Bending die and ram assembly for tube bending machine

An improved bending die and ram assembly is provided for use in a tube bending machine used for bending metal tubing of the type used, for example, in vehicle exhaust systems and the like. The machine features a bending die having a convexly curved die face for bending engagement with a metal tube supported by a pair of backshoe dies mounted on an outwardly pivoting pair of back gates. The bending die is advanced by the ram assembly along a line extending between the back gates to engage and bend the metal tube, with the back gates swinging outwardly in opposite directions as the tube is bent. The ram assembly utilizes retractor hooks which cooperate with lugs projecting from the underside of the bending die to permit the die to be attached and detached from the ram assembly in a drop-in, lift-out manner that does not require tools. Following a bending operation, the retractor hooks engage the lugs to pull the bending die away from bent tube during retraction of the ram assembly.

BACKGROUND OF THE INVENTION 
This invention relates generally to improvements in radius bending dies of 
the type used in tube bending machines for bending metal tubing or the 
like to a selected configuration, wherein such bent tubing may be used, 
for example, in vehicular exhaust and tailpipe systems, etc. More 
particularly, this invention relates to an improved bending die that is 
detachably secured within a novel ram assembly which enables the bending 
die to be mounted onto the tube bending machine in an efficient, drop-in 
manner that allows various sized bending dies to be interchanged without 
the use of accessory tools. 
Tube bending machines in general are relatively well known in the art for 
use in bending metal tubing to a selected configuration. Such tube bending 
machines are commonly used by automotive vehicle repair shops to shape a 
length of metal tubing in a customized fashion for use in a vehicle 
exhaust or tailpipe system. A typical tube bending machine includes a 
bending die carried by a hydraulic ram for advancement into bending 
engagement with a length of metal tubing supported by a pair of backshoe 
dies mounted respectively on an outwardly pivoting pair of back gates. The 
bending die has a convexly curved, typically semicircularly shaped bending 
die face which cooperates with complementary die faces of the backshoe 
dies to define a channel of generally circular cross section having a 
diametric size closely matching the size of metal tube being bent by the 
machine. The bending die is advanced along a line extending between the 
pivot axes of the back gates and pushes into the supported metal tube, 
thereby causing the back gates with their backshoe dies to react by 
pivoting outwardly in unison and in opposite directions away from the 
bending die. This combination of bending die and back gate pivoting motion 
cooperates to bend the metal tube through a selected angle, in accordance 
with the advancement stroke length of the bending die. 
One commercial example of a tube bending machine of this general type is 
marketed under the trademark BLUE BOY, by American Machine & Hydraulics, 
Inc., of Newbury Park, Calif. See also U.S. Pat. No. 3,388,574. 
A major problem previously associated with mounting the bending die arises 
from the need to interchange bending dies of different radius of curvature 
in order to bend tubing into a desired configuration. Many prior bending 
dies cannot be rapidly detached and substituted by a different, 
appropriately sized die. Another general problem encountered with use of 
bending dies occurs during retraction of the bending die from the bent 
tubing, when tubing engagement forces and/or slight tubing compression can 
cause the bending die to stick or hang up on the tubing. Positive 
mechanical retraction of the bending die is needed for these reasons, but 
prior mechanical arrangements for positive retraction have been 
incompatible with simple die changeover. 
In one common bending die mounting configuration, the bending die includes 
two rearwardly extending pins for sliding reception into open bores in a 
pusher block carried by the hydraulic ram. A mechanical stop is 
interlocked with at least one of the pins so that when the pusher block is 
retracted, the mechanical stop is engaged by the pusher block to retract 
the bending die. In this attachment arrangement, bending die removal is 
prohibited unless the mechanical stop is first removed. Accordingly, 
manipulative steps often requiring the use of tools are required to change 
bending dies. Moreover, removal of parts such as mechanical stops can 
result in the parts being misplaced or lost, causing further delays in 
machine operation. 
Other prior mounting configurations have been designed to permit faster 
changeover of the bending die. For example, the pusher block has been 
provided with a hinged mechanical clamp or with upstanding pins to 
interlock with an appropriately apertured bending die, to permit bending 
die installation or removal without separate mechanical retractor stops. 
However, such past solutions generally have been less than ideal. 
There exists, therefore, a significant need for an improved bending die 
which can be mounted onto the pusher block in a manner that permits the 
bending die to be easily and quickly changed without tools or accessory 
parts, wherein the bending die incorporates means for physically 
retracting the bending die from bent tubing at the conclusion of a bending 
step. The present invention fulfills these needs and provides further 
related advantages. 
SUMMARY OF THE INVENTION 
In accordance with the invention, an improved bending die and ram assembly 
is provided for bending a metal tube in a tube bending machine. The 
improved bending die attaches to ram means such that the bending die is 
normally biased outwardly therefrom and can be easily interchanged with 
other differently sized bending dies without requiring the use of tools or 
accessory parts. The bending die drops into engagement with the ram means 
in a manner that enables one bending die to be easily and quickly lifted 
out of engagement with the ram means so that another bending die can be 
rapidly substituted therefor. The ram means slides along a guide rail to 
advance the bending die during a bending operation, and the die is 
maintained in alignment on the rail by lugs provided on the underside of 
the bending die. Following the bending operation, retractor hooks on the 
ram means advantageously engage and positively retract the bending die 
away from bent tubing and prevent the bending die from rising during 
disengagement and retraction of the die from the bent tubing. 
The tube bending machine comprises a machine frame carrying a hydraulic ram 
having the bending die attached thereto. The bending die has a 
conventional convexly curved bending die face presented toward a pair of 
side-by-side back gates mounted on the machine frame for swinging movement 
in opposite directions. Backshoe dies are mounted respectively on the back 
gates and cooperatively support the metal tube in a position for bending 
engagement by the bending die. The bending die is advanced by the ram 
toward the metal tube along the guide rail which extends along a line 
passing between the back gates and their associated backshoe dies. As the 
bending die engages the metal tube, the back gates and their backshoe dies 
are pivoted outwardly in opposite directions, with the combined die 
movements bending the metal tube through a selected angle. Support grooves 
of generally semicircular cross section are formed in the bending die and 
in the backshoe dies to cooperatively define a generally circular channel 
within which the metal tube is supported during a bending procedure, with 
the diametric size of this channel conforming generally with the diametric 
size of the tubing to be bent. 
In a preferred form of the improved bending die and ram assembly associated 
therewith, the bending die includes a pair of downwardly projecting lugs 
defined by bolt heads, or the like, extending from the underside of the 
bending die. The bending die is easily engaged with the hydraulic ram by 
positioning the die in front of the ram with the bolt heads in sliding 
engagement with opposite sides of the guide rail. One or more compression 
springs react between the bending die and a ram pusher block to normally 
bias the bending die outwardly from the pusher block. When that the 
bending die initially engages the metal tube, the biasing action of the 
springs advantageously maintains the die in tension against the tube so 
that an operator can rotatably adjust the position of the tube to an 
orientation appropriate for the desired bend. During advancing motion, the 
bolt heads extending from the bending die slide along the guide rail 
within elongated slots cooperatively defined by the guide rail and a pair 
of elongated retractor hooks that extend outwardly and forwardly from the 
pusher block on either side of the guide rail. 
A number of advantages are achieved by the use of the retractor hooks to 
retain the bending die with respect to the pusher block. More 
specifically, the retractor hooks and the bending die lugs cooperate with 
the guide rail to align the bending die thereon and prevent straying of 
the bending die to the right or left while in motion. Following a forming 
operation, the retractor hooks provide means for physically retracting the 
bending die from bent tubing, thereby preventing sticking of the bending 
die on the bent tubing. Such retraction can be enhanced by spacing the 
bolt heads sufficiently from the bending die to underlie the retractor 
hooks, whereby the bolt heads further prevent lifting of the die during 
rearward movement. Following retraction, the slots defined in part by the 
hooks allow for quick and easy removal of the bending die by merely 
sliding the bending die within the slots until the bolt heads are 
relocated out of interlocking engagement with the curved ends of the 
hooks, and then lifting the bending die out of the ram assembly. 
Other features and advantages of the present invention will become more 
apparent from the following detailed description, taken in conjunction 
with the accompanying drawings which illustrate, by way of example, the 
principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the exemplary drawings, an improved tube bending machine, 
referred to generally in FIG. 1 by the reference numeral 10, is provided 
for bending a metal tube particularly such as a metal tube of the type 
used for vehicle exhaust and tailpipe systems. The tube bending machine 10 
features an improved bending die 12 movable into bending engagement with a 
metal tube 14 (FIG. 3) which is supported by a pair of backshoe dies 16 
mounted on a pair of outwardly swinging back gates 18. 
The improved bending die 12 quickly and easily attaches to a pusher block 
22 having retractor hooks 23 in a simple drop-in manner to form a ram 
assembly 24 (FIG. 5). The bending die 12 can be rapidly detached from the 
pusher block 22 by merely lifting the bending die out of engagement with 
the retractor hooks 23. This feature of the ram assembly 24 beneficially 
enables multiple bending dies 12 to be interchanged without requiring the 
use of tools or accessory tooling die components, thereby reducing the 
operator time absorbed in switching bending dies as well as the number of 
parts which must be organized and maintained by the machine operator. The 
ease and speed with which bending dies can be interchanged with the 
present invention provides a significant advantage because vehicle exhaust 
systems utilize metal tubing of different standard diametric sizes and 
accordingly, to provide a full service tube bending capability, a machine 
owner is continually required to change the bending die size to match 
different diametric sizes of metal tubing. 
The retractor hooks 23 function to alleviate a problem which is commonplace 
in the tube bending art, namely, the tendency for prior bending dies to 
stick or hang up on bent tubing following a forming operation. This 
problem can be caused by tubing engagement forces and/or slight tubing 
compression that interlock the bending die with the bent tubing. To 
address this problem, the retractor hooks 23 are used as a positive 
mechanical link for physically pulling the bending die 12 away from the 
bent tubing when the ram assembly 24 is hydraulically retracted. The 
retractor hooks 23 also serve to prevent the bending die from rising 
during disengagement and retraction from bent tubing. A further advantage 
of the present invention is that the bending die 12 is designed to 
maintain a predetermined path while in motion without straying to either 
side. 
The general construction and overall operation of the tube bending machine 
10 is in most respects conventional in the art. More particularly, with 
reference to FIG. 1, the tube bending machine 10 comprises an upright 
rigid machine frame 26 which is desirably supported by small rollers or 
caster wheels 28 for easy portability, for example, about an automobile 
repair shop. The machine frame 26 supports a primary hydraulic cylinder 30 
and an auxiliary hydraulic cylinder 32 mounted generally one on top of the 
other in coplanar relation. A standard pump 34 is also carried by the 
frame 26 for supplying hydraulic fluid under pressure through conduits 36 
to the hydraulic cylinders 30 and 32, with appropriate controls 38 being 
provided to control fluid porting to and from the cylinders. Such fluid 
porting is effective to extend and retract an upper hydraulic ram 40 
associated with the primary cylinder 30 and a lower hydraulic ram 42 
associated with the auxiliary cylinder 32, all in a manner known to those 
skilled in the art. 
The upper or primary hydraulic ram 40 terminates in the pusher block 22 
presented toward the backshoe dies 16. The bending die 12 is carried by 
the pusher block 22 for advancing movement toward the backshoe dies 16 
into bending engagement with the metal tube 14, as will be described in 
more detail. As previously noted, this bending die 12 is adapted for rapid 
removable mounting onto the pusher block 22. A convexly curved die face 44 
is defined by the bending die 12 and conventionally has a generally 
semicircular shape presented toward the backshoe dies 16. This bending die 
face 44 is channeled to define a recessed groove 46 of generally 
semicircular cross sectional shape, with the diametric size of the groove 
46 corresponding closely with the diametric size of the tube to be bent. 
When metal tubing of a different diametric size is to be bent, the bending 
die 12 is removed from the machine 10 and replaced with an alternate 
bending die (not shown) having a recessed groove in the die face thereof 
sized to correspond with the diametric size of the metal tube to be bent. 
The alternate bending die may also have a convex plan shape formed with a 
different radius of curvature, if desired. The present invention enables 
alternate bending dies to be rapidly installed, as will be detailed 
hereinafter. 
The bending die 12 is advanced during machine operation by the hydraulic 
ram 40 along a centerline passing between the two back gates 18. In this 
regard, as viewed best in FIG. 1, the two back gates 18 are mounted 
side-by-side on the machine frame 26 for individual pivoting movement 
about a respective pair of vertically oriented bearings 48 (FIGS. 3 and 4) 
positioned in laterally offset relation from the bending die path of 
motion. As viewed in FIGS. 3 and 4, the back gates 18 are pivotal between 
a closed or side-by-side position (FIGS. 1 and 4) to an open position in 
laterally outward spaced relation (FIG. 3). In this regard, the back gates 
18 operate in generally the same manner as the tube bending machine 
described in U.S. Pat. No. 3,388,574, which is incorporated by reference 
herein. The backshoe dies 16 are geometrically shaped to provide stable 
support for the metal tube 14 to be bent during advancement of the bending 
die 12 into bending engagement with the metal tube. A preferred backshoe 
die construction is disclosed in copending application Ser. No. 
07/128,624, now U.S. Pat. No. 4,833,907 which is incorporated by reference 
herein. 
More particularly, the bending die 12 is advanced by the upper hydraulic 
ram 40 (FIG. 2) towards the backshoe dies 16. Further bending die 
advancement brings the die into engagement with the metal tube 14 
supported by the backshoe dies 16 and causes the backshoe dies to pivot 
outwardly in opposite directions (FIG. 3), with the combined motion of the 
various dies bending the metal tube without significant disruption of the 
circular cross section. The angle of the bend formed in the tube 14 is 
functionally related to the depth of the stroke of the bending die 12, and 
may be suitably preset by angle control mechanisms (not shown) as 
described, for example, in U.S. Pat. No. 3,388,574. Moreover, the radius 
of curvature of the formed bend is controlled by the convex contour of the 
bending die face 44. For optimum machine control, the outward swinging 
movement of the back gates 18 is resisted by the auxiliary hydraulic ram 
42 coupled by chains 50, or the like, to the back gates. After completion 
of the desired angle bend, the rams 40 and 42 are retracted for subsequent 
advancement to form another bend in the metal tube. 
In accordance with the invention, the bending die 12 has two holes 52 
drilled and tapped on its underside with two shoulder bolts 54 screwed 
into these holes. The shoulder bolts 54 define lugs which interact with 
the retractor hooks 23 to allow quick and easy changeover of the bending 
die on the machine without the use of accessory tools/parts. The ram 
assembly 24 (FIG. 5) is mounted for guided sliding motion in a direction 
toward and away from the backshoe dies 16 upon a guide rail 56. The guide 
rail 56 has a profile which fits into a slot in the underside of the 
pusher block 22 to provide a sliding engagement therebetween. The 
retractor hooks 23 each comprise a base having an arm extending forwardly 
therefrom which terminates in a curved free end. The retractor hooks 23 
are secured to the pusher block 22 on opposite sides of the guide rail 56 
by bolts 57 that pass through holes in the base into threaded engagement 
with holes 58 in the pusher block. The elongated shape of the retractor 
hooks provides open-sided channels 60 that cooperate with the guide rail 
56 to define elongated slots 62 (FIG. 4) for retaining the heads of the 
shoulder bolts 54. 
The front face of the pusher block 22 has a pair of bores 64 for retaining 
a pair of compression springs 66 disposed between the bending die 12 and 
the pusher block such that the springs 66 normally bias the bending die 12 
outwardly from the pusher block (FIG. 2). These springs will compress upon 
advancement of the bending die into engagement with the tube, and force 
application attributable to the bending die will substantially increase. 
Further forward motion of the hydraulic ram 40 will force the bending die 
12 into abutment with the pusher block 22, thereby effectively removing 
the biasing influence of the fully compressed springs from the system and 
eventually causing outward swinging of the backshoe dies to bend engaged 
tubing (FIG. 3). 
When the ram 40 is in the retracted position, the bending die 12 is easily 
loaded into the ram assembly 24 by lowering the die down upon the guide 
rail 56 in a manner allowing the heads of the shoulder bolts 54 to drop 
into the channels 60 in the two retractor hooks 23. The action of the 
springs 66 upon the bending die 12 will urge the bolts 54 along the 
elongated slots 62 in an outwardly or forwardly direction from the pusher 
block 22. However, upon installation, the bolts 54 will be spaced from 
curved distal or free ends 68 of the retractor hooks 23 and will not enter 
into a vertically interlocking engagement with the ends 68 until the 
retractor hooks 23 are used to retract the bending die 12 (FIG. 4). This 
mounting arrangement enables bending dies of different sizes to be 
removably attached to the front of the pusher block. 
The heads of the shoulder bolts 54 ride along the sides of the guide rail 
56 to beneficially keep the bending die aligned thereon and prevent the 
die from straying to either side while in motion. The retractor hooks 23 
also cooperate with the bolts 54 to affix the bending die in alignment 
upon the rail. 
The shoulder bolts 54 will remain retained within the elongated slots 62 
throughout a bending operation. However, the location of the bolts within 
said slots will change, as evidenced in FIGS. 2-4. Initially, prior to 
engagement of the bending die 12 with the metal tube 14, the bolts 54 are 
normally biased into a first position (FIG. 2), whereat the bolts are 
spaced inwardly or rearwardly from the curved hook ends 68 and are not 
interlocked in the vertical sense with the ends 68. Once bending of the 
metal tube has been completed, retraction of the ram assembly will result 
in the curved retractor hook ends 68 grasping the bolts 54 such that the 
bolts are located within the slots 62 at a second position (FIG. 4) 
whereat the bolt heads are vertically interlocked with the curved hook 
ends 68. 
Following retraction, the bending die 12 is rapidly detached from the 
pusher block by sliding the bending die within the slots 62 in a "return" 
direction toward the pusher block. This relocates the bolts 54 from the 
second position to the first position, thereby clearing the bolt heads 
from the curved hook ends 68. Once the bolts 54 are proximate the first 
position, an operator merely has to lift the bending die straight up to 
disengage the die from the ram assembly. The drop-in attachment of the 
bending die to the ram assembly and its lift-out detachment therefrom can 
advantageously be executed entirely without tools. As a further advantage, 
smaller sized bending dies can be installed without requiring accessory 
tooling components such as adapter plates. 
A primary functional advantage achieved by the present invention is 
provided by the retractor hooks 23 upon completion of a bending operation. 
As the upper hydraulic ram 40 retracts the pusher block 22 away from the 
backshoe dies 16, the curved hook ends 68 engage the shaft diameters of 
the shoulder bolts 54 and draw the bolts backwardly. In this manner, the 
hooks 23 provide a mechanical link for pulling the bending die away from 
bent tubing. This advantageously prevents the bending die from sticking to 
the bent tubing. 
In accordance with another advantage provided by use of the retractor 
hooks, the curved hook ends 68 fit between the underside of the bending 
die and the bolt heads to trap the shoulder bolt heads under the retractor 
hook lower surfaces so that the bending die cannot lift up during 
disengagement and retraction of the die from bent tubing. The bolt heads 
are captured in this manner in the retraction step illustrated in FIG. 4. 
This feature prevents the bending die from rising during retraction, 
thereby preventing the die from possibly marring a bent tube with an 
upwardly directed movement. Alternatively, the shoulder bolts 54 can be 
threaded completely into the underside of the bending die such that the 
bolt heads are flush therewith. This configuration will still position the 
bolt heads for engagement by the curved hook ends during retraction, 
without vertical interlock. 
From the foregoing, it will be appreciated that the improved bending die 
and ram assembly of the present invention effectively provides means for 
physically retracting the die from engagement with bent tubing. Moreover, 
a savings in operational time is realized by the invention's provision for 
quick and easy interchangeability of the bending die in a drop-in, 
lift-out manner which obviates the need for tools. 
A variety of modifications and improvements to the invention described 
herein will be apparent to those skilled in the art. Accordingly, no 
limitation on the invention is intended by the description herein or the 
accompanying drawings, except as set forth in the appended claims.