disturbed by cutting a hole or any type of opening. However, typical fuel tanks have at least a fill opening and an opening for the fuel delivery module which cannot be avoided, as well as other openings for vent valves and similar type of valves. If additional valves are required one way to avoid having to first cut an opening before welding the valve to the tank sidewall is to attach the valve to the inside of the container. 
       SUMMARY OF THE INVENTION 
       [0005]    To at least partially overcome at least some of the disadvantages associated with prior art welding systems, the present invention relates to an apparatus which in use is adaptable for the mounting and heat fusing of a selected component to a workpiece at a contact surface located either along an interior or exterior portion of the workpiece sidewall. In one preferred mode of operation the welding system includes one or more hooked-shaped support arms which have a size selected to permit their insertion through an access opening formed in the workpiece sidewall to position a heating or welding device and/or a selected component against a contact surface disposed along an interior portion of a hollow workpiece. More preferably the welding system incorporates a pair of hooked-shaped support arms which respectively carry a heating device and a component holding device, and which move to sequentially melt and position a selected component against the contact surface. 
         [0006]    Accordingly, an object of the present invention is to provide a welding system which is adapted for use in securing a selected component to a contact surface internally disposed within the interior of a hollow workpiece. 
         [0007]    Another object of the invention is to provide a hot plate welding system which includes at least one hot plate welding unit having at least one hot plate carried on a hot plate holding arm and/or a component holding unit having a selectively operable component holder carried on a component holder carrying arm, and wherein the carrying arms are sized for insertion through an access opening formed into the interior of a hollow workpiece, so as to allow the movement of hot plate and/or a component releasably secured in the component holder to be moved against an internal workpiece contact surface. 
         [0008]    Another object of the invention is to provide a compact hot plate welding system which allows for the more rapid and efficient partial melting of a workpiece contact surface, and the subsequent positioning of a selected component thereagainst in the production of a finished article. 
         [0009]    In yet another object, the present invention seeks to provide an economical welding system which includes both workpiece melting and component holding units, and which is positionable on the arm of a single operational robot, and operable through a series of preprogrammed indexed movement to position and secure a selected component to a workpiece contact surface. 
         [0010]    A further object of the invention is to provide a hot plate welding system which is adapted for the simplified mounting on the movable wrist of the robot arm of a 6-axis robot, and which is actuable to both partially melt a workpiece contact surface, and thereafter position and fuse thereto a selected component in the production of a finished product. 
         [0011]    To at least partially achieve some of the aforementioned objects, the present invention provides a welding system for fusing or otherwise heat welding a selected component to the contact surface workpiece. Although not restricted, preferably the present invention is adapted to weld or otherwise heat fuse components, such as grade vent valves, other types of valves and valve retaining brackets to a workpiece, and preferably a plastic or composite workpiece. Most preferably the invention is adapted to partially melt and secure a component to an internal contact surface of a blow molded workpiece such as fuel tank or other fluid reservoir, such as those used for brake or washer fluids. Although not essential, at least one, and more preferably both the component and contact surface of the workpiece must be formed from a heat fusible material such as Nylon™, ABS, PVC, HDPE, polypropylene, polyethylene or other suitable thermoplastics. Where the workpiece is preferably oriented with a composite or multi-layer sidewall construction, the contact surface is provided along an interior workpiece sidewall spaced a distance of about between about 5 and 80 cm therefrom from either a cut or preformed access opening. 
         [0012]    The welding system is provided with a carriage and at least one of, and preferably both a component holding or positioning unit and workpiece melting unit. The component holding unit and workpiece melting unit each include a respective holding arm assembly and preferably also an associated support assembly used to secure and movably mount the holding arm assembly to the carriage for movement therewith. In the workpiece heating unit a heating or welding unit is mounted towards a distal end of the holding arm assembly. The component holding unit is provided with a component holder which is selectively operable to fixedly grasp or release the selected component in its mounting to the workpiece. 
         [0013]    Although not essential one simplified construction, the carriage is provided for rotatable movement relative to a carriage rotation axis to selectively move the component holding unit and workpiece melting units between a number of preprogrammed indexed positions. The indexed positions include a melt operations position, wherein the heating or welding unit is brought into contact with the workpiece and activated to soften or partially melt the contact surface in advance of the component being moved thereagainst; and a fixture placement position, where the component holder moves the component into juxtaposition with the softened contact surface to cool and fuse with the workpiece. 
         [0014]    The holding arm assemblies may take a number of shapes and/or forms. Preferably, each holding arm assembly includes at least one rigid hooked or curved holding arm. The holding arms extend or are otherwise positionable in an extended orientation so as to generally project outwardly and curve radially relative to the carriage rotation axis. More preferably, the holding arms have a size and curvature selected to allow for their substantially unhindered sliding insertion at least part way through a workpiece access opening, to move the heating device and/or component holder associated therewith into general alignment with the contact surface. Although not required, to provide a more compact construction, the curved holding arms may be mounted for pivoting movement relative to the carriage axis, so as to be positionable in both the extended position and a retracted position wherein the outer holding arm ends are pivoted inwardly towards the rotation axis. In an optimum configuration, the holding arms of both the welding unit and the holding component unit are mounted to the carriage and have a corresponding shape and curvature selected such that if both simultaneously extended, the holding arms orient in a generally S-shaped orientation symmetrically through the carriage rotation axis. 
         [0015]    Preferably, the component-holding unit has a similar construction to the workpiece welding unit, with each including a linear slide assembly. The component holder operable to releasably grip and transport a selected seal plug component from a seal plug supply station optionally to a preheating station and then into juxtaposed alignment with the contact surface, for heat fusing thereto. 
         [0016]    In a preferred use of the welding apparatus, the heating device is initially used to soften and/or partially melt the contact surface. To move the heating device to the melt operations position, the heating device holding arm is extended, and the carriage is first moved to an initial melt-start position with the carriage raised and the heating device initially aligned over the access opening. The carriage is next lowered towards the access opening while rotating forwardly about its rotation axis, to slide the heating device and its associated holding arm through the access opening to a pre-melt position, with the heating device in general alignment with the melting contact surface. To soften or otherwise partially melt the contact surface, the heating device is activated and then moved to the melt operation position, against and preferably partially into the contact surface. Movement of the heating device against the contact surface may be effected by the displacement of the carriage, as for example by its mounting on a suitable gantry frame or robot arm. More preferably, however, the support assembly securing the holding arm to the carriage includes one or more linear slides which allow for the selective relative movement of the holding arm assembly relative thereto. Following contact surface melting, the carriage is rotated in a reverse direction and raised withdrawing the heating device and its associated holding arm from the workpiece interior in the reverse operation. 
         [0017]    Immediately following the heating device withdrawal and with the component holding arm extended, the carriage is rotated to move the component holder with the component secured thereby into initial compound alignment over the access opening. Further forward rotation of carriage about the rotation access while the carriage moves towards the access opening moves the component holder and the component into the workpiece interior to a pre-placement position, wherein the component is generally in alignment with the partially melted contact surface. The component holder arm is then moved towards the contact surface, to position the component in a fixture placement position against the melted contact surface, and thereafter allowed to cool, fusing the component to the workpiece. 
         [0018]    Following final positioning of the component, the component is released and the carriage is again rotated in the reverse direction and raised to withdraw the component holder and its associated holding arm from the workpiece interior. 
         [0019]    Accordingly, in one aspect the present invention resides in a hot plate welding system for melt connecting a component to a contact surface of a workpiece having an access opening spaced therefrom, the system including: a component mounting assembly comprising a carriage, a component holding unit and workpiece melting unit, each of the component holding unit and workpiece mounting unit being secured to said carriage for movement therewith, the workpiece melting unit including: a heating device, a hooked heater-holding arm, and a heater-holding arm support, the hooked heater-holding arm curving in a first plane from a proximal end portion to a distal end portion and being sized for sliding insertion through said access opening, the heating device being secured towards the distal end portion of the heater-holding arm and being sized for insertion through said access opening the heating device being activatable to partially melt or soften the contact surface of the workpiece, the distal end portion of the heater-holding arm being selectively movable in said first plane along an associated generally radially extending path between a melt start position, where said distal end of the heater-holding arm is positioned adjacent to said access opening, and an extended pre-melt position, where said heater-holding arm is moved through said access opening to a position with said heating device in general alignment with said contact surface, the component-holding unit including a component holding device, a hooked component-holding arm and a component holding-arm support, the component-holding arm curving in said first plane from a proximal end portion to a distal end portion and being sized for sliding insertion through said access opening, the component-holding device being secured towards the distal end portion of the component-holding arm and sized for insertion through said access opening, the distal end portion of the component-holding arm being selectively movable in said first plane along an associated generally radially extending path between a component-feed position, where said distal end of the component-holding arm is positioned adjacent said access opening, and an extended pre-mount position, where said component-holding arm is moved through said access opening to a position with said component-holding device in general alignment with the contact surface. 
         [0020]    In another aspect, the present invention resides in a welding system for forming a weld connection between a contact surface of a workpiece and a component to be connected thereto, the system including: a component mounting assembly comprising a carriage, a component holding unit and workpiece melting unit, each of the component holding and workpiece mounting units being mounted to said carriage, the workpiece melting unit including a workpiece welding device, and a welding-unit holding arm which curves from a proximal end to a distal end, and a first arm support, the welding device secured towards the distal end of the welding-unit holding arm and being activatable to melt and/or soften the contact surface, the welding-unit holding arm being pivotally coupled to the first arm support member for selective movement about an associated pivot between a first position wherein the distal end of the welding-unit holding arm is moved outwardly to a remote position relative to the carriage and second position where the distal end is moved inwardly relative thereto, the component-holding unit including: a component holder, a component-holding arm which curves along a length portion between a proximal end to a distal end, and a component arm support member, the component holding arm being pivotally coupled to said component arm support member for selective movement about an associated pivot between a first position wherein the distal end is moved inwardly relative thereto. 
         [0021]    In a further aspect, the present invention resides in a hot plate welding system for forming a plastic weld connection between an internal contact surface of a generally hollow workpiece and a component to be connected to the contact surface, the workpiece having an access opening spaced from the contact surface, the system including: a component mounting assembly comprising a carriage, a component holding unit and workpiece melting unit, at least one of the component holding and workpiece mounting unit being mounted to said carriage for movement therewith, the workpiece melting unit including: a hooked heater-holding arm, the hooked heater holding arm curving in a first plane from a proximal end portion to a distal end portion and being sized for sliding insertion through said access opening, a hot plate mounted at the distal end portion of the heater-holding arm, and sized for insertion therewith through said access opening, the hot plate being activatable to partially melt or soften the contact surface, a first actuator operable to effect non-linear movement of the distal end portion generally in said first plane between a melt-operation start position, where said hot plate is moved outwardly an interior of the workpiece and adjacent to said access opening, and a pre-melt position, where said hot plate is moved through said access opening to a position in general alignment with said contact surface, the component-holding unit including: a hooked component-holding arm curving in said first plane from a proximal end portion to a distal end portion and being sized for sliding insertion through said access opening, a component holder mounted towards the distal end portion of the component-holding arm and sized for insertion therewith through said access opening, the component holder being selectively operable to fixedly retain or release the component, a second actuator operable to effect non-linear movement of the distal end portion of the component-holding arm in said first plane between a component-feed position, where said component holder is moved outwardly from the interior of the workpiece adjacent said access opening, and a pre-mount position, where said component holder is moved through said access opening to a position in general alignment with the contact surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Reference may now be had with the following description taken together with accompanying drawings in which: 
           [0023]      FIG. 1  shows a perspective view of a hot plate welding system used in the positioning and securement of a valve bracket component to an internal contact surface of a blow molded fuel tank in accordance with a preferred embodiment of the invention; 
           [0024]      FIG. 2  shows an enlarged schematic view of the component mounting assembly used in the hot plate welding system of  FIG. 1 ; 
           [0025]      FIG. 3  shows an enlarged perspective view of the workpiece melting unit used in the hot plate welding system of  FIG. 1 ; 
           [0026]      FIG. 4  shows an enlarged partial perspective view of the component-holding unit used in the hot plate welding system of  FIG. 1 ; 
           [0027]      FIG. 5  illustrates the component mounting assembly of  FIG. 2  with a hot plate of the workpiece melting unit oriented in an initial melt-start position above a fuel tank access opening; 
           [0028]      FIG. 6  illustrates schematically the component mounting assembly of  FIG. 2  with the hot plate workpiece melting unit moved into the interior of the fuel tank of  FIG. 1  in a pre-melt position; 
           [0029]      FIG. 7  illustrates schematically the hot plate of workpiece melting unit of  FIG. 2  repositioned in a melt operations position during contact surface melting; 
           [0030]      FIG. 8  illustrates schematically the component mounting assembly of  FIG. 2  with the component holder of the component-holding unit oriented in a component-start position over the access opening; 
           [0031]      FIG. 9  illustrates schematically the component mounting assembly of  FIG. 2  with the component holder and component holding arm moved to an initial pre-placement position; and 
           [0032]      FIG. 10  illustrates schematically the component mounting assembly of  FIG. 2  showing the final positioning of component holder in a fixture placement position in the securement of the component against the workpiece contact surface. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    The present invention relates to a hot plate welding system  10  used in the securement of a component, such as a valve bracket  12 , to a desired contact surface  14  disposed along the interior sidewall  16  of a hollow fuel tank preform  18 . In a most preferred use, the preform  18  is blow molded with the sidewall  16  being of a multi-layer of composite construction which defines a hollow interior  20 , and which includes a multi-layer sidewall construction incorporating HDPE and EVOH layers. Although not essential, preferably the valve bracket  12  is formed from HDPE for optimum melt welding and fusing to the contact surface  14 . An access opening  22  is formed through the sidewall  16  at a laterally spaced distance of between about 5 and 80 cm, and more preferably 20 to 50 cm from the contact surface  14 . 
         [0034]      FIG. 1  shows best the welding system  10  as including a single robot  30  and modular component mounting assembly  32 . The robot  30  is provided with a single robot arm  34  which is adapted for preprogrammed indexed movement in 6-axis, and which further includes a terminal-most wrist  36  which is selectively reciprocally rotatable about a rotation axis A 1 -A 1  ( FIG. 2 ). As shown in  FIG. 1 , the component mounting assembly  32  is coupled to the robot arm wrist  36 . In this manner, the component mounting assembly  32  is movable by the robot  30  both in 6-axis movement together with the robot arm  34 , and in rotation about the axis A 1 -A 1  with rotary movement of the wrist  36 . As will be described, in use the component mounting assembly  32  is indexed in movement through a preprogrammed manufacturing cycle by means of the robot arm  32  through a series of workstations and/or positions to successively grasp, position and fuse to the contact surfaces of successively positioned preforms  18 , individual valve bracket  12  in the manufacture of finished fuel tanks. 
         [0035]    The component mounting assembly  32  is shown best in  FIGS. 2 to 4  as including generally rectangular steel carriage plate  40 , a workpiece melting unit  42  and a component-holding unit  44 . In a simplified form, the carriage plate  40  is formed as a generally planar rectangular aluminum or metal plate which is bolted directly to the end of the wrist  36 . The carriage plate  40  is preferably fixedly secured to the wrist  36  at its geometric centre, and in an orientation with the plate  40  extending in a plane generally normal to the axis A 1 -A 1 . In this configuration, the rotation of the wrist  36  moves the carriage plate  40  in rotation about the axis A 1 -A 1 . 
         [0036]      FIGS. 2 and 3  show best the workpiece melting unit  42  as including a hot plate  48 , a holding arm assembly  50  and an associated support assembly  52 . The holding arm assembly  50  is shown best in  FIG. 2  is generally hooked-shape and include a pair of rigid parallel spaced curved arm members  56   a , 56   b . The arm members  56   a , 56   b  have the identical shape and profile and extend radially from a proximalmost end  60  along an arc of between about 70 and 120°, and preferably about 90°, merging with a distalmost end portion  62 . The arm members  56   a , 56   b  are maintained in their fixed spaced apart relationship by one or more metal braces  64  which are positioned to provide the holding arm assembly  50  with sufficient rigidity. As shown best in  FIG. 2 , the hot plate  48  is secured to the holding arm assembly  50  adjacent to the distalmost end portions  62  of the arms  56   a , 56   b.    
         [0037]    The hot plate  48  and hooked arm members  56   a , 56   b  have a size and length selected to permit their substantially unhindered sliding insertion through the fuel tank access opening  22  to permit positioning of the hot plate  48  in general alignment with the contact surface  14 . As shown best in  FIGS. 2 and 3 , the support assembly  52  associated with the holding arm assembly  50  includes a linear slide plate  66  a slide actuator  68  and a curved support arm  70 . 
         [0038]    The linear slide plate  60  is slidably mounted to the carriage plate  40  for linear movement along a line tangential to the axis A 1 -A 1 . In this regard, the slide actuator  68 , which in a simplified construction may comprise an electric stepping motor or a hydraulic or pneumatic ram is selectively operable to move the slide plate between an initial rest position and a biased position displaced linearly therefrom. As will be described, a load sensor  72  is most preferably electronically coupled to the slide actuator  60  and provides control signals thereto. 
         [0039]    Although not essential, most preferably the curved support arm  70  is integrally formed with the linear slide plate  66 . More preferably, the support arm  70  is provided as a generally planar arm which has a dimension and curvature generally corresponding to the dimension and curvature of a proximal portion of the arm members  56   a , 56   b.    
         [0040]    As shown best in  FIGS. 2 and 3 , the holding arm assembly  50  is pivotally secured to the support arm  70  by way of a pivot  74 . The holding arm assembly  50  is coupled to the support arm  70  with each of the arm members  56   a , 56   b  on a respective side thereof, and with the holding arm assembly  50  being rotatable about the pivot  74  in a plane normal to the axis A 1 -A 1  between the extended position shown in  FIG. 2 , wherein the distalmost ends  62  of the arm members  56   a , 56   b  are moved radially outwardly relative to the axis; and the retracted position shown in phantom in  FIG. 4 , in which the distalmost ends  62  of the arm members  56   a , 56   b  are pivoted inwardly towards the axis A 1 -A 1 . 
         [0041]    As shown best in  FIG. 2 , in the extended position, the braces  64  are most preferably brought into bearing contact with an interior edge portion of the support arm  70  to provide the workpiece melting unit  42  with enhanced structural rigidity under load forces. 
         [0042]    In a preferred construction, a pneumatic cylinder  76  is mounted on the slide plate  66  for sliding movement therewith. The pneumatic cylinder  76  includes an extendable cylinder arm  78  which is in turn secured to the holding arm assembly  50 . It is to be appreciated that the activation of the cylinder  76  permits the selective movement of the holding arm assembly  50  between the retracted and extend positions. 
         [0043]      FIGS. 2 and 4  show best the component-holding unit  44  as including a component holder  88 , a holding arm assembly  90  and an associated support assembly  92 . The component-holding unit  44  is secured to the carriage plate  40  in an inverse position to the welding unit  42  and symmetrically opposed thereto about the axis A 1 -A 1 . Although not essential, most preferably the holding arm assembly  90  is provided with substantially the identical construction and configuration as the holding arm assembly  50 . In this regard, the holding arm assembly  90  is generally hooked-shaped and includes a pair of rigid curved arm members  96   a , 96   b  which extend generally normal to the axis A 1 -A 1  from respective proximalmost end portions  100  along an arc of between about 70 and 120°, and preferably 90°, to merge with linear distal end portions  102 . The component holder  88  is mounted to the distalmost portion  102  of the arm members  96   a , 96   b . The component holder  88  is selectively actuable to grasp or release the valve bracket  12  in its positioning and securement against the contact surface  14 . The component holder  88  and arm members  96   a , 96   b  are thus provided with a size and length selected to permit their substantially unhindered sliding insertion through the fuel tank access opening  22  to permit the positioning of the valve bracket  12  in general alignment with the contact surface  14 . 
         [0044]    The support assembly  92  is formed having substantially the same profile and configuration as support assembly  52 . The support assembly  92  includes a linear slide plate  116 , a slide actuator  118  and a curved support arm  120 . The slide actuator  118  is most preferably of the identical construction of slide actuator  68  and is regulated by an associated load sensor  122  to effect the linear displacement of the slide plate  116  relative to the carriage plate  40  along an associated tangential path. Most preferably, the slide plate  116  is displaceable along a linear direction parallel to the direction of displacement of the slide plate  66 . 
         [0045]    The curved support arm  120  preferably is provided with the identical configuration as the support arm  70 . The holding arm assembly  90  is pivotally secured to the support arm  120  by way of an associated pivot  124  for movement in a plane normal to the axis A 1 -A 1 . The holding arm assembly  90  is thus movable between a retracted position wherein the distalmost portions  102  of the arm members  96   a , 96   b  are spaced radially inwardly towards the axis A 1 -A 1 , and an extended position (shown in  FIG. 8 ) in which the component holder  88  moves outwardly a distance remote therefrom. An associated pneumatic cylinder  126  is mounted to the slide plate  116  for movement therewith. The pneumatic cylinder  126  includes an extensible cylinder arm  128  which is secured to the proximalmost end  100  of at least one of the arm members  96   a , 96   b , and which is selectively extended or retracted to effect movement of the holding arm assembly  90  about the pivot  124 . 
         [0046]    Although not essential, more preferably the support assembly  92  is further provided with a component hot plate  130 . The component hot plate is secured to the slide plate  116  so as to be engagable by and partially melt a selected valve bracket  12  held by the component holder  88  when the holding arm assembly  90  is retracted. It is to be appreciated that the positioning of the component hot plate  130  on the support assembly  92  provides for increased operational efficiencies and allows for the partial melting of the valve bracket  12  during hot plate melting of the preform  18 . 
         [0047]    The use of the hot plate welding system  10  is described best with reference to  FIGS. 5 to 10 . In the mounting of a valve bracket  12  to the fuel tank preform  18 , the pneumatic cylinder  76  is actuated to move the holding arm assembly  50  to its fully extended position. Simultaneously, the robot  30  ( FIG. 1 ) is actuated to move the carriage plate  40  to the initial melt-start position shown in  FIG. 5 , wherein the hot plate  48  is positioned directly over the access opening  22 , such that the alignment of the contact surface  14  and access opening  22  is parallel with the rotational plane of the arm members  56   a , 56   b  and  96   a , 96   b . Concurrently, or immediately prior to the positioning, the valve bracket  12  is secured by the component holder  88  by either its movement to a desired component pick up station, or by a suitable component feed assembly (not shown). From the melt-start position, the robot arm  34  is actuated to simultaneously lower the carriage plate  40  towards the preform  18  in the direction of arrow  150  while effecting its forward rotation about the axis A 1 -A 1  in the direction of arrow  160 . It is to be appreciated that the movement of the carriage plate  40  thus effects the sliding movement of the hot plate  48  and holding arm assembly  50  to the pre-melt position shown in  FIG. 6 , wherein the hot plate  48  is generally aligned with a spaced a marginal distance from the contact surface. 
         [0048]    Following movement of the hot plate  48  to the pre-melt position, the slide actuator  68  is activated to effect the upward linear movement of the slide plate  66 , moving the hot plate  48  into bearing contact with and into the contact surface  14  to effect its partial melting. Most preferably, the load sensor  72  is provided to regulate the degree of melting the contact surface  14 . When the sensor  72  senses that the hot plate  48  has been displaced a desired distance into the contact surface  14 , the sensors signals the slide actuator  68  to lower and return the linear slide plate  66  to its initial position. 
         [0049]    Most preferably, concurrently while the hot plate  48  effects melting of the contact surface, the component hot plate  130  is activated, and the pneumatic cylinder  126  extended to move the valve bracket  12  into melt contact therewith. In this manner, both the preform  18  and valve bracket  12  may be concurrently melted to maximize operating efficiencies. 
         [0050]    Immediately following the melting of the preform  18 , the robot  30  is again activated to rotate and raise the carriage plate  40  in the reverse directions of arrows  150 , 160  and effect the sliding withdrawal of the holding arm assembly  50  from the preform interior  20 . 
         [0051]    Once withdrawn, the pneumatic cylinder  76  is extended to move the holding arm assembly  50  to the retracted position shown in  FIG. 8 . Concurrently, the pneumatic cylinder  126  is retracted to extend the holding arm assembly  90  of the component holding unit  44  orienting it in the component-start position shown in  FIG. 8 , in which the valve bracket  12  and component holder  88  are positioned immediately above the access opening  22 . 
         [0052]    With the component holder  88  so positioned, the robot  30  ( FIG. 1 ) is indexed to again lower the carriage plate  40  in the direction of arrow  150 ′, while effecting its forward rotation in the direction of arrow  160 ′, to rotate and slide the component holder  88  and holding arm assembly  90  into the preform interior  20 . The component holder  88  and holding arm assembly  90  are moved inwardly until the valve bracket  12  assumes the pre-placement position shown in  FIG. 9 , aligned with and adjacent to the melted contact surface  14 . Once so positioned, the slide actuator  118  is activated to effect linear upward movement of the slide plate  116  and arm members  96   a , 96   b  to move the valve bracket  12  against the contact surface  14 . Following either a predetermined period of time and/or on sensing a preselected load, the load sensor  122  signals the slide actuator  118  to return the slide plate  116  to the deactivated position, and the robot arm  34  is rotated and raised in the reverse direction of arrow  150 ′, 160 ′ and raised to effect the sliding withdrawal of the component holder  88  and arm assembly  90  from the preform interior  20 . 
         [0053]    Following the withdrawal of the hot plate welding system  10  from the interior  22  of the preform  18 , the manufacturing cycle is repeated for the manufacture of subsequent fuel tank products. 
         [0054]    Although the detailed description describes the use of pneumatic cylinders  76 , 126  to effect the extension or retraction of the holding arm assemblies  50 , 90 , the invention is not so limited. Other means of effecting holding arm movement such as electric motors or other hydraulic cylinders could also be used and will now become apparent. Further, although the pivotal movement of the holding arm assemblies  50 , 90  advantageously provides a welding system  10  having a more compact and space efficient profile, it is to be appreciated that the curved arm members  56 , 96  could be rigidly secured to the carrier plate  40 . 
         [0055]    Although the detailed description describes the arm members  56 , 96  as curving and rotatable in a common plane generally normal to the rotation axis A 1 -A 1  as allowing for simplified programmed movement, it is to be appreciated that other arm configurations could also be provided. 
         [0056]    Although the detailed description describes the preferred aspect of the invention as used to position a valve bracket  12  to an interior contact surface  14  of a gas tank preform  18 , the invention is not so limited. The present apparatus is equally suited for use in the securement of a variety of different types of components to the interior or exterior surface of other types of blow molded, injection molded and/or cast workpieces. 
         [0057]    Although the hot plate welding system  10  describes the mounting of the workpiece melting unit  42  and component-holding unit  44  on a single carriage plate  40 , in a less preferred construction, the melting unit  42  and component-holding unit  44  could be mounted to separate carriages, each secured to a dedicated robot or robot arm for independent movement. 
         [0058]    While the detailed description describes the use of load cells or load sensors  72 , 122  to limit movement of the slide plates  66 , 116  the invention is not limited. Other activating/deactivating devices could also be used and will now become apparent. By way of non-limiting example, instead of a load cells  72  and/or  122  a spring loaded trigger mechanism could be provided. The spring trigger mechanism need not provide force feedback, but may operate on a sensor once the spring is compressed by the hot plate and/or component making contact with the fuel tank wall. 
         [0059]    Although the detailed description describes and illustrates various preferred aspects, the invention is not so limited. Many variations and modifications will now occur to persons skilled in the art. For a definition of the invention, reference may be had to the appended claims.