Assembly line for producing a steel coffer from sheet metal plate

The assembly line for producing a steel coffer (2) for ceiling and/or wall structures, in particular for interior finishing and construction of ships, for transportable and movable buildings, for sheds, hotels and the like, from a sheet metal plate (1) comprises a cutting and/or stamping station (3), a bending press (4) with an associated manipulator (5) and an associated roller-ball table (6) and a welding station (7), as well as at least one trolley (8) in the form of an underfloor vehicle, an underfloor trolley, or the like, which can move back and forth under these stations (3, 5, 7). The bending press (4) is combined with a manipulator (5) designed as a semi-portal crane, which is movable with respect to this press (4) and has a gripper which is also movable, adjustable in height and rotatable around the height axis, by means of which the sheet metal plate (1) is fed in its required positions to the bending press (4). The bending press (4) has a hold-down device which can be swiveled to compensate various sheet metal thicknesses.

The invention relates to an assembly line (installation) by means of which 
it is intended to produce steel coffers as finished components for 
ceilings and/or wall structures at a plurality of stations in a continuous 
run. 
A large number of steel coffers is required as wall elements and bearing 
floors in the course of erecting large buildings, as well as for interior 
finishing and construction of buildings and ships, which coffers consist 
of multiply beveled steel sheets of a large length and width, which are to 
be provided with trough-openings and fastening holes and are to have 
welded-on reinforcing sections. 
In actuality, this coffer production is performed elaborately by means of a 
plurality of machines, and the known bending presses are not designed for 
beveling long sheets, so that the steel coffers are of only small 
dimensions and therefore their number used is increased and the total 
construction is made more expensive.

It is the object of the invention to develop an assembly line, by means of 
which it is possible to produce a steel coffer incorporating all required 
structural characteristics for later use, having a large surface and made 
of various sheet metal thicknesses from a sheet metal plate in the course 
of an automatic run-through and at manipulable processing positions with 
short clock times in an efficient and economical manner. 
This object is attained in accordance with the invention by the 
characterizing features of claim 1; the subsequent dependent claims 2 to 6 
contain advantageous further developments of the embodiment of the 
assembly line. 
It is a further object of the invention to provide a bending press for 
beveling of long sheet metal plates of different sheet metal thicknesses 
at an even bending pressure and large bending angles, which can be 
integrated into the assembly line as a long multi-component. 
This object is attained by the characteristic of claim 7 and the subsequent 
claims 8 to 13 containing advantageous further developments. 
A further object is considered to be the provision of a manipulator 
cooperating with the bending press, which introduces the sheet metal plate 
into the bending press and removes it therefrom and has many free degrees 
of movement. 
This object is attained by means of claims 14 to 16. 
One concept of the invention is seen to lie in the entire assembly line, a 
second, independent concept of the invention lies in the special 
characteristics of the bending press, and a third concept of the invention 
lies in the combination of the bending press with the specially designed 
and operating manipulator. 
By means of the assembly line of the invention it is possible to produce in 
an efficient and economical manner large numbers of steel coffers within 
short clock times (clock time 17 min.), which have all structural 
characteristics required for later use and a large-surface design. 
The bending installation is one of several stations of the assembly line 
and comprises three bending presses which can be coupled, an underfloor 
trolley (bogey truck), a manipulator and a roller-ball table. 
The bending presses, having individual lengths of 4 m and operating in 
accordance with the bending process, are individually controlled but 
designed in such a way that they can simultaneously work on the workpiece 
(sheet metal plate) without gaps in the manner of a battery of two or 
three presses. 
The manipulator is embodied as a movable semi-wall crane, has a movable 
gripping and rotating device for the sheet metal plate and positions it in 
the bending press without the need for stops. Manipulation of the sheet 
metal plate takes place in one processing plane. The sheet metal piece or 
coffer is supported on the roller-ball table. The manipulator here needs 
only to overcome inertia and frictional resistance. 
The job of the underfloor trolley, which can be moved along the X axis in 
an elongated gap of the roller-ball table, is to convey the sheet metal 
piece always into the same position and to hand it over to the 
manipulator, as well as to take over an already bent coffer in the same 
position and to convey it on to the next station. 
The bending press (one or a plurality of coupled bending presses) has been 
optimized for bending sheet steel of approximately 4 to approximately 6 mm 
and with a breaking resistance of 400 N/mm.sup.2. 
The bending power of the press is 850 kN. The press can be put under a load 
of 1200 kN for short periods of time, in which case it can also be 
supplied with a more powerful oscillating motor. 
It is possible to assign each one of the three bending presses separate 
individual press tables, or a common press table of 12 m length. 
The bending press has a large pivot and work range of 600 mm with a free 
through-opening of the same size. To process a workpiece of a length of 12 
m, shorter and at the same time stable press units are used in the battery 
of three presses. 
Each press is mainly made of parts which are screwed together. 
The rigid C-frame of the bending press is embodied as a welded structure 
and the total processing of the C-frame takes place in one chucking. The 
screwing surfaces for guides, oscillating motors and bearings are milled 
and turned. 
The drive for the bending cheek is performed by two lateral double toothed 
quadrants. A hydraulic oscillating motor drives a torsion shaft in the 
center, on the ends of which pinion gears are fastened to the left and 
right of the C-frame. 
The bending press is designed for 90.degree. bending. The size of the 
bending cheek and the bending drive make pivoting around an angle of 
120.degree. possible. The bending cheek is guided in each C-frame via many 
support rollers with spherical running surfaces and guide rollers with 
eccentrics. For improved load distribution, the support rollers with their 
fixable eccentric shafts are appropriately resilient. Spherical running 
surfaces prevent loads on the edges of the rollers. The guide rollers are 
also resiliently mounted. They are mounted at a short distance from the 
guide rail, so that they are not subjected to the deformation forces of 
the C-frame. 
The bending forces are guided via the cheek and the bending cheek body as 
far as the support rollers. 
The C-frame has a bearing above this roller guide for the bending cheek, in 
which an eccentric shaft is supported. The eccentric disks are 
double-seated in the eccentric eye of the connecting flange. 
A blocking cylinder eye has been attached on the upper part of the flange. 
Each one of the eye flanges is screwed together with the hold-down device. 
On one side of the center eccentric eye, the shaft can be driven by a 
hydraulic oscillating motor via a toothed reduction gear. A pivot lever is 
fastened on the eccentric shaft on the other side of the center eccentric 
eye. The hold-down device is pivoted away in a controlled manner by the 
oscillating motor by means of a pivot lever. In the course of this, the 
oscillating motor must be assisted by the blocking cylinders. 
The deformation forces of the hold-down device and the C-frame are not 
transmitted to the bearings. 
The oscillating motor is screwed to the C-frame by means of the flange. 
When bending narrow sheet metal plates, the manipulator is located in the 
vicinity of the hold-down device. The hold-down device then does not pivot 
away freely. In this case pivoting must take place controlled and coupled 
with the corresponding displacement of the manipulator. This control is 
performed by the oscillating motor via the rotation transmitter. The 
oscillating motor, together with the blocking cylinder causes the pivoting 
of the hold-down device. 
First, the oscillating motor generates the hold-down force (the force 
between the table and the hold-down device) via the eccentric. In the 
course of bending, it is reduced to a defined residual clamping force. 
During bending the oscillating motor is under oil pressure. 
The blocking cylinder is automatically locked on the piston side as soon as 
it has moved into the end position. 
It remains locked until the hold-down device is pivoted away. The blocking 
cylinder has such dimensions that it can take up the hold-down reaction 
forces as well as the bending reaction forces. 
The blocking cylinder with the eye flange, the hold-down device and the 
eccentric shaft with the bearings together form a coupling mechanism which 
is driven by the eccentric shaft. The position of the eccentric has been 
set in such a way that an optimal setting of the foot of the hold-down 
device is possible for various sheet metal thicknesses. The size of the 
eccentric of approximately 12 mm has been set in consideration of the 
necessary lift of approximately 15 mm of the hold-down device. Lifting 
makes the displacement, free of sliding, of the workpiece possible for 
follow-up bending. 
A support surface for the guide rail carrier has been welded on above the 
blocking cylinder bearing on all C-frames of the bending machine formed by 
the bending presses. A surface for screwing on a guide rail carrier has 
also been formed at the bottom on the rear part of the C-frame. These 
surfaces allow the simultaneous connection of the three bending presses 
with the manipulator within the tolerances of processing exactness, which 
is of extraordinary importance for producing the coffers. The bending 
machine together with the manipulator constitutes a functional unit. 
The job of the manipulator is to take over the sheet metal plate from the 
previous station, to service the bending press and to transfer the formed 
sheet metal plate for further processing, for example for inserting and 
welding transverse bows, trapezoidal sections, etc. 
Manipulation of the sheet metal piece takes place in one processing plane. 
The sheet metal piece or coffer is supported on the roller-ball table. In 
the bending station, the workpiece is fed to the bending machine by the 
portal crane in the correct position. It is never lifted off the 
roller-ball table. The sheet metal piece is merely received by clamping 
cheeks of the manipulator via two retaining bolts welded to the sheet 
metal piece. These bolts are parallel to the X axis and are therefore in 
fixed connection with the coordinate system. 
The sheet metal plate is cut and provided with holes in the laser station. 
It is transferred along the X axis to the manipulator exactly in the 
center of the roller-ball table by an underfloor trolley in the center of 
the transfer line. The retaining bolts are hollow. 
Thus, the sheet metal piece is always moved into the same transfer 
position. Positioning of the manipulator can be selected to remain within 
rough limits, because the clamping cheeks (clamping chucks) have 
sufficiently large openings. For this reason the trolley guidance in this 
station can be selected to be relatively simple. 
The construction of the crane and the manipulator and the selection of the 
guide elements make possible highly exact positioning, so that the 
tolerance range and the assembly techniques are sufficient and no 
positioning stops are needed on the roller-ball table and the bending 
machine. 
The sheet metal processing technique in the preceding stations has been 
simplified and made less expensive because of the design without stops. 
The manipulator is embodied in welded full-box construction as a 
semi-portal crane with a support column. This design allows a light 
construction. 
An exemplary embodiment of the invention is shown in the drawings, shown is 
in: 
FIG. 1, a top view of an assembly line for steel coffers, consisting of a 
cutting and/or stamping station, a bending press with a manipulator and a 
roller-ball table, and a welding station, 
FIG. 2, a lateral view of the bending press with manipulator, 
FIG. 3, a top view of the bending press with manipulator, 
FIG. 4, a back view of the bending press with manipulator, 
FIG. 5, a lateral view of the bending press with the hold-down device 
pivoted downward into the clamping position (solid lines) and in the 
lifted position of the hold-down device in dash-dotted lines, 
FIG. 6, a lateral view of the bending press with the hold-down device 
pivoted up. 
The assembly line for producing a steel coffer (2) for ceiling and/or wall 
structures, in particular for interior finishing and construction of 
ships, for transportable and movable buildings, for sheds, hotels and the 
like, from a sheet metal plate (1) comprises a cutting and/or stamping 
station (3), a bending press (4) with an associated manipulator (5) and an 
associated roller-ball table (6) and a welding station (7), as well as at 
least one trolley (8) in the form of an underfloor vehicle, an underfloor 
trolley, or the like, which can move back and forth under these stations 
(3, 5, 7). 
A pre-treatment station (9) is disposed upstream of the cutting and/or 
stamping station (3), and a roller conveyor (10) is connected to the 
welding station (7). All stations (9, 3, 4, 2 and 10) are disposed behind 
each other in the pass-through direction (A) of the sheet metal plate (1) 
and result in a straight work run. 
Notches (1a), openings (1b) and reamed holes (1c)--see FIG. 1--are cut into 
the sheet metal plate (1) at the cutting and/or stamping station (3). 
The circumferential edge of the sheet metal plate (1) is formed into a 
singly-- or multiply-beveled edge (1d)--see FIG. 1 in steps in the bending 
press (4), wherein the roller-ball table (6) is used as the support for 
the sheet metal plate (1) and the manipulator (5) grasps the sheet metal 
plate (1) at its fitting marks (1c), formed by the reamed holes (1c) 
and/or retaining bolts provided therein, and inserts it for the individual 
forming steps into the bending press (4) and takes it out of it again; in 
the process the sheet metal plate (1) continues to lie on the roller-ball 
table (6) and only its position is changed (displacement or turning) in 
this support plane. 
Reinforcement sections (2a) are placed in the formed sheet metal plate (1) 
in the welding station (7) at distances to form a grid and are cyclically 
welded--see FIG. 1--, after which the steel coffer (2) is finished and is 
transported out of the assembly line by the roller conveyor (10). 
It is preferred to dispose two trolleys (8), which can be moved on a 
continuous guide (11), under the stations (9, 3, 4, 6, 7 and 10), wherein 
the first trolley (8) operates on a movement path (FW1) starting at the 
pre-treatment station (9) and extending to the center of the roller-ball 
table (6), and thus the bending press (4), while the movement path (FW2) 
of the second trolley (8) extends from the center of the roller-ball table 
(6) into the area of the roller conveyor (10). 
The trolleys (8) move the sheet metal plate (1) into the individual 
stations (3, 6, 7, 10) and stop there for processing of the sheet metal 
plate, or move on in steps. 
The cutting and/or stamping station (3) has two carriages (13), which can 
move back and forth in the longitudinal direction (A) of the sheet metal 
plate on guides (12) in a limited work area and respectively have two or a 
plurality of tools, preferably plasma/laser cutter heads, stamping or 
drilling tools, and guide rollers (15) are associated with these carriages 
(13) for stops for the sheet metal plate in the longitudinal direction and 
retractable stops (16) for the transverse stop of the sheet metal plate, 
as well as collet chucks (17) for locking in the aligned sheet metal plate 
(1) (FIG. 1). 
The roller-ball table (6) is constituted by a table (6a) of large surface, 
which adjoins the receiving side of the bending press (4), extends 
transversely to the run-through direction (A) of the sheet metal plate 
across the width of the adjoining stations (3, 7), takes up at least the 
length of the bending press (4) and has a plurality of spheres (6b) 
rotatably seated in it. 
The welding station (7) has a welding apparatus (18) containing a plurality 
of welding heads (19), to which a feed device (20) is assigned, which 
places the reinforcement sections (2a) into the pre-formed sheet metal 
plate (1) in an aligned manner; both devices (18, 20) are adjustably 
seated on guides (21) in the run-through direction (A) of the sheet metal 
plate and are brought into their work positions in synchronicity with the 
sheet metal plate (1) which is cyclically transported by the trolley (8). 
The pre-treatment station (9) upstream of the cutting and/or stamping 
station (3) is used to preform sheet metal plates (1), welding sheet metal 
plates (1) together into a large-surface sheet metal plate (1), for 
sandblasting, or the like. 
As can be seen from FIGS. 2, 5 and 6, the bending press (4) has a press 
table (23) fixed in a C-frame (22), a hold-down device (24) movable in 
height and a bending cheek (27) which is pivotable in height in a guide 
(26) around the horizontal bevel shaft (bending shaft) (25). 
The hold-down device (24) is seated in the C-frame (22) with a horizontal 
eccentric drive (28), pivotable in height by means of a hydraulic 
oscillating motor (29) and a blocking cylinder (30) which is actuated by a 
pressure medium. 
By means of its eccentric drive (28), the hold-down device (24) can be 
adjusted with a small pivot stroke (H) in its pivoted-down clamping 
position (solid lines in FIG. 5 and dash-dotted lines in FIG. 6), in which 
it cooperates with the press table (23), and independently of pivot and 
blocking cylinders (30) which lock it in this clamping position, with 
bending pressure for various thicknesses (S) of sheet metal plates, and 
can be lifted (dash-dotted lines in FIG. 5) to release the sheet metal 
plate (1), and the hold-down device (24) is pivoted up into the open press 
position (solid lines in FIG. 6) by means of its eccentric drive (28) and 
the released pivot and blocking cylinder (30). 
The eccentric drive (28) has an eccentric shaft (31) rotatably seated in 
the C-frame (22), on which a gear wheel (33), driven by a gear wheel (32) 
of the hydraulic oscillating motor (29) flanged on the C-frame (22), and 
an eccentric (34) with a rotary disk (35) and a driver (36) formed on it 
are seated; the hold-down device (24) is seated with a swivel bearing (37) 
around the eccentric (34) and is motionally connected with it, and the 
driver (36) of the eccentric (34) cooperates in a non-positive manner with 
the swivel bearing (37) for pivoting the hold-down device upward. 
The pivot and blocking cylinder (30) is located above the eccentric drive 
(28) and is seated with its cylinder (30a) around a horizontal pivot shaft 
(38) on the C-frame (22), and hingedly engages with its piston rod (30b) 
the swivel bearing (37) of the hold-down device (24) in a horizontal pivot 
shaft (39) above the eccentric (34). 
The bending cheek (27) is seated on two pivot segments (40), which are 
respectively positively guided in a crank guide (26) in the form of a 
roller guide extending on a circle in the C-opening (41) of the C-frame 
(22), are embodied as toothed quadrants and are pivotable in height via a 
hydraulic pivot drive (42) with drive pinions (43) . 
As shown in FIG. 4, the C-frame (22) is formed by three C-stands (22a), 
connected with each other by connecting pipes (44) and the press table 
(23), and maintained at a distance from each other. An eccentric drive 
(28) with a hydraulic oscillating motor (29) is seated on each C-stand 
(22a) and all three eccentric drives (28) are motionally connected by an 
eccentric shaft (31) acting as a torsion shaft. 
A pivot and blocking cylinder (30) is seated on each C-stand (22a), and the 
hold-down device (24) is supported via respectively a swivel bearing (37) 
by the eccentric drive (28) and is connected with the blocking cylinders 
(30). Thus, the bending press (4) has a total of three eccentric drives 
(28) and three pivot and blocking cylinders (30). 
The bending cheek (27) can be pivoted in height by means of pivot segments 
(40), guided on the crank guide (26) of each C-stand (22a), and a central 
hydraulic oscillating motor (42) via a continuous torsion drive shaft 
(43a), on which the drive pinions (43) are seated, which mesh with the 
toothed pivot segments (40). 
It is preferred to introduce into the assembly line a long bending press 
constituted by three or more aligned bending presses (4) which are 
controlled to operate synchronously and are combined into a modular 
component, so that it is possible to bevel even very long sheet metal 
plates of up to 12 m in respectively one bending step. 
The long bending press (4), formed of three presses (4), is illustrated in 
FIGS. 1, 3 and 4. 
The manipulator (5) in accordance with FIGS. 1 to 4 is constituted by a 
semi-portal crane, which is movable, guided on upper and lower guides (45, 
46) of the bending press (4), parallel to the bending edge (25) and which 
has, on its cantilevered arm (47) extending transversely to the direction 
of movement (A) over the roller-ball table (6), a vertical gripper (49), 
which is movable in the longitudinal direction of the cantilevered arm 
(47), can itself be moved vertically and is rotatable around its vertical 
axis (48), for gripping the sheet metal plate (1) which is to be fed to 
and removed again from the bending press (4) for the individual bending 
steps. 
The semi-portal crane (5) is supported with the lower end of its upright 
support column (50) on the guide (45) disposed on the bottom of the back 
of the C-frame (22) facing away from the C-opening (41), and is seated 
with its cantilevered arm (47) in the guide (46) fixed on the top of the 
C-frame (22); both guides (45, 46) are formed by rails (profiled section), 
on which the semi-portal crane (5) can be moved by means of rollers (51). 
The gripper (49) has a telescoping column (52), itself movable in height, 
the upper end of which is supported, with the interposition of a live ring 
(53), on a carriage (54) which is movably suspended on a cantilevered arm 
(47), and which column has on its lower end a horizontal support arm (55) 
with two clamping chucks (56), disposed apart from each other and 
cooperating with the fitting marks (1c) of the sheet metal plate (1). 
The drive for the manipulator (5) is indicated by (57) in FIG. 2, and the 
end switches (58) for the limitation of the travel of the manipulator (5) 
are shown in FIG. 4. 
Furthermore, the drive (59) for the carriage (54) and the drive (60) for 
the live ring (53), as well as the hydraulic pump (61) assigned to them 
are illustrated in FIG. 2; the lift device (62), controlled by lift 
limiting sensors (63), is disposed in the telescoping column (52). 
The oscillating motor (29) for the eccentric drive (28) and the oscillating 
motor (42) for the bending cheek (27) are controlled by rotation 
transmitters (65, 66), and the pivot and blocking cylinder (30) is 
embodied with a control element (sensor) (64) for locking and releasing 
its piston rod (30b) (FIG. 2). 
The roller-ball table (6) is not shown in FIG. 2, instead the trolley (8) 
with its guide (11) is shown in dash-dotted lines. 
The sheet metal plate (1), prepared in the pre-treatment station (9), is 
pulled into the cutting and/or stamping station (3) by the trolley (8) and 
is aligned on the guide rollers (15) and stops (16). 
The two cutting and/or stamping devices (13, 14) prepare the notches (1a) 
in the corners of the sheet metal plate (1), and the openings (1b) and the 
reamed holes (1c) by means of plasma-- or CO.sub.2 -laser cutting or by 
stamping and/or drilling. 
In the process, the trolley (8) fixes the aligned sheet metal plate (1) by 
means of the chucks (17) and the two devices operate in a limited work 
area (X, Y), and the sheet metal plate (1) is moved on in steps (clocked 
movements) by the trolleys (8) after each work area (X, Y) until the 
entire length of the sheet metal plate has been worked. 
Retaining bolts are inserted into the reamed holes (1c) and welded in. 
Then the sheet metal plate (1) is transported on the roller-ball table (6). 
The formed sheet metal plate (1) is now taken over by the manipulator (5), 
which services the bending press (4), for the individual bending steps. 
For this purpose the gripper (49) moves downward on the sheet metal plate 
(1) and its clamping chucks (56) grip the fitting marks (1c), and then the 
sheet metal plate (1) is inserted into the opened bending press (4) for 
performing the first bending step while maintaining its seat on the 
roller-ball table (6). 
Because the manipulator (5) can move the sheet metal plate (1) in the plane 
of the sheet metal plate by means of the semiportal crane and the gripper 
carriage (54), and can turn it by means of the live ring (53), the sheet 
metal plate (1) is displaced inside the bending press (4) for each new 
bending step and, for making a new profiled edge section (1d), is taken 
out of the bending press (4), placed into the new position and returned 
into the bending press (4) again, the manipulator (5) always grasping the 
sheet metal plate (1) by its fitting marks (1c). 
The travel distance (MW) of the manipulator (5) extends over nearly the 
entire length of the bending press (4). 
To perform each bending step for the profiled edge section (1d) of the 
sheet metal plate (1), the hold-down device (24) is pivoted down, firmly 
clamps the sheet metal plate (1) between itself and the press table (23) 
and then the bending cheek (27) is pivoted upward in a controlled manner. 
Afterwards the bending cheek (27) is pivoted back downward and the 
hold-down device (24) is lifted, so that the sheet metal plate (1) can be 
prepared in the press (4) for the subsequent bending step, and displaced. 
When the profiled section (1d) has been finished on the one side of the 
plate, the manipulator (5) takes the sheet metal plate (1) out of the 
bending press (4), turns the sheet metal plate (1) around and again 
inserts it into the bending press (4) for bending the profiled section on 
the next side of the sheet metal plate, in the course of which the same 
bending steps are repeated. 
During each bending step the eccentric drive (28) keeps the pivoted-down 
hold-down device (24) under great pressure against the sheet metal plate 
(1) lying on the press table (23). In the process, the pivot and blocking 
cylinder (30) is extended and locked (FIG. 5). 
The eccentric drive (28) is actuated by its oscillating motor (29) for 
lifting the hold-down device (24), i.e. for releasing the sheet metal 
plate (1) so it can be displaced in the C-opening (41) for the subsequent 
bending step; in the process, the gear wheel (32) turns the eccentric 
shaft (31) via the gear wheel (33) and thus also the eccentric (34), and 
the pivot and blocking cylinder (30) remains locked in its extended 
position during this. 
Now, because of the rotation of the eccentric (34), the hold-down device 
(24) is positively lifted by its swivel bearing (37) seated around the 
eccentric (34) and is slightly lifted off the sheet metal plate (1) over a 
short lift-pivot path (H)--in the course of this the hold-down foot (24a) 
of the hold-down device (24) moves away from the bending edge (25) on a 
movement path which is directed obliquely upward and outward--at an 
inclination of approximately 45.degree.--into the hold-down position shown 
by dash-dotted lines in FIG. 5, and the sheet metal plate (1) is released 
for displacement. 
The short lift-pivot path of the hold-down device (24) is made possible by 
the hinged connection (29) with the pivot and blocking cylinder (30), in 
spite of its being locked. 
The eccentric (34) is turned in the opposite direction for renewed clamping 
of the sheet metal plate (1) and in this way the hold-down device (24) is 
again pressed against the sheet metal plate (1). 
This lift-pivot path (H) of the hold-down device (24) at the same time 
makes possible the compensation for different thicknesses of sheet metal 
plates of approximately 4 to 10 mm, so that by means of the eccentric (34) 
the hold-down device (24) exerts the same high pressure on each sheet 
metal thickness within the above mentioned thickness range. 
With thinner or thicker sheet metal, the rotation of the eccentric (34) 
takes place at a smaller or larger angle of rotation and in this way the 
adaptation of the hold-down device (24) to the respective sheet metal 
thickness. 
The pivot and blocking cylinder (30) is released for opening the bending 
press (4) and the eccentric drive (28) is turned further and, when its 
driver (36) pushes against the swivel bearing (37), the hold-down device 
(24) is pivoted upward. 
The released cylinder (30) is retracted at the same time and supports the 
upward pivot movement of the hold-down device (24). 
Based on the continuous eccentric shaft (31) and the disposition of three 
eccentric drives (28) of each bending press (4), which has a length of 
approximately 4 m, the parallel pivoting of the hold-down device (24) is 
assured, even in connection with short bending ranges wherein the 
hold-down device (24) acts on the sheet metal plate (1) only with a 
portion of its length; thus, no one-sided load on the hold-down device 
(24) is created. This also applies in connection with the long bending 
press (4) formed by three presses (4). 
Beveling of the profiled edge sections (1d) on all four sides of the sheet 
metal plate (1) is made possible by the notches (1a) in the corners. 
After all bending processes have been completed, the manipulator (5) 
removes the formed sheet metal plate (1) and transfers it to the second 
trolley (8), which transports it to the welding station (7). 
The trolley (8) moves the sheet metal plate (1), which is fixed in its 
position, in steps through this station (7), in which the feed device (20) 
inserts the reinforcement sections (2a) into the sheet metal plate (1) 
aligned at distances to form a grid, and then the welding device (18) 
welds the sections (2a) to the sheet metal plate (1) by means of its 
controllable welding heads (19). 
Subsequently the finished steel coffer (2) is moved out of the welding 
station (7) by the trolley (8) onto the roller conveyor (10) to be moved 
away and the fabrication process is finished. 
The finished steel coffer (2) constitutes a coffer element in a box shape 
having a wall (2b) which itself is flat and a circumferential, multiply 
beveled profiled edge section (1d), and which has, beneath its flat wall 
(2b), the reinforcement sections (2a) fastened there, has the openings 
(1b) and connecting holes (1b) in the circumferential profiled edge 
section (1d), and in the corners has notches (1a) for beveling the 
profiled edge sections (1d) and for inserting supports, while being 
provided with fitting marks (1c) in the form of holes or bolts in its flat 
wall (2b).