US2417794A

US2417794A - Punch press having a die cushion

Info

Publication number: US2417794A
Application number: US467428A
Authority: US
Inventors: Herbert B Werner
Original assignee: Verson Allsteel Press Co
Current assignee: Verson Allsteel Press Co
Priority date: 1942-11-30
Filing date: 1942-11-30
Publication date: 1947-03-18
Anticipated expiration: 1964-03-18

Description

arch 18, 1947. BQ WERNER $41279 I PUNCH PRESS HAVING A DIE cusruou Filed Nov. 59'. 1942 @aicnted Mar. 18,1947

Nines PUNCH PRESS HAVING A CUSEON Herbert B. Werner, Chicago, Ill... assignor to Verson Allst'eel Press Compam, Ghicago, m, a corporation of Delaware Application November 30, 1M2, Serial No. 467,42fi

(ca. ire-.45)

5 Claims. l

The present invention relates to punch presses. More particularly, it relates to punch presses having die cushions.

I For performing some types of metal drawing operations on a punch press it is necessary to hold the rnetalblank tightly in place during the drawing step, so that the metal will flowsmoothly into the die cavity without the formation of wrinkles. been used for accomplishing this blank holding step.

One arrangement is to use a multiple action press, that is, a press having two or more slides operating difierentially with respect to each other. For-performing the above operation a blank holding slide first moves downwardly and clamps the blank in place. When it has reached the blank holding position, it stops and remains in. this position until the completion of the drawing operation, after which it recedes prior to, or along with the slide carrying the metal drawing memher. The principal dimculty with multiple action presses having blank holding slides is that they are expensive. Another expedient has, therefore, been frequently used in conjunction with single action presses for accomplishing the same general objective. This arrangement is known as a die cushion.

With the die cushion arrangement, the reciprecalling die is surrounded by an annular blank holding member, or clamping ring, which moves therewith. This blank holding member during the downward stroke of the press is brought against the blank and squeezes the blank against an draw ring surrounding the lower fixed die member. Thisannular draw ring is yieldingly supported upon a die cushion and moves downwardly under restraint along with the reciprocating member.

Cushions of this type are usually hydraulic, that is, a hydraulic cylindersupports the draw ring, and the fluid, in the cylinder is permitted to In the past, two arrangements have tion to provide a press having a die cushion of large capacity, which is adapted to'beoperated with considerably less power than has heretofore been thought possible.

Yet another object of the present invention is to provide a novel punch press die cushion arrangement such that the energy required to operate the die cushion comes only partially from the press flywheel and crank.

Yet another object of the present invention is to provide a novel arrangement for duplicating escape against the restraining effect of a pressure control valve.

The die cushion operates and dissipates energy during substantially the entire length of the stroke. It necessitates the loss of considerable energy, therefore. to operate a die cushion in conjunction with a punch press. Because of the energy required to ouerate a die cushion, such cushions have never heretofore been feasible on presses of medium or large size; For instance, a. punch press die cushion which supports a draw ring against a pressure of say three hundred tons,

and which moves through astroke ofisix inches the performance cl .9. double action press with a single action press.

Still another object of the present invention is to provide a novel die cushion which can exert the same, or greater, draw ring pressures as previously used, but which requires only approximately lb% of the energy heretofore thought necessary for its operation.

Yet another object of the present invention is to provide a novel punch press accessory which serves the usual blank holding function of an ordinary tyne die cushion without requiring more than MW, of the energy conventionally used in a die cushion of similar capacity.

Yet another object or the present invention is to provide a novel die cushion arrangement which accomplishes the above set forth objective and which further has an upward stripping capacity or approximately the same intensity as the down ward capacity or" the cushion.

Yet another object of the present invention is to accomplish all of the above in a simple manner and at comparatively low cost.

Other objects and advantages will become apparent from the following description of a pre= ferred embodiment of my invention, illustrated in the accompanying drawing, in which similar characters of reference refer to similar parts, and

in which the figure is a diagrainmatic sectional view or a punch press and die cushion, arrangement incorporatingthe present invention.

Inasmuch as the construction of iswell known, and since the present invention'is of a comparatively simple nature from a niechanical standpoint, and, therefore, will be read= ily understood by all skilled in the art, the invention has been illustrated diagrammatically. In

punch presses the figure I have illustrated a typical punch press slide, indicated by the numeral l0, having a die l2, provided with a cavity i4, and an annular blank holding surface or clamping ring it.

Beneath the slide I have shown a typical bolster plate ll supporting a punch member 20, which is generally complementary-in shape to the cavity l4. This punch is surrounded by an annular draw ring 22, in alignment with theblank holding surface l5.

The bolster plate is supported upon a bed It, while a second plate 24 rigidly secured in the press frame therebeneath supports the piston 26 of a die cushion indicated generally by the numeral 28. This piston is fitted to a cylinder 30, which is movable upwardly and downwardly relative to piston 28, and which supports the draw ring 22 upon pins".- Vertical movement of the draw ring 22 is therefore possible when accompanied by similar movement of the cylinder 30.

The space within the piston 28 and the cylinder 30 is filled with hydraulic fluid 33, and this fluid communicates through a pipe 36 connecting the draulic fluid, which is maintained under air pressure, the air being communicated to the reservoirby a pipe 38. There is an outlet 40 at the lower portion of the reservoir, which is connected through a check valve 42 with the pipe 36. Thus, any time pressure is released from the surface of the draw ring 22, that is; wheneverthe slide in moves upwardly, air pressure within the tank 34 will force hydraulic fluid through the outlet 43, through the check valve 42, through the pipe 36, and into the cylinder 28 to elevate the cylinder and draw ring.

During the downstroke of the press, that is, while the draw ring 22 is moving downwardly, hydraulic fluid will be forced from the cylinder 28, but will be prevented from entering the outlet 40 of the tank 34 by reason of the closing of the check valve 42. This fluid, however, can pass through a branch conduit 44 leading to the tank 34. This branch conduit is equipped with a pressure control valve 46, which prevents the flow of fluid therethrough until a certain predetermined pressure has been imposed upon the inlet side of this valve. In other words, no fluid, excepting a small amount which may leak through the check valve 42, can return to the tank 34 during the downstroke of the press until the pressure upon the fluid in the die cushion cylinder 28 has reached the predetermined pressure at which the control valve 46 is set.

Beneath each end of the slide I0, I have located what may be referred to as energy recovery cylinders 48; These two cylinders may be considered as identical, two being used to balance the press as will hereafter appear. Inasmuch as they are substantially identical, only one of these recovery lower end of this piston passes through an opening 54 located at the lower end of the cylinder, and a packing gland 58 may be used to seal the openingaround this piston. The upper end of the piston is connected to a piston rod 58, which passes upwardly through a close fitting opening,

.the pipe 38 by a branch pipe 80.

The area of the effective portion of the piston 52, that is, the annular surface at the upper end of the piston, is approximately 45% of the eifective area of the piston 28, thus, the effective area of the two pistons 52 together is approximately 90% of the area of the piston 26.

For a purpose to be described presently, a solenoid relief valve 82 is connected in parallel with the check valve 42. This solenoid valve is of the type which remains closed excepting when energized. It receives its energy from a, source of electrical potential indicated by the battery 64, connected to the solenoid valve through a normally open limit switch 88. The limit switch is located adjacent to the cushion cylinder 30 where a bracket 88 attached to the side of the cushion will close the limit switch and open valve 62 when the cushion is in its uppermost position. Immediately after the cushion starts its downward movement, the switch 66 will be opened, thereby closing Valve 62.

This device operates in the following manner: During the downward stroke of the slide to, the blank holding surface or clamping ring 16 is brought against the upper face of the draw ring 22. Prior to contact between the faces l6 and 22, the cylinders 48 are kept filled with fluid forced from the reservoir 34. As soon as contact is made, the draw ring is forced downwardly, thus tripping the limit switch 66 and pushing the hydraulic fluid from the cushion. 28. The hydraulic fluid flows into the pipe 38, where it is connected by the pipe to the recovery cylinders 48. Within the recovery cylinders the fluid pressure is brought to bear against the upper annular faces of the pistons 52 and urges these pistons downwardly. Inasmuch as 90% of the fluid forced from the die cushion enters the recovery cylinders 48, it will be appreciated that the two piscylinders need be described, however.

Referring to the left hand recovery cylinder 48, it will be seen that this cylinder is secured in an opening in the bed l8 and is provided in a ton rods 58 will pull downwardly upon the slide ill with of the energy developed in the die cushion 28, less small frictional losses.

From the above it will be seen that 90% of the energy required to collapse the die cushion 28 will be developed within the recovery cylinders and, therefore, will actually have come from the die cushion itself. Therefore, the energy required to be stored in the flywheel for urging the die cushion downwardly is only 10% of the energy actually absorbed by the die cushion in holding the blank.

It will be appreciated that the effective areas of the pistons 52 could theoretically be exactly equal to the efiective area of the die cushion, in which case of the energy, less frictional losses, would be returned to the slide, In the construction of punch presses, however, where frequently no two presses are alike and each one must be engineered separately, and also inasmuch as there may be some slight leakage in the check valve 42, it will be seen that it is generally not feasible to attempt to recover all of the energy developed by the die cushion. The given figure of 90% is suihciently high, however, to enable recovery of substantially all of the energy, and still low enough to overcome difficulties incident to engineering and constructing the press.

Since only 90% of the hydraulic fluid forced from the cushion 28 can enter the recovery cylinders 48, the extra %.,minus whatever-small amount leaks through the check valve 42 will be returned to the reservoir 34 through the pressure control valve 46. After the completion of the downward stroke, the slide Ill moves upwardly,i-thus lifting the pistons 52, therebyreturning the hydraulic fluid from the recovery cylinders 48 to the cushion 28. The amount of hydraulic fluid thus returned will not completely fill the cushion, inasmuch as the capacity of the die cushion is greater than the capacity of the recovery cylinders 48. The

additional hydraulic fluid, in the present instance approximately 10% is forced into the die cushion from the reservoir 34 by reason of the air pressure therein, thus returning the die cushion to the upper limit of this stroke. 7

, After the die cushion has reached the upper limit of its stroke, no more hydraulic fluidv can be accommodated in the die cushion cylinder. The slide 10 and pistons 52 continue their upward movement however, thereby forcing hydraulic fluid into the pipe 60. If it were not for the solenoid relief valve 62, this excess fluid would necessarily have to find its way back through the high pressure relief valve 46, thereby dissipating considerable energy. As has been explained previously-however, the die cushion opens the limit switch 65 as soon as it reaches the upper limit of its stroke, thereby opening the relief valve 62 and permitting fluid forced into the pipes 60 by the pistons 52 after the die cushion has completed its upward stroke to return to the reservoir 34 through the valve 62 rather than through the valve 46. V

During the upward stroke of the press considerable stripping action can be developed by the die cushion if necessary. Under normal conditions the die cushion will accommodate more hydraulic fluid during its upward stroke than is forced into the pipes 60 by the pistons 52, this excess fluid being. supplied through the check valve 42 from the reservoir 34 under approximately 100 pounds per square inch pressure. However, should the die cushion stick at any point and not continue upward movement along with the slide Ill, the continued upward movement of the pistons 52 will close the check valve 42 and raise the pressure in the die cushion until the high pressure relief valve 46 opens.

tributed. As a matter of fact, only one cylinder need beused if this cylinder directs its efiort against the slide at its substantial center. For instance, a single cylinder of this type could be located above the slide inthe press crown. or in This develops in the die cushion the same force as is used for blank holding purposes. This high stripsome similar central location. The construction illustrated is preferred, however, inasmuch as die cushions are frequently installed upon a previously constructed press, and by having the recovery cylinders and die cushion closely associated beneath the bolster plate, the design of these elements and the hydraulic circuit is simplified,

although as explained above, if desired, the recovery cylinders may be arranged in other locations if it appears desirable in some particular instance.

While I have shown and described particular embodiments of my invention, it will be apparent I to those skilled in the art that numerous modifications and variations may be made without departing from the underlying principles of the invention. I therefore desire, by the following claims, to include within the scope of the invention all such modifications and variations by which substantially the results thereof may be obtained by substantially the same or equivalent means.

I claim:

1. A die cushion arrangement for use with a punch press having a frame, a slide reciprocable therein, and means for reciprocating said slide, comprising: a die cushion having a variable volume fluid chamber and located within said frame,

for supporting a draw ring or similar element, recovery piston and cylinder means connected between the press slide and the frame for urging the slide downwardly when hydraulic fluid is forced into said piston and cylinder means, means including a closed fluid circuit extending between said chamber and said piston and cylinder means hydraulically connecting said recovery piston and cylinder means to said die cushion so that fluid forced from said die cushion is communicated to said recovery piston and cylinder means, means including a source of fluid under pressure and a check valve enabling the fluid to flow from said source to said closed fluid circuitfor fillin said piston and cylinder means with fluid during that portion of, the down stroke of a press cycle before said die cushion is acted upon by the press slide, said check valve remaining closed during the up stroke of the press cycle to confine the fluid to said closed circuitso that the fluid forced from said piston and cylinder means is communicated to said die cushion to restore it to its "rest position, and hydraulic pressure relief means to permit the escapeunder restraint of hydraulic fluid from said closed fluid circuit when a predetermined pressure is reached in said circuit on both the down and up strokes of the press cycle.

2. A punch press comprising a frame, a slide reciprocable in said frame, a die cushion associated with said frame, a member on said slide for collapsing said die cushion when said slide moves toward said die cushion, a cylinder immovably mounted relative to said frame, conduit means hydraulically connecting said cylinder with said die cushion, a piston reciprocable in said cylinder and rigidly secured to said slide, whereby the major portion of the energy transferred from said collapsing member to said die cushion is recushion with said hydraulic storage means, said connecting means including a pressure relief valve, other conduit means connecting said storage means with said die cushion means and said cylinder, the last said conduit means including a check valve for preventing flow of hydraulic'fluid from said die cushion means toward said storage means thereby to communicate the fluid forced from said cylinder to said die cushion on the up stroke of a press cycle to restore said die cushion to "rest position, and means to maintain the fluid in said storage means under pressure, whereby said cylinder is filled with fluid through said check valve during the initial portion of the down stroke of a press cycle.

3. In a press having a frame, a slide movable in opposite directions, a fluid operable cushion means cooperating with said slide to cushion the pressing action thereof, a cylinder-piston assembly operatively connected between the 'slide and the frame, a source of fluid under pressure, and conduit means interconnecting the cushion means, the cylindenpiston assembly and the source of fluid, a check valvein said conduit means permitting flow of fluid to the cylinder-piston assembly during the initial portion of a press cycle before the slide acts upon the cushion means, whereby pressure fluid expelled by the cushion means when moved in one direction is supplied to the cylinder-piston assembly to effect operation thereof to move the slide in the pressing direction, and said check valve in the conduit means preventing flow of fluid to said source, whereby pressure fluid expelled from the cylinder-piston assembly upon the initial portion of the return movement of the slide is conveyed to. the cushion means to move it in the opposite direction.

4. In a press having a slide movable in opposite directions and fluid operable cushion means cooperating with said slide to cushion the pressing action thereof, a cylinder-piston assembly operatively connected to said slide, and means including closed circuit conduit means interconnecting the cushion means and cylinder-piston assembly, a source of fluid under pressure, and a conduit including a check valve and a high pressure relief valve connecting said source to said circuit, whereby pressure fluid expelled by said cushion means when movedin one direction is supplied by the cylinder-piston assembly to efiect operation thereof to move the slide in the pressing direction, and the check valve preventing flow of fluid to the source whereby pressure fluid expelled from said cylinder-piston assembly upon th return movement or the slide is conveyed to the cushion means to move it in the opposite direction. l

5. In a press having a slide movable in opposite directions and fluid operable cushion, means cooperating with said slide to cushion the pressing action thereof, a cylinder-piston assembly operatively connected to said slide, and means including closed circuit conduit means interconnecting the cu hionmeans and the cylinder-piston assembly, a source of fluid under pressure, a concheck valve, and means for opening said valve means when the cushion means is in its normal position.

' r HERBERTB. WERNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,664,485 Rode Apr. 3, 1928 1,861,337 Ernst May 31, 1932 2,269,778 Merrill Jan, 13, 1942 2,294,451 Ernst Sept. 1, 1942 2,300,162 Maude Oct. 27, 1942 2,305,610 Ernst Dec. 22, 1942 2,354,003

Ernst Jilly 18, 1944