Method and apparatus for detecting press tool failure

A tool support and monitoring assembly for a press. The tool includes upper and lower die shoes, back-up plates, and upper and lower die tooling. The die tooling is secured to the back-up plate and includes a first surface facing the back-up plate and an opposite second surface. The back-up plate defines an air plenum which is connected to a pressure monitoring device. The die tooling defines a plurality of small bores which communicate with the air plenum. The bores extend from the first surface toward the second surface of the die tooling. The pressure monitoring device detects air pressure in the air plenum and bores, and shuts down the press to prevent a subsequent stroke when a pressure drop indicative of tool failure is detected.

BACKGROUND OF THE INVENTION 
The present invention is directed toward a method and apparatus for 
monitoring a tool in a press. It is important to monitor the condition of 
a tool to determine when the tool has failed, and to prevent a subsequent 
press stroke which can lead to catastrophic failure. Unfortunately, 
monitoring the condition of the tool is not easy due to the harsh 
operating environment. Several methods of monitoring tools have been 
proposed, each having its own drawbacks. 
U.S. Pat. No. 3,444,390 discloses a press impact sensor which is mounted to 
a platen beneath a lower die. The sensor is a piezo-electric sensor which 
converts pressure or shock waves into electrical signals. The sensed 
signals are compared to a reference signal and, when the signals fall 
outside a predetermined normal range, the press is shut down to prevent a 
subsequent strike. U.S. Pat. Nos. 3,930,248 and Re. 30,298 disclose a 
similar piezo-electric control circuit. U.S. Pat. No. 4,023,044 discloses 
a similar pressure monitoring arrangement for a punch press. 
U.S. Pat. Nos. 4,936,126; 4,987,528; 4,918,616; 4,750,131; 4,698,991; 
4,651,273; 4,633,720; and 4,593,547 disclose methods for sensing die 
pressure and defective parts. 
U.S. Pat. No. 3,555,865 discloses a press having an upper die, a lower die, 
a fixed anvil or platen, and a sow block disposed between the lower die 
and the fixed platen. The platen has a series of passageways formed 
therein through which hydraulic fluid flows to an area between the sow 
block and the platen to form a cushioning film therebetween. 
There exists a need in the art for a simple and reliable method and 
apparatus for sensing failure of a tool in a press. There also exists a 
need in the art for a method for controlling a press to prevent a 
subsequent stroke in the event of tool failure. 
SUMMARY OF THE INVENTION 
The present invention is directed toward a simple and reliable apparatus 
and method for monitoring a press tool for failure. The present invention 
is further directed toward a method for controlling a press to prevent a 
subsequent stroke upon detection of tool failure. 
In accordance with the present invention, a tool includes upper and lower 
die shoes, a plurality of back-up plates secured to the die shoes, and die 
tooling secured to the back-up plates by one or more attachment bolts. The 
back-up plate has a plurality of annular grooves formed on a surface 
thereof which faces the die tooling. At least one of the grooves receives 
a seal to define a space between the at least one groove, the back-up 
plate, and the tool. An air plenum is in communication with the space. A 
bore extends through the back-up plate and serves as an air inlet through 
which pressurized air is introduced into the air plenum. 
In further accordance with the present invention, the die tooling has a 
plurality of air passages formed therein which extend from the surface of 
the die tooling facing the back-up plate toward an opposite surface of the 
die tooling. The air passages are aligned with the air plenum, and are 
supplied with pressurized air therefrom. 
In further accordance with the present invention, the air inlet of the 
back-up plates are fluidly connected to each other by an air line. The air 
line has a pressure transducer therein which communicates pressure signals 
to a pressure monitoring device. When the tool fails pressurized air is 
released from the air passages and/or the air plenum. The drop in air 
pressure is detected by the pressure monitoring device. The pressure 
monitoring device continuously monitors the air pressure signal and sends 
signals to the press control device when the sensed pressure exceeds 
reference limit(s). When the sensed pressure exceeds the limit(s), the 
press control device shuts down the stamping press to prevent a subsequent 
stroke which may result in catastrophic failure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
It should be noted that in the detailed description which follows, 
identical components have the same reference numeral, regardless of 
whether they are shown in different embodiments of the present invention. 
It should also be noted that, in order to clearly and concisely disclose 
the present invention, the drawings may not necessarily be to scale and 
certain features of the invention may be shown in somewhat schematic form. 
With reference to FIG. 1, a press tool 10 according to the present 
invention is illustrated. The press tool 10, which is a removable assembly 
inserted into a stamping press (not shown), includes upper and lower die 
tooling 12, 14, back-up plates 16, 18, and upper and lower die shoes 20, 
22. The upper die or upper die tooling 12 may also be referred to 
hereinafter as the movable or first dies and the lower die or lower die 
tooling 14 may be referred to hereinafter as the fixed or second dies. 
Each upper die 12 is secured to an associated upper back-up plate 16, and 
each lower die 14 is secured to an associated lower back-up plate 18, as 
illustrated. The upper back-up plates 16 are secured to the upper die shoe 
20, and the lower back-up plates are secured to the lower die shoe 22. 
The upper die shoe 20 is secured to a ram (not shown). The lower die shoe 
22 is secured to a fixed support or bolster (not shown). The ram is 
reciprocally movable between a first, upper position (FIG. 1) and a 
second, lower position. When the ram is in the first, upper position, the 
upper dies 12 are upwardly spaced from the lower dies 14. When the ram is 
in the second, lower position, the upper dies 12 are in contact with the 
lower dies 14. The upper position corresponds to zero degrees of 
crankshaft rotation or top dead center, and the lower position corresponds 
to 180 degrees of crankshaft rotation or bottom dead center. 
Generally, a piece of metal to be formed is placed between associated ones 
of the upper and lower dies 12, 14 when the ram is in the upper position. 
As the ram is moved into the lower position, the piece of metal is 
deformed between the upper and lower dies 12, 14. After the ram is moved 
upwardly away from the lower position, the deformed metal is removed from 
the lower die 14. In a sequential press having plural stations, a transfer 
mechanism (not shown) may move the deformed metal to an adjacent set of 
upper and lower dies for further forming. It is submitted that the 
stamping press and method described hereinbefore is conventional and well 
known in the art. 
The following overview of the press control system according to the present 
invention is provided. In the present invention an air line 50 connects 
the upper and lower back-up plates 16, 18 to a pressure transducer. The 
pressure transducer transmits an analog signal corresponding to the sensed 
pressure to a pressure monitoring device. The pressure monitoring device 
includes a converter, to convert the analog pressure signal into a digital 
signal, and a software program, to interpret the digital signal. 
If the sensed pressure is within predetermined acceptable parameters, the 
pressure monitoring device sends a signal to the press control device 
indicative of same. However, if the sensed pressure is outside the 
predetermined acceptable parameters, and thereby indicates that the tool 
has failed, the pressure monitoring device transmits a signal to the press 
control device indicating that the press should be stopped. The press 
control device controls starting and stopping of the press in response to 
the signals provided to it, such as the signal from the pressure 
monitoring device. Although monitoring of the tool condition is described 
hereinafter relative to the lower die tooling 14, it is considered 
apparent that the description is equally applicable to the upper die 
tooling 12. 
The back-up plate 18 may be universal in design or may be custom made to 
correspond with the configuration of the associated lower die tooling 14. 
Due to the large variation in tool configurations, custom made back-up 
plates are routinely required. Accordingly, it is to be understood that in 
the description to follow, the lower die tooling 14 and back-up plate 18 
are presented in schematic form to illustrate the preferred embodiment of 
the present invention, and the present invention is not limited to the 
specific appearance or configuration of the die tooling/back-up plate 
specifically illustrated herein. 
With reference to FIGS. 2-4, the illustrated and preferred back-up plate 18 
includes a threaded central bore 24 which receives an attachment bolt 26 
to releasably secure the die tooling 14 thereto. The back-up plate 18 is, 
in turn, releasably secured to the lower die shoe 22 by mechanical 
fasteners. 
Radially surrounding the central bore are three annular grooves 30, 32, 34. 
The radially inner and outer grooves 30, 34 are adapted to receive O-rings 
36a, 36b to seal the die tooling 14 to the back-up plate 18. The 
intermediate groove 32 serves as an air plenum, and may be wider or 
otherwise have a greater volume than the inner and outer grooves 30, 34, 
as necessary to provide the desired capacity and pressure characteristics. 
A bore 38 extends through the back-up plate 18 and communicates with the 
intermediate groove 32. The bore 38 serves as an air inlet through which 
pressurized air is introduced into the air plenum or intermediate groove 
32. 
The die tooling 14 has a first, generally planar surface 40 facing the 
grooved surface 42 of the back-up plate 18. The O-rings 36a, 36b seal the 
area defined between the O-rings, the first surface 40 of the die tooling 
14, and the back-up plate 18. 
The die tooling 14 has a plurality of small bores 44 extending from the 
first surface 40 toward the opposite, second surface 46. The bores 44 
align and fluidly communicate with the air plenum or intermediate groove 
32 and the bore 38. Experimentation has found that three small bores 
positioned 120 degrees apart performs satisfactorily. Naturally, more or 
less than three bores may also be employed without departing from the 
scope and spirit of the present invention. 
The small bores 44 stop a short distance below the second surface 46. The 
distance is chosen so as to be as close to the second surface 46 as 
possible without weakening the die tooling. It is noted that the second 
surface 46 of the die tooling 14 is engaged by the metal being formed, and 
is most likely to fracture. 
When multiple die tooling is accommodated in a single tool, such as the 
tool 10 shown in FIG. 1, the air inlets 38 of each of the back-up plates 
16, 18 are connected together by means of air lines or conduits 50 in a 
daisy-chain type fashion. As such, the back-up plates 16, 18 and upper and 
lower die tooling 12, 14 are fluidly interconnected in a serial fashion 
and define a pressurized system. 
The system is continuously provided with pressurized air from a compressed 
air source, preferably at a low pressure of between about 20-30 psi, and 
then monitored in the fashion described hereinafter to determine when one 
of the die tooling 12, 14 fails. The supplied pressure counteracts 
unavoidable small system leaks, and establishes a constant set point or 
reference level. 
A pressure transducer is provided in the air line downstream of the die 
tooling 12, 14, and senses the air pressure in the system. The transducer 
provides an analog electrical signal corresponding to the sensed air 
pressure to a pressure monitoring device. As used herein, the pressure 
monitoring device includes a signal conditioning device and a software 
control program. The output from the pressure monitoring device is 
supplied to the press control device. The press control device is operable 
to start and stop the press in response to signals which it receives, 
including signals from the pressure monitoring device. 
The signal conditioning device, such as a signal conditioning board, 
converts the analog pressure signal into a digital pressure signal. The 
computer software program interprets the digital pressure signal and sends 
control signals to the control device to operate the press in accordance 
with the sensed pressure. One software control program used satisfactorily 
by applicants is sold under the tradename SAMVIEW by Signature 
Technologies, Inc., of Dallas, Tex. 
The signal conditioning device receives numerous other signals from sensors 
in the press monitoring system, and these signals are converted and 
supplied to the press control device. Typically, these sensed parameters 
are correlated to the angular position of the crank shaft to provide a 
reference point for analysis. 
During the 360 degrees of crank shaft rotation, the die tooling 12, 14 
engage and deform metal for only a fraction of the time. During this 
active portion or working stroke, which is typically only the portion of 
the stroke before and after bottom dead center, or between about 120 and 
240 degrees of crank shaft rotation, the upper die tooling strikes and 
deforms the metal and then moves away from the formed piece of metal. 
With reference to FIG. 5, a function of the software program provided by 
the pressure monitoring device is to monitor the sensed pressure relative 
to a set point pressure and, if there is a substantial change, prevent a 
subsequent press stroke. Preferably, there are inner and outer limits 60, 
62 above and below the set point pressure. Typically, the sensed pressure 
varies slightly during a cycle, but will stay within the inner limits 60. 
If the sensed pressure passes the inner limits 60 as indicated by arrow A, 
it is indicative of some problem, and the pressure monitoring device will 
send a signal to the press control device to shut down the press at top 
dead center or zero degrees rotation. If the pressure passes through the 
outer limits 62 as indicated by arrow B, indicative of a serious failure 
in the pressurized system, the pressure monitoring device will send a 
signal to the press control device to shut down the press immediately. 
While the preferred embodiment of the present invention is shown and 
described herein, it is to be understood that the same is not so limited 
but shall cover and include any and all modifications thereof which fall 
within the purview of the invention. For example, if the die tooling does 
not have a central attachment bolt, only one outer seal will be necessary 
to seal the space between the die tooling and the back-up plate. Also, the 
seals and grooves are not limited to being circular in shape. It is also 
contemplated that the seals could be unnecessary if a satisfactory 
metal-to-metal sealing contact could be reliably provided.