GB1564669A

GB1564669A - Car body weldingn assebly system

Info

Publication number: GB1564669A
Application number: GB9877/78A
Authority: GB
Original assignee: WELDESIGN SpA
Current assignee: WELDESIGN SpA
Priority date: 1977-03-14
Filing date: 1978-03-13
Publication date: 1980-04-10
Also published as: IT1082801B; ES467799A1; DE2810822C2; JPS53134747A; SE423979B; DE2810822A1; SE423979C; SE7802854L; DE7807583U1

Description

(54) CAR BODY WELDING ASSEMBLY SYSTEM (71) We, WELDESIGN Societa per Azioni, an Italian Joint Stock Company, of 108 Via Canelli, Turin, ITALY, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the follow instatement: represent invention relates to a car body welding assembly system. In the motor vehicle construction industry most motor vehicles bodies are manually welded on continuous flow carrousel gate lines. Different loosely assembled bodies may be prescheduled to move through the line on pallets or trucks with matching side locating or "framing" gates, manual welding being employed as required for whatever body is moving on the line.

Some body assembly plants employ what are called "framing bucks" which hold all the main components - underbody, sides and top - in proper relation in a single special fixture, with manual welding likewise being employed to accommodate different welding requirements for any particular body. In some cases automatic multiple spot welders are mounted on a framing head with pivoting pillars; however, in such cases the weld locations are fixed for each particular body with no provision for programming the welding heads to perform different welding operations for different bodies.

In one case, for a particular car model having three body styles, programmable robots were provided for respot or finish welding at successive fixed stations. Provision was made for initial framing of the main components at a first "framing" section where trucks carrying the underbody moved continuously along with matching framing side gates for the individual body styles, the welding being performed partially by hand and partially by automatic welding heads which, however, were limited to perform welding at those weld spots which were common for all three body styles; the continuous flow trucks returned to starting position at the end of each weld cycle. Hand welding was employed for any spots which differed for the various body styles.

Automatic welding by robot welding machines programmed for automatic change for the different body styles, then took place in a second, intermittent flow, section after the body geometry had been fixed in the first, continuous flow, carrousel framing station. Following the intermittent flow through the second section provision was made for the trucks to resume continuous flow through a third section where finish respot welding was performed manu ally.

In the case of automatic lines the transfer system is always a rigid system, which requires fixed steps from each welding station to the next one and a predetermined route for the parts with a preset and constant speed of the transfer.

The disadvantage of this known system consists specifically in its rigidity, which makes it extremely difficult and expensive to introduce or eliminate supplementary or intermediate operations, and makes it necessary to rebuild all tooling for the production of a different model of car which must go through the same line.

The present invention seeks to provide an improved system of assembly by welding, which overcomes many of the disadvantages of the above mentioned known systems, as well as their limitations and inconveniences, serving to increase the flexibility, at a reduced cost, of automatically welding different vehicle bodies in random progression on the same line. Moreover the cost of changeover retooling for new body styles can, by employing the present invention, be substantially reduced.

According to the present invention a motor vehicle body welding system adapted to operate on motor vehicle bodies of at least two different types, comprises means for accurately positioning the underbody part of a loosely preassembled motor vehicle body, means for accurately positioning other components of a loosely preassembled body relative to the said underbody part thereof, and means for welding the said other components together and to the said underbody part of said vehicle body while these parts are accurately held in position whereby to fix the geometry of the body, the said means for accurately positioning other components of a loosely preassembled body including interchangeable locator means each shaped to cooperatively engage one of the different types of vehicle body to be welded, the said means for welding the said other components being programmable whereby to perform welding operations at different points on different types of body to be welded.

Preferably the system includes transportable pallets having means for accurately locating an underbody at the framing station. As used herein, the term "framing station" will be understood to refer to a station at which a number of loosely preassembled components are finally adjusted to their exact relative positions by means of automatic locating frames, termed "side gates" provided with a plurality of locators engageable against reference points on the body which is then welded together with at least sufficient welds to hold the components securely and rigidly in position with respect to one another.

The supporting and transferring devices for the pallets can be made either as self-contained locomotive transferring units, or as an incremental transfer line, or as a non-synchronous transfer line.

The framing station is preferably provided with at least two different types of "side gates" each of which is equipped to operate on one type of body different from those for which the other types of side gates are equipped. The side gates may be provided with means for displacing to the operative position the required type of side gate, the other being in a waiting or standby position.

The welding devices of the framing station are preferably welding robots having different programmes chosen each time, by a programmable controller, according to the type of body to be welded.

Thus, the welding system may incorporate intermittent transfer of different bodies to one or more fixed framing stations, and rigid pallets for accurately mounting the underbody, which pallets may be mounted on self-propelled trucks or moved in a shuttle system or by a continuous conveyor with means for disengagement of the pallet drive at the framing station or stations. The side gates provided at a given framing station may be interchangeable with other side gates or otherwise adapted to accommodate different bodies with provision for programmed welding to meet the requirements of each different body by one or more robot welding units. Reciprocable rapidly interchangeable side gates may be provided where required to accommodate the side components of different bodies and a plurality of framing stations may be employed to accommodate as many different bodies as the manufacturer wishes to assemble in a single system.

The system of the present invention differs from any of the aforementioned known prior art systems in a number of important respects. All manual welding can be eliminated and all automatic welding can be performed at fixed welding stations downstream from the framing station or stations thereby avoiding the need for welding heads to move with a continuous flow line. In the preferred embodiment different car bodies can be accommodated at the same framing station by the provision of rapidly interchangeable forming frames having programmable welding units adapted for automatic change to the different welding requirements of each of the different types of motor vehicles body to be accommodated.

Optionally, a given side gate may be equipped with automatically interchangeable locators which may be adapted for different bodies such as the two-door and the fourdoor version of a given model, which are otherwise generally similar in total body configuration. Provision may be made for accommodating different pallets for supporting different underbody parts where required for different bodies and complete flexibility may be achieved in order ultimately to be able to handle any number of different car body models and styles in any mixed order within a single system in which all the welding operations are performed automatically.

Further flexibility, and economy, in changing over to a new model of vehicle is provided by minimizing the special tooling required for locating specific body components in the side gates and on the pallets and this. together with the flexibility of the programmable welding units themselves, drastically reduces the expense of a model changeover.

Thus. the advantages of the invention lie principally in the fact that it provides an automatic motor vehicle body assembly line which is programmable in order to be able to vary the programme simply and automatically according to each type of motor vehicle body to be assembled, which pro vides for varying at any time the proportion of the production rate of one type of motor vehicle body with respect to another type, and which permits retooling for a new type of motor vehicle body in a very short period and with minimized investment costs.

Various embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front view, partially sectioned, of a framing station constructed in accordance with the principles of the present invention; Figure 2 is a schematic longitudinal section taken on the line II - II of Figure 1; Figure 3 is a schematic plan view of a part of a motor vehicle body assembly line employing the system of the present invention; Figure 4 is a schematic side view of a modified assembly line including a different form of framing station from that of Figure 1 and 3; Figure 5 is a plan view of the assembly line shown in Figure 4; Figure 6 is a sectional view taken on the line VI - VI of Figure 5; Figure 7 is a schematic plan view of a further modified assembly line incorporating an alternative embodiment of the invention; Figure 8 is a side view of a part of a side gate equipped with interchangeable locators for two-door and four-door versions of a given model; Figure 9 is a plan view of the side gate illustrated in Figure 8; Figure 10 is a side view on an enlarged scale, of a detail of the side gate shown in Figures 8, 9; and Figure 11 is a detail, on a further enlarged scale, of part of Figure 10.

Referring now to the drawings. there is shown in figures 1 and 2 a framing station 10 adapted to accommodate and weld one or other of two different motor vehicle bodies; for example the two-door and four-door versions of the same model. The framing station 10 includes an input frame 12 at the input end and an output frame 14 at the output end. The upper parts of the two frames 12 and 14 are provided with two rails which extend lengthwise across the station 10. Two longitudinal lateral guides are arranged at the base of the framing station 10 each comprising a plurality of rollers 20 with vertical axes, which guide a selfcontained motorised transfer unit 22 having wheels 24 which are guided and controlled along a route through a motor vehicle body assembly and welding plant by known suitable control means.

A pallet 26 is positioned (by manual or suitable mechanical means) on the transfer unit 22 which can be raised and lowered by means of pneumatic or hydraulic actuators 28. The pallet 26 is provided with locating devices 27 and clamping devices 29 matching the underpart 31 of a motor vehicle body 30 which has been loosely preassembled with the pressed sheet metal elements of which it is made being provisionally connected prior to being clamped on the pallet.

The framing station 10 is provided with four reference sockets 32 for centering respective spherical self-centering projections 34 mounted on the pallet 6.

On each side of the framing station 10 are two side gates 36 on the upper ends 38 of which are mounted rollers 40 which run on rails 16 and permit the side gates 36 to turn about the axes of the rails 16 and to run lengthwise on such rails. The lower ends 42 of the side gates 36 each have two stops 44 which serve to locate reference surfaces 46 of the pallet 26.

As shown in Figure 1 the lower ends 42 of the side gates 36 are located by means of a partially spherical roller 48 in a fork 50 placed on a control lever 52, which can pivot about its lower end as shown by the arrow "L" of Figure 1 whereby to accommodate, by means of the roller 48 and the fork 50, pivoting of the respective side gate 36 about the axis of rail 16.

Each gate of a pair of opposite side gates 36 has clamping devices, one of which is indicated 37 in Figure 1, adapted to engage the preassembled body 30 so as to determine its final geometry. The clamping devices carried by the gates 36 of one of the two pairs of facing side gates differ from those carried by the gates 36 of the other pair so that it is possible to utilize one pair of side gates 36 or the other for welding two different types of loosely preassembled bodies.

The framing station 10 is provided with a number of programmable welding robots 54, each provided with a welding gun 54a for performing spot welding.

The equipment described above operates as follows: before the transfer unit enters the framing station 10 pneumatic or hydraulic actuators 28 raise the pallet 26 on which the loosely preassembled body 30 is clamped. After the unit has entered the framing station 10, the actuators 28 lower the pallet 26 until its spherical centering projections 34 engage the locating sockets 32. At this stage the two side gates 36 which were spaced apart to allow the body 30 to enter between them (as shown in broken outline on the right hand side of Figure 1) close by pivoting about the axes of the rails 16 until their stops 44 abut against the reference surfaces 46 of the pallet 26. As a result of this pivoting movement the side gates 36 clamp the loosely preassembled body 30 to determine its final geometry.

When the body 30 is clamped by the pallet 26 and the two side gates 36 the welding robots 54 start to operate as programmed.

Such robots 54 perform different welding cycles according to the type of body 30 located at the framing station 10 and the choice of the programme is made by a suitable programmable controller or process computer which may control the entire system. At the end of their welding cycle the robots 54 disengage themselves and the side gates 36 are unclamped from the body and swung - outwardly to an open position by means of the arms 52. Subsequently the pallet 26 is lifted up and carried out of framing station 10 by the powered transfer unit 22.

When a body 30 of the alternative type from the one just discussed enters the framing station 10 the control system informs a control unit and this transfers the pair of side gates 36 as soon as its working cycle is completed, replacing it with the other pair of side gates which are suitable for the new body 36, which gates were previously in a standby position.

Figure 3 illustrates schematically a part of a welding plant which uses the equipment described with reference to Figures 1 and 2.

An automatic store 56 controlled by suitable means (not shown) houses a plurality of pallets 26 which are provided with means for engaging a plurality of lower reference points with which the vehicle bodies are provided, whereby to rigidly and accurately locate the lower part of a motor vehicle body under construction. Before entering into an adjacent loading station 58 each transfer unit 22 passes in front of the automatic store 56 where it receives a pallet equipped to support the type of body which is about to arrive, loosely assembled, at the loading station.

The bodies are loosely preassembled in an assembly area (not shown in the drawing) and then pass on to the loading station 58, transfer being effected by means of a suitable overhead conveyor (also not shown).

The bodies are then loaded onto the pallet by a downstroke lift. Once the transfer has been effected the bodies are disengaged from the lift and automatically clamped to the pallet by suitable known means. The bodies are clamped on the pallet in registration with the above mentioned lower reference points and are then transferred bv the powered transfer units along paths indicated schematically by the arrows A and B of Figure 3, to one of two framing stations, the first of which is indicated in Figure 3 with the reference numeral 60. The arrow B of Figure 3 leads to a second framing station, not illustrated, in parallel with the station 60: further such parallel framing stations may be provided if the flow rate of car bodies demands it. In this latter case a selection may be made by a suitable control ysstem which identifies the framing station corresponding to the loosely assembled body to be welded. Where more than one identical framing station is employed to meet production requirements, the control system may also identify either a free station or the one which is closest to the completion of its work cycle for the conveyor to direct the next loosely assembled body towards.

The welding operation is then performed at station 60, and this determines the final geometry of the finished body as previously described. The body, thus geometrically defined and welded in a fixed geometrical configuration, is then transferred to a series of subsequent welding stations 62, 64, 66 etc., the number of which may be more or less in accordance with the required flexibility of the system. At these subsidiary welding stations completion welding is preformed in order to give the body its required mechanical strength.

In the modified embodiment shown in Figure 4 to 6 two different types of bodies respectively indicated 30a and 30b carried on correspondingly equipped pallets indicated 26a and 26b pass through a framing and welding station 110 by means of an incremental transfer line generally indicated 122 onto which the bodies 30a, 30b previously loaded onto pallets 26a, 26b, are loaded by means of a lift 74. The framing and welding station 110 is provided, like station 10 described with references to Figures 1 and 2, with two pairs of side gates 36a and 36b running lengthwise on rails 16 and able to swing over a limited arc about the axes of these rails. The side gates 36a are likewise provided with locators and clamps (not shown) to give bodies 30a carried by pallets 26a their final geometric form before they are welded by robots 54, while the side gates 36b are similarly equipped to operate in an anlogous way on the bodies 36b carried on the pallets 26b.

In the example shown, a body 30a carried by a pallet 26a is clamped between side gates 36a and a pair of side gates 36b is in a standby position.

Loading of the bodies onto the pallets is performed at a loading station 68 which includes two vertical mechanized pallet stores 70a and 70b, one on each side of the transfer line 122. Each store is provided with a store transfer means schematically indicated 72, to feed a pallet selected by a programmable controller (not shown) to a conveyor 74 which brings it to a position where the corresponding loosely preassembled body is loaded onto it. The assembly comprising the pallet and body is then inserted onto the assembly line 122 by the lift 75.

At the exit from the welding station 110 the pallets are separated from their respective bodies which have now acquired a stable configuration, and by means of a downstroke lift 76 and an underneath return line 122a are transferred to the base of the lift 74 to be reinserted into their respective stores 70a and 70b at the loading station 68.

Figure 7 shows schematically an alternative modification to the previously described equipment, for applymg the side gates against the loosely preassembled bodies supported by relevant pallets, and for automatically interchanging such pairs of side gates according to the type of body at the welding station. This modified arrangement may be used either in a system in which the pallets are moved by means of selfcontained transfer units, such as is shown in Figure 1 to 3, or in a system in which the pallets are moved by means of an incremental transfer line such as that shown in Figures 4 to 6.

In Figure 7 there is shown a framing station 210, provided with welding robots 54 at which two types of bodies 36a and 36b may be accepted, these being conveyed by an incremental transfer line 122. A circulating device for the side gates 30a and 30b is arranged on each side of the framing station 210. Each circuit includes an incremental forward displacement branch 78 along which the side gates travel lengthwise parallel to the bodies, their displacement being synchronized with the pallet motion; a fast return branch 80 along which the side gates also travel lengthwise; a transverse branch 82, in advance of the framing station, which moves the chosen side gates into an operating position adjacent the pallet carrying the relevant loosely preassembled body; and a transverse branch 84 downstream from the welding station for transferring the side gates from the end of the forward displacement branch across to the fast return branch.

Two stores 86 feed the two return branches 80 of the two circuits with the required pairs of side gates 36a or 36b by means of suitable transfer units 88 which are also used to draw back into the respective stores 86 the side gates arriving on the downstream transverse branch 84 unless they are to be immediately reused in which case they are fed straight back along to return branch 80.

Referring now to Figures 8 and 9 there is shown the outline 30 of a two-door version of a motor car body with, in broken outline, the four-door version of the same model.

The part of the outline common to the two car bodies is indicated generally 300; the part of the outline belonging solely to the two-door version of the car body is indicated 300a, and the broken outline, representing the art of the outline belonging solely to the four-door version of the car body is indicated 300b.

One of two side gates 136 with which a welding station is provided is shown in position against the motor car body. This side gate 136 carries a plurality of locator units, indicated schematically in Figures 8 and 9, suitable for engaging the preassembled car body at a number of reference points, in such a way as to confer its definitive geometry on it.

The locator units are of three different types; the first type 370 is provided with reference elements suitable for engaging Parts 300 of the motor car body common to both versions of the model, a second type 370a provided with reference elements suitable for operating only on parts 300a of the motor car body belonging to the door-door version of the model and a third type 370b provided with reference elements suitable for operating only on parts 300b of the motor car body belonging to the four-door version. The locator units 370 of the first type thus engage the reference points on that part of the car body indicated with the reference 300 both in the case of the two-door version and in the case of the four-door version of the model.

In correspondence with each reference point on a part 300a of the car body belonging solely to a two-door model, or to a part 300b of the car body belonging solely to a four-door model the side gate is provided with one or other of two further types of locator units 370a, 370b as appropriate, the locator units of the second type 370a being intended to operate only when there is located in the welding station a preassembled car body of the two-door type, and the locator unit 370b of the third type being intended to operate only when there is in the welding station a preassembled motor car body having four doors.

As is illustrated in detal in Figure 10, on a support element 406 carried by the side gate 136 are pivoted, for turning movement about an axis 407, a locator unit 370a of the second type indicated in the operative position. and a locator unit 370b of the third type indicated in the inoperative position.

The pair of locator units 370a and 370b operate on a reference point indicated A in Figure 11.

The displacement of the two locator units 370a, 37019 between their operative and inoperative position is effected by means of two pneumatic or hydraulic cylinders 412, 413 which are supported in a pivotable manner about an axis 420 on the support element 406. The piston rod 408 of the cylinder 412 is pivoted to the locator unit 37()a by a pivoted coupling 410, and the piston rod 409 of the cylinder 413 is pivoted to the locator unit 370b by a pivoted coupling 411.

The locator unit 370a carried one fixed reference element 418 and two movable referance elements 416, 417, which latter are turnable about respective axes 419 and 421. The rotation of the movable reference elements 416, 417 is controlled via a transmission of a known type (not shown in the Figures) by respective actuators 414, 415, the fixed part of which is rigidly connected to the locator unit 370a.

Likewise, the locator unit 370b carries a fixed reference element 426 and two movable reference elements 424, 425 turnable respectively about two axes 427, 428 the rotation of which is controlled by two actuators 422, 423, the fixed parts of which are rigidly connected to the locator unit 370b.

As can be seen in Figure 4, at the point on the car body on which the locator unit 370a operates there are assembled three metal elements 434, 435 and 436 against which engage the abutment surfaces 431, 433 and 432 of the three reference elements 417,416 and 418.

If a car body arriving at the framing station is of the type having two doors, the actuators 412 and 413 maintain the locator unit 370a in its operative position and the locator unit 370b in its inoperative position.

After the preassembled car body has entered into the framing station the side gates are brought close to it as described above to engage the various reference points and confer onto it its definitive geometry. In particular, at the reference point A, by operation of the actuators 414 and 415, the abutment surfaces 431 and 433 of the movable reference elements 416 and 417 are carried into engagement, with the metal elements 434 and 435 thus locking them and the abutment surface 432 of the fixed reference element 418 firmly together in their definitive positions.

After welding, the actuators 414 and 415 control the rotation of the movable reference elements 416 and 417 to disengage them from the metal elements 434, 435, 436 and the corresponding other reference elements of the other locking units (not shown) of the side gate under consideration are also disengaged, whereupon the side gate is then displaced laterally away from the car body.

Similar operations are accomplished by means of the locator unit 370b on a car body having four doors. In this case the actuator 412 is retracted to bring the locator unit 370a to its inoperative position and the actuator 413 is extended to bring the locator unit 370b to its operative position.

WHAT WE CLAIM lS: 1. A motor vehicle body welding system adapted to operate on motor vehicle bodies of at least two different types, comprising means for accurately positioning the underbody part of a loosely preassembled motor vehicle body, means for accurately positioning other components of a loosely preassembled body relative to the said underbody part thereof, and means for welding the said other components together and to the said underbody part of said vehicle body while these parts are accurately held in position whereby to fix the geometry of the body, the said means for accurately positioning other components of a loosely preassembled body including interchangeable locator means each shaped to cooperatively engage one of the different types of vehicle body to be welded, the said means for welding the said other components being programmable whereby to perform welding operations at different points on different types of body to be welded.

2. A motor vehicle body welding system as claimed in Claim 1, in which the means for accurately locating a motor vehicle underbody part comprise transportable pallets, different pallets being shaped to accommodate different underbody parts.

3. A motor vehicle body welding system as claimed in Claim 1 or Claim 2, in which the means for accurately positioning the other components of a loosely preassembled body including interchangeable side gates at a framing station, each side gate having means for accurately positioning the said other components of a selected body type.

4. A motor vehicle body welding system as claimed in Claim 3, in which the interchangeable side gates carry respective locator means adapted to engage laterally against components of an associated body type.

5. A motor vehicle body welding system as claimed in Claim 3 or Claim 4, in which there are further provided means for displacing different side gates into or away from an operative position at the framing station.

6. A motor vehicle body welding system as claimed in any of Claims 1 to 5, in which the said welding means are programmable robots having welding heads adapted to weld a plurality of spots whereby to join the said other components and the said underbody part of a motor vehicle body at

Claims

**WARNING** start of CLMS field may overlap end of DESC **. to the locator unit 370b by a pivoted coupling 411. The locator unit 370a carried one fixed reference element 418 and two movable referance elements 416, 417, which latter are turnable about respective axes 419 and 421. The rotation of the movable reference elements 416, 417 is controlled via a transmission of a known type (not shown in the Figures) by respective actuators 414, 415, the fixed part of which is rigidly connected to the locator unit 370a. Likewise, the locator unit 370b carries a fixed reference element 426 and two movable reference elements 424, 425 turnable respectively about two axes 427, 428 the rotation of which is controlled by two actuators 422, 423, the fixed parts of which are rigidly connected to the locator unit 370b. As can be seen in Figure 4, at the point on the car body on which the locator unit 370a operates there are assembled three metal elements 434, 435 and 436 against which engage the abutment surfaces 431, 433 and 432 of the three reference elements 417,416 and 418. If a car body arriving at the framing station is of the type having two doors, the actuators 412 and 413 maintain the locator unit 370a in its operative position and the locator unit 370b in its inoperative position. After the preassembled car body has entered into the framing station the side gates are brought close to it as described above to engage the various reference points and confer onto it its definitive geometry. In particular, at the reference point A, by operation of the actuators 414 and 415, the abutment surfaces 431 and 433 of the movable reference elements 416 and 417 are carried into engagement, with the metal elements 434 and 435 thus locking them and the abutment surface 432 of the fixed reference element 418 firmly together in their definitive positions. After welding, the actuators 414 and 415 control the rotation of the movable reference elements 416 and 417 to disengage them from the metal elements 434, 435, 436 and the corresponding other reference elements of the other locking units (not shown) of the side gate under consideration are also disengaged, whereupon the side gate is then displaced laterally away from the car body. Similar operations are accomplished by means of the locator unit 370b on a car body having four doors. In this case the actuator 412 is retracted to bring the locator unit 370a to its inoperative position and the actuator 413 is extended to bring the locator unit 370b to its operative position. WHAT WE CLAIM lS:

1. A motor vehicle body welding system adapted to operate on motor vehicle bodies of at least two different types, comprising means for accurately positioning the underbody part of a loosely preassembled motor vehicle body, means for accurately positioning other components of a loosely preassembled body relative to the said underbody part thereof, and means for welding the said other components together and to the said underbody part of said vehicle body while these parts are accurately held in position whereby to fix the geometry of the body, the said means for accurately positioning other components of a loosely preassembled body including interchangeable locator means each shaped to cooperatively engage one of the different types of vehicle body to be welded, the said means for welding the said other components being programmable whereby to perform welding operations at different points on different types of body to be welded.

6. A motor vehicle body welding system as claimed in any of Claims 1 to 5, in which the said welding means are programmable robots having welding heads adapted to weld a plurality of spots whereby to join the said other components and the said underbody part of a motor vehicle body at the framing station.

7. A motor vehicle body welding system as claimed in Claim 1, in which there are further provided a plurality of welding stations having further welding means for completing additional spot welds, after the geometry of said body has been fixed by welding at the framing station.

8. A motor vehicle body welding system as claimed in any of Claims 3 to 7, in which the side gates comprise a main structure

which is common to different bodies and different locator units adapting each side gate to a particular body.

9. A motor vehicle body welding system as claimed in Claim 8, in which each side gate is provided with different locators thereon adapted for different bodies, said side gate also carrying other locators having a common position for said different bodies.

10. A motor vehicle body welding system as claimed in Claim 8 or Claim 9, in which the locators adapted for different bodies are selectively movable between operative and inoperative positions whereby to adapt the side gate for different bodies.

11. A motor vehicle body welding system as claimed in any of Claims 2 to 10, in which there are provided means for storing different pallets for different underbodies near a body loading station of the system in advance of the framing station, and means for introducing into the loading station a suitable pallet for each different underbody to arrive at the loading station.

12. A motor vehicle body welding system as claimed in any of Claims 2 to 11, in which there are provided conveyor means for transporting the pallets to and from the framing staton.

13. A motor vehicle body welding system as claimed in any of Claims 2 to 11, in which there are provided self-propelled support means for transporting the pallets to and from the framing station.

14. A motor vehicle body welding system as claimed in Claim 12, in which the conveyor means for transporting the pallets to and from the framing station comprise an incremental conveyor.

15. A motor vehicle body welding system as claimed in any of Claims 3 to 14, in which there are provided means for storing different side gates for different motor vehicle bodies to be welded by the system, means for transporting different side gates to the framing station in accordance with the requirements of different motor vehicle bodies, and means for returning the side gates to storage upon completion of welding at the framing station.

16. A motor vehicle body welding system as claimed in any of Claims 3 to 15, in which the side gates are turnable about an upper axis between an inclined open position to permit introduction between them of a loosely preassembled body carried by a pallet and a substantially vertical position in which the locator means on the side gates clamp the body in its proper configuration for welding.

17. A motor vehicle body welding system as claimed in Claim 16. in which the side gates are supported on rails whereby the side gates can be displaced between a standby position and an operative position, the rails also serving as the fulcrum for the said turning movement of the side gate in the operative position.

18. A motor vehicle body welding system substantially as hereinbefore described with reference to, and as illustrated in, any one of the embodiments shown in the accompanying drawings.