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INTRODUCTION TOHYDRAULIC

PRESSESS

Q.S. Khan(B.E. Mech.)

TANVEER PUBLICATIONSHYDRO-ELECTRIC MACHINERY PREMISES

12-A, Ram-Rahim Uduog Nagar, Bus Stop Lane, L.B.S. Marg,Sonapur, Bhandup (west), Mumbai - 400 078 (India)

E-mail: [email protected]

(3)Hydraulic Presses

www.freeeducation.co.in“Design and Manufacturing of Hydraulic Presses.” ©: Q.S. Khan

1. Introduction to Hydraulic Presses 51.1 Main Cylinder 61.2 Blank Holding Cylinder 61.3 Ejector Cylinder 61.4 Top Platen 61.5 Bottom Platen 61.6 Moving Platen (Pressing Platen) 61.7 Column, Nut and Check-Nut 61.8 Guides 61.9 Press-Table 61.10 Power-Pack Units 61.11 Control Panel 61.12 Manifold Blocks and Hydraulic Pipings 71.13 Ram, Piston -Rod 7

2. Terms Related to Hydraulic Presses 92.1 I.D. of the Cylinder 92.2 Ram (Piston Road) Diameter 92.3 Day-Light 92.4 Shut Height 92.5 Stroke of Cylinder 92.6 Table Size 92.7 Distance between Columns 92.8 Throat Distance 92.9 Table Height 92.10 Overall Size of Press 92.11 Weight of Press 92.12 Oil-Tank Size 92.13 Pressing Capacity 92.14 Working Pressure 102.15 Maximum Pressure 102.16 Speed of Ram 102.17 Cycle Time 102.18 Mode of Operation 10

3. Terms Related to Feature of Hydraulic Presses 123.1 Press with Double Action Cylinder 123.2 Press with Single Action Cylinder 123.3 Press with Regenerative Circuit 133.4 Press with two Working Speed 133.5 Press with Pressure-Compensation Feature 133.6 Press with De-Compression Feature 133.7 Press with Pre-Stressed Column 133.8 Press with Cution Cynder, Ejector Cylinder,

Blank Holding Cylinder, Auxiliary Cylinder 143.9 Verticle Press 14

INDEX



3.10 Horizontle Press 143.11 Up-Stroke Press 143.12 Down-Stroke Press 153.13 Single Day-Light Press 153.14 Multi Day-Light Press 15

4. Classification of Hydraulic Presses 164.1 Round Column Press 164.1.1 Tow Column Press 164.1.2 Three Column Press 174.1.3 Four Column Press 174.2 Fabricated Column Press 174.2.1 Four Column Press 184.2.2 Two Column Press 184.3 C-Frame Press 184.4 Close Frame Press 194.5 Fabricated Chamber Press 20

5. Design Of Press-Body 215.1 Bending Stress 215.2 Fatigue and Endurance Limit 235.3 Selection of Type of Construction of Hydraulic

Press-Body 235.4 Vertical-Plate type of Construction 235.5 Box-Section type of Construction 245.6 I-Section type of Press-Body Construction 255.7 Single Solid-Plate Type of Construction 265.8 Design of Press-Body with Vertical Plate Type of

Costruction 265.9 Design Procedure 275.10 Design of Cylinder Mounting Plate (Plate No. 3) 305.11 Design of Column Supporting Plates (Plate No. 4) 315.12 Design of Re-Inforcement Ribs (Plate No. 5) 315.13 Design of I-Section Type of Construction 32



1.1 INTRODUCTION TO HYDRAULIC PRESSES

FIGURE NO.1.1, HYDRUALIC PRESS

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(1) Main Cylinder(2) Blank Holding Cylinder(3) Ejector Cylinder(4) Top Platen/Top Cylinder(5) Bottom Platen/Bottom Frame(6) Moving Platen(7) Column Pillars(8) Nut & Check-Nuts

(9) Side Guides (for column)(10) Press-Table(11) Foundation Plate(12) Power Pack Unit(13) Control Panel(14) Manifold Block(15) Hydraulic Piping



1.1 Main Cylinder: -

Main cylinder is the most importantpart of a hydraulic press. Cylinder developspushing or pulling force required to carryout desired operation, using pressurizedhydraulic fluid.

1.2 Blank Holding Cylinder: -

Blank holding cylinders are used inthose hydraulic presses in which rawmaterial which is to be press must be heldfirmly in position, at the time of pressingoperation by main cylinder. for example indeep drawing press , blank is held by blockholding cylinder at the time of deep Drawingoperation.

1.3 Ejector Cylinder: -

These hydraulic cylinders are usuallymounted bellow the bottom platen, and usedto eject component which are alreadypressed by main cylinder, and requires someforce to get removed from die in which theygot pressed. For example pressedcomponent stuck in die after cold formingejected by ejector cylinder.

1.4 Top Platen: -

Top platen is a steel fabricated or steelcast structure located upper side of a verticalpress, and withstand compressive andbending load developed by hydrauliccylinder.

1.5 Bottom Platen: -

Bottom platen is a steel fabricated orsteel cast structure located lower side of avertical hydraulic press, and withstandcompressive and bending load developed byhydraulic cylinder. It also used as a press-table in down-stroke presses.

1.6 Moving Platen [Pressing Platen]:

Moving platen is also a steel fabricatedor cast structure. Locate between mainhydraulic cylinder and pressing table. It isattached to Ram of cylinder and guided byside columns of press. Moving platen exert

force on the job placed on press–table.

1.7 Column, Nut & Chuck-nut: -

Columns are round Bar or fabricatedstructure. It binds top and bottom platentogether firmly. Round bars are threaded atends and nuts are provided to hold platen inposition check- nuts are provided to avoidloosening of main nuts.

1.8 Guides: -

Guides are provided to ensure perfectparallel and vibration free movement ofmoving platen. Guides may be Round, V-Type, or flat, depending upon use and typeof columns.

1.9 Press-Table: -

Press-Table is a thick steel plate eitherintegral part of bottom platen or separatelybolted to it. It is perfectly machined andprovided with T-slots or tapped holes formounting of dies and fixtures. Movingplaten attached to ram travel forward andexert force on jobs placed on this press-tableto carry out the pressing operation.

1.10 Power Pack Units: -

This is most important part of machine.It pumps oil under control pressure and flowinto the cylinder to impart it desired speedand to develop desire force. Power packconsists of hydraulic valves, pump, oil tank,cooler, hydraulic accessories, manifoldblock and piping etc. Hydraulic pump maybe driven by electric motor or I.C. engine.

1.11 Control Panel: -

It controls overall operation andperformance of hydraulic press, bycontrolling power pack unit. It consists ofmotor starter, push-button, indicating lamp,current and voltage indicator, contactor,timer etc. Control panel gets it feedbackfrom hydraulic press by means of limitswitch, pressure switch, proximity-switch,thermo couple etc.



1.12 Manifold Block and HydraulicPiping: -

Every hydraulic valves and pumps hasnumber of oil port [holes] such as suctionport, delivery port, tank line [return line]port, drain line port, pilot line port, oil port[A] for forward motion of cylinder, oil port[B] for return motion of cylinder etc.

All these ports [oil holes] should beinter-connected with each other, as well aswith oil tank and hydraulic cylinder incorrect manner and sequence for correctoperation and motion of press. These inter-connection of various hydraulic componentby means of special seamless steel pipe andspecial end-connection fittings are calledhydraulic piping.

To reduce extensive piping, leakageand maintenance, hydraulic valves aremounted on a solid metal block, and theiroil ports are inter connected by drilling holesin metal block. This solid drilled metal blockis called manifold block.

1.13 Ram, Piston-rod: -

Piston-rod is a round bar, which isattached to piston, and moves in and outfrom cylinder for pushing and pullingoperation. For small diameter it is called,piston - rod. When diameter of piston-rodis same as cylinder inside diameter, thenpiston-rod is called as Ram. But in generalall the piston-rod of higher diameter is calledram.



1.2 TERMS RELATED TO HYRAULIC PRESSES

CHECK NUT

OV

ER

AL

L H

EIG

HT

OVER ALL DEPTH

A

SH

UT

HE

IGH

TT

AB

LE

HE

IGH

TS

TR

OK

E

DA

YL

IGH

T

A

OVER ALL WIDTH

SECTION-AA

TABLE SIZE

DISTANCE BETWEEN COLUMN

SIDE GUIDE

MOVING PLATEN

COUPLING PLATE

COLUMN

TOP PLATEN

NUT

I.D. OF CYLINDER

RAM DIA.

FIGURE NO. 2.1, FOUR COLUMN TYPE HYDRUALIC PRESS

FOUNDATION PLATE

PRESS TABLET - SLOT PLATE

BOTTOM PLATEN



2.1 I.D. of the Cylinder :-

This is the inside diameter of cylinder.This dimension helps in calculating thepressing capacity ( tonnage ) of press andapproach and pressing speed of Ram (PistonRod ).

2.2 Ram ( Piston Rod ) Diameter: -

This is out side diameter of Ram. Thisdimension helps in calculating strength ofcylinder. This dimension depends ontonnage of cylinder, stroke of cylinder, typeof operation to be performed i.e. pulling orpushing and return speed. For highertonnage, long stroke and high return speedRam diameter is more. For pulling operationRam diameter is comparatively less. Forexample steel-rope and chain testingmachines.

2.3 Day-Light: -

This is the maximum distance betweenpress-table and moving platen, when Ramis at complete retracted position.

2.4 Shut Height: -

This is the minimum distance betweenpress-table and moving platen when Ramis at most extended position.

2.5 Stroke of Cylinder: -

Day light – shut height = stroke. Strokeis maximum distance to which Ram cantravel.

2.6 Table Size: -

Table size is clear area on press table,which could be used for pressing operation.

2.7 Distance between column: -

This is the distance between twocolumns of the press. Left to right and frontto back. Distance between columns is keptmore than table size as some clearance is

always kept to avoid any damage to columnduring production operation.

2.8 Throat Distance: -

This specification is only for C-Framepress, This is distance between central axisof cylinder and rear most inside surface ofC-Frame.

2.9 Table Height: -

This is distance between groundlevel and working surface of press-table.

2.10 Overall Size of Press: -

This is the complete length, width andheight of press including power pack unitpiping and panel. This figure indicates floorarea and roof height required for press.

2.11 Weight of Press: -

This is net weight of press includingall accessories. This figure is useful fortransportation and making foundation.

2.12 Oil Tank Size: -

This is the maximum oil storagecapacity of oil tank of power pack unit. It isgenerally 5-10 times discharge capacity ofhydraulic pump used.

Terms related to performance ofhydraulic press

2.13 Pressing Capacity: -

This is the maximum force, whichcould be developed in the hydraulic press,for carrying out desired pressing operation.

In single cylinder hydraulic press, it isforce developed by main hydraulic cylinder,while in multi cylinder hydraulic press, it isthe sum of force developed by all thecylinders, which are used for direct pressingoperation. Those cylinders, which do notinvolve in desired pressing, but carry outsecondary work such as material filling and

1.2 TERMS RELATED TO PHYSICALPARAMETERS OF HYDRAULIC PRESS



ejection etc, are not considered incalculating pressing capacity of press.

2.14 Working Pressure: -

This is the pressure at which pumpsupply oil to the hydraulic system in normalworking operation.

2.15 Maximum Pressure: -

This is the maximum pressure at whichsystem could be operated without over-loading the system. Above this pressurehydraulic valves could mal-function andpress structure may deform. Hence forsafety, hydraulic system are designed formaximum pressure and operated at workingpressure, which is less than maximumpressure.

2.16 Speed of Ram: -

Generally Ram has three speeds. Fastapproach speed, slow pressing speed & fastreturn speed. To reduce operation cycle timehydraulic power packs are designed in sucha way that it could delivery high flow of oilat low pressure and comparatively low andcontrolled flow of oil at higher pressure.This enables Ram of hydraulic cylinder totravel at higher speed at no load conditionand slow down for carrying out pressingoperation.

High approach speed at which Ramtravels and come close to material to bepressed is called fast approach speed.Comparatively slow and controlled speedat which Ram presses the material is calledpressing speed.

High return speed at which ram retractis called fast return speed.

2.17 Cycle Time: -

This is the time, which press takes tocomplete one production cycle. It includesmaterial loading time, fast approach timeof ram, slow pressing time, processing time,fast return time and time taken to unloadthe finish component.

Some time hydraulic press has to bekept in compressed condition to somepredetermined time for heating, cooling orcuring purpose. Time for which materialkept compressed condition is calledprocessing time. For example Bakelite iskept compressed in hot condition forthermosetting. In plastic injection moldingdies are kept close after injection of moltenplastic for cooling purpose. Fiberglasspanels are just kept compressed withoutheating and cooling for curing.

Idle cycle time is sum of fast approachtime, slow pressing time and fast returntime.( or time which press take to completeone idle cycle without doing any productiveoperation)

Cycle time gives judgment regardingproduction of press per hour or per shift.While idle cycle time give idea regardingspeed and performance of press ascompared to other press.

2.18 Modes of Operation: -

Auto - mode, Semi – auto - mode, andManual - mode. These terms are used whencontrol panel is used in hydraulic press.

2.18.1 Auto Mode: -

Auto mode [Automatic mode ofoperation] is that state or condition ofmachine in which if only once “cycle startpush button” is pressed then machine willgo automatically through all the sequenceof operation, and after completing one cycleit automatically starts the next cycle andkeep on repeating it. Press will keep onrunning and repeating production cycles tillit is stopped manually or it get stop signalfrom timer, counter, material feeding orcollect ing arrangement or machineprotective system against over heating, filterchoking etc.

Hydraulic presses for laminationstamping, honing machine etc are operatedin this mode.



2.18.1 Semi Auto Mode: -

Semi auto mode (semi automaticmode) is similar to the auto mode but pressstopped after completing one productioncycle. For next cycle again “cycle start pushbottom” has to be pressed.

Plastic injection molding machine,Bakelite moulding press, Rubber mouldingpresses are operated in this mode.

2.18.2 Manual Mode: -

In this mode, all the operations arecarried out by pressing corresponding push- button. As soon as push-button releasedram halts. This mode is also called inchingmode as Ram could be operated for a inchor fraction of inch of stroke as per the willof operates. This mode is also used forsetting of press before switching over tosemi auto or auto - mode.

Dishing press, straightening pressesand generally operated in manual mode.



In this chapter we will define some ofthe terms and feature, which a pressmanufacture refers in his literature or usesin discussion with his customer regardingdesign, manufacturing and supply ofhydraulic press.

3.1 Press with Double ActionCylinder: -

Double action cylinders are thosecylinders which can takes power stroke inforward as well as reverse direction. Suchcylinder can apply pressing force as well aspulling force. Both forward and reversestroke achieved by pumping oil undercontrolled pressure and flow condition,from both the oil port of cylinder. All thegeneral purpose and standard presses usesthese types of cylinders. (For further detailrefer chapter of Hydraulic Cylinder.)

FOUR COLUMN DOWN STROKE

WITH DOUBLE ACTION CYLINDER

FIG. 3.1

HYDRAULIC PRESS

TABLE SIZE

I.D. OF CYLINDER

RAM DIA.

FIG. 3.2

WITH SINGLE ACTION CYLINDER

FOUR COLUMN UP STROKE HYDRAULIC PRESS

MOVING PLATEN

Colu

mn

casi

ng fo

r Pre

-Stre

ssin

g

3.2 Press with Single ActionCylinder: -

Single action cylinder can take powerstroke only in forward direction. Returnstroke may be achieved by additionalhydraulic cylinder or by gravity (i. e. ownweight of ram and platen)

High capacity cylinder when bore ofcylinder is more than 1000 mm, and honingthe bore of cylinder become difficult, in suchcases cylinder are made single action.

Also in case of up-stroke press, whenmoving platen weight is sufficiently highand return speed is not very critical than toreduce cost of press, cylinder are madesingle action and return stroke achieved bygravity (For further de tail refer chapter ofHydraulic Cylinder.)

3. TERMS RELATED TO FEATURES OFHYDRAULIC PRESSES



3.3 Press with Regenerative Circuit :-

Regenerative circuit is a specialhydraulic circuit in which we get highforward speed as compare to commonhydraulic circuit using same capacity ofpump and electric motor. This is achievedby re-pumping exhaust oil coming out fromreturn port of cylinder back to forward portof cylinder using some hydraulic values.(For detail kindly refer chapter ofHydaraulic Circuits.)

For some operations presses withregenerative circuits are more productive ascompare to common presses. Regenerationcircuits are commonly used in coining,marking, bakelite molding press etc.

3.4 Press with two Working Speed :-

In a production cycle of press,generally pressing time is less as compareto time taken for approach and return stroke.Hence to save idle time press are designedfor two operating speed. Fast approach andreturn speed and slow pressing speed. Suchpresses are much productive as compare tosingle speed press.

3.5 Press with Pressure-compensation Feature :-

Some time press has to hold job underpressure for long time for curing. In suchcases motor stops after press develops thedesired load. Internal leakage is commonin hydraulic system due to wear and tear ofinternal component of valves, hydraulicseals etc. Due to such leakage pressuredrops. But if material to be cured gets lesspressure than specified pressure, than it mayget spoiled. Hence press is designed in suchaway that if pressure drops thanautomatically motor starts, develops theright pressure and stops automatically. Suchpresses are called press with pressurecompensation feature. (Refer chapter ofHydaraulic Circuits for further details aboutpressure compensation circuit)

3.6 Press with De-compressionFeature :-

Whenever there is a stress, strain isbound to be there. Body of all press deflectswithin elastic limit. As pump slowlydevelops pressure elongation of presscolumn and deflection of press body aresmooth and without vibration. And thedeflection and elongation is maximum,when press achieves maximum pressingcapacity. Solenoids operated directioncontrol

value are so fast in operation that theytake only 0.3 sec to get change over, andthat means within 0.3 sec pressurized portof the cylinder gets connected to tank line,and there is sudden fall in pressure.

Such sudden fall of pressure result insudden fall of stress and strain, and severejerk and vibration in press body. Thisphenomenon is highly undesirable andshould be avoided.

Hence presses are designed in such away that the pressure slowly gets reducedfrom maximum to tank line pressure beforetaking return stroke of cylinder. Suchpresses are called press with de-compression feature. To know howdecompression - could be achieved (Kindlyrefer chapter of Hydaraulic Circuits.)

3.7 Press with Pre-stressed Column:

All presses deflect under load. Someof the deflection is due to stress developedin press body and some of the deflection isdue to clearance between various parts ofpress.

Such deflections are undesirable inhydraulic press used for precision operation.Deflections due to clearance are much moreas compared to deflection due to stress. Suchdeflections are avoided by pre-stressing thecolumns of press.

For pre-stressing columns in roundcolumn press, additional casing is provided



around column. Refer Fig. No. 3.1. The rodsare stretched and bolts tightened, thenstretching released. As nuts are tightenedin pulling condition of cylinder the stressand strain in press-body was in reversedirection and casing around column wasunder compression. Hence on releasingpulling load, outer casing will remain undercompression load, up to certain extent andcolumns will remain in tension.

While doing initial stressing of columnand column casing, the platen and otherparts of press deflect in press-body, and ascolumns are permanently stress in tension,hence the press part also remain under somestress and will not deflect backcorresponding to clearance

Initial columns are loaded to ratedpress tonnage. In operation, compression getreleased corresponding to load.

Presses with such feature are calledpress with pre-stressed column, Aluminumextrusion presses are generally designed inthis way.

3.8 Press with Cushion Cylinder,Ejector Cylinder, Blank-holdingCylinder, Auxiliary Cylinder :-

Such presses are not any special typesof presses, but these are the presses withaddition cylinder, for easy and moreaccurate and productive operations.

1] Cushion Cylinder:- Somecomponent requires support from bottomside at the time of pressing operation. Suchsupport only offer some resistance, and donot block the movement of main cylinderand component, these bottom support arecalled cushion, and hydraulic cylinderprovided for cushion is called cushioncylinder (e.g. deep drawing operation)

Cushion could be achieved byproviding spring, rubber etc. also. But ifcylinder is provided then resistance ofcushion could be accurately controlled.Hence when cushion is required in pressing

operation, presses with hydraulic cushioncylinder are better and productive.

2] Ejector Cylinder:- Ejectors arerequired to eject the job jammed in die afterpressing operation. A hydraulic cylinderprovided to eject the component is calledejector cylinder.

3] Blank holding :- Blank holdingisrequired to hold the job before and at thetime of pressing operation. A hydrauliccylinder provider for blank Holding is calledblank holding cylinder. Both the featurescould be achieved by various means. But ifhydraulic cylinders are provided themparameter could be accurately controlled.Hence when pressing operation requireejection and blank holding and cost is not adeciding criteria in selecting a press thempresses with ejector and blank holdingcylinder are more productive.

4] Auxiliary cylinder :- Auxiliarycylinder are those cylinder which areprovided in press not to perform the mainpressing operation, but to assist maincylinder in carrying out it s functionsmoothly and efficiently. For exampleauxiliary cylinder are provided along withsingle action cylinder for retract ion.Auxiliary cylinder also provided formiscellaneous operation such as Die sliding,material filling etc.

3.9 Vertical Press: -

In vertical press axis of main pressingcylinder and press is perpendicular to theground (Refer figure No. --) majority ofpress are vertical.

3.10 Horizontal Press: -

In this type of press axis of mainpressing cylinder and press is parallel to theground. (Refer Figure No. ---) For exampleAluminum / Brass extrusion press.

3.11 Up-Stroke Press: -

This is a type of vertical press in whichmain pressing cylinder is mounted in bottom



platen and it take up-ward power stroke(Refer Figure No. 3.2)

3.12 Down-Stroke Press: -

This is also a type of vertical press inwhich main pressing cylinder is mountedin top-plate and it take down - ward powerstroke. (Refer Figure No.3.1)

3.13 Single-Day Light Press: -

In this type of press there is a singleclear gap between moving platen attachedto Ram and press-table mounted on pressbody.

3.14 Multi-Day Light Press: -

In this type of press number of additionplates are added between moving platen andpress-table to press number of jobs at a time.Plywood, rubber, molding, core - pressingetc are example of multi - daylight hydraulicpress.

Component to

Day light

Day light

Day light

be pressed

Figure No. 3.3, Multi Day-light Press Figure No. 3.4, Three Day-light Press



Basically all presses are same in theirbasic constitution. They have four mainmajor components.

1 Hydraulic cylinder :- Hydrauliccylinder converts the pressure energy inhydraulic fluid into useful pressing force.

2. Press body :- It withstands the forcedeveloped by the hydraulic cylinder.

3. Power pack unit :- This unitsupplies pressurized hydraulic fluid in thecylinders under controlled pressure andflow.

4. Control panel :- Control panelgoverns over-all operation and performanceof a press.

Presses are designed and manufacturedin different shapes and sizes to suit thespecific production, accuracy, strengthrequirement, and economic constraints.Depending on their shapes, design and theycould be divided into six broad categories.

1. Round column press.2. Fabricated column press.3. Close- frame press.4. C-Frame press.5. Fabricated chamber press.6. Non-Conventional press.

4.1 Round Column Press: -

Main features of these types of pressesare their round columns. In these types of

4. CLASSIFICATION OF HYDRAULIC PRESSESpresses top and bottom platen arefabricated and machined individually andthen held together by means of roundcolumns and nuts. As all the componentscould be machined individually andaccurately hence these types of pressesare most accurate types of presses, ascompared to all other types of presses.(Columns are also referred as pillars).

Round column presses could be furthersub-divided into three categories.

1. Two columns press.2. Three columns press.3. Four columns press.

4.1.1 Two Column Press: -

In case of two columns press, top andbottom platens are tighten together by meansof only two round columns.

Hydraulic presses, which are requiredto be very accurate and pressing load alwaysremain at the central axis of main cylinder,and also there is no chance of taking anyeccentric load, then two column types ofpresses are used. For example, Lead andsolder wire extrusion press. In this type ofpress material is always fed in fix containerand load is applied by plunger attached tothe Ram. Hence load always remain atthe central axis of main cylinder. Hydraulicuniversal tensile testing machine is anotherexample of this type of press.

Figure No. 4.1 Horizontal Two Column Extrussion PressFigure No. 4.2

Vertical Two Column Press

Side ViewRear Side ViewSide View

Front View



4.1.2 Three Column Press :-

In three column presses top and bottom platen are tighten together by mean of threeround columns.Old aluminum and copper extrusion presses of higher capacity were designedin this way. These presses were horizontal, high speed and made for mass production.

Three -column design is stronger than two-column design. Advantage of this type ofdesign in caseof extrusion press is that ample space is available for shearing the rejectedbillet and loading red hot billets in container by means of over head crane.

4.1.3 Four Column Press:-

In four columns presses top andbottom platen are tighten together bymeans of four round column. Thesetypes of presses are widely used inindustry as compared to other typewhere occurecy is more criticalbetweenDies. For example, powercompacting presses, plastic injectionmoulding machine etc.

Rear Side ViewSide View

Figure No. 4.3 Horizontal Aluminium Copper and Extrussion Press

4.2 Fabricated column press : -

In this type of presses top and bottom platens are permanently welded together with thehelp of fabricated columns. Fabricated column presses are more sturdier, economical andhas less deflection under load as compare to round column presses.

Fabricated column press also could be divided into two categories.

(1) Fabricated Four-column press.(2) Fabricated Two-column press or H-Frame press.

Figure No. 4.4 Four Column Hydraulic PressSide ViewFront View



4.2.1 Fabricated Four Column Press: -

High capacity hydraulic presses with largesize table are manufactured on the design offabricated four-column press. As it is sturdierand gives ample space to work and inspect pressingoperation from all sides, as compare to, two-column press.

For example, deep drawing press forautmobile body, punching and blanking of largesize of M.S.Steel etc.

4.2.2 Fabricated Two Column Press or H-Frame Press: -

Medium and low capacity and economicalpresses are manufactured on the design offabricated two - column or H-Frame press.

In low capacity presses rolled M.S. channelor I-section are used as side column and in caseof medium capacity press it is fabricated fromsteel plate.

Rubber molding, variable-day-light pressesused in garages are example of H-Frame press.

4.3 C-Frame Press: -

In these types of presses, press-body is of C-Shaped. When free space required from three sidesof press table to work for loading and unloadingof pressed component then this type of pressesare designed.

These types of presses are most fragile,susceptible to deflection and cracking from insidecorners, if not designed and used correctly ascompare to other type of press. As main cylinderplaced eccentric to central axis of press-body, itapplies eccentric load on press-body hence heavierpress-body is required as compare to same capacityof other type of press.

These types of presses are also called as singlepress. Some example of C-Frame presses are asfollow.

S.V.F.V.

Figure No. 4.5, Four Column Press

Figure No. 4.6, H-Frame Press

Figure No. 4.7, C-Frame Press

Front View Side View



Figure No. 4.8, Hydro pneumatic ‘C’ Press.

Figure No. 4.9, 150 Ton ‘C’ Pressfor Bending and Straighting

of Rolled Section

4.4 Close-Frame Press: -

In case of close-frame press, over all structure of press is in a shape to square ring. A schematicdiagram of close-frame press is shown in figure No. 3.10. In case of small size of presses, theyare made by cutting window in steel plates and assembling together two or more such plates to makea press-body. In this type minimum welding is required as top, bottom and side columns are allinternal

In case of large presses required for general fabrication, such as dishing, plate- bending,straightening and pre-pinching of plates for rollings top, bottom platens and side columns are fabricatedseparately then welded together .

Difference between fabricated column press and close-frame presess are as follow.

1) Generally accuracy is critical in case of fabricated column press, and generally accuracy isnot very critical in case of large size of close frame press

2) Side columns of fabricated column presses are long compared to top & bottom platen, andsome times column extend down the bottom frame and form the standing-leg or foot of press whileClose -Frame presses rest on their bottom platen only.

3) Large size of Fabricated column presses are made in premises of press manufacturerthen supplied.

These presses are accurate and requires machining of fabricated platens and columns andthen assembled together. Parallelism and flatness of platens is controlled as per standards of machinedesign. While in case of large size of close-frame press as a accuracy may not be very critical,hence manufactures of press may manufacture press body him self or he can give fabrication drawingof press body to customer and customer himself can fabricates it, if he has the facility and knowledge.As many time press body does not require machining, hence parallelism and flatness are not as perstandards.

Figure No. 4.10, Close Frame Press for Making Dish ends



4.5 Fabricated Chamber Press :-

In this type of hydraulic press a steel fabricated box-structure or container form themain body of hydraulic press. Main cylinder, various doors, feeding arrangement auxiliarycylinder are mounted on these fabricated box-structure as per the requirement of productionand operation. Fabricated chamber act as load bearing member of press. Some time theyalso act on container for material to be compressed. Bailing presses and extrusion press aresome of the example of these types of presses.

A schematic diagram of fabricated chamber press is as follow.

Figure No. 4.12, Scrap Bailing Press

FabricatedChamber

FeedingHoper

Power PackSide Door for Material Injection

Top Door

Hydraulic Cylinder Fabricated chamberPlunger Container

Die

Figure No. 11 Extrusion Press

Hydraulic Presses


(21)

5.1 DESIGN OF PRESS-BODY

Most difficult and risky part of design, in a press is design of “Press-body”. This isbecause we can not easily and clearly define the type and magnitude of force acting on anystructural member of press-body. To simplify the theoretical design work we take followingsteps.

1. We simplify the pattern of force acting in a press-structure, and ignore the complexaction and reaction forces acting on various structural member.

2. We take high factor of safety, and over design various structural member, consideringfull load of cylinder will act on them. While in actual various other member will share theload.

3. We try to calculate the dimension of a standard section namely; I-section, Box-sectionand Vertical-plate, to withstand the force develop by cylinder. But modify them drasticallyto suit the over all design and dimension of press-body.

Hence whatever we are going to study and calculate is simplified and approximatedesign. If you want to do exact calculation then kindly read the “ Plate and shell design”written by Timo and Shinko. But what ever simple calculation we do, on same calculationand design author of this book has manufactured more than hundreds of press of all typeswhich are working most satisfactory in industry.

Before proceeding to the actual design calculation, we revise some of the basicengineering knowledge, which are essential for design purpose.

5.1 Bending Stress: -

When a static or dynamic load acts on any part of hydraulic press, then along withsimple, tensile, compressive, shear stress, it also develops bending stress.

Consider a beam subjected to a bending moment M as shown in figure.

Figure No. 24.1

'N

'C

y '

'AR

N

M

y

C

A

'E

Surface

'D

'B

Neutral

E

D

B M

f t

f c

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Due to bending moment fiber AB will be under compression, fiber CD is under tension. At NE fibers areneither under tension or compression. This surface is called neutral surface. The intersection of the neutralsurface with any normal cross-section of the beam is known as neutral axis.

The bending equation is given byM = fb = EI Y R

Where M = Bending moment at the given section fb = Bending stress I = Moment of inertia of the cross-section about the neutral axis.Y = Distance from the neutral surface to the extreme fiber. E = Young’s modulus of the material of the beam R = Radius of curvature of the beam. Z = Section modulus

From above equation bending stress is given by

fb = M x y = M = M/Z I I/y

For bending moment formula, we made following assumption: -

1. The material of the beam is perfectly homogeneous. And isotropic (That is, it is same material throughoutand of equal elastic properties in all the direction)

2. The material of beam obeys Hook’s law.3. The Young’s modulus E is same in tension and compression.

Note: - In case of symmetrical section, the neutral axis passes through its geometrical center. While in case ofunsymmetrical center, centroid is to be calculated and then extreme fiber distance is obtained.

Sr. No.

Section Area (A)

Moment of Insertion (I)

Section Modulus Z=I/y

1

h X

bY

Y

X

bh

Ixx = bh3 /12 Iyy = bh3 /12

Zxx = bh2 /6 Zyy = bh2 /6

2

y

X dX

y

/4 d2

Ixx = Iyy = d4/64

Zxx = d3/32

3

x

y

x

y

h

b

1

b1

h

hb-h1b1

Ixx = (bh3/12)- (b1h1

3/12) Iyy = (bh3/12)- (b1h1

3/12)

Zxx = (bh3-b1h1

3) / 6h Zyy = (bh3-b1h1

3) /6b

4

hxa

xh

a

1

12

hb-h1b1

Ixx = (ah3/12- a1h1

3) /12

Zxx = (ah3-a1h1

3)/ 6h

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5.2 Fatigue and Endurance limit :-

When a material subjected to repeated stress. It fails at stresses much below the yieldpoint stresses. Such type of failure of a material is known as fatigue. The failure is usuallycaused by means of a progressive crack formation which are usually fine and microscopicsize, and which get developed due to tool mark while machining.

A standard polished specimen is subjected to cyclic bending in a fatigue testing machine.bending load on specimen varied and number of cycle counted after which the specimenfailed. When a stress and number of cycle graph plotted. It is found that material will not failwhatever may be the number of cycle, bellow a certain stress level. This stress is known asendurance or fatigue limit (fe). For steel fatigue limit is half of its ultimate tensite stress.Fatigue limit increase with increase in surface finish of material.

Stress

y

Figure No.24.2

No of cycle

efx

5.3 Selection of Type of Construction of Hydraulic Press- Body.

Hydraulic Press-body is designed and made on four standard type of cross-section andconstruction; newly

1. Vertical Plate type of Construction.2. Box-Section type of Construction.3. I-Section type of Construction4. Single horizontal plate type of Construction.

Depending on various parameters we select anyone type of above-mentioned standardCross-section,. Then we calculate size of a standard selected cross section; the calculatedsize of cross sections may or may not shites to the required dimension of press. Hence aftercalculating the size we modify them without decreasing strength to suit the press dimension.

Some of the parameter on basic to which various type of construction is selected is asfollow.

5.4 Vertical-plate type of construction: -

When size of platen is almost equal to the outside diameter of cylinder, and cylinderis to be inserted in press body (platen) to reduce the dimension of press them vertical platetype design for press-body is selected.

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Distance between platenis required to be minimum

Press table

Cylinder out side diameter

Press table.almost equal to size of

Figure No.24.3

VERTICAL PLATE TYPE OF CONSTRUCTION

'X'

'X'

CYLINDER MOUNTING PLATE.

SECTION - 'X X'

VERTICAL LODETAKING PLATES.

5.5 Box-section type of construction: -

When platens of hydraulic press-body can be completely enclosed, and there is noopening in platen for cylinder mounting, ejector or for any other purpose, then box constructionfor complete press-body or any of its platen or column is selected.

Plate bending and dish end making press

out side press-bodyCylinder mounted

Section at "xx"

Box section

Hydraulic cylinder

Top plate

Figure No.24.4

x

x

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5.6 I-section type of press-body construction :-

When the size of press-body or any of its platen is large enough, as compare to cylinderdimension, and there are windows and opening in press-platens, for cylinder mounting,guide rods etc,

Then for such complete press-body or any of its platen, or column I-section type ofconstruction is selected.

Figure No. 24.5

Four column press used for sheet metal pressing

Seaction at "AA"

A

A

Figure N0.24.6

For design purpose we consider as too I-beam consider as too I-beam supporting the cylinder and taking its load

While manufacturing we select and fabricate plate is such away that same strength and cross sections size we get and over all press-diameter also achieved

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5.7 Single-solid plate type of construction; -

When capacity of press is less, it size is also small and a simple press is to be made thensingle solid plate type of construction is selected.

A

A

Hydraulic cylinder

Section at "AA"

Power pack unit

MAKING HYDRUALIC PRESS

Figure No.24.7

5.8 Design of press-body with vertical plate type of construction

This type of construction is selected when width of cylinder side plate is almost equalto outside diameter of cylinder, and cylinder is to be accommodated in platen. Or there islarge opening in platen and making side vertical plate into an I-section is not possible.

Example of this type press is, adjustable platen type general-purpose press used ingarages, as shown in following figure.

A general design of vertical plate type of construction is as follow

Section at `xx'

3

Front view

xTop View

2

Side View

4

1 x

1

5

Figure No. 24.8

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In above drawing, the name and purpose of platen are as follow.

Plate No. Name of Plate Purpose of Plate 1. Main vertical plate It withstand the force developed by hydraulic cylinder. 2. Cylinder supporting plate It support the cylinder it transferor load developed by cylinder

to plate no.1. It avoid backing- in of plate no.1 3. Cylinder mounting plate This is used to hold the cylinder with platen. 4. Column supporting plate These plates transfer load from plate no.1 to columns 5. Reinforcement ribs. These plates are used to strengthen the press body. They avoid

Buckling of plates and given strength against twisting 5.9 Design Procedure: -

Design of main vertical plates

1. We assume that top platen is made from single vertical plate.2. We assume that the cylinder apply force on sindle vertical plate at single point.3. We assume that press has only two columns, both attached at both end of single

vertical plate and column also offers reactions at single point.

Reation offer byside column

Force applied byCylinder

2W

L aX

Figure No. 24.9

Section at `xx'2

W

W X

b

1. Single vertical plate is similar to simply supported beam with bending stress, Hencewe are bending equation as follow

(M ÷ I) = (fb ÷ y) = (E ÷ R)

M= Bending moment at given sectionFb= Bending stressI= Moment of inertia of the cross section about the neutral axisY= Distance from the neutral surface to the extreme fiberE= Young modular of the material of the beamR= Radius of curvature of the beamFrom above equation bending stress is given by.

Fb= y x( M÷I) = M÷(I÷y) =M÷Z.

I÷y = Section modular =Z

M =wl÷4

I =ab³÷12

Y =b÷2

Hence

Fb = M÷2 = WL÷4÷( ab³÷12)÷(b÷2)

Fb= (WL÷4)÷ (ab² ÷6)

In above equation fb is known as it depends on material of construction of vertical

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plate. W and L are also known, as W is cylinder capacity and L distance between columns ofpress. Hence only a’ and b are unknown.

‘a’ and ‘b’ that is thickness and height of vertical plate is divided by trial and errormethod.

2. Criteria to decided‘ a’ and ‘b’ while dividing value of plate thickness (a) and heightof plate (b), following figure and fact must be remembered.

a. Press-body or press-platen one all welded structures. Each plate in platen is weldedto many other plates. Welding produce distortion. Single vertical plates also get distorted tosome extent. Hence thickness of plate must be sufficiently high to minimize the distortion.

b. Moment inertia of plate is above equation is (ab³÷12). For a safe and constant bendingstress (fb), a slight increase in height (b) result in high reduction of plate thickness (a).

Hence a higher valve of (b) is always desirable. But large height of vertical plate, resultis difficulty in fabrication of press-structure

Hence valve of (a) and (b) always should be divided considering convenience infabrication.

c. Generally length of press-platen (L+ Column thickness) and height (b) are in ratio of2:1 to 3:1.

d. Press is operated by workman. For higher production it should be convenient inoperation. The table height should be easy to loading-unloading component to be processed.Hence height (b) should be selected according.

e. Press should look good esthetically. Hence it is over all dimensions should beproportionate. Hence height (b should be selected as per width and height of press.

Step-II:-

a) Once thickness (a) and height (b) of main vertical plate is calculated to withstandfall face developed by cylinder, we proceed further for design of press-body as follow.

b) We split single vertical plate in to two plates with half the wall thickness (9÷2), aswe require minimum two plates to completes a press platen in category of vertical platedesign

Figure No. 24.10

Section at `xx'

2a

b

a2

Cylinder with two vertical plates.X

L+Column widths

X

c). Two vertical plates has to be connected to each other firmly and cylinder also shouldbe supported from all our sides. Hence we provide two additional plates adjust to cylinder,and interconnecting plates no.1, as shown in following diagram. We name these plates asplate no. (2).

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Figure No. 24.11

Front View

Top View

Plate No.1

Plate No.2

Plate No.2

Plate No.1

b. If press consist of only vertical plates and columns, and loads one perfectly concentricto center of axis of cylinder and press- body, then also press will work , and its structure notgoing to fail.

But in actual practice load is never concentric to axis of press, and load on platen isalso of twisting type along with bending a compressive load. Which result in twist of verticalplates, and platen.

When load is eccentric, and it is causing twisting load on press-platen, then we can notexactly say that only half the cylinder load is coming on each of the two vertical plates .Wealso can’t predict that which plate is taking less load.

Because all these uncertainties, we over design the press platen, make such assumptions,which seems to be absurd. But then also for safe design we do it.

c. For design of platen no. 2, we assume that cylinder is only supported by platesno.2, and plate no.2 is transferring load from cylinder to plates no1 as shown as followingsketches

Figure No. 24.12

Section at `xx'

Plate No.1

Plate No.2

XFront View

X

d. Plate no.2 is welded to plate no.1. To transferor cylinder load to plate no. 1,wecalculate the welding required for safe transfer of load. Then depending on size of welding,we divide the size of plate no.2.

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Figure No. 24.13

P = (t x l x fs)

Shear strength of joint for single paralell fillet

C

45°

Plate No.1

2

A B

D

Plate No.2

Plate No.1

45°

Leg or size of weld.

Throat thicknessA

45°

tB

Reinforcement

Plate No.2 C

e. The joint between plate no.1 and plate no. 2 is subjected to shear stress. Hence shear strength of thejoint for said double parallel fillet type of wielding joint could be calculated as

2 (tl2 x fb)

t= Size of weldl= Length of welding joint. Generally we keep it same as (b) that is height of plate no.1fb= Permissible shear stress of welded-metal.

We assume that each joint withstand half the force developed by cylinder.

W2= 2(td2 xfb)

In above equation all the parameters are known except (t). Hence it can be calculated. The thicknessof plate No.2 will be twice the valve of (t), and height same as plate No. 1, that is (b).

f. Some time we get valve of (t) too small. In that case we use thumb rule. We should keep thethickness of plate no.2 between 50 to 100% of thickness of plate no. 1, and height between 75 to 100% ofplate no.1

Hence first we reduce height to reduce weld length (l) and increase weld size (t). And if even afterreducing length up to 75% the final thickness plate no.2 we get less than 50% of plate no.1 then we selectits thickness as 50% an height 75% of plate no.1.

5.10 Design of cylinder mounting plate (plate No.3):-a. Cylinder is fitted in press body. The place where cylinder is fitted should be machined properly so

that central axis of cylinder should be as per requirement of press body.

b. When cylinder applies load on component to be pressed it equally pushes-back the platen onwhich it is mounted. If the plate on which it is mounted is perfectly matching to cylinder, this cylinder willapply a uniformly distributed load. And it surface is not matching properly then will apply a concentratedload.

Bending stress in case of concentrated load is much higher than uniformly distributed load. Hencecylinder-mounting plate should be perfectly machined

c. Cylinder has it on weight. A 1000 Ton capacity cylinder with 1000mm stroke way weight about 5Ton. Some time cylinder should pull the component instead pushing in such care the bolts fixing cylinderto the cylinder mounting plate should be of sufficient size. Plate should also be sufficiently thick to haverequired number of threads.

d. The size of cylinder mounting plate is decided on above three criteria. First thickness of plated isdivided on the basic size and number of bolt it has to accommodate. There some thickness is added asmachining allowance. Width of cylinder mounting plate is equal to or more than size of cylinder mountingflange. Depth or length of plate is as per depth of press-plates.

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and machining allowanceThickness as per bolt size

Depth

Width as per cylinder

Figure No.24.14

Depth as per plate

Width

Thickness

5.11 Design of column supporting plates (Plate No. 4)

a. In case when column press between two main vertical plates and welded directly toit , then these plates are not required.

b. When plates is fully cover from one side by cylinder mounting plate, then this plateis provided to transferor the load from press platen to press column.

c. Thickness and height of this plate is same as plate No.2.

Figure No.24.15

Figure No.——— is an exaggerated sketch to show the importance of plate no. 4 . Itload is transferred only through cylinder mounting plate (No.3). Then plate (No.3) maydished out under load as shown in sketch.

Plate No.4 provided strength to plate No.3 and transferor load from column to plateNo. 1 through out its height.

5.12 Design of Reinforcement Ribs (plate No.5)

a. In case of long press –body, in which distance between both column are too much,then additional stiffeners one required between plate No.2 and plate No.4

b. In absence of stiffener the plate No.1 try to buckle in following way.

e. In case of vertical plate design as cylinder is almost pressing against vertical plate, hence cylindermounting plate do not take any bending load, and used mainly to hold cylinder in position. Whileremaining three design this plate also take bending load, and very critical in press-body.

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Figure No. 24.16

2

1

1

4

Hence to reinforce the strength of platen ribs or thin plate one provided.

a. Ribs could be provided in following two ways.

Figure No. 24.17

Cross-ribbing

Parallel ribbing

Cross –ribbing give more strength as ribs also take the bending load. While in case ofparallel ribbing, rib parallel to plate No.1 and 4 could not take any bending load.

a. Height of ribbing plate one kept same as plate No.1, and thickness between 20 to40% of thickness of plate No.1 or between 6mm to 20mm.

b. Cross-ribs and ribs parallel to plate No.1 also under go the bending load and sharesome of the load of plate No. 1. Hence their thickness and reduction in thickness of plateNo.1 can be calculated. But those complicated calculations are beyond the scope of thisbook. Hence we do not discuss it.

5.12 Design of I- section type of construction.

When Size of press-plant is large enough, as compare to holes or opening providedfor hydraulic cylinder or ejector etc. And when it is not possible to make a box-section, thenbest alternative is to design press body on basis of design of I-section.

Majority of presses designed on basis of I-section design. And particularly cylinderside platen when cylinder is filled in press-body is mostly I-section design.

An example of I-section construction for press-frame is as follow.

3

Section at ̀ BB'

6

4

7

1

A

5

1

Figure No.24.18

Section at `AA'B

B

A

TOP VIEW

2

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In above drawing, the name and purpose of plate are as follow.

Plate No. Name of Plate. Purpose of Plates. 1. As described in table. 2. -do- 3. -do- 4. -do- 5. -do- 6. Platen-cover-plate This plate is mounted other side of cylinder mounting plate

or press-table. Size of this plate is square as cylinder-mounting plate or press- table. And purpose is to give plate No. 1 and 3, an I-section shape.

7. Cylinder supporting ribs. There rib gives addition support to cylinder. Avoid dishing of cylinder mounting plate, and avoid collapsing of vertical head bearing plate no.1

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