US2438951A - Hydraulic overload-release device or cushion for presses - Google Patents

Description

April 5, 1948- w. T. STEPHENS 2,438,951

HYDRAULIC OVERLOAD-RELEASE DEVICE OR CUSHION FOR PRESSES Filed Oct. 3, 1944 2 Sheets-Sheet 1 April 6, 1948. w. T. STEPHENS 2,438,951

HYDRAULIC OVERLOAD-RELEASE DEVICE OR CUSHION FOR PRESSES Z5 Z3 Z y O z5 Patented pr. 6, 1948 HYDRAULIC ovEnLoAn-namssn novios on cUsmoN ron rnsssns william rr. Stephens, cieviana,.omo, signor to Hydraulic Control Engineering Company, Y Cleveland, Ohio, a corporation of Ohio Appucanonbctober s, 1944, serial No. 551,045

This invention relates to power driven presses, and more particularly to safety means comprising overload-release devices often termed cushions to prevent damage to presses, dies, or associated parts, due to excessive pressure resulting from insufcient accommodationfor the stroke length of the ram. l

It is a general object of the present invention to provide a novel and improved safety or cushion device of general application for presses of the power actuated type. 1

More particularly it is an object of the invention to provide a novel liquid cushion or overload-release device adapted to be interposed be tween a press ram or plunger and the tool or punch holder, which device enables the press to exert its thrust on the work up to a predetermined pressure, whereupon the device yields to prevent damage. In this application the term cushion will be used as a convenient short term in place of the more extensive statement in the rst paragraph above.

It is a further object of the invention to provide a `hydraulic cushion of the type described which automatically returns to itsneutral position on the withdrawal stroke of the press.

An important `object of the invention consists in providing a hydraulic cushion which is self--` contained and independent of the setting of the press stroke in relation to the permitted or desired movement of the die or punch parts.

Another important feature of the invention resides in arranging the cushion device to be entirely self-contained, automatic and independent of the press stroke setting or operation.

, 3 Other and further objects and features of the invention will be more apparent to those skilled in the art from a consideration of the accom-l panying drawings and the following specification, wherein is disclosed a single exemplary embodiment of the invention, with the understand- Fig. 1.

In the operation of presses of various types,

vand particularly those. in which the press stroke is achieved through mechanical means, the operation of setting up the press is an extremely tedious one. If it is assumed that material of a predetermined thickness is to be punched, bent or shaped between a stationary die on the press bed and a punch `or plunger operated by the press ram, it will be apparent that the stroke of the press ram must be accurately regulated so that at the end of the` ram stroke there remains between the flat face of the die and the punch a 'distance which is just the thickness of the mateforce is reached the cushion releases and the ram a perforated die and punch, the latter being mov- ,s

rial to be operated on. If this is not accurately achieved in one way or anothentoo much pressure may be applied to the material on `the die and something will be distorted or broken either in the press or in the dies. Even if an extremely accurate setting is worked out by a careful operator, there is always the possibility, particularly when working with thin material, of `unintentionally' feedingtwo blanks to the press. This is often fatal to the dies or other parts. Considerable eiiort` has been expended to prevent feeding of blanks in multiple.

In accordance with the present invention ahydraulic cushion device is interposed between the punch holder, which is normally supported on the ram of the press, and this ram. It is arranged to permit the press to exert pressure on the punch only` up to a predetermined force. When this may continue its motion without exerting more than this pressure on the dies. whereby they are 5 prevented from being damaged. The relative that the punch and die are always at a predeteri Obviously presses are of numerous types and application and perform all sorts of operations. The device of the present invention is of general application. and for the sake of simplicity of description it has been shown associated with a press in which the ram operated slide moves in guides and approaches the bed which supports the die along a vertical axis. It also `discloses able by the press ram, but obviously any other This insures full clearance for feeding pair of cooperated members for performing work on blanks or the like may be substituted.

Referring now to the drawings, it will be seen that only portions of the press are indicated, including the bed I0, which is a stationary rigid structure for supporting the die l2 or other member for operating on the blanks. ,'I'hisrdie is shown as supporting a blank I4 or other part to have work performed. thereon. A cooperating punch I5 mounted on a punch plate I3 PeIfOI'mS the work on the blank and is supported by a suitable punch holder I'I. The manner shown for attaching the punch to the punch holder forms no part of the present invention, but care must be seen that it is an extremely rigid connection, insuring against any misalignment ot the cooperating punch and die during the stroke of the machine.

The punch holder I1 is attached, as shown, by bolts I8 to the under face of a slide member 20 (Fig. 2), which includes a cross head portion 2I provided with guides 22 reciprocably mounted in ways 23 in a stationary member 24 formingpart of the press frame which is attached to the bed. This slide is reciprocable for operating the punch press under the action of a ram 25 connected by suitable ball and socket structure 26 to the thrust member 2'I of any conventional power press device capable of reciprocating the slide with adequate power to perform the desired fwork on the blanks. It is common to use cams, toggles and the like for imparting movement to the ram 25. Some presses are provided with stroke adjusting means and others permit relative adjustment only to the initial positions of the punch and die when the press is fully opened so that at the bottom of the stroke these parts are appropriately spaced to handle the blank.

In accordance with the present invention a hydraulic cushion is inserted between the ram and punch holder so that the length of the punch stroke can be restricted by the work to less than that of the press ram without damaging any part of. the equipment. For this purpose the slide 2| has formed integrally therewith and extending from one side thereof a large cylinder 30 having an enlarged lower end to receive the punch holder; 'Ihe cylinder is provided with a bore 3| preferably cylindrical and co-axial with but of greater diameter than the ram 25, which in this case is a cylindrical rod. The lower end of this ram is reduced in diameter and threaded as at 32 to receive the internally threaded upper end33 of a pilot rod 34. Shoulders as at 35 and 36 on the ram and pilot rod respectively provide for clamping between them a piston 38 when these two parts are securely threaded together. This piston, tted with appropriate packing, is a close llt in bore 3|.

'I'he upper end of the cylinder bore is closed by a telescoping cylinder head 40 having a radial flange appropriately secured against the end of the cylinder block 30 by a series of studs. The ilange overlies the end of the cylinder block and is packed to insure its liquid tightness. It is bored and bushed as at 42 to receive and guide the ram 25. A suitable form of fluid tight packing 43 is provided to insure against leakage. Y A similar and even more sturdy lower cylinder head 45 is providedv and its flange is recessed in the enlarged lower end of the cylinder block and is sufficiently thick so that the heads of studs 46 can be recessed therein, as shown, so as not to interfere with the punch holder I1. 'I'his cylinder head is bored as at 48 to form a close working ilt for the pilot rod and is packed as at 50 t0 secure fluid tightness. The whole assembly is carefully built and aligned so that movement of the piston in its cylinder can take piace without binding. Accurate alignment is achieved through the guiding of both the ram and the pilot in the spaced cylinder heads. Y

i Each cylinder head projects within the cylinder bore and its inner end is somewhat reduced in diameter as at 52 and 53 to provide extensions of the chambers formed on the two sides of the piston. Each of these chambers is pierced by a pair of fluid connections arranged on opposite sides of the cylinder 30. At the left these connections 55 and 56 at the top and bottom respectively open into a vertical passage 51, which provides for liquid connection between the top and bottom chambers on opposite sides of the piston.

This passage 51 opens through the top of cylinder block 30 and is somewhat reduced in diameter near the bottom as at 58, where it receives .a valve seat member 53 secured in position by a set screw 60 received in a circumferential groove therein. The valve seat is a p ress t in the bore 58 so as to secure liquid tightness. It is vertically drilled to receive the tubular hollow stem 6I of a relief lvalve 62, the head of which has a tapered conical surface on the under side engaging with a. correspondingly shaped seat in the top of the member 59. Lateral boresl 63 through the hollow stem, which has a close working lit in the vertical passage through the seat member,

permit liquid to move upwardly when the valve is lifted from its seat under the action of excess pressure in the lower chamber. A pilot stud on the head of the valve member centers the lower end of the biasing spring 64, which normally holds the valve closed. The upper end of the spring abuts a slidable guide member 66 arranged in a bore in the screw cap 61, which closes the upper end of the passage 51. A screw 68 passes through this cap for adjusting the position of the guide 66 to regulate the tension of the spring.

On the other side of the cylinder member the vertical passage 'III extends between the horizontal connections 'II and 1-2 to the upper and lower chambers, respectively. The connection 1I is somewhat enlarged and receives the lower or sleeve portion of a valve 'I3 similar to that described in connection with the other passage but of greater diameter. It acts only as a check valve. The requirement here is for valve opening at lower pressure, and this is achieved by increasing the diameter and softening the spring.

The valve seats at the counterbored junction of the passage 'III and connection 1I and is held shut by a. very light short spring 'I5 non-adjustably housed in the central chamber of a cap 16 which closes the end of the connection.

For operation of the cushion, the spring 64 is regulated to the desired tension by adjustment of the screw 68 which extends through the cap and is locked in position by an appropriate lock nut and maintained fluid tight by an acorn nut 80. 'Ille chambers above and below. the piston, the connections 55, 56, 1I and 'I2 and the vertical passages 51 and 10 are substantially completely filled with a suitable liquid. The normal position of the parts on the down stroke of the press is as shown. Both valves are seated. Under these conditions the slide is forced to move downward in unison with the ram and its piston by the action of the liquid beneath the piston. The punch then operates on the blank to the extent desired, but in i I a,4ss,es1

the event that the stroke ofthe punch press has been set longer than thespace between the punch plate and the top of the blank, continued movel ment of the ram, ii' notl relieved, wouldbend or 62, causing it to lift from its seat against the action of its spring 6l and relieve the pressure. With the type of valve illustrated'4 in Fig. l a minute quantity of air in the system improves the ope erationV since it provides for a slight unbalance at the two sides of the valve and allows the head to lift when the appropriate pressure diiierential occurs and before communication is eiiected through the valve. A ball type valve, being more nearly balanced, can be operated with a system practically i'ull of liquid. When the expression substantially full is used it refers to a system in which only a bubble or two of air is included, such as might be necessary to take care of expension and contraction due to temperature diferentials. The liquid discharged thru the relief valve iiows up through passage 51 and the upper connection 55 to fill the space vacated in the top of the cylinder asthe piston moves downwardly. Since 'the pilot and the ram are of the same diameter the exact amount of iiuid fills in above the piston as is discharged beneath it. The maximum pressure which the press can exert under these conditions is predetermined by the setting of 'the spring 6I and should be less than the force necessary to damage any part of thepress. In fact the setting should be such that just slightly more than the force necessary to form the blank is exerted.

It will be noted that the valve. 13, in the passage 10 is automatically closed against relieving under face or the blank plate and the upper face of the work will come together before the ram will have completed its maximum travel, and here the relier valve comes into-play, permits the slide to stop and the ram to continue for its full stroke.

I` claim:

1. A-hydrauliccushion for use with a press having a nxed bed and a movable ram, comprising in combination, a punch holder, a slide adapted to carry said holder, a uniforn sectioned space in said slide, a piston operable in said space,` means the pressure just described, both by its spring and the action of the iiuid on its head. When the power press has completed its stroke and the ram begins to withdraw, the combined weight of the slide and its associated parts and the friction of the punch in the die holds the slide down lowing stroke which will start with the parts in the position illustrated in the drawing.

It will be appreciated that in a normal press without the equipment of this invention, that the distance D between the under face of the punch plate and the top of the blank must never be less than the stroke or travel of the slide or ram of the press or serious damage may result. When the press is equipped with a cushion in accordance with this invention the distance D may be less than the ram travel by any amount equal to the stroke S or the piston 38 before any damage can result. This permits setting of the press prior to its operation with much less accuracy, for so long as the distance D is less than the travel or the ram by a distance not greater than S no harm can come to the parts of the equipment i! the setting of the reliefvalve 62 is such that pressure onlyv securing 4said piston for movement with said rarn a passage `connecting `the chambers on opposite sides of said piston, and a relier valve biased to close said passage to resist movement of the piston in relation to the slide, said valve being set to open at a pressurein said space between that necessary for the operation of the press andthat which might damage the same. i

2. A hydraulic cushion for use with aipress hav-` ing e, lixed bed and a movable ram, comprising in combination, a punch holder, a slide adapted to carry said holder, a cylinder in said slide having its axis substantially parallel to the axis of movement of the slide, a piston operable in said cylin-V der, means securing said piston for movement with said ram, a passage connecting the chambers on opposite sides of said piston, and a relief` in combination, a punch holder, a slide adapted to carry said holder, a cylinder in said slide, a piston operable in said cylinder, means securing said plstonfor movement with said ram, a passage connecting the chambers'on opposite sides of said piston, a relief valve biased to close said passage to resist movement ofthe piston in relation to the cylinder and slide but set to yield at a predetermined pressure, and a check valve opening against pressure opposite to that tending to open the relief valve.

4. A hydraulic cushion for use with a press having a iixed bed and a movable ram, comprising in combination, 'a punch holder, a slide adapted to carry said holder, a. cylinder in said slide, a. piston operable in 'said cylinden, means securing said piston for movement with said ram, a passage connecting the chambers on opposite sides of said piston, a. relier valve biased lto close said passage to resist movement of the piston in relation to the cylinder and slide, a check valve opening against pressure opposite to that tending to open the relief valve, and means to adjust the bias on said relief valve whereby the pressure exerted .by the press before relief can be regulated.

5. A hydraulic cushion for use with ay press having a fixedv bed and a reciprocable ram, comprising in combination, a slide, ways guiding said slide for movement toward and from the bed in a path coextensive with that of the ram, a punch holder mounted on said slide, said slide having a cylinder bore therein parallel to the axis of the slide, a piston working in said cylinder and secured to said ram, heads closing said cylinder and forming chambers on opposite sides of` the pis` ton, a passage connecting said'chambers all being substantially, iilled with liquid, means.` in said passage to resist flow from the chamber on the punch holder side of the piston to the other until the pressure reaches a predetermined value, and means to adjust said value.

6. A hydraulic cushion for use with a press having a fixed bed and a reciprocable ram, comprising in combination, a slide, ways guiding said slide for movement toward and from the bed in a path coextensive with that of the ram, a punch holder mounted on said slide, said slide having a. cylinder bore therein, a piston working in said cylinder and secured to said ram, heads lclosing said cylinder and forming chambers on opposite sides of the' piston, a passage connecting said chambers all being substantially nlled with liquid, means in said passage closed against fluid pressure of less than a predetermined amount to prevent now from the chamber on the punch holder side of the piston to the other, and a check valve positioned in said passage adapted to open at low pressureto ow in the reverse direction.

'7. A hydraulic cushion for use with a press having a fixed bed and a reciprocable ram, comprising in combination, a slide, ways guiding said slide for movement toward and from the bed in a path coextensive with that of the ram, a punch holder mounted on said slide, said slide having a cylinder bore therein coaxial with said ram, a piston working in said cylinder and secured to said ram, heads closing said cylinder and forming chambers on opposite sides of the piston, a passage connecting said chambers all being substantially filled with liquid, means to immobilize the liquid on the power stroke of the press, means to relieve the liquid from the chamber on the side of the piston exerting the pressing force when said force exceeds a predetermined amount, and means to return the relieved liquid to said chamber on the withdrawal stroke of the ram.

8. A hydraulic cushion for use with a press having a fixed bed and a reciprocable ram, comprising in combination, a slide, ways guiding said slide for movement toward and from the bed in a path coextensive with that of lthe ram, a punch holder mounted on said slide, said slide having a cylinder bore therein, a piston working in said cylinder and secured to said ram, a head closing the cylinder on the end adjacent the punch holder, liquid in the chamber thus formed, and

a relief valve associated with said chamber and adjustable to open at a predetermined pressure to release said liquid to prevent damage to the press.

`9. A hydraulic cushion for use with a press having a fixed bed and a reciprocable ram, comprising in combination, a slide, ways guiding said slide for movement toward and from the bed in a path coextensive with that of the ram, a punch holder mounted on said slide, said slide having a cylinder bore therein, a piston working in said cylinder and secured to said ram, a head closing the cylinder on the end adjacent the punch holder, liquid in the chamber thus formed, a relief valve associated with said chamber and adjustable to open at a predetermined pressure to release said liquid to prevent damage to the press, and a check valve in shunt to said relief valve and adapted to open on opposite pressure conditions.

10. A hydraulic cushion for -use with a pressA having a fixed bed and a reciprocable ram, comprising in combination, a slide, ways guiding said slide for movement toward and from the bed in a path coextensive with that of the ram, a punch holder mounted on said slide, said slide having a cylinder bore therein, a piston working in said cylinder and secured to said ram, a pilot rod extending from the piston opposite the ram, heads closing the cylinder and portedl respectively for the ram and pilot rod. a packing in each head port, a passage connecting the chambers formed on opposite sides of said piston, liduid normally filling the passage and the chamber through which the pilot rod passes, a relief valve in said passage, means biasing said valve closed against escape of liquid from the last mentioned cham-ber but set to yield at a predetermined relief pressure` and af'check valve in said passage automatically closed against escape of liquid from the last mentioned chamber under any pressure conditions but opening in the opposite direction at low pressure.

11. A hydraulic cushion for use with apress bore and secured to said ram, a pilot rod extending from the piston opposite the ram, heads closing the bore and ported respectively for the ram and pilot rod, a packing in each head port. a passage in said slide, lateral connections from the ends of said passage each to one of the chambers formed at opposite sides of the piston, liquid lling the chambers, passage and connections. a valve seat in said passage, a valve member cooperating with said seat. a spring in said passage to bias the valve shut, and means extending through the end of the passage to adjust the tension of the spring, said valve being movable against said spring by excess pressure in the chamber surrounding said pilot rod.

12. A hydraulic cushion for -use with a press having a fixed bed and a reciprocable ram, comprising in combination, a slide, ways guiding said slide for movement toward and from the bed, a punch holder mounted on said slide, said slide having a bore therein, a piston working in said bore and secured to said ram, a pilot'rod extending from the piston opposite the ram, heads closing the bore and ported respectively for the ram and pilot rod, a, packing in each head port, two passages in said slide each having lateral connections from the ends thereof to the chambers formed at opposite sides of the piston. liquid lling the chambers, passages and connections, a relief valve in one of said passages, means biasingsaid valve to open only on occurrence of excess pressure in one of said chambers and a check valve in the other passage opening to pressure in the other chamber.

13. A hydraulic cushion for use with apress having a fixed bed and a reciprocable ram, comprising in combination, slide for movement toward and from the bed in a rectilinear path, a punch holder mounted on said slide, said slide having a, bore therein, a

piston working in said bore and secured to said ram, a pilot rod extending from the piston ol).- positethe ram, heads closing the bore and ported respectively for tl e ram and pilot rod, a packing in each head port, two passages in said slide each having lateral connections from the ends thereof to the chambers formed at opposite sides of the piston, liquid filling the chambers, passages and connections, a relief valve in one of said passages, means biasing said valve to open only on occurrence of excess pressure in one of said chambers, an extension from `one of the said connections through the side of said slide, a check valve at the Junction of said connection a slide, ways guiding said spring.

WILLIAM T. STEPHENS.

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

UNITED STATES PATENTS Number Name Date 1,893,187 Urbanek et al Jan. 3, 1933 Number Name Date Payne Sept. 19, 1922 Urbanek et al July 18, 1933 Scott July 15, 1913 Cotton Jan. 18, 1927 Rode Apr. 3, 1928 Flynn Apr. 21, 1936 MacColl Aug. 13, 1878 Walker Apr. 25, 1916 Pels June 2, 1931 Brandt Mar, 31, 1931

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