Apparatus and method for cushioning the action of draw dies operating in a stamping press and the like

A draw die operable within a straightside press includes a lower die shoe with a lower die; pressurized lift cylinders each having an upwardly extending piston rod and an axial resistance to compression; a generally ring-shaped cushion defining a central hole and a plurality of lock beads extending upwardly in spaced-apart relation surrounding the central hole, wherein the cushion surrounds the punch, is sized and configured to support a blank atop the beads and over the punch for draw forming the blank over the punch, and is supported by the lift cylinders; a plurality of cushion units held by the shoe and each having an upwardly extending piston rod and an axial resistance to compression; an upper die defining a second stamping shape which mates with the first stamping shape; a plurality of hydraulic shock absorbers held by the upper die and having an axial resistance to compression and a piston rod that extends downwardly toward the cushion. A ram mechanism moves the upper die downwardly where the shock absorbers engage the cushion and accelerate it downwardly, depressing the lift cylinders somewhat. Upon further downward movement of the upper die and cushion, the cushion cylinders become engaged and offer sufficient resistance as they are depressed to bind a blank between upper die and cushion and to draw form the blank between the two dies. After reaching the bottom of the stroke, the upper die retracts upwardly, along with the cushion lifted by the lift cylinders, but the pistons rods of the self-contained cushion units are delayed in their upward return by an internal valving system.

FIELD OF THE INVENTION 
The present invention relates to the field of stamping presses, and 
specifically to an apparatus and method for cushioning the action of draw 
dies operating in stamping presses and the like. 
BACKGROUND OF THE INVENTION 
For many years, double action or "toggle" presses were the industry 
standard for forming large metal parts such as automobile hoods. A toggle 
press has an outer ram that comes down and binds the blank to be formed. 
An inner ram with a punch having the desired part shape then follows 
through to draw the blank into a complementary shaped die cavity. In the 
quest for speed and efficiency, much of the industry is now using 
straightside or transfer presses which is the forming press to form the 
initial shape from the flat metal blank. Next, the part passes through a 
series of individual stations or presses to complete the necessary die 
operations, all in one combination process. Unfortunately, toggle presses 
are relatively slow and form the part in an inverted or upside down 
orientation. In most cases then, the toggle press will most likely have to 
include a turnover station following the draw operation. A solution to the 
speed and inversion problem is the use of the straightside press. Unlike 
the toggle press, where the outer ram comes down gently to bind the blank 
for drawing. Straightside presses have but a single ram with an upper die 
or binder that is actuated by the throw of the press crank cycling at up 
to 30 strokes per minute and at up to 30 inch strokes. The die cushion or 
lower binder surrounds a lower punch which defines the complementary part 
shape to the cavity of the upper die. The cushion floats around the punch 
and is supported in an up position upon a series of gas springs that 
collectively offer adequate force to bind the blank for the draw 
operation. When the upper die binder face meets the floating cushion and 
blank, the blank is instantly contained between the upper and lower binder 
faces. The impact between the ram and cushion at this instant is 
tremendous and is the result of the fast moving ram contacting the 
stationary cushion. The shock caused by this impact causes great damage to 
the press drive and creates undesirable pressure spikes in the individual 
cushion unit seals. After contact, because the ram force exceeds the 
resistance force of the gas cylinders, the ram, blank and cushion continue 
downward at the automatic press cycle speed until the they reach the 
bottom of the stroke, at which point the blank has been formed to the 
desired shape. At this point, the cushion cylinders have been compressed, 
and their resistive force has increased in accordance with the compression 
ratio of the nitrogen gas (Boyle's law). Cushion forces for major 
automotive dies commonly operate in the range of 200 to 300 tons. When the 
press ram reaches bottom position and starts its upstroke, the nitrogen 
gas cushion springs with their intensified pressure forces against the 
upper die throughout the die cushion upstroke. These forces cause major 
press drive damage, and stamping facilities have long been seeking a 
method to unload the cushion forces at the bottom of the press stroke so 
the cushion forces do not follow through causing such damage. Thus, while 
gains have been made in speed and efficiency form the use of straightside 
presses versus toggle presses, the wear and tear inherent in the 
application of straightside presses continues to plague its users. 
What is needed is a way to abate or eliminate the wear and tear resulting 
from the high impact and recoil effect inherent in straightside presses 
using nitrogen spring-loaded die cushions and to delay the die cushion 
"up" force such that the primary cushion force will not follow the press 
ram "up" stroke. 
SUMMARY OF THE INVENTION 
Generally speaking, apparatus is provided for cushioning the action of draw 
dies operating in a straightside stamping press. The apparatus includes a 
shock absorber for overcoming the inertial impact between the ram driven 
upper die shoe and the motionless cushion surrounding the forming punch. 
The apparatus also includes a delayed return cushion unit that provides 
the cushion with high tonnage resistance to movement when the ram slams 
into the cushion, thereby enabling proper binding of the blank, but 
conversely permits the ram to return to its upper position without the 
added tonnage of the resistance cushion units following it back up. The 
apparatus further includes assembly and use of the shock absorbers, 
cushion units, and other press components to maximize the operation of the 
press while minimizing the attendant wear and tear thereon. 
A draw die operable within a straightside press includes a lower die shoe 
with a lower die; pressurized lift cylinders each having an upwardly 
extending piston rod and an axial resistance to compression; a generally 
ring-shaped cushion defining a central hole and a plurality of lock beads 
extending upwardly in spaced-apart relation surrounding the central hole, 
wherein the cushion surrounds the punch, is sized and configured to 
support a blank atop the beads and over the punch for draw forming the 
blank over the punch, and is supported by the lift cylinders; a plurality 
of cushion units held by the shoe and each having an upwardly extending 
piston rod and an axial resistance to compression; an upper die defining a 
second stamping shape which mates with the first stamping shape; a 
plurality of hydraulic shock absorbers held by the upper die and having an 
axial resistance to compression and a piston rod that extends downwardly 
toward the cushion. A ram mechanism moves the upper die downwardly where 
the shock absorbers engage the cushion and accelerate it downwardly, 
depressing the lift cylinders somewhat. Upon further downward movement of 
the upper die and cushion, the cushion cylinders become engaged and offer 
sufficient resistance as they are depressed to bind a blank between upper 
die and cushion and to draw form the blank between the two dies. After 
reaching the bottom of the stroke, the upper die retracts upwardly, along 
with the cushion lifted by the lift cylinders, but the pistons rods of the 
self-contained cushion units are delayed in their upward return by an 
internal valving system. 
The delayed return cushion units each include an outer tube having an inner 
diameter; a base plate disposed at the bottom of the cylinder; an 
annular-shaped head plate disposed at the top of the cylinder and having 
an inner cylindrically-shaped wall; an inner tube having in outer diameter 
and in inner diameter and mounted to extend between the head plate and the 
base plate coaxially within the outer tube; an annular-shaped outer piston 
coaxially mounted between the inner and outer pistons to reciprocate 
between the head plate and the base plate; an inner piston/rod coaxially 
mounted in the inner tube to reciprocate vertically therein between a 
retracted, compressed position and an extended, rest position, the rest 
position including the piston/rod extending through the inner 
cylindrically-shaped wall of the head plate and upwardly of the head 
plate; wherein the outer tube, base plate, head plate, inner tube, outer 
piston and inner piston define: a gas chamber bounded by the outer tube, 
inner tube, head plate and outer piston, an outer hydraulic chamber 
bounded by the outer tube, inner tube, base plate and outer piston, and in 
inner hydraulic chamber bounded by the inner tube, base plate and inner 
piston; seal means for preventing leakage of gas from the gas chamber and 
hydraulic fluid from the hydraulic fluid chambers; passageway means 
providing communication between the outer hydraulic chamber and the inner 
hydraulic chamber and including a check valve permitting substantially 
unrestricted fluid flow from the inner hydraulic chamber to the outer 
hydraulic chamber, but severely restricting fluid flow from the outer 
hydraulic chamber to the inner hydraulic chamber; gas in the gas chamber 
having a pressure greater than ambient pressure; hydraulic fluid disposed 
in the inner and outer hydraulic chambers; and, means for retaining the 
head plate, base plate, inner tube, out piston and inner piston contained 
substantially entirely within the outer tube. 
It is an object of the present invention to provide an improved stamping 
draw press operation. 
It is another object of the present invention to provide apparatus for 
stamping presses that will abate the impact of the die against the 
motionless cushion. 
It is a further object of the present invention to provide apparatus for 
stamping presses that will abate the recoil force exerted on the cushion 
and ram mechanics on the upstroke of the press cycle. 
Further objects and advantages will become apparent from the following 
description of the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purposes of promoting an understanding of the principles of the 
invention, reference will now be made to the embodiment illustrated in the 
drawings and specific language will be used to describe the same. It will 
nevertheless be understood that no limitation of the scope of the 
invention is thereby intended, and that any alterations or modifications 
in the illustrated device, and any further applications of the principles 
of the invention as illustrated therein are contemplated as would normally 
occur to one skilled in the art to which the invention relates. 
Referring now to FIGS. 1 and 2, there is shown a draw die operable within a 
straightside press 10 equipped with apparatus for cushioning the action of 
the die in accordance with the preferred embodiment of the present 
invention. Die 10 generally includes a lower die shoe 11, a punch 12, a 
pad or "cushion" 13, a set of four (4) lift cylinders 15, a plurality of 
delayed return cushion units 17, an upper die shoe 18, upper die 20, and a 
set of hydraulic shock absorbers 21. As with other presses of this type, 
punch 12 is fixedly mounted to lower shoe 11 and has a top surface 22 
which defines the desired shape of the part to be formed. For purposes of 
discussion of the current embodiment, and as seen by the plan view outline 
23 of punch 12 (FIG. 1), the part intended to be formed by die 10 is an 
automobile hood. The present invention is not intended to be limited to 
the formation of hoods, or of auto parts. Further, the present invention 
and its components are contemplated to have applications outside of the 
stamping industry. 
Cushion 13 is a ring that encircles punch 12 and has an outer surface 24, 
an inner surface 25, an upper surface 26 and a lower surface 27. Cushion 
13 thus defines a central hole that is bounded by inner surface 25 and 
through which extends punch 12. The outer profile of cushion 13, in 
overall plan view, is rectangular, as shown by the outline of outer 
surface 24 (FIG. 1) and the inner profile defined by inner surface 25 in 
plan view has the same shape as the plan view shape (at 23) of punch 13. 
Upper and lower surfaces 26 and 27 are parallel to each other and 
orthogonal to outer and inner surfaces 24 and 25. Cushion 13 is thus sized 
to reciprocate vertically around punch 12, but is held floating in the up 
and rest position (as seen in the left half of FIG. 2) by the lift 
cylinders 15. There are four lift cylinders 15, one at each corner, 
mounted in cavities in lower shoe 11. Each cylinder 15 is a standard, 
three ton nitrogen gas cylinder with a piston rod 30 that may reciprocate 
between a retracted, compressed position and an extended, rest position. 
In the rest position, piston rod 30 extends about 7 inches from the floor 
31 of lower shoe 11. In its compressed position (right half of FIG. 2), 
piston rod 30 is flush or extends just slightly above floor 31. Numerical 
values for dimensions, weights, pressures and other characteristics are 
used herein for purposes of describing one proposed embodiment. It should 
be understood that such values will vary with the type and size of the 
part to be formed and with the desired operating characteristics of the 
corresponding press. 
A plurality of lock beads or draw beads 32 for binding a blank 33 extend 
upwardly from upper surface 28, proximal to inner surface 25, and thus 
surround punch 12. Lift cylinders 15 are sized so that, in the rest 
position, piston rods 30 support cushion 13 high enough so that its upper 
surface 26 is approximately one inch above the highest point on punch 12. 
That is, in the rest position, a blank 33 may be positioned over punch 12 
and supported around its periphery by beads 13 of cushion 13, as shown in 
the left side of FIG. 2. Depending on the size of the blank and on the 
profile of the punch, blank 33 will not touch punch 12 in this rest 
position, prior to the descent of the upper die 20. 
The plurality of delayed return cushion units 17 sit within cavities in 
lower die shoe 11 in a spaced relationship around punch 12 and under 
cushion 13. In the present embodiment, there are 34 cushion units 17. As 
will be described, each cushion unit 17 has a piston rod 36 that extends 
upwardly approximately six inches above the floor 31 of lower shoe 11. 
Upper die 20 defines a cavity 37 with an inner surface 38 that mates with 
the top surface 22 of punch 12 to define the shape of the part to be 
formed. Upper die 20 also defines a lower, planar surface 39 and is 
mounted to the underside of upper die shoe 18 which is mounted to a ram 
(not shown) which drives shoe 18 and upper die 20 down against cushion 13 
and punch 12 to form the desired part. The set of hydraulic shock 
absorbers 21 comprises four shock absorbers 21 that are mounted at the 
corners of upper die shoe 18 and upper die 20, and in substantial 
alignment over the four lift cylinders 15. As will be described, each 
shock absorber 21 engages with a plunger or adapter 40 that extends one 
inch below lower planar surface 39. Lower die shoe 11 has four guide posts 
43, one extending upwardly from each of its corners, and upper die shoe 
has a corresponding bushing 44 at each of its corners, each bushing sized 
to receive a guide post therein to ensure alignment between upper shoe 18 
and lower die shoe 11 when the two are brought together. 
Referring to FIGS. 3 through 5, there is shown a delayed action cushion 
unit 17 in accordance with the preferred embodiment of the present 
invention. Cushion unit 17 generally includes an outer tube 47, an inner 
tube 48, a head plate 49, a base plate, 50, an inner piston and rod 
combination 51, an outer piston 52, a check valve 53, a disc-shaped check 
valve retainer 54, and a rod end cover 55, upper and lower lock rings 56 
and 57, lock pins 58 and 59, set screw 60, and various seals to be 
described. Outer tube 47 is cylindrically-shaped and defines upper and 
lower, inner annular recesses 65 and 66, respectively, that are 
hemi-circular in cross-section. Inner tube 48 is also cylindrical and 
defines upper and lower annular recesses 67 and 68 for receipt of 0-rings 
and defines a pair of diametrically opposing, outer transverse recesses 69 
and 70 that are arcuate in cross-section and juxtaposed just above lower 
recess 68. Outer and inner tubes 47 and 48, respectively, are made of 
hardened tool steel. 
Head plate 49 is generally cylindrically-shaped and made of hardened tool 
steel. It has an outer diameter substantially equal to the inner diameter 
of outer tube 47 and defines an inner generally cylindrical wall 71 which 
has an inner diameter substantially equal to the outer diameter of the 
upper portion of inner piston and rod combination 51. Head plate 49 also 
defines an upper annular recess 72, the lower portion of which is radiused 
at 73 to match that of upper lock ring 56 so that lock ring 56 will seat 
snugly around head plate 49 at the bottom of recess 72, as shown. Head 
plate 49 defines a cylindrically shaped flange 74 extending downwardly 
therefrom and having an inner radius substantially equal to the outer 
radius of inner tube 48. Head plate also includes a fill port 75 for 
injecting nitrogen gas into the gas chamber 77 of cushion unit 17, as 
described herein. A valve core (not shown) is provided for insertion into 
fill port 75 to enable injection of nitrogen gas into gas chamber 77. The 
valve core may be of any appropriate type that permits injection of 
pressurized gas from a pressurized gas source. At the lower end of cushion 
unit 17, base plate 50 is round in cross-section, made of hardened tool 
steel, and defines a lower annular recess 78 that has a rectangular 
cross-section to define an outer cylindrically shaped wall 79 and an upper 
planar and annular shoulder 80. At the intersection of shoulder 80 and the 
outer cylindrical wall 81 of base plate 50, an annular recess 82 is 
defined which is radiused to match that of lower lock ring 57 so that lock 
ring 57 will seat snugly within recess 82, as shown. Base plate 50 has a 
top surface 85 and defines concentric central recesses 86, 87, 88 and 89, 
each recess having a generally cylindrical outer wall, and each of 
recesses 87, 88 and 89 having a diameter that is less than the diameter of 
the recess above it. The uppermost recess 86 has a diameter substantially 
equal to the outer radius of inner tube 48. Recess 87 has a diameter 
substantially equal to that of the outer diameter of disc-shaped check 
valve retainer 54. Recess 87 includes a planar annular floor 90 which has 
defined therein a rectangular cross-sectioned, annular recess 91. Recess 
88 has a diameter slightly less than the inner diameter (at 92) of 
retainer 54 and substantially equal to the outer diameter of the lower 
cylindrical portion 93 of check valve 53. The lowest recess 89 is in 
communication with a transverse passage 94 which is defined in base plate 
50 and is in communication with upwardly angled and diametrically opposed 
passages 95 which are also defined in base plate 50 and open up through 
top surface 85 into outer hydraulic chamber 96 of cushion unit 17, as 
described herein. Base plate also defines a pair of parallel and 
diametrically opposed holes 98 and 99 (FIG. 4) that are sized and 
positioned so that, when inner tube 48 is positioned down into top recess 
86, outer transverse recesses 69 and 70 align with holes 98 and 99, 
respectively, and lock pins 58 and 59 may be inserted through holes 98 and 
99 to lock inner tube 48 to base plate 50 as shown. Lock pins 58 and 59 
are made of hardened drill rod, but the use of other suitable materials in 
other suitable configurations is also contemplated. Base plate 50 also 
includes an oil fill port 100 and a vent port 101 which are disposed 
approximately 90 degrees from passages 95 (FIG. 5). Fill port 100 extends 
vertically from the bottom surface 102 of base plate 50 and up through top 
surface 85 and into communication with outer hydraulic chamber 96. Vent 
port 101 extends vertically from the bottom surface 102 of base plate 50 
and opens up into the annular recess 91 defined in floor 90 of recess 87, 
and thus just below check valve retainer 54. Check valve retainer 54 (FIG. 
6) has a generally disc-like shape and defines a hole 125 spaced between 
midway between it inner and outer cylindrical surfaces 126 and 127. Thus, 
when check valve retainer 54 is seated within recess 87 and over annular 
recess 91, vent port 101 is in communication through annular recess 91, up 
through hole 125 and onto the chamber surrounding check valve 53. As with 
fill port 75, valve core members of any suitable type (not shown) are 
provided for insertion into fill and vent ports 100 and 101 to enable 
injection of oil or other appropriate hydraulic fluid into hydraulic 
chambers 96 and 97 and to permit venting thereof. 
Check valve 53 is preferably a Kepsel brand check valve, model number 2216, 
commercially available from Kepner Products Company, 995 N. Ellsworth 
Avenue, Villa Park, Ill. 60181, and oriented to permit free flow in the 
downward direction, as viewed in FIG. 3. The Kepsel valve 53 has a cone 
shaped poppet (not shown) with a small orifice therethrough which meters 
the return flow of oil in the upward direction, as viewed in FIG. 3. Other 
check valves may be used to achieve a desired flow rate or to satisfy 
other operating or construction parameters. (One such alternative 
embodiment is shown in FIG. 12.) Valve 53 has a main cylindrical body 103 
and a lower cylindrical body portion 93, the diameter of main body 103 
being slightly less than that of lower body portion 93, thereby creating a 
shoulder 104. Lower body portion 93 also includes an o-ring 105 mounted 
within an annular recess, as shown. 
Piston and rod combination 51 (hereafter referred to as piston/rod 51) is 
made of hardened tool steel and has an upper piston rod portion 108 and a 
lower piston portion 109. The outer diameter of piston rod portion 108 is 
substantially equal to the inner diameter of head plate 49, and the outer 
diameter of piston portion 109 is substantially equal to the inner 
diameter of inner tube 48. Piston portion 109 defines a downwardly opening 
cavity 110 that is sized to be slightly larger than the Kepsel check valve 
53 so that piston/rod 51 may translate to the bottom of its stroke and 
valve 53 will be received within cavity 110, as shown in FIG. 3. Piston 
rod portion 108 defines a central, upwardly opening cavity 112. Hex-headed 
set screw 60 has been adapted to screw into the top of cavity 112 as shown 
and has been provided with an o-ring to effect a fluid-tight seal thereat. 
The outer diameter of piston rod portion 108 is slightly less than the 
inner diameter of inner tube 48, thus creating an outer cavity 113, in 
assembly of cushion unit 17, bounded by piston rod portion 108, inner tube 
48, head plate 49 at the top and larger diameter piston portion 109 at the 
bottom. Central cavity 112 is in fluid communication with outer cavity 113 
via four passages 114 that extend outwardly from central cavity 112, as 
shown. 
Outer piston 52 is annular and has a rectangular cross-section at any 
section thereof as shown in FIG. 3. Piston 52 has top and bottom surfaces 
117 and 118, respectively, and has inner and outer cylindrical surfaces 
119 and 120, respectively. Annular recesses are defined in inner and outer 
surfaces 119 and 120, respectively, to receive annular seals 121, 122, 123 
and 124. Any suitable seals may be used for seals 121-124 which can 
operate at temperatures up to 400.degree. F. and should be capable of 
withstanding a maximum operating pressure of 5000 psi. However, the 
precise type, brand and characteristics of each seal will vary with the 
attendant parameters such as the type of fluid to be kept sealed, the 
operating pressures, the temperatures, and so on. Likewise, the other 
seals described herein may also be of any suitable type to prevent leakage 
of the fluid medium from the corresponding chamber under the design 
parameters of the cushion unit. 
Seals are also provided by o-ring 131 between outer tube 47 and head plate 
49, by o-ring 132 between outer tube 47 and base plate 50, by o-ring 133 
between inner tube 48 and head plate 49, and by o-ring 134 between inner 
tube 48 and base plate 50. An appropriate seal 136 is provided in an outer 
recess of piston portion 109 of piston/rod 51 to provide a seal between 
inner tube 48 and piston portion 109. A wear ring 137 is provided in an 
outer recess of piston portion 109, between piston portion 109 and inner 
tube 48, just above seal 136 to keep piston portion 109 centered within 
inner tube 48 and prevent wear thereto as it reciprocates within inner 
tube 48. A second wear ring 138 is likewise provided, in a recess in head 
plate 49, between piston rod portion 108 and head plate 49. And just above 
wear ring 138, a rod wiper 139 is mounted within a recess in head plate 49 
to help keep foreign matter from entering cushion unit 17 along piston/rod 
51 as it reciprocates. Cover 55 is generally disc-shaped; is made of 
molded neoprene rubber; and, is sized to be seated within outer tube 47, 
around piston/rod 51 and atop head plate 49, as shown. 
The dimensions of all mating surfaces of the components of cushion unit 17 
are properly fitted per the specifications of the seals. 
To assemble cushion unit 17: rod wiper 139, wear ring 138 and o-ring 131 
are applied to head plate 49, and head plate 49 is inserted into outer 
tube 47. Lock ring 56 is then inserted. O-rings 133 and 134 are applied to 
inner tube 48; seal 136 and wear ring 137 are applied to piston portion 
109; seals 121-124 are applied to outer piston 52; suitable valve cores 
are inserted into base plate 50; and, o-ring 132 is applied to base plate 
50. Check valve 53 with its o-ring 105 is seated within recess 88 of base 
plate 50; check valve retainer 54 is positioned into recess 87 and around 
check valve 53; and, inner tube 48 is lowered into recess 86 and secured 
thereat by lock pins 59, as shown. The inner diameter of inner tube 48 is 
less than the outer diameter of retainer 54 so inner tube 48 holds 
retainer 54 in place in recess 87, and the inner diameter of retainer 54 
is substantially equal to the outer diameter of main body 103 of check 
valve 53, but is less than the outer diameter of lower portion 93 of check 
valve 53 so check valve retainer 54 seats against shoulder 104 and holds 
check valve 53 firmly in place in recess 88. Piston/rod 51 is then 
inserted into inner tube 48. With the base plate sub-assembly sitting on 
the assembly table with piston/rod 51 pointing up, the outer tube 
sub-assembly is slid over the base plate sub-assembly until the outer tube 
sub-assembly bottoms out to the table. The entire assembly is turned over 
and lock ring 57 is inserted. At this point, there is a little play in the 
components, but upon charging the gas chamber, head plate 49 and base 
plate 50 will be biased axially outwardly, and cushion unit 17 will be 
fully assembled. 
As assembled and shown in FIGS. 3 and 6, cushion unit 17 defines four 
pressure chambers: gas chamber 77 bounded by outer tube 47, inner tube 48, 
head plate 49 and outer piston 52; outer hydraulic chamber 96 bounded by 
outer tube 47, inner tube 48, base plate 50 and outer piston 52; inner 
hydraulic chamber 97 bounded by piston portion 109, inner tube 48, check 
valve retainer 54 and Kepsel valve 53; and piston rod gas chamber which 
includes central cavity 112, and outer cavity 113. Central cavity 112 is 
provided to enable sufficient volume for the air in outer cavity 113 to 
compress when piston/rod 51 rises from its compressed position (FIG. 3) to 
its extended, rest position (FIG. 6). The compression of air therein upon 
extension of piston/rod 51 is negligible in relation to the other 
operating pressures of cushion unit 17. 
To charge cushion unit 17 with nitrogen and oil, unit 17 is placed in the 
"rod up" position; a valve core is inserted into fill port 75; a 
pressurized gas source is connected with fill port 75; and, gas is 
injected thereat into gas chamber 77 to the desired psi. For purposes of 
description of the present embodiment, gas chamber 77 is charged to 
approximately 2000 psi. The gas source is removed, and the fill port is 
covered with an appropriate o-ring boss (not shown) as a secondary seal. 
Cushion unit 17 is then turned over and the valve core (not shown) is 
inserted into fill port 100. A hydraulic fluid adapter (not shown) is then 
attached to fill port 100 and oil is injected until overflow occurs. Then 
a valve core (not shown) is inserted into vent port 101. A suitable o-ring 
boss is then applied to cover off the vent port 101. An additional 
quantity of oil is then injected as "reserve" oil. The amount may vary 
depending on size and characteristics of the particular cushion unit 17 
and its uses. In the one embodiment, with gas chamber 77 charged to 1900 
psi, an additional quantity of oil increased the gas pressure to 2000 psi. 
The oil source is then removed and a suitable o-ring boss is attached to 
close off fill port 100. FIG. 6 shows a cushion unit 17 fully charged with 
its piston/rod 51 in the extended, rest position. In this rest position, 
the pressure in gas chamber 77 is approximately 2000 psi, and thus the 
pressure in outer and inner hydraulic chambers is also 2000 psi. The extra 
charge of oil after cushion unit 17 was already full raised outer piston 
52 about 1/4 inch above base plate 50. 
In operation in the present embodiment, an input force F applied downwardly 
to the top 144 of piston/rod 51 meets a resistive force of approximately 
five tons. That is, such force F acts through piston/rod 51, through the 
incompressible oil in inner chamber 97, through check valve 53 (which does 
not inhibit flow from inner chamber 97 to outer chamber 96), through the 
incompressible oil in outer chamber 96, through outer piston 52 and 
against the gas at 2000 psi in chamber 77. Due to the surface areas of the 
piston faces in this embodiment, the 2000 psi pressure in chamber 77 
translates to a five ton output resistive force back through piston/rod 
51. Any applied force F (such as from the ram driven upper die 20) greater 
than five tons will overcome the resistive force and cause piston/rod 51 
to move downwardly. As piston/rod 51 moves downwardly at the downstroke 
rate of upper die 20, oil is forced uninhibitedly through check valve 53 
and into outer chamber 96, which causes outer piston 52 to rise, thus 
reducing the volume of gas chamber 77. As a result, the pressure of the 
nitrogen gas in chamber 77 increases. If the applied force F is great 
enough, piston/rod 51 will be driven to its retracted, compressed position 
shown in FIG. 3, whereupon the gas pressure in chamber 77 will rise to 
approximately 3060 psi, and outer piston will rise to the position shown 
in FIG. 3. The compression ratio of nitrogen gas volume rod "in" versus 
rod "out" is 1.53:1. That is, the ratio of pressures in gas chamber 77 
when piston/rod 51 is in the extended, rest position and outer piston 52 
is thus in the down position shown in FIG. 7 versus when piston/rod 51 is 
in the retracted, compressed position and outer piston 52 is thus in the 
up position shown in FIG. 3, is 1.53:1, in the present embodiment. 
If the applied force F is suddenly removed, the 3060 psi gas pressure acts 
through piston 52 to urge oil to flow from outer chamber 96, through check 
valve 53 and into inner chamber 97. Because of the action of the Kepsel 
check valve 53 and the selected small orifice in the poppet valve (not 
shown), the flow of oil therethrough is severely restricted. In the 
present embodiment, an applied force F well in excess of five tons may 
drive piston/rod 51 down in a fraction of a second depending upon the 
press specifications. Upon an equally fast removal of such applied force 
F, check valve 53 acts to limit the return of oil from outer chamber 96 to 
inner chamber 97, and the resulting rise of piston/rod 51 from the 
compressed to extended positions shown, is the cushion unit upstroke rate 
and is held to about three seconds. This upstroke rate may be modified to 
suit the particular application of cushion unit 17. 
Referring now to FIG. 8, there is shown a hydraulic shock absorber 21 in 
accordance with the preferred embodiment of the present invention. Shock 
absorber 21 generally includes an outer tube 147, a head plate 148, a base 
plate 149, a piston and rod combination 150 (hereafter referred to as 
piston/rod 150), a rod end cover 151 and upper and lower lock rings 152 
and 153, respectively. Like outer tube 47 of cushion unit 17, outer tube 
147 is generally cylindrical, made of tool steel, defines an inner 
cylindrical wall 154, and has upper and lower outer, annular recesses 156 
and 157 of circular cross-section to receive therein upper and lower lock 
rings 152 and 153, respectively. Head plate 148 is made of hardened tool 
steel and has a circular cross-section with an outer diameter 
substantially equal to the inner diameter of outer tube 147. Like head 
plate 49, head plate 148 defines an annular recess that is radiused at its 
bottom end to receive upper lock ring 152 therein. Head plate 148 further 
defines gas fill port 161, oil fill port 162 and vent port 163. Like gas 
fill port 75, oil fill port 100 and vent port 101, ports 161-163 are sized 
and configured to receive valve core members of any suitable type to 
provide valved injection and venting of gas and liquid into and out of the 
respective chambers. Head plate 148 also defines a central cavity 165 that 
is circular in cross-section and sized to receive a piston for 
reciprocation therein. Base plate 149 is made of hardened tool steel, has 
an outer diameter substantially equal to the inner diameter of outer tube 
147 and has an annular shape with an upper surface 166 and an inner 
cylindrical surface 167. Like head plate 148, recess 157 of base plate 149 
is radiused at its upper portion to receive lower lock ring 153 therein. 
Piston/rod 150 is made of hardened tool steel and has an upper tubular 
piston portion 170, a central disc-shaped piston portion 171 and a lower 
piston rod portion 172. Upper tubular portion 170 has an outer diameter 
that is substantially equal to the diameter of cavity 165 of head plate 
147. Upper tubular portion also defines a central cavity 173 that is in 
communication with cavity 165, as shown. The outer periphery of central 
disc-shaped piston portion 171 defines a central, cylindrically-shaped 
surface 177 and upper and lower frustoconically-shaped surfaces 178 and 
179, respectively, the diameters of which decrease away from surface 177. 
The diameter of central, cylindrically-shaped surface 177 is selected 
specifically to be a certain amount less than the diameter of inner wall 
154 of outer tube 147, the difference therebetween being directly related 
to the rate at which the hydraulic medium may flow under pressure from one 
side of piston portion 171 to the other between surfaces 177 and 154. In 
one embodiment, cylindrically-shaped surface 177 has an axial height of 
0.2 inches and frustoconically-shaped surfaces 178 and 179 each have 
axially heights of 0.4 inches (the axial thickness of piston portion 171 
thus being 1.0 inch), and the diameter of piston portion 171 is 
3.9+/-0.000/0.001 inches and the diameter of inner wall 154 is 
4.0+/-0.003/0.000 inches. It is an important object in the present 
embodiment to provide a gap between central surface 177 and inner wall 154 
that is approximately 0.001 inches to provide a controlled metering of 
liquid from one liquid chamber to the other. Other embodiments are 
contemplated wherein the diameter of and shape of disc-shaped portion 171, 
including the shape of outer surfaces 177-179, may vary to achieve a 
desired flow rate or other desired operational characteristics. Piston rod 
portion 172 has an outer diameter that is substantially equal to the inner 
diameter of base plate 149. 
Assembled as shown in FIGS. 8 and 9, shock absorber 21 defines three 
pressure chambers: gas chamber 184 essentially comprising cavities 165 and 
173 and bounded by the inner surface of cavity 165, the top surface 185 of 
piston portion 170 and the inner surface of cavity 173; upper hydraulic 
chamber 186 bounded by piston portion 170, piston portion 171, outer tube 
147 and the lower annular surface 187 of head plate 147; and, lower 
hydraulic chamber 189 bounded by piston rod portion 172, piston portion 
171, outer tube 147 and the upper annular surface 166 of base plate 149. 
Seals 191 and 192 are mounted in recesses in head plate 147 to provide a 
seal between piston portion 170 and head plate 148, and specifically to 
prevent fluid leakage between gas chamber 184 and upper hydraulic chamber 
186. Likewise, a seal 193 is mounted within a recess in base plate 149 to 
prevent leakage of fluid downwardly out of lower hydraulic chamber 189. As 
with head plate 49, a wear ring 196 and a rod wiper 197 are mounted within 
recesses in head plate 148 to center piston/rod 150 and prevent wear 
thereto and to keep foreign matter from entering lower hydraulic chamber 
189 during reciprocation of piston/rod 150. 
In assembly, gas chamber 184 is charged with nitrogen gas to a pressure of 
approximately 500 psi. This pressure may vary, but it should be enough to 
keep piston/rod 150 in the extended, rest position shown in FIG. 8, 
whereby piston rod portion extends approximately one inch down below lower 
surface 195 of shock absorber 21. Oil is then filled through oil fill port 
162 with vent port 163 held open until all the air is out of both chambers 
186 and 189. 
As described above and referring to FIGS. 10 and 11, a passageway 198 is 
defined down through upper die 20 and upper die shoe 18 (die 20 and upper 
die shoe may comprise a single unit as shown in FIGS. 9 and 10 and are 
referred to commonly thereat as upper die 20). Passageway 198 comprises 
upper, middle and lower sections 201, 202 and 203, respectively. The inner 
diameter of the upper section 201 is greater than that of middle section 
202, thus creating an annular shoulder 204 therebetween. The inner 
diameter of middle section 202 is greater than the inner diameter of lower 
section 203, thus creating an annular shoulder 205 therebetween. The inner 
diameter of upper section 201 is slightly greater than the outer diameter 
of shock absorber 21. Plunger 40 has a large head 206 with a round 
cross-section and outer diameter that is slightly less than the inner 
diameter of middle section 202. Plunger 40 also has a rod 207 extending 
coaxially downwardly from head 206, and rod 207 has an outer diameter that 
is less than the inner diameter of lower section 203. 
In use, plunger 40 is dropped down into passageway 198 where head 206 rests 
within middle section 202 atop shoulder 205, and rod 207 extends through 
lower section 203 and approximately one inch below lower planar surface 39 
of upper die 20. Shock absorber 21 is then dropped down into passageway 
198 where it rests within upper section 201 and atop shoulder 204, and 
wherein the downwardly extending piston rod portion 172 just touches head 
206, as shown in FIG. 9. When die 20 is mounted to the underside of a ram 
(not shown), the top of passageway 198 is closed off, and shock absorber 
21 and plunger 40 are securely housed within passageway 198. Plunger or 
adapter rod 40 may vary in length and is used to adapt shock absorber 21 
for use with dies of varying thicknesses. 
With press 10 in the open or top dead center position shown in the left 
half of FIG. 2, and with the 34, five ton cushion units 17 held in lower 
shoe 11 surrounding punch 12 as shown, and with the four shock absorbers 
21 mounted to and in engagement with the corresponding plungers 40 which 
extend down one inch below lower planar surface 39 of upper die 20, and 
with a cushion 13 weighing approximately 6 tons and supported by four, 3 
ton lift cylinders 15, press 10 operates as follows: 
Upper die 20 is rammed down from top dead center toward the motionless 
cushion 13 at a downstroke rate The downstroke rate, and the ensuing 
upstroke rate, are typically a sinusoidal function of time, but may vary 
as desired. If the downstroke rate and upstroke rate are set at other than 
a sinusoidal rate, then the parameters of cushion units 17 and shock 
absorbers 21 should be modified appropriately to accomplish the cushioned 
action described herein. Plunger rods 207 engage the top 26 of cushion 13. 
The sudden input through rod 207 to piston/rod 150 causes piston/rod 150 
to move upwardly within outer tube 147, but due to the very small gap 
between piston portion 171 and inner wall 154, telescopic movement of 
piston/rod 51 is not instantaneous, and therefore cushion 13 also begins 
to move. The parameters of shock absorbers 21 are chosen so that during 
the time it takes for piston/rod 51 to move the one inch from its 
extended, rest position (FIGS. 8 and 10) to its retracted, compressed 
position (FIGS. 9 and 11), cushion 13 has moved down only one inch. 
Restated, it is given that the rate of descent of die 20 stays 
substantially constant (unchanged from the contact with and resistance 
from cushion 13). When plunger rod 207 contacts cushion 13, die 20 
continues to advance, but because of the metered hydraulic flow within 
shock absorber 21, piston/rod 150 takes X seconds to be compressed. By the 
time X seconds have elapsed, piston/rod 150 and plunger rod 207 have 
completely retracted, and lower planar surface 39 has essentially engaged 
upper surface 26, engaging and binding blank 33 therebetween. But also 
during that time X, cushion 13 has been moved downward one inch. Thus, 
while the downwardly charging upper die 20 has descended two inches, the 
six ton cushion, backed by the combined 12 ton lift cylinders 15 have only 
been moved one inch. The heretofore tremendous impact of the die 20 
slamming into the motionless cushion and instantly accelerating it to the 
same speed as the die has been drastically reduced. 
Upon descending one inch from its upper, rest position, cushion 13 has now 
engaged with the 34, five ton cushion units 17. Further descent of die 20 
and cushion 13 will be with a combined compressive force between the two, 
roughly equal to the combined resistance of the four lift cylinders 15 
(three tons each) and the 34 cushion units 17 (five tons each) or roughly 
182 tons. With this compressive force, blank 33 is securely bound and it 
will be able to be drawn between punch 22 and cavity 37 as desired. 
When die 20 and cushion 13 reach their nadir, the ram mechanism (not shown) 
reverses direction and lifts die 20 back up at a rate similar to its 
descent. Instead of cushion units 17 instantly following cushion 13, die 
20 and the ram mechanics back up with their combined stored force which 
would exceed 170 tons, thus causing tremendous damage to the ram 
mechanics, check valve 53 retards the back flow of oil from outer chamber 
96 to inner chamber 97 in each cushion unit 17. While it takes die 20 only 
about one second to return to top dead center, it takes each piston/rod 51 
roughly three seconds to return to the extended rest position. Thus, 
cushion 13 separates at its bottom surface 27 from the piston/rods 51 
substantially instantaneously upon the beginning of the press up-stroke. 
Referring to FIG. 12, there is shown the lower portion of a cushion unit 
210 in accordance with another embodiment of the present invention. In 
unit 210, the Kepner check valve 53 has been replaced by another check 
valve assembly comprising a check valve retainer plate 211, a 
frustoconically shaped poppet 212, a cylindrically shaped guide member 213 
and a spring 214. 
It is apparent from the description herein that cushion units 17 are 
self-contained. That is, cushion units 17 provide their cushioning and 
delay functions without reliance on any external pneumatic, hydraulic, 
electrical or other power source or cooling source connection. This is 
primarily because the ratio of the volume of working fluid versus the 
volume of the entire cushion unit apparatus provides a large heat sump and 
surface area for dissipation of heat. If desired, the exterior surface of 
outer tube 47 of cushion unit 17 may be erose. That is, the exterior 
surface may be made with ribs or a similar outwardly extending 
configuration to increase the surface area thereat, and therefore to 
increase the rate of heat transfer away from the cushion units. Such 
self-contained configuration permits a wide latitude in the use of the 
cushion units 17 without regard to design constraints relating to a power 
supply. Thus, just a few or many such cushion units 17 may be employed 
without running hydraulic lines or designing an elaborate hydraulic 
source, for example. Likewise, shock absorbers 21 provide a large heat 
sump and surface area for dissipation of heat and are self-contained, 
giving great latitude to the number used and their placement. 
Alternative embodiments are contemplated wherein shock absorber 21 and 
cushion unit 17 are used in machines other than the press disclosed here. 
It is also contemplated that either shock absorber 21 or cushion unit 17 
could be omitted from the press 10 or replaced by another device to 
provide an alternative operation. It is contemplated that either shock 
absorber 21 or cushion unit 17 could be inverted. That is, for example, 
cushion unit 17 could be constructed so that the piston/rod portion is 
mounted in stationary fashion to the shoe and the cylinder portion could 
be disposed to move upon direct or indirect engagement with the cushion. 
It is also contemplated that, like shock absorber 21, cushion unit 17 
could be provided with a plunger or similar extension to transmit 
engagement with the cushion. 
Embodiments are also contemplated which more or less cushion units 17 and 
more or less shock absorbers 21. 
As used herein, the term "substantially identical" can mean equal to within 
less than a thousandth of an inch or less or can mean closely similar in 
size. The degree of similarity will be understood between such compared 
components to be whatever optimizes the performance of the correspondent 
part. Also, language is used to indicate structural and operational 
relationships. It is to be understood, however, that alternate 
configurations are contemplated as would occur to one skilled in the art. 
For example, "vertical" is used herein to describe reciprocation of 
pistons within the cushion unit when it is oriented as shown in the 
corresponding drawings. It is nevertheless understood that the cushion 
unit could operate along a horizontal axis, for example, and the piston 
action would consequently also be along the horizontal. 
While the invention has been illustrated and described in detail in the 
drawings and foregoing description, the same is to be considered as 
illustrated and not restrictive in character, it being understood that 
only the preferred embodiment has been shown and described and that all 
changes and modifications that come within the spirit of the invention are 
desired to be protected.