Patent Publication Number: US-2019185085-A1

Title: Modular production line system and method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of U.S. Provisional Application No. 62/584,252 filed Nov. 10, 2017. 
    
    
     TECHNICAL FIELD 
     This invention relates to automotive closure manufacturing, and more particularly to vehicle body closure panel production. 
     BACKGROUND OF THE INVENTION 
     As shown by example in  FIG. 1 , it is known in the art relating to automotive closure manufacturing that a production line process for production of parts for multiple vehicle models (e.g., five models) is built at its inception to accommodate all of the models. The required floor space and necessary equipment must be reserved and provided in the production facility in the beginning in order to be able to produce a sufficient amount of parts needed for all five models. In other words, the production line is configured to produce the total jobs per hour (JPH) for all five models combined, even if any or all of the second, third, fourth, or fifth models are to be introduced at a later date from the first model. Since all of the equipment is provided at inception of the production line, the technology that can foe introduced to the line is limited to the technology available at the time of inception of the first model. Also, at inception the footprint (area or floor space) of the production line is a maximum for the total number of models to be produced, even if some of the models will not be produced until a later date. 
     SUMMARY OF THE INVENTION 
     The present invention provides a modular, flexible, multi-model production line system and method that can add additional product/models to the line over time without the need to reserve production facility floor space and production equipment in advance. The modular production line can be expanded to support required production volumes of added product models without the need for the required equipment to be present at the inception of the line. Also, future products and/or models can be added to the flexible, modular production system even if the future products are distinct from the existing products/models produced in the line, and new production methods and technology may be added to the system at any time. The modular production line system and method thereby allows for flexible production of multiple parts in a single line and for the introduction of future models and technology into an existing production line. 
     More particularly, a modular production system in accordance with the invention includes an endless transport path defining a loop. A plurality of work cells, in which forming processes such as shaping, joining, and similar are performed on a workplace, are disposed in a sequence along the transport path. The work cells include an inner spot welding cell, an inner remote laser welding cell, and an outer roller flanging and laser welding cell. A transporter follows the transport path and selectively transfers the workpiece between the work cells along the transport path. A controller controls the transporter along the transport path, whereby the transporter selects at some of the work cells and makes a stop at the selected work cells, and the transporter bypasses any unselected work cells. 
     The inner spot welding cell may include a panel fixture and a spot welding device that performs inner spot welding of workpieces on the panel fixture. The inner spot welding cell may also include additional panel fixtures. 
     The inner remote laser welding cell may include a panel fixture and a laser welding device. The inner remote laser welding cell may also include additional panel fixtures. The inner remote laser welding cell may further include additional laser welding devices. 
     The outer roller flanging and laser welding cell may include panel fixtures, roller flanging devices, laser welding devices, and container towers and/or storage racks that store finished workplaces. The outer roller flanging and laser welding cell may also include additional panel fixtures, container towers, and/or storage racks. 
     An additional work cell may be added along the transport path. 
     The workpiece may be a vehicle body closure panel. The workpiece may be moved from the transporter into one of the selected work cells, and the workpiece may be moved back to the transporter after being worked on in the selected work cell. 
     The system may also include a plurality of multi-axis robots each including an arm. The robots move the workpiece to and from the transporter and move the workpiece within the work cells. 
     In another arrangement, a modular production line system in accordance with the invention includes an endless transport path defining a loop. A plurality of work cells in which forming processes are performed on vehicle body closure panels are disposed in a sequence along the transport path. A transporter follows the transport path and selectively transfers the workplace between the work cells along the transport path. A controller controls the transporter along the transport path, whereby the transporter selects at least some of the work cells and makes a stop at the selected work cells, and the transporter bypasses any unselected work cells. 
     A method of manufacturing vehicle body closure panels in accordance with the invention includes the steps of selectively transferring a workpiece between a plurality of work cells disposed in a sequence along an endless transport path defining a loop, the work cells including an inner spot welding cell, an inner remote laser welding cell, and an outer roller flanging and laser welding cell, by providing a transporter that follows the transport path and moves the workpiece between the work cells along the transport path, and a controller that controls the transporter along the transport path, wherein the transporter selects at least some of the work cells, and makes a stop at the selected work cells, and the transporter bypasses any unselected work cells; and performing at least one of inner spot welding the workpiece in the inner spot welding cell, laser welding the workpiece in the inner remote laser welding cell, and roller flanging and laser welding the workpiece in the outer roller flanging and laser welding cell. At least some of the work cells along the transport path are selected and utilized, and any unselected work cells are bypassed. 
     The controller may cause the workpiece to be moved into and out of the selected work cells, and the controller may cause the workpiece to be moved past any unselected work cells. The method may further include multi-axis robots controlled by the controller, wherein the multi-axis robots move the workpiece into, out of, and within the selected work cells. 
     The method may further include the step of adding an additional work cell along the transport path. The method may also include the step of adding additional equipment to at least one of the work cells. 
     More than one type of finished part may be produced from the workpieces by selectively choosing work cells among the plurality of work cells and/or by selectively choosing to utilize certain processes within the work cells. 
     These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a plan view of a prior art production line; 
         FIG. 2  is a plan view of a modular, flexible production line system and method in accordance with the invention producing a single model; 
         FIG. 3  is a plan view of the modular production line system and method further incorporating production of a second model into the line; 
         FIG. 4  is a plan view of the modular production line system and method further incorporating production of a third model into the line; 
         FIG. 5  is a plan view of the modular production line system and method further incorporating production of a fourth model into the line; 
         FIG. 6  is a plan view of the modular production line system and method further incorporating production of a fifth model into the line; 
         FIG. 7  is a flowchart of a method of producing a single model in the system shown in  FIG. 2 ; 
         FIG. 8  is a flowchart of a method of producing a second model in the system shown in  FIG. 3 ; 
         FIG. 9  is a flowchart of a method of producing a third model in the system shown in  FIG. 4 ; 
         FIG. 10  is a flowchart of a method of producing a fourth model in the system shown in  FIG. 5 ; 
         FIG. 11  is a flowchart of a method of producing a fifth model in the system shown in  FIG. 6 ; and 
         FIG. 12  is a flowchart of a production line method in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in detail, the modular production system and method includes an endless transport path defining a production loop. A plurality of work cells, each for performing a certain forming process or processes on a workpiece such as a vehicle closure panel, are disposed along the transport path. The forming processes may generally include shaping, joining, and the like, such as welding, flanging, hemming, etc. A transporter, such as an automated guided vehicle (AGC/AGV) and associated tooling cart, transfers in-process workpieces between cells along the transport path. Each work, cell may include production equipment such as but not limited to multi-axis robots including arms, panel fixtures, turntables, storage racks, hemming devices, spot welding devices, laser welding devices, roller flanging devices, belt line hemming devices, impact beam assembly devices, and the like. A controller that may include a CPU or similar controls the transporter along the transport path. The same controller or an additional controller or controllers may control the multi-axis robots and other equipment in the work cells to affect and synchronize the flow of workpieces in and through the system. A plurality of different models of parts can be produced in the system by selecting and utilizing some or all of the cells along the transport path and/or bypassing other unselected cells along the path (i.e. “selectively transferring” the workpiece between the cells). Further, additional cells can be added along the transport path and/or additional equipment can be added to existing cells to support production of additional models. 
     As shown fey example in  FIGS. 2 and 7 , the modular production line system  110  may at inception include a subset of work cells for producing a first vehicle closure panel model (model  1 ). The work cells may include, in sequential order, an inner spot welding cell  112 , an inner remote laser welding cell  114 , and an outer roller flanging and laser welding cell  116 . In-process workplaces are transferred between cells using automated guided vehicles  118  and associated tooling carts that are controlled by a controller  120  and moved along an endless transport path  122  defining a production loop. The automated guided vehicle controlled by the controller begins the process at a home starting location  124  (step S 1110 ), and at step S 1102  the automated guided vehicle moves the tooling cart first from the home starting location  124  to a station  126  at the inner spot welding cell (first cell)  112  on the transport path. The inner spot welding cell includes a plurality of turntables  128 , in this case three, each including a plurality of spot welding fixtures  130 . The inner spot welding cell also includes a plurality of multi-axis robots  132  controlled by a controller  134 . One of the robots loads and unloads workplaces from the tooling cart  118 . Other robots move the workpieces to and from one or more spot welding fixtures  130  and/or perform inner spot welding on the workplaces that are placed in the spot welding fixtures. At step S 1104 , one of the robots unloads a workpiece  136  from the tooling cart and brings the workpiece into the inner spot welding cell for operations to be performed on the workpiece at the welding fixtures. Once inner spot welding of the workpiece is complete at step S 1106 , the robot loads the workpiece back onto the tooling cart at step S 1108 . At step S 1110 , the automated guided vehicle next moves the tooling cart along the transport path to a station  138  at the inner remote laser welding cell (second cell)  114 . The inner remote laser welding cell includes a turntable  128  including a plurality of laser welding fixtures  140 , and a plurality of multi-axis robots  132  controlled by a controller  142 . One of the robots loads and unloads workplaces from the tooling cart, and another robot performs inner remote laser welding on the workplaces that are placed in the laser welding fixtures. At step S 1112 , the robot unloads the workpiece from the tooling cart, at step S 1114  inner remote laser welding is performed on the workpiece in the cell, and at step S 1116  the robot loads the workpiece back onto the tooling cart. At step S 1118 , the automated guided vehicle then transports the tooling cart along the transport path to a station  144  at the outer roller flanging and laser welding cell  116  (third cell). The outer roller flanging and laser welding cell includes a plurality of turntables  128 , in this case four. One of the turntables is located at an impact beam assembly station  146  at which impact beam assembly is performed, another of the turntables is located at a roller flanging station  148  at which roller flanging is performed, another of the turntables is located at a belt line hemming station  150  at which belt line hemming is performed, and another of the turntables is located at a laser welding station  152  at which laser welding is performed. Each of the stations  146 ,  148 ,  150 ,  152  includes various fixtures  156 . The outer roller flanging and laser welding cell also includes a plurality of multi-axis robots  132  controlled by a controller  154 . One of the robots loads and unloads workplaces from the tooling cart, and other robots move the workplaces to and from stations in the cell and/or perform the operations (roller flanging, laser welding, and the like) on the workpieces. The outer roller flanging and laser welding cell further includes outer panel racks  158  that store outer panels to be joined with inner panels, and final assembly racks  160  that store finished, finally assembled workplaces. The cell may also include tracks  162  along which some of the robots  132  move in the cell. At step S 1120 , one of the robots unloads the workpiece from the tooling cart, at step S 1122  processes such as roller flanging, laser welding and/or other operations are performed on the workpiece in the cell, and at step S 1124  the finished workpiece is loaded onto one of the final assembly storage racks. At step S 1126 , the automated guided vehicle then continues along the transport path  122 , returns to the home location  124 , and begins the process again. 
     Turning to  FIGS. 3 and 8 , when a second model is later introduced into the modular production line  210  (like reference numerals in the drawings indicate the same or similar elements), the automated guided vehicle  218  may for example be configured to stop at certain cells and to bypass other cells for production of the second model (model  2  in  FIG. 3 ). For example, the workplaces produced for the second model may only enter the inner spot welding cell  212  (first cell) and the outer roller flanging and laser welding cell  216  (third cell), and may bypass the inner remote laser welding cell  214  (second cell). Also, additional equipment may be added to the existing cells for production of the second model. For example, panel fixtures  230  and robots  232  may be added to the inner spot welding cell  212 , and outer panel racks  258 , final assembly storage racks  260  and/or panel fixtures  256  may be added to the outer roller flanging and laser welding cell  216 . The inner spot welding cell  212  includes a plurality of turntables  228  each including a plurality of spot welding fixtures  230 . The inner spot welding cell also includes a plurality of multi-axis robots  232  controlled by a controller  234 . One of the robots loads and unloads workplaces from the tooling cart  218 . Other robots move the workplaces to and from one or more spot welding fixtures  230  and/or perform inner spot welding on the workpieces that are placed in the spot welding fixtures. The inner remote laser welding cell  214  includes a turntable  228  including a plurality of laser welding fixtures  240 , and a plurality of multi-axis robots  232  controlled by a controller  242 . One of the robots loads and unloads workplaces from the tooling cart, and another robot performs inner remote laser welding on the workplaces that are placed in the laser welding fixtures. The outer roller flanging and laser welding cell  216  includes a plurality of turntables  228 . One of the turntables is located at an impact beam assembly station  246  at which impact beam assembly is performed, another of the turntables is located at a roller flanging station  248  at which roller flanging is performed, another of the turntables is located at a belt line hemming station  250  at which belt line hemming is performed, and another of the turntables is located at a laser welding station  252  at which laser welding is performed. Each of the stations  246 ,  248 ,  250 ,  252  includes various fixtures  256 . The outer roller flanging and laser welding cell also includes a plurality of multi-axis robots  232  controlled by a controller  254 . One of the robots loads and tin loads workplaces from the tooling cart, and other robots move the workpieces to and from stations in the cell and/or perform the operations (roller flanging, laser welding, and the like) on the workpieces. The outer roller flanging and laser welding cell further includes outer panel racks  258  that store outer panels to be joined with inner panels, and final assembly racks  260  that store finished, finally assembled workpieces. The cell may also include tracks  262  along which some of the robots  232  move in the cell. At step S 1200 , the automated guided vehicle  218  begins the process at the home start location  224 . At step S 1202 , the automated guided vehicle  218  controlled by the controller  220  moves the tooling cart along the transport path  222  first from the home starting location  224  to the station  226  at the inner spot welding cell (first cell)  212 . At step S 1204 , one of the robots  232  unloads a workpiece  236  from the tooling cart and brings the workpiece into the inner spot welding cell for operations to be performed on the workpiece at the welding fixtures. Once inner spot welding of the workpiece is complete at step S 1206 , the robot loads the workpiece back onto the tooling cart at step S 1208 . At step S 1209 , the automated guided vehicle bypasses the inner remote laser welding cell (second cell)  214  and does not stop at the station  238  at the second cell. At step S 1218 , the automated guided vehicle then transports the tooling cart along the transport path to the station  244  at the outer roller flanging and laser welding cell  216  (third cell). At step S 1220 , one of the robots  232  unloads the workpiece from the tooling cart, at step S 1222  roller flanging, laser welding and/or other operations are performed on the workpiece in the cell, and at step S 1224  the finished workpiece is loaded onto one of the final assembly storage racks  260 . At step S 1226 , the automated guided vehicle then continues along the transport path  222 , returns to the home location  224 , and begins the process again. 
     When a third and subsequent models are later introduced into the modular production line, new cells may be constructed and added to the line in order to accommodate the production volume (jobs per hour requirements) for the added models. Any additional floor space needed for the production line can be located anywhere in the production facility since the workpieces are transferred between cells by the automated guided vehicles. For each newly introduced model, the automated guided vehicle can be configured to stop at existing cell(s) if the process(es) performed at the cell(s) can be utilized for the new model, and/or the automated guided vehicle can be configured to travel to and stop at new cells as necessary. Since newly introduced models can use new cells, then new product types, constructions, and technology can be introduced into the production line. 
     Specifically, as shown by example in  FIGS. 4 and 9 , when a third model (model  3  in  FIG. 4 ) is introduced into the modular production line  310 , a new inner spot welding cell  364  and a new outer roller flanging and laser welding cell  366  may be added to the production line. Also, new laser welding fixtures  340  may be added to the existing, original inner remote laser welding cell  314 . The new inner spot welding cell  364  includes a plurality of turntables  328 , in this case three, each including a plurality of spot welding fixtures  330 . The new inner spot welding cell  364  also includes a plurality of robots  332  controlled by a controller  368 . One of the robots loads and unloads workpieces from the tooling cart. Other robots move the workpieces to and from one or more spot welding fixtures  330  and/or perform inner spot welding on the workpieces that are placed in the spot welding fixtures. The new outer roller flanging and laser welding cell  366  includes a plurality of turntables  328 , in this case four. One of the turntables is located at an impact beam assembly station  346  at which impact beam assembly is performed, another of the turntables is located at a roller flanging station  348  at which roller flanging is performed, another of the turntables is located at a belt line hemming station  350  at which belt line hemming is performed, and another of the turntables is located at a laser welding station  352  at which laser welding is performed. Each of the stations  346 ,  348 ,  350 ,  352  includes various fixtures  356 . The new outer roller flanging and laser welding cell  366  also includes a plurality of robots  332  controlled by a controller  370 . One of the robots loads and unloads workpieces from the tooling cart, and other robots move the workpieces to and from stations in the cell and/or perform the operations (roller flanging, laser welding, and the like) on the workpieces. The new outer roller flanging and laser welding cell  366  further includes outer panel racks  358  that store outer panels to be joined with the inner panel workpieces, and final assembly racks  360  that store finished, finally assembled workpieces. The cell may also include tracks  362  along which some of the robots move in the cell. The existing, original inner spot welding cell  312  includes a plurality of turntables  328  each including a plurality of spot welding fixtures  330 . The inner spot welding cell  312  also includes a plurality of multi-axis robots  332  controlled by a controller  334 . One of the robots loads and unloads workpieces from the tooling cart  318 . Other robots move the workpieces to and from one or more spot welding fixtures  330  and/or perform inner spot welding on the workpieces that are placed in the spot welding fixtures. The existing, original remote laser welding cell  314  includes a turntable  328  including a plurality of laser welding fixtures  340 , and a plurality of multi-axis robots  332  controlled by a controller  342 . One of the robots loads and unloads workpieces from the tooling cart, and another robot performs inner remote laser welding on the workpieces that are placed in the laser welding fixtures. The existing, original outer roller flanging and laser welding cell  316  includes a plurality of turntables  328 . One of the turntables is located at an impact beam assembly station  346  at which impact beam assembly is performed, another of the turntables is located at a roller flanging station  348  at which roller flanging is performed, another of the turntables is located at a belt line hemming station  350  at which belt line hemming is performed, and another of the turntables is located at a laser welding station  352  at which laser welding is performed. Each of the stations  346 ,  348 ,  350 ,  352  includes various fixtures  356 . The outer roller flanging and laser welding cell  316  also includes a plurality of multi-axis robots  332  controlled by a controller  354 . One of the robots loads and unloads workplaces from the tooling cart, end other robots move the workplaces to and from stations in the cell and/or perform the operations (roller flanging, laser welding, and the like) on the workplaces. The outer roller flanging and laser welding cell  316  further includes outer panel racks  358  that store outer panels to be joined with inner panels, and final assembly racks  360  that store finished, finally assembled workplaces. The cell may also include tracks  362  along which some of the robots  332  move in the cell. The process begins at the home starting location  324  (S 1300 ). From the home starting location, at stop S 1302  the automated guided vehicle  318  controlled by the controller  320  moves the tooling cart first front the home starting location and stops at a station  372  at the new inner spot welding cell (first cell)  364 . At step S 1304 , a robot  332  unloads a workpiece  336  from the tooling cart and brings the workpiece into the new inner spot welding cell. Once inner spot welding of the workpiece is complete at step S 1306 , the robot loads the workpiece back onto the tooling cart at step S 1308 . Next, the automated guided vehicle bypasses the station  326  at the original inner spot welding cell (second cell)  312  at step S 1309 , and proceeds to and stops at the station  338  at the inner remote laser welding cell (third cell)  314  at step S 1318 . At step S 1320 , a robot  332  unloads the workpiece from the tooling cart, at step S 1322  inner remote laser welding is performed on the workpiece in the cell, and at step S 1324  the robot controlled by the controller loads the workpiece back onto the tooling cart. At step S 1325 , the automated guided vehicle bypasses the station  344  at the original outer roller flanging and laser welding cell (fourth cell)  316 , and proceeds along the transport path and at step S 1328  stops at a station  374  at the new outer roller flanging and laser welding cell (fifth cell)  366 . At step S 1330 , a robot  332  controlled by the controller unloads the workpiece from the tooling cart, at step S 1332  roller flanging, laser welding and/or other operations are performed on the workpiece in the cell, and at step S 1334  the finished workpiece is loaded onto one of the storage racks  360 . At step S 1336 , the automated guided vehicle then continues along the transport path  322 , returns to the home location  324 , and begins the process again. 
     Turning to  FIGS. 5 and 10 , when a fourth model (model  4  in  FIG. 5 ) is introduced into the modular production line  410 , a new inner remote laser welding cell  476  may be added to the production line. The new inner remote laser welding cell includes turntables  428  each including a plurality of laser welding fixtures  440 , and a plurality of robots  432  controlled by a controller  478 . One of the robots loads and unloads workpieces from the tooling cart, other robots perform inner remote laser welding on the workpieces that are placed in the laser welding fixtures, and one of the robots may move workpieces within the cell. Also, in the production line  410 , new panel fixtures  430  may be added to the existing (added) inner spot welding cell  464  and the existing (added) outer roller flanging and laser welding cell  466 , and new storage racks  358 ,  360  may be added to the existing (added) outer roller flanging and laser welding cell  466 . The existing, original inner spot welding cell  412  includes a plurality of turntables  428  each including a plurality of spot welding fixtures  430 . The inner spot welding cell  412  also includes a plurality of multi-axis robots  432  controlled by a controller  434 . One of the robots loads and unloads workpieces from the tooling cart  418 . Other robots move the workpieces to and from one or more spot welding fixtures  430  and/or perform inner spot welding on the workpieces that are placed in the spot welding fixtures. The added inner spot welding cell  464  includes a plurality of turntables  428  each including a plurality of spot welding fixtures  430 . The added inner spot welding cell  464  also includes a plurality of robots  432  controlled by a controller  468 . One of the robots loads and unloads workpieces from the tooling cart. Other robots move the workpieces to and from one or more spot welding fixtures  430  and/or perform inner spot welding on the workpieces that are placed in the spot welding fixtures. The existing, original remote laser welding cell  414  includes a turntable  428  including a plurality of laser welding fixtures  440 , and a plurality of multi-axis robots  432  controlled by a controller  442 . One of the robots loads and unloads workpieces from the tooling cart, and another robot performs inner remote laser welding on the workpieces that are placed in the laser welding fixtures. The existing, original outer roller flanging and laser welding cell  416  includes a plurality of turntables  428 . One of the turntables is located at an impact beam assembly station  446  at which impact beam assembly is performed, another of the turntables is located at a roller flanging station  448  at which roller flanging is performed, another of the turntables is located at a belt line hemming station  450  at which belt line hemming is performed, and another of the turntables is located at a laser welding station  452  at which laser welding is performed. Each of the stations  446 ,  448 ,  450 ,  452  includes various fixtures  456 . The outer roller flanging and laser welding cell  416  also includes a plurality of multi-axis robots  432  controlled by a controller  454 . One of the robots loads and unloads workpieces from the tooling cart, and other robots move the workpieces to and from stations in the cell and/or perform the operations (roller flanging, laser welding, and the like) on the workpieces. The outer roller flanging and laser welding cell  416  further includes outer panel racks  458  that store outer panels to be joined with inner panels, and final assembly racks  460  that store finished, finally assembled workpieces. The cell may also include tracks  462  along which some of the robots  432  move in the cell. The added inner spot welding cell  464  includes a plurality of turntables  428  each including a plurality of spot welding fixtures  430 . The added inner spot welding cell  464  also includes a plurality of robots  432  controlled by a controller  468 . One of the robots loads and unloads workpieces from the tooling cart. Other robots move the workpieces to and from one or more spot welding fixtures  430  and/or perform inner spot welding on the workpieces that are placed in the spot welding fixtures. The added outer roller flanging and laser welding cell  466  includes a plurality of turntables  428 . One of the turntables is located at an impact beam assembly station  446  at which impact beam assembly is performed, another of the turntables is located at a roller flanging station  448  at which roller flanging is performed, another of the turntables is located at a belt line hemming station  450  at which belt line hemming is performed, and another of the turntables is located at a laser welding station  452  at which laser welding is performed. Each of the stations  446 ,  448 ,  450 ,  452  includes various fixtures  456 . The added outer roller flanging and laser welding cell  466  also includes a plurality of robots  432  controlled by a controller  470 . One of the robots loads and unloads workplaces from the tooling cart, and other robots move the workpieces to and from stations in the cell and/or perform the operations (roller flanging, laser welding, and the like) on the workpieces. The added outer roller flanging and laser welding cell  466  further includes outer panel racks  458  that store outer panels to be joined with the inner panel workpieces, and final assembly racks  460  that store finished, finally assembled workpieces. The cell may also include tracks  462  along which some of the robots move in the cell. From the home starting location  424  at step S 1400 , the automated guided vehicle  418  controlled by the controller  420  moves the tooling cart first from the home starting location  424  along the transport path  422  and stops at a station  472  at the previously added inner spot welding cell (first cell)  464  at step S 1402 . At step S 1404 , a robot  432  unloads a workpiece  436  from the tooling cart and brings the workpiece into the inner spot welding cell  464 . Once inner spot welding of the workpiece is complete at step S 1406 , the robot loads the workpiece back onto the tooling cart at step S 1408 . Next, the automated guided vehicle bypasses the station  426  at the original inner spot welding cell (second cell)  412  at step S 1409 , and at step S 1418  proceeds to and stops at the stations  438 ,  480  at the original inner remote laser welding cell and the new inner remote laser welding cell (third and fourth cells)  414 ,  476 . At step S 1420 , a robot  432  unloads the workpiece from the tooling cart, at step S 1422  inner remote laser welding is performed on the workpiece in the cells, and at step S 1424  a robot  432  loads the workpiece back onto the tooling cart. At step S 1427 , the automated guided vehicle bypasses the station  444  at the original outer roller flanging and laser welding cell (fifth cell)  416 , and at step S 1438  proceeds along the transport path and stops at a station  474  at the previously added outer roller flanging and laser welding cell (sixth cell)  466 . At step S 1440 , a robot  432  unloads the workpiece from the tooling cart, at step S 1442  roller flanging, laser welding and/or other operations are performed on the workpiece in the cell, and at step S 1444  the finished workpiece is loaded onto one of the storage racks  460 . At step S 1446 , the automated guided vehicle then continues along the transport path  422 , returns to the home location  424 , and begins the process again. 
     Turning to  FIGS. 6 and 11 , when a fifth model (model  5  in  FIG. 6 ) is introduced into the modular production line  510 , new panel fixtures  530  may be added to the existing (added) inner spot welding cell  564  and new panel fixtures  556  may be added to the existing (added) outer roller flanging and laser welding cell  566 . The original inner spot welding cell  512  includes a plurality of turntables  528  each including a plurality of spot welding fixtures  530 . The original inner spot welding cell  512  also includes a plurality of multi-axis robots  532  controlled by a controller  534 . One of the robots loads and unloads workpieces from the tooling cart  518 . Other robots move the workpieces to and from one or more spot welding fixtures  530  and/or perform inner spot welding on the workpieces that are placed in the spot welding fixtures. The added inner spot welding cell  564  includes a plurality of turntables  528  each including a plurality of spot welding fixtures  530 . The added inner spot welding cell  564  also includes a plurality of robots  532  controlled by a controller  568 . One of the robots loads and unloads workpieces from the tooling cart. Other robots move the workpieces to and from one or more spot welding fixtures  530  and/or perform inner spot welding on the workpieces that are placed in the spot welding fixtures. The original remote laser welding cell  514  includes a turntable  528  including a plurality of laser welding fixtures  540 , and a plurality of multi-axis robots  532  controlled by a controller  542 . One of the robots loads and unloads workpieces from the tooling cart, and other robots perform inner remote laser welding on the workpieces that are placed in the laser welding fixtures. The added inner remote laser welding cell  576  includes turntables  528  each including a plurality of laser welding fixtures  540 , and a plurality of robots  532  controlled by a controller  578 . One of the robots loads and unloads workpieces from the tooling cart, other robots perform inner remote laser welding on the workpieces that are placed in the laser welding fixtures, and one of the robots may move workpieces within the cell. The original outer roller flanging and laser welding cell  516  includes a plurality of turntables  528 . One of the turntables is located at an impact beam assembly station  546  at which impact beam assembly is performed, another of the turntables is located at a roller flanging station  548  at which roller flanging is performed, another of the turntables is located at a belt line hemming station  550  at which belt line hemming is performed, and another of the turntables is located at a laser welding station  552  at which laser welding is performed. Each of the stations  546 ,  548 ,  550 ,  552  includes various fixtures  556 . The original outer roller flanging and laser welding cell  516  also includes a plurality of multi-axis robots  532  controlled by a controller  554 . One of the robots loads and unloads workpieces from the tooling cart, and other robots move the workpieces to and from stations in the cell and/or perform the operations (roller flanging, laser welding, and the like) on the workpieces. The original outer roller flanging and laser welding cell  516  further includes outer panel racks  558  that store outer panels to be joined with inner panels, and final assembly racks  560  that store finished, finally assembled workpieces. The cell may also include tracks  562  along which some of the robots  532  move in the cell. The added outer roller flanging and laser welding cell  566  includes a plurality of turntables  528 . One of the turntables is located at an impact beam assembly station  546  at which impact beam assembly is performed, another of the turntables is located at a roller flanging station  548  at which roller flanging is performed, another of the turntables is located at a belt line hemming station  550  at which belt line hemming is performed, and another of the turntables is located at a laser welding station  552  at which laser welding is performed. Each of the stations  546 ,  548 ,  550 ,  552  includes various fixtures  556 . The added outer roller flanging and laser welding cell  566  also includes a plurality of robots  532  controlled by a controller  570 . One of the robots loads and unloads workpieces from the tooling cart, and other robots move the workpieces to and from stations in the cell and/or perform the operations (roller flanging, laser welding, and the like) on the workpieces. The added outer roller flanging and laser welding cell  566  further includes outer panel racks  558  that store outer panels to be joined with the inner panel workpieces, and final assembly racks  560  that store finished, finally assembled workpieces. The cell may also include tracks  562  along which some of the robots move in the cell. From the home starting location  524  at step S 1500 , the automated guided vehicle  518  controlled by the controller  520  moves the tooling cart first from the home starting location along the transport path  522  and at step S 1502  stops at a station  572  at the previously added inner spot welding cell (first cell)  564 . At step S 1504 , a robot  532  unloads a workpiece from the tooling cart and brings the workpiece into the inner spot welding cell  564 . Once inner spot welding of the workpiece is complete at step S 1506 , the robot loads the workpiece back onto the tooling cart at step S 1508 . Next, the automated guided vehicle bypasses the station  526  at the original inner spot welding cell (second cell)  512  at step S 1509 , bypasses the station  538  at the original inner remote laser welding cell (third cell)  514  at step S 1517 , bypasses the station  580  at the previously added inner remote laser welding cell (fourth cell)  576  at step S 1525 , bypasses the station  544  at the original outer roller flanging and laser welding cell (fifth cell)  516  at step S 1527 , and at step S 1538  stops at the station  574  at the previously added outer roller flanging and laser welding cell (sixth cell)  566 . At step S 1540 , a robot  532  unloads the workpiece from the tooling cart, at step S 1542  roller flanging, laser welding and/or other operations are performed on the workpiece in the cell, and at step S 1544  the finished workpiece is loaded onto one of the storage racks  560 . At step S 1546 , the automated guided vehicle then continues along the transport path  522 , returns to the home location  524 , and begins the process again. 
     With reference to  FIG. 12 , a method of manufacturing vehicle body closure panels includes providing a transporter such as an automated guided vehicle on an endless transport path that defines a loop and a controller that controls the transporter along the transport path. The transporter follows the transport path along which a plurality of work cells (for example, a first cell, a second cell, and a third cell) are disposed in a sequence. The work cells may be, for example, an inner spot welding cell, an inner remote laser welding cell, and an outer roller flanging and laser welding cell. The controller causes the workpiece to be moved into and out of selected work cells, and the controller causes the workpiece to be moved past any unselected work cells. Multi-axis robots controlled by the controller move the workpiece into, out of, and within the selected work cells. The transporter begins at a location that is a home position (step S 1600 ), and a workpiece loaded onto a tooling cart that is connected to the transporter. If the first cell is not required for the workpiece (“NO” at step S 1601 ), the transporter bypasses the first cell at step S 1603 . Otherwise, if the first cell is required (“YES” at step S 1601 ), the transporter moves along the transport path to the first cell and makes a stop at the first cell at step S 1602 . A multi-axis robot moves the workpiece from the tooling cart into the first cell at step S 1604 . Operations are then performed on the workpiece, such as, for example, inner spot welding at step S 1606 . When the operations in the first cell are complete, a multi-axis robot removes the workpiece from the first cell and places the workpiece back onto the tooling cart at step S 1608 . Next, if the second cell is not required for the workpiece (“NO” at step S 1611 ), the transporter bypasses the second cell at step S 1609 . Otherwise, if the second cell is required (“YES” at step S 1611 ), the transporter moves to the second cell and makes a stop at the second cell at step S 1610 . A multi-axis robot moves the workpiece from the tooling cart into the second cell at step S 1612 . Operations are then performed on the workpiece, such as, for example, inner remote laser welding at step S 1614 . When the operations in the second cell are complete, a multi-axis robot removes the workpiece from the second cell and places the workpiece back onto the tooling cart at step S 1616 . Next, if the third cell is not required for the workpiece at step S 1619 , the transporter bypasses the third cell (“NO” at step S 1617 ). Otherwise, if the third cell is required (“YES” at step S 1619 ), the transporter moves to the third cell and makes a stop at the third cell at step S 1618 . A multi-axis robot moves the workpiece from the tooling cart into the third cell at step S 1620 . Operations are then performed on the workpiece, such as, for example, outer roller flanging followed by laser welding at step S 1622 . When the operations in the third cell are complete, a multi-axis robot may place the finished workpiece onto a storage rack at step S 1624 . If the third cell was bypassed, the workpiece may be removed from the tooling cart and placed on a storage rack at step S 1629 . After the third cell, the transporter and associated tooling cart may then continue along the transport path back to the home location at step S 1626  and start the process again. 
     Additional work cells may be added along the transport path, and the transporter may selectively transfer workpieces between original and added work cells, by selecting at least some of the work cells and making a stop at the selected work cells, and bypassing any unselected work cells. Additional equipment may also be added to the existing work cells, allowing for additional operations to be performed on a workpiece or for operations to be performed on a variety of different workpieces within the work cells. 
     Although the invention has been described by reference to a specific embodiment, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiment, but that it have the full scope defined by the language of the following claims.