Adjustable clamp die for tube bending machine

A clamp die apparatus for co-operating with the bend die of a tube bending apparatus during tube bending has a support bolster adapted for adjustable mounting on a bend arm of a tube bending machine and a primary clamp die rigidly mounted on the support bolster for clamping a portion of a tube against a bend die of the bend arm. A secondary clamp die is movably mounted on the support bolster for movement between an extended position alongside the primary clamp die and a retracted position spaced rearwardly from the primary clamp die. Each clamp die has a clamping surface for bearing against a portion of a tube to be bent, and the clamping surfaces of the primary and secondary clamp dies are aligned to form a clamping surface of extended length when the secondary clamp die is in the extended position. The primary clamp die alone forms a reduced length clamping surface when the secondary clamp die is in the retracted position.

BACKGROUND OF THE INVENTION 
The present invention relates generally to tube bending machines, and is 
particularly concerned with an adjustable clamp die for a tube bending 
machine. 
Automatic bending machines such as the machines described in U.S. Pat. Nos. 
3,974,676 and 4,063,441 of Homer Eaton, assigned to Eaton-Leonard Corp., 
are arranged to form a series of pre-programmed bends in a length of pipe. 
An automatic bending machine typically has a fixed, elongated machine bed 
on which pipe is supported and advanced to a bend head at one end of the 
machine bed. The pipe at the bend head is gripped between bend and clamp 
dies, and these dies are rotated together to form a bend in the pipe. The 
dies are retracted, and the pipe is again advanced to the next bend 
position. 
One problem with existing bend and clamp die arrangements is that, when the 
clamp die is relatively short, slipping of the pipe may occur when a 
portion of a long, straight pipe section is to be bent. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a new and improved 
clamp die apparatus for a tube bending machine. 
According to one aspect of the present invention, a tube bending apparatus 
is provided which comprises a rotatably mounted bend die, a clamp die 
assembly co-operating with the bend die for clamping a portion of a tube 
between the clamp die and bend die, and a drive assembly for driving the 
bend die and clamp die assembly between a first position aligned with the 
axis of the tube and a second position rotated relative to the straight 
tube axis to bend the tube about the bend die, the clamp die assembly 
comprising a clamp die base, a first, fixed clamp die rigidly mounted on 
the base and having a clamp axis aligned with the tube axis in the first 
position, a second, adjustable clamp die rotatably mounted on the clamp 
die base for movement between an extended position alongside the first 
clamp die, and a retracted position rotated away from the first clamp die, 
and a second clamp die drive assembly for driving the second clamp die 
back and forth between the extended and retracted positions. The first and 
second clamp dies each have a clamping surface for bearing against a 
portion of a tube to be bent, and the clamping surfaces are aligned to 
form a continuous clamping surface when the second clamp die is in the 
extended position. 
The first clamp die opposes the bending die at all times to clamp a portion 
of the tube to be bent between the bending die and clamp die. When 
necessary, the second clamp die is rotated into alignment with the first 
clamp die to form an elongated clamp die, resisting slipping of the tube 
during bending. The second clamp die will be used primarily when bending 
part of a long, straight tube section. 
When the secondary clamp die is not needed, for example when two bends are 
located close together, the secondary clamp die is retracted out of the 
way and the primary clamp die only is used to grip the tube. When two 
bends are positioned close together, a short section of clamp die will be 
sufficient, partly because the placement of the clamp die relative to the 
previous bend essentially locks the tubing under bend in position. When 
the spacing between the location of a bend to be formed and the previously 
formed bend is greater than a predetermined maximum, the risk of slipping 
is such that the secondary clamp die should be used to bear against the 
tube and resist any slipping. Thus, in this situation, the secondary clamp 
die is moved into the advanced position. In either case, a drive or 
actuator rotates the bend and clamp dies together between a first position 
aligned with the axis of the advancing tube and a second position rotated 
from the first position so as to bend the tube about the bend die. 
In a preferred embodiment of the invention, the drive assembly comprises a 
hydraulic cylinder and piston mechanism. Preferably, the secondary clamp 
die is rotatably mounted on the support for movement between the extended 
and retracted position, and is linked to the drive assembly by a two part 
linkage of two link members. The first link member is pivoted at one end 
to the support and at the opposite end to the second link member, and is 
pivoted to the drive assembly at a location between its opposite ends. The 
second link member is pivoted at one end to the first link member and at 
the opposite end to the secondary clamp die. 
The secondary clamp die preferably has an extension arm which is rotatably 
mounted on the support at its free end, and is connected to the two part 
linkage at an intermediate position between a clamping face of the die and 
the end of the extension arm. Preferably, opposing stop faces are provided 
on the extension arm and support base for engagement when the secondary 
clamp die is in the extended position, to prevent further motion of the 
clamp die beyond this position. The secondary clamp die is positioned such 
that it will not interfere with the tubing being bent when it is in the 
retracted position. In a preferred embodiment of the invention, the 
secondary clamp die rotates through an angle of 90.degree. between the 
extended and retracted positions. 
Thus, the clamp die assembly of this invention essentially provides a clamp 
die of adjustable length, with the length adjustment being achievable 
quickly and easily simply by rotating the secondary clamp die between 
extended and retracted positions. In the extended position, the secondary 
clamp die is located alongside the primary clamp die and provides an 
extended length die face. In the retracted position, the secondary clamp 
die is moved away from the primary clamp die to leave only a short 
clamping surface. When using the primary clamp die alone, bends can be 
made relatively close to one another. Bends can be made in relatively 
long, straight sections of tubing by using both the primary and secondary 
clamp dies to form a longer clamp die, reducing the risk of slipping.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 to 3 illustrate a clamp die apparatus according to a preferred 
embodiment of the present invention for positioning at the forward end of 
tube bending machine in bend head 12 as illustrated in FIGS. 4 and 5 so as 
to oppose the bending die 14. The bending machine is otherwise of the type 
shown and described in U.S. Pat. No. 4,063,441 (hereinafter '441 patent), 
the contents of which are incorporated herein by reference, and other 
parts of the machine are therefore not illustrated or described in detail. 
Although the apparatus 10 is primarily intended for incorporation in a 
bending machine of the type described in the aforementioned patent, it 
will be understood that it may alternatively be incorporated in other 
types of rotary bending machines. 
The bending machine basically comprises a fixed, elongated machine bed 16, 
the forward end of which is visible in FIGS. 5, on which a moving carriage 
(not visible in the drawings) is mounted. Pipe or tube 18 is gripped by a 
rotatable chuck (not visible in the drawings) on the carriage, and the 
carriage advances the tube towards the bend head 12 mounted at the forward 
end of the machine bed 16. A swinging bend arm assembly 22 is mounted at 
the forward end of the machine. The bend arm assembly 22 carries the bend 
die 14 and the clamp die apparatus 10, which opposes the bend die 14. The 
swinging bend arm assembly 22 is mounted for rotation with the bend die 
about the axis 24 of the bend die, carrying the clamp die apparatus and 
its operating mechanism as it rotates, in the manner described in the 
above referenced '441 patent. The machine also includes a fixed pressure 
die 26 which opposes the bend die in the initial, solid line position of 
FIG. 5. 
The tube 18 extends between the bend die and the opposing pressure die and 
clamp die apparatus. The clamp die apparatus 10 will now be described in 
more detail with reference to FIGS. 1 to 3. The apparatus basically 
comprises a support base or bolster 30, a primary clamp die 32 rigidly 
mounted at one end of bolster 30, and a secondary clamp die 34 rotatably 
mounted on the bolster for rotation between an extended position as 
illustrated in FIGS. 1 and 2, and a retracted position as illustrated in 
FIG. 3. The bolster 30 is adjustably carried on the bend arm assembly for 
movement between an advanced, clamping position as illustrated in FIGS. 4 
and 5, and a retracted, inoperative position, in the same manner as the 
clamp die bolster described in the '441 patent referred to above. A clamp 
die adjusting block 31 secured to the bolster 30 has a depending toothed 
face (not visible in the drawings), the teeth of which mesh with a rack 
fixed to the top of a bend arm slide, as described in the '441 patent. 
Operation of this mechanism will not be described in detail here since it 
is identical to that described in the '441 patent. 
The primary clamp die 32 has a relatively short, arcuate clamping face 36 
for engagement with one side of the tube 18 to grip the tube between 
clamping face 36 and the opposing face of the bending die 14 as the swing 
arm rotates about axis 24. The secondary clamp die 34 has an arcuate 
clamping face 38 which matches that of the primary clamp die and forms an 
extension of the clamping face of the primary clamp die when in the 
extended position of FIGS. 1 and 2. In the extended position, the clamping 
faces of the primary and secondary clamp dies are aligned on the same 
clamping axis and are side-by-side to form one continuous, elongated 
clamping face. The secondary clamp die has a longer clamping face than the 
primary clamp die. Thus, when the secondary clamp die is in the extended 
position, it will bear against the tube 18 and resist any tendency of the 
tube to slip as the swing arm rotates to form the bend, as indicated in 
FIGS. 4 and 5. 
Although both of the clamping faces 36 and 38 are straight in the 
illustrated embodiment in order to form a straight bend in the plane of 
the clamp die and bending die, the clamp faces may alternatively 
incorporate bends or arcs in order to accommodate any desired bends out of 
the plane of the bend and clamp dies, for example as described in U.S. 
Pat. No. 4,495,788 of Traub, assigned to Eaton-Leonard Corporation, which 
describes different die shapes to accommodate different bend forms and 
compound bends. The opposing bend die face will also be shaped to 
accommodate the desired bend form in such cases. 
As noted above, the clamp die apparatus in the illustrated embodiment is 
designed for forming bends in the plane of the bend and clamp dies, in an 
otherwise straight length of tube. Preferably, the length of clamping face 
38 of the secondary clamp die is longer than that of the clamping face 36 
of the primary clamp die 34. The length of the clamping face of the 
primary clamp die 34 is preferably in the range of 1" to 2", while the 
length of the clamping face of the secondary clamp die is in the range 
from 1" to 4". In one specific example of a straight die, the face 36 had 
a length of around 2" while the face 38 had a length of around 4", making 
a possible total clamp face length of 6". 
A hydraulic drive assembly 40 for moving the secondary clamp die between 
the extended and retracted positions is pivotally secured at one end to a 
rear end of the support member or bolster 30 via pivot pin 42. The 
assembly 40 comprises hydraulic cylinder 44 and piston or ram 46, which is 
connected to the secondary clamp die via a toggle linkage 45. Linkage 45 
comprises a series of pivoted links 47,48 and 49. The first or rearmost 
link 47 is pivoted at one end to the bolster 30 via pivot pin 50, and is 
pivoted at the opposite end to the second link 48 via pivot pin 54. The 
hydraulic ram 46 is secured at its free or outermost end to an 
intermediate point on the first link 47 via pivot pin 55. Thus, extension 
and retraction of ram 46 will cause the link 47 to rotate about the fixed 
pivot 50. The hydraulic cylinder 44 is pivotally mounted to allow for the 
necessary rotation or angular movement of the drive assembly 40 due to the 
linkage design as the ram moves between the extended position of FIG. 2 
and the retracted position of FIG. 3. 
The second link 48 is an adjustable toggle link and is pivoted at one end 
to the first link, as noted above, and at the opposite end to the third 
link 49 via pivot pin 56. The third link 49 is rigidly secured to the 
secondary clamp die 34, and has a projection 57 pivotally secured to the 
bolster 30 via pivot pin 58. Thus, the toggle linkage causes link 49 to 
rotate about pivot pin 58 and thus moves the clamp die 34 between the 
extended and retracted positions, rotating the link 49 and clamp die 
through 90.degree., as illustrated in FIGS. 2 and 3. 
As noted above, the hydraulic cylinder assembly will rotate slightly to 
accommodate the linkage movement back and forth between the positions of 
FIGS. 2 and 3. The cylinder will rotate clockwise between the extended 
position of FIG. 2 and the retracted position of FIG. 3. This movement is 
used to actuate a pair of proximity switches 60 mounted on the bolster 30 
adjacent cylinder 44. A bracket 62 secured across the cylinder has an 
extension or flange 64 projecting over switches 60, with an opening 66 
above the switches. The location of the opening 66 relative to the 
switches will determine which of the switches is actuated. When the 
cylinder is in the position of FIG. 2, where the ram is extended, the 
uppermost switch is partially covered while the lowermost switch is not 
covered. The uppermost switch is actuated in this position and sends a 
control signal to the control software of the system. When the cylinder 
rotates back into the position of FIG. 3, the uppermost switch is 
uncovered and the lowermost switch is covered and actuated, sending a 
different control signal to the software. This information is used for 
system control. 
The system software may be designed to operate the hydraulic drive assembly 
to extend or retract the secondary clamp die depending on the type of bend 
to be formed. The linkage arrangement is such that, when the ram is fully 
extended as in FIG. 2, the first and second links 47 and 48 extend in a 
straight line and the thrust line of the hydraulic piston or ram is 
substantially aligned with the bearing or pivot between the first and 
second links. This provides a high rigidity for the supplemental clamp die 
when in the extended or operating position of FIGS. 1 and 2. The secondary 
clamp die will therefore bear against the tube when in the operative 
position, resisting slipping of the tube as it is bent. An inclined stop 
member 68 is preferably secured to the bolster via bolt 69, and forms a 
stop surface for the aligned first and second links in the extended 
position of FIG. 2. 
When bends are to be formed close together, the secondary clamp die 34 is 
not needed and may in fact interfere with the tubing being bent. Thus, in 
this situation, the clamp die 34 is moved into the retracted or 
inoperative position by retracting ram or piston 46, pulling back the 
linkage 45, which in turn pulls back the arm or link 49 on which the clamp 
die 34 is mounted, rotating the link 49 about pivot 58 until the clamp die 
34 swings away from the primary clamp die 32 into the retracted position, 
as illustrated in FIG. 3. In this position, the short, primary clamp die 
can be used in conjunction with the bend die to form closely adjacent 
bends in a tube. 
If a bend is to be formed which is in a long straight length of tube, and 
not close to any previously formed bend, the secondary clamp die 34 is 
advanced into the extended position illustrated in FIGS. 2, 4 and 5. As 
illustrated, in this position the clamp face 38 of this die will bear 
against an opposing surface portion of the tube 18, acting to resist 
slipping. With the clamp dies advanced into position opposing the bend die 
14 and gripping tube 18, as in FIG. 5, the bend arm is actuated in a 
conventional manner to rotate the entire assembly about the axis 24 of the 
bend die, as illustrated in dotted lines in FIG. 5. This forms a desired 
bend in the tube. Once the bending operation is complete, the clamp die 
apparatus is retracted to release the tube, the bend arm is rotated back 
into position with the clamp dies adjacent the pressure die 26, and the 
next portion of tube 18 is advanced. From FIG. 5, it can be seen that, if 
the secondary clamp die is in the retracted position of FIG. 3 while a 
bend is being formed, it will not interfere with the bending operation. 
In the preferred embodiment described above, the secondary clamp die is 
rotated back and forth between the advanced and retracted positions by 
means of a toggle linkage. However, the secondary clamp die may 
alternatively be connected directly to the hydraulic ram for axial or 
linear movement back and forth between an advanced position and a 
rearwardly retracted position. The toggle linkage is preferred, however, 
since movement will be smoother and there will be less risk of the linkage 
and clamp die jamming on any other parts of the clamp die bolster with a 
rotational movement than with an axial or sliding movement. Additionally, 
although the drive assembly is a hydraulic cylinder and piston in the 
preferred embodiment, other drive mechanisms may alternatively be used, 
such as a lead screw, rack and pinion, or the like. 
Although the primary and secondary clamp dies in the illustrated embodiment 
are straight clamp dies, curves may be incorporated into the dies if 
required for special purpose bending, or bending out of the plane of the 
clamp die, as will be understood by those skilled in the field. The clamp 
die apparatus as described above therefore allows the length of a clamp 
die to be adjusted readily between a relatively short die face and a 
longer die face, depending on the location of the bend to be formed. Such 
an adjustment could only be accomplished in the past by completely 
removing a clamp die and replacing it with a new, longer or shorter, clamp 
die. The die length adjustment with this apparatus can be performed 
automatically by the bend software, based on whether a bend is being 
formed close to a previously formed bend or in a long, straight tube 
section. 
Although a preferred embodiment of the present invention has been described 
above by way of example only, it will be understood by those skilled in 
the field that modifications may be made to the disclosed embodiment 
without departing from the scope of the invention, which is defined by the 
appended claims.