US2642023A - Hydraulic press - Google Patents

Description

June 16, 1953 L 'zlMMERMAN 2,642,023

HYDRAULIC PRESS Filed Nov. 8, 1949 5 Sheets-Sheet l W, ,Maf/@M25 ATT'YS June 16, 1953 L. ZIMMERMAN 2,642,023

HYDRAULIC PRESS Filed Nov. a, 1949 5 Sheets-Sheet 2 1N VEN TOR.'

LOUIS ZIMMERMAN FIG. 2

June 16, 1953 zlMMERMAN 2,642,023

I HYDRAULIC PRESS June 16, 1953 L. zlMMr-:RMAN l 2,642,023

HYDRAULIC PRESS Filed Nov. 8, 1949 5 Sheets-Sheet 4 INVENTOR.- LOUlS ZIMMERMN ATT'YS June 16, 1953 ZIMMERMAN 2,642,023

HYDRAULIC PRESS Filed NOV. 8, 1949 5 Sheets-Sheet 5 wx FIG 5 FIG. e

a L fm 22a so 3&9

\ To TANK 3| 30d 3o gm soc 5 'n' 44 30P:F T18:-

"""' Y l 3o' 30e 'L 5%/ INVENTOR.- "f//W .3 LOUIS ZIMMERMAN lbum, Y Miwt ATT'Ys Patented June 16, 1953 PATENT oiFFgl'cfE fammes e il Y-Tliis invention :relates to *hydraulic presses of the'typefemployingftwoisldesfarrangeirasfaniinner for iw'orksperforming fs'lide :and :an souter :.or work-holding slide, hy'chaulic lflui'd pressure mperate imeans factuating the :slides in the lworleing rdireotion, fthe A work-holding slide ibeing fsup'- ported by the work-performing slide sto smove therewith aand also relatively thereto, mean's Theillg provided Ito `provide .fa :"lag 'between the engagement of'Nahe-"workday rthewok-holdingfslide and 'fthe A'e'fecztive engagement f df the workaperforming fs'lide mvvith fthe wvork, #the 7Work--'holding slide being lifted away frnm fthe work :by @reason o'f "the retraction :of tthe work-performing slide.

.According .to `A'the:presentinvention apress Vof the aforesaid'ftype :is characterised 'by 4the combination :with the 'work-holding :slide :of hydrauf licallyfoperacteti pressure applyingzmeans adapted l to japply :a :predetermined :work-holding pressure to the work-rholdng slide 'andoffnieans responding 1to the aforesaid :predetermined fpressure to isolate :the ysaid hydraulically :operated pressure applying -means from the isouree Iof `uid ypriessure when a '.predetamnined eworkeholding -pressure iis reached, iand :also fof adjustable :duid pressure means yieldingly opposing said isolatmg -fopera'tion :and :adapted to maintain said predeteminedpressnre constant over the whole o'f :the phase fn'fithe Working cycle.

llln ,an embodiment of fthe invention reach vgaecumulator consists pf fan fair fchamber `,separated by a `diaphragm v:from :a -low fpressure eylinder accommodating ,ea spring floaded piston `.engaged by a high pressure piston :valve Aioperatingin .opposition -to `.the n,said fspring imeans and .the `'air cushion, said piston ,valve ,operating yacross 1a supply -i-eonduit .to the work-holding cylinders and -.leeing .adapted :to be actuated Aley ifluid ,prese sure from zthese work-holding cylinders when .v it exceeds a predetermined amount so as .to act upon vgthe spring loaded piston Avto displace `vthe fluid in the said `low Lpressure cylinder into the air receiver, this .displacement .of i the isa'd piston valvefbeingiadaptedto .expose a previously open shutoff valve xagainst the .inu'ence .of ispring means'to 'fluidpressuresbas 'to move the shutoi valve .to lthe .closed position vand isolate 'the work-holding cylinders from the 'source .of supply of -`Huid pressure, and further :means oeing provideidwhereby at theeon'lusion of the draw ders vented oiiitoiproduee apressure dference to -feiect -openirigff the isaid shut0`i valve to provide a 'free fo-w ffrom :thework-holdingcylinders to main supply tank.'

iIn 'order ithat fthe jinvention r`may ibe A'clearly understeod andreaitlil'y fca'rriel .finto effect Adraw-- ings rare sappended 'hereto illustrating fan Jembodimen't theredt fand ^-wherein, v

`Figure 1 iis a A"flowfrrniitdiagram-coftheloydraulie Epress in the #raised yposition Yof the ffs'lides. Figure '32 *is fa view Afs'inilen' to Eigure -1 'but showingithe lpositionvdffthe valveandother parts wherein ith'e @slides lhave *been moved downwardlytothefpositionfwherethe Pllanlihdlder! or-clamp slide is eontacmngsh'ewvork. v Figure 3-is abview similar toligureZlbutfshowing ithe draw fsli'de #at the -`end fo'f k'the ldrawing stroke. Y Y

Fgureekl isi-a fsimilarltol-Figures l, 2, and 1B but showing *the -main dvalve shifted 'to elevate the Lslies and illustratin'g 1'the slides as they `'are moving upwardly away from ithe work..

VFigure/1 5 is la sectional elevation df 'oneof the air aecumuletors `showing' the parts `rthereof lbeforeipressure frs-exerted yo'n'ftl'le 'tilanlhlderslide ,-liguref 6 is al view similarftcvFigureV 5 fbu't fshowing the position fogfithe parte 'of fthe Iaeeumulaltor when Jpressure iis being applied to `-4the blanleholder slide. Figure "7 is "a diagrainm'atic fvrew of fthe Yar rangement of portsgand passages ini-a y'cheekand holiingivalvefofitlfrje apparatus. In-the various 'gures'oithe t'drenvin'g ithenotationml 'adi acentl perrforniing f'sliiieand-permitted to move fdown-J wardgly inf advance-whereof. i

*The peuter Vor we rief-hldirrg rslide carries ftwo pairs or-othersuitablemmiber and symmetr-ical arrangeme nvdrflupstanding pistons Hl' Lslidable yiin Xed vertical work-holding cylinders 5, and disposed along the vertical axis of the press is a ram d, or number of rams disposed symmetrically with respect to said Vertical aXis, xed to the head of the work-performing slide and operating within a fixed central cylinder 1 or number of cylinders. Assuming that there is only one cylinder 1, its head has an inlet 8 connected by a conduit 9 to the main pressure pump IS via a four-way valve il, the shuttle IIa of which is actuated alternately in opposite directions by a pair of solenoids IIb, IIc remotely controlled. The head of the cylinder 'l is also fitted with a pre-fill Valve I2 communicating with the interior of the cylinder and with an oil supply pipe leads from the pre-fill valve I2 to another part of the said four-way valve I I, this latter conduit having a branch connection I3 to a holding check valve I4 from which extends a conduit I5 connected by branch pipes i3, I1 to the lower ends of two or other suitable number of pullback cylinders I 5 the pistons il or which are urged upwards when it is required to return the inner or work-performing slide to the raised position. rIhe pistons ISyare connected to the inner slide I.

The said conduit I3 extending from the prell valve I2 of the main cylinder has branches I3a to pre-ll Valves 20 of the work-holding cylinders 5, these latter pre-fill valves communicating with the main supply tank 2|, and heads of the cylinders 5 communicating via lines 22 to the valve housings 23 surmounting low pressure cylinder heads 24 of air pressure accumulators 25. Each low pressure cylinder head.24 has its interior isolated from the appropriate air chamber 25 by a diaphragm 26 (see Figures 5 and 6) in a diaphragm chamber 21. A spring 28 urges a piston 29 upwardly within such cylinder to yieldingly oppose downward forcing of a piston valve 30 in a bore 3U in the valve housing 24.` This piston valve 3E! controls the supply of fiuidpressure to the work-holding cylinders 5. The driving connection from the pump supply I Vto the work-holding cylinders Via the appropriate parts of the valve housings 24 containing the piston Valves 30 is effected by branches 3I taken off the conduit 9 via a branch 32, through check valve 34', and branch 32a containing a check valve 32' having a decompression orice, the conduit 9 being that connecting the aforesaid four-way valve II to the pressure inlet of the main cylinder 1.

Each pre-i'ill check valve l2, 20 may be of any desired construction but preferably comprises a piston valve element maintained in closed position by a coiled compression spring operating on the rod of a poppet valve and urged to open position against spring action by aafluid pressure actuated piston at the end ofthe rod remote from the valve, this fluid pressure being obtained from the conduit I3 leading from the aforesaid four-Y way valve and branches I3a therefrom.` YThese pre-ll check valves 2D are opened by fluid pressure only when the ram B operating vthe inner slide I is being urged upwards. On the downward stroke, by reason of the connection of the pre-fill check valves with the maintank 2I, a pre-filling operation is obtained by reasonvof the suction generated inside .the cylinders during the initial or idle pressure stage until the, main pres- 4 sure takes charge for driving the pistons 4 of the work-holding cylinders 5.

Pilot pressure for actuating the valve I I is obtained from a pilot pump 33 which may be driven off the motor 35 driving the main pump I0, suitable ltering means 36 and cooling means 31 being provided in association with these pumps, and a relief valve 38 being provided in the supply conduit from the pump to the four-way valve.

The aforesaid air accumulators with their associated hydraulic uid low pressure cylinders 24 and valve housings 23 accommodating the aforesaid piston valves comprise units each fluid thereto when a predetermined pressure is reached as well as maintain that pressure. Each 'air' chamber 25 has a connection 39 from its llower end to an air pressure and tonnage gauge Y 40, a blow-off valve 4I and air pressure regulator 42, its upper end being in communication with the diaphragm chamber 21 having the integral upstanding cylinder comprising the said low pressure cylinder 24, the chamber 21 being perforated as at 21 where it forms the lower wall of the cylinder 24 and securing in position the' diaphragm 26 which at the appropriate time yields to permit oil from the low pressure cylinder 24 to enter the chamber 21. The connection 22a to each line 22 is taken 01T theupper enlarged end of the bore 30'.

It will be appreciated from the foregoing that the valve housing 23 has a high pressure cylinder, i. e. the bore 3S' containing the piston valve 3B whichis co-aXial with the low pressure cylinder. Hence, when the `predetermined fluid pressure in each cylinder 5 is reached, as determined by the setting of the respective air pressure regulators 42 the duid pressure reaction from each workholding cylinder 5 becomes substantially wholly effective upon the piston valves 30 through line 22, and when the work holding stage has been reached'th'e piston valves 30 will be urged downwards to the position sho-wn in Figure 6 against the influence of the air Vaccumulai'fors 25 and springs 28. will be established between the fluid pressure in lboreSIl and passage 30h through bore 30uI whereupon cut-off valves 44 loaded to a predetermined extent by springs 44a, are urged upwardly to the closed position-of Figure 6 each across an associa-ted inlet 3Id receiving the appropriate line 3 I. The work-holderrelief and decompression valve Y 45 normally remains closed and, when closed,

the pressure of fluid Vin line S0 and its connecting lines 49 will `maintain the check valves 50 in closedV position, thereby enabling iluid pressure in passage h to close valve 44. Thus, flow of fluid through lines 3l will be stopped and pressure within the accumulator vwill be equalized to maintain the holding pressure in the blank holder cylinders 5, and the iiuid within the accumulaltor will, in effect, have been isolated from the source of fluid supply.

Each Valve housing 23 has an outlet 33d to the viav a bore I4a with the branch I3" when valve When this occurs communication ing conduit 5. MI is .irriterai-sed' nosition. -Valve MI ghasabore I=4I,a-;con 1mnnicating fzWithf-aerelief valve hlaact- ,fing to -close -i-off :an -ioutlet .there 43a receiving lthe line f4.3 leading .to the iworkeholding--Ecylinders i5 :via fthe .four-way valvesandqconduit; 34 as aaforesaid. .The bore :Illia-,ofthe valve LM iis-continued right :through the valvfefso fthat -:when a:shuttle 'valve .I42 operated l:from rtheesolenoid :.I'l fcloses by the'actionfofitslspring vfIfd'lia liu-id :from conduit I will pass through valve :MI vtothe' space ithereabovefandg-because of :the larger jarea, foresthe fsolencid is energised :to move `-valve 1h12 yi,dmvnvnirolly communication :will 'doe :established fbetweenvthe ispace'fabovefvalve .IM land -passage :Ifc 36o :release `the ihtdraulio ipnessure iabov-.e :the :valveIAl back-.to :thebranch I f ilhegoperation of thepress is faswfollows':

Referring initiallyao AFigure al fof the drawings, thesslides -are shown in elevated j position 4'and at rest. .Inthismosition theuidiin pull-Ibach cylinders i, l-iwilliholdthe rslides l.elevated andwthe duid in hold-down cylinders-5 :willidiave become @substantially exhausted. .The 'shuttle '.:piston .dI-,In of tion :as fshown. .The ishuttle #Ha contains rtherein an .elongated fbore al lfd .having :an opening rat one side vthereof Y.communicatingffwith zcon'duit @I lla leading :from the fpumpgandghasfother fopenings :at each v-end ethereo'f communicating izby :means :of passages Iy Ierand I. lj in' the'valve body with-conduit -I-Ig 4which lazextendstto thezfluid .tank. .The pump it!) .mumps :hydraulic .-fluid ffrom tank T through conduit Illbaand through :line yIllaato the valve IiI. Itiwillzbe vdent, therefore, thatin the position fof :the fparts-:and `thershuttle the valvel Ii in Figureiltcduidzwillbezpurnpedfromthe tankvto-ithe valve through bore rLId, andwthrough the massages flilevzand ttf ito the conduit IIrg backitothetank.

When lit ,ris desired sto place' :press :in roperation rand :to flower the islides, ssolenoid '1I It fwill be :energized itormoveithefshuttle ztowa'rdfthe left as;itappears`=in E'igure 2=of the -fdrawingszand solenoid I`14' of valve lIlI swillfalso be energizedato'torce cation v`will be established lbetween the `.passages above and Aloelowvvalve member I'4:.I u:thereby :releasing fthepres'sureiiabovesvallve :member Ii4l rand perrrttingzttozbefimseated. )Art-thisnromentithe Weight iof the slides zclonnected :to i.the vpull-:back cylinders I8 through the piston rods-lt@ cause ther-slide'sao rbe ilowered dueno I.then'ihiase rif Ythe pressure on the iuidmithinthe fpull-fback-fcylinders. The pressure released because fof the opera-tion fof valve M :permitting a :free jlow of theuidfout-ofipull-#backi cylinders iiithrough :the conduits@- h6 ,fand I-FI throughcon'duit :i5 tovalve :1I-14.

` Referring nonr forfafmoment toFigure ;-'7 ,-:theerluid entering-:conduitdr willspassthrough the passages IAN-rand `supwardls' :through the bore xllla. -At this time, the solenoid 1M. ;is-renergiaed :so that the 4shuttle `valve M2 risvin .fits lowermost mosition, establishing #communication between the area above \.valve I-4.I :and )passageway rl3c. iSince there-is no pressure onrmemberuldfl 'and .theipressure below itis =nowf.-greater1thanthe pressure on the 'topiof s valve :member al IH :this valve member will becomeunseated `andpermit `the free :flow :of fluid `through conduit :I3 -to conduit nIii tout of the valve |14. f Y

:Referring .back to lFigure 2 again the .arrowsj indicate )passage of :lluid from "I 3 tothenonnect- I 3 `:and upwardly =therethrough -into shuttle dita. maville :been imoved valve I I. The

I cumulators.

6 toward fthe;=left,';it 4`will-be .seen that communicaytion -v1ihhe established between `:conduit 1Ij3 and passage V-,I Ijfin -ithe-valve body which iwill icarry the iluidzback .fto the tank .through .conduit '.IIg. At the sametimegthepump I0 isforcing fluid under pressure .strom the 'tank through conduits .lb :and 1|.0a1into the valve .and v communication n with-:conduit 40a is now established with'conduit .8. :Some of the fluid, thereforawillgpass downwardly tinto cylinder g1- and some will alsofbe `bypassedlrom conduit -B through conduit 32 to unseat icheck 'valve f3.4 whereupon the flow of `.fluid will -contimie the direction `of the ,arrows through valve 32' and the various .lines 3 I Vrtothe inlet Ia: of each-accumulator.

Vleferring for la 1moment to jFigure 5, z it will 4be seen that `the -Tluid flow wi-thinthe :accumulator from bore 31a ithereinwill be upwardly around valve member i4 :and valve member '130 through passage 22a and intoline .212 :connected Vto the head of l:nach of hold-down cylinders 5,

`Sincefthe movementdownwardly of lthe-various pistons'ilv andzthezrarnt iszrelatively fastin their initial ;-stages fthe dluidbeing v.pumped vinto the cylinders .-5 andthe =cylinder -1 cannot be relied upon :to :force the `pistons l.and ram downwardly. vThe initial downwardmovementis-due tothe .releaseA of the fluidloolred in'the'pull-back cylinders .I'8 and the suction vcreated vby the downward movement of pistons 4 andiramw willfbe sufficient to open the -pre-ll valves 20 `rand VI2 thus ipermitting additional .fluid Afrom the tankto enter the Arespective cylinders.

"This downward :fmovementcontinues until just before fthevclamp-,or blank holder slide reaches the blank whereupon-fthesolenoid I4' `'ln-valve Id is l'de-'energized:allowing spring Ill-2a to movethe shuttle |42 upwardly .and :stop further ifree ilow of 'duid therethrough. At thisvpoint fluid .from the pull-back oylin'ders I'-8 through .lines It and I-'I'to7thefconduit1l 5 iwill `flow -at a `slower Tate `and will pass vupwardlythrough :the passage .lfd I'a in valve member -rI4 I. :Since the Vfluid therein will be trapped, a suicient pressure will rbe built up dueto theilarger-.aremat',thetop of valve-member 'I4:I ato-seat-Jthis valve'whereupon'communicationvvill'fbeestablishedbetween the branch of the `passage IAIa/.to thecheck valve 44a; This will rcause a slowing down :of `the blank holder slide although .-lit Twill not stop -moving -entirely because fluid from the ,fpumpis still-.being passed through ythe -accumulators :into the vhold-down cylinders. Movementofthe-blank holder slide willftherefore;continueuntilthe blank is reached whereupon continued flcw.of-1luidinto the holddown cylinders 5 Ywill build `lllslfressure,

.Since the-,clamp .slide Yand draw slide connected Y with pistonsY I9 :willstill.movedownwardly but at a .slowerirate and theflow `of .fluid from the vpullback cylindersd through conduits t6, l?, and

' I5 vis .blockedbythe seating of .valvernember .I fl I a pressure -Will-be built :up within .valve IA until the ,pressure of Athe spring vwhich normally closes check valve 14a has `been overcome. At this pointthe flowa of kfluid will then ,be .through valve L4 Aoutwardly through conduit -43 `and back to val-ve II Vias A`indicated `by the .arrow -in Figure 2 adjacent theiconduit A3.

It will also beseenthat Whenthe shuttle IIa is `in the `position shown :in Figure .v2 the .conduits 4.3 =and "Ml will be in communication whereupon the fow lof 'fluid ffrom `valve i4 will :be xcarried through conduit Stand-.past Atheopen-A cheek valve- 34 toiconduit 3.I .andethence Lto the various Y ac- This condition just described prevails after the blank holder slide is in clamping position whereupon pressure in the hold-down cylinders Will continue to increase. Since the fluid from pull-back cylinders I8 passing through the conduits 43 and 34 joins with the nuid being pumped through conduit 9 and some of which also is conveyed to conduit 32 and thence to line 3|, it will be clear that this fluid from cylinders I8 will be used to charge the hold-down cylinder 5 in the clamping position of the blank holder slide. The air pressure against the diaphragm 26 in each of the accumulators may vary as between the individual accumulators or may be the same depending upon the setting of the various valves 42. The air pressure for each accumulator will be predetermined and preset. As the pressure in each hold-down cylinder 5 continues to build up, a point will be reached where the pressure therein will become equalized with the pressure in the head of the accumulator associated therewith. When this pressure reaches or exceeds the air pressure within-the accumulator, then the shuttle valve 3B will be forced downwardly from its position in Figure 5 to its position in Figure 6. When this occurs the hydraulic fluid above valve 39 will pass through the bore 30a therein and into bore 30h. Valve 59 will be normally maintained in its closed position as shown in Figures 5 and 6 because of the connection of conduit 49 with valve 45 through line 60. Valve 45 being closed, the iluid in line 49 will be maintained under pressure. The continued building up of the pressure in bore 30D will thereupon elevate valve member 44 against the force of spring 44a from its position f shown in Figure 5 to its position in Figure 6.

When the conditions of Figure 6 prevail the flow of uid through lines 3| will be stopped because valve member 44 has closed the passage thereof through bore 3I`a. At this point the re-' quired clamping pressure will be exerted by the blank holder slide against the blank. The draw slide I, however, will continue to move downwardly to perform the drawing operation on the blank and since the iiuid being pumped from the tank through valve I I is prevented from being carried any place else, it will pass downwardly through conduit 9 and within cylinder 1 against 4the head lof ram 6. Suflicient pressure will have been built up by this time to enable the draw slide to perform its drawing operation.

As soon as the drawing operation begins, the solenoid I4 of valve I4 will again be energized to allow free flow of the additional uid in pullback cylinders I8 through lines I6, I'I, and I5 and through valve I4 back to the four-way valve I I to furnish additional fluid for pumping against the head of ram 6 to insure a sufcient build-up of pressure for performing the drawing operation.

This condition prevails in Figure 3 at which time the drawing operation is completed and the valve I4 is open for free flow of fluid therethrough.

At the end of the drawing operation, solenoid I4' is again de-energized and the solenoid IIc is energized to move the shuttle I la of the four-way valve I I toward the right to the position shown in Figure 4. The various arrows adjacent the respective conduits in Figure 4 illustrate the flow of fiuid on the upstroke of the slides. It must be remembered that the clamp slide must remain in place in clamping position while the draw slide is being elevated for stripping purposes. The pressure, therefore, remains in hold-down cylinders 5 until just before the clamp slide is picked up by the draw slide.

Referring to Figure 4, with the shuttle IIa in the right-hand position all of the fluid pumped from the tank and passing to valve II through conduit Illal will pass out of valve II through conduit I3. Since conduit I3 is connected directly with pre-fill valve I2 in the head of cylinder 1, there will be sufcient pressure to open this valve and allow the upwardly moving ram 6 to force fluid from the cylinder outwardly through the valve back into the tank.

Since valve I4 is now'again de-energized and the shuttle |42 is in its elevated position, -the valve member I4I will be seated so that the fluid passing through conduit I3 will also pass through line I 3 into valve I4 and will unseat valve |40 against the pressure of its spring to establish communication with the outlet I5 which conducts the fluid rthrough conduits I6 and I7 into the bottom of the pull-back cylinder I8. This action will cause the Lpistons I9 to rise carrying with them the draw slide I and allowing iluid above ram 6' to be discharged through the now open pre-fill valve vI2 into the tank.

This condition will prevail until just before the draw slide reaches the flanges 3 on the clamp slide to pick up the clamp slide and carry it upwardly. Just before such position is reached a slow-down of the draw slide is caused by opening valve 45. Any suitable switch means can be arranged to cause the operation of valve 45 at the proper time. The valve 45 is operated by a solenoid, and suitable switches (not shown) are mounted on the draw slide -to energize and deenergize the solenoid to operate valve 45. The use of such switches to operate valves have noi'l been shown herein since they form no part ofthe present invention. As soon as this occurs, fluid from' line 49 will slowly pass through valve and line 60 and outwardly through conduit 45a back to the tank. As soon as this occurs the pressure of the fluid in passage 30o in the accumulators will move valve 50 upwardly due to the release of pressure thereabove and permit some fluid to be carried back to the tank through conduit 30d. This will also cause a reduced ow of fluid through conduit I3 be-v cause some of the fluid through conduit I3 will now be free to pass through line to valve 45 and outwardly through conduit 45a. This reduced flow of fluid through line I3 will obviously cause a slow-down of the movement upwardly of pistons I9 and, consequently, the draw slide connected thereto.

This condition prevails only momentarily, however, whereupon after contact is made between the draw slide and clamp slide flange 3, valve 45 is again closed and the full force of 4the fluid throughv line I3 will continue to elevate the pistons I9 of the pull-back cylinders and to maintain the various pre-ll valves in open position. rlhe release of the pressure within vthe accumulators while valve 50 is open will be sufficient to cause the air pressure to take over and force valve member 30 upwardly to the position shown in Figure 5. The release of pressure in bore 39h will, at the same time, permit valve member '44 Ito be lowered and open the passage into conduit 3l. Therefore, as the draw slide and clamp slide both move upwardly due to the pressure within pull-back cylinders I8, any fluid which' does not pass through the pre-ll valves 2i) into the tank will be caused to flow through conduits 22 from the hold-down cylinders 5 through the accumulators and outwardly through conduits 3| which will join the ow of iluid in conduit I3' to aid in the continued elevation of the draw slide.

condition will continuel' untilfbothslicles have reaclidtlieinuppermst positinillustrated in Figure 1 whereupon the. solenoids IIb and. l|c willbeQd'eenergized and permit..the shuttleI4- lul ofv4 valve l'lf'to Yagain assume its y neutralA position through 'thea frce ofthe spri A' e I, endthe'reofl! to` hol'd thc-fluid n: the linesand aintainathe lines elevatedl whilelf'the -circlatesfluidlto and`fromt'heltanl'. l l y Itmay'beadvsable, ifdes'iredo-introd1ce-intp tliegsystenasm'allvolume highip'res'sure p3 lfllc tliel, discharge Vo'f'wlfizl'i islected to Ithe :commori fluid; vpressure Iin'e 3I feeding the various accumulators, If for any reason such as minute leakage or expansion of the frame during the draw phase of the stroke cycle the work-holding capacity of the accumulators has been prema- -turely depleted, the pump IIJc has the effect of maintaining thisv pressure by pumping additional iiuid into the lines 3|. It is evident, therefore, that the work-holding `pressure can be maintained indenitely and for purposes of die setting it can be built up and maintained independently of work-slide action.

From the foregoing description, it will be evident that two particularly novel features have been introduced into hydraulic presses by means of the present invention. The first and perhaps most important is the provision of the air pressure accumulators which can be independently regulated as to air pressure to thereupon cause the blank holder slide to exert different pressures at different points thereon against the blank by merely turning the regulator valve 42. This feature eliminates the necessity of the operator actuating the slide several times to determine what pressure is being obtained. In Ithe present case the valve regulator is adjusted to the desired and predetermined air pressure and this pressure must be overcome by the hydraulic pressure before the blank holder slide will exert its clamping action. Since these accumulators are connected in the line which leads from the source of fluid supply to the hold-down cylinders, they allow the predetermined pressure to be built up in the holddown cylinders and then stop any further now of iiuid to those cylinders as long as the pressure is maintained.

The other feature also of considerable importance is that which utilizes the fluid from the pull-back cylinders to charge the hold-down cylinders when the blank holder slide reaches clamping position. This is accomplished as stated above when the pressure in valve I4 is sufficient to unseat valve member 14a whereupon fluid from the pull-back cylinders iiows outwardly through conduit 43 and line 34 and joins with the uid in line 3| being pumped thereto from conduit 9.

I claim:

1. A hydraulic press comprising a draw slide for performing work on a blank, a clamp slide for clamping the work in place while work is performed thereon, uid operated drive means to move said clamp slide to clamping position, fluid operated pull-back means to move said slides away from the blank, conduit means connected with said pull-back means to discharge fluid displaced Itherefrom by movement of the draw slide toward the blank, a source of fluid under pressure, a conduit connecting said source with said drive means for the clamp slide, a spring loaded valve in said last named conduit, adjustable fluid pressure accumulator means connected with said source and with said drive 'means to main-tain said clamp slide at a steady predetereste rest` movement tlf;ereo'fl,fyielded);lL means operabler in'responsef-to continue'dmovement of saidL drawjv until theA presslir'edn` saiddrive-y meansn for theI clamp-*slide reaches --af- Vpredetermined amount, and :meansresponsi'vetoisaidfpredetermined* pressure to isola sa'idfdr'ivejmeans fromsaidisource, whe'rely'"-sai'elpredetermined pressure is maintained.

' 2. In a hydraulic press having a clamp slide and a draw slide for performing work on a blank, a plurality of hold-down cylinders, a fluid actuated piston in each of said cylinders connected to said clamp slide for moving said clamp slide to clamping position, a iiuid actuated ram for moving said draw slide to perform a drawing operation, a plurality of pull-back cylinders, a fluid actuated piston in each of said pull-back cylinders connected to said draw slide for moving both of said slides in a direction away from the blank, a source of hydraulic uid under pressure, an air controlled accumulator in the uid line connecting said source with each of said holddown cylinders, whereby fluid under pressure directed from said source to said hold-down cylinders will pass through said accumulators, means for regulating the air pressure in each of said accumulators to a predetermined amount, and means in each accumulator for stopping flow of fluid to its associated hold-down cylinder when the pressuretherein reaches the predetermined air pressure, wherebythe pressure on the clamp slide will be maintained.

3. In a hydraulic press having a clamp slide and a draw slide for performing work on a blank, a plurality of hold-down cylinders, a fluid actuated p-iston in each of said cylinders connected to said clamp slide for moving said clampV slide to clamping position, a fluid actuated ram for moving said draw slide to perform a drawing operation, a plurality of pull-back cylinders, a uid actuated piston in each of said pull-back cylinders connected to said draw slide for moving both of said slides in a direction away from the blank, a source of hydraulic fluid under pressure, conduits connecting said source with said holddown cylinders and with said pull-back cylinders, a valve in said conduits between said source and all of said cylinders, and means including said valve and conduits for charging said hold-down cylinders with hydraulic fluid discharged from said pull-back cylinders.

4. In a hydraulic press having a clamp slide and a draw slide for performing work on a blank, a plurality of hold-down cylinders, a fluid actuated piston in each of said cylinders connected to said clamp slide for moving said clamp slide to clamping position, a uid actuated ram for moving said draw slide to perform a drawing operation, a plurality of pull-back cylinders, a fluid actuated piston in each of said pull-back cylinders connected to said draw slide for moving both of said slides in a direction away from the blank, a source of hydraulic uid under pressure, conduits connecting said source with said hold-down cylinders and with said pull-back cylinders, a valve in said conduits between said source and all of said cylinders, means including said valve and conduits for charging said hold-down cylinders with hydraulic fluid discharged from said pull- 11 back cylinders, an aircontrolled accumulator in the conduit between said source and each of said hold-down cylinders, whereby fluid under pressure directed from said source to said hold-down cylinders will pass through said accumulatore, means for regulating and establishing a predetermined air pressure in each of said accumulators, and means in each accumulator for stopping fiow of fluid to its associated hold-down cylinder when the fluid pressure therein reaches said predetermined air pressure, whereby the clamp slide pressure on the blank will be maintained.

LOUIS ZIMMERMAN.

V References Cited in the iile of this patent UNITED STATES PATENTS Number Name Date Dnzl May 20, 1941 Dinzl *June 3, 1941 Pocock Nov. 24, 1942 Ernst June 6, 1944 Ernst et al July 18, 1944 Nowak et al Aug. 29, 1944 Davis July 10, 1945 Ernst Dec. 4, 1945 Rode et al Aug. 31, 1948

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