Method and apparatus for aligning die stamping press platens

The invention includes a self-aligning die platen assembly for use with a cooperating die platen assembly to form a die set. The self-aligning die platen assembly comprises a die shoe and a platen having a working face for operational cooperation with a corresponding working face of the cooperating die platen assembly. The platen is mounted in the die shoe and has a freely rockable condition therein which permits the platen to be moved into an aligned operational position in which its working face conforms to the corresponding working face of the cooperating die platen when the assemblies are closed. The die platen assembly also includes a locking element for securely maintaining the self-aligning platen in the operational position. A preferred locking device includes a low temperature melting alloy.

BACKGROUND OF THE INVENTION 
The present invention relates to an improved self-aligning die platen 
assembly for use in die stamping presses to facilitate the operation of 
such devices. 
Die stamping machines perform various operations on a number of substrates 
including paper, plastic, metal film and ceramics. These stamping machines 
include mutually cooperable die assemblies or a die assembly in 
cooperation with an anvil platen. A stamping machine must undergo a series 
of preparatory set-up steps directed to obtaining parallelism to the 
extent possible to achieve conformity between corresponding working faces 
of the die assemblies or die assembly and platen. In general, the 
preparatory steps needed to achieve the parallel conforming relationship 
involve preliminary placement of the die, followed by numerous trial runs 
and adjustments of the die until parallelism between corresponding working 
faces is achieved. This process is time consuming as well as requiring 
considerable operator skill. Nevertheless, no matter the stamping machine 
used, it is necessary that the corresponding working faces of the die 
assemblies or the die assembly and platen be in a parallel conforming 
relationship. 
For example, in the case of a die being used against a cooperating flat 
platen working face, it is not uncommon for portions of the operating edge 
of the die's working face to be of greater height than other portions. 
Therefore, when the die is moved toward a workpiece positioned on the 
cooperating platen, those portions of the working face of the die which 
are highest engage the workpiece before the other portions of the working 
face. As a result, the cut, crease press, lamination or perforating line 
is not uniform throughout the extent of the die. 
One manner of aligning the working faces of the platen and a die used in 
the prior art involves using a spring loaded platen and an epoxy. The 
springs are attached to the under side of the platen and placed within a 
die shoe reservoir. The reservoir is then backfilled with an epoxy that is 
cured while the press is held in a closed position. The epoxy fills in 
around the springs and holds the springs and platen in alignment. A major 
drawback is that once the epoxy has been set, the platen can not be 
repositioned without destroying it. In order to reposition the platen, the 
platen, springs and epoxy must all be removed from the die shoe and a new 
platen having new springs and new epoxy must be provided. This does not 
allow for repetitive, economical platen alignment with different 
cooperating platen assemblies. 
U.S. Pat. No. 5,517,910 to Skahan, incorporated herein by reference, 
suggests a self-leveling, rocking die platen for a die stamping press 
having a piston which rocks within a fluid chamber for the self-leveling 
of the die platen assembly. Skahan discloses that the piston moves within 
the fluid so that each time the die assembly is closed, the platen moves 
to achieve parallelism with the upper platen assembly. This platen 
requires the user to wait until the piston has rocked into position before 
the operation of the press can be carried out. Also, the piston is never 
secured relative to the shoe. Instead, it is free to rock and rotate 
relative to the shoe when the press is in an open position. Furthermore, 
the hydraulic fluid used to support Skahan's piston and platen compresses 
under high loads. This compression allows the platen to move out of 
position with the cooperating platen, resulting in inconsistent cuts, 
folds or perforations. 
There is a decided need in the art for an improved die set which maintains 
alignment between corresponding working faces of cooperating assemblies 
while permitting the assemblies to be reused for different operations 
without replacing expensive components. 
It is an object of this invention to overcome the disadvantages of the 
prior art by providing an economical, reusable die set and a method of 
operating such die set. 
SUMMARY OF THE INVENTION 
Broadly defined, the present invention includes a self-aligning die platen 
assembly for use with a cooperating die platen assembly to form a die set. 
The self-aligning die platen assembly comprises a die shoe and a platen 
having a working face for operational cooperation with a corresponding 
working face of the cooperating die platen assembly. The platen is mounted 
in the die shoe and has a freely rockable condition therein which permits 
the platen to be moved into an aligned operational position in which its 
working face conforms to the corresponding working face when the 
assemblies are closed. The die platen assembly also comprises a locking 
element operatively associated with the platen. The locking element is 
selectively and repeatedly changeable between a first condition to 
maintain the platen locked in the operational position when the assemblies 
are opened and a second condition to release the platen to the freely 
rockable condition. 
The locking element includes a material which is solid in the first 
condition and liquid in the second condition. More preferably, the 
material is a low temperature melting alloy. 
The present invention also includes a method of aligning cooperating die 
platen assemblies having mutually opposed platens. One of the platen 
assemblies is self-aligning and has a normally rockable condition. The 
method includes closing the assemblies to move the self-aligning platen 
into an aligned operational position conformed to the opposed platen. The 
method also includes releasably securing the self-aligning platen while 
said assemblies are closed and opening the assemblies while securely 
maintaining the self-aligning platen in the operational position. The 
method further includes releasing the self-aligning platen from its 
operational position back to the rockable condition. 
The self-aligning platen is secured by converting a material from a liquid 
state to a solid state and released by converting the material from a 
solid state to a liquid state. Preferably, the material is a low 
temperature melting alloy. 
In a preferred embodiment the metal alloy is melted outside the cavity and 
then introduced into the cavity through the filling port. It is also 
contemplated that the cavity may be filled by pouring the alloy into the 
cavity. Further, the alloy may be placed within the cavity and then melted 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a stamping press 10. The press includes a lower bolster 12 as 
well as an upper, opposed press head 14. The bolster 12 and head 14 are 
interconnected by conventional means such as columns 16. 
As best seen in FIG. 2, the stamping press 10 includes an operating die set 
20. The die set 20, for the purpose of illustrating the advantages of this 
invention, is shown as having an upper die platen assembly 30 having a die 
50, as well as a lower self-aligning die platen assembly 40. It is to be 
understood that the principles of this invention are applicable to die 
sets utilizing different types of dies and upper die shoe assemblies. 
The assemblies 30, 40 are interconnected and supported for shifting 
movement of the upper die platen assembly 30 by the upright, shouldered 
bushings 22. Upper die platen assembly 30 is essentially conventional and 
is in the form of an elongated, substantially rectangular upper plate 
mounted on posts 24 which are received in the bushings 22. 
As shown in FIG. 1, the die platen assembly 30 includes a die 50 fixedly 
mounted to the lower face of plate 32. The die 50 includes a mount 52 
secured to plate 30 and a working face 56 for operatively contacting the 
substrate and the lower assembly 40. 
Lower platen assembly 40 aligns platen working face 94 with working face 56 
of die 50 by moving working face 94 into an operational position in which 
parallelism exists between the working faces 56, 94. The lower assembly 40 
includes a substantially rectangular metallic die shoe 42 having an upper 
surface 44. Bushings 22 are supported by shoe 42. The center of shoe 42 
includes a downwardly extending cylindrical cavity 60. The cavity 60 
includes a circular cross section, but could have any appropriate cross 
section. Cavity 60 has vertically extending sidewall 62 and lower surface 
64. As best shown in FIG. 4, cavity 60 is also provided with an aperture 
70 in sidewall 62. Filling port 72 extends from an outer surface of shoe 
42 to the aperture 70. A low temperature melting alloy 66 is introduced 
into the cavity through filling port 72. 
Lower platen assembly 40 also includes a self-aligning platen subassembly 
80 which is mounted within cavity 60 so that the subassembly 80 can freely 
rockably move relative to cavity 60. The subassembly 80 includes a lower 
piston 82 having a bottom face 86 and a vertical sidewall 88 having a 
peripheral recess 90. A pressure seal 92 is positioned within the recess 
90 for sealingly engaging with the sidewall 62 of cavity 60 in order to 
maintain the alloy 66 within the cavity 60. 
The subassembly 80 further includes an upper platen 84 which is affixed to 
piston 82 by conventional means such as a series of bolts (not shown). The 
platen 84 includes a working face 94 for supporting a workpiece and for 
operationally cooperating with the working face 56 of die 50. When the 
platen assemblies are closed, working face 94 and working face 56 are 
moved toward each other causing the platen 84 of subassembly 80 to rock 
within cavity 60 so that working face 94 conforms to the configuration of 
working face 56 when the closure is complete, thereby achieving 
parallelism between the working faces with the platen 84 in its aligned 
operational position. 
While in a solid state, the alloy 66 locks the platen 84 in the aligned 
operational position and thereby maintains parallelism between working 
faces 56, 94. When converted to its liquid state, the alloy releases 
platen 84 and allows it to rock so that a new operational position can be 
established. Parallelism can be achieved multiple times between the same 
or different working faces by selectively convening the alloy 66 from a 
liquid state to a solid state and back to a liquid state. 
The low temperature melting alloy 66 locks the platen 84 in its aligned 
operational position when the working faces 56, 94 have achieved 
parallelism. The alloy preferably has a melting temperature between 100 
and 1000 degrees Fahrenheit, and more preferably between 104 and 750 
degrees Fahrenheit. Most preferably, the melting temperature is between 
117 and 302 degrees Fahrenheit. The low melting temperature makes the 
alloy 66 easy to handle and does not require elaborate and extensive 
melting equipment. 
The volume of the alloy 66 does not experience substantial, if any, change 
when it solidifies from its liquid state to its solid state. Also, the 
alloy exhibits high compressive strength which allows it to bear the heavy 
loads applied by such devices as die and laminating presses. Generally, 
the alloy is transformed from a solid to a liquid using heat. The alloy is 
returned to its solid state by cooling the liquid. The alloy can be 
repeatedly transformed between a liquid state and a solid state without 
harming the alloy. 
A preferred material is a fusible low temperature melting alloy. Many such 
materials are commercially available. One acceptable such alloy is 
available from the Cerro Metal Products Company under the trade name 
"Cerrobend". This alloy comprises 50 percent bismuth, 26.7 percent lead, 
13.3 percent tin and 10.0 percent cadmium and has a melting temperature of 
about 158 degrees Fahrenheit. The "Cerrobend" alloy maintains its volume 
within cavity 60 and when in a liquid state allows the platen to rock. 
Some acceptable alloys contain indium. Under certain conditions, other 
materials such as thermoplastics and waxes may be used. 
The use of illustrative die set 20 carried by press 10 is best shown in 
FIG. 2. FIGS. 2 and 3 show the assemblies 30, 40 being moved from an open 
position, solid lines, to a closed position, phantom lines, to create 
desired cuts, crease lines, perforations, laminations or other alterations 
in the workpiece. As the assemblies 30, 40 are brought into the closed 
position, the platen 84 rocks relative to cavity 60 while working face 94 
operationally engages the work piece and conforms to the corresponding die 
working face 56, thereby establishing parallelism between the faces. The 
platen 84 is then releasably secured in an operating position so that 
parallelism is maintained when the assemblies 30, 40 are opened during 
operation of the press 10. The operational position of the platen 84 can 
be repeatedly adjusted as discussed above. The vertical rest position of 
platen 84 can be altered by the amount of liquid metal 66 introduced 
within cavity 60. 
A platen subassembly 80 may be mounted within upper platen assembly 30 as 
part of press head 14. Alternatively, a series of smaller piston and 
platen subassemblies 80 may be provided, either as a part of lower bolster 
12 or incorporated into the upper platen assembly 30, in order to cover 
larger platen areas, as for example in presses having a platen area in the 
order of 20.times.24 inches. In addition, the platen 84 has a plurality of 
elongated passageways 96 designed to receive heating coils 98 which are 
provided for heating the platen 84 and the low temperature alloy 66 within 
the cavity 60. Alternatively or additionally, die shoe 42 may be provided 
with heaters 58 for melting the alloy 66. 
Many possible embodiments of the invention may be made without departing 
from the scope thereof which is defined by the appended claims. It is to 
be understood that all the matter set forth herein or shown in the 
drawings is illustrative and not limiting to the present invention. It 
will be understood that certain features and subcombinations have utility 
and may be employed without reference to other features or 
subcombinations. The self-adjusting platen assembly may be used with 
different types of presses and is not limited to the presses discussed 
above.