FR2578464A1 - ASSEMBLY INSTALLATION OF VEHICLE BODY PARTS - Google Patents

Abstract

MANUFACTURING OF AUTOMOTIVE PARTS. MOTOR VEHICLE BODY PARTS ASSEMBLY INSTALLATION INCLUDING A CONFORMATION STATION INCLUDING MEANS 64, 71, 68 FOR TILTING THE CHASSIS 25, 25A OF THE TRANSPORT FRAME SO THAT THE PARTS WHICH ARE SUPPORTED BY THE ELASTIC CLAMPS 31 THIS COMES TO COINCIDE WITH DRAWERS 85 OF THE SAID STATION AND TWO MOBILE TROLLEYS 120, 126 PERPENDICULARLY IN THE DIRECTION OF MOVEMENT OF THE TRANSPORT FRAMES 2 AND SUPPORTING EACH OF THE POINT WELDING UNITS 123 IN ORDER TO CARRY OUT IN A SINGLE CYLCLE OF THE CYLCLE. DIFFERENT PARTS CARRIED BY THE TWO CHASSIS 25, 25A.

Description

The present invention relates to an

  for the assembly of different parts of coaches

  serie for the realization of a motor vehicle.

  The invention relates to installations of the type com

  taking mobile transport frames along a determined circuit and intended to receive the parts to form

  part of the bodywork, these frames being then

  mined at a conformation station where the parts are

assembled by spot welding.

  The prior art has known for a long time

  These have been years of installations of this kind, but they have always required a large workforce. Since the appearance of robots, we tried to automate more and more these facilities and the US patent 4,256,947

is aimed at this type of installation.

  This one describes a set including a li-

  along which move frames of trans-

  port, each frame comprising of conformation tools for fixing the parts to be assembled, these being arranged

  so that the outer faces of these pieces, that is,

  say in the example shown, the sides of vehicles are vis-à-vis and there is provided a workstation in which the frame is inserted and which comprises movable doors that press the internal parts of the parts, this post comprising spot resistance welding robots to weld together the different parts

of the bodywork.

  Such an installation has a large number

  disadvantages and can not ensure regular production.

  Indeed, each transport frame includes manual shaping tools for the parts which requires to position in a rigorous manner said parts and the opening and closing of these tools require a

important amount of time.

  Each transport frame is therefore specific to the model of vehicle to be manufactured and a simple modification of the model leads to the manufacture of another

transport frame.

  Movable doors support inside the

  parts which makes it impossible to conform and assemble

  rigorous treatment of said parts. Indeed, in bodywork, it is known that the parts to be assembled must imperatively be applied by their outer surface on a support otherwise there are deformations that make the

unusable parts.

  Finally the station includes robots to realize

  the welding points and we know that these robots are relatively slow, given the complex movements that they must perform and different welding points that are often provided in very different places

  angularly to each other. As a result

  the stopping time of the transport frame at the post is

  very important and such a line can not ensure a

  compatible with the manufacturing requirements in

  automobile industry. To overcome this disadvantage,

  the winder has proposed a line with taps with several stations working simultaneously, but such a solution far from improving the installation complicates, increases the cost and may lead to the manufacture of very different parts so that they can not no longer be mounted. Indeed, we know that whatever the

  care taken in manufacturing, there are always

  lances, and by multiplying the positions one arrives automati-

  a body part with slightly different dimensions compared to each

  those carried out at another post.

  The present invention aims at an installation

  which remedies these various disadvantages.

  The installation according to the invention is of the type comprising a line with different workstations of the mobile transport frames along the line and means for immobilizing each transport frame in front of each work station a forming station and welding by points of the different parts of the bodywork and is characterized in that each transport frame comprises a frame connected to a conveyor and supporting articulated by their upper edge two chassis whose lower edge is guided in the rails, each frame comprising a series of clamps elastic members whose limbs are mounted elastically so as to simply hold the different parts to be assembled, the forming station comprising a fixed structure with two planes supporting a series of bezels arranged so as to extend in the frames between the elastic clamps, the fixed structure being arranged to extend between said chainstays ssis when the transport frame is in the shaping station and each bezel having a bearing surface for supporting a portion of the outer lateral surface of the parts of the bodywork to be assembled and a jack controlling a pressing tool for clamping said piece against the support surface, said conformation station, further comprising means for tilting the frames so that the parts, which are supported by the elastic clamps, coincide with the bezels are taken up and shaped by them; , two mobile carriages perpendicular to the direction of movement of the transport frames and supporting each of the spot welding units to realize in a single cycle the assembly

  different parts carried by the two frames.

  Thanks to such an installation, we win a

  appreciable time, since the loading of

  port does not require any positively precise clamping etc.

  In addition, a single conformation station is sufficient because the shaping time and assembly time is very short

  and it is therefore ensured that all the parts obtained

naked will be identical.

  According to another feature, the line comprises at each end an elevator and a top floor having sidings for storing the transport frames and a station for removing the finished parts from the frames of the transport frames and evacuating them from the vehicle. line. Such an arrangement allows a saving of space

  appreciable and the return of empty transport frames is

fectue at the top.

  Following a detail feature, the line

  has two longitudinal U-section rails in the-

  which are guides of preyus rollers along the lower edge of the frames, each rail comprising at each post

  openings in which are perpendicularly movable

  the rails of the shoes in which the rollers are housed, the shoes being connected to motor means

  to selectively control the approximation and spread

  hooves of a rail and corresponding hooves of

the other rail.

  The invention will now be described in more detail with reference to embodiments

  given by way of example only and

  FIG. 1 is a schematic elevational view of an installation, according to the invention, FIG. 2 is a plan view of the installation of FIG. 1, FIG. 3 is an elevational view of FIG. FIG. 4 is an elevational view, on a larger scale, showing part of a transport frame, FIG. 5 is an elevation view of an elastic clamp, FIG. plan schematically the guide rails of the transport frames, Figure 7 shows in end elevation the conformation station,

  Figures 8, 9, 10 show in different elevation

  Figure 11 and 12 are elevational views which show, respectively, the first, the position of the resilient clips on the transport frame and the second the position of the bevels, on the plane of the conformation station,

  Figure 13 and Figure 14 are schematic views

  showing how a piece held by an elastic gripper is taken up by a bezel, FIG. 15 is a schematic elevational view showing the forming station, the transport frame being shown in the open position, FIG. 16 is an elevational view showing

  the whole of the station of conformation in position

  green, Figure 17 is an elevational view showing the whole of the conformation station in the welding position.

  Figure 18 shows in elevation the unloading station

  Figure 19 shows in elevation, from one side a detail of the unloading station, Figure 20 is a sectional view along the line XX-XX of Figure 18,

  Figure 21 is a plan view showing the

rail position 1.

  Figures 1, 2 and 3 show the layout

  general line of the installation according to the invention.

  Such a line comprises two stages A and B, stage A comprising a rail 1 on which are guided transport frames 2. These frames are provided with a conveyor,

  well known in the industry, and not described here in detail.

  The installation consists of a metal structure

  4 of which one end is provided with an elevator 17 a vertically movable portion 6 supporting a rail section 7 which in the high position of the movable part

  6 coincides with the rail 1, whereas in the posi-

  low section 7 coincides with a rail extending to the lower floor B.

  The installation comprises, at its other end

  Another elevator 8 with a movable part 9 which has a rail section which can coincide in the high position with the rail 1 and in the lower position with the rail, each elevator is controlled from a motor 18

provided on structure 4.

  On the lower floor B, there are two workstations 10 and 11 a conformation station 12 and

  welding stations 13, 14 and 15 provided with robots 16.

  Each transport frame (see Figures 3 and

  4) comprises a rigid metal frame 20 extending horizontally

  zontalement and comprising a member 21 for its suspension to the rail 1 or 5, said frame 20 having along one side

  of the clevises 22 between the wings of which

  tilting on legs 23 tabs 24 integral with a frame 25. Along a second longitudinal side of the frame opposite that provided with yokes 22, there are provided clevises 26 which are traversed by pins 27 on which

  articulated legs 28 integral with a chassis 25a identified

to the frame 25.

  Each frame 25, 25a is formed of profiles, assembled to form a rigid frame whose lower edge is provided with tabs 29 on which rollers 30 are rotated in order to cooperate with rails provided on the floor B. 25, 25a comprises a series of

  elastic tongs 31 which are arranged so as to

  temporarily hold the various constituent parts

  a side or a part of a side of a motor vehicle.

  For example, in the embodiment of FIG. 4, the side of the vehicle comprises a number of parts which are stamped separately and which are placed in the frame 25 or 25a in a position corresponding to their assembly, one can thus predict that a piece 33 corresponding to the bottom of walking, the piece 34 corresponding

  at the foot of the middle, an amount 35 etc. are separate pieces

  trimmed which must be assembled. The elastic grippers 31 thus serve to preposition the various pieces 33, 34 etc. and the workers occupying the positions 10 and 11 place different pieces at the desired locations in them.

  resiliently engaging said tongs 31.

  FIG. 5 shows on a larger scale one of the elastic grippers 31, which comprises a plate 36 fastened to the corresponding edge of the frame 25 and integral with a plate 37 supporting two shafts 40 and 41 on which

  respectively 42 and 43 branches.

  The plate 37 is shaped so as to have a housing 53 intended to receive the external surface of a profile 54 constituting here a windscreen pillar, this housing having two wings 38 each supporting

an adjustable stop 39.

  On the plate 37 are fixed two blocks 48 and

  which support compressive springs 44 and 45

  respectively intended, the first to cooperate with the branch 42 to apply it against the stop 39 and the second to push the branch 43 against the corresponding stop 39. Screws 49 and 51 are provided to adjust the tension of the springs 44 and 45 and a cover plate

  to maintain the branches 42 and 43.

  Such an elastic clamp makes it possible to receive and maintain a workpiece, such as the profile 54, but also allows a relatively easy extraction of the workpiece. In FIG. 5, a resilient clip 31 is shown in detail, but in the following explanations

  such a clamp will be schematically represented to

  to understand the functioning of the installation

  tion. Stage B comprises two rails 60 and 61 which are

  placed on the ground and in which the guaran-

lets 30 chassis 25 and 25a.

  Each rail 60 or 61 is arranged so

  that each frame 25 or 25a extends substantially vertically

  calmly, however, at each station 10 to 15 it is planned

  means for modifying the angular position of the frames

  sis 25-25a. In Figure 6 there is shown a detail of

trant said means.

  At each station 10 to 15 there is provided a motor

  64 which drives through a reducer two cracks

  65 and 66. The rack 65 is integral with a

  bar 67 supporting two shoes 68 inserting in the-

  corresponding vertices 69 of the rail 60.

  The rack 66 supports, at its end

  a bar 70 whose ends comprise two

  bots 71 fitting into openings 72 of rail 61.

  Clogs 68 and 71 affect the same section

  the rails 60 and 61 and are arranged in such a way that

  a frame 25 and 25a is stopped at station 10 the rollers are housed in said shoes. Thus the motor 64 can control, or the spacing of the lower edges

  chassis 25-25a is on the contrary their approximation.

  At station 10 it is the gap which is

  in order to facilitate the positioning of the parts 34, 35, etc. As seen in FIG. 6, each station 11 to 15 is equipped in the same way as the station 10 to make it possible to modify the angular position of the chassis and 25a and for each of these positions,

  same references as those used for this item 10.

  Figures 7, 8, 9 and 10 show the structure

of the conformation station 12.

  This station includes a metal frame de-

  signed, as a whole, by the reference 80 and fixed to the ground, this frame having feet 81 between which is arranged the motor 64, and two inclined planes 82 and 83, the assembly constituting a rigid structure perfectly indeformable.

  Each inclined plane 82 and 83 has a se-

  of bezels 85 which are each intended to receive one or more pieces which are supported by the tongs

  elastic bands 31, to train them definitively and to

  hold together during a first welding operation

by points.

  The various parts 34, 35, 54 etc. are made by stamping and, to allow the stamping tool to be cleared these parts are against undercut. Some parts of these pieces can also stick together. The bezels 85 allow to give the pieces the final shape and to make a rigid assembly

  of these parts during the welding operation.

2578464 -

  Figures 8, 9 and 10 show different types of

weights 85.

  The bezel of Figure 8 comprises a fixed part 86 which has bearing surfaces 87, 88 and 89 on which come to rest, in the embodiment shown here, two stamped parts designated by the references 90 and 91. These pieces can match by

  example in part 34 of Figure 4.

  On the body 86 is fixed the body 92 of a

  pneumatic valve provided with tips 100 and 101 intended to be

  -selectively connected to a source of compressed air for

  der tilting in an active direction (arrow f) of a pressure tool 95 or, on the contrary to clear it. Of course, when one of the tip is connected to the air source

  tablet, the other is in the open air.

  The pressing tool 95 has a first backing surface 96 for clamping a portion of the workpiece 90 against the bearing surface 87, a second backing surface 97 for clamping the middle portion of the workpiece 90 against the surface 88 and finally a spout 98 which maintains applied against each other the

rooms 90 and 91.

  Figure 9 shows another embodiment of

  the bezel 85 for example to receive the foot of medium 34 which is formed of a first U-shaped section 110

closed by a second profile 111.

  The bezel of Figure 9 comprises a body 112 with a bearing housing 113 and a pneumatic cylinder 114 having a pressure tool 115 for clamping the two profiles 110 and 111 against each other against

support housing 113.

  Figure 10 shows a variant of a bezel 85 for supporting, for example, a rear portion of the rear parts of the vehicle body,

  this piece being referenced 117.

  The bezel of Figure 10 includes a body

  118 with a bearing surface 119 for the workpiece 117, a

  Pneumatic rinse 116 provided with a pressing tool 106 to block the workpiece 117 against the bearing surface 119o As can be seen in FIGS. 11 and 12, the elastic pins 31 and the dredges 85 have positions such that when a chassis 25 or 25a is located opposite

  of an inclined plane 82, 83 he can be approached from that

  without the bezels 85 running the risk of

frame or tongs 31.

  As can be seen in Figure 15, when

  transport 2 arrives at the conformation station 15

  it occupies an inclined position corresponding to the posi-

  loading stations 10 and 11 so that

  chassis 25, 25a guided in the rails 60 and 61 can not-

  along the bezels 85. When the frames 25, 25a are located opposite the inclined planes 82, 83 the rollers are arranged in the corresponding shoes 68 and 71, and the support frame 2 is stopped. The motor 64 controls the tilting of the frames 25 and 25a on the axes 23 and 27 in the direction of the arrows g. During this tilting, (see FIGS. 13 and 14), the pieces 33, 34, 35, etc., which are held by the elastic grippers 31, are placed against the bearing surfaces of the bevels (88, 119, 113), then the cylinders (92, 114, 116) are actuated so that the pressure tools (95, 115, 106) press the parts and

  hold them during the welding operation.

  As the elastic clamps 31 just hold the parts without excessive stresses, they do not oppose the conformation and the tightening which is

  85. When welding is effected

  We have a set which has a certain hold and which can pass to the different following positions. After welding

  the pressing tool (95, 115, 106) of the bezel 85 is de-

  25-25a frames 2 are returned to their initial position by the shoes 68 and 71 which are pushed by the racks 65-66 actuated

by the corresponding motor 64.

  FIGS. 16 and 17 show the whole of the shaping station 12. This station comprises a locking system 129 of the transport frame 2 which cooperates with a pin 132 of the frame 20 and which will be described further in

detail in Figures 18 and 19.

  On one side of the frame 80 is provided a carriage 120 supported by rollers 125 rolling on rails 121 and supporting a frame 122 on which are fixed resistance spot welding assemblies 123, these sets 123 being arranged so as to to form soldering points which assemble the different parts

  constituting a side or a part of a side of the vehicle.

  These sets 123 are provided to achieve the weld points in a single cycle. Along a rail 121 is fixed a rack 124 with which cooperates a pinion 105

  driven by an electric motor with a reducer 128.

  There is provided a second carriage 126 disposed on the opposite side with respect to the carriage 120 and which supports

  resistance spot welding assemblies 127 those

  ci being intended to ensure in a single cycle an assembly of the different parts supported by the frame 25a. The carriage 126 is supported by rollers 125a guided on the rails 121a and the assembly is controlled from an electric motor 128a on which is locked a pinion 105a cooperating with a rack 124a. The spacing and the approximation of the carriages 120 and 126 can be controlled

  simultaneously so that the welding sets 123-

127 work simultaneously.

  It will be noted that the trolleys 120 and 126 can

  to be placed in a position very far from the building

  which gives easy access to

  123 and 127 to replace, modify,

  parry or arrange them in different positions for

  the realization of other models of vehicles. We can

  recommend moving the carriages 120 and 126 separately.

  After the welding assemblies 123 and 127 have assembled the parts, the frames 25 and 25a are brought back to the initial position and the transport frame is moved to the station 13 where robots 16 perform a part of the points of rotation. additional welding, then the transport frame 2 is brought to the station 14 or robots 16 still perform various other welding points and finally to the station 15 or other robots 16 establish the final welding points, the sides of the vehicles are then completed and the transport frame 2 arrives in the elevator 8 or it is brought back to the upper stage A. At this stage, there is provided an unloading station 130 with two mainpulers 131. In Figure 18 is shown only the one of the manipulators, the other being identical and arranged symmetrically with respect to a vertical plane passing through the longitudinal axis of the frame 20. At the upper stage A is mounted a blocking system ge 129 of the transport frame 2, such a system being provided in particular at the conformation station 12 and the various positions 10, 11, 13, 14 and 15 to ensure a

  exact situation of transport executives 2 at different

  various posts. This blocking system 129 is carried by

  a metal structure 133 which has, in its su-

  a guide slot 134 formed by two bars and in which a pin 132 engages in the median lower intermediate part of the frame 20, while the rollers 30 are guided in rails 136 provided in said upper stage A. The structure 133 supports a jack 137 whose piston rod 138 is connected to a slide 139 guided in sleeves 140 carried by a plate 141 secured to the structure 133 and whose free end is terminated by a latch 143 formed by a U-shaped piece with divergent wings

to block the pin 132.

  The manipulator 131 comprises a dovetail slide 145 in which is guided a carriage 146 having a thread 147 in which is screwed a screw

  endless 148 driven by a motor 149 with a gearbox.

  The carriage 146 comprises a frame 150 on an axis

  151 of which articulates a first connecting rod 152 whose

  end is articulated on an axis 153 carried by a

  clevis 159 provided at the free end of the rod 154 of the piston

  tone of a cylinder 155 whose body is articulated on an axis 156.

  On axis i53 is articulated one of the extremes

  Tees of a rod 161 whose other end is articulated on an axis 162 carried by a reference 163 articulated on an axis 164 on the frame 150 and connected by an axis 165 to a mobile support 166. The mobile support 166 is also supported by a link 168 articulated at one end on an axis 167 of the frame 150 and at the other end on an axis 169 provided on said movable support. This produces a kind of deformable parallelogram. Mount 150 features

  a stop 170 intended to bear against the edge

  lower side of the vehicle, while the movable support 166 has in the vicinity of its upper end a stop 171 intended to cooperate with the upper edge of the

vehicle side.

  The slide 145 is inclined towards the

rail 136.

  The transport frame 2 to be unloaded arrives opposite the station 130 is locked by the latch 143 which cooperates with the pin 132, then the manipulator 131 is controlled so that the carriage 146 moves in the direction of the transport frame 2 the stop 170 bearing against the lower inner edge of the vehicle side, the cylinder is then controlled in the direction of shortening

  of the rod 154 so that the mobile support 166 is

  raises and that the stop 171 pauses against the inner surface of the upper edge of the vehicle side, it can then be extracted from the resilient clamps 31 which retain it. The engine 149 is then controlled to make

  turn the screw 148 in the direction corresponding to a distance

  transporting the carriage 146 of the transport frame 2 so that the vehicle side is brought to a conveyor 176 where it is taken back and routed to other stations. Of course, the mobile support 166 is returned to its position

  to release the vehicle side when

  that it is hooked to the conveyor 176.

  The conformation station 12 is protected by

  grids 180 for reasons of personnel safety.

  Each station 10, 11, 12, 13, 14 and 15 has

  a blocking system 129 to ensure a

  identical days of chassis 125 and 125a during the works

carried out at different posts.

  The operation of the installation is the following

  efore. A free transport frame 2 is moved to

  the rail 1 so as to be brought to the elevator 17, this last

  Denier down the movable part 6 with said frame 2 which is brought to the first station 10. Workers arranged on either side of this station take parts deposited in bins placed behind them and ask them in order established in chassis 25 and

  25a so that said parts are maintained by the pins

these elastics 31. The station 10 allows to partially fill each frame 25, 25a, the frame of

  transport 2 being during this operation blocked by a device 129 (see Figure 19) while the chassis 25 and 25a, by the shoes 68 and 71

* are inclined to be more accessible to workers.

  The transport frame 2 is then moved to position 11 where workers finish it with stamped parts held by the resilient clamps 31. At this station the frames 25 and 25a are also inclined and the transport frame 2 is positioned by a

locking system 129.

  When the transport frame 2 is completely filled with stamped parts, it is moved to be brought to the shaping station 12, it is stopped in a good position by the locking system 129 and the lower edges of the frames 25 and 25 are brought together. by the shoes 68, 71 (see Figures 16 and 17). During the tilting of the chassis 25-25a the dredgers 85 come to conform the parts and tighten them in the final position then the carriages 120 and 126 are approached in order to place the

  Welding sets 123, 127 in the right positions.

  The various assemblies 123, 127 produce welding points in order to assemble the different parts together, then the carriages 120 and 126 are separated from each other, the frames 25-25a are then brought back by the hooves 68 and 71 in their initial position. To allow this process the bevels 85 are open and the parts, which now form a set since they are assembled by welding, still maintained by the

  elastic tongs 31 are released from said bezels 85.

  The locking system 129 is unlocked and the transport frame 2 is brought to the station 13 o it is wedged by a locking system 129, robots 16 performing the various welding points required to obtain

a perfectly rigid piece.

  Finally, the transport frame goes to stations 14 and 15 where other robots 16 still form points

Welding.

  After these last operations the framework of trans-

  port 2 is brought into the elevator 9 to be returned to the upper floor A o it is routed to the station 130 (see Figures 18, 19 and 20) or the manipulator 131 clears the finished part

and removing it on the conveyor 176.

  The transport frame 2 is then brought to

  the rail 1 in a waiting position for a new pro-

cess.

  Figure 21 shows in plan the layout of the

  This rail may have, in an intermediate part,

  three lanes 181, 182 and 183 which constitute sidings for, for example, three different types of transport frames 2. On the same line one may have to make sides of motor cars with differences, for example a vehicle with a rear hatch, and a

  other vehicle with a trunk. The pieces constitute

  killing these two types of vehicles are therefore slightly different.

  25-25a frames must therefore be arranged with different resilient clamps 31. We can therefore provide on the sidings 181, 182 and 183 transport frames 2 corresponding to different models of

vehicles.

  The transport frame corresponding to a

  may be of a different color from that of a

  model so that postal workers 10 and 11

garnish properly.

  In case the arrangement of the drageoirs

  should be different for each model, on the same

  In my opinion, several stations of conformity could be

  12 each corresponding to a car model to achieve. The installation according to the invention has many advantages. In particular, it makes it possible to appreciably reduce the production time of a bodywork part, for example a car side. It ensures that the parts produced will all be identical because only one conformation station is only

  necessary to make the body part. It allows

  also saves space because it is realized

  on two floors. Finally, it can be easily modified

  quickly and quickly when the vehicle model

duire is changed.

  Of course, the invention is not limited to the embodiments which have just been described and

  represented. Many modifications can be made

  detail without departing from the scope of the invention.

Claims (3)

  1 - Assembly installation of car parts   automobilized vehicles - of the type comprising a   line with different workstations,   port (2) movable along the line and means for securing each transport frame in front of each station   (10, 11, 13, 14, 15), a workstation,   (12) and spot welding the various parts of the bodywork characterized in that each transport frame (2) comprises a frame (20) connected to a conveyor   and supporting, articulated by their upper edge two chas-   sis (25,25a) whose lower edge is guided in the rails (60 and 61), each frame (25, 25a) comprising a series of elastic grippers (31) whose branches are mounted   elastically in order to simply maintain the differences   parts to be assembled, the forming station (12) comprising a fixed structure (80) with two planes supporting a series of bezels (85) arranged to be able to extend in the frames (25, 25a) between the elastic clamps (31), the fixed structure (80) being arranged to extend between said frames (25,25a) when the transport frame (2) is in the shaping station (12) and each bezel (85) having a surface bearing (119) for supporting a portion of the outer side surface of the parts of the bodywork to be assembled and a jack (116) controlling a pressing tool (121) for clamping said workpiece against the bearing surface (119), said shaping station further comprising means (64) (71,68) for tilting the frames (25,25a) so that the pieces which are supported by the elastic grippers (31) coincide with the bevels ( 85) are repeated and conformed by them and two chari moving cells (120,126) perpendicular to the direction of movement of the transport frames (2) and supporting each of the spot welding units (123) in order to achieve in a single cycle the assembly of the different parts carried by the two frames (25,25a).   2 - Assembly installation of car parts   motor vehicle bodies, according to the claim   1, characterized in that the line comprises at each end   an elevator (17,9) and an upper stage (A)   both sidings for storage of transport frames (2) and a station (130) for removing finished parts from frames (25,25a) of transport frames (2) and evacuate them from the line.   3 - Assembly installation of car parts   motor vehicle bodies, according to the claim   1, characterized in that the line comprises two rails   longitudinal sections (60, 61) in U-section in which are guided   rollers (30) provided along the lower edge of   sis (25,25a), each rail (60, 61) having at each pos-   te (10,11,12,13,14,15) openings (69,72) in which   * They are movable perpendicularly to the rails of the shoes (68,71) in which are housed the rollers (30), the shoes (68,71) being connected to motor means (64)   to selectively control the approximation and spread   hooves of a rail and corresponding hooves of the other rail.