Tube bending machine

A tube bending machine comprises a bending table mounted on a support turnable about an axis and coaxially carrying an inner bending template surrounded by at least one outer bending template which is shiftable along said axis relative to the inner bending template so that a portion of the tube to be bent may be pressed by clamping means carried by the bending template against the outer surface of the inner or the outer bending template. The bending machine comprises further guide means including a releasable collet for guiding the tube toward the bending templates, the guide means being mounted on the support movable in longitudinal direction of the tube to be bent and in a direction transverse to the longitudinal direction.

BACKGROUND OF THE INVENTION 
The present invention relates to a tube bending machine with a bending 
table tiltable about an axis and which includes a bending template, 
clamping means movable toward and away from the bending template and an 
advancing carriage including a releasable clamping collet, which during 
the bending operation is movable toward the bending template. 
During bending of tubes it is usually desired to make successive bends in 
the tube with the same bending radius to avoid during the bending of the 
tube a change of the bending templates. However, in many applications it 
is necessary to make successive bends with a different bending radius. For 
instance, during the bending of exhaust tubes for motor vehicles it is 
desirable to calculate the bending radius of the tube in order to obtain 
with the exhaust tube a predetermined pressure. This predetermined bending 
radius can, however, not be used for subsequent bending of the tube. 
Tube bending machines are known in the art which comprise two superimposed 
fixedly arranged bending templates of different diameters. In using these 
known tube bending machines, the tube to be bent is first manually applied 
to the first bending template and, after bending, manually applied to the 
second bending template. This procedure is not only rather cumbersome but 
leads also to unexact results. 
In order to bend tubes with different bending radii, one proceeded so far 
by bending a plurality of tubes with a first bending radius, by removing 
then the tubes from the bending machine and storing the same in the region 
of the machine, whereafter the used bending template has been removed from 
the bending machine and a new bending template with a different diameter 
has been placed thereon, whereafter the bent tubes are again placed into 
the machine to be provided with a subsequent bend having a different 
bending radius. This procedure is likewise not only cumbersome and time 
consuming but leads also to difficulties with respect to the exactness of 
the distances and angular positions of the successive bends with different 
bending radii. If the tube after a first bend or a plurality of first 
bends with the same bending radius is taken out of the machine, then it is 
difficult to place the tube bent in two or three different planes again 
into the bending machine. This requires to place the tube manually into 
the machine. A further difficulty arises to maintain the original position 
at which the tube has been held by the advancing carriage and the clamping 
collet connected thereto during the renewed placement of the tube into the 
clamping collet so that in the finished bent tube the distances between 
the bends of different bending radii and the angular position of the 
subsequent bends with different bending radii could not exactly be 
maintained. These difficulties also required additional adjusting 
operations on the finished tubes. Such subsequent adjusting operations 
are, however, not economical during serial production of tubes in which a 
great number of bent tubes have to be produced per time unit. From the 
above, it will be clear that bending of tubes with a plurality of 
subsequent bends of different bending radii has not been possible up to 
now with fully automatic, especially numerically controlled tube bending 
machines. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a tube bending machine 
which avoids the disadvantages of such tube bending machines known in the 
art. 
It is a further object of the present invention to provide a tube bending 
machine, especially a fully automatic, numerically controlled tube bending 
machine with which tubes may be bent exactly with successive bends of 
different bending radii without change of the clamping in the tube 
advancing means. 
With these and other objects in view, which will become apparent as the 
description proceeds, the tube bending machine according to the present 
invention mainly comprises support means, a bending table mounted on said 
support means tiltable about an axis, template means mounted on the 
bending table for tilting with the latter about said axis in which the 
template means comprise at least two coaxially arranged templates of 
different diameters movable relative to each other along said axis, 
clamping means on the bending table for clamping a portion of a tube to be 
bent against a respective one of the templates, guide means including 
releasable collet means for guiding a tube to be bent in longitudinal 
direction toward the template means, and means for moving the guide means 
in a direction transverse to the longitudinal direction. 
With the bending machine according to the present invention it is, 
therefore, possible to provide in a tube successive bends with different 
bending radii without removing the tube intermediate the bends from the 
bending machine. Furthermore, during shifting of the templates relative to 
each other the tubes to be bent remain clamped in exactly predetermined 
positions so that the tubes may be bent with great exactness. 
The present invention permits, therefore, to make successive bends with 
different bending radii in a numerically controlled tube bending machine 
in which the tubes may be exactly maintained in all positions during the 
bending so that resilient spring back of the tube may be considered and 
controlled by the bending program. 
During the bending in numerically controlled tube bending machines, the 
tube remains always properly clamped. At first it is clamped in the 
clamping collet which is carried by the advancing carriage. When the 
clamping collet is opened for a short time, for instance, removed to 
another position, then the tube remains clamped during this time between a 
bending template and the clamping means so that the tube is properly held 
in the bending machine. This holds true also if the clamping collet is 
released in order to permit a return stroke of the advancing carriage so 
that the latter may again advance the tube, whereafter the tube is again 
clamped by the collet while a portion of the tube is pressed by the 
clamping means against the bending template which is subsequently turned 
to provide the desired bend in the tube. 
The construction according to the present invention permits also a quick 
change of the bending templates since the bending templates of different 
diameters remain connected to the bending table and the bending templates 
are movable relative to each other in such a manner so that during bending 
of the tube about bending templates of different diameters the bending of 
the tubes occurs always at the same elevation relative to the bending 
table. 
If a bending mandrel is used during the bending of the tubes, then a 
further feature according to the present invention includes a mandrel 
holder which is movable transverse to the advancing direction of the tube 
to be bent, whereby the mandrel holder is moved simultaneously and through 
the same distance in this transverse direction as the transverse movement 
of the advancing carriage. 
According to a further feature of the present invention the outer bending 
template surrounds the inner bending template. Both templates are provided 
with peripheral grooves which in this case are arranged in a plane normal 
to the axis along which the templates are movable. 
Preferably the inner bending template is arranged about a shaft, which is 
mounted in a turntable provided in the bending table, and movable in axial 
direction and the inner bending template is surrounded by an outer bending 
template which is liftable by the shaft above the inner template. 
The outer template has preferably a top wall extending transversely over 
the inner template and the aforementioned shaft has adjacent one end 
thereof a shoulder abutting against the top wall of the outer template so 
that the latter may be lifted above the inner template during upward 
movement of the shaft. With a similar construction it is in a simple 
manner also possible to use three or even more bending templates of 
different bending radii which may be used in quick succession to each 
other, whereby for instance the first bend is carried out with the bending 
template of the smallest bending radius, whereafter a subsequent bend may 
be carried out with the largest bending template and a next-following bend 
may be carried out again with the smaller bending template. The bending 
templates of different bending diameters remain mounted on the bending 
table and by axial movement of the templates relative to each other it is 
possible to bring each time the desired bending template into action, 
whereas the non-used bending template is lifted above the respective used 
one. In order to obtain this it has been found especially advantageous 
that the lifting shaft, if three bending templates are used, is 
constructed as a stepped shaft providing two shoulders of different 
outside diameters which are spaced in axial direction from each other a 
distance equal to the inner height of the templates to be lifted. If only 
two bending templates are used, then the stepped shaft has only a single 
shoulder. By coaxial arrangement of for instance four bending templates 
which are telescopically arranged within each other, the stepped shaft has 
to be provided with three shoulders. The number of shoulders provided on 
the shaft is, therefore, smaller by one than the number of bending 
templates. 
The apparatus includes further means for moving the lifting shaft in axial 
direction and such moving means preferably comprise a cylinder mounted on 
the bending table, a piston connected to the other end of the lifting 
shaft and slidably guided in the cylinder and means for feeding pressure 
fluid into and out from the cylinder to opposite sides of the piston. In 
this way it is possible to quickly lift the non-used bending template 
hydraulically or pneumatically above the bending template to be used. 
According to a further feature of the present invention, the drive shaft 
for turning the bending table is hollow and coaxially surrounds the 
lifting shaft serving to shift one or more of the bending templates 
provided. 
The cylinder in which the piston of the lifting shaft is slidably arranged 
is preferably connected to the cylindrical extension of a turntable 
coaxial with the lifting shaft on which the bending templates are mounted. 
In order to bring the bending template into an exact angular position with 
respect to the bending table, it is also suggested that the aforementioned 
cylinder is provided with a coaxial outer chain gear cooperating with a 
chain drive by means of which the turntable and the bending template 
thereon may be turned. An appropriate scanning device may cooperate with 
the chain drive to establish the angular position of the bending 
templates. 
In order to reduce the action of the forces occurring during the bending of 
the tubes onto the bending templates it is also suggested according to the 
present invention to maintain the outer surface of the inner bending 
template in contact with the inner surface of the surrounding outer 
bending template. This will also assure an exact centralizing of the 
telescopically arranged templates. 
The templates are connected to the turntable for turning movement therewith 
by a key extending transverse to the axis of the turntable. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawing and more specifically to FIG. 1 of the same, 
it will be seen that the tube bending machine 10 according to the present 
invention comprises a support or housing 11 constructed from steel sheets 
welded together and provided at its front end with a projecting extension 
12 which carries a bending table 13 tiltable about a vertical axis. A rail 
14 extending in the longitudinal direction of the support 11 and the 
extension 12 thereof is mounted on the upper surface of the aforementioned 
members on which a slide 15 is movable in direction of the double-headed 
arrow 16 toward and away from the bending table 13. The slide 15 carries a 
housing 18 which in turn carries a cylinder 19 provided at its free end 
with a clamping collet 20 for clamping a tube 17 to be bent in the 
machine. The elements 15, 18 and 19 constitute guide means or a feed 
carriage for guiding a tube 17 to be bent toward the bending table. The 
aforementioned guide means are provided with a laterally projecting 
hydraulic cylinder 21 cooperating with the cylinder 19 for moving the same 
in direction of the double-headed arrow 22 transverse to the elongation of 
the rail 14 for a purpose as will be described later on. The portion of 
the tube 17 projecting beyond the clamping collet 20 is brought into 
engagement with the peripheral surface of a template 23 mounted on the 
upper surface of a turntable 24 coaxially arranged with the tilting axis 
of the bending table 13 and movable with the latter. The tube 17 is 
pressed onto the peripheral surface of the bending template 23 by a chuck 
25 having a clamping jaw 26 and the chuck with its clamping jaw is 
operated by the piston rod 27 of an operating cylinder 28 connected at its 
right end, as viewed in FIG. 1, to an abutment 29 projecting upwardly from 
the bending table 13. A block 70 is arranged on the extension 12 laterally 
of the bending template 23 movable in direction of the double-headed 
arrows 71 and 72 by conventional means not shown in the drawing relative 
to the bending template 23 to prevent buckling of the tube 17 away from 
the bending template during bending of the tube. If a mandrel is used 
during bending of the tube 17, which is advisable during bending of the 
tube along a small bending radius, then the mandrel rod 30 is connected at 
its outer end projecting towards the left, as viewed in FIG. 1, beyond the 
housing 18 to cylinder-and-piston means 32 for moving the mandrel rod 30 
in the direction of the double-headed arrow 32. The cylinder 31 is mounted 
on a slide 34 and movable in a direction as indicated by the double-headed 
arrow 33 by a hydraulic cylinder 36 mounted on the support 11 and having a 
piston rod 35 (FIG. 2) engaging the cylinder 31. 
FIG. 2 shows a slight modification of the abovedescribed arrangement in 
which the rail 14 is not mounted on the upper surface of the support 11 
but laterally therefrom in form of a cylindrical rod 14a. The housing 18 
in this construction is movable in the longitudinal direction of the rod 
14a and the piston rod of the cylinder 21 carried by the housing 18 is 
connected to the cylinder 19 carrying the tube 7 to be bent. The clamping 
device 28 and 26 in this construction is arranged in a starting position 
substantially normal to the elongation of the unbent tube 17 and the block 
70 may, therefore, be omitted in this modified arrangement. 
After having thus described the basic construction of the tube bending 
machine, reference is now had to FIG. 4 showing a tube 17 provided with 
two successive bends along different bending radii R.sub.1 and R.sub.2. 
In order to bend a tube in the manner as shown in FIG. 4 without removing 
the tube from the bending machine, the latter is provided, as shown in 
FIG. 5, with two bending templates 23 and 23A mounted on the turntable 24 
of the machine, whereby the outer bending template 23A surrounds the inner 
template 23. The two templates 23 and 23A are provided at the peripheral 
surface thereof respectively with semicircular peripheral grooves 38 and 
39, the centers of which are arranged in a common plane, that is the 
centers of the two grooves have the same distance from the upper surface 
of the turntable 24. 
The extension 12 of the support or machine housing is composed of steel 
plates or steel sheets welded together which are referred to in the 
cross-section of FIG. 5 with the reference numerals 12, 121, 122, 123, 
124, 125 and 126. This box-shaped hollow housing 12 carries two coaxial 
bearings 40 and 41 in which the main drive shaft 42 is turnably mounted. 
The hollow drive shaft 42 is rotated by means of a chain gear 43 connected 
thereto by key 54 and engaged by chain 44, which in turn is driven by a 
motor, not shown in the drawing. The hollow drive shaft 42 is fixedly 
connected at its lower end, for instance by welding, to a bottom plate 45 
connected to the bending table 13. The bending table 13 carries as 
mentioned in the description of FIG. 1, the chuck 25 with the clamping jaw 
26. The arrangement of the chuck 25 shown in FIG. 5 is slightly different 
from that shown in FIG. 1. In the construction shown in FIG. 5 the 
operating cylinder 28 with the piston rod 29, which is connected by a bolt 
46 to the chuck 25 is arranged laterally on the bending table 13. In 
addition a screw spindle 47 turnably mounted in a lug 48 projecting 
upwardly from the bending table 13 is provided, in which the spindle can 
be turned by means not shown in the drawing connected to the square free 
end 49 of the spindle 47. The operating cylinder 28 is tiltably mounted by 
means of a bolt 50 on the bending table 13. 
A lifting shaft 51 extends coaxially through a bore in the inner template 
23 and the lifting shaft 51 is mounted for movement in axial direction in 
a central bore of the turntable 24 which extends also through a 
cylindrical extension 52 of the turntable. The bending templates 23 and 
23A are provided at the bottom faces thereof with a radially extending 
groove in which a key 53 is inserted, which in turn is also mounted in a 
corresponding radial groove on the upper surface of the turntable 24. In 
this way the bending templates 23 and 23A are connected to the turntable 
24 for turning movement therewith. 
When the main drive shaft 42 is turned by the chain drive connected 
thereto, the bending table 13 connected in the aforementioned described 
manner to the main drive shaft 42 is also turned with the latter. During 
bending of a tube, a portion of the latter is pressed by the chuck 25 and 
the clamping jaw 26 thereof by means of the piston rod 29 of the operating 
cylinder 28 against the peripheral surface of the bending template 23 or 
23A, and a pin 67 projecting from the chuck 25 engages into a 
corresponding bore 68A of the bending template 23A so that the latter is 
turned together with the bending table. If the outer template 23A is 
lifted in the manner as will be described later on beyond the inner 
template 23, the chuck 25 is shifted laterally so that the pin 67 will 
engage in a corresponding bore 68 of the inner template 23. In this way 
the respective template is turned about the axis of the shaft 51 during 
tilting of the bending table about this axis. 
A cylinder 55 is connected by means of a stepped connecting ring 56 
provided at its outer peripheral surface with screw threads to the lower 
end of the cylindrical extension 52 of the turntable 24. Appropriate 
locking means, not shown in the drawing, are provided for preventing 
unscrewing of the connecting ring. The lifting shaft 51 extends into the 
cylinder 55 and carries at its lower end a piston 57 slidably guided in 
the cylinder. Bores 58 and 59 in the region of opposite ends of the 
cylinder 55 serve for connecting conduits thereto for feeding pressure 
fluid into and out from the cylinder to opposite sides of the piston 57 so 
that the lifting shaft 51 may be raised or lowered as desired. 
The outer bending template 23A has a top wall 60 extending over the upper 
surface of the inner template 23 and the top wall 60 is provided with a 
central bore through which a reduced diameter portion 62 of the lifting 
shaft 51 extends. The reduced diameter portion 62 is provided with an 
outer screw thread onto which a nut 63 is screwed engaging the upper 
surface of the top wall 60 of the outer template 23A. A shoulder 64 at the 
junction of the reduced diameter portion 62 and the remainder of the 
lifting shaft 51 engages the bottom surface of the top wall 60 of the 
outer template so that the latter is constrained to follow the axial 
movement of the lifting shaft 51. 
An annular chain gear 65 surrounds the cylinder 55 and is connected thereto 
for turning movement therewith by a key 66. The gear 65 is driven by a 
chain drive including another chain gear 65a driven by a hydraulic motor 
67 connected to the bottom plate 45 of the bending table 13, so that the 
cylinder 55, the turntable 24 connected thereto and the templates 23 and 
23A may be turned to a starting position before the next bend of a tube is 
carried out. 
The above-described arrangement will be operated as follows: 
Assuming the first bend of the tube 17 is carried out about the outer 
template 23A then the various elements of the turntable are arranged in 
the manner as shown in FIG. 5 by means of which a tube portion is clamped 
by the clamping means 25, 26 against the outer periphery of the outer 
template 23A and the bending table 13 is then turned by operating the 
chain drive 43, 44. Since the pin 67 is engaged in this position in the 
bore 68A of the outer template 23A, the outer template 23A is turned 
together with the bending table 13 and so is the turntable 24 and the 
inner template 23 since both templates are connected to the turntable by 
the key 53. Subsequently thereto, the clamping means 25 and 26 are opened 
so that the pin 67 is withdrawn from the bore 68A and the bending table 13 
is moved back by the chain drive 43, 44 to its starting position. The tube 
17, is properly held during opening of the clamping means by the clamping 
collet 20. Subsequently thereto the cylinder 19 carrying the clamping 
collet 20 is moved by the cylinder-and-piston arrangement 21 toward the 
right, as viewed in FIG. 5, to remove the tube out of the groove 39 of the 
outer template 23A. Subsequently thereto pressure fluid is fed through the 
opening 59 in the cylinder 55 below the piston 57 on the lifting shaft 51 
so that the latter is raised to lift the outer template 23A above the 
inner template 23. The inner template 23 is then moved to its starting 
position by operating the hydraulic motor 67 which in turn drives over the 
chain drive 65a, 65, the cylinder 55 and the turntable 24 connected 
thereto and therewith also the inner template 23 connected by the key 53 
to the turntable. The tube is then shifted in axial direction by advancing 
the guide means 15, 18 and 19 in the direction toward the template. 
Subsequently thereto, the tube 19 with the clamping collet 20 is shifted 
by the cylinder-and-piston arrangement 21 so that the tube will engage in 
the groove 38 of the inner template 23 and then the clamping means 25, 26 
are moved towards the left, as viewed in FIG. 5, to clamp the tube portion 
against the inner template 23 and simultaneously the free end of the pin 
67 is moved into the bore 68 of the inner template. The bending table 13 
is then again turned about the axis of the shaft 51 by operating the chain 
drive 43, 44 to make the second bend in the tube. It is to be understood 
that if a mandrel is used during the bending operation, the mandrel rod 30 
has to be moved in longitudinal and transverse direction by the 
cylinder-and-piston arrangements 31 and 36 together with the corresponding 
movement of the cylinder 19 carrying the clamping collet in longitudinal 
and transverse directions. The same holds true with the block 70 shown in 
FIG. 1. 
FIG. 7 illustrates in cross-section an arrangement in which three bending 
templates 23, 23A and 23B are used which are arranged one in the other. 
The two outer templates 23A and 23B have top walls 60, respectively 68. 
The lifting shaft 51 is a stepped shaft provided with two axially spaced 
shoulders 64 and 69, respectively adapted to engage the bottom surfaces of 
the top walls 68 and 60. The shoulders 64 and 69 are spaced in axial 
direction from each other a distance substantially equal to the inner 
height of the outermost template 23B. 
FIG. 8 illustrates an outermost template 23B lifted by the lifting shaft 51 
to an unoperative position. If the lifting shaft 51 is further raised the 
middle template 23A may also be lifted by engagement of the shoulder 69 
with the bottom surface of the top wall 60 to thereby move the middle 
template 23A likewise to its inoperative position. As evident from FIGS. 7 
and 8 a quick lifting and lowering of the templates 23A and 23B is assured 
by hydraulically or pneumatically operating the shaft 51. 
FIG. 3 schematically illustrates a top view of the three bending templates 
whereby for simplification of the drawing the top walls 60 and 68 are 
omitted in FIG. 3. 
It is to be understood that the varying fluid-operated cylinders and 
hydraulic drive motors of the tube bending machine according to the 
present invention may be automatically controlled in a manner known per se 
by punched tapes or computers. 
FIG. 8 shows also, differing from FIG. 7, that the three templates are 
provided with grooves of different cross-section. Thus the innermost 
template 23 has a semicircular groove 38 for a small tube diameter, 
whereas the intermediate template 23A has a groove 38a of the same size as 
in FIG. 7, and the outermost template 23B has a groove 38b for a larger 
tube diameter. In this way it is possible to adopt the bending machine 
according to the present invention quickly for bending tubes of different 
outer diameters. It is mentioned that it happens often that tubes of 
larger diameter are pushed over tubes of smaller diameter or that such 
tubes of different diameters are connected by a socket joint. With the 
machine of the present invention it is, therefore, possible also to bend 
tubes of different diameters. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of tube 
bending machines differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
tube bending machine having bending templates of different diameter which 
can be respectively placed in operating position by shifting the same in 
axial direction relative to each other, it is not intended to be limited 
to the details shown, since various modifications and structural changes 
may be made without departing in any way from the spirit of the present 
invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can by applying current knowledge 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.